Home GEOGRAPHY INTERNAL FORCES ~ PHYSICAL GEOGRAPHY FORM 5 & 6

INTERNAL FORCES ~ PHYSICAL GEOGRAPHY FORM 5 & 6

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INTERNAL FORCE

Earth movements;

a) 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

a. Tension

b. Compression

c. Shear

a) 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

b)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.

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

Causes of diastrophism

1) Conventional current- in the aesthnosphere

2) Isostasy -maintenance of equilibrium

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

A) 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

1. 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

2. 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)

3. 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

1. 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).

2. Heave is the lateral rock block displacement.

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

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

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

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

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

Landforms resulting from faulting

1. Rift Valley.

2. Block mountains

3. Plateau and basins

4. Fault scarps

5. Tilt blocks

6. Depressions

1. 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;

i. Rift valley by tension

ii. Rift valley by compression

iii. Place tectonics

i. Rift valley by tension

-Rock layers are subjected by tension
– Faults develop / development of faults

ii. 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.

iii. 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

1. The great African Rift valley

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

3. Mid-Atlantic rift valley

4. Red sea rift valley

5. 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

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

2. 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.

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

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

5. 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

2. 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;

i. By tension

ii. By Compression

i. By Tension

a) Rock layers are subjected to tension

b) Development of parallel faults

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

a) Rock layers are subjected to compression

b) Development of parallel fault

c) The middle block is unstable and is squeezed up.

Example of Block Mountains

1. Uluguru mountain

2. Usambara mountain

3. Rwenzori mountain

4. Black forest and Vosges mountain

5. Sinai mountain

3. 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.

4. TILT BLOCKS

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

Example.

1. U.S.A Rocky mountain

2. Somali

Dominated by faults raised

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

5. 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

1. 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.

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

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

4. 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

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

6. Leads to earthquake

b) 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

i. 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

ii 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.

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

iv. 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.

v. 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: 1. Atlas – N.W Africa

2. Cape ranges – S.A

N. AMERICA: 3. Rocky Mountain – western part

4. Appalachian – Eastern Part of USA

S. AMERICA: 5. Andes Mountain – Western side

EUROPE: 6. Alps Mountain – Central Europe

7. Ural Mountain – Separates Asia and Europe

ASIA: 8. Himalayas – Central Asia

AUSTRALIA: 9. Great Dividing Ranges

Characteristics of Fold Mountains

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

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

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

4. 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:

a) 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.

b) 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

THE IMPACT OF EARTH QUAKES

Is the shaking of the ground due to the sudden vibrations.

Are vibrations of the earth crust caused by volcanic eruptions.

Sudden vibration of the earth caused by rupture and sudden movements of rocks that have been strained beyond their elastic limit.

It takes a short time, hardly reaches 5 minutes.

Causes of earth quakes

1} Diastrophic movement

Movement of plates one tectonic plate sliding over or past another plate

2} Volcanism

Intrusion between crustal rocks can cause sudden vibrations intrusion or extraction causes vibration

3} Human activities

E.g. explosion of bombs for example atomic nuclear bombs which can cause shaking in a very large area.

A transportation large airplane trains.

Dynamites

Major causes are diastrophic movement:

This can be explained by the theory of elastic rebound.

There are compressions forces which make the crustal rocks bend.

The forces build up strain when the strain is so great it will result into breakage of the crustal rocks to release energy. The energy will cause seismic waves. The seismic waves will cause the shaking vibration of the earth.

The place where earth quake occurs /origin of earth quake the point where the breaking occurs is called focus.

This breakage only occurs in the solid part of the earth (earth crust) between 8-100km beneath the surface of the earth.

From the focus, seismic waves are sent to all directions and the point vertically above the focus is called epicenter (on the earth crust) point of the surface of the earth vertically above the focus .Epicenter refers to the point where the effect of the earth quake is the greatest

Types of seismic waves

Two main types of seismic waves;

i) Body waves

ii) Surface waves

i) Body waves

Travel through the crust. There of two types

a) Primary (p) waves

These are compression waves. These can be transmitted through solids, liquid s and gasses. They are transmitted to all.

Can be pass on the center of the earth and be felt on the other

They are fastest can travel 8km/sec.

Crustal rocks move back and forth in the direction of wave movements

b) Secondary (s) waves

These are shear waves. These can only pass through solids. They are slower, when they reach the mantle there reflect (bend). They speed is 4km, sec.

