Lithosphere: Exogenic Processes Online Test 11th Geography Lesson 8 Questions in English

At Mahabalipuram, Chennai, Tamil Nadu, the 6-meter-high and 5-metre wide rock estimated to weigh over 250 tons is known locally as Krishna’s Butter Ball. Its original Tamil name is “Vaanirai Kal” which literally translates to “Stone of The Sky God”.

The processes which occur on earth’s surface due to the influence of external forces are called as exogenic processes. Weathering, mass wasting and denudation are the major exogenic processes.

The elements of nature capable of doing the exogenic processes are termed as gradational agents. For instance, the wind, river, glacier, waves and ground water.

Weathering is the process of disintegration and decomposition of rocks. It is due to the action of climate, plants, animals and other living organisms which cause the rocks to break down physically, chemically and biologically.

There are three types of weathering. They are physical weathering, chemical weathering and biological weathering.

Physical Weathering is the disintegration of rock mainly induced by elements of weather. It produces smaller, angular fragments of the same rock. It is caused by the change in temperature, pressure, water and wind. Physical weathering is further divided into different categories. They are thermal weathering, frost wedging and exfoliation.

In arid and semi-arid areas, the temperature increases, heat up and expand the rocks during the day and contract the rock materials when cooling at night. Under extreme temperature conditions, due to alternate expansion and contraction, the rocks crack and eventually split. The thermal weathering is of two types. They are; (a) Granular disintegration and (b) Block disintegration.

Rocks generally heat or cool more on the surface layers. The alternate changes in temperature could cause their outer layers to peel off from the main mass of the rock in concentric layers just as the skin of an onion. The process by which curved layers of rock breakaway from the rock beneath them leaving behind dome shaped monoliths is called exfoliation. It is also called as ‘onion weathering’.

Exfoliation occurs commonly in the arid areas.

Almost all liquids contract when frozen, but when water freezes it becomes larger in size or takes up more space.

Chemical weathering is the decomposition of rock. For example, it creates altered rock substances, such as kaolinite (china clay) from granite.

The types of chemical weathering are as follows: 1. Solution, 2. Oxidation, 3. Hydrolysis, 4. Carbonation and 5. Hydration.

Oxidation: When oxygen combines with water and iron, it weakens the rock and breaks it. Example, rusting of iron.

Hydrolysis is the chemical breakdown of a rock substance when combined with water and forms an insoluble precipitate like clay mineral. The most common example of hydrolysis is feldspar found in granite changing to clay.

Biological weathering is the alteration of rock by the action of plants, animals, and man. Burrowing and wedging by organisms like earthworms, termites, rodents, etc., help in exposing the rock surfaces to chemical changes with the penetration of moisture and air.

Mass wasting is the movement of a large mass of rock, soil and debris downward by the pull of gravity. It is also called a mass movement or slope movement. It may happen suddenly or slowly. Generally, mass wasting is classified by the type of material involved (mud, soil, and rock) and type of motion (fall-free-falling pieces, slide material moves along the rock slope and flow–material mixed with water).

Great mass of bed rock moves downward by rotational slip from a high cliff is known as slump. Most common reason for slumping is erosion at the base of the slope which reduces the support for overlying sediments.

Rock falls occur when pieces of rock break from a cliff. Frost wedging may also eventually loosen large blocks causing them to fall. The accumulation of rock debris at the base of a steep slope is called talus.

Debris slide is more extensive and occurs on a larger scale than slump but there is a little amount of water. The materials involved in debris slide are a mixture of soils and rock fragments.

Mudflow is a liquid mass of soil, rock debris and water that moves quickly down a well-defined channel. They occur most often in mountainous semiarid environments. A mudflow originating on a volcanic slope is called a lahar.

Debris becomes mixed up completely and flows as liquid mud. It often carries large boulders which can be very destructive. When earth material moves down a hillside as a fluid-like mass, it is called an earth flow. These flows typically occur in humid areas on steep slopes with thick, clay rich soil that becomes saturated with water during storms.

The deadliest type of debris flow is the debris avalanche. It is a rapidly churning mass of rock debris, soil, water, and air that moves down steep slopes. The trapped air may increase the speed of an avalanche by acting as a cushion between the debris and the underlying surface.

