What feature made movement by land possible?

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

2. Rift valleys

3. fold mountains

4. Escarpments

5. Basins

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

2. Tilt blocks

3. Rift valleys

4. Fault scarps/escarpments

5. Plateaus

6. basins

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

;) I got your back!

i think it is the third one.

answer; grew into towns and cities;