Lithosphere Ii Exogenetic Processes
Class 9 | Social Science — Geography | Unit 2
Class 9 Unit 2 Geography
Unit 2 Lithosphere – 2 Exogenetic Processes
Learning Objectives
To comprehend the various external processes of the Earth
To study the different types of weathering and the resultant features
To learn how the weathered materials are transported by different agents.
To study about the features formed by erosion transportation and deposition of natural agents
Introduction
The Earth is a dynamic system that undergoes various changes due to internal and external processes. The continuous interaction of these two processes controls the structure of the earth's surface. The external processes are the consequence of solar energy and gravitational forces, whereas the internal processes are an outcome of the earth's internal heat.
2.1 Weathering
Weathering is the breaking, disintegration and decomposition of materials of the earth's crust by their exposure to atmosphere. There are three types of weathering Physical weathering, Chemical weathering and Biological weathering
Physical weathering
It is the breakdown of rocks without changing their chemical composition, through the action of physicalforces. The constant freezing and thawing of rocks during the night and day leads to the expansion and contraction of rocks. Cracks are formed and disintegration occurs eventually. Exfoliation, block disintegration, granular disintegration, are the Major types of physical weathering.
Exfoliation
The alternate heating and cooling on rounded rock surfaces leads to the peeling of rocks, layer by layer like an onion. This is called exfoliation. sheeting and shattering are the other forms of exfoliation.
Granular Disintegration:
Granular disintegration takes place in crystalline rocks where the grains of the rocks become loose and fall out. This is due to the action of temperature.
Block Disintegration:
Repeated expansion and contraction of rocks during day and night respectively causes stress on the joints of the rocks which results in block disintegration
HOTS
Is weathering a pre-requisite in the formation of soil?
Facts
The disintegrated rock materials, in due course of time, are weathered further, to form soil. Soil is a mixture of disintegrated rock material and decayed organic matter called humus.
Chemical Weathering
Disintegration and decomposition of rocks due to chemical reactions is called Chemical Weathering. This is predominantly high in the hot and humid regions such as the equatorial, tropical and sub tropical zones. Chemical weathering takes place through the processes of oxidation, carbonation, solution, and hydration. The agents of Chemical weathering are Oxygen, Carbon-dioxide, Hydrogen and water.
Oxidation
Oxygen in the atmosphere reacts with the iron found in rocks, thus leads to the formation of iron oxide.This process similar to the rusting of iron, pressure of air and water is known as oxidation, which results in the weakening of rocks.
Carbonation
Carbonation is the mixing of water with the atmospheric carbon-dioxide, forming carbonic acid. Carbonation is important in the formation of caves, in limestone region. When the carbonic acid reacts with the carbonate rocks, the rocks get disintegrated.
Solution
The dissolution of rock substances in water result in the loosening of the rock particles. This inturn breaks down the rocks.
Hydration
Absorption of water into the mineral structure, certain chemicals in the rock enlarge in size in humid conditions. These minerals found in the rock swell and this results in the development of cracks and the rock wears down. This type of weathering is called hydration.
Biological Weathering
Biological weathering occurs due to the penetration and expansion of plant roots, earthworms, burrowing animals (rabbits, rats) and some human activities.
2.2 Gradation
Gradation is the process of levelling of the land by means of natural agents like rivers, ground water, winds, glaciers, and sea waves. These agents produce various gradational relief features in due course of time. Gradation takes place in two ways: degradation and aggradation
Gradation is the levelling land surface by various natural agents. Aggradation is building up of landforms due to natural agents. Degradation is eroding of land surface
Agents of Gradation
Running water (River) -(Fluvial Land forms)
The work of running water (rivers) is the most extensive among all the other agents of gradation. Rivers originate on higher landforms like, mountains, hills and plateaus that receive water from various sources like the rain, glaciers, springs, lakes, etc. The place where the river originates is called catchment area and where it joins the sea is known as mouth.