Creep is a slow and gradual movement of soil downhill. Its velocity is typically less than a centimetre per year. Freezing and thawing contribute the soil creep by progressively moving soil particles down the hill. Creep is manifested at the surface by things like tilted utility poles, fences and trees Vegetation helps reduce the rate of soil creep.

Gradation is the process by which the earth’s surface gets levelled. It can be further divided into degradation, the process of eroding the earth’s elevated surface and aggradations, the process of filling up the earth’s depressions.

The forces which act on the surface of the earth are termed as Gradational agents. Water, wave, wind, ice are the important gradational agents.

The streams have a huge capacity to erode the rock over which they flow. In fact, the formation of the river channel is the result of the erosional capacity of the stream. The erosional capacity of the stream depends on its volume of water and velocity of flow. The river performs three types of work. They are erosion, transportation and deposition.

The breaking of rocks by the river in along its course is called erosion. Erosional work of a river is performed mechanically and chemically.

River erosion is carried out in the following ways: i. Hydraulic action, ii. Corrasion (abrasion), iii. Corrosion (solution) and iv. Attrition.

Corrasion (abrasion) refers to the breaking of rock in the bed and on the bank by fragments carried by the stream.

Attrition refers to the eroded materials carried by the stream strike against each other.

Hydraulic action refers to the physical force of the moving water which breaks the rocks in its course.
Corrosion (solution) refers to the dissolving process of soluble minerals by the splashing of stream water.

Stream carrying the fragmented materials broken by the stream is called transportation. After erosion, the eroded materials get transported along with the running water.

The transportation of eroded materials is carried in four ways: 1. Traction, 2. Saltation, 3. Suspension and 4. Solution.

Some of the fragments of the rocks move along the bed of a stream by bouncing continuously. This process is called as saltation.

The holding up of small particles of sand, silt, and mud by the water as the stream flows is called suspension.

When the velocity of the stream decreases, the stream deposits sand, silt and other fragments. It is called as the deposition. When a river moves in a gentle slope, its speed reduces and river begins to deposit its load. The river starts depositing larger materials first and smaller and finer materials are carried further down to the mouth of the river.

Middle stage is the matured stage of a river. Vertical erosion or deepening of the valley is significantly reduced. Lateral erosion is the dominant work. Due to the lateral erosion of this stage, the widening of the valley occurs. The volume of the river water increases and the slope of river is moderate. The depth of the river is deep here.

The lower stage is the final stage of a river where the valleys are extremely broad and it has generally gentle slope. The valley becomes almost flat which is called a peneplain.

The place where two rivers join is called as the confluence. The mountain which has two river systems draining on either side of the slope is termed as the water divide.

The valley is formed in Upper stage of a river. The place where a river starts is called a source. In the mountain stage, the number of small streams originates from different locations. They are called Tributaries.

Most of the peneplain forms low residual hills with steep slopes which are called as Monadnocks. Th e main work of the river in this stage is the deposition. The depth of the river is shallow here. When the main river splits into many small rivers, they are called as the distributaries. The place where the river ends is called mouth of the river.

Gorges are formed due to active down cutting of the valleys. So, a Gorge is a narrow and deep river valley which has steep slopes.

Canyons are extended form of gorges. Canyons represent very deep, narrow but long valleys. Th e steepness of the valley sides depends on the nature of the rocks. Th e Grand Canyon of the Colorado River in the state of Arizona, USA having a length of 482.8 kilometres and depth of 2088.3 meter is the largest canyon in the world.

Rapids are stream sections with extremely strong currents, numerous obstacles, and steps in their streambeds.

A waterfall is a vertical drop in a streambed. Both water fall and rapids are formed by vigorous erosion. Series of a waterfall in a river is called as Cascade.

A plunge pool is a deep depression in a stream bed at the base of a waterfall. It is created by the erosional forces of falling water at the base of a waterfall.

Angel Falls, in Venezuela, is Earth’s highest waterfall (979 m).

The valleys made by the rivers are erosional landforms. The valley is formed in the youthful stage of the river erosion. Due to the steep slope and large volume of water, the river cuts its bed vertically forming narrow and deep river valley. This is called as V-shaped valley.

