GEOGRAPHY FORM THREE
STRUCTURE
OF THE EARTH
Physical
geography can be simply defined as the study of the structure of the Earth and
the forces which affect it. These forces are categorized into two kinds:
internal and external forces. Internal
forces are
forces which act within or beneath the Earth‘s crust. These forces result into
various Earth movements such as vertical and horizontal movements, vulcanicity
and earthquakes. External forces are
forces which act inside the earth‘s surface and result into various geomorphic
processes such as mass wasting and weathering. The earth is composed of inner
and outer zones (layers). The outer layer of the earth comprises of the
atmosphere, biosphere and hydrosphere, while the inner layer includes the
crust, mantle and core
The Earth's Crust, The Mantle, The Core and their Respective
Characteristics
Concentric Zones of the Earth
Identify
concentric zones of the earth
The
earth is composed of three internal, concentric layers of increasing densities.
These layers are the crust, mantle and core. They are made up of
different layers of rocks, with their densities increasing towards the centre
of the earth. That is, densities of rocks that make up the earth increase as
you move from the surface towards the interior
The
Crust (Lithosphere)
This is
the outermost part of the earth. It consists of silica and aluminium (sial). It
forms the upper layer of the continent and is mostly composed of granite rocks.
The layer below SIAL is called SIMA. This layer is made of silica and
manganese. It is a layer of basaltic rocks which are denser and underlies the
continental block to form the ocean floor.
The
Mantle (Mesosphere)
This is
the layer below the crust. It is composed of iron and manganese. It lies
between the crust and the core. The layer which separates crust and mantle is
called Mohorovic discontinuity. The mantle is made up of very dense and hot
igneous rocks, found in semi liquid states. It extends downwards 2900 km and
the temperature ranges between 5000°C and 7000°C. The density of the mantle is
3 – 3.3 g/cm3. It is divided into two parts namely, the upper and lower mantle.
The upper mantle is rigid and combines with the crust to form a layer called
lithosphere. Below the upper mantle there is a layer called asthenosphere
The
Core (Barysphere)
This is the innermost layer of the earth. It is composed of
nickel and iron. Its diameter is approximately 2500 – 2700 km and its
temperature is around 5500°C. The average density of the barysphere is about
5.2 g/cm3. Most geographers believe that the core is divided into solid and
liquid core. The total mass of the earth is about 5.976 x 1021 tonnes.
Structure
of the Earth
The Variation in Density and Thickness of the Concentric Zones
of The Earth's Crust
Account
for the variation in density and thickness of the concentric zones of the
earth's crust
ROCKS
A rock
is an aggregate of mineral particles found in soft, solid or unconsolidated
state. The earth‘s crust consists of rocks and rocks consist of a combination
of different minerals. All minerals are formed from one or more of eight main
elements. These are: oxygen, silicon, potassium, sodium, calcium, magnesium,
iron and aluminium.
Rocks
can be broadly categorized into three types. These are igneous rocks,
sedimentary rocks and metamorphic rocks. These kinds of rocks are classified
according to their origin, chemical composition and age.
The Characteristics of The Earth's Crust, The Mantle and The
Core
Describe
the characteristics of the earth's crust, the mantle and the core
Variations
in characteristics of the three interior zones of the earth are the result of
temperature and pressure as they increases from the surface to the center of
the earth.Factors which accounts for such variations includes: pressure on the
underlying materials, weight of the underlying materials, radioactivity, magma
movement and heat generated during the formation of the earth.
Types of Rocks of the
Earth's Crust
The Types of Rocks of the Earth's Crust
Identify
types of rocks of the earth's crust
Igneous rocks
These
rocks are formed when molten rock cools and solidifies. All igneous rocks
originate inside the earth where they are under great pressure. Igneous rocks
do not occur in layers and they don‘t contain fossils which are the
chemically-changed remains of ancient plants and animals embedded in rocks.
These rocks solidify either within the earth‘s crust and form intrusive
features or outside the earth‘s surface and form extrusive features.
Igneous
rocks are formed when the molten magma is forced out from the upper mantle to
the earth‘s surface, where it cools and solidifies due to low temperature.
Crystals form on cooling and the rocks are called crystalline rocks.
There are two main types of igneous rocks:
1. Plutonic: these have solidified deep in the crust and
they are seen on the surface only after being exposed by prolonged erosion.
2. Volcanic: these
have been poured on the earth‘s surface where they are called lavas.
Characteristics of
igneous rocks
·
Igneous rocks reflect light.
·
They are not found in layers.
·
They do not contain fossils.
·
They are crystalline rocks.
·
They are formed through cooling and solidification of magma.
·
They can undergo metamorphic and weathering processes.
·
They contain different minerals like iron, magnesium etc.
Many igneous rocks are found in Dodoma, Iringa and in the shores
of Lake Victoria (Mwanza). The main examples are granite, gabbro, basalt and
diorite. Some are found in Kilimanjaro and Rungwe (Mbeya) such as basalt,
pumice, diorite, gabbro, syenite and peridotite rocks.
Granite
Basalt
rocks
Sedimentary rocks
Sedimentary
rocks are found in layers; they contain fossils and are very soft. These are
weathered particles formed through deposition and lithification processes.
Sedimentary rocks are formed when the sediments are accumulated, compacted and
cemented together. The sediments are compacted by compression to form
sedimentary rocks. These are called stratified rocks.
Characteristics of
sedimentary rocks
·
They are formed when particles or sediments are accumulated,
compacted and cemented together.
·
They contain fossils.
·
They are found in layers (strata).
·
They do not reflect light.
·
They are non-crystalline rocks.
·
They can undergo metamorphic process.
Types of sedimentary rocks
Mechanically-formed
sedimentary rocks
These are formed through weathering process. When weathering
agents erode and deposit rock particles, they are accumulated, compacted and
cemented together to form sedimentary rocks. Examples of mechanically formed
sedimentary rocks are clays, gravels and alluviums (all deposited by water),
moraines, boulder clay and gravels (deposited by ice) and loess (deposited by
wind); sandstones and shale.
Sandstone
Shale:
Shale occurs in a wide range of colours that include: red, brown, green, grey,
and black.
Chemically-formed sedimentary rocks
These are formed through chemical precipitation process. They
include carbonate (as it is in stalactite and stalagmite), sulphate, chloride,
etc. The main examples are gypsum, rock salt, lignite, dolomite, flint, borax,
limonite, haematite, etc.
Dolomite
Organically-formed sedimentary rocks
These are formed through mineralization process of decaying and
decomposition of dead organisms such as animals and plants. The remains of
living organisms are accumulated, compacted and cemented together to form these
sedimentary rocks. The main examples are chalk (limestone) and coral (formed
from animals), and peat, coal and lignite (formed from plants).
Lignite rocks
Limestone
Chalk
Coal
Coral
rocks
Metamorphic rocks
These
are rocks which have changed their shape, size, appearance or chemical
composition due to the contact of heat, pressure or both. This process is
referred to as metamorphism. Any rock can be changed into a metamorphic rock.
Examples of metamorphic rocks are slate, marble and granite.
Characteristics of
metamorphic rocks
·
They are very hard due to prolonged action of heat and pressure.
·
Any type of rocks can be subjected to metamorphic rocks.
·
They can undergo weathering process.
The main examples of
metamorphism in rocks include the following:
·
Sandstone to quartzite.
·
Coal to graphite.
·
Limestone to marble.
·
Clay to slate.
·
Granite to gneiss.
Gneiss
ROCK
CYCLE
This is
the cycle in which rocks tend to change from one type to another. For instance
igneous rocks may change to metamorphic rocks or sedimentary rocks; sedimentary
rocks to metamorphic or igneous rocks, etc. It is a relationship in which rocks
tend to change from one type of rock to another.
Necessary conditions for
rock cycle to take place
1. First,
the molten rocks erupt from the interior of the earth and then cool and
solidify to form igneous rocks.
2. Secondly,
the igneous rocks are subjected to denudation process to form sedimentary
rocks.
3. Third,
either igneous or sedimentary rocks undergo metamorphism, due to prolonged heat
and pressure, to form metamorphic rocks.
4. Fourth,
metamorphic or igneous rocks can undergo weathering process through erosion and
transportation of sediments which are further deposited in layers in the ocean
or lake floors where they are cemented and consolidated to form sedimentary
rocks and vice versa.
5. Fifth,
metamorphic or sedimentary rocks can be subjected to heat and pressure where
melting take place and later cooling, due to low temperature, to form igneous
rocks.
The rock
cycle
Simplified geological time scale
The
geological time scale is a chart for dating the history of the earth including
rock span. It tries to explain the age of rocks as far back as 600 million
years ago.
The simplified geological time scale
|
Era |
Period |
Years
in millions before present |
Major
geological events in Africa |
Man
and animals |
|
Cenozoic |
Quaternary |
1 |
Glaciation of East
Africa mountains.Formation of river terraces and raised beaches. |
Age of man |
|
Tertiary |
163 |
Formation of the
Atlas mountains. Lava flows in Ethiopia. |
Age of mammals. |
|
|
Mesozoic |
Cretaceous |
135 |
Deposition ofmarine
sediments in the Sahara and Southern Nigeria. Formation of Enugu coalfield. |
Age ofreptiles |
|
Jurassic |
180 |
Break-up of
Gondwanaland and Marine invasion of East Africa coastlands and separation of
Malagasy Island from mainland. |
||
|
Triassic |
230 |
Drakensburg lavas
and formation of upper Karro beds. Volcanic activity in West Africa. |
||
|
Paleozoic |
Permian |
280 |
Formation of lower
Karro beds. Formation of rich coal deposits in Tanzania and South Africa. Ice
age in central and South Africa. |
Age of amphibians |
|
Carboniferous |
345 |
Cape fold formed. |
||
|
Devonian |
405 |
Marine invasion of
Libya, the Sahara and Western Sudan. Continental basins formed by crustal
warping |
||
|
Silurian |
425 |
Continental
sedimentation in Zaire basin,Tanzania and South Africa, followed by intensive
folding. |
||
|
Ordovician |
500 |
Extensive deposition
of sediments.Formation of sandstones in Guinea, Mali, Volta basin and North
West Ethiopia |
Age of marine
invertebrates |
|
|
Cambrian |
600 |
Marine invasion of
Western Sahara and Kalahari basin. |
||
|
Proterozoic |
Pre Cambrian or
Archarean |
Glaciations of
Africa South of Equator.Extensive metamorphism of oldest known fossilized,
unicellular algae formed in Swaziland and Mali. |
Algae |
The Mode of Formation for each Type of Rocks and their Economic
Importance
Explain
the mode of formation for each type of rocks and their economic importance
The importance of rocks
1. Rocks
are very important in the formation of soils which can be used for agricultural
production.
2. Rocks
are used for building purposes: some rocks such as limestone, sandstone,
gravels and sand are used for building houses, construction of roads, etc.
3. Some
rocks are used as sources of energy or fuel such as coal and petroleum (mineral
oil).
4. Limestone
is widely used for cement manufacturing. In Tanzania, cement is produced at
Tanga, Mbeya and Wazo Hill.
5. Salt
extraction: salt usually originate from rock accruing strata, for instance, in
Tunisia and Morocco there are large deposits of salt.
6. Manufacture
of chemicals: some rocks contain nitrate or phosphate, while others have
potash. This kind of rocks can be used for making dyes, fertilizers and
medicines.
7. Mineral
deposits: mineral ores occur in veins of some rocks such as igneous rocks. The
minerals are formed when the magma coos down. Valuable minerals extracted from
rocks include gold, lead, tin, silver, diamond, copper, zinc, aluminium,
calcium and manganese.
8. Some
rocks are so impressive such that they attract tourist to come and view them.
In so doing, the country earns a lot of foreign exchange.
9. Some
rocks are used for decoration of houses as ornaments or they are grinded to
produce powder which is used for decoration.
Simplified Geological
Time Scale
The Geological Time Scale
Describe
the geological time sale
The geological time scale(GTS) is a system of chronological measurement that relates
stratigraphy to time, and is used by geologists,paleontologists, and otherEarth
scientists to describe the timing and relationships between events that have
occurred throughout Earth’s history.
FORCES THAT AFFECT THE EARTH
The
earth can be affected by two forces which may result into various landforms.
Forces that act on the earth can be grouped into internal and external forces.
Forces Causing Earth Movements
The Forces Which Cause Earth Movement and their Origin
Explain
the forces which cause earth movement and their origin
INTERNAL FORCES:These are forces which
operate within the earth‘s crust. Internal forces include vulcanicity and earth
movements, that is, horizontal (lateral) and vertical movements. These forces
may result into formation of several landform features.
EXTERNAL FORCES: These
are natural forces that operate on the earth’s surface. The forces mainly act
on the earth’s crust or close the surface of the earth. Often the features
produced by these forces are seen on the surface of the earth. They include
mountains, volcanoes, moraines and valleys, just to mention a few
Radial/Vertical
Movement
The Vertical/Radical Movement
Describe
the vertical/radical movement
The
earth is in constant motion and this movement results to a number of features
such as mountains, plateaus and plains. Such features are due to both lateral
and vertical movements. These movements exert great force of tension and
compression which later results to very impressive features. Earth movements
are either vertical or lateral.
The Resulting Features from the Vertical Movement
Identify
the resulting features from the vertical movement
Vertical earth movements: These
are up and down movements which cause the crustal rocks to fault. These
movements result to a number of landforms such as plateaus, block mountains,
rift valleys, basins, etc.
Lateral or Horizontal
Movement
How Horizontal Movements Take Place
Explain
how horizontal movements take place
Lateral earth movements: These
are sideways movements of the earth’s crust which cause the crustal rocks
either to fold, fault or form joints. Features which are produced due to this
movement are such as fold mountains, rift valleys, block mountains, etc.
Different Features Produced by Horizontal Forces
Identify
different features produced by horizontal forces
Features
associated with earth movements
Rift Valley
Rift
valley is a trough or hollow which may result from both vertical and lateral
movements of the earth’s crust. It is formed when two faults develop parallel
to each other. It can develop either by tensional forces or compressional
forces.
Formation of rift valley by tensional forces
This is formed when tensional forces move away from each other.
These forces of tension produce faults and the block between two parallel
faults subsides to form a rift valley.
Formation of the Rift Valley by compressional forces
This is
formed when horizontal forces act towards each other. These forces of
compression produce faults on the outside of the two parallel faults and the
pieces of land on either side are lifted up above the general level of the
ground to form a rift valley.
Diagrammatically, formation of the Rift Valley occurs like this:
Examples of rift valleys include:
·
East African rift valley – Africa;
·
Jordan rift valley – Asia;
·
Rhineland rift valley – Europe.
Block mountain (horst)
A block mountain refers to a table-like mountain formed due to
the influence of faulting that leads to rising of crustal rocks. It is nearly a
flat surface. A block mountain can be formed by either tensional or
compressional forces. This is when the earth’s movements cause parallel faults
which results into uplifting of some parts.
Examples of block mountains are:
·
Usambara and Uluguru, in Tanzania;
·
Ruwenzori, in Uganda;
·
Vosges and Black Forest, in Europe; and
·
Mount Sinai in Asia.
Plateau
A
plateau is a large, extensive uplifted part of the earth’s crust which is
almost flat at the top. The top of the plateau is mostly a plain. Plateaus were
formed during Mesozoic and Jurassic eras. It was due to uplifting of the
earth’s crust. Such landforms include those of East African and Brazilian
plateaus. High plateaus especially in tropical latitudes are used for
agriculture and settlement.
Basin
A basin is a large, extensive depression on the earth’s surface.
Most basins are formed due to vertical movement of the earth.
Examples of basins include:
·
an inland drainage e.g. Congo basin;
·
Chad basin; and
·
Amazon basin.
Vulcanicity
Difference between Vulcanicity and Volcanicity
Differentiate
vulcanicity from volcanicity
This
refers to all the various ways by which molten rock (magma) and gases are
forced into the earth‘s crust and onto its surface. Vulcanicity therefore
includes volcanic eruptions, which lead to the formation of volcanoes and lava
plateaus and geysers, and the formation of volcanic features such as
batholiths, sills and dykes, etc, in the earth‘s crust.
Causes of Volcanicity and Resulting Features
Explain
causes of volcanicity and resulting features
There
are two types of vulcanicity namely, intrusive vulcanicity and extrusive
vulcanicity
Intrusive
(internal) vulcanicity
This
occurs when the magma cools, solidifies and forms features within the earth‘s
crust before it reaches the earth‘s surface. The features (landforms) formed by
this process are sometimes termed as intrusive (internal) features.
The
following are the landforms formed through intrusive vulcanicity:
Dyke
This is a wall-like feature cutting across the bedding planes.
It is formed when magma cools and solidifies vertically across bedding planes.
The dyke is termed as a small-scale intrusive feature. Sometimes the dyke may
form a waterfall when exposed to the earth‘s surface due to denudation
processes.
Examples
of dykes are Mwadui dyke in Tanzania, Gabbro dyke in Lesotho, and Tyolo dyke in
Malawi.
Sill
This is an intrusive feature which lies horizontally along the
bedding planes. It is formed when magma cools and solidifies horizontally along
a bedding plane. Like the dyke, the sill is termed as a small-scale intrusive
feature.
An
example of a sill is Fouta Djallon ranges in Guinea.
Laccolith
This is an intrusive feature which looks like a dome. It is
formed when the magma cools and solidifies in anticline bedding plane.
Sometimes it can be exposed to the earth‘s surface following denudation processes.
Lapolith
This is an intrusive feature which looks like a saucer in shape.
It is formed when magma (molten rocks) cools and solidifies in a syncline
bedding plane.
Examples
of lapoliths are found in South Africa especially in Trans Vaal province.
Batholith
This is a very large mass of magma which cools and solidifies in
the earth‘s crust. Sometimes if forms the root or core of a mountain.
Batholiths are made of granite and they form surface features only after they
have been exposed to the earth‘s surface by denudation. Sometimes batholiths
resist erosion and form uplands.
Examples
of batholiths are found in Zimbabwe, Tanzania, Zambia and Gabon (The Chaillu
Massif).
Phacolith
This is a lens-shaped mass of igneous rock. It is formed when
magma cools and solidifies at anticline and syncline in folded rocks.
An
example of a phacolith is The Gordon Hill in UK.
Features Resulting from the Processes of Volcanicity
Classify
features resulting from the processes of volcanicity
Eruption
of magma, either intrusive or extrusive, results in the formation of features.
Intrusive features are the result of cooling and solidification of magma inside
the crust. The features formed includes dyke, sill, laccolith and batholith.
Extrusive features include the formation of volcanoes, domes, craters and
calderas.
Distribution of Major Volcanic Zones in the World
Locate the
distribution of major volcanic zones in the world
Extrusive
(external) vulcanicity
This is
the type of vulcanicity that occurs when molten rocks reach the surface of the
earth. When magma emerges at the surface it is called lava. This forms features
called extrusive features of vulcanicity. The following are landforms due to
extrusive vulcanicity:
Acidic lava cone
This is a cone made of viscous lava. Normally lava cones have
high heights and break into small fragments. The acidic lava always cools
faster than basic lava because is it viscous.
Examples
of acidic lava cone include:Mount Kilimanjaro found in Tanzania (East
Africa).Mount Kenya found in Kenya (East Africa).Mount Fuji found in
Japan.Mount Vesuvius found in Italy.
Basic lava cone
This is a cone made up of basic (fluid) lava. Normally cones
have gentle slopes and spread over a long distance.
Examples
of basic lava cones are Mauna Loa cone of Hawaii and basaltic dome of
Nyamlangir, near to Lake Kivu in DRC.
Ash and cinder cone
This is a cone made up of ashes and stones that erupted from
beneath (interior) the earth to form a concave cone. The slopes of a cone are
usually concave due to the spreading tendency. Lava is blown to great heights
when it is violently ejected, and it breaks into small fragments which fall
back to the earth and build up a cone.
Several
ash and cinder cones occur just south of Turkana, in Kenya. These are Likaiyu
and Teleki (both cinder cones), and Nabuyatom (ash cone).Other examples of
cinder cones outside Africa are Volcano de Fuego, in Guatemala and Paricutin,
in Mexico.
Crater
The crater is a small depression on the volcanic cone or
mountain. It is sometimes filled with water to form a crater lake. It is formed
when volcanic eruption ceases and leaves a hole on the basic lava cone. An
example of a crater is Ngorongoro crater in Tanzania.
Volcanic plug
This is a big rock which plugs or blocks the top of the pipe. It
is formed when lava solidifies quickly to block the pipe. Examples of volcanic
plugs are Mount Palace in France and Hoggar mountains in Algeria.
Composite cone
This type of a cone is formed of alternate layers of ash and
lava. The volcano begins each eruption with great violence forming a layer of
ash. As the eruption proceeds, the violence ceases and lava pours out forming a
layer on top of the ash.
Examples
of composite cones are Mount Kilimanjaro, in Tanzania and Mount Cameroon. Other
examples outside Africa are Vesuvius, Etna and Stromboli, all of which are in
Italy.
Caldera
This is
a large depression on top of a volcanic cone. It is formed when a composite
volcano explodes so violently that its top is blown off and disintegrates into
a mass of rocks and ashes, leaving the crater greatly enlarged. This huge
crater-like depression is what we call a caldera. Sometimes a caldera can be
filed with water to form a caldera lake. Lake Shala, in Ethiopia, is the
largest caldera lake in the world.
Examples of calderas are:
·
Ebogar caldera, in Cameroon; and
·
Longonot caldera, in Kenya, which lies in the Eastern Rift
Valley, about 140 km south of Mount Kenya.
The stages in the
formation of a caldera
First stage:Magma cannot escape to the surface and collects
under the lower crust.
Second stage:An 'uplifted bulge' begins to form under the lower
crust as the magma chamber enlarges.