The crustal rock to move from side to side perpendicular, at right angle to the direction of wave movement.

Produces shadow zone to the area which the secondary waves do not pass

ii) Surface waves

These travel through the surface rocks and are of two types,

a) Love (L)waves (b)Rayleigh (R)waves

a) Love (L)wave

Move from side to side at right angles to the direction of wave movement.

b) Ray Light waves

– Have a vertical circular movement very similar to that of water in sea wave. They move

Up and down

The energy moves form one point to the next.

THE STRUCTURE OF THE EARTH SHOWING THE PATHS OF EARTH QUAKE WAVES BASED ON VARIOUS GEOPHYSICAL MEMOIRS.

MEASUREMENT OF SEISMIC WAVES

i. Magnitude: – The size of quake is measured on Richter scale (size of magnitude is measured on Richter scale) ranges 0 – 8.9

Total energy released which is transmitted to all direction is measured on Richter scale.

ii. Intensity – The effect / damage experienced on the surface or on the ground / destruction. Measure on Mercalli scale which ranges from 1-12.

1 is the smallest effect detected by seismograph
12 is the most catastrophic effect.

Global distributions of earth quakes

MAP OF THE WORLD SHOWING THE ZONES OF E.Q

The majority of E.Q occurs in narrow belts which mark the boundaries of tectonic plates. The main types of regions where they occur are:

1. The mid-ocean ridges

2. The ocean deeps and volcanic islands

3. Regions of crustal compression

Major E.Q are caused by the movement of tectonic plates e.g. the North American and Pacific Plates result in Horizontal movements along San Andreas Fault in California.

The only parts of Africa which have E.Q are located in the Great Rift Valley Region of East Africa and in parts of North – West Africa. Most of the E.Q occurring in Africa is relatively mild. However, serious earthquakes occurred in El Asnam in 1954 and in Agadir in 1960.

THE MAJOR EARTH QUAKE AND VOLCANIC BELTS ON THE WORLD

Effects of Earth quakes

1. Destruction of life. For example in Iran, 20 thousand people died, In Morocco. Chile.

2. Destruction of property, breaking of buildings example in Morocco where building and transportation system collapse.

3. Can cause faulting / joints e.g. San Andreas in California.

4. Displacement of crustal rocks can be vertical or lateral. (Land can be uplifted) e.g. San Andreas.

5. Can cause land slide which can cause some blockage on transport system or rivers. Also open up deep cracks in the surface rocks eg. The El Asnam E.Q in Algeria.

6. Devastation especially in cities.

7. Tsunami. Great seismic waves which are caused on the ocean flow due to earth quakes.

Precautions against Earthquake

Natural disaster, how to reduce its negative impact.

i. Discourage settlement on those areas which are frequently prone to earth quake.

ii. Run to open space

iii. Build houses which are shock absolve.

iv. Do not build tall buildings on areas prone to Earthquake.

v. Avoid using explosives especially exploding atomic bombs, nuclear bombs.

vi. Seismologist(seismographers) should detect the Earthquake and inform the people

B. EXOGENETIC FORCES WHICH SCULPTURE THE SURFACE OF THE EARTH.

These are external forces. They operate on the surface of the earth.

a) Denudation:

These are destructive forces which lower the earth’s surface

i. Weathering / mass wasting

ii. Erosion

iii. Transportation

b) Deposition – Constructive process which raise the eland

VULCANICITY (VULCANISM)

Is a process whereby molten (magma) material from the interior of the earth is injected into between the crustal layers the earth crust rocks or ejected on the earth surface.

This material can be inform of gases where gaseous material or in liquid or solid.

Material which is injected between rock layers form intrusive igneous rock while that which is ejected out in the surface form extrusive igneous rock.

Intrusive magma form intrusive features of Vulcanism while extrusive magma form extrusive features of Volcanism (lava). The shape of the features form depends on the nature and weakness or strength of the bedrock.

VULCANICITY

Vulcanicity includes extrusive and intrusive while volcanicity is a subset / part of vulcanicity (surface manifestation of vulcanicity).

Causes of Volcanism

1. Intensive Pressure: –

This pressure is so high and it finds the line of weakness where it can come out. The line of weakness is found on the boundaries of tectonic plates. Pressure causes high temperature and hence it tends to release with molten material and this causes.

