GEOGRAPHY FORM TWO WORK
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They are also called endogenic or endogenetic processes. These are processesoperating in the interior of the earth resulting in
e
landforms.
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They include folding, faulting and vulcanicity. Formation of landforms by internal land forming processe (i) Nature of rocks 1.e. soft rocks are more elastic
ms landforms
henc
compared to hard/rigid rocks. (ii) Age of rocks i.e. young rocks are elastic
andforms compared
to old rocks.
(111) Typeof earth movement involv
vertical earthmovement
forms different landforms.
(iv) The intensity and scale of
forces in
forms different landforms co
le strong tectonic forces easily tectonic forces.
Tensional forces
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Compressional forces
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Shear forces
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Gravitational forces
Types of Earth Movements —kcse2007 ntal earth movement
b) Vertical earth movement (a) Horizontal earth movements
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These movements are also known as lateral/orogenic earth movements. They are displacement of the earth’s crustal rocks along a horizontal plane due to tectonic forces causing rocks to stretch, shorten or shear.
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Causes of Horizontal Earth movements.
(i)
crust. Tensional forces which pull the crustal rocks apart causing stretching of the earth
(ii) Compressional forces which push crustal rocks tow be compressed/shorten.
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each other
ing them to
Effects of horizontal Earth movements
(i) They cause strain and stretching of crustal rocks due to tensional forces which cause formation of cracks/faults.
(ii) They cause squeezing and shortening of crustal rocks due to compressional forces which also cause formation of faults.
(iii) They cause crustal rocks to shear by slipping past each other or by dividing into layers which is causedby shearforces. Resultant features of Horizontal earth Movements. Y
Faults
Rift valleys Escarpments v
Basins
Y
Tilt blocks
Y
Block mountains
(b) Vertical earth movements
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These are also known as epeirogeni They are displacement of crustal roc earth surfaces or towards its c
Reed) Pete Go
s of the earth either towards the
(111) 7ilting- crustal rocks tilt if forcesof unequalmagnitudeact on them ie a
Effects of vertical earth movements. downwards. (i) They cause subsiding/sinking/down warping or pulling (ii) They cause uplifting/upwarping or pushing of crusta ware (iii) Theycause tilting of crustal rocks or shearing in vertical di ue to greater uplift
on one side.
Resultant
Tilt blocks Rift valleys
1. Magma Movemer within the earth’s crust-kcse 2017
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Molten rock (me o orcedto intrudeinto the earth’scrustthrough a line of weakness caus x displacement. rocks areforced to move/give way to intruding magma as their place is taken ruding magma. el
2.
Convectional currents in the mantle.
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mantle The on the high currents crustal to temperatures develop move rocksstrong laterally causing in convectional theand them interior vertically alsoofto currents. the move. (in earth circular cause motion), molten exerting magma ina the frictional upper drag
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Large quantities of mag large voids/hollows. Force of gravity then ts on
the crustal rocks overlying the voids, exerting pressure on
the rocks.
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Eventually th
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stal rocks crumble inwards to fill up the voids/hollows