Third stage:Cracks appear on the surface. Gas and ash erupt from
the magma chamber through these cracks.
Fourth stage:The magma chamber collapses and a depression is
formed. This is called a caldera.
Geysers
and hot springs
1. A
geyser refers to the forceful emission of hot water and steam from the ground
to a high level in the air. The ejected water contains fine materials such as
volcano mud, which later form fertile soils. Geysers are found in Iceland,
North Island and New Zealand.
2. A hot
spring refers to natural outflow of superheated water from the ground. It contains
mineral substances in solution. Hot springs are found in Iceland, in Europe;
and Kenya and Ethiopia, in Africa.
Hot
springs are also found in Manyara National Park, Songwe, in Mbeya and in
Nigeria.
Lava
plateau
This is an extensive and flat landform which is formed when
molten magma flows onto the earth‘s crust through fissure. Examples are found
in Ethiopia highland, Bui plateau in Nigeria and Daccan plateau in India.
Distribution of major
volcanic zones in the world
The distribution of volcanoes is as shown in the world map
below. Most volcanoes are found in continents bordering the Pacific Ocean, an
area referred to as Ring of Fire. The Ring of Fire is the name for the area
around the Pacific Ocean where so many of the world‘s volcanoes are found.
Besides volcanoes, there are also more earthquakes in Ring of Fire than the
rest of the world. Many islands, like the Hawaiian Islands, are formed from
volcanoes.
The Economic Importance of Volcanoes
Assess the
economic importance of volcanoes
Vulcanicity results to features that are of economic value to
man as outlined below:
1. The
larva poured onto the earth‘s surface following vulcanicity forms a fertile
soil upon weathering. This soil supports agriculture as well as forestry.
Examples of fertile volcanic soils that resulted from volcanic activities are
the rich acidic soils on the slopes of mounts Kilimanjaro, Kenya and Elgon,
which supports the growth of coffee, banana, tea and other crops.
2. When
the magma solidifies, it forms hard rocks that can be quarried and used to
construct roads, bridges, houses and other infrastructures.
3. Spectacular
features formed upon vulcanicity such as mountains, calderas, caldera lakes,
cones, geysers and hot springs are interesting to look at. As such, they
attract tourist and hence earn foreign currency to the country.
4. Vulcanicity
brings minerals from deep the earth‘s crust to close or onto the earth‘s surface.
Various minerals and gemstones are mainly found in the volcanic regions.
Diamond in Mwadui is mined from the volcanic plugs and dykes. Gold and silver
are associated with the Nyanza batholith in Kenya.
5. Geysers
can be harnessed to generate geothermal electricity. Geothermal power is tapped
from geysers in volcanic regions. In East Africa, geothermal power stations are
established at Olkaria near Naivasha in Kenya.
6. Hot
water from hot springs is pumped into homes during winter to heat up homes.
This is done in cold countries like Iceland and New Zealand.
7. People
use hot springs and pools of hot water as spas. They bathe in the water for the
purpose of curing certain diseases.
8. Some
crater lakes are a source of salts and other minerals while others support fishing
activities, for example Lake Chala. Some lakes are a source of fresh water for
domestic and industrial uses.
Earth-quakes
Earthquake, Epicenter and Focus
Define
earthquake, epicenter and focus
Earthquakes
refer to the sudden shaking or vibrations of the earth’s crust due to sudden
and rapid displacement of tectonic plates along the line of weakness (faults).
It occurs mainly in volcanic eruption zones (see a map of volcanic zones
above). The point from which the earthquake originates is known as focus and
the intensity of earthquakes can be measured by using an instrument called
seismograph. The point on the surface vertically above the focus is called
epicentre
How Earthquake can be Detected
Describe
how earthquake can be detected
The
intensity and magnitude measure the strength of the earthquake. These are
obtained by detecting the Seismic waves using instruments called seismograph or
seismometer.
Intensity
is a measure of how hard the earthquake shakes the ground. It is determined
through the effects produced by the earthquake. Intensity varies from one place
to another. While the intensity of a specific earthquake varies, its magnitude
does not vary. So it is important not to confuse magnitude with intensity.
The
scale which measures the intensity is called Mercalli scale. It ranges from
undetectable, moderate, strong to major catastrophe. Magnitude refers to the
total amount of energy released and it is given on the Ritcher scale. This
scale ranges from 0 to 8.9.
The Causes and Effects of Earthquake
Explain
the causes and effects of earthquake
Causes of earthquakes
·
Faulting of the lithosphere caused by tectonic movement where
one plate slides over another plate.
·
Vulcanism can cause occurrence of the earthquake. This is due to
the fact that the magma moves under the influence of intense pressure from
within the earth’s interior.
·
Mass wasting like land slide and rock fall can cause occurrence
of earthquake, but this is for local scale.
·
Falling objects from the atmosphere such as meteorites may lead
to the shaking earth’s crust.
·
Man’s influence through his activities such as mining using
explosives like dynamites and transport vessels like trains and heavy trucks.
Effects of earthquakes
1. They
can cause loss of life and property. An earthquake is a natural disaster.
Whenever it occurs, it causes a lot of disturbances including loss of life and
properties. For example, the earthquake that hit Toro in Uganda in 1966 killed
157 people, injured about 1300 people and destroyed about 6000 houses. The
earthquake which occurred in California–Mexico border in 1975 caused damage
running into millions of dollars and injured 100 people on both sides of the
border where most of them suffered cuts from flying glass and debris. And the
earthquake that occurred in Northridge in the San Fernando Valley in California
in January 1994 killed 61 people and caused damage estimated at ten to thirty
billion dollars. This damage includes the cost of structures that collapsed
such as California Highway, when the earthquake turned the flyover to ruins.
2. They
can displace parts of the earth’s crust vertically or laterally.
3. They
can raise or lower parts of the sea floor. The Agadir earthquake in Morocco in
1960 raised the sea flour off the coast. In some areas the depth of the sea
decreased from 400 m to 15 m after the earthquake.
4. They
can raise or lower coastal rocks. In the Alaskan earthquake of 1899, some
coastal rocks were raised by 16 m.
5. They
can cause landslide and open up deep cracks in the surface rocks. The El Asnam
earthquake in Algeria, in 1954, destroyed an area of radius 40 km and opened up
deep cracks up to 3 m deep.
The possible Areas where Earthquake is likely to Occur on the
World Map
Locate the
possible areas where earthquake is likely to occur on the world map
Precautionary measures to avoid high damage from earthquakes
·
Refraining from building high-rising structures on the land
vulnerable to earthquake as well as strengthening buildings by using reinforced
concrete, steel frames, deep foundations and light roofs.
·
Geologists should detect epicentres and tell the people to
evacuate the places likely to be affected by earthquakes.
·
To avoid constructing very large water bodies like Kariba dam
which can cause the earthquakes due to the weight of water and other materials.
·
Discouraging the use of explosives like dynamites in breaking
the rocks during mining and construction operations.
External Forces
These
are natural forces that operate on the earth’s surface. The forces mainly act
on the earth’s crust or close the surface of the earth. Often the features
produced by these forces are seen on the surface of the earth. They include
mountains, volcanoes, moraines and valleys, just to mention a few.
Mass Wasting
Define
mass wasting
Mass wasting, also known as slope movement or mass movement, is the movement of the
weathered materials downslope due to gravitational forces accompanied by rain
action.
Types of Mass Wasting
Identify
types of mass wasting
Types
of mass movement are distinguished based on how the soil, regolith or rock
moves down the slope as a whole. Based on this factor, mass wasting can be
categorized or grouped into two types. These are slow and rapid mass movements, each with
its own characteristic features, and taking place over timescales from seconds
to years.
Slow
mass movement
This is
the movement of soil at very slow speed, water acting as the lubricant. Slow
mass wasting is categorized into several types. These are as follows.
Soil creep
Soil creep is the slow movement of the soil downhill afterit
gets soaked by water. This process is very slow andits evidence is provided by
tilting of trees and falling of buildings and fences.
Sol creep is activated by any process that loosens the soil, making
it easy to move gradually down the slope. The following factors influence soil
creep:
a. Alternate
heating and cooling of the soil particles.
b. The
freezing of water in the soil causing frost heaving.
c.
Removal of the soil further downthe slope.
d. Percolation
of water into the soil, acting as a lubricant.
e.
Ploughing of the soil, a factwhichmakes the soil loose and more
mobile.
Talus Creep
This is also a very slow mass movement of screes. It is very
common on sides of mountains, scarps and valleys. It takes place due to the
processes of thawing and freezing and is more pronounced in high latitude
regions.
Rock creep
Individual
rock blocks may move very slowly down a slope. It occurs commonly where
individual rock blocks are lying over clay materials. In the presence of
moisture, the clay surface becomes slightly slippery. The rock blocks may creep
slowly down the slope under the influence of gravity.
Solifluction
This is
the slow movement or flowing of weathered materials, especially when mixed with
water and gravels. It is limited on highlands and cold regions.
Rapid
mass wasting
This
involves the movement of materials in form of mudflow,land slide, rock fall and
earth flow.
Earth flow
This
type of movement occurs in humid regions. The materials on the earth’s surface
gets so saturated with water that it gains much weight, and starts to move down
the slope under the influence of gravity.This normally occurs on the slopes of
the hills or mountains. The removed earth material leaves a shallow scar on its
place of origin and it creates terraces or mounds in its destination.
Mudflow
Mudflow
is the movement of a large mass of unconsolidated rocks down the slope when
saturated with water. It flows in semi liquid state. It is common in desert
slopes, which are not protected by a cover of vegetation. This occurs, for
instance, during a torrential storm when more rain falls than the soil can
absorb.
Land slide
This is the rapid movement of surface rocks and soil down a
steep slope such as a cliff face. It includes slumping and sliding of
materials. During the movement, the block tilts and leaves holes. It is common
inwelljointedlimestone rocks, shale or clays. The common forms of landslides
are slump, debris slide,rock slide, rock fall, debris fall and avalanche.
Rock fall
This is thefree-fallingof a single mass of rock, common on steep
slopes of mountains and along scarp slopes of the sea. This is the most rapid
of all mass movements. If a rock fall occurs repeatedly, for a long time, the
broken rocks collect at the bottom of the slope in a mound calledtalus.
The Factors which Cause Mass Wasting
Describe
the factors which cause mass wasting
Mass wasting is caused by a number offactorswhichinclude the
following:
1. Gradient or slope:When the gravitational
force acting on a slope exceeds its resisting force, slope failure (mass
wasting) occurs. Mass wasting is very common and severe in areas with steep
lands as compared to flat or moderately flat lands.
2. Weathering:Various processes of weathering weaken and
loosen the rock, hence accelerating the process of mass wasting. For example,
oxidation of metallic elements and hydration of the minerals in rocks create
lines of fracture and, consequently, the onset of mass wasting.
3. Amount of water present in the rocks:Water
can increase or decrease the stability of a slope depending on the amount
present. Small amounts of water can strengthen soils because the surface
tension of water increases soil cohesion. This allows the soil to resist
erosion better than if it were dry. If too much water is present the water acts
as lubricating agent, reducing friction, and accelerating the erosion process,
resulting in different types of mass wasting (i.e. mudflows, landslides, etc.).
Water also increases the mass of the soil, this is important because an
increase in mass means that there will be an increase in velocity and mass
wasting is triggered. This is due to the fact that water lowers resistance of
the soil material to gravitational forces and this facilitates movement.
4. Vegetation:The roots of plants help bind the soil
particles together making the soil resistant to agents of erosion and
weathering. A compact soil cannot be eroded easily by running water, animals,
wind or other agents of erosion. This makes the soil hard to break and hence
resistant erode. Mass wasting processes, such as soil creep, cannot occur
easily in soilswell-coveredwith vegetation. Also the mass of vegetation cover
blocks and prevents movement of the eroded material.Plants remove water from
the ground via absorption. This reduces the amount of water in the soil and
hence the bulkiness and weight of the soil. By so doing, they reduce the
quantity of water in the soil. And because water lubricates the soil particles,
enabling them to move, reducing this water means minimizing mass wasting.The
sliding of bedding planes over each other is also reduced.
5. The nature or type of the rock materials:Clay
soil is compact and resistant to various types of soil erosion agents and mass
wasting as compared to sandy soil, which is normally loose and easy to remove
and transport by water, gravity, wind, etc. Thus, mass wasting may be more
severe on sandy soil than its counterpart clay soil under similar prevailing
conditions.
6. Overloading:When the soil accumulates in one location as a
heavy mass of the rock material, it can be moved either by action of
gravitational force or application of just a little force. Landslides occur as
a result of the soil accumulated on a sloping land to an extent of exceeding
the resistant force of gravity. Movement occurs when the gravitational force
exceeds the resistant force of soil material.
7. Earthquakes:Earthquakes cause sections of the mountains
and hills to break off and slide down. Earthquake tremors tend to loosen the
soil material and make it easy to be removed and transported. It can accelerate
rock falls, landslides and soil creeps.
8. Human activities:Theactivities of man such
as cultivation, burning, mining, transportation, animal grazing, etc,
removesthe soil cover or leads to shaking of the soil. These activities leads
to loosening of the soil particles and hence making it ease to remove and carry
away. Quarrying by undercutting the slope creates a vacuum underneath the soil.
This accelerates the earth movement in the form of landslide, soil creep and
mudflow, especially when accompanied by tremors cause by earthquake or heavy
vehicles passing nearby.
9. Climate:Climate has a great influence on mass wasting.
Areas that receive heavy rains often experience mass movements, such as
landslides and soil creep, more often compared to dry areas. On the other hand,
a little amount of rainfall does not wet the soil and so cannot cause the soil
to move.In cold regions, alternate freezing and thawing triggers mass wasting.
When the water in the soil freezes it expands. This causes the soil to be
lifted up. In the due course, the rock particles are split apart of broken
down. This entire process causes movement of the soil material down the slope.
10. Vulcanicity:Volcanic activity often causes huge mudflows
when the icy cover of a volcano melts and mixes with the soil to form mud as
the magma in the volcano stirs preceding an eruption.
The Effects of Mass Wasting to the Environment
Assess the
effects of mass wasting to the environment
Mass wasting has significant effects to the environment. The
following are some of the effects of mass wasting to the environment:
1. Formation of scars and bare land:When a
large mass of soil moves, such as it occurs in landslide, the process leaves
behind a large portion of eroded, bare and unproductive land. This land is
often not easily colonized by plants, a fact which stimulates further erosion
on the bare scar. Scars are very common on slopes of mountains such as mounts
Kilimanjaro, Kenya andRwenzori.
2. Soil erosion:When mass movement takes
place, the load often removes almost all the vegetation on its way. This
exposes the land to agents of erosion such as wind, animals, water, ice, waves,
etc. Also the place from which the material has been removed forms a scar upon
which water, ice and other agents of erosion can act and remove the soil,
further leading to gullies, depressions and gorges.
3. Formation of new landforms:The materials removed and
transported to a distant location may form hills at their destination and form
scars and depressions at the place of origin.
4. Formation of lakes:Materials of landslide
can block ariverbedand valley, preventing downward movement of water. The
blocked water accumulates on the upper side of a river valley to form a lake.
Examples of such lakes include LakeBujukuintheRwenzoriMountains,Nyabihohoin
Uganda andFunduziin South Africa. Lake San Cristobal in Colorado, USA, was
formed when mudflow dammed (blocked) a river in the San Juan Mountains.
5. Diversion of a river course:The landslide material
can block the naturalriver bed, forcing the river to divert and form a new
route. This makes the river leave its usual flowing course, and form a new
course. The direction of flow of the river is thus changed. This happened in
the Rif Atlas Mountains of Morocco in 1963 when a mudflow pushed the course of
RiverRhesana100 metres to the east.
6. Formation of a fertile soil:If the removed material
comes from a fertile land, it can form a fertile soil at the place of
destination, where fertile soil never existed, and encourage agricultural activities
to take place.
7. Damage to property:Different categories of
landslides may cause various damages to property and can adversely affect other
resources. The effects of landslide are dangerous because they destroy
everything in their path. Roads are blocked, hampering traffic flow. Homes,
buildings and other infrastructures are destroyed. The water mains, sewers and
power transmission lines are disrupted. Oil and gas production and
transportation facilities are ruined.Farms are also destroyed by various forms
of mass wasting.
8. Loss of life:As human populations
expand and occupy more and more of the land surface, mass movement processes
become more likely to affect humans. The table below shows the impact of mass
movement processes on human life over the last century.
|
Year |
Location |
Type |
Fatalities |
|
1916 |
Italy, Austria |
Landslide |
10,000 |
|
1920 |
China |
Earthquake triggered
landslide |
200,000 |
|
1945 |
Japan |
Flood triggered
landslide |
1,200 |
|
1949 |
USSR |
Earthquake triggered
landslide |
12,000-20,000 |
|
1954 |
Austria |
Landslide |
200 |
|
1962 |
Peru |
Landslide |
4,000-5,000 |
|
1963 |
Italy |
Landslide |
2,000 |
|
1970 |
Peru |
Earthquake related
debris avalanche |
70,000 |
|
1985 |
Columbia |
Mudflow related to
volcanic eruption |
23,000 |
|
1987 |
Ecuador |
Earthquake related
landslide |
1,000 |
|
1998 |
Nicaragua |
Debris avalanche and
mudflow triggered by heavy rains during Hurricane Mitch |
~2,000 |
|
2001 |
El Salvador |
Earthquake-induced
landslide |
585 |
|
2006 |
Philippines |
Rain triggered
debris avalanche |
>1100 |
|
2009 |
Taiwan |
TyphoonMarakottriggered
landslide |
397 |
|
2010 |
Gansu, China |
Rain triggered
mudflows |
1287 |
|
2013 |
Northern India |
Heavy rain triggered
landslides |
5700 |
Weathering
Define the
term weathering
Weathering
refersto a processeswhere by rocks disintegrate into small particles due to the
agents of weathering such as water, ice, wind, wave, etc. The process results
from the forces of weather, that is, changes in temperature, frost action and
rain action.
Types of Weathering
Identify
types of weathering
The main forms of weathering include:
·
Mechanical weathering;
·
Chemical weathering; and
·
Biological weathering.
Mechanical
weathering
This is
also referred to as physical weathering. It is a type of weathering caused by
changes in temperature. It is common in areas where there are extreme changes
in temperature such as hot deserts, arid and semi arid regions.
Mechanical
weathering include the following types:
Exfoliation
Thisprocess
occurs due to temperature change. During thedaytimerocks expand due to high
temperatures and contract during the night due to low temperatures.Alternate
heating and cooling set up powerful internal stress in the top layer of the
rocks.The stress produces fractures which cause the outer layer to pull away leading
to the cracking and disintegration of rocks into small particles.
The peeled off rock fragments fall to the bottom of the standing
rocks and are subjected to further alternate expansion and contraction and
disintegrate to even smaller fragments. The fragments collect at the base of
the standing rocks to form mounds of steeply sloping rock fragments calledtalusorsometimesscrees, but
the term is better used for angular rock particles produced by the action of
frost. The rocks that remain standing as exfoliation takes place are calledexfoliation domes. Exfoliation domes occur
in desert, semi-desert and monsoon regions. There are many exfoliation domes in
the Egyptian, Kalahari, Sahara and Sinai deserts.
Frost action
This is common in temperate regions where temperature falls up
to freezing point. When temperature falls (freezing point) water collects in
the rocks and it freezes, its volume increases causing the crack to deepen and
widen. Usually it involves the freezing of water in the cracks during the night
and thawing (melting) during the day in mountainous areas.This action of
thawing (melting) and freezing of water in the cracks causethe rocks to shatter
(break) into angular fragments which form screes and talus. After thawing the
cracks deepen further.
Alternate wetting and drying
This usually occurs in tropical regions. These areas have
seasonal rainfall and they get rain during summer season and during winter
season they are dry. This causes the blocks to disintegrate.
Differences between Weathering Processes
Differentiate
weathering processes
Chemical weathering
Chemical weathering involves the decomposition of some of the
minerals contained in a rock. Some rocks decompose when they come into contact
with water (H2O), or oxygen (O2) and carbon dioxide (CO2),
two of the gases that make up air.Chemical weathering includes the following
processes:
1. Oxidation– This happens when oxygen combines with a
mineral. It takes place actively in rocks containing iron, when oxygen combines
with iron to form iron oxides. This process is often preceded and accompanied
by hydrolysis.The new minerals formed by oxidation are often easily attacked by
other weathering processes.
2. Carbonation– This process occurs when hydrogencarbonate
ions react with a mineral to give a solublecompoundwhichcan be carried away in
solution. Hydrolysis often accompanies carbonation.
3. Solution–This refers to dissolution of a mineral with
a chemical substance.Rainwatercombines with both atmospheric carbon dioxide and
oxygen to form weak carbonic acid. CO2(g) + H2O(l) → H2CO3(aq).So
when the rain reaches the ground it consists of a weak acid called weak carbonic
acid. This acid helps to dissolve many insoluble minerals into minerals soluble
in water, and which can be carried away in solution. When rain containing weak
carbonic acid falls in a limestone region, it reacts with limestone (calcium
carbonate) and dissolves it into soluble calcium hydrogen carbonate, which can
easily be carried away in solution.CaCO3(s) +H2CO3(aq)
→ Ca(HCO3)2(aq)In limestone regions, the rocks are
dissolved and produce features like grikeandclint(trough and ridge).
4. Hydration– This is the process in which some minerals
absorb water and swell up, causing internal stress and fracture of the rocks.
5. Hydrolysis– This process involves the reaction of
hydrogen (in the water) with certain mineral ions (in a mineral). This gives
rise to the formation of different chemical compounds that can be easily
weathered through other weathering processes.
NOTE: Usually
two or more chemical weathering processes take place at the same time. Chemical
weathering is most marked in hot wet regions.