Intrusive features of vulcanism

1.Dykes

2.Sill

3.Lacolith

4.Batholith

5.Lopolith

6.Phacolith

7.Minor features.

The shape of the intrusive features depends on nature and strength or weakness of the bedrock.

Fluidity which is very fluid it will move very far and form linear features.

Thick, accumulate (viscous) and solidify and form features.

1. Dykes: Intrusion of magma which solidify vertically across bedding rock strata or can be inclined magma.

They are pillar like structures.

These dykes can be exposed by denudation. It depends if the rocks of the dyke is more resistance (harder) than the surrounding rocks, the surrounding rocks will be eroded and form a rigid.

And if the dyke is soften than the surround rock it will be eroded and form a depression.

Example: The dyke which give rise to waterfalls or rapids such as Howick falls on the River Mgeni in S.A, Dyke ridges on the S W side of the Kaap Valley S.A, West of Lake Turkana (Rudolf) where dyke form trenches in sedimentary Turkana grits.

2. Sill: Is a horizontal sheet of intrusive rocks where magma has solidified between rock layers / bedding layers.

The magma is very fluid and moves very far

If it cuts across a river, it can cause a water fall. Due to erosion the river erodes the surface but when crossing the dyke or sill the rocks are hard to erode but after crossing the rock it will erode faster and after many years will form H₂O fall.

Examples: In Cape Province of S.A are buttes which have a sill capping, Kinkon falls in Guinea.

4. Lacolith: is a dome shaped of intrusive magma (caused by accumulation of viscous magma which pushes the overlying rock layers to bend upward.

Laccoliths are near the surface

Examples: Fonjay massif and Ambereny massif in Madagascar, Henry Mountains in southern Utah to the west of the Colorado River.

4. Batholiths: Are very large masses of igneous rock which are formed deep in the crust (plutonic).

Examples are granites which are made up of large crystals because cooling has taken a very long time.

They normally form roots for mountains.

Batholiths’ can be exposed by denudation.

Examples: Granite batholiths in S.w peninsula of England and in beuttany,Tanzania batholith in Mwanza and Iringa,sinda batholith, East Zambia, Cape coast batholith in Ghana and Sinso batholiths in Uganda.

5. Lopolith: They are saucer like feature formed by sagging.

Very large saucer shaped intrusion shape may be due to increased weight causing sinking. After denudation the upturned edges sometimes form out facing scarps.

Examples: the bushveld basin in the Transvaal in S.A, sierra lione peninsula.

6. Phacolith: These are intrusive solidification of magma on the anticlines and synclines of rock strata.

Extrusive features of volcanism:

Magma which reaches the surface is called lava

LAVA: Can come out in two ways;

(i) Through fissure eruption/linear

Magma wells up and pours out into the surface through a crack or a whole

(Explosion) quietly

(ii)Vent eruption: Magma is forced out through a vent or central opening violently.

Types of materials given out during eruption

i) Gaseous Materials – Gases are emitted during the course of an eruption include gaseous compound of sulphur, hydrogen, carbon dioxide.

ii) Liquid – There is lava which can be mobile (flow faster) or viscous tephra (accumulate and flows).

– Acidic Lava

-Basic Lava

iii) Solid – Solid materials are ejected, some are fragment of the country rock; e.g. Scoria, pumice, cinder (lapilli), volcanic bombs.

Those which come out explosively will spread out far. But will fall and cool and build landforms.

Some of these materials will cool and accumulate and build landforms. Those which come out slowly build up a volcano.

VOLCANO – Is a mould or a cone like features or a circular in shape build up through volcanic activity (is a result from volcanic activities)

Types of Volcano

Active Volcano
Domant Volcano
Extint Volcano

Volcanic Landforms

Ash and Cinder cone (scoria cones).

– These cones are building up by pryroclastic material solidifying around the vent.

– Formed by vent eruption cinder are small round particles either from the interior of the earth or have solidity after being exposed out of the crust. Examples: South of L. Turkana in Kenya, Likaiyu and Teleke (both under cinder cone) and Nabuyatom (ash cone)

The structure of an ash and cinder cone

Lava Cones – A hill or type of a cone which is formed by lava (cumulo dome)

(a) Acidic Lava – This is viscous and will not flow very far from the vent but accumulates around the vent to form sleep sided cones. Viscous lava can form a spine (is a steep hill) has more silica.

