FORM two
Geography
TEACHing
NOTES.
, FORM 2 GEOGRAPHY
INTERNAL LAND FORMING/ENDOGENETIC
PROCESSES
-Processes operating in the interior of the earth resulting in the formation of
natural physical features or landforms.
They are caused by earth movements.
Examples of these processes are folding, faulting and Vulcanicity.
Formation of land forms by internal land forming processes is determined by:
Nature and age of earth materials
Type of movement involved
Intensity and scale of movement involved
Crustal Earth Movements
-Displacement of the earth’s crustal rocks.
They are brought about by tectonic forces which originate and operate in the
interior of the earth e.g. tensional forces (which operate along horizontal plane
moving away from each other), compressional forces (which operate along
horizontal plane moving towards each other), shear forces (which move past
each other with unequal strength) and gravitational forces (which attracts things
to the earths centre).
Earth movements are of 2 types:
1. Horizontal/lateral/orogenic movements
2. Vertical/epeirogenic movements
Horizontal Earth Movements
-Movements which act along a horizontal plane within crustal rocks.
They are caused by tensional and compressional and shear forces.
Effects
They cause:
Strain and stretching of crustal rocks due to stretching caused by
tensional forces which cause formation of cracks or faults.
Squeezing and shortening of crustal by compressional forces rocks which
cause them which also cause formation of faults.
Crustal rocks to shear by slipping past each other or by dividing into
layers which is caused by shear forces.
Results of Horizontal Earth Movements
-results in the formation of the following features:
1. Faults 4. Escarpments
2. Rift valleys 5. Basins
3. fold mountains 6. Tilt blocks
, 7. Block mountains
Vertical Earth Movements
-Movements which occur along the earth’s radius or towards the earth’s surface
or towards its centre.
Effects
Causes:
Subsiding/sinking/downwarping or pulling of crustal rocks
downwards.
Uplifting/upwarping or pushing of crustal rocks upwards
Tilting of crustal rocks or shearing in vertical direction due to
grater uplift on one side.
Results of Vertical Earth Movements
1. Raised cliffs 5. Plateaus
2. Tilt blocks 6. basins
3. Rift valleys
4. Fault scarps/escarpments
Causes of Earth Movements
(a) Magma movement within the earths crust.
(b) Gravitational force
(c) Convectional currents in the mantle
(d) Isostatic adjustment
Magma Movement within the Earths Crust
When magma moves with force pushing crustal rocks horizontally
or vertically.
When magma moves from reservoir and leaves empty spaces onto
which crustal rocks are pulled inwards.
Gravitational Force
-When the attractive force of the earth pulls crustal rocks into empty spaces left
after magma escaping from the reservoir.
Convectional Currents within Mantle
, -When convectional currents in magma in mantle drug crustal rocks by friction.
Horizontal movement of currents cause horizontal movements while vertical
cause vertical movements.
Isostatic Adjustment
-Rising of continental masses to restore the upset state of balance between sial
and sima layers.
-Isostacy is the state of balance between sial and sima layers.
It can be disturbed by erosion on continents and melting of continental ice
sheets.
The reduced weight causes continental masses to rise.
( skip 8 lines for diagaram klb bk 2 pg2 )fig 1.3
Theories Explaining the Earths Movements
A theory is reasoned ideas intended to explain facts or ideas.
There are 2 theories which explain the earth’s movements namely the
Continental Drift Theory and the Plate tectonics theory.
i)Theory of Continental Drift
Its proponent was A. Wegener.
It explains the origin of 6 continents.
It states:
The earth was a single sialic land mass called Pangaea surrounded by a
huge ocean called Panthalasa whose floor was a mass of sima.
Pangaea broke into two parts called Laurasia (N. Hemisphere) which lay
around equator and Gondwanaland (S. Hemisphere) which lay around
south pole which were separated by a narrow ocean called Tethys (the
present Mediterranean Sea).
Laurasia broke into Laurentian Shield and Fennoscandia (Europe, Asia
and N. America) and moved northwards to their present positions.
Gondwanaland broke into Africa, Australia, S. America and Antarctica
and India subcontinent.
Africa and India drifted northwards.
Evidences Supporting the Theory
1. Fitting of western coast of Africa and S. America into a jigsaw.
2. Discovery of coal 40◦N and 55◦N which was formed by burying of
tropical vegetation.
3. Considerable displacement of rocks along some faults e.g. along
the Great Glen Fault of Scotland.
4. Cape and Buenos Aires folds resemble one another by having east
west trend.