Biological weathering:When plants grow on
rocks, their roots penetrate into rockjointswhichlater force the rocks to break
apart. Also man contributes much to rock disintegration through farming
activities, mining, quarrying and construction. Macro- and microorganisms also
disintegrate rocks through burrowing and by mineralization process. Bacteria,
for example, in the presence of air, break somemineralswhichare dissolved in
the soil. Plants also absorb minerals from the soil by their roots. Decayed
vegetation produce organicacidwhichremain in the soil. All of these actions
help to weaken the rocks.
The Significance of Weathering
Assess the
significance of weathering
Weathering is important to man in the following ways:
1. Weathering
leads to soil formation. Soil is formed through the process of weathering of
rocks. Various forms of weathering lead to rock disintegration and hence
formation of the soil. The soil is an aggregate of organic and inorganic
particles formed by different processes of weathering.
2. Weathering
may shape the rocks into attractivefeatureswhichcan attract tourists and hence
earn the country and communities the much needed foreign exchange. An example
of a feature that can attract tourists is the Bismarck Rock on the south shore
of Lake Victoria.
3. The
processes of weathering weaken the rocks such thatthey can be easily acted upon
by agents of erosion. The process helps to shape the earth and produce various
landforms. This, in turn, influences the type of human activities that can take
place in an area. So the process is very important in supporting life.
4. When
the rocks are weathered they become weak and hence easy to exploit, e.g. by
quarrying. This process also helps to break up large rocks into small fragments
such as sand, which is used for construction purposes.
5. Weathering
serves as carbon sink.Any process that reduces the amount of carbon dioxide
from the atmosphere is termed ascarbon
sink. Some processes of weathering involve absorption of carbon
dioxide from the atmosphere. This helps to remove excess carbon dioxide from
the atmosphere. Limestone and other carbon-based sedimentary rocks are
important carbon sinks.
Erosion and
Deposition by Running Water, Ice, Wind and Wave Action
The Concept of Erosion and Deposition
Define the
concept of erosion and deposition
River
refers to a mass of water flowing through a definite channel over a landscape
from river source to river mouth. River source is the place where a river
starts. It may be in the melt water from glacier e.g. river Rhome (France), a
lake, e.g. Lake Victoria, the source of river Nile, a spring e.g. Thames
(England) or it can be formed following steady rainfall e.g. river Congo. River
mouth can be anywhere a river pours its water, e.g. a lake, ocean or sea.
How Agents of Erosion and Deposition Operate on the Landscape
Examine
how agents of erosion and deposition operate on the landscape
The
river has three functions as it flows through its channel. These are river
erosion, transportation and deposition.
River
erosion
Erosion of a river operates in three ways, that is, head ward,
vertical and lateral erosions.
·
Heard ward erosion– this
is the cutting back of the river at its source. It is through this erosion that
a river increases its length.
·
Vertical erosion– this
is erosion by which a river deepens its channel.
·
Lateral erosion– This
is the wearing away of the sides of a river by water and its load. It is
responsible for widening of a river valley.
River erosion involves four related processes. These are
abrasion (corrasion), attrition, corrosion (solution) and hydraulic action.
·
Hydraulic action:This is
the process whereby the force of moving water plucks and sweeps away loose
materials, such as silt, gravel and pebbles. Materials plucked by hydraulic
action are responsible for bank caving and slumping.
·
Corrasion (abrasion):This is
when the load of the river rubs against the bed and sides of the river channel.
This causes wearing away of the sides and bed of the river. The amount of load
determines the nature of erosive power and rate of erosion. This is a source
ofpotholesin the river bed.
·
Attrition:This is
when the rock fragments in a river’s load are broken into small fragments due
to collision against one another as the load is carried downstream along the
river channel. As the river moves along its course, its fragments get
progressively smaller because of disintegration and wearing away.
·
Corrosion (solution):River
water dissolves certain minerals leading to dissolution and disappearance of
some rocks, e.g. limestone, rock salt and chalk.
River
transport
This is the process which involves carrying away of the
weathered and eroded, loose materials from one place to another. The materials
carried out by river is called load. River transports its load in four ways.
These ways are as follows:
1. Saltation– this is the process in which small pieces of
the rock fragments are carried by a river while bouncing on theriver bed.
2. Traction– this is the dragging or rolling of large
boulder such as pebbles along itsriver bed.
3. Suspension– This involves transport of fine or light
materials like silt and mud, which are carried in suspension forms. This is
common when the river flow is too strong.
4. Solution– this involves moving some materials that
dissolve in water, which are carried away in solution form.
A river
transports its load until it has insufficient energy to transport it any
further. When this happens, the load is deposited.
River deposition
A river deposits its load when its volume and speed decrease. A
river volume decreases when:
1. itenters
an arid region especially a hot desert;
2. itcrosses
a region composed of a porous rocks e.g. sand and limestone; and
3. duringthe
dry seasons or in a period of drought.
A river speed decreases when:
1. itenters
a lake or sea; or
2. whenit
enters flat or gently slopping plain such as a valley bottom.
Deposition
takes place when the river has insufficient energy to carry its entire load.
The first part of the load that is dropped consists of boulders and pebbles.
The last part to be dropped is the fine sediment, calledsilt. Deposition takes place at any point in a river’s course.
THE
LONG PROFILE OF A RIVER
The long profile of a river is the line following the course of
a river from its source to its mouth. Three courses or sections of a river can
be distinguished. These are:
·
The upper course.
·
The middle course.
·
The lower course.
The upper course/section
This is the first stage of a river. It is sometimes called the
youth or torrent course.Its characteristics are as follows:
1. It is
the river source.
2. The
speed of a river is high.
3. Most of
the works of the river include vertical erosion.
4. The
cross-section of a river valley in this section of a river is V–shaped.
5. The
slope of a profile is very steep.
6. It is
sometimes utilized for hydroelectric power (H.E.P) generation.
Erosional and Depositional Features for each Agent
Examine
erosional and Depositional Features for each Agent
The main features of the upper section are deep and narrow,
V-shaped valley; a steep gradient; pot holes on the river bed; interlocking
spurs and waterfalls and rapids, often with plunge pools.
·
V–shaped valley: this
is a deep, narrow valley at youth/first stage of a river.
·
Pot holes:These
are circular depressions on theriver bed. They are formed when pebbles carried
by the swirling water cut circular depressions in the river’s bed.
·
Interlocking spurs:Aninterlocking spur, also known as anoverlapping spur, is one of any of a
number of projecting ridges that extend alternately from the opposite sides of
the wall of a young,V-shaped valleydown
which a river with a winding course flows. Each of these spurs extends
laterally into a concave bend of the river such that when viewed either
upstream or from overhead, the projecting ridges, which are calledspurs, appear to "interlock" or "overlap" in a
staggered formation like the teeth of a zipper.As the river erodes the
landscape in the upper course, it winds and bends to avoid areas of hard rock.
This createsinterlocking spurs.
·
Waterfalls and
rapids-Waterfall:Awaterfallis a
place where water flows over a vertical drop in the course of a stream or
river. A waterfall is formed when there is sudden change or drop in the bed of
a river. Although waterfalls can occur in almost any part of a river’s course,
they are most common in the upper course. Examples of waterfalls are Owen Falls
in Uganda, Victoria Falls in Zimbabwe and The Livingstone
The Yosemite Falls in USA
·
Rapids:These
are sections of a river where theriverbedhas a relatively steep gradient,
causing an increase in water velocity and turbulence.Rapids are characterised
by the river becoming shallower with some rocks exposed above the flow surface.
As flowing water splashes over and around the rocks, air bubbles become mixed
in with it and portions of the surface acquire a white colour, forming what is
called "whitewater".Rapids occur where the bed material is highly
resistant to the erosive power of the stream in comparison with the bed
downstream. Very young streams flowing across solid rock may be rapids for much
of their length.
·
Plunge pool:This is
a large depression formed at the base of a waterfall.
·
Gorge:It is a
steep, narrow and elongated valley. A gorge often is formed when a waterfall
retreats upstream, e.g. a gorge found in Victoria Falls.
The middle/maturity stage/section
This is
the second stage of a river. The main features of this section are bluffs and
waterfalls and rapids.
The characteristics
features of the middle course of a river valley
1. The
speed of a river is fairly low.
2. Most of
the work of a river is transportation.
3. The
cross–section of a valley in this section is an open V.
4. The
slope of a relief is gentle
5. The
volume of a river increases.
6. Lateral
erosion predominates.
Features associated with
the middle course of a river valley
1. Bluffs:These are steep slopes of the truncated spurs
in middle course where interlocking spurs turn into bluffs.
2. Waterfalls and rapids:Waterfalls and rapids can
also be found in the middle stage of the river valley. This is mainly caused by
riverrejuvenation which increases erosive activity and transportation,
hencedevelopment of waterfalls.
The old/lower stag
Third is
the third stage of a river. The main features of the lower section of a river
valley are a flood plain; braided river; ox-bow lake; levee and deferred
tributary and delta.
Its characteristics are as follows:
1. It is
the river mouth.
2. Always
there are gradient falls or slope falls.
3. The
main work of a river is deposition.
4. The
cross–section of a valley is a U–shaped valley.
5. The
speed of a river is decreased.
6. The
river valley is very wide.
The Importance of Erosional and Depositional Features to Human Beings
Assess the
importance of erosional and depositional features to human beings
Some
features resulting from erosion and deposition are very important to human
beings in the following ways: Loess form very fertile soil in desert land,
water falls attract tourists, headlands in coastal areas are natural ports.
Coastal features form breeding places for fish, coral reefs are used as
building materials and for settlement.
Artificial Forces
The Meaning of Artificial Forces that cause Earth Movements
Explain the
meaning of artificial forces that cause earth movements
These
are forces that are caused by human beings through their activities such as
farming, mining, setting up settlements, road construction, transport, etc. In
the previous sections we learned about the natural forces that affect the
earth. We saw that the forces act on and within the earth. These forces occur
naturally with little or no human intervention.
In this
section, we shall deal with forces that occur as a result of human actions,
hence called artificial or man-made forces. Man is considered as an agent of
denudation, that is, he takes part in destruction or removal of some parts of
the earth’s surface. This shows that man can modify natural landforms and,
therefore, acts as the agent of weathering, mass wasting, erosion,
transportation and deposition on the earth’s surface.
Human modification of the land helps loosen large chunks of
earth and cause them to slide downhill. Man produces forces that affect the
earth through the following activities:
·
Removing vegetation:A slope
with lots of vegetation is less susceptible to mass movement than a bare
slope.Bare, exposed soil is very easily eroded, and can contribute to mass
movement activity.Vegetation: helpshold soil, loose rock, andregolithtogether
by its roots; reducesthe direct erosive impact of rainfall and other
precipitation; activelyreduces ground moisture by using it to contribute to
plant growth; and produceslitter and organic products (leaves, twigs, grasses,
fruits) that help stabilize the soil.
·
Mining:In the
course of mining, man uses machines to dig the soil and blast rocks. These
activities results to earthtremorswhichloosen the soil particles making then
vulnerable to removal by agents of weathering and denudation. Blasting also causes
fractures in rocks, a fact which makes them less stable and resistant to shear
and stress. If this happens, especially on steep slopes, the probability of
occurring landslide is very high.
·
Farming activities:Farming
involves digging the soil by using farm implements such as hoes, tractors,
harrows, spades, etc.These activities involvesbreaking up the soil and rocks by
the implements. In this way, crop cultivation directly leads to weathering and
erosion. Overstocking (keeping many animals in just a small piece of land) also
leads to soil erosion. This is because overstocking is usually accompanied with
overgrazing, an act which removes the vegetation cover. This triggers soil
erosion and other weathering processes.
·
Building and
construction:Breaking up the soil for construction of houses and other
infrastructures can dramatically increase the potential of mass movement. These
processes involve tearing rocks to get room for setting up infrastructures such
as roads, railways, airports, seaports, etc. This leads to destruction of the
soil, hence triggering mass movement, weathering and erosion.
·
Fishing:Fishermen
in less developed countries sometimes use weapons such as dynamites to kill and
catch fish. Tremors produced by these illegal fishing tools can cause
fracturing of the coastal rocks. This causes both weathering and erosion.
·
Navigation:In some
few cases, marine vessels accidentally crush onto stones in water, peeling or
breaking then into pieces. This leads to rock disintegration, a typical form of
weathering.
·
Transport:Vibrations
from machinery, traffic, weight loading, stockpiling of rock or ore from waste
piles and from buildings and other structures loosen the soil and make it prone
to soil erosion and weathering.
·
Construction of dams and
canals:Construction of dams, such as theMteradam in Tanzania and canals
such as the Suez Canal in Egypt, involves removing a large junk of rock. This
breaks up the soil, leading to weathering and soil erosion.
·
Warfare:The use
of atomic bombs and other heavy weapons in war leads to destruction of the
soil.During times of war, heavy and destructive weapons such as atomic bombs,
shells, rockets and grenades are dropped or fired towards the enemy. When these
weapons fall on land, they detonate and blow up a large mass of the earth,
causing weathering and erosion.Military equipment such as tanks, heavy trucks
and caterpillars break up rocks over which they pass. At the same time, they
loosen the soil and carry away some of it as they move along.
The Causes and Effects of Artificial Forces
Describe
causes and effects of artificial forces
Apart from the effects caused by natural forces that affect the
earth, man-made (artificial) forces have an effect of creating artificial
landforms and features on the earth’s surface. These include the following
features:
1. Man-made
lakes such as LakeCahoraBassain Mozambique, Lake Volta in Ghana, LakeKaribain
Zambia (the world's largest artificial lake and reservoir by volume) and Lake
Nasser in Egypt.
2. Man-made
rivers in the form of canals such as Suez and Panama Canals.
3. Wells
and boreholes
4. Roads,
harbours, railways, airports, bridges, etc.
SOIL
Soil Formation
Soil
Define
soil
The
term soil is derived from the latin word “solum” which means ground. Therefore
can be defined as the uppermost surface layer of loose or unconsolidated
material which overlies the crystal rocks and on which plants grow.ORSoil is
the natural body of mineral, organic and nutrient constituents which result
from the interaction of the country rock with the environmental factors of
climate, topography, plant and animal life.
Factors for Soil Formation
Describe
factors for soil formation
Soil
formation (pedogenesis) is principally initiated by the weathering of the
parent rocks. Weathering can be chemical or mechanical. But the type of soil
and rate of soil formation depend on a number of interacting factors (interplay
of factors) in a particular environment, hence soil is the product of its own
environment.
Soil continuously changes. The changes are generally slow but in
certain circumstances, especially where human activities are involved, the
changes can be rapid. The study of soil involves understanding the factors
responsible for its formation. These factors are parent materials, climate,
living organisms, topography and time:
1. Parent Material (Rock):This is the most
important factor in soil formation since it determines the type of soil formed,
soil colour, soil depth, the rate of soil formation, soil structure, soil
texture, porosity and mineralogical composition or its fertility. It also
influence soil maturity, such that if the rock is hard, It takes a long time
for soil to mature while the rate of maturity is fast where the parent rock is
soft. The fast maturity of soils, formed from soft rock is due to the fast rate
of weathering process. Mature soil are deep and productive while immature soils
are shallow and less productive.
2. Living Organisms (Biotic):These include the
influence of plants, animals as well as human beings. Vegetation influence both
chemical and mechanical weathering leading to the development of the soil
profile. Also vegetation contribute to soil fertility by adding humus in the
soil after dying and decomposing. Some plant roots (legumes) have nodules with
bacteria that fix nitrogen into the soil. Plants roots modify the soil by
increasing porosity, improving the soil depth and aeration.Micro - organisms
are active in decomposition of the organic matter to form humus. Burrowing animals
facilitate weathering process by loosening the soil particles. Lastly man’s
activities like cultivation, break up the rocks into smaller fragments. Man
also adds humus to the soil which contribute to soil profile development.
3. Climate: The important variables under climate
include temperature, precipitation and wind. Temperature affects the rate of
decomposition of organic matter, it contribute to soil profile development
through weathering as well as the rate soil development. Where there is high
temperature, soil development tends to be fast due to the fast rate of
weathering, and where temperature is low, there is also a low rate of soil
development due to the low rate of weathering process. Precipitation also
affects soil profile development. In some areas soil is eroded, leading to soil
profile destruction while in areas deposition leads to positive soil
development due to accumulation of weathered materials and organic matter.
Rainfall adds moisture, which facilitate both chemical and mechanical weathering
and hence soil profile development. Wind has both positive and negative impacts
on soil profile development. It can erode the soil through deflation leading to
soil degradation or it can deposit some materials at the edge of the desert to
form the soil called loess.
4. Relief (topography):The role of topography in
soil formation is mostly indirect. It influences climate and vegetation. It
controls the rate and nature of weathering, removal and deposition
(redistribution) of the soil parent materials. The most important aspects of
topography as a factor of soil formation are slopes; altitudes, aspects and
location along the slope. Soil erosion is rapid on steep slopes and less on
gentle slopes.Therefore on steep slopes soil profiles are shallow while on gentle
slopes they are expected to be deeper. Also leaching are more pronounced in the
upper-slope areas leading among other things to well-drained soil.Altitude
affects soil mainly through the action of climate and vegetation. Altitude
lowers temperature and increases precipitation. Thus leads to zonation of
climate, vegetation and soil along hillsides. In terms of aspects, the side
that receive more sunshine tends to have well developed soil than the side
which receives low amount of sunshine since isolation accelerate plants growth
and the weathering process.
5. Time: The time factor may be associated with the age of the country
rock especially those on which soil have been directly formed. It may also be
associated with the duration of the operation of soil formation process, that
is whether the soil has sufficient time to form mature profiles and associated
characteristics or not. When soil formation has taken a long and enough time,
soil tends to be more mature, they are usually deep and well developed.
The Importance of Soil
Assess the
importance of Soil
The following is importance of soil formation
1. Medium for plant growth.Soil is where most plants
grow. Soil provides anchorage for the plants as well as protection of roots
from damage.It is where or a medium through which water, air and nutrients are
made available to plants. The well-aerated soil facilitates the absorption of
water and nutrients from the soil by plants.
2. Soil support animal life.As soil support plant
life it also support animal life because plants are the source of foods to
animals and this is most for herbivores. Also some animals eat soil as food in
form of salt licks for example pregnant women who lack some minerals in their
bodies.
3. Soil provide habitat for living organisms.In the
soil there are some animals living there example burrowing animals like
rodents, earthworms and termites
4. Provide sites for agricultural activities.The
fertile soil promotes agriculture activities, both animal husbandry and crop
cultivation. This is because soil supports the growth of pasture for animals.
5. Provide settlement.Soil influences
distribution of settlement for example the areas with good fertile soil are
densely populated compared to the areas with poor soil.
6. Soil provide building materialsSoil is
used in making bricks, tiles and white wash. All these materials are used in
building houses, bridges etc. Also soil is used directly in road construction
7. Source of mineralsThere are some minerals
found in soil that can be extracted for commercial purposes. Also it is used to
manufacture fertilizers as it contain minerals for example the fertilizers that
contain phosphate e.g. In Minjingu (Manyara) region.
8. It provides raw materials for pottery and ceramics.Soil is
used in making pots and these help to provide income to those who engage in
this activity.
Soil Composition and Properties
Illustrate
soil composition and properties
Soil is made up of the following components
·
Organic matter (humus)
·
Inorganic matters (minerals)
·
Soil water and soil air
Organic
matter (humus)
This
form 5% of the total volume and is made up plant and animal remains. Humus is
formed as a result of decomposition of animal/plants remains.
Importance of humus
·
It improves the structure of the soil
·
It regulates the soil temperature.
·
It leads to higher agricultural production.
Inorganic
matter (minerals)
This
forms 45% of total volume and is made up of minerals from the parent rock.
Minerals constitute some nutrients needed by plants for growth.
Soil
water
This
forms 25% of the total volume. It is one of the important soil constituents. It
is derived essentially from rainfall especially from infiltration; Too much
water in the soil leads to leaching and hence loss of nutrients.
Importance of water to soil
·
It regulate the soil temperature
·
It control the chemical process like chemical weathering as well
as mechanical weathering
·
It helps in the solution and transfer of nutrients in the soil.
Soil
Air
This
forms 25% of the total volume and constitutes the soil atmosphere from which
plants and animals obtain oxygen for their metabolism. Air accelerates
oxidation and biological activities and aerated soil lead to good production
while poor aerated soil will lead to poor production.
Soil Profile and
Characteristics
Soil Profile
Define
soil profile
Soil
profile is the vertical section of the soil from the surface to the parent rock
characterized in distinct layers (horizons), usually of different textures and
colours. Ideal soil profile has horizons A, B, C.
Soil Profile and its Characteristics
Illustrate
soil profile and its characteristics
Physical
properties of the soil include soil profile, soil depth, soil colour, soil
texture and soil structure
Chemical properties of the soil includes soil P.H, carbon
exchange and leaching.
·
A – Horizon – Is the top most layer which include organic matter
to form Ao. This horizon varies in colour from place to place example dark to
grey. It is also called the zone of eluviation from which the materials are
washed down through leaching.
·
B – Horizon – Is also called the zone of accumulation or
illuviation. In this layer materials washed from the A – horizon are deposited
or accumulated. Accumulation of washed down materials lead to formation of
another layer called Hard Pan.Horizon A and B are also referred to as Solum
(soil) such that A – horizon is the top soil and B - horizon is the sub soil
·
C – Horizon is the partially weathered parent rock from which
the soil develops. It is underlain by D – Horizon which is a fresh non -
weathered parent rock.
Simple Soil Classification
Soil According to Textural Groups
Classify
soil according to textural groups
SOIL
DEPTH
Soil
depth is the variation of soil from place to place due to materials influenced
by the nature of the rock as well as duration of the soil forming processes.
Soil is shallow especially in steep slopes due to erosion and in areas where
the underlying rock is hard. Other places have deep soil due to soft parent
rocks.