The swirling movement of the water falling into the plunge pool is called eddying.

An interlocking spur, also known as an overlapping spur, is a projecting ridge that extends alternately from the opposite sides of a V-shaped valley. A river with a winding course flows down the interlocking spur.

The kettle-like small depressions in the rocky beds of the river valleys are called potholes. They are always cylindrical in shape. Potholes are generally formed in coarse-grained rocks such as sandstones and granites.

The narrow step like flat surfaces on either side of the valley floor are called river terraces. They represent the level of former valley floors.

Raised bed and a bank of the river due to frequent flooding and deposition of the sediments is called levees.

Peneplains represent low featureless plain having undulating surface and remnants of convex-concave residual hills.

An estuary is a partially enclosed coastal body of brackish water with one or more rivers flowing into it, and with a free connection to the open sea. The inflow of both sea water and fresh water provide high levels of nutrients both in the water column and in sediment. Hence, it makes estuaries among the most productive natural habitats in the world.

A meander is a winding curve or bend in a river. Meanders are the result of both erosional and depositional processes. They are typical landform of the middle and lower course of a river. This is formed by vertical erosion, lateral erosion, and deposition within the floodplain.

Oxbow lake is a free-standing body of water formed when the meander is cut off from the main river. This landform is so named because it resembles horse shoe.

Narmada river estuary is located in Gujarat.

Alluvial fans are often found at the foot of arid or semiarid mountain ranges where intermittent streams flow. An alluvial fan is a fan shaped deposit of gravel, sand and other smaller particles of sediment.

Alluvial fans are found in Kosi river, Himalayan region, Death Valley National Park and along the sides of the Colorado River at Grand Canyon National Park, U.S.

Delta is found in the old stage of a river. It is the triangular shaped landform made up of alluvial deposition in the mouth of the river. It is named after the fourth Greek alphabet called delta.

The Ganges Brahmaputra delta is the largest delta in the world.

Delta is classified into the following based on the shape and kind of the load deposited by the river. They are 1. Arcuate Delta, 2. Estuarine Delta, 3. Birds foot Delta, 4. Lacustrine Delta, 5. Truncated Delta, 6. Abandoned Delta and 7. Cuspate delta.

Estuarine Delta is formed at the mouth of submerged rivers depositing down the sides of the estuary.

when the river shifts its mouth, the delta already made is left abandoned. Such a delta is called abandoned delta.

Sea waves and ocean currents modify and even destroy deltas deposited by the river through their erosional work. Thus, eroded and dissected deltas are called truncated deltas.

Yellow river delta, China and the Western part of Ganga delta made by Hoogly river, India are the examples of Abandoned delta.

Seine River of France is the example of Estuarine Delta.

Arcuate Delta is a bowed or curved delta with the convex margin facing the body of water. It is also known as fan-shaped delta.

Lacustrine Delta is formed when a river flows into a lake

Birds foot Delta are formed due to deposition of finer materials by river water. Deposited alluvial material divides the river into smaller distributaries. Such delta is also called as finger delta.

Cuspate delta is a tooth shaped delta formed when a single distributary flows through and deposits its load on its either side.

River Nile Delta in Egypt and Ganga Delta in India are examples of Arcuate Delta. Mississippi river delta, the USA is the example of Birds foot Delta, Lough Leanne river delta, Ireland is the example of Lacustrine Delta and Tiber River of Italy is example of Cuspate delta.

A glacier is a huge mass of ice that moves slowly along the mountain slope. The term “glacier” comes from the French word glace which means ice.

Glaciers are often called “rivers of ice”. It forms where the accumulation of snow exceeds its ablation over many years.

The places where the snow lies for the whole year are called snow fields. The imaginary line above which there is a permanent snowfield is known as the snow line.

The snowfields are always situated above the snow line. The snow line differs according to latitude, amount of snowfall, the direction of the wind and the physical features of the region. Snow starts melting below the snow line.

The world’s largest glacier is the Lambert Glacier in Antarctica, more than 96 km wide and 435 km long and 2,500 metres deep.

The Glaciers are of three types. They are; 1. Continental Glaciers 2. Ice Caps 3. Mountain and Valley Glaciers.