Geography
TEACHing
NOTES.
, FORM 2 GEOGRAPHY
INTERNAL LAND FORMING/ENDOGENETIC
PROCESSES
-Processes operating in the interior of the earth resulting in the formation of
natural physical features or landforms.
They are caused by earth movements.
Examples of these processes are folding, faulting and Vulcanicity.
Formation of land forms by internal land forming processes is determined by:
Nature and age of earth materials
Type of movement involved
Intensity and scale of movement involved
Crustal Earth Movements
-Displacement of the earth’s crustal rocks.
They are brought about by tectonic forces which originate and operate in the
interior of the earth e.g. tensional forces (which operate along horizontal plane
moving away from each other), compressional forces (which operate along
horizontal plane moving towards each other), shear forces (which move past
each other with unequal strength) and gravitational forces (which attracts things
to the earths centre).
Earth movements are of 2 types:
1. Horizontal/lateral/orogenic movements
2. Vertical/epeirogenic movements
Horizontal Earth Movements
-Movements which act along a horizontal plane within crustal rocks.
They are caused by tensional and compressional and shear forces.
Effects
They cause:
Strain and stretching of crustal rocks due to stretching caused by
tensional forces which cause formation of cracks or faults.
Squeezing and shortening of crustal by compressional forces rocks which
cause them which also cause formation of faults.
Crustal rocks to shear by slipping past each other or by dividing into
layers which is caused by shear forces.
Results of Horizontal Earth Movements
-results in the formation of the following features:
1. Faults 4. Escarpments
2. Rift valleys 5. Basins
3. fold mountains 6. Tilt blocks
, 7. Block mountains
Vertical Earth Movements
-Movements which occur along the earth’s radius or towards the earth’s surface
or towards its centre.
Effects
Causes:
Subsiding/sinking/downwarping or pulling of crustal rocks
downwards.
Uplifting/upwarping or pushing of crustal rocks upwards
Tilting of crustal rocks or shearing in vertical direction due to
grater uplift on one side.
Results of Vertical Earth Movements
1. Raised cliffs 5. Plateaus
2. Tilt blocks 6. basins
3. Rift valleys
4. Fault scarps/escarpments
Causes of Earth Movements
(a) Magma movement within the earths crust.
(b) Gravitational force
(c) Convectional currents in the mantle
(d) Isostatic adjustment
Magma Movement within the Earths Crust
When magma moves with force pushing crustal rocks horizontally
or vertically.
When magma moves from reservoir and leaves empty spaces onto
which crustal rocks are pulled inwards.
Gravitational Force
-When the attractive force of the earth pulls crustal rocks into empty spaces left
after magma escaping from the reservoir.
Convectional Currents within Mantle
, -When convectional currents in magma in mantle drug crustal rocks by friction.
Horizontal movement of currents cause horizontal movements while vertical
cause vertical movements.
Isostatic Adjustment
-Rising of continental masses to restore the upset state of balance between sial
and sima layers.
-Isostacy is the state of balance between sial and sima layers.
It can be disturbed by erosion on continents and melting of continental ice
sheets.
The reduced weight causes continental masses to rise.
( skip 8 lines for diagaram klb bk 2 pg2 )fig 1.3
Theories Explaining the Earths Movements
A theory is reasoned ideas intended to explain facts or ideas.
There are 2 theories which explain the earth’s movements namely the
Continental Drift Theory and the Plate tectonics theory.
i)Theory of Continental Drift
Its proponent was A. Wegener.
It explains the origin of 6 continents.
It states:
The earth was a single sialic land mass called Pangaea surrounded by a
huge ocean called Panthalasa whose floor was a mass of sima.
Pangaea broke into two parts called Laurasia (N. Hemisphere) which lay
around equator and Gondwanaland (S. Hemisphere) which lay around
south pole which were separated by a narrow ocean called Tethys (the
present Mediterranean Sea).
Laurasia broke into Laurentian Shield and Fennoscandia (Europe, Asia
and N. America) and moved northwards to their present positions.
Gondwanaland broke into Africa, Australia, S. America and Antarctica
and India subcontinent.
Africa and India drifted northwards.
Evidences Supporting the Theory
1. Fitting of western coast of Africa and S. America into a jigsaw.
2. Discovery of coal 40◦N and 55◦N which was formed by burying of
tropical vegetation.
3. Considerable displacement of rocks along some faults e.g. along
the Great Glen Fault of Scotland.
4. Cape and Buenos Aires folds resemble one another by having east
west trend.