SOIL COLOUR
Soil colour is determined by the mineralogy composition from
which the soil is derived and organic matter content. It varies from one place
to another. Soil colour can be used for classification and description of soil
of a certain place. The colours are grouped into:
·
Dark (Black, grey, dark grey and dark brown)
·
Bright (yellow, orange, red, redish brown)
·
Light (whitish – grey, white)
Some
soil can have one colour throughout like red earths and yellow brown.
SOIL
TEXTURE
This refers to the degree of coarseness or fineness of the soil
materials especially soil mineral particles. It can also be referred to as
variation in the particle size.According to soil texture, soil can be
classified as
1. Course
sand 2 to 0.2 mm diameter
2. Fine
sand 0.2 to 0.02 mm diameter
3. Silt
0.02 to 0.00 mm diameter
4. Clay
less than 0.002 mm
5. Loan
soil i.e. mixture of sand, clay and silt
IMPORTANCE OF SOIL
TEXTURE
1. It
influences the soil porosity, permeability, compaction, and structure
2. It
influences plant growth
3. It
influence cultivation during the agricultural activities
4. It
influences soil resistance against erosion
5. It
influences soil fertility
SOIL
TEMPERATURE
Soil
has certain degree of temperature and this tend to vary from place to place due
to the variation in the climatic conditions. In cold areas like Tundra regions
soil is also cold this is due to the small amount of insolation received there.
In tropical areas soil are warm due to high intensity of insolation heating the
surface.
IMPORTANCE OF SOIL
TEMPERATURE
It controls biochemical and chemical processes especially the
decomposition of organic matter and plant growth.
·
It determines the existence of micro- organisms in a certain
area.
·
It controls the amount of moisture in the soil
SOIL
POROSITY
This
refers to the total volume of pores or spaces between particles of the soil
materials in undisturbed soil.
Soil porosity is influenced by
·
Soil texture – The finer the particles the greater will be the
total surface area. Hence the soil with fine particles like clay has greater
porosity.
·
Structure of the soil also influences permeability.
SOIL
STRUCTURE
This
refers to the arrangement of soil particles into aggregate compound particles.
Individual undisturbed soil is called ped. The aggregation of soil particles
produce peds of different shapes and sizes when aggregation is absent as in
loose sand soil, the soil is described as structure less. Strongest of the soil
is influenced by its organic matter.
IMPORTANCE OF SOIL
STRUCTURE
·
It determines water retention capacity and aeration
·
It is an indicator of soil fertility or sustainability for
agricultural activities
·
It influences plant growth by influencing the root penetration
and water retention
CHEMICAL
PROPERTIES
SOIL REACTION (PH)
Soil
reaction is the term used to describe the degree of acidity and alkalinity in
the soil and it results mainly from climate. This degree of acidity and
alkalinity in the soil is expressed in the PH.
PH is
the value which is measured in terms of the hydrogen ion concentration.PH scale
runs from 1 to 14.The PH 7 is neutral.Any condition below 7 is acidic and any
condition above 7 is alkaline.
IMPORTANCE OF SOIL PH
·
It helps in determining the selection of crops and agricultural
distribution
·
It affects plant growth such that where there is too much
acidity there will be poor plant growth. This is because the increase of
acidity leads to the increase in leaching which affects soil structure.
LEACHING
This is
another chemical property of soil referring to the process in which nutrients
are washed down in solution from the top- soil layer. During leaching process
the bases are washed down leading to concentration of hydrogen ions which in
turn cause the increased acidity in the top soil.Leaching is very effective in
wet conditions.
SIMPLE HYPOTHETICAL
PROFILE FOR MATURE SOIL
The
soil profile varies from one place to another depending on the variation in
environment conditions.
For
example under deciduous forest, soil with little organic matter can be produced
(brown earth or brown forest soil) while in mid latitude grasslands deep black
earth soil (chernozem) is formed.Chernozem has a lot of organic matter. In the
desert area the soil profile usually lack the Ao horizon due to scarcity or
absence of vegetation.
SIMPLE SOIL
CLASSIFICATION
Soil
classification refers to the grouping of soils according to specific
characteristics, such as properties or factors like climate also soil can be
classified according to the age, texture and colour. One common classification
is that based on texture.
According to the soil texture triangle, there are three main
textures namely sand, silt and clay. This is based on the size of their
particles as discussed earlier. The percentage content of each one of these
determines the type of soil according to texture. Note that sandy soil have
sand content of over 45%, clay soil have above 27% while silt soil have silt
content of above 40%.
Soil Texture Triangle
·
SAND:This
soil consists mainly of coarse and fine sand and contain very little amount of
clay such that it is not sticky when wet and is loose when dry, percentage of
sand is above 85, that of clay is up to 10 and silt is up to 15. When such soil
is rubbed, it does not leave any film on the fingers.
·
LOAMY SAND:This
consist most of sand but with sufficient clay such that it gives it a slight
plastic quality when it is very moist. When it is rubbed between fingers it
leaves a slight film of fine material, sand particles account for 70% to 90%,
clay up to 15% and silt up to 30%
·
SANDY LOAM:This
soil has high percentage of sand between 43% and 85% with clay content of up to
20% and silt up to 50%. It moulds easily when it is sufficiently moist but does
not stick easily to the fingers.
·
LOAM:In this
soil, sand and silt dominate with an average of 40% each while clay account for
about 20% on average. It moulds easily when it has sufficient moisture and does
stick to the fingers to some extent.
·
SILT LOAM:It has
a high percentage of silt of between 50% and 87%, sand between 13% and 50% and
clay up to 27%. It is moderately plastic and not very sticky it has a smooth
soapy feeling due to high content of silt.
·
SAND CLAY LOAM:This
has over 45% sand, up to 28% silt and clay between 20% and 35%. It can be a bit
sticky because of the clay content but quite porous because of the sand.
·
CLAY LOAM:Sand
content between 20% and 45% silt between 15% and 53% clay between 27% and 40%.
This one has sticky distinction when moist because of clay.
·
SILT CLAY LOAM:The
amount of sand is between 27% and 60%, silt between 40% and 78% and clay
between 27% and 40%. The high silt content makes it smooth and has a soapy
feeling. It is less sticky than clay loam or silt clay.
·
SILT:This
have over 80% silt particles, up to 20% sand and less than 12% clay. It is
predominantly smooth and has a typical soapy feeling of silt.
·
SANDY CLAY:Sand
between 45% and 65%, silt up to 20% and clay between 35% and 55%. In the
presence of sufficient moisture this soil is plastic and sticky clay and sand
are dominant.
·
CLAY:The
proportion of sand goes up to 45%, while that of silt is up to 40% clay account
for above 40%. The soil is sticky when moist and has a plastic feel. It can be
rolled into threads when moist and can be moulded into different shapes. And
can retain fingerprints.
·
SILT CLAY:Sand up
to 20%, silt between 40% and 60% and clay between 40% and 60%. This soil is
composed of almost fine particles throughout. It is smooth and has to some
extent the soapy feel of silt but has a degree of stickiness because of the
high proportion of clay.
Soil Erosion
Soil Erosion
Define
soil erosion
In this
subtopic there are various concepts to be discussed, these are definition of
the term, agents of soil erosion and how they work, types of soil erosion and
its effects on social and economic activities. Also, demonstrating ways of
controlling soil erosion through the application of various conservation
techniques.
Soil
erosion is the wearing away, detachment and removal of soil materials from one
place to another place through agents like water, wind and ice.
How Agents of Soil Erosion Work
Examine
how agents of soil erosion work
There
are several agents of soil erosion these are water, wind and ice.
WATER
Water is the most important agent of soil erosion , the erosion
by water involves the following:
·
Splash erosioncaused
by moving water from rain, this tends to remove some of the materials from one
place to another.
·
Sheer erosionwhich
involves the removal of the uniform cover of the soil by surface run-off on
gentle slopes.
·
Rills erosionthat
leads to the formation of small channels called rills on the surface.
·
Gully erosion,that
leads to the formation of deep troughs called gullies due to severe under
cutting
·
River erosion,takes
place in the specific Chanel called river valley
WIND
Wind is
another agent of soil erosion. It takes place in arid and semi-arid or where
soil is loose. The soil in such areas is dry, loose and unprotected because of
the scarcity of vegetation. It is turned into dust which is then blown away by
wind.
Types and Effects of Erosion to Social and Economic Activities
Describe
types and effects of erosion to social and economic activities
There
are main two types of soil erosion which are normal geological erosion and
accelerated soil erosion
NORMAL
GEOLOGICAL EROSION
Is the
wide spread type of erosion that occurs wherever there is a natural flow of
energy and matter on the earth’s surface without man’s influence. It is
fortunately very slow and so not normally injurious to the soil cover of the
world.
ACCELERATED
SOIL EROSION
Is the
type of erosion associated with man’s activities (man included). It is
spectacular (very destructive) therefore it has attracted man’s attention. Its
side effects include physical loss arising from the reduced crop yield and
total crop failure and or wasted efforts and money spent on unsuccessful soil
conservation projects.
EFFECTS OF SOIL EROSION
Soil erosion leads to the followings effects both socially and
economically:
·
Pollution of water bodies due to the introduction of materials
eroded from the surrounding areas.
·
Loss of fertility which in turn causes the reduction in yields
or total crop failure
·
Migration of people from areas affected to the areas which have
not been affected by erosion.
·
Over flooding of the rivers as a result of the creation of the
small channels leading to the river system.
·
Deforestation as a result of the death of plants due to the loss
of soil
·
Loss of habitat as a result of deforestation caused by the loss
of soil
·
Soil erosion can lead and accelerate rock weathering by exposing
the underlying rock to the weathering agents like temperature
·
It leads to the cost incurred in during the process of
conserving the soil, which has been eroded.
·
Soil erosion can destroy transport and communication systems
like roads, railway lines and telephone posts
·
It can lead to the destruction of houses, rendering people
homeless.
Population Growth and Rate of Soil Erosion on the Quality of
Life
Relate
population growth and rate of soil erosion on the quality of life
As discussed above we can see that soil erosion can affect the
quality of life of the people positively and negatively.
·
When the region is severely affected by the soil erosion, where
crop production is impeded, when useful soils are carried away, the region
experiences shortage of food. This causes famine and malnutrition. With
inadequate nutrition child mortality rate goes up and population growth is
impeded.
·
When the foundation of existing buildings and roads are eroded.
Accessibility to areas is made difficult. Such areas are isolated in terms of
social services such as hospitals and education. The general health and welfare
of the people become poor leading to increase in mortality and lowering of
population.
·
When life becomes unbearable in the rural areas because of
severe soil erosion, able-bodied persons especially men migrate to urban areas
to other better areas in search of employment. This reduce population in the
affected areas as well as the required man power to develop the areas.
The ways of Controlling Soil Erosion through the Application of
Various Conservation Techniques
Demonstrate
ways of controlling soil erosion through the application of various
conservation techniques
The following are the some of the central measures that can be
taken to control erosion:
·
Afforestation and
Reforestation:Afforestation is the planting of trees where no forest has been
known to exist.Reforestation is the planting of trees on land that previously
had a forest.
·
Control of bush fires:When
open grassland are burnt the soil is directly exposed to agents of erosion.
·
Controlled open grazing:Overgrazing
which is another cause of soil erosion should be avoided by mulching the number
of livestock kept on any piece of land.
·
Erecting brushwood
barriers:On land where gullies have developed, barriers of brushwood or
even stone walls can be constructed across the gullies to help trap the soil.
·
Construction of cut-off
drains:Cutoff drains are open trenches which are dug across the slope
and soil is heaped on their down – slope sides to form a kind of ridges. These
drains prevent large amount of water that might have resulted in formation of
rill, gully and sheet erosion from down the slope.
·
Constructing of dams and
weirs:These are structure that are built across river’s valley for the
purpose of controlling a river flow or for retaining water in a large reservoir
within the valley. They may be made of earth’s (earth dam) and stone (rock fill
dam).
·
Use of artificial
waterways:An artificial waterway is a small channel that is constructed
down a slope and into which surface run-off collects. Normally water from
cut-off drains as well as from terraces should be discharged into rivers or
into non-erodible areas such as stony grounds.
ELEMENTARY SURVEY AND MAP
Meaning and Types of Survey
Simple Land Survey
Explain
the meaning of simple land survey
Surveying
is the science of measuring and record distances, angles and heights on the
Earth’s surface to obtain data from which accurate plans and maps are made.
Surveying
is also the art and science of making or taking measurements both linear and
angular on the Earth’s surface at different positions for the purpose of producing
a plan or map.
Angular measurementmeans measuring the
distance from a given reference point to an observed object. The distance is
measured in a clockwise direction from North.
Linear measurementis the distance measured
along the surface of the ground such as a horizontal distance.
Purpose of surveying
1. To
prepare maps and plans
2. To
calculate areas and distance
Types of Simple Land Survey
Explain
the types of simple land survey
Surveying can becategorisedinto various types or branches
depending on its purpose, function and nature. Thetypes or branches include:
a. Topographical survey:This kind of survey is
carried out for the purpose of preparing topographical maps.
b. Geodetic survey:This kind of survey is
carried out with the aim of knowing the Earth’s shape and size (the Earth's
configuration)
c.
Cadastral survey:This
kind of survey is conducted with the aim of preparing a legal document such as
house plans, town or city boundaries, etc. It is mainly used for ownership
purposes.
d. Engineering surveys:This kind of survey is
conducted for the building and construction layout of railways, bridges and
roads.
e.
Geological survey:This
kind of survey is conducted with the aim of knowing the distribution of rocks
and minerals under the Earth’s surface.
f.
Topographical surveying:This
kind of survey is carried out for the purpose of preparing topographical
maps.Topographical maps are those maps whose contents include both man-made
features such as linear features (roads, railways, telephone lines, water
systems, and electricity poles) and natural features such as rivers, oceans,
mountains, etc.The topographical survey has the following ways or methods of
conducting the survey: 1.Chainortapesurvey; 2. Theprismaticcompasssurvey;
3. Theplanetablesurvey;
4. The technique of levelling.
Chain Survey
Chain/Tape Survey
Describe
chain/tape survey
It is a
method of Surveying in which no angles are measured but only linear measurement
is taken in the field by using a chain or tape measure.It measures a series of
straight lines on the ground with a chain or tape measure and all fixed points
relative to theline of traverseeither
by right angles (offsets) ortie lines.
Types of Equipment used in Chain/Tape Surveying
Explain
different types of equipment used in chain/tape surveying
Chain
·
Thechainis made
up of steel wire which is divided intolinksandtogs(rings) to facilitate folding.
·
It is sometimes used as a unit of measurement
·
It has brass handles at both ends for easy handling. Thelinkis 0.2m or 200mm in diameter.
·
The length is 20m or 30m.
Tape
·
Steel tape
·
Linear tape
Atapeis made from fiberglass or a steel strip and is 10m, 20m or 30m
in length graduated in 10mm divisions and numbered at each 100mm (10)
divisions.It is used for measuring short distances
Ranging
poles
Ranging polesare made up of wood or
light metal and measure about 2m long at the top. The equipment has steel
shades on its legs so it can be stuck into the ground. Ranging poles are
painted red and white so that they can be easily seen even from a distance.
They are used for making stations.
Arrows
Arrowsare made of steel wire of diameter 4mm and their ends are bent
into a circle where red cloth is tied to facilitate visibility. They are used
for showing points on the ground.They are also used for counting the number of
chains while measuring a chain line.
Pegs
Pegsare made of wood 40mm square by 50cm long and are used for
permanently marking positions during survey
Surveyors'
band
Thesurveyor’sbandis made of a steel strip
which is rolled into a metal frame with a winding handle. It is 30m, 50m or
100m long. Is used in projects where more accuracy measurement is required.
Cross
staff
Thecrossstaffis made of metal or wood
witheyeslipsat
right angles and is used to measure right angles from the line of traverse
Notebook
Notebooksare used during field
work to record data obtained. The notebook should be of good quality and 150mm
x100mm in size
A hard
pencil and a rubber
Hardpencilsare used for drawing in
the field and arubberis used
to erase mistakes or errors which are made. A pencil should be HB or HHB.
Chain/Tape Surveying Activities at School Level
Practice
chain/tape surveying activities at school level
Methods and procedures involved in chain survey
·
A survey team involves three people, theleadingchainmanorleader, thefollowerandthebooker.
·
The chain is thrown to extend it and disentangle any knots
·
The leader takes ten arrows and a ranging rod, and the follower
takes a ranging rod
·
The follower erects his ranging rod/pole at the firstbasepointand places a brass handle of the chain against
the ranging rod.
·
A leader straightens the chain and inserts an arrow at end of
the brass handle. Offsets and tie lines can now be taken.
·
The leader drags the chain so that the follower’s end is on the
leader’s arrow; the follower moves to another point and places his ranging pole
behind the arrow. This procedure is then repeated.
The importance and usefulness of chain surveying
1. It is
suitable for small areas of fairly open ground.
2. It is
used to fill in details on a map whose large features have been surveyed by
other methods.
3. It is
used in mapping small areas of flat or near-flat ground and associated objects,
for example paths, roads and railways.
4. It is
used in adding detail to existing plans or large maps.
Advantages of chain surveying
1. It is
the simplest method of surveying through the old method.
2. It is
suitable for surveying clear areas.
3. It
tends not to attract attention.
4. It is
suitable for surveying a flat surface on the Earth’s surface, for example a
school compound.
5. It can
be read easily and quickly.
6. It can
withstand wear and tear.
7. It can
be easily repaired or rectified in the field.
Disadvantages of chain survey
1. It is a
slow method of surveying.
2. It is
the oldest method of surveying
3. It is
not suitable for surveying large areas.
4. More
difficult areas cannot be chain surveyed.
5. Errors
may be encountered due to the use of many chains and other reasons.
6. It is
time consuming.
7. They
are heavy and take too much time to open or fold.
8. They
become longer or shorter due to continuous use.
9. When
the measurement is taken in suspension, the chain sags excessively
The Importance of Survey
Explain
the importance of survey
Importance of surveying
1. It help
to prepare a topographical map which shows the hills, valleys, rivers,
villages, towns, forests, etc. of a country.
2. It
helps to prepare a cadastral map showing the boundaries of the fields, houses
and other properties.
3. It help
to prepare an engineering map which shows the details of engineering works such
as roads, railways, reservoirs, irrigation canals, etc.
4. It help
to prepare a military map showing the road and railway communications with
different parts of a country.
5. It
helps to prepare a contour map to determine the capacity of a reservoir and to
find the best possible route for roads, railways, etc.
6. It
helps to prepare a geological map showing areas including underground
resources.
7. It
helps to prepare an archaeological map including places ancient relics exist.
MAP READING AND MAP INTERPRETATION
Concept of Map Reading
The Concept of Map and its Importance to Social Economic
Activities
Explain
the concept of map and its importance to social economic activities
Map
reading is the process of identifying features on a map by using symbols and
signs or names. This technical work requires certain skills that any map reader
must possess.
Map
interpretation refers to interpretation of the symbols and signs used on map
into ordinary language by indicating the features they represent and draw
logical conclusions from the information as represented by the symbols.
Importance
of map reading
Map reading is very important to social and economic activities.
Maps are drawn for different purposes and once drawn they can serve as databases
from which various information can be obtained and used for a myriad of social
and economic benefits.
a. Geological
maps provide information about the type and distribution of rocks in an area.
This knowledge is of great help to builders who can use it to find out where to
obtain certain rocks for construction. This knowledge can also be used by
mineral prospectors to locate possible areas where they can obtain mineral. The
information on soil types can be used by civil engineers to establish the stability
of the on which to build roads and other structures.
b. Relief
maps provide information to many people in many ways. For example, civil and
architectural engineers need to know relief of an area so that they can plan in
advance how to overcome relief barriers in their construction plans. It also
important to large scale farmers as they need relief to plan for the extent of
farms and also to determine the possibility of mechanization (use various
machines in agricultural production).
c.
Drainage maps are useful to civil engineers as they can use them
to get prior knowledge on how to construct bridges, roads, railways and other
infrastructures. It is also useful to agriculture as such maps indicate
possible sources of water for irrigation of crops, watering livestock and for
other general farm uses.Weather and climate maps are useful especially to
people interested in agriculture. They provide information on the kind of crops
to be grown and the type of livestock to keep in a certain area.
d. Vegetation
maps show the distribution and type of vegetation in a region. This gives a
clue on the kind of social and economic activities that can be carried out in
an area.
e.
Soil maps are very useful to agricultural officers as they can
use the information about soil types to advise farmers on the type of
fertilizers to use, soil requirements and proper soil management practices.
f.
Maps provide information on the relationship between phenomena
or events. For example, maps showing the location of volcanoes also indicate
the connection between volcanoes and earthquakes. Earthquakes are very common
in areas with numerous volcanoes. This will give people crucial information on
the possibility of occurring vulcanicity so that they can avoid setting
settlements on such hazardous areas.
g.
Maps provide background information as compared to present work.
For example, maps showing distribution of forests in the past may be compared
to the present maps to draw conclusion on the extent of vegetation change
through deforestation, afforestation or reforestation.
h. Maps
provide valuable information for statistical analysis. Therefore, they are very
useful to researchers and any field of study.
Essentials of a Map
Identify
essentials of a map
Essentials of a map are the necessary prerequisites that a map
should have. All maps in general require the following qualities or essentials:
1. Title – The
most basic component of a map is its title. The title should refer to
everything the map covers. It could be a basic name of a country, such as
"Tanzania," or it could be more extensive, such as "Water Tables
in the Western Saharan Desert." The title should clearly state what the
cartographer’s intentions and goals are; it should be specific, and it should
not include irrelevant information.
