The Dynamic-Earth And Consequence

GEOMORPHOLOGY

Is the science which deals with development of land forms, (relief features).

MAJOR PROCESS WHICH SCULPTURE THE EARTHS CRUST

There are two major forces;

1. Endogenetic /internal processes

2. Exogenetic /external processes

1. ENDOGENETIC PROCESS.

These are force which takes place beneath under the surface of the earth, and they are categorized as;

Earth movement:

vulcanism

2. EXOGENETIC PROCESS

These are external force taking place on the earth surface.

These are force of gradation;

Destructive process(denudation) (Degradation)

Aggradations (constructive process. (Deposition)

INTERNAL FORCE.

Earth movements;

Lateral and Vertical movements

Diastrophism

Is the movement of the solid crust (lithosphere which is made up of upper mantle and crust).The movement can be gradual or rapid. Gradual is the slow movements like what happens in the isocracy.

Can be rapid or sudden as it occurs during earthquakes.

Effects of diastrophism

i. Tension

ii. Compression

iii. Shear

i) Tension

When two forces move /act away from each other, the result strain is called tension which involves the extension of the surface of the crust to produce joints and normal fault

ii) Compression

When two force moves toward one another, it result into compression which involve contraction of the crustal rocks to produce fold and thrust fault.

iii) Shear

When two forces acting parallel to each other through in opposite direction the result is called shear.

Causes of diastrophism

i. Conventional current- in the aesthnosphere

ii. Isostasy -maintenance of equilibrium

iii. Expansion and contraction of rocks due to heating (intrusion of magma between crustal rocks )

FAULTING

What is a fault?

Is a fracture or a crack on the crustal rocks caused by tensional or compression forces.

Compressional will lead to bending and breaking of the rocks

Faulting is the process whereby will result into vertical or horizontal displacement of the crustal rock. Either shear, normal fault.

Types of faults

Normal fault

Is caused by tensional forces in such a case; Foot-wall – Is the upper rock face on the lower side on the fault, it is marked by a low angle (less than 900).

Caused by tensional forces.

There is an up throw and down thrown which bring the displacement of the hanging wall relative to the foot wall, hanging wall is brought down while foot wall is brought up.

Hanging wall

Is the upper rock face on the upper side on the fault wall. It comes out with a very high angle. Any angle more than 900.

Foot wall hanging wall

Foot wall-Is the upper rock face of the lower side the upper rock. Marked by low angle.

NORMAL FAULT

Thrust/Reversed fault

Is the reverse of the normal fault. /is the opposite of normal fault.

This is caused by compression forces.

Hanging wall is displaced upward relative to the foot wall. (Low angle of dip)

Tear / strike / Trans current faults.

This is a vertical structure. The fault plain is vertical or almost vertical. It is caused by shear forces. There is lateral displacement of the crustal rocks. (Parallel but opposite directions).

– Caused by shear forces

Terminologies which are associated with faulting

Shift – Is the total movement of the rock along the fault line.

It involves both slip (the movement along the fault) and throws (the vertical change on the level of the strata).

Heave is the lateral rock block displacement.

Hade is the angle of inclination of the fault plane from the vertical.

Hanging wall is the rock face on the upper side of the fault.

Foot wall is rock face on the lower side of the fault.

Up throw is the mass of rock which has moved upward along the fault.

Down throw is the mass of rock which has moved downward along the fault.

i. Landforms resulting from faulting

ii. Rift Valley.

iii. Block mountains

iv. Plateau and basins

v. Fault scarps

vi. Tilt blocks

vii. Depressions

RIFT VALLEY

An elongated trough bounded by in facing fault scarps along more or less parallel faults

Formation of a rift valley

Theories on formation of the rift valley; There are Many theories but popular ones are 3;

Rift valley by tension

Rift valley by compression

Place tectonics

Rift valley by tension

-Rock layers are subjected by tension

-Faults develop / development of faults

Rift valley by compression

Rock layer are subjected by compression

The side blocks are unstable whereby there is upthrust over the middle block / masses on either side the faults were thrust up higher than the central block (side blocks slide upwards and leave behind the central block)

A rift valley is formed where by the sharp edges are attacked by erosion.