Example: Mount Pelee Martinique West Indies.

(b) Basic Lava Cone – Is very fluid, mobile. It spread far from the vent and it builds up gentle sloping cones.

Example: Mauna Loa – Hawaii.

iii. Composite cone – This is formed by alternating layers of ash and lava

Note: These composite cones forms high composite peaks – (give highest peaks on the surface of the earth) e.g. Mountain Cameroon, Mount Kilimanjaro, Mount Vesuvius.

Iv. Plug Volcano (Volcanic neck) – They are cylinder like shaped it occupies the vent of a dormant or extinct volcano. It solidifies on the vest, and blocks the mountain forming dormant volcano.

Caldera (Basal Wreck) – Is a large shallow cavity (depression) on the top of the volcano.

How formed

Formed by violent eruptions which remove the former top of the volcano.

NB:

Water can accumulate in the caldera and form Caldera lakes e.g. Lake Toba in Sumatra (Indonesia) and Crater Lake in USA and Bosumtwi in Ghana

Caldera; Ngorongoro in Tanzania, Mount Meru in Tanzania, Longonot in the Eastern Rift S.W of Kenya.

Stages in the formation of a caldera

v) Lava Plateau – Result from fissure eruption. When lava is up welled then spreads to a wide area and when it solidifies forms lava plateau. (fairly high level lava plateau) (Basalt plateau which is acidic in nature). E.g. In Sahara, Algeria, Morocco and in S.S – Drakensberg Plateau, North America – Snake plateau, Deccan plateau in India.

vi) Other minor features associated with volcanism.

a) Hot spring – Natural outflow of hot H₂O from the ground. E.g. In Mbeya, Arusha, Mara – Majimoto.

FORMATION OF GEYSERS

a) Geysers – Superheated H₂O and steam is drawn out with great force and sometimes explosively in comes periodically.

b) Solfatara – Is a volcano which releases only steam and gas. The large % of gas is sulphur.

c) Fumaroles – Emission of steam

d) Mofatte– Emission of carbon dioxide.

Stages / life cycle of Volcano.

1. Active volcano – One which is definite / takes place periodically in recent time. Example oldonyo in Tanzania, Mufungiro in Uganda, Italy Vesuvius.

2. Dormant Volcano (sleeping) – Has erupted before but has stayed dormant for a long while and not sure if it will erupt again or not. E.g. Mount Kilimanjaro, Mount Meru, it has signs of eruption

3. Extinct (dead) Volcano – A volcano which has remained dormant and doesn’t have any signs of eruption.

Global Distribution of Volcanoes and lava Plateau

Vulcanicity occurs in areas where the earth’s crust disturbed. These are the areas where weaknesses in the crustal rocks provide an easy passage for volcanic materials to escape into the earth’s crust or onto the surface of the earth. For this reason volcanic features and active volcanicity are associated with weaker parts of the crust.

These include;

They are common along the zones of plate tectonic convergence mainly to oceanic and continental plate where the oceanic place subjected into aesthnosphere and get heated producing magma then rises through the line of weakness.

A long the zones of divergence where the crust spread apart giving to a line of weakness through which magma pass.

In regions of faulting like along the great East African rift valley.

In regions where folding as fractured the crustal rocks.

WORLD DISTRIBUTION OF VOLCANOES AND LAVE PLATEAUS

Economic importance of Vulcanicity

Positive importance

1. Some lava out – Pouring have weathered to give fertile soils. These regions are of important agriculture value. E.g. Deccan plateau in India.

2. Volcanic activity sometimes results in the formation of precious stones and minerals. These occur in some igneous and metamorphic rocks e.g. Diamonds of Kimberley, Copper deposits of U.S.A.

3. Some hot springs are utilized for heating and supplying hot water to building in New Zealand and Iceland.

4. Volcanic eruptions also provide geothermal power, which can be utilized for electric generation. Geothermal power is used in Kenya and Ethiopia

5. Volcanic eruption can attract tourists and lead to the development of tourist industry in the country.

6. The calderas resulting into lakes can be useful for fishing, irrigation.

7. Volcanic activities result into the formation of different volcanic land forms such as Volcanic Mountains, which are attractive to tourists.