2. Scale – shows the relationship
between map distance and ground distance. For example, the scale 1:100000,
indicates that one centimetre on the map represents 100,000 cm (1 km) on the
ground.There are three types of scales: (a) Statement scale – this is a map
scale stated in words or it is a verbal scale. The words “one centimetre to one
kilometre” is an example of a statement scale. (b) Representative fraction –
this is a means of expressing the relative size of a map or drawing by a
fraction or ratio e.g. or 1:100. This means that one unit on the map represents
one hundred units on the ground. (c) Linear scale/graph scale – this is a line
showing the distance on the map that represents a given distance on the ground.
A linear scale is divided into two parts: Primary section – it is placed on the
left-hand side of the linear scale. Secondary section – this is placed on the
right-hand side of the linear scale.
3. Key – every
map must have a key. The key is a vital tool in understanding and interpreting
the map. The key should explain every feature or symbol contained on the map.
It should reveal what every marking means and sometimes provide additional
information. For example, a city may be represented by a large black dot of a
certain size on a map, and the key may explain that this represents a city with
a population greater than one million people.
4. Margin/boundary/frame – it is
essential that all maps be enclosed in a frame for neatness.
5. North direction/compass orientation – this is the direction towards the North in those maps drawn to
grid system. All maps must have a compass orientation. Because the primary
purpose of a map is to provide and insight into directions, a map has to be
able to show which way is which on a compass. Most maps have "North"
at the top and "South" at the bottom, but all maps should have an
official representation of the compass orientation.
6. Date – to
give context to a map, the date of publication should be present. As maps are
continually updated with additional information and improved accuracy, it is
important to know the time when your map was published. For example, viewing a
map of Tanzania published in 1980 might still be useful but will not be as
accurate as one published in 2014.
Reading and
Interpreting Topographical Maps
Features on a Map
Recognise
features on a map
Topographical
maps are types of maps which describe the physical (natural) and man-made
(artificial or cultural) features of a given area. The physical features
include relief, vegetation, and drainage, among others. Some of the cultural or
artificial features are roads, railways, cities, towns, dams, schools, and many
other structures built by man.
Relief
features
Relief
refers to the physical landscape as shown by the configuration of the surface
of the earth that is brought about by landform features. The methods of showing
relief in topographical maps include the use of spot heights, trigonometrical
stations, contour lines and form lines.
Spot
height
This is
a point on a map with its exact height above a known level e.g. from the sea
level. The position and height of the points have been determined by surveyors.
The spot height is marked with a dot followed by the numbers indicating height
of the land for example .750. The units of height, whether in metres or feet,
are quoted in the key of the map as well as below the linear scale.
Spot
heights are useful as a guide to the general relief of the area. The map user
can easily determine the high points of the area especially where the area
represented on the map is an undulating plain or plateau.
Trigonometric
station (point)
This is
a point on a map with its exact height fixed usually on a hill top, mountain
peak or other visible positions. They are the highest points on any locality.
The trigonometrical points are commonly marked by a triangle followed by the
numbers indicating the height for example Δ725
On the
map, the height of each station is written against a symbol. The units of
height are not indicated but can be deduced in the same way as spot heights.
Hill
shading
Hill shading is a method of representing relief on a map by
shading hills as if light is shinning on them.
Hill
shading
Hill
shading depicts the shadows that would be cast by high ground if light were
shining from a certain direction.
Layer
colouring/tinting
Layer
tinting/colouring is a method of showing relief by colour. A different colour
is used for each band of elevation. Each shade of colour, or band, represents a
definite elevation range. The key is printed on the map margin to indicate the
elevation range represented by each colour. However, this method does not allow
the map user to determine the exact elevation of a specific point—only the
range can determined.
Hachures
Hachures
are short, broken lines used to show relief. Hachures are sometimes used with
contour lines. They do not represent exact elevations, but are mainly used to
show large, rocky outcrop areas. Hachures are used extensively on small-scale
maps to show mountain ranges, plateaus, and mountain peaks.
Hachures are also used to show the direction and steepness of
slopes. The lines are drawn to follow the slope of the land or in the direction
in which water would run on them.
Hachures
Contours
and form lines
Contour
lines, sometimes called isohyepes, isoline or isopleth are lines drawn on a map
joining all places with the same height above sea level. The value of each
contour line is written on it. They are normally drawn in thick brown colour.
Form
lines are lines on a map which join points of approximately the same height
above sea level. These are used as “fill-in” lines to show out the nature of
the slope (form) of the land and the various landforms, hence the name “form
lines”. They are drawn by estimating the height of the land with the help of
spot heights and trigonometrical stations as well as the contours.
They
are usually drawn in thin brown lines and their values are not normally shown
on them. Contours and form lines are the main methods of showing relief on
topographical maps. For practical purposes, form lines are also regarded as
contours. On maps of scale 1:50 000, they are normally drawn in brown colour.
Spot heights and trigonometrical stations are also used alongside contours.
Contours
do not cross one another for the simple reason that a single point cannot have
two different heights. If contours appear on a map to be merging, it is an
indication of a very steep slope that is vertical or nearly vertical. The
contour of higher value obscures those below it.
The contour interval is the difference in
height between any two successive contours. It is also known as the vertical interval (V.I.)
of the map. On the 1:50 000 maps of East Africa, the contour interval is
usually twenty metres (20 m). This information is indicated in the key
accompanying each a map and also indicates the units of height used on the
particular map.
The contour interval is constant for all areas of a given map.
Contours are very useful as they help in identifying various landforms,
including type and trend of slope of the land. The shape formed by a collection
of contours enables us to identify different types of landforms. The succession
of contours enables us to see the changes in relief.
Contour
lines showing changes in relief
Slopes
A slope
the inclination or slant of the land. This inclination varies considerably,
resulting in the following types of slopes:
Gentle slope
This is shown by contours that are evenly spaced and drawn far
apart. On a 1:50 000 topographical map, the space between two successive
contours is more than 1.5 cm.
Gentle
slope
Steep slope
A steep slope is shown by contours that are drawn very close
together. The closer the contours are, the steeper the slope. The space between
any two successive contours is less than 1.5 cm.
Steep slope
Diagrammatic
representation of gentle and steep slope
Regular slope
This is
an even or a constant slope. It is shown by contours that are evenly spaced,
that is at relatively regular intervals. A regular slope can be gentle or
steep. The surface of the land would look smooth.
Irregular slope
This is
also known as uneven slope. It is indicated by unevenly spaced contours. It too
can be gentle or steep. They indicate a rugged landscape.
Convex slope
This type of a slope is indicated by contours that are closely
packed on the lower slope (indicating steep slope) but become more widely
spaced on the upper section of the land (indicating gentle slope). The slope
curves outwards like the surface of a convex lens. It is steeper towards the
bottom and gentle towards the top.
Convex
slope
Concave slope
A concave slope is represented by widely spaced contours
(indicating gentle slope) on the lower slope and closely packed contours
(indicating steep slope) on the upper part of the slope. On this type of slope,
the land is steeper on the higher ground and gentler on the lower ground. The
slope curves inwards, just the opposite of the convex slope.
Concave
slope
Valley
A valley is an elongated depression sloping towards a drainage
basin such as a sea, lake or swamp, and which may contain water or may be dry.
On a topographical map, the contours indicating a valley form a ‘V-shape’. The
apex (sharp end) points towards the higher ground and contours open out towards
the lower ground. The pattern of contours also shows valleys at different
stages of development. A valley in its youthful stage is shown by contours that
are close together. The gap between contours becomes progressively wider as the
valley reaches its mature stage and eventually the old stage.
Some
valleys may have rivers flowing in them as indicated by arrows in the figure
above.
Spur
A spur
is also known as salient. It is a prominent projection of raised land from
higher ground, such as a hill or mountainside into lower land. Then spurs
sometimes interlock, and hence the name interlocking spurs. Spurs are depicted
by contours that form a similar pattern to that of valleys. The difference is
that in the case of spurs, the apex of the ‘V-shape’ of the contours points
towards the lower ground and the ‘V’ opens towards the higher ground (see the
figure above). By studying the values of the contours, one can tell which the
higher ground is and which the lower ground is. But if the values of contours
are not provided, the shape of the ‘V’ alone can suffice to provide this
information.
Hill
A hill is an upland that rises above the general relatively low
ground but it is of less height than a mountain.
The
shapes of hills are quite variable. Some appear to have a regular shape while
others are irregularly shaped.
Regular hills look evenly shaped and tend to be conical in
shape. On topographical maps, these are depicted by a group of concentric
contours that give a hill a rounded shape.
A
regularly shaped hill
Some hills are irregularly shaped. This may due to erosion, the
presence of a massive rock outcrop or due to other geomorphological processes.
Ridge
A ridge is a fairly narrow and elongated hill or range of hills
with steep slopes on all sides. The top of a ridge may have a number of peaks
formed by hills that form a range. Some ridges are watersheds that separate
rivers which flow in different directions or parallel to each other. On
topographical maps, ridges can be identified by closely packed and elongated
contours that drop on all sides into lower ground. The upper part of a ridge is
called brow. Before reaching the top of the ridge, there is usually a section
of gently sloping land called a shoulder.
Col, saddle and pass
A col
is a small depression on a ridge or in a hilly area, which is located between
adjacent peaks of hills. In the position of a col, there are no contours drawn.
A saddle is described as a broad flat col in a ridge between two mountain
peaks. The term saddle is sometimes used interchangeably with col. Their only
difference is that a saddle is wider than a col, that is, the two mountain
summits separating a saddle are far apart while those separating a col are very
close.
A pass is a fairly narrow but deep gap in a mountain range or
between high hills in a low land. It is like a deepened saddle or col. Its name
originates from the fact that travellers across a hilly or mountainous country
would use such a gap for easy crossing from one side of the hills to the other.
Watershed
A watershed is a line separating headstreams, i.e., river
sources that flow to different river systems. It is a boundary line. On a
ridge, it would be the crest of that ridge. On topographical maps, a watershed
is not indicated by contours. Its position can be deduced and traced along a
line that passes above the last contours of the ridge. Its position can also be
determined by examining the direction of flow of rivers originating from that
highland.
Watershed
The
diagram shows two streams (A) that have joined together to form the main stream
(B).
Escarpment
An escarpment is a very steep side of an elongated highland. If
it is formed through the process of faulting, it is called a fault scarp.
Loosely, the name is used to refer to the whole highland with very steep slopes
on one side, a plateau on top and gentle slopes on the opposite side. On
topographical maps, an escarpment is shown by closely packed contours on the
scarp side that forms a scarp slope, and more widely spaced contours on the
opposite side, called the dip slope. The steep side forms a concave slope while
the dip slope is fairly even. The tops of some escarpments form plateaus while
others, especially the smaller ones, form ridges.
Escarpment
Plateau
This is an upland covering a considerably large area, and whose
top surface is almost flat. It is bordered by steep slopes that lead to lower
ground or may rise into the surrounding mountains. On a topographical map, a
plateau is shown as a wide area surrounded by a common contour of the same
height or two contours that are of the same height on both sides.
Plateau
Plain
A plain
is a continuous tract of relatively flat land covering a broad area of lowland.
Some plains may be raised but the slopes are very gentle. Plains occur as
lowlands and at the bottoms of valleys but also on plateaus or uplands at high
elevations.
On topographical maps, a plain is shown by contours that are
very widely spaced. Some rivers, if present, may be seen to have meanders.
Plain
Depression
A depression on a contour map is shown by contour lines with
small marks pointing towards the lowest point of the depression. The first
contour line with the depression marks and the contour line outside it have the
same elevation.
Cliff
A cliff is described as a steep rock face that is vertical or
nearly vertical. Cliffs are common in mountainous or hilly areas and along the
shores of lakes and seas. On topographical maps, cliffs are shown by contours
that are so closely packed that they appear to merge into one another. To
emphasize the presence of the cliff, a special symbol is drawn on top of the
contours as shown in the figure below.
Cliff
Summary of the relief features
The following diagram summarizes some relief features shown by
contour lines on topographical maps. The summary can be used as a quick
reference when revising representation of relief features on a map.
Some relief features are usually shown in the key. The following
key shows some of the symbols that are used to depict various relief features
on topographical maps.
Information from Maps
Generate
information from maps
Description
of relief
It is important to be specific when describing the relief of an
area represented on a map. The following steps should be followed:
1. Provide
a general description of the relief of the area. State clearly whether it is
mountainous, hilly, a plateau, lowland, valley, etc. State the general altitude
of the area by mentioning the possible lowest and highest points and their
actual or approximate heights as well as their specific locations on the map.
You can get this information from contour lines, spot heights or
trigonometrical points. It is important to give as accurate height as possible.
2. If
distinct relief regions occur on a map, the area should be divided into
distinct regions, e.g. highland, plateau, lowland, swampy area, etc. Each area
should then be described in detail by mentioning the features present in the
respective area. Describe the slopes and ranges in their heights, the nature of
slopes, types of slopes, general direction of the slope and the landforms found
in the area as well as their characteristics.
3. Locate
the relief or landform features present in the area and describe their
distributions and locations on the map. These features can be located by using
grid references, points of the compass or the nearest named places. In case of
slopes, describe the type and direction of slope and comparative steepness or
gentleness. Use the appropriate terms for describing types of slopes e.g.
regular, convex, concave, gentle, etc.
VEGETATION
On
topographical maps, only selected types of vegetation are shown. These are
forests, thicket, bamboo, riverine trees (also known as galleric or riverine
forests), woodland, scrub, scattered trees, palms and swamp vegetation.
The
specific swap plants such as mangrove trees, swap trees, marsh plants and
papyrus can be deduced from the type of swap shown on the map.
The
symbols on the map that are used to represent various vegetation types are
often interpreted in the map key.
Describing vegetation
When
describing natural vegetation on a topographical map, first identify and name
all types of vegetation shown on the map. Then describe each vegetation type
separately. Indicate the location of each type of vegetation by using the grid
reference or compass direction. For example, one may state “There is a dense
forest on the eastern area of the map and mangrove trees along the river.”
If some
vegetation types are named on the map, e.g. “Nyandarua Forest”, use the name
given to locate the position and type of vegetation. The area covered by
particular vegetation should also be estimated and given.
It is
important to find out the reason for the particular distribution. These reasons
are deduced from the information given on the map, which is referred to as
evidence. For example, an area with large permanent rivers indicates that the
area receives high rainfall. This may be the reason for the existence of dense
forests in the region.
DRAINAGE
Drainage
is the natural or artificial removal of surface and sub-surface water from an
area. Drainage also includes other features such as lakes, swamps, canals, and
ponds which are related to water. However, water tanks and cattle dips are not
features of drainage because these features are built by people who also fill
them with water. These constructed drainage features are also called
hydrographic features. Map makers use blue as the conventional colour for water
features.
Rivers and streams
These
are referred to as water courses in some maps. They are shown by blue lines.
The size of a river is indicated by the size of the blue line. The thicker the
line is, the bigger the river. The very thin lines represent streams. The names
of some rivers are written in blue print along the lines representing the
rivers.
Permanent
rivers are shown by continuous blue lines while the broken blue lines represent
intermittent (seasonal) rivers. If a river appears to abruptly end somewhere on
the land, it means that it disappears into the ground at that point. This
implies that at that point where it disappears then rocks are probably very
porous or are limestone type or there is a fault line. Normally, a river ends
in another river, a swamp, lake or sea. Rapids and waterfalls, like river
valleys, are relief features found along a river course and are therefore not
in the category of drainage features.
The
symbols used to show them on small rivers are not the same as those used on
large rivers. These should be carefully studied. The presence of waterfalls and
rapids may indicate presence of alternating hard and soft rock along the river.
They
may also imply presence of protruding resistant rock outcrops on the river bed
or sudden change in the slope of the river bed.
Lakes
A lake
is a body of water occupying a sizeable basin, depression or hollow in the
ground. It is bigger than a pond. A lake with no indication of water flowing
out of it is regarded as an area of inland drainage.
Natural
lakes are shown using a light blue shade of stipples. Seasonal lakes are
indicated by a series of broken, blue, short lines with the word “lake” written
on them or by the name of the lake. Man-made lakes (reservoirs) are shown by a
dark blue tint behind a black line that cuts across the river.
Sea
A
portion of an open sea is represented by a pale blue colour that is shaded with
stipples. Its coastline is indicated by a blue line.
Swamp
A swamp is a wetland with its associated vegetation. Swamps are
common where the ground forms a shallow depression. There are various types of
swamps and they are shown by different symbols which can be identified in the
key. The different types of swamps shown on 1:50000 maps of East Africa are:
a. Mangrove
swamps – these are found in the shallow parts of the sea shore, and around sea
inlets.
b. Tree
swamps – water-logged areas that have a significant number of trees and some
other smaller plants growing in them. There are some water-logged areas where
trees are so many that they form a forest. Such a forest is called a swamp
forest.
c.
Papyrus swamp – dominated by papyrus reeds. These are common on
plateaus and lowlands.
d. Marsh –
an area that experiences temporary flooding, and the land is usually wet and
poorly drained. It is characterized by plants such as rushes, reeds and
sledges, with occasional water-tolerant trees. At the coast, where flooding is
due to water, it is called a salt mash.
e.
Bog – spongy water-logged area with a surface layer of decaying
vegetation. The papyrus swamp, marsh and bog are all shown by the same symbols
on a 1:50000 scale topographical map of East Africa.
f.
Seasonal swamp – a very shallow basin and flat area of ground
that become flooded during the rainy period for some months, but which dry up
during the dry season. On a topographical map, they are shown by a group of
broken blue lines.
Ponds, waterholes, boreholes, wells and springs
·
Apondis a
small mass of stagnant water that is commonly found along courses of small
rivers. Most ponds are constructed by people but some occur naturally. They are
shown as dark blue areas on topographical maps.
·
Awaterholeis a
shallow and broad pit that traps rainwater. Some waterholes are natural while
others are constructed by people to provide drinking water for livestock or
wild animals. For coloured map sheets, the letters “WH” against a small blue
circle is the common symbol for this feature. If an alternative symbol is used,
it can easily be identified in the key.
·
Aboreholeis a
deep hole drilled in the ground for the purpose of obtaining underground water.
The initials “BH” against a blue circle are used to represent it on a topographical
map.
·
Awellis a
hole, larger than a borehole, which is dug in the ground for obtaining
underground water that is fairly close to the surface. This is shown by a blue
circle and a letter “W” or letters “We” against it.
·
Aspringis a
place where underground water flows out from the ground to the surface
naturally. It is indicated by a blue circle and letter “S” or letters “Spr”
against it. New editions of topographical maps may have these symbols modified.
Note: These
symbols are clearly indicated in the key of the map. It is advisable to always
study the key before proceeding to identify and interpret the various symbols
drawn on the map. Some modifications of the symbols may be expected. So you
should not get confused by cramming the symbols off head.
Irrigation canals
An
irrigation canal is a channel that is dug in the ground for the purpose of
carrying water from a river, well or lake to a farm. On maps, they are shown by
blue lines that are usually written against them.
Ditches and drains
These
are trenches that are normally constructed in water-logged areas for the
purpose of draining water from the land. On a topographical map, they are shown
by straight blue lines with some of them having definite angles. The ward
“ditch” or “drain” may be written against the line.
Though
water tanks, cattle dips and wind pumps are connected with water, they are not
drainage features but are cultural features for saving water. The presence of
many permanent rivers, streams, lakes and swamps is an indication of high
amounts of rainfall received in the area. On the contrary, if many of these
features are seasonal, it implies that the area receives low rainfall. Numerous
waterholes, boreholes and irrigation canals in an area may also be an
indication that the area receives low rainfall and that it experiences water
shortage.
Description of drainage
When
describing drainage, one should first identify the various drainage features
and name them. Describe each feature in turn by describing the distribution of
that feature in the area represented and locate it on the map. State the
general quantity, volume or size of the feature and describe the
characteristics of each, for example, seasonal permanent, big or small, etc.
when describing rivers, it is important to comment on the stream density,
general direction of flow of the rivers, the sizes of rivers and stage of
development, i.e., youthful, mature or old-age. Identify river drainage
patterns as well.
Information from Maps in Relation to Daily Activities
Interpret information
in relation to daily activities
Human
(artificial) features on topographical maps reflect human activities taking
place in the area covered by the map. Many human activities are in the form of
“land use” which refers to the ways in which land is utilized in the area. The
human activities represented on topographical maps include the following:
Agriculture
Agriculture
is the cultivation of crops and/or rearing of livestock. In modern times, the
term has been expanded to include fish farming, beekeeping and poultry farming.
On
topographical maps, crop plantations are shown as light, green shading. A
letter indicating the name of the plantation crop may be printed over the shade
e.g. “S” for sisal, “Su” for sugarcane and “C” for coffee. These symbols are
also indicated in the key.
The
name of the crop could also be indicated by the plantation name e.g., Tungi
Sisal Plantation. If the name of the crop is not indicated on the plantation,
it may be identified using other indicators on the map. For example, the
presence of a tea factory, coffee factory or decorticator may imply the
plantation crop is tea, coffee or cotton, respectively. In the absence of any
indicator of a crop that might be grown on the plantation, there is a
possibility that the plantation may be that of trees, i.e., natural or planted
forest. Small-scale farming activities are not shown directly on the map.
However, they may be deduced from symbols, factories or stores. The presence of
a tobacco processing factory or tobacco store implies that tobacco is grown in
the area. The presence of flour mill or posho mill indicates that maize is
grown in the area.
A
ginnery implies that cotton is grown in the area. A cereals board may imply
that people in the area grow grain crops such as maize, millet, wheat, etc.
Livestock
rearing is indicated by the presence of cattle dips, grazing grounds, cattle
markets, ranches,, stock holding grounds, waterholes, a water tank in an
isolated place, a slaughter house office or abattoir, a butchery, veterinary
office, dairy farm, creamery and dairy farming schools, and many others. Any
evidence that relates to livestock rearing is enough to draw a conclusion about
livestock farming.