Courses of River:
Rivers generally originate from mountains and end in a sea or lake. The whole path that a river flows through is called its course. The course of a river is divided into: 1. The upper course (2). The middle course and (3). The lower course
1. The Upper Course Erosion is the most dominant action of river in the upper course. In this course, a river usually tumbles down the steep mountain slopes. The steep gradient increases the velocity and the river channel performs erosion with great force to widen and deepen its valley. The land features carved by a river in its upper course are V-shaped valleys, gorges, canyons, rapids, pot holes, spurs, and waterfalls.
(2). The Middle Course The river enters the plain in its middle course. The volume of water increases with the confluence of many tributaries and thus increases the load of the river. Thus, the predominant action of a river is transportation. Deposition also occurs due to the sudden decrease in velocity. The river in the middle course develops some typical landforms like flood plains, meanders, ox-bow lakes etc.,
(3). The Lower course The river, moving downstream across a broad, level plain is loaded with debris, brought down from its upper and middle courses. Large deposits of sediments are found at the level bed and the river, splits into a number of channels called distributaries. The main work of the river here is deposition and it develops typical landforms like delta and estuary.
Tributary – Small streams that join the main river. Example River Bhavani
Distributary – River channels that get separated from the main river. Example River Kollidam.
Erosional Landforms of River
Gorges and Canyons: When the river flows through a mountainous region made up of hard rocks, it forms a valley with almost vertical sides called gorge. In India, deep gorges have been formed by Brahmaputra and Indus in the Himalayas. A deep gorge with steep sides that runs for hundreds of kilometres is referred to as canyon Example Grand Canyon of the river Colorado in the U.S.A.
Waterfall When a river flows in a region where hard rocks lie over soft rocks horizontally, the soft rocks get eroded quickly and the hard rocks projects outwards. Thus, the river falls vertically from a steep slope to form a waterfall. When the water falls with great force, it erodes the rock material beneath and creates a depression called a plunge pool. Shallow fast flowing water in a stream is called a rapid or river jumps The highest waterfalls in the world is Angel falls (979 meter) in Venezuela. Rapid
V-shaped valley A 'V'- shaped valley is formed by the vertical erosion of the river where the valley is deepened and widened.
Pot hole Due to the river action, cylindrical holes are drilled vertically in the river bed, with varying depth and diametre. These are called pot holes.
Meander As the river loaded with debris flows slowly, it forms sweeping loops and bends. It is referred to as meanders.
Ox bow lake Meanders in due course of time become almost a complete circle with narrow necks. This in turn gets abandoned and forms a lake. This is called an Ox-bow lake. The world's largest oxbow lake is Lake Chicot is Arkansas of USA. Lake Kanwar in Bihar (India) is Asia's largest fresh water ox bow lake.
Depositional Landforms of River
Alluvial Fan
A fan shaped deposition made by the river at the foothills is called an alluvial plain
Flood Plain
Fine sediments are deposited on river banks when a river floods. These sediments make the region rich and fertile. This is called a flood plain. As the height of the river banks gets increases due to continuous deposition of a flooded river, levees are formed.
Estuary:
Estuary is formed where the rives meets the sea. Deposition of silt by the river is not possible here in the estuaries like delta as if the waves keep on eroding the deposits. Ex. River Narmada and Tapti.
Delta
A triangular shaped low lying area formed by the river at its mouth is called delta. Deltas have fine deposits of sediments enriched with minerals. Example Cauvery Delta, Tamil Nadu.
Facts
The Greek letter (Triangle shape pronounced delta closely resembles the triangular delta of the river Nile. Sunderban Delta formed by the river Ganga-Brahmaputra is the largest delta in the world. The world's best known geyser is the Old Faithful geyser in the Yellowstone National Park in Wyoming, U.S.A
Karst Topography
As an agent of gradation, underground water creates distinct landforms in limestone regions called Karst Topography. Ground water is an active agent in limestone regions. Karst topography is formed due to the dissolution of soluble rocks such as limestone, dolomite and gypsum. Limestone topography of Western Slovenia extends for a distance of 480 km in length and 80 km in width which is termed as Karst in the Slavic language. The world's largest karst area is the Nullarbar located on the Great Australian Coast. Karst regions are also found in Southern France, Spain, Mexico, Jamaica, Western Cuba, Central New Guinea, Sri Lanka and Myanmar.