Ice caps is the covering of snow and ice on the oceans of poles. The ice caps can cover vast areas with the extensive accumulation of snow and ice. Example, Svartissen ice cap in Northern Norway.

The continental glaciers are found in polar regions. In these areas, all the precipitation is in the form of snow. The snow that falls from year to year gradually gets accumulated. As a result, these regions are covered by an extensive ice mass. This is known as ice sheet or continental glacier.

Mountain and Valley Glaciers are also known as Alpine glaciers. They flow like tongues of ice down through the mountain valleys from the ice caps. The piedmont glaciers form continuous ice sheets at the base of mountains. The valley glaciers or Alpine glaciers are found in higher regions of the Himalayas and on all such high mountain ranges of the world.

The rate of movement or the speed of a glacier depends upon the size of the glacier and the slope of the valley. Sometimes, the surface of the glacier forms cracks known as Crevasses. Crevasses are the deep fissure of variable width in the surface of a glacier. These crevasses are dangerous to the Mountaineers.

The glacier performs three actions namely erosion, transportation and deposition.

A glacier erodes its bedrock by the action of (1) Plucking and (2) Abrasion. A glacier during its lifetime creates various landforms which may be classified into erosional and depositional landforms.

The landforms created by glaciers are mainly found in the mountainous regions/ The Erosional landforms of Glaciers are 1. U-Shaped Valley, 2. Hanging Valley, 3. Cirque and Tarn, 4. Aretes, 5. Horn, 6. Nunataks and 7. Fjord.

A Cirque or Corrie is an amphitheatre shaped hollow basin cut into a mountain ridge. It has a steep-sided slope on three sides, an open end on one side and a flat bottom. When the ice melts, the Cirque may develop into a Tarn Lake and the whole thing appears like a big armchair.

Aretes is a steep-sided, sharp-tipped saw-toothed ridges which have undergone glacial erosion from two sides. These comb-like ridges are called as arete.

The fjord is formed as a steep-sided narrow entrance like feature at the coast of a glaciated region where the stream meets the coast. Fjords are common in Norway, Greenland and New Zealand.

A rock mass surrounded by ice is called Nunatak. It stands out as an island in the ice.

If the summit of the Arete is roughly inclined, it gives rise to pyramidal peaks which are known as horns. Example, Matterhorn of Alps-Switzerland.

U-Shaped Valley is a typical glacial feature. Since glacial mass is heavy and slow moving, erosional activity is uniform in all directions. A steep-sided curved bottom valley has a U-shaped profile.

When the glaciers melt or recede, they deposit the rock material, brought by them, forming hillocks of various shapes and sizes. The depositional landforms of the glaciers are; 1. Moraines, 2. Outwash Plain, 3. Esker, 4. Drumlins and 5. Kames.

Drumlins is an inverted boat-shaped deposition in an outwash plain caused by deposition.

Kames are the number of ridges formed along the ice front.

Moraines are the piles of dirt and rock that are deposited by a glacier as it moves across the landscape. These debris fields exist in places where glaciers have moved through in the past. There are many kinds of glacial moraines that form.

Moraines are generally classified based on their location. They are 1. Lateral Moraines, 2. Ground Moraines, 3. Medial Moraines, 4. Terminal or End Moraines and 5. Recessional Moraines.

Lateral moraines are ridges of debris that run parallel to the sides of a glacier. This is often accompanied by scraping of the valley sides which means the debris from the moraine creates high ridges above the glacier.

The recessional moraine runs across the landscape behind a terminal moraine. They are caused by times when the glacier slows or stops in its movement. It is formed because the receding glacier pauses in certain places for a long time before continuing its movement.

Ground moraines are glacial depositions formed on the floor of glacial valley. Ground moraines can be deposited in between lateral moraines in the case of many alpine glaciers.

When the glacier reaches its lowest point and melts, it leaves behind a layered deposition of rock debris, clay, sand, gravel, etc. This layered surface is called as an Outwash Plain.

Esker is a winding ridge of depositions of rock, gravel, clay, etc, running along a glacier in an outwash plain. The Eskers resemble the feature of an embankment and are often used for laying roads.

Any limestone, dolomite or gypsum region showing typical landforms produced by the action of groundwater through the process of solution and deposition is called as Karst Topography (Karst region in the Balkans).