Based
on the type of crops grown in an area, one can draw conclusion on the type of
climate experienced in that area. For example, tea and coffee are usually grown
on an area that experience high rainfall and with moderate temperatures. Crops
such as sisal, millet and cassava indicate that the area receives low rainfall
and experiences high temperatures.
Likewise,
the type of livestock kept in an area can be useful in making conclusions about
the climate of that area. Dairy farming indicates that the area has cool
climate and receives high amounts of rainfall. Beef cattle farming, pastoralism,
ranching and camel rearing all indicate that an area receives low amounts of
rainfall. This may be a clear indication that the area experiences a dry
climate.
Forestry
The
presence of forests and forest reserves on a map indicate that forestry is
practised. The presence of forestry can also be indicated by features such as
forestry training school, forest station, or forest guard post. The presence of
sawmills within or near a forest indicates that lumbering may be taking place
in the area.
Fishing
On topographical maps, the presence of water body does not
indicate the presence of fishing activities. In conjunction with the presence
of a water body, we have to look for the following evidences to conclude,
beyond reasonable doubt, that fishing activities are taking place on the water
body shown on the map:
a. The
presence of the symbols of fish traps at the edge of a water body.
b. The
named places such as fishing village, fish ponds, and hatcheries near a water
body. We can also look at the presence of Fisheries Departments, fish markets,
Fishing Cooperative Society, a fish processing plant, etc.
Mining
Mining
activities are often indicated by a particular symbol that is included in the
key. Words such as “Gold Mine” may also be used to conclude that mining
activities are taking place in that particular area. Mining, however, should
not be confused with quarrying.
Quarrying
Quarrying
is the activity involving excavating stones, sand or soil from the ground. A
special symbol with the word “quarry” written against it is used on
topographical maps to indicate where quarrying is carried out. This is
different from mining and that is why both activities are shown by different
symbols.
Trading
This is
a commercial activity involving buying and selling of commodities. On
topographical maps, it is indicated by letters “TC” which are initials for
Trading Centre in areas where there are settlements. Other evidences of trading
include shops, markets and petrol stations.
Transportation
This
involves the movement of people, goods and animals from one place to another.
It is evidenced by the presence of transportation infrastructures such as
roads, railway lines, footpaths, tracks, airports, seaports, pipelines, etc.
The symbols representing these structures are often provided in the key.
Communication
This
refers to the means of conveying or exchanging information. The evidence of
communication services and activities includes the presence of a wireless
station, post office (PO), telegram (Tg), telephone (T) and telephone lines,
and a satellite station.
Industries
These
are evidenced by the presence of manufacturing and processing factories or
industries in an area. They may be shown and named on maps. Examples of
industries include sisal and tea processing factories, coffee pulping plant,
floor or posho mill, bakery, creamery, cement factory, motor vehicle assembly,
fruit processing factory, sawmill, ginnery or simply the word “factory” or its
abbreviation “Fcty” are all evidences of industrial activities.
Tourism
Tourism
may indicated by such features as camping site, hotel, recreational grounds,
game reserve, national park, museum, historical monument, tourist resort,
historical sites and nature reserve.
Administration
Various
administrative activities can be identified from abbreviations on the map.
These are given in a list in the margin of the map. They include provision of
security as evidenced by the presence of a Police Station or Police Post,
judicial services as evidenced by the presence of courthouse, and other administrative
offices such as District Commissioner (DC) and Regional Commissioner (RC).
Other
human activities
Besides
the activities described above, there are other activities that people engage
in on daily basis. These include teaching and provision of other education
services indicated by the presence of school, college, university or training
institution.
Health
services are indicated by the presence of a hospital, dispensary, health centre
or medical laboratory.
Religious
services are indicated by the presence of church, mosques or temple.
Recreational services are evidenced by the presence of golf clubs, golf
courses, stadium or other recreational grounds.
Description
of human activities
When describing human activities in a given area on a topographical
map, the following steps should be followed:
a. Identify
each activity and support it with evidence form the map.
b. Describe
the distribution of the activity in the area of the map using conventional
methods.
c.
Give reasons, using available evidence, for the distribution of
and factors that may appear to favour the activity.
INTERPRETATION
OF SETTLEMENTS
A
settlement is a place where people dwell. On topographical maps, settlements
are depicted by dots or blocks, which may be black or grey in colour. Dots are
identified in the key as huts or houses. They represent semi-permanent
structures that are typical of rural settlements in Africa.
Black
squares or rectangular blocks depict permanent buildings like those built of
stones or bricks and roofed with iron sheets or tiles. A collection of these
permanent buildings in one area is shown as a solid block. This represents a
town or an area with permanent buildings.
Description of settlements
Settlements are described based on their concentration or
alignment. In terms of concentration, they may describe as follows:
·
Dense – when there is a high concentration of individual blocks
or dots in a given area.
·
Moderate – when f individual blocks or dots are neither high nor
low.
·
Sparse – when individual blocks or dots are few and spread over
a wide area.
On the
basis of alignment, settlements can be described as follows:
Nucleated or clustered
In this pattern, settlements are in groups or clusters. The
reasons why settlements are concentrated in a particular area include the
following:
a. A
limited land for settlement.
b. Security
and defence – in rural areas people may need to live in groups for collective
defence.
c.
Availability of social services such as educational, health,
transport, and communication facilities
d. Availability
of economic opportunities like mining, trade, employment, etc.
e.
Conducive climatic conditions which favour a better living such
as the absence of diseases or disease vectors such as tsetse flies, mosquitoes,
etc.
f.
Fertile soils which favour agricultural activities.
g.
Government policies – the government’s land policies can also
have a lasting effect on location of settlements. For certain reasons, the
government can set up policies which prohibit establishment of settlements in
particular areas.
Nucleated settlement
Scattered or dispersed
In this pattern, the settlements appear to be randomly dispersed
over the area. It is typical of rural areas where people own individual pieces
of land and set up their own dwellings anywhere on their lands. It can be found
in new settlement schemes. The distribution may be any of the types discussed
above. The factors behind this type of settlement include the following:
a. Readily
available land for settlement without any restrictions.
b. A
fertile soil that attracts a large population. The land is sub-divided into
small plots.
c.
Availability of water within easy reach by families.
d. Generally
reliable security over a wider area. There is therefore no need for group
defence measures.
Scattered settlement
Linear
In this pattern, settlements are set up in a line form along
certain features such as roads, railways, coastlines, etc. Some of the factors
leading to development of this pattern include:
a. Presence
of a road, motorable track or footpath for easy transport.
b. Presence
of a river that may provide water for domestic and commercial use.
c.
A coastline or shoreline that is favourable for fishing.
d. Suitable
terrain, e.g. the foot of an escarpment where the slope is gentle and where
they may be scarp springs for water.
e.
Infrastructure planning like in plantations where settlements
are set up in lines.
Linear settlement
Besides
describing the distribution of settlements in terms of the density and
patterns, the factors that influence their distribution should be identified by
examining the map carefully. Such factors include relief, vegetation, drainage,
transport and other economic activities as may be found indicated on the map.
Note:
The description of settlement as dense, moderate or space is often termed as
forms of settlement and description as scattered, linear or nucleated is termed
as settlement patterns. So, one should not confuse the two terms when referring
to settlements.
PHOTOGRAPH READING AND INTERPRETATION
Types of Photographs
Types of Photographs
Identify types
of photographs
A
photograph is an image or a picture of an object which is recorded by a camera
and then printed on a paper. Photograph interpretation is a process of reading,
measuring and interpreting photographs for obtaining reliable information about
natural or human features and their environment. In other words, photograph
interpretation can be defined as analysis and examination of photographs so as
to be able to identify natural or artificial features.
Photographs
are classified according to the viewpoint or position from which they are
taken. They can be taken from the ground or from the air. This then basically
gives us three major types of photographs namely, horizontal, oblique and
vertical photographs.
Horizontal
or ground photographs
These
are photographs that are taken from the ground when the camera is at the same
level as object(s) being photographed. There are two categories of horizontal
photographs as described below:
Horizontal close-up photographs
These are categories of horizontal photographs in which the
camera focuses on a particular object such as a house. The object of focus is
shown very clearly. On the other hand, objects in the background are obscured,
and generally, the background is not seen clearly.
Horizontal general-view photographs
These are photographs that focus on a wide area of the field.
Several objects are clearly shown in these photographs. Objects close to the
camera appear larger than those far away from the camera. The area whose
objects are obscured from the camera by those objects close to the camera is
called the dead ground.
Horizontal
general-view photograph
Oblique
photographs
These
are types of photographs that are taken from an angle, usually from the top of
a hill, tower or cliff. There are two categories of oblique photographs as
described below:
Ground oblique photographs
These are taken when the photographer is standing in elevated
ground, such as top of a hill, building or cliff, and holds the camera at an
angle pointing towards the lower ground. The photograph can also be taken when
the photographer is standing at the bottom of an elevated ground, with the
camera pointing towards the higher ground (See the photograph below). So,
whether the photograph is taken from the top or bottom of an elevated ground,
the resulting photograph is called ground oblique photograph. In this kind of
photograph, the images closer to the camera are larger than those far away.
Ground
oblique photograph
Aerial oblique photographs
These
photographs are taken from the sky with the camera tilted at an angle towards
the ground. The photographer may take the photograph from a helicopter or
low-flying aeroplane. These photographs cover quite a large area of land. They
are similar in many ways to the ground oblique photographs. Objects near the
camera appear slightly larger than those far away.
An aerial oblique photograph which does not cover the horizon is
called a low aerial oblique photograph, while that which includes the horizon
is called a high aerial oblique photograph.
LOW aerial oblique photograph
HIGH
aerial oblique photograph
Vertical
photographs
These photographs are the ones that are taken from the air with
the camera directly above the scenery, pointing vertically to the ground. The
camera focuses on specific features on the ground though the area surrounding
those features is also shown.
Vertical
aerial photograph
Differences between Ground, Vertical and Oblique Photographs
Differentiate
between ground, vertical and oblique photographs
A photograph has three parts as described below:
a. Background
– the area farthest from the camera.
b. Foreground
– the area nearest to the camera.
c.
Middle ground – the area between the background and the
foreground, which is at middle distance from the camera.
Each of
the three parts of the photograph can further be sub-divided into three parts
to give nine combinations which form the nine minor parts of the photograph as
shown in the table below:
|
Left |
Centre |
Right |
|
Left background |
Centre background |
Right background |
|
Left middle ground |
Centre middle ground |
Right middle ground |
|
Left foreground |
Centre foreground |
Right foreground |
For
easy description of locations on a photograph, it is appropriate to use these
divisions. It is inappropriate to use such terms as ‘top’ or ‘bottom’ when
referring to areas or parts of a photograph. Also it is not acceptable to use
points of the compass such as ‘east’, or ‘north’ unless there is sufficient
information to enable one to determine the compass directions of the photograph.
Reading and
Interpreting Photographs
Features Presented on Photographs
Read
features presented on photographs
The same as reading maps, reading a photograph means studying
and identifying the various objects shown on the photograph. Interpreting a photograph
means examining the objects or a combination of objects shown on the photograph
for the purpose of judging their significance. It involves translating the
information by describing the features shown in the photograph. Photograph
interpretation involves the following:
a. Determining
the title of the photograph.
b. Estimating
time and season the photograph was taken.
c.
Estimating direction or position of the photographer.
d. Estimating
the size of the features.
e.
Identifying and interpreting physical features.
f.
Identifying and interpreting human activities.
g.
Suggesting possible location of the scenery in the photograph.
Determining
the title
A
suitable title of the photograph can be obtained by studying the photograph
carefully. The information obtained in the photograph determines the choice of
the title.
Features
shown on the photograph can be natural or man-made. It is important to study
the photograph carefully and identify these features.
Photographs
show landscapes, activities on land, water surfaces or sky or a combination of
all of these. The information contained in the background, middle ground and
foreground should be carefully studied. Such information, when combined with
one’s geographical knowledge can be used to establish the title of the
photograph.
Estimating
time and season
If we
know where the photograph was taken, it may be possible to tell the time of the
day when the photograph was taken. If it was taken in the tropics on a sunny
day, long shadows imply that the time of the day was either early morning or
late afternoon. If the shadows are short, it implies that the time of the day
was just before or afternoon. In the temperate regions, both in the southern
and northern hemispheres, the sun never gets overhead at noon. It remains at an
angle. The shadows are also shortest at noon and point northwards in the
northern hemisphere and southwards in the southern hemisphere. Therefore, based
on the knowledge of the zones of the earth and the movement of the sun, one can
tell when the photograph was taken and be able to determine a part of the
hemisphere on which it was taken.
We can
also draw conclusions about weather, season or even climate of the area at the
time the photograph was taken. A bright clear sky with dry vegetation may
suggest a dry period or season. Thick vegetation, young crops and or flowering
plants in the field and a sky full of cloud cover or rain suggest a rainy
season or period. In temperate regions, clear sunny conditions with healthy
vegetation and flowering plants or plants with fruits indicate a summer season.
Plants with young leaves, others in bloom and fields full of grass could be an
indication of spring season. Foggy sky with leafless trees and some snow on the
ground is an indication of winter season.
The
type of clothing worn by people appearing in the photograph and the nature of
houses can be a clue to the prevailing weather or the type of climate. When
people appear to be wearing heavy clothing with faces almost completely
covered, hand gloves and heavy boots, it is an indication of cold weather,
likely to be winter in temperate regions.
When
the weather is hot, people wear light clothing and some may even wear
broad-rimmed hats. If people are seen basking in the sun by the swimming pool
it also indicates a warm sunny, hot weather. When houses appear to have
slanting roofs, it is an indication that the region experiences a lot of
precipitation, either rainfall or snow. Slanting roofs facilitate easy flow of
water or snow from the roof of the house. Simple houses with flat roofs
indicate a region that experience little precipitation or that is dry in most
of the year.
Activities
going on in the field could also suggest the type of a season. If people are
seen planting crops, it is planting season. The rainy season is either near or
it has just started. If people are seen weeding, it is the growing season for
crops and there is reduced rainfall.
If people are photographed harvesting the crop, it is the
harvesting season and is probably dry season because harvesting normally takes
place during dry season with a few exceptions. The time of the year could also
be indicated by a combination of phenomena in the photograph.
Maize
harvesting
Estimating
direction
This
refers to identifying the position of the photographer after studying the
relative sizes of objects in the photograph. It is possible to estimate the
direction on a photograph using shadows. This is possible if the time and place
where the photograph was taken are known. For example, if a photograph shows a
tree whose shadow is on the right and it is indicated that it was taken within
the tropics and in the morning, then the photographer was facing south. The sun
and the shadow are always in the opposite sides of the photograph. If the sun
is in the east, the shadow will always be cast westwards and vice versa. If the
shadow is pointing towards you and the photograph was taken in the afternoon
(meaning that the sun was in the west), the photographer was facing westwards.
With such information, it is then possible to fix compass points on a
photograph.
The other alternative for identifying the position of the
photographer or cameraman is by observing the size of objects in the
photograph. The objects close to the photographer appear larger those far away.
The objects apparently appear to decrease in size as their distance from the
photographer increase. Therefore, the part of the photograph showing huge
objects is the place close to where the photographer stood. Study the
photograph below carefully and keenly. Can you tell the position of the
photographer?
Size of
images gives a clue on the photographer’s position
Estimating
the size of features
Due to
perspective nature of photographs, especially with regard to the ground general
view photographs, it is not ease to measure and calculate possible distances
from them. It is, however, possible to work out approximate sizes of objects
using familiar objects in the close-up photograph such as a person, ruler or
coin. This gives an impression of the relative sizes of the objects and from
this we can be in a position of estimating the size of a given object in a
photograph.
That is why, we normally see a coin, hammer or ruler or any
known object placed against rock strata to give us an idea about the size of
the rock.
We see
a person standing against a cliff or tree so that we can use that person to
estimate the height of the cliff or tree. This is done by first estimating the
height of the person and comparing it with the height of the object and then
estimating how many times the tree is taller than the person. In this way, we
can estimate the height of crops such as tea, coffee and sisal.
A ruler
placed against the face of a rock can be useful in estimating the thickness of
the rock layer. Since the length of the ruler is known, its actual length as it
appears in the photograph can be used to estimate how many ruler lengths there
are in the whole rock layer.
It is
difficult to determine distances and areas accurately in photographs. This is
because objects in a photograph are not of uniform size and height. Objects in
the foreground always appear larger than objects of the same size in the
background.
Natural and Manmade Features in the Fore, Middle and Background
of the Photograph
Identify
natural and manmade features in the fore, middle and background of the
photograph
Many
physical features shown in the photograph can be identified and interpreted.
These features include relief, drainage, and vegetation, among others.
Relief
Before
interpretation of other physical features, it is important to first identify
relief features on the photograph. Start by giving a general idea about the
area shown in the photograph. In describing landscape and landforms, it is important
to go even further and describe the forces and processes that are responsible
for their formation and modification. This is an essential aspect of relief
interpretation. Relief features in the photograph may include the following
features:
Flat landscapes
These
landscapes occur both in lowland and highland areas. They are called plains in
the lowlands and plateaus in the highlands. Plains altitudes are less than 500
metres while plateau altitudes are more than 500 metres above sea level.
It is
impossible to tell the average area of the land directly from a photograph.
However, other features appearing in the photograph, such as part of the sea,
crops and other economic activities may be used in estimating the altitude.
Where there is an accompanying topographical map of the area, it would then be
easier to state the height of the land from the map.
Where
there is no sufficient information to tell the height of the land, relief may
be described as flat. One can then suggest that it is probably a low-lying
plain or a plateau surface. Some flat areas may be described as flat lowlands
or highlands.
Hilly areas
A hilly
landscape is shown on photographs as having varied relief of hills and valleys
that are not isolated on a flat landscape. Where hills appear to have the same
height across the entire landscape, such a landscape is probably a dissected
plateau. Streams have cut valleys across former flat land and some interlocking
spurs may be visible towards valleys. Ridges, escarpments and conical hills may
easily be identified according to their appearance.
Mountainous relief
This
kind of relief stands at an altitude of more than 2000 metres above sea level.
As such, not all rising features identified on photographs are mountains. The
relief of mountainous areas is characterized by very steep slopes often with no
human settlements. The slopes may have vegetation covering them, which could be
forests.
At much
higher levels, snow might be seen. The type of trees growing could give a clue
about the altitude of the land. If there are crops growing or animals reared,
these could also give a clue as to the altitude. Certain crops such as wheat
and apples are high-altitude crops. Likewise, animals such as merino sheep and
dairy cattle are also reared in high-altitude areas within the tropics.
Identifying relief features on vertical aerial photographs is
not straight-forward. The following guidelines could assist in identifying
different types of relief:
1. Flat
areas would appear as areas with light colour tone except in regions covered
with dense vegetation such as forested areas. Rivers may have big meanders
while roads, footpaths and railways are generally straight, with gentle bends
in some places.
2. Hilly
areas could be identified by examining river streams. The streams could be
joining one another and getting wider downstream. Hilly areas are the source of
rivers. The colour tone in hilly areas is generally dark.
Drainage
Drainage features such as rivers, lakes and seas may easily be
identified in all types of photographs. Different aspects of rivers can be
studied on a photograph. These include the shapes of river valleys, stages of
development and various features. Based on the presence of certain features,
one can tell the nature of the rock over which the river flows. For example,
the presence of rapids and waterfalls is an indication that the river is
flowing over steep land. River meanders are an indication that the river is in
it mature or old-age stage. Interlocking spurs indicate that the river valley
is made of alternating layers of hard and soft rocks.
A
meandering river
Drainage
patterns are easier to identify on vertical aerial photographs. The colour tone
of areas covering deep water appears darker than those of shallow water. The
various functions of the river can also be identified.
Vegetation
Photographs
show all types of vegetation in the photographed area. Planted (artificial) and
natural forests appear to be distributed unevenly, with planted forests usually
in clear straight lines. In planted forests trees tend to be of the same type,
size and height because they were planted at the same time.
The
plant characteristics that may appear on the photograph can be used as a guide
to the general types of vegetation, for example savannah or semi-arid vegetation.
The following guidelines should be used when describing vegetation on a given
photograph:
Identify the types of vegetation, for example, forests,
thickets, grasslands and swamp plants. Describe the plants, giving details such
as height, shape and appearance of leaves. Where possible, give the names of
species of plants, e.g. jacaranda, cacti, eucalyptus trees, etc. Planted
vegetation should be distinguished from the natural ones by their
characteristics. Proper interpretation of vegetation calls upon application of
geographical knowledge outside the photograph as well.
A planted
forest
Soil
A clue
on the type of soil in a photographed area may be given by the types of crops
grown and appearing on the photograph. Rice, for example, grows well in clay soil.
Tea and coffee require volcanic soil. Coconuts and cashew nuts thrive well in
coastal regions with sandy soils, and a variety of horticultural crops thrive
in loam soils.
Proper
interpretation of the soil requires an application of one’s general knowledge
of geography learnt in classroom as well as knowledge from other disciplines.
Climate
Weather
and climate are not shown directly on photographs. Features contained in a
photograph can be used to make conclusions about the climate of a photographed
area. The type of crops grown and vegetation on the photograph can be used as a
clue to establish the climate of a place. Vegetation types and crops can also
provide evidence about the season or climate of a place. For example, the
presence of many cacti signifies an arid or semi-arid region, and hence a
desert or semi-desert climate.
Crops
such as sisal are grown in hot areas that receive low rainfall while sugarcane
thrives in warm to hot climate with high rainfall. The type of clothing people
in the photograph are wearing can give an indication about the weather and
possible climate.
Interpreting Features Presented on the Photograph
Interpret
features presented on the photograph
Human
activities on a photograph are depicted by various forms of land use. The uses
of land may in form of agriculture (crop cultivation and animal husbandry),
forestry, settlement, wildlife conservation, mining and construction of
infrastructures, among other uses.
