fault is a break, crack or a fracture in the Earth crust produced by vertical
and lateral movements within the earth’s crust.
Faulting is one
of the internal land form bulding process which shapes the earth’s surface.
It is caused by earth movements, which create forces of tension and compression
that are either lateral or vertical.
If forces of tension and compression
are created by earth movements the rocks of the earth crust may fracture or crack.
thus the faults are formed . The line along which rocks have fractured is called
Tension causes a normal fault,
compression causes a reverse fault and lateral movement produces
a tear fault.
Escarpments is a steep
sided feature bordering a rift valley which develops when faulting is accompained
by upward or downward movement of adjoining parts of the crust.
Types of faults
These are formed by the forces
of tension. If the rocks are under tension ,faults will be formed
and the centre block may sink down relative to its neighbours. Normal faults are
common in East Africa.
These are also known as thrust faults and are
caused by the forces of compression when the strata or layers are compressed or
pressed together the rocks will crack and faults will be formed. One block of
rocks may override another to form a black mountain or a horst. Such faults are
common in western Uganda. The Rwenzori mountain is an example of a block mountain
formed by thrust faults.
When lateral movement is taking place
particularly during an earthquake, tear faults may occur. Tear faults are also
known as wrench or transform faults. If a tear
fault occurs across the course of a river, then the river’s course may be
FORMED (PRODUCED) AS A RESULT OF FAULTING
has produced a variety of physical features over the surface of the earth. Among
the most remarkable features are;
A block mountain is also known as a Horst.
It is formed when the middle block which is bounded by more or less parallel faults
is made to rise or is uplifted by the compressional forces. The best example of
a block mountain in East Africa is mount. Rwenzori ranges, also known as the mountains
of the moon. Others include Mathews ranges and Nyiru Ndoto in Northern Kenya.
Tilt blocks are formed when one side of the
middle block is uplifted higher than the other side. The top of the middle block
will not be flat but will be tilted. E.g. west Kenya tilt block, which rises to
about 1900 metres towards lake Victoria.
Escarpments are steep cliff-like slopes. Escarpments are said to have
been formed during the formation of the rift valleys.
escarpments are steep and may extend several hundreds
of kilometres.When escarpments are eroded, they become fault scarps.
Examples of such escarpments in East Africa include:
(or Aberdare) (Kanya)
rift valley i san elongated traugh bound by two in-facing escarpments.
valleys are long, narrow depressions on the earth surface bounded by more or less
parallel faults. A rift valley is also known as a graben.
valleys are thought to have been developed either from the action of tensional
forces in the crust or from the action of compressional forces.
East Africa rift valley system extends southwards from the Red sea. Through Ethiopia
and East Africa to Malawi.
east Africa rift valley covers a distance of approximately 5,600km .it is divided
into two branches that is, the western rift valley and the eastern rift valley.
Western branch stretches from lake Albert in Uganda to lake Malawi. The eastern
branch stretches from lake Turkana in northern Kenya to lake Malawi.
width of the rift valley varies from place to place. The average width is between
50km and 60km.
the floor of the rift valley there are a number of rift lakes and volcanic craters
such as longonat crater and menengai craters.
of the rift valleys
of theories have been put forward to explain the origns of rift valleys. However,
two have remained popular thus, there the two theories which attempt to explain
the origin of rift valleys. One relies on the forces of tension and the other
on the forces of compression. Both theories depend on upward swells, along the
sides of which faults develop.
1: Tensional forces
Tension forces act on the layers of rock.
Gradually two parallel faults appear and the central block begins to subside (sink).
in between sinks in forming a rift valley. The land on either sides stays in place.
subsidence a depression with steep fault scarp sides i.e. a rift valley is formed.
It is trapped in position by later pressure.
2. Compressional forces
Layers of rocks are subjected to compressional forces.
Faults develop and the outer blocks move upwards (Reverse faults are formed).
Central block stays in place and a rift valley is formed.
have been formed on the floor of the rift valley and they vary in size, depth
and salinity. Examples of the salty lakes are Natron, and Magadi. The rift valley
has several in land water basins which contain lakes.
valley lakes of East Africa
Natron || || |
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AREAS IN EAST AFRICA
There are faulted areas in east
Africa outside the rift valley such as:
rift at Kisumu.
face of which is the Nandi scarp
mountains have fault scarps
of the Rift valley to the people of East Africa
beautiful scenery attracts tourists
in the Rift valley provide fish. Forexample L.Tanganyika,
valley lakes provide water for domestic and agricultural use
help in navigation (water transport).
on the slopes are sources of timber
slopes are used for crop farming and settlement due to fertile soils
valley lakes are used for mining forexample soda ash from L. Magadi
of little rainfall (rain shadow) provides pasture for grazing|
purposes or research
conservation. Forexample game parks in rift valley areas.
faced by the people living in the Rift valley areas of East Africa.
- High temperatures
lead to shortage of water.’’
(tremors) which destroy property
rainfall or drought in the Rain shadow areas
means of transport and communication because of the steep escarpments
lakes because of high temperatures and high evaporation rates
erosion and land slides especially on the steep slopes
East African Rift Valley
has resulted into the formation of high mountains in East Africa. For example
the Rwenzori in western Uganda, the southern highlands and the Usambara mountains
in Tanzania and the mathew ranges in Kenya. These are the most productive areas,
where both cash crops and subsistence crops are grown.
highlands receive abundant and reliable rainfall.
valley lakes for example L. Tanganyika, lake Turkana, lake Naivasha and lake Baringo
are fishing grounds.
of these lakes have fresh water which can be used for irrigation and also for
domestic purposes and industrial use.
contains vast deposits of soda ash, which is one of the most important minerals
presents an impressive scenery which can be used for tourism. For example L.Nakuru
has millions of colourful flamingos and other birds.
highlands have been made into National parks and game reserves e.g. the slopes
of the Nyandarua and Rwenzori mountains . These parks attract many tourists.
can also cause the formatiom of waterfalls such as the Karuma falls, Murchison
caused by faulting
and mountains hinder transport development.
valleys are very hot and only suitable for grazing because they are in the rain
shadow unless irrigation is practised as with the case of mubuku.
is severe soil erosion and mass wasting on the step slopes which result in the
destruction of soil surface, crops and at times people's property. For example
is difficult to settle on the steep areas on the rift valley escarpments.