Rift valley by plate tectonic

Rift valley from a single fault. This is from 2 blocks which have a gap in between where by the plates are diverging and magma will well up and attach itself with the diverging plates and the gap the remains will form a rift valley.

Examples of Rift valley

The great African Rift valley

Rhine rift valley (it is between block mountains, Vosges and black forest block mountains)

Mid-Atlantic rift valley

Red sea rift valley

Jordan rift valley

Great African rift valley

One of the most outstanding physical graphic features on the continent.

Extension: starts from the middle east (Jordan – river Jordan)

It extends south wards to River Zambezi (Mozambique). (Beira) its length is 7200km of which 5000km are in Africa.

In East Africa the Rift Valley breaks / splits into 2 branches; Eastern branch it is marked by some lakes; lake Turkana, Lake Magadi, Lake Victoria, Lake Natron, Lake Manyara, Lake Nyasa.

The Western branch is marked by lakes; Lake Tanganyika, Lake Albert, Lake Edward.

The Western branch disappears in Uganda and not noticed in Sudan.

Characteristics of Great Africa Rift Valley

It is bounded by series of fault scarps which are evident in parts of Kenya and N. Tanzania (Manyara)

The floor is almost flat but there are some features which are higher above the sea level like Ruwenzori Mountain which are about 500m above the sea level. And also deep depression likes Lake Tanganyika which is 650m below sea level and the second deepest lake in the world.

The lakes in the rift valley are narrow and deep because they follow the shape of the fault.

The width of the floor of the rift valley varies from place to place from 50 km to 100 km. .

The sides the great R.V have the highlands like mountain adjusted on the sides volcanic mountains.

A MAP OF EAST AFRICA SHOWING THE GREAT AFRICAN VALLEY

BLOCK MOUNTAIN (HORSTS).

These are local / isolated landforms which have been elevated above / raised above the general level of the land. They stand high above the ground like blocks which are flat topped with steep sides. These landforms are common in areas of faults.

Formation

There are two theories;

By tension

By Compression

i. By Tension

Rock layers are subjected to tension

Development of parallel faults

The side blocks will subside and leaving the middle block higher than the others by compression.

Rock layers are subjected to compression

Development of parallel fault

The middle block is unstable and is squeezed up.

Example of Block Mountains

Uluguru mountain

Usambara mountain

Rwenzori mountain

Black forest and Vosges mountain

Sinai mountain

FAULT SCARPS (Escarpment)

Are steep slopes where the land falls abruptly from higher levels to lower levels caused by vertical movements of the crust along the fault line. Can be caused by tension or compression but can be modified by denudation.

Example: Chunya – Tanzania

A fault scarp which occurs across a river result into waterfalls.

TILT BLOCKS

The landscape of angular ridges and depressions formed by series of tilt fault blocks.

Example.

U.S.A Rocky mountain

Somali

Dominated by faults raised

PLATEAU

extensive raised land with sleep sides (table land) e.g. East Africa generally is a plateau / Africa is a plateau in general

BASINS

Are the down warping (sagging). Intermountain basins.

A basin examples: L. VICTORIA, L. KYOGA, GREAT BASIN IN NEVADA, ZAIRE BASIN.

Study Question.

With examples discuss the effects of faulting in East Africa.

Fault is a fracture or a crack on the crustal rock caused by tensional or compression forces. Faulting is the process whereby will result into vertical.

Positive effects

i. Formation of rift valleys e.g. East Africa rift valley

ii. Formation of block mountains i.e. Uluguru

iii. Formation block of plateau and basins. Lake Victoria

iv. Formation of escarpments. Chunya/ kalambo fall in Zambia

v. Formation of the H₂0 falls where fault scraps occur across the river course lakes from basins of lakes rift valley lakes / river Kagera has change.

vi. River reverse direct due to faulting / the direct due to basins which were formerly flowing west ward and forced flow east ward.

vii. Faulting caused the development of rectangular patterns as tributaries forces to flow through the broken rocks and gets converge to the main river.

viii. Occurrence of hot springs. Spring is the natural outflow of water from the ground in an areas there is weakness i.e. in mbeya Tanzania

ix. Displacement of features e.g. San Andreas fault

x. Leads to earthquake

FOLDING

Compression forces and folding

compression forces can cause folds of the rock layers (strata)

The degree of folding will depend on the intensity of operating forces and the nature of rock.