The word “karst” literally means “rocky mountain” comes from a region in former Yugoslavia that includes Croatia and Slovenia. The word is derived from the Slavic word Kras.

The erosional landforms formed due to the action of groundwater are 1. Sinkholes, 2. Doline, 3. Lappies, 4. Uvala, 5. Polje and 6. Caves.

Lappies are the irregular grooves and ridges formed when most of the surfaces of limestone are removed by solution process.

A doline is a closed depression draining underground in karst areas. It can be cylindrical, conical, bowl or dish shaped. The diameter ranges from a few meters to many hundreds of meters. The name doline comes from dolina, the Slovenian word meaning valley.

A sinkhole is an opening more or less circular at the top and funnel-shaped towards the bottom. When as sinkhole is formed solely through the process of solution, it is called as a solution sink.

Polje is an elongated basin having a flat floor and steep walls. It is formed by the coalescence of several sinkholes. The basins often cover 250 square km and may expose “disappearing streams.” Most of these basins have steep enclosing walls that range from 50 to 100 meter in height, giving rise to the name “blind valley.”

Series of smaller sinkholes coalesce into a compound sinkhole is called uvala.

Caves normally have an opening through which cave streams are discharged. Caves having an opening at both the ends are called tunnels.

The Depositional Landforms due to Ground water are formed within caves. They are 1. Curtains, 2. Stalactite, 3. Stalagmite and 4. Pillars.

Deposition of calcite forming icicles growing upward from the cave floor is called as stalagmite.

Rain water drips from long crack in a cave roof forms a continuous strip of calcites. It is called as curtains.

Drops of water containing dissolved limestone seep down through cracks in the cave roof. Drops of water lose carbon dioxide and deposit calcite. Overtime deposition of calcite forms pillars hanging down from the roof of the cave. It is called as stalactite and where the stalactite stretches towards the sides are known as Helactites.

The wind is the main geomorphic agent in the arid region. Wind in arid region has greater speed which causes erosional and depositional activities in the desert. The landforms which are created by erosional and depositional activities of wind are called as Aeolian Landforms.

The action of the wind is carried in the following ways; 1. Deflation, 2. Abrasion and 3. Attrition.

Removal of sand and dust particles by wind. It forms depression in the desert. When depression is filled with water, it is called as Oasis.

Sand particles carried by the wind striking each other is known as attrition.

Action of wind in which sand particles carried by the wind strike against the rock is known as Abrasion.

The Erosional Landforms of Wind are 1. Deflation Hollows, 2. Mushroom Rock, 3. Yardang and 4. Zeugen.

Zeugen is a landscape of alternate horizontal ridges and furrows made by the action of wind abrasion. It may be as high as 30 m height.

When deflation causes a shallow depression by persistent movements of wind, they are called as deflation hollows.

A mushroom rock, also called rock pedestal, or a pedestal rock, is a naturally occurring rock whose shape, as its name implies, resembles a mushroom. In deserts, a greater amount of sand and rock particles are transported close to the ground by the winds which cause more erosion in the lower part of the rock than the top. These result in the formation of rock pillars shaped like a mushroom with narrow pillars with broad top surfaces.

Yardangs are extensively grooved, fluted, pitted and irregular rock ridges or reliefs of about 1 to 10 meters high running parallel to the prevailing winds. They are caused by differential erosion. When the sand-laden wind corrades zones of softer or weaker rock between harder vertical ridges from old lake sediment where soft, consolidated rock and bedrock surfaces are eroded into alternating ridges and furrows.

Large-scale yardangs are found in Egypt (near Kom Ombo, north of Lake Aswan).

The Depositional Landforms of Wind are 1. Sand dunes, 2. Loess and 3. Pediplains.

When the high relief structures in deserts are reduced to low featureless plains by the activities of wind, they are called as Pediplains.

In several large areas of the world, the surface is covered by deposits of wind transported silt that has settled out from dust storms over many thousands of years. These depositions are called as Loess.

Dry hot deserts are good places for sand dune formation. According to the shape of a sand dune, there are varieties of sand dune forms like Barchans, Seif dune, etc. The barchan is one of the classic desert landforms. It is a crescent-shaped dune with the horns of the crescent stretching out in the leeward direction. Barchan dunes may reach more than 27 meter in height.