Karst Areas in India
Western Bihar - Guptadham caves
Uttarakhand - Robert cave and Tapkeshwar temple
Madhya Pradesh - Pandav caves Pachmari hills
Bastar district in Chattisgarh - Kutumsar
Andhra Pradesh (Visakhapatnam) - Borra caves
Erosional Landforms of Underground Water
Most of erosion takes place due to the process of solution. When rain water mixes with carbon-di- oxide and enters into a limestone region, it dissolves and destroys much of the limestone. As a result, landforms such as Terra rossa, Lappies, sinkholes, swallow holes, dolines, uvalas, poljes, caves and caverns are formed.
Terra Rossa (Italian term for Red soil)
Deposition of red clay soil on the surface of the Earth is due to the dissolution of limestone content in rocks. The redness of the soil is due to the presence of iron oxide.
Lappies
When the joints of limestone rocks are corrugated by groundwater, long furrows are formed and these are called LAPPIES.
Sinkhole
A funnel shaped depressions formed due to dissolution of limestone rock is called sinkholes. Their average depth ranges between three and nine meters
Do You Know?
The World's deepest sinkhole is China's xianozhai Tienkang at 2172 feet. There are as many as 15000 Sinkholes in Illinois
Activity
Take a trough filled with sand. empty a portion of sand in the middle and fill it with sugar. Now level the sand over the sugar. Pour water into the trough and observe what happens. The sugar dissolves and forms a depression. This is similar to the formation of sinkhole.
Caves and Caverns
Caves and caverns are subterranean features of karst topography. Caves are hollows that are formed by the dissolution of limestone rocks when carbon di oxide in air turns into carbonic acid after its reaction with water. They vary in size and shape. Caverns are the caves with irregular floors. Example Guptadham caves in Western Bihar. All types of deposits in the caves and caverns are collectively called speleothems which includes travertines, tufa, dripstones. Swallow Holes, Uvalas, Dolines, Poljis are other erossional Features of karst regions predominant in other parts of the world.
Facts
Cave insects lose their senses of sight and develop extraordinary long antenna to compensate the loss of sight.
Depositional Landforms of Underground Water
It is interesting to know that a variety of depositional features are formed on the floor, ceiling and walls of the caves and caverns of the Karst Topography.
Stalactite, Stalagmite and Column
When the water containing dissolved calcite gradually drips from the ceiling of the caves, water evaporates and the remaining calcite hangs from the ceiling. Thus Stalactites are formed. When the calcite deposits rises upward like a pillar Stalagmites are formed. Sometimes, Stalactites and Stalagmites meet together to form Columns or Pillars.
Glaciers:
A Glacier is a large mass of ice that moves slowly over the land, from its place of accumulation. It is also known as 'River of ice'. The place of accumulation is called snowfield. The height above which there is a permanent snow cover in the higher altitude or latitude is called snowline. Higher the latitude, lower the snowline from sea level.
HOTS
Snowline of Alps is 2700 metre where as the snowline of Greenland is just 600 metre. Find out the reason.
Activity Fake Snow
Materials needed:-Cup of Baking Soda, Shaving Cream
Method - Pour one cup of baking soda, Spray the shaving cream The snow will start forming almost immediately
The gradual transformation of snow into granular ice is called 'firn' or ' neve' and finally it becomes solid glacial ice.
Erosional Landforms of Glacier
Glaciers are powerful erosive agents. Some of the important erosional landforms are Cirque, Aretes, Matterhorn, U-shaped valley, Hanging valley, Fiords etc., Most of these glacial features are predominantly seen in countries like Switzerland, Norway etc.,
Cirque
The glacier erodes the steep side walls of the mountain and forms a bowl-shaped armchair like depression, it is termed as Cirque.
Arete
Aretes are narrow ridges formed when two cirque walls joined