There are several degrees of fold / types of folds

Simple fold – is a symmetrical fold resulting into upthrow called anticline and a down throw called syncline.

This type of fold has more or less equal limbs, where we have the axis which divided the fold into more or less equal limbs. (Limbs are the sides of a fold) (Symmetrical fold).

Compression force

Asymmetrical fold – Is a greater degree. One limb of the fold is longer than the other. (And gentler) unequal limb. The other is shorter and steeper.

Over fold – One limb / asymmetrical limb is pushed over the other limb.

Recumbent fold – This is a complex fold where one limb on the fold is almost inverted over the other limb, to greater degree. Almost horizontal to the surface.

Over thrust (napped) fold – When the pressure is very great a fracture can occur in the fold (along the crust plain) and one limb is pushed forward over the other limbs. NW highlands of Scotland.

Effect of folding on the earth’s crust

The major effects is the formation of Fold Mountains where three are anticlines and depressions (geosynclines) where there is down fold (syncline).

Fold Mountains

Are categories into old fold mountains and young fold mountains.

Formed during per-Cambrian era e.g. Appalachian, cape ranges, Europe Mountains Ural.

Young Fold Mountains

Recently formed, examples the Rocky, Andes, Atlas, Alps, Himalayas and etc. They form highest peaks over the earth surface e.g. Mount Everest highest peak point, on the Himalayas (over 8000mts).

Global distribution of Fold Mountains

AFRICA:

Atlas – N.W Africa

Cape ranges – S.A

N. AMERICA:

Rocky Mountain – western part

Appalachian – Eastern Part of USA

S. AMERICA:

Andes Mountain – Western side

EUROPE:

Alps Mountain – Central Europe

Ural Mountain – Separates Asia and Europe

ASIA:

Himalayas – Central Asia

AUSTRALIA:

Great Dividing Ranges

Characteristics of Fold Mountains

They are very extensive – covering thousands of kilometers over continents, they are not isolative.

They are high (height) especially young fold mountains make the highest peak e.g. Mount Everest.

Age some are young (narrow and long) and some are old fold mountain.

Some have undergone complex processes that is or genesis like volcanism, denudation (effects of geomorphic processes)

Economic importance of fold mountain positive and negative aspects

1. They are climatic modifiers in terms of temperature and rainfall. By forming high peaks where by the peaks have snow although they lie on tropics.

2. Have dense forests of the world like Asia, North America. They produce hard and soft woods which are used for various uses. (timber-lumbering)

3. Tourism – tourist attraction

4. Source of the major rivers of the world. Rockies and Appalachian (Mississippi river) River Ganges, Indus, Irrawaddy in the Himalayas’, Australia River, China – {R.Sikiang, river Hwang Ito, Yangtze Kiang.}

5. They are source of minerals especially in the Rockies like copper, gold etc. South America also

6. Barrier to communication

7. Topography of some mountains discourages settlement.

DISTRIBUTION OF FOLD MOUNTAINS AND MOUNTAIN ROOTS

Fold Mountains are not uniformly distributed in the continents. They are distributed along the margins of the continents where plates collided. The young fold mountains form their own belts and the old fold mountains also form their own belts as well.

Distribution of Young Fold Mountains

Young fold mountains from the alpine chains. The Alpine chain are the active mountain making belts and they constitute the narrow zones most of which lie along the continental margins. The mountains in these belts were formed during the Cainozoic era. They are curved and each curve is called an alpine arc. These arcs are linked in sequence to form two principal mountain belts as follows:

Circum – Pacific Belt: This rings the Pacific Ocean. In the North and South America, this belt is largely on the continents and includes Andes and Cordilleran ranges. In the western part of the Pacific Ocean, they take form of Island arcs running through Aleutians, Japan and the Philippines.

Eurasian – Indonesian Belt: This starts from the west at Atlas Mountains in North Africa, through the near East and Iran to join Himalayas. Then it continue to South Eastern Asia into