Agriculture
This
includes crop cultivation and livestock rearing. It is practised at subsistence
and commercial levels. It is easy to identify agricultural activities on ground
photographs. To be able to identify these features on vertical aerial
photographs, it requires close examination of the features.
Some
evidences that can be used to establish the kind of agricultural activities
taking place in an area shown on the photograph are summarized in the table
below:
|
Type
of farming |
Evidences
to look for |
|
Subsistence crop
farming |
·
Some houses are permanent while others are
temporary ·
The land is often divided into small plots
owned and cultivated by individual farmers ·
Mixed farming is practised ·
Simple farming tools such as hoes, mattocks,
pangas and rakes are used ·
Fields are separated by hedges |
|
Subsistence
livestock farming |
·
Indigenous and exotic animal breeds are kept ·
Animals are grazed on grassland or semi-arid
vegetation ·
Large herds of local cattle (zebu), goats
and sheep |
|
Commercial livestock
farming |
·
Large fields divided into paddocks ·
Presence of cattle sheds near farm houses ·
Windmills for water supply ·
Presence of water tanks, ponds or reservoirs
in the dry areas ·
Evidence of livestock infrastructures such
as cattle dips or spray races, abattoir, cattle bomas, slaughter slab, etc. ·
High grade exotic or crossed cows with large
udders ·
Milking parlour with milking machines, and
milk processing plants ·
Indoor grazing units |
|
Commercial crop
farming |
·
Presence of cash crops on an extensive area ·
Evidence of modern farming methods, e.g.
farm machinery ·
Facilities for collecting crops, e.g. sheds
and stores ·
Presence of access or feeder roads within
the farm |
|
Plantation farming |
·
A single crop covering extensive stretches
of land, e.g. sugarcane, tea, coffee, sisal, wheat ·
Processing factories ·
Presence of storage facilities, e.g. silos ·
Many labourers in the fields ·
Nucleated settlement within the farm. These
are usually for the workers’ housing ·
Presence of a network of roads crossing the
farm – to facilitate mechanization and haulage of inputs and produce to and
from the farm, respectively |
Not all
the listed evidences in the table for a single type of farming will be
available on a single photograph. However, information available may suffice to
draw conclusions about the type of farming.
Apart from the types of farming, there are other aspects to be
considered when describing and interpreting photographs. These include:
·
farming characteristics and the areas where such a type of
farming is practised;
·
the advantages and limitations of the type of farming;
·
the effects of each type of farming to the environment; and
·
the government policy on each type of farming.
Subsistence farming
Livestock husbandry
Sugarcane
plantation
Settlement
A
settlement comprises of a group of buildings in an area where people live and
carry out social and economic activities. However, some settlements are made up
of institutional, industrial and commercial buildings most of which may not
comprise of living houses. Settlements may be of two types, namely, rural and
urban settlements.
In photographs, rural settlements can be indicated by the
following features:
a. Many
semi-permanent and a few permanent buildings such as grass-thatched houses or
iron-roofed houses with mud or brick walls
b. Evidence
of farming, cattle herding or fishing activities
c.
Unplanned or unevenly distributed dwellings or presence of
villages Planned settlements in rural areas are associated with institutions or
plantations.
Rural
settlement
Urban settlements can be identified by the following features:
a. Permanent
buildings, which dominate the area
b. Regular
street patterns
c.
Buildings with several storeys
d. Many
large buildings and warehouses indicating an industrial area
e.
High numbers of people (if they are shown on the photograph)
f.
Many motor vehicles on the road, which may lead to traffic jams
g.
Port facilities such as docks, cranes, warehouses and containers
Urban
settlement
Not all
the listed evidence above will be found on a single photograph. However, there
should be sufficient evidence to lead one to make a distinction as to the type
of settlement. Settlement patterns can be easily recognized especially from the
ground oblique and aerial photographs.
Industrial
and mining activities
Various
features signalling the presence of industrial and mining activities may also
appear on a photograph. It is important that one is familiar with a wide
variety of photographs on which these features are shown.
The following evidence can be used as a guide in identifying
industrial and mining activities on a photograph:
a. Factory
buildings with tall chimneys that might be issuing a lot of smoke into the air
b. Nucleated
settlements in the neighbourhood, likely to be the labourers’ houses
c.
Tall chimneys emitting flames and a network of pipes with large
tanks in the distance could indicate an oil refinery
d. Large
warehouses close to a building that looks like a factory
e.
Large open pits, large excavators and lorries carrying loads of
rocks could indicate open cast mining
f.
A large area with derricks (oil rigs) could point to an oilfield
where oil is mined
Lumbering
Lumbering activities could be indicated by the presence of the
following features/activities:
a. People
cutting trees using manual or power saws
b. People
loading timber onto lorries or tractor trailers
c.
Logs floating down the river
d. Logs
piled near a saw mill
e.
Large forest clearings with tree stumps and piles of logs
A pile of
logs
Transport
and communication
Various forms of transport and communication appear differently
on photographs. Modes and means of transport can also be identified on a
photograph. The following are some of the clues on transport:
a. Motor
vehicles and roads
b. A
railway line with or without a train; or just the presence of a named railway
station
c.
A large tamaracked or murram road with buildings on one side, a
control tower. Aeroplanes may be seen, or just the presence of a named or
symbolized airport may be indicated on a photograph.
d. Presence
of ports, boats, ships or large water bodies
e.
Animals carrying loads on their backs
Facilities
for communication may be indicated by the presence of telephone lines,
telephone booths, satellite dishes, buildings with masts and wires connecting
the masts, post office, radio or television station, newspapers or newspaper
stands, etc. Other human activities represented on photographs can also have
relevant clues that enable one to identify the presence of given communication
facilities.
APPLICATION OF STATISTICS
Concept of Statistics
Statistics
Explain
the concept of statistics
Statistics
is the study of collection, analysis, interpretation, presentation, and
organization of data. Data refers to crude or uninterrupted information.
In
applying statistics to, for example, a scientific, industrial, or societal
problem, it is necessary to begin with a population or process to be studied.
Populations can be diverse topics such as "all persons living in a
country" or "every household in a village". It deals with all
aspects of data including the planning of data collection in terms of the design
of surveys and experiments.
Types
of statistics
Two main statistical methodologies are used in data analysis,
namely, descriptive statistics and inferential statistics.
a. Descriptive statistics summarizes
data from a large sample using indexes such as the mean or standard deviation.
Descriptive statistics are distinguished from inferential statistics (or
inductive statistics), in that descriptive statistics aim to summarize a
sample, rather than use the data to learn about the population that the sample
of data is thought to represent.
b. Inferential statistics draws
conclusions from data that are subject to random variation (e.g., observational
errors, sampling variation). Descriptive statistics are most often concerned
with two sets of properties of a distribution (sample or population): (i) Central tendency (or
location) – this seeks to characterize the distribution's central or typical
value. (ii) Dispersion (or
variability) – this characterizes the extent to which members of the
distribution depart from its centre and each other.
Types of Statistical Data
Differentiate
types of statistical data
When
working with statistics, it’s important to recognize the different types of
data. Data are the actual pieces of information that you collect through your
study. For example, if you ask five of your friends how many pets they own,
they might give you the following data: 0, 2, 1, 4, 18. (The fifth friend might
count each of her aquarium fish as a separate pet). Not all data are numbers;
let’s say you also record the gender of each of your friends, getting the
following data: male, male, female, male, female.
Most data fall into one of two groups: numerical or categorical.
·
Numerical data. These data have meaning as a measurement, such as a person’s
height, weight, IQ, or blood pressure; or they’re a count, such as the number
of stock shares a person owns, how many teeth a dog has, or how many pages you
can read of your favourite book before you fall asleep. Statisticians also call
numerical data quantitative
data. Numerical data can be further broken into two
types: discrete and continuous. Discrete data represent
items that can be counted; they take on possible values that can be listed out.
The list of possible values may be fixed (also called finite); or it may go from 0,
1, 2, on to infinity (making it countably
infinite). Continuous
data represent measurements; their possible values cannot be counted
and can only be described using intervals on the real number line. For example,
the exact amount of gas purchased at the filling station for cars with
20-gallon tanks would be continuous data from 0 gallons to 20 gallons,
represented by the interval [0, 20], inclusive. You might pump 8.40 gallons, or
8.41, or 8.414863 gallons, or any possible number from 0 to 20. In this way,
continuous data can be thought of as being uncountably infinite. For ease of
recordkeeping, statisticians usually pick some point in the number to round
off.
·
Categorical data: Categorical data represent characteristics such as a person’s
gender, marital status, hometown, or the types of movies they like. Categorical
data can take on numerical values (such as “1” indicating male and “2”
indicating female), but those numbers don’t have mathematical meaning and you
couldn’t add them together. Other names for categorical data are qualitative data, or Yes/No data.
·
Ordinal data: These
data mixes numerical and categorical data. The data fall into categories, but
the numbers placed on the categories have meaning. For example, rating a
restaurant on a scale from 0 (lowest) to 4 (highest) stars gives ordinal data.
Ordinal data are often treated as categorical, where the groups are ordered
when graphs and charts are made. However, unlike categorical data, the numbers
do have mathematical meaning. For example, if you survey 100 people and ask
them to rate a restaurant on a scale from 0 to 4, taking the average of the 100
responses will have meaning. This would not be the case with categorical data.
Statistical data can be expressed in different levels or scales
of measurement. These are:
a. Nominal scale: This type of scale has
qualitative property such that one my decide to express the data as
‘excellent’, ‘good’, ‘fair’ or ‘poor’ and maybe use grades, e.g. A, B, C, D and
so on. Nominal scale may also include numerical values. For example one may
decide to let 1, 2, 3 and 4 stand for ‘excellent’, ‘good’, ‘fair’ or ‘poor’ or
vice versa.
b. Ordinal scale: This scale involves
ranking, so it is also qualitative in nature. The data involves rank orders or
positions among events or objects. These statistics attempt to provide quality
or position. For example, if Chacha scored 5% in Geography Test while Tibaijuka
scored 95%, then we can say that the former ranked number 19 while the latter
ranked number 1 out of 20 students. Sometimes, values such as ½ of the class
scored below 50% in Geography may be included in the ranking.
c.
Interval scale: This
type of scale employs truly quantitative values and allows the use of
mathematical operations such as adding, subtracting, multiplying and dividing.
At no time is zero present in this scale. For example, the range of temperature
in which rice grows well is 25°C and 45°C; most livestock keepers get between
10 and 15 litres of milk per cow per day.
d. Ratio scale: This is a type of scale
that is used to make comparisons between values or quantities. For example,
MsIku harvested 50 sacks of maize which is twice MrAritamba obtained from the
same acreage because the former applied fertilizer and good farming practices
while the latter did not.
|
Scale |
Properties |
Examples |
|
Nominal |
Indicates a
difference, without any implied ordering |
Religion:
1=catholic; 2=protestant; 3=Jewish; 4=Muslim; 5=other |
|
Ordinal |
Indicates a difference,
and the direction of the difference(e.g., more or less than) |
Attitude on a
subject:1=strongly disagree, 2=disagree; 3=don't care / don't know; 4=agree;
5=strongly agree |
|
Interval |
Indicates a
difference, with directionality and amount of difference in equal intervals |
Temperature in
CelsiusOccupational Prestige (12-96) |
|
Ratio |
Indicates a
difference, the direction of the difference, the amount of the difference in
equal intervals, an absolute zero |
Temperature in
KelvinIncomeYears of schooling |
Variables
A
variable is anything or characteristic that data may have, or an attribute
which changes in value under given conditions. Variables include population
size, age, sex, altitude, temperature and time.
There two broad types of variables, namely, independent and
dependent variables.
a. An independent variable is a
variable factor which influences the changes of other variables or outcomes.
The independent variable is also known as manipulated variable.
This is the factor manipulated (controlled) by the researcher, and it produces
one or more results known as dependent
variables. There may be more than several dependent variables, because
manipulating the independent variables can influence many different things. For
example, an experiment to test the effects of a certain fertilizer, upon plant
growth, could measure height, number of fruits, and the average weight of the
fruits produced. All these are varied analyzed factors, arising from the
manipulation of one independent variable, the amount of fertilizer.
b. A dependent variable is an
outcome or result that has been influenced by other variables. A dependent
variable does not influence or change other variables. The dependent variable
responds to independent variable. It is called dependent because
it “depends” on the independent
variable. In any research, you cannot have a dependent variable without
an independent variable. Any alteration in the independent variable will change
the dependent variable.For example, you might be interested to carry out an
experiment to determine the influence of the concentration of phosphorus
fertilizer on maize growth. To conduct this experiment, you grow maize in
similar conditions of soil and atmospheric environment but vary the quantity of
fertilizer in each test (independent variable). Then
you measure the height of maize plants (dependent
valuable) after a certain interval of time to find out the influence of
the fertilizer on maize growth. The value of the height you will obtain will
obviously depend on the amount (concentration) of the fertilizer applied. And,
in this case, you will obviously get different heights depending on the
quantity of fertilizer applied.
Graphical Data
Present
data graphically
After
data have been collected, the next step is to present the data in different
ways and forms. Some of the forms in which the data may be presented include
charts, graphs, lists, diagrams, tables, essays, graphs, histograms, and even
sketches.
Line
(linear) graphs
Line graphs have unique properties that distinguish them from
other graphs. The properties of line graphs are as follows:
a. The
graphs are drawn by plotting a dependent variable against an independent
variable and points are joined by a line.
b. The
values on the y-axis start at point zero.
General procedure for drawing line graphs
a. Get the
required data for plotting the graph.
b. Identify
the independent and dependent variable. Statistically, the independent
variables are placed on the x-axis while the dependent variables are placed on
the y-axis.
c.
Decide on the vertical scale depending on the graph space and
values of the independent variable available.
d. Decide
on the horizontal spacing of the graph according to graph space available.
e.
Draw and divide the vertical and horizontal axes depending on
the respective scales.
f.
Plot and join the points to get the graph.
g.
Write the title of the graph you have drawn.
h. Indicate
the scale of the graph.
i.
Show the key for the graph if need be.
Line graphs can be sub-divided into:
a. Simple
line graphs
b. Group
(comparatives) line graphs
c.
Compound line graphs
d. Divergent
line graphs
Simple line graph
Presenting
the statistical data by a simple line graph is the most common and popular
method. The simple line graphs are easy to construct and interpret. They have
many uses which include showing temperature, farm outputs, population, and
mineral production, among others.
Construction
procedure:
The graph can be drawn after getting the required data. Consider
the following table which shows the average monthly temperature recorded in a
certain weather station:
Average monthly temperature for station X
|
Month |
Jan |
Feb |
Mar |
Apr |
May |
Jun |
Jul |
Aug |
Sept |
Oct |
Nov |
Dec |
|
Temp (°C) |
23 |
24 |
26 |
28 |
29 |
28 |
26 |
26 |
26 |
27 |
26 |
25 |
The following procedures may be used:
1. Identify
the variables. The dependent variable is temperature and the independent
variable is months.
2. Determine
a vertical scale. Assume that the graph space available is 6 cm vertically.
Vertical scale = maximum value of the divided by the graph space availablee.g.
30°C/6 cm = 5°C per centimetre. Therefore, in the vertical axis (x-axis), 1 cm
will represent 5°C
3. Determine
the horizontal scale (y-axis) depending on the available space. Let, for
instance, 1 cm represent one month.
4. Draw
both axes and label them: y-axis for temperature and x-axis for months.
5. Plot
the points and join them by a smooth line to make a curve.
6. Insert
the title and scale.
The following is a simple line graph showing monthly temperature
for station X.
Average monthly temperature for Station X
Source:
Hypothetical data
Scale
·
Vertical – 1 cm:3°C
·
Horizontal – 1 cm:1 month
Advantages of simple line graphs
1. They
are easy to draw, read and interpret.
2. They
show specific values of data, so if you are given one variable the other can
easily be determined.
3. They
show patterns in data clearly, meaning that they visibly show how one variable
is affected by the other as it increases of decreases.
4. They
enable the viewer to make predictions about the results of data. So they allow
for determination of intermediate or continuing values.
5. It is
easy to read the exact values against plotted points on straight line graphs.
6. A
broken scale can be used when the value starts at a large number.
Disadvantages of simple line graphs
1. They
can only be used to show the data of one item over time.
2. One can
change the data of a line graph by not using consistent scales on the axis.
3. They
can give a wrong impression on the continuity of data even when there are
periods when data is not available.
4. They do
not give a clear visual impression of the actual quantities.
Group (comparative) line graph
A group line graph is also known by the following terms:
·
Comparative line graph
·
Composite line graph
·
Multiple line graph
·
Polygraph
A group
line graph involves drawing more than one line on the same statistical graph. It
shows the relationship between sets of similar statistics for two or more
items.
Usefulness of a group line graph
·
Comparing different values or trends in two or more data
variables.
·
Examining the possibility of a relationship existing between the
distributions of a number of variables over time.
·
Comparing the distribution of the same variable at different
places.
Construction:
The
method of drawing a group line graph is the same as for a simple line graph.
Therefore, to draw each single line in a group line graph, follow similar steps
used for construction of the simple line graph.
The following things should be considered before drawing the
graph:
1. The
lines drawn should not be uniform in colour, thickness, general appearance, etc
(See the graph below in which each line has a different colour).
2. The
number of lines that a graph can accommodate should not exceed 5, meaning that
not more than 5 items should be compared in a single graph.
The following table shows banana production (in tonnes) by three
villages in Ingwe Division, Tarime district. These data have been used to plot
the group (comparative) line graph as shown below:
Banana
production by three villages
|
Village/Year |
Geisangora |
Itiryo |
Bungurere |
Nyansincha |
|
2000 |
10 |
15 |
25 |
25 |
|
2001 |
20 |
10 |
15 |
20 |
|
2002 |
3 |
10 |
10 |
15 |
Source: Hypothetical data
Maize
production by three villages between 2000 and 2002
Advantages of group line graph
1. The
quantity of each component is shown clearly by different line shadings.
2. Time
and space are saved since all the line graphs are drawn at ago as a group.
Disadvantages of group line graph
1. The
lines can be overcrowded and hence become difficult to read and interpret if
many data are involved.
2. It does
not give a clear visual impression of actual quantities.
Compound line graph
A
compound line graph is used to analyse the total and the individual inputs of
the specific commodities or economic sectors. The graph involves drawing two or
more lines, each line corresponding to one item in a different year or region.
The items are differentiated from each other or one another by shading
differently.
Construction:
The
table below is used for construction of the graph. The table contains
hypothetical figures for mineral exports between 2010 and 2012.
|
Year/Mineral |
Diamond |
Gold |
Tanzanite |
|
2010 |
10,000 |
16,000 |
20,000 |
|
2011 |
20,000 |
25,000 |
32,000 |
|
2012 |
25,000 |
35,000 |
40,000 |
Procedure:
·
Simplify the data to make the presentation work easy by dividing
each value by 1000.
|
Year
/Mineral |
Diamond |
Gold |
Tanzanite |
|
2010 |
10 |
16 |
20 |
|
2011 |
20 |
25 |
32 |
|
2012 |
25 |
35 |
40 |
·
Add the values for each year to get the cumulative export: 2010
= 10+16+20 = 46; 2011 = 20+25+32 = 77; 20112 = 25+35+40 =100; These values will
be used to determine the uppermost height of the graph. They will also help
estimate the scale to be used. In case of the above data, the highest value is
100. So if we want to use the scale of 1 cm to 1 tonne (1000 tonnes in
reality), the uppermost height of our graph will be 100 cm (see the graph drawn
·
Plot the values for mineral exports against years on a graph.
Usually the line graph for data with the highest values is drawn first. Thus,
first draw the line graph for tanzanite since it has the highest values,
followed by that of gold and finally diamond.
·
Draw the second line graph above the first one to show the next
component. To get the values for plotting the second line graph, add the values
of the first item (in this case, tanzanite) to that of the second item (gold)
for each year, thus: 2010 = 20+6 =36; 2011 = 32+25 =57; 2012 = 40+35 =75
·
Draw the line graph for the last item (diamond) above that of
the second item. To get the values for plotting this graph, add the values for
the second item to those of the last item, thus: 2010 = 36+10 =46; 2011 = 57+20
=67; 2012 = 75+25 =100
·
Shade the component parts between the line graphs using
different shadings as shown.
·
Label the axes, show the key and indicate the scale used to
construct the graph.
Advantages of compound line graph
1. Total
values are shown clearly and easily.
2. It
gives good visual impression.
3. Combining
all graphs in one saves time and space.
Disadvantages of compound line graph
1. Graph
construction is difficult and time-consuming.
2. It
involves a lot of calculations which are difficult and time-consuming.
3. It is
difficult to read and interpret the value for any one commodity for any
particular year.
Divergent line graph
A
divergent line graph is a line graph which shows how variables deviate from the
mean. The mean is represented by zero axis drawn horizontally across the graph
paper.
|
Year |
Yield
(tonnes) |
|
2012 |
1000 |
|
2013 |
1500 |
|
2014 |
500 |
|
2015 |
3000 |
Construction
·
Sum up the values of all items or commodities. 1000 + 1500 + 500
+ 3000 = 6000
·
Calculate the arithmetic mean (average) of the values. 6000/4 =
1500 Thus the arithmetic mean () = 1500
·
Calculate the deviation from the mean of each value as shown in
the table below.
Deviation
from the mean value
|
Year |
X |
X – |
|
2012 |
1000 |
-500 |
|
2013 |
1500 |
0 |
|
2014 |
500 |
-1000 |
|
2015 |
3000 |
+1500 |
·
Plot the graph using the values of deviation from the mean; and
remember to include the title and scale of the graph.
Advantages of divergent line graph
1. It
clearly shows how items fluctuate from the mean.