Seif dunes are long ridges of sand. In general, they are aligned in the direction of the prevailing wind. The slip face of seif dunes are probably formed by eddies. The depressions between seif dune ridges are swept clear of sand by the winds. The ridges run for long distances, sometimes several kilometres.

Horizontal movement of sea water caused by the wind, rotation of the earth, etc., are called waves.

Waves carry out the erosive work in the following ways. They are 1. Abrasion, 2. Hydraulic action, 3. Corrosion and 4. Attrition.

The waves striking against the coast with eroded materials is called abrasion.

Abrasion is also called as the corrasion.

The action of dissolving soluble rocks by waves is termed as the corrosion or solution.

Eroded materials like boulders and rocks knock together to wear out into smaller particles. This is called attrition.

Sea shore is the zone of land between high tide and low tide.

Foreshore is the portion of the beach subject to wave action during non-storm conditions.

Offshore is the shallow zone of the continental shelf.

Backshore is the beach zone starting from the limit of frequent storm waves to the cliff base.

Coastline is the boundary where the land meets the sea. Swash is the waves washing up the beach. Shore line is boundary between land and water.

Erosional landforms dominate rocky coasts but are also found in association with predominantly depositional landforms. Landforms by the Erosion of Waves are 1. Sea cliff, 2. Wave Cut Platform, 3. A sea cave, 4. A blowhole, 5. Arch, 6. The stack and 7. Stump.

Rock cut flat surfaces in front of a cliff are called wave-cut platform. They are slightly concave upward. It is also formed when blowhole is collapsed.

The steep rocky coast rising almost vertically above seawater is called sea cliff.

A sea cave is a hollow excavated by waves in a zone of weakness on a cliff. The cave depth is greater than the entrance width. Sea caves usually form at points of geological weakness, such as bedding planes, joints, and faults. A 90-meter-long sea cave is found in the Loliem beach in Canacona in Goa.

The world’s most extensive cave is 1.5 km long Matainaka cave in New Zealand.

A blowhole may form in the roof of a sea cave by the hydraulic and pneumatic action of waves, with fountains of spray emerging from the top. If blowholes become enlarged, they may collapse.

The stack is a steep and often vertical column of rock in the sea near a coast, formed by wave erosion.

The stack is formed when the natural arch is collapsed. It is also called chimney rock, needles, columns, pillars, skerries, etc. Stump is the worn-out stack.

Arch is formed when the sea cave is cut right through by wave action. The arch is termed as sea tunnel if it is comparatively longer.

Depositional landforms developed by the sea waves include the beach, bar, lagoon, spit, tombolo, barrier island, etc.

Beach is an elongated stretch of sands, pebbles, gravels, etc deposited along the coast. It can be a sandy beach or pebble beach. Praia da Cassino beach in Brazil is the world’s longest beach stretching for 200 km from the Rio Grande to the border with Uruguay.

Marina beach, Chennai is the second longest beach in the world.

The Bar is a stretch of sand deposition off the shoreline. The larger form of a bar is called barrier.

The Lagoon is enclosed seawater between the bar and the coast. For example, Pulicat lake, located in the Tamil Nadu and Andhra Pradesh is a lagoon.

A Tombolo is a bar connecting an island with the coast.

Spit is a long, narrow ridge of sand or pebble with one end connected to the coast and the other end running into the sea. For example, Rameshwaram, Tamil Nadu.

The Canyon of Gandikota is situated on the Penna River is known as the Grand Canyon of India.

Gandikota, Kadapa district of Andhra Pradesh is known for its spectacular gorge formed by river Pennar that cuts through the Erramala hills. This handsome piece of Nature’s architecture is known as the Hidden Grand Canyon of India. Magnificent Gandikota fort is located majestically on top of this gorge.

Belum Cave found in Andhra Pradesh is the second largest cave system in India. In fact, geologists have also found surplus deposits of Quartz in the stalactite and stalagmite formations of the cave. Adjacent to Gandikota fort, lies a magnificent lake that is believed to have been established by emperor Sri Krishnadevaraya using water from the Pennar river.