2. It
compares the values of the items and hence facilitates a sound conclusion.
3. It
shows both the positive (profit) and negative (loss) phenomena.
4. It is
easy to construct, read and interpret.
Disadvantages of divergent line graph
1. It
involves many calculations and hence time-consuming.
2. It
might be difficult to interpret if one lacks statistical skills.
3. It is
applicable for only one item per graph.
Bar graphs
A bar
graph is also called bar chart or columnar graph. This method is used to
present data which are not continuous. This means that in a bar graph there is
no relationship between or among data.
Bar
graphs emphasize individual amounts and their relative variations. When drawing
such graphs, bar width in a graph is kept constant while bar lengths change in
size as per the amount of the independent variable in question.
Though
the bars can also be drawn horizontally, they are usually drawn vertically. The
bars should be separated from one another by a space.
Types of bar graphs:
a. Simple
bar graphs
b. Group
or comparative bar graphs
c.
Compound bar graphs
d. Divergent
bar graphs
Simple bar graph
A
simple bar graph is drawn to show a single item per bar. It mainly represents
simple data.Consider the data in the table below which shows the value of sisal
exported by Tanzania between 1900 and 1993:
|
Year |
Sisal export (Tsh ‘000) |
|
1990 |
106126 |
|
1991 |
107430 |
|
1992 |
142601 |
|
1993 |
161180 |
|
1994 |
202425 |
Construction:-
1. Choose
the appropriate scale. However, note that the table below is not drawn to scale
– it was drawn using the computer. All hand-drawn graphs must indicate the
scale used. For, example, in our graph below, we might have chosen 1 cm to
represent 10,000 tones, in which case we could obtain the values 5, 10, 15, 20
and 25 that we could have used to plot the graph.
2. Draw
the axes and insert the bars. Note that all the bars must have the same width
and spacing.
3. Shade
the bars uniformly by using shade, lines, crosses, dots, etc.
4. Insert
vertical and horizontal scales and the title.
Tanzania sisal export
Scale:
1 cm to 50,000 tonnes
Advantages of a simple bar graph
1. It is
simple to construct, read and interpret.
2. It has
a good visual impression.
3. It can
be used to compare how the amount of an item varies from time to time.
Disadvantages of a simple bar graph
1. It is
limited to only one item or commodity and hence not suitable for massive data.
2. Not
suitable for continuous data such as temperature.
Group (comparative) bar graph
A
comparative bar graph consists of several bars drawn side by side on the same
chart for the purpose of comparison. The technique involves grouping of bars in
a chart. The graph can be used to show how production of certain commodities
varies each year.
Construction:
The
procedure for construction of the comparative bar graph is similar to that of
drawing the simple bar graph except that the simple bar graph contains a single
bar while the comparative bar graph comprises of multiple bars.
Consider
the data in the table below, showing agricultural production in metric tonnes.
|
Year/Commodity |
1986 |
1987 |
1988 |
|
Sorghum |
1200 |
5000 |
8000 |
|
Tea |
9000 |
7000 |
6000 |
|
Tobacco |
3000 |
5000 |
4000 |
The graph for the data is as shown below.
Group
(comparative) bar graph showing crop yields in ‘000 kg (1986-1988)
Advantages of a group bar graph
1. The
total values are expressed well for illustration of points.
2. It is
easy to construct, read and interpret.
3. The
importance of each component is shown clearly.
Disadvantages of a group bar graph
1. It is
difficult to compare the totals of each item/component.
2. Trends
such as fall and rise cannot be shown easily.
Compound
(divided) bar graph
This is
a method of data presentation that involves construction of bars which are
divided into segments to show both the individual and cumulative values of
items. The length of each segment represents the contribution of an individual
item in the total length while that of the whole bar represents the total
(cumulative) value of the different items in each group.
Construction
·
Get the data needed for presentation. For example, consider the
table below, which shows the number of tourists who visited the named Tanzania
National Parks from 1998 to 2002.
|
Year
/park |
1998 |
1999 |
2000 |
2002 |
2003 |
|
Manyara |
120,000 |
160,000 |
172,000 |
170,000 |
203,000 |
|
Serengeti |
175,000 |
160,000 |
148,000 |
185,010 |
201,000 |
|
Tarangire |
29,000 |
30,000 |
54,100 |
79,000 |
102,000 |
|
Mikumi |
100,000 |
110,000 |
111,000 |
150,000 |
183,400 |
·
Simplify the data (to make the presentation work easy) by
dividing each value by 10,000. Then add the values to get the total for each
year. The simplified data are as shown in the table below.
·
Determine the scale of the bar length based on the highest total
value. In this case, the highest total value is 68 (20 + 20 + 10 + 18). Recall
the construction of the compound line graph! If we choose 1 cm to represent 1
tourist (10,000 tourists in reality), then the length of the tallest bar will
be 68 cm. Note that the maximum height of a graph for each year equals the
cumulative total values for each year (i.e. 43, 46, 48, 59, 68).
·
Decide on the bar spacing, for example, 1 cm apart.
·
Draw the axes and label them.
·
Start by drawing bars that represent the highest values.
·
The first sets of bars to be drawn are those that represent the
highest values. On top of these, the second highest segments are drawn. The
last segments to be drawn are those with the lowest values in general.
·
To make it easy to follow the rise and fall of individual
values, a soft line could be drawn across bars to separate individual segments.
·
Colour or shade the segments to improve the appearance and
simplify interpretation.
·
Inset the scales, key and title.
Compound
(divided) bar graphs showing tourist visits in 0’000 (1998-2002)
Advantages of compound (divided) bar graph
1. It is
easy to read and interpret as the totals are clearly shown.
2. It
gives a clear visual impression of the total values.
3. It
clearly shows the rise and fall in the grand total values.
Disadvantages of compound (divided) bar graph
1. The
values of individual segments above the first set are difficult to establish
because they don’t start at zero. To get the correct values of the top
segments, you have to add the figures, which is difficult for someone not well
equipped with statistical skills.
2. The
graph is very difficult to construct and interpret.
3. It is
not easy to represent a large number of components as this would involve very
long bars with many segments.
Divergent bar graph
A
divergent bar graph is a graph which shows the fluctuation of individual items
from the mean.
Construction:
1. Calculate
the arithmetic mean (average) of the items.
2. Subtract
the mean from each item.
3. Draw
the graph using the resulting values.
4. Insert
the scale and title of the graph.
The
data below show the enrolment of Form One students at Mara Secondary School
from 1980–1985. Study the table and present the data by a divergent bar graph.
|
Year |
Number
of students |
|
1980 |
100 |
|
1981 |
150 |
|
1982 |
175 |
|
1983 |
200 |
|
1984 |
225 |
|
1985 |
300 |
Procedure:
·
Find the arithmetic mean:
·
Subtract the mean from each item:
|
Year |
Number
of students |
X – |
|
1980 |
100 |
-92 |
|
1981 |
150 |
-42 |
|
1982 |
175 |
-17 |
|
1983 |
200 |
8 |
|
1984 |
225 |
33 |
|
1985 |
300 |
108 |
·
Choose a suitable scale and construct the graph using the
obtained values (X – ).
A
divergent bar graph showing student enrolment (1980-1985)
Advantages of divergent bar graph
1. Fluctuation
in values, which helps to detect the problem in general terms, is shown.
2. It is
important for comparison of positives and negatives.
3. Profit
(success) or loss (failure) can easily be deduced.
4. They
are simple to construct, read and interpret.
Disadvantages of divergent bar graph
1. Graph
construction is time-consuming since it involves many steps.
2. The
calculations involved may be difficult to someone who is poor at mathematics.
3. It is
limited to analysis of only one variable.
Divided circles (pie charts)
A divided circle is also known as pie chart, circle chart or pie
graph. The chart involves dividing the circle into “pie slices” to represent
and show relative sizes of data. The size of each slice or segment is always
proportional to the value it represents. Divided circles can appear in two
forms:
a. Simple divided
circles.
b. Proportional
divided circles.
A
simple divided circle involves a single set of data whereas the proportional
divided circle involves more than one set of data such that the circles will be
proportional to the total quantity that each circle represents.
Simple divided circle
Construction:
·
Obtain the data to work on. Study this hypothetical record
showing enrolment of Form One students in selected Secondary Schools in Tarime
District:
A table showing student enrolment in selected schools in Tarime
District
|
Name
of school |
Number
of students |
|
Nyansincha |
85 |
|
Bungurere |
80 |
|
Nyanungu |
78 |
|
Magoto |
78 |
|
Tarime |
65 |
|
Nyamongo |
70 |
|
Total |
456 |
·
Calculate the total number of students as shown in the table.
·
Calculate the angle in a circle that would represent the number
of students enrolled in each school. For example, 85 out of 456 students
enrolled in Nyansincha Secondary School will be represented in the circle by a
segment with an angle of 85/456 ×630 = 67 degrees.This will give the following
results:
|
Name
of school |
Number
of students |
Degrees |
|
Nyansincha |
85 |
67° |
|
Bungurere |
80 |
63° |
|
Nyanungu |
78 |
62° |
|
Magoto |
78 |
62° |
|
Tarime |
65 |
51° |
|
Nyamongo |
70 |
55° |
|
Total |
456 |
360° |
·
Draw a circle of a reasonable size.
·
Using a protractor, draw a radius from the 6 o’clock mark to the
centre of the circle.
·
Starting with the largest segment representing a specific
component, measure and draw its angle from the centre of the circle.
·
Do the same for other components in ascending order.
·
Divide a circle into segments according to the sizes of the
angles.
·
Shade the segments and write the title and key of the drawn
graph.
Student
enrolment in selected Secondary Schools in Tarime District
Advantages of divided circles
1. It is
easy to compare components as they are represented by angles.
2. Analysis
and interpretation of data is easy.
3. It is
easy to assess the proportion of individual components against the total.
4. Construction
of this graphical representation is relatively simple.
5. It is
easy to determine the value of each component since it is indicated on each
segment.
6. Visual
impression of the individual components is clear and facilitates the
understanding of the information in the data.
Disadvantages of divided circles
1. It is
time-consuming because it involves a lot of calculations.
2. The
represented actual values remain hidden as the values shown on the faces of the
segments may be in percentages.
3. Where
the range of data is large and involves small and big values, accurate
construction of the chart is difficult.
4. When
the values of data set vary slightly, it is difficult to visualize the
proportional differences between values (as it is the case in the pie chart
above).
The Importance of Statistics to the User
Explain
the importance of statistics to the user
Statistics is important in geography because of the following
reasons:
1. It
enables the geographers to handle large sets of data and summarize them in a
way that can be easily understood.
2. It can
also enable the geographers to make comparisons between geographical phenomena,
e.g. to compare the amount of rainfall and agriculture production or population
distribution in different regions, etc.
3. Statistics
translates data into mathematical ways which make the application of
quantitative techniques possible.
4. It
enables the geographers to store the information in forms of numbers, graphs,
tables, charts, etc.
5. Statistics
give precise rather than generalized information. This offers a lot of
satisfaction to the user.
6. Statistics
is very useful for planning at local and national levels. For example,
statistics on census can be used to plan for social services.
How Massive Data can be Summarised
Describe
how massive data can be summarised
The
massive data collected from the field have to be summarized so as to make it
easy to read, interpret and apply. The massive data can be summarized by the
following ways:
Frequency
distribution
A
frequency distribution shows a summarized grouping of data divided into
mutually exclusive classes and the number of occurrences in a class. It is a
way of showing unorganized data e.g. to show results of an election, income of
people for a certain region, sales of a product within a certain period,
student loan amounts, etc. Some of the graphs that can be used with frequency
distributions are histograms, line charts, bar charts and pie charts. Frequency
distributions are used for both qualitative and quantitative data.
Frequency
distribution helps to determine how many times a certain score occurs in a
sample. In statistics, a frequency distribution is a table that displays the
frequency of various outcomes in a sample. Each entry in the table contains the
frequency or count of the occurrences of values within a particular group or
interval. In this way, the table summarizes the distribution of values in the
sample.
Consider
the following table which shows family size of 20 families which were
interviewed in a certain village:3, 2, 2, 4, 3, 7, 8, 1, 3, 6, 2, 2, 4, 5, 6,
4, 3, 4, 5, and 2.
The data can be summarized in a frequency table thus:
a. Arrange
the scores in a descending order from 8 to 1. It is advised to arrange the
scores in ascending order.
b. Distribute
each score in the sample to determine the number of times each score occurs
(frequency) in the data sample.
The
frequency indicates how many times a score or event appears or occurs in a
sample.However, in each case, it is certainly difficult to deal with individual
scores separately. In such cases, a grouped frequency is used.
The steps for making a grouped frequency are as follows:
1. Decide
about the number of classes. Too many classes or too few classes might not
reveal the basic shape of the data set; also it will be difficult to interpret
such a frequency distribution. The maximum number of classes may be determined
by formula: Number of
classes = C = 1 + 3.3log(n) or C = √n(approximately) where n is the total
number of observations in the data.
2. Calculate
the range of the data (Range = Max – Min) by finding minimum and maximum data
value. Range will be used to determine the class interval or class width.
3. Decide
about the class interval denote by h and obtained by h = Range/Number of
classes
4. Decide
the individual class limits and select a suitable starting point of the first
class which is arbitrary, it may be less than or equal to the minimum value.
Usually it is started before the minimum value in such a way that the midpoint
(the average of lower and upper class limits of the first class) is properly
placed.
5. Take an
observation and mark a vertical bar (|l) for a class it belongs. A running
tally is kept till the last observation. However, it is not always necessary to
show tallies in the Frequency Distribution Table because the frequency column
serves the same purpose.
6. Find
the frequencies, relative frequency, cumulative frequency etc. as required.
Frequency distribution table
|
Class
interval |
Frequency |
Cumulative
frequency |
|
0 – 9 |
4 |
4 |
|
10 – 19 |
9 |
13 |
|
20 – 29 |
8 |
21 |
|
30 – 39 |
3 |
24 |
|
40 – 49 |
4 |
28 |
|
50 – 59 |
7 |
35 |
|
60 – 69 |
5 |
40 |
|
70 – 79 |
4 |
44 |
|
80 – 89 |
2 |
46 |
Characteristics of the class interval
1. A score
appears only once. That means no score should belong to more than one class.
2. The
size of the class interval should be the same. No score should fall in more
than one class. Arrange the class intervals in order of ranks as shown in the
frequency distribution table above.
3. The
class intervals should always be continuous.
4. The
range of class interval should be between 3 and 20. Thus, the intervals should
not be below 3 and not above 20.
From the summarized data in the table above, one can identify
two concepts:
a. Apparent
upper limit
b. Apparent
lower limit
These
limits (or boundaries) are seen in each class interval. The apparent lower
limit opens the class interval while the apparent upper limit closes the class
interval.The table above shows 80, 70, 50, 40, 30, 20 and 10 as apparent lower
limits and 89, 79, 69, 59, 49, 39, 29, 19 and 9 as the apparent upper limits.
Apart
from the two concepts above, the table has real limits which are not visible.
These are 0.5 below or above the apparent limits.
From
the above summarized data, other measures of statistics can be deduced. Such
measures include the measures of central tendency, measures of dispersion
(variability), measures of relationship (correlation) and measures of relative
position.
Simple
Statistical Measures and Interpretation
Methods of Presenting Simple and Mixed Data
Describe methods of presenting
simple and mixed data
Measures of central tendency
(averages)
A measure of central tendency is
a single value that attempts to describe a set of data by identifying the
central position within that set of data. As such, measures of central tendency
are sometimes called measures of central location. They are also classed as
summary statistics. The mean (often called the average) is most likely the
measure of central tendency that you are most familiar with, but there are
others, such as the median and the mode.
The mean, median and mode are all
valid measures of central tendency, but under different conditions, some measures
of central tendency become more appropriate to use than others. In the
following sections, we will look at the mean, mode and median, and learn how to
calculate them.
The Mean, Mode and Median
Calculate the mean, mode and median
Arithmetic mean
The mean (or
average) is the most popular and well known measure of central tendency. It can
be used with both discrete and continuous data, although its use is most often
with continuous data. The mean is equal to the sum of all the values in the
data set divided by the number of values in the data set. So, if we have n
values in a data set and they have values x1, x2, ..., xn, the sample mean,
usually denoted by (pronounced x bar), is:
This formula is
usually written in a slightly different manner using the Greek capital letter,
∑, pronounced "sigma", which means "sum of...":
Example 1
In English exam, students
obtained the following percentage scores: 45, 42, 35, 86, 40, 56, 87, 40, 35,
74, 68 and 50
The arithmetic
mean of the score is:
The average score was 54.8%
Advantages of
the mean
1. It is rigidly
defined by a mathematical formula
2. It is easy to
understand and calculate
3. It is based on
all observations
4. It is
determined in all cases
5. It is suitable
for further mathematical treatment or manipulation
6.
Compared to other averages, arithmetic mean is affected least by
fluctuation of sampling
Disadvantages
1. It is greatly
affected by extreme values of the data
2. It cannot be
obtained if a single observation (item) is missing
3.
It is not appropriate in some distributions
Median
The median is the middle score
for a set of data that has been arranged in order of magnitude. Suppose we want
to find the median from the data below:
65, 55, 89, 56, 35, 14, 56, 55,
87, 45, 92
We first need to rearrange that
data in order of magnitude (smallest first):
14, 35, 45, 55, 55, 56, 56, 65,
87, 89, 92
Our median mark is the middle
mark - in this case, 56 (highlighted in bold). It is the middle mark because
there are 5 scores before it and 5 scores after it. This works fine when you
have an odd number of scores, but what happens when you have an even number of
scores? What if you had only 10 scores? Well, you simply have to take the
middle two scores and average the result. So, if we look at the example below:
65, 55, 89, 56, 35, 14, 56, 55,
87, 45
We again rearrange the data in
order of magnitude (smallest first):
14, 35, 45, 55, 55, 56, 56, 65,
87, 89
Only now we have to take the 5th
and 6th score in our data set and average them to get a median of 55.5.
Advantages of
the median
1. It is easy to
calculate and understand
2. It can also be
calculated in qualitative data
3. It is
appropriate for skewed distribution
4. It is not
affected by all extreme observations. Hence, it is a better average than the
arithmetic mean when extreme observations are present.
5.
The values of a median can be obtained graphically.
Disadvantages
1. It is not
suitable for further mathematical treatment.
2. It is not
rigidly defined.
3. It is based on
all values or observations.
4. Compared to
mean, median is more affected by fluctuation of sampling.
5.
In case of ungrouped data, rearrangement of values in order of
magnitude becomes necessary.
Mode
The mode is the
most frequent score in a data set. It represents the highest bar in a bar chart
or histogram. You can, therefore, sometimes consider the mode as being the most
popular option. An example of a mode is presented below:
Normally, the
mode is used for categorical data where we wish to know the most common
category, as illustrated below:
We can see
above that the most common form of transport, in this particular data set, is
the bus. However, one of the problems with the mode is that it is not unique,
so it leaves us with problems when we have two or more values that share the
highest frequency, such as below:
Another problem
with the mode is that it will not provide us with a very good measure of
central tendency when the most common mark is far away from the rest of the
data in the data set, as depicted in the diagram below:
In the above diagram the mode has
a value of 10. We can clearly see, however, that the mode is not representative
of the data, which is mostly concentrated around the 2 to 3 value range. To use
the mode to describe the central tendency of this data set would be misleading.
Advantages of
the mode
1. It is simple to
compute.
2. It is easy to
understand and calculate. In some cases it can be located merely by inspection.
The value of the mode can be obtained graphically from the histogram.
3. It gives a
rough idea of the differences of the data set.
4.
It is the only average that can be used when the data is not
numerical.
Disadvantages
1. It is not
rigidly defined; hence it is unstable for large samples.
2. It is
independent of sample size except under special circumstances.
3. It is not based
on all the values of the data.
4. Mode is not
suitable for further mathematical treatment.
5. As compared to
mean, mode is affected to a great extent by the fluctuation of sampling.
6. There may be
more than one mode (as is the case in the previous graph).
7.
There may be no mode at all if none of the data are the same. 8.
It may not accurately represent the data.
The Significance of Mean, Mode and Median
Explain the significance of mean,
mode and median
Measures of
central tendency are very useful in statistics. Their importance is because of
the following reasons:
1. To find representative value: Measures of
central tendency or averages give us one value for the distribution and this
value represents the entire distribution. In this way averages convert a group
of figures into one value.
2. To condense data: Collected and
classified figures are vast. To condense these figures we use average. Average
converts the whole set of figures into just one figure and thus helps in
condensation.
3. To make comparisons:To make comparisons of two or
more than two distributions, we have to find the representative values of these
distributions. These representative values are found with the help of measures
of the central tendency.
4.
Helpful in further statistical
analysis: Many techniques
of statistical analysis like Measures of Dispersion, Measures of Skewness,
Measures of Correlation, and Index Numbers are based on measures of central
tendency. That is why measures of central tendency are also called measures of
the first order.
Interpretation of Data using Simple Statistical Measure
Interpret data using simple
statistical measures
In the section about averages
(mean, mode and median), we learned how to calculate the mean for a given set
of data. The data we looked at were ungrouped and the total number of elements
in the data set was not that large. The method is not always a realistic
approach especially if you are dealing with grouped data.
Assumed mean (A), like the name
suggests, is a guess or an assumption of the mean. It doesn't need to be
correct or even close to the actual mean and choice of the assumed mean is at
your discretion except for where the question explicitly asks you to use a
certain assumed mean value.
Assumed mean is used to calculate
the actual mean as well as the variance and standard deviation.
Measures of
central tendency can be calculated from grouped data, for example:
Calculation of measures of
central tendency for grouped data
Study the
frequency distribution table below:
Calculation
from the table:
Assumed mean (A) = 12
Note: we find the class
interval by using the class limits as follows: i = upper class
limit – lower class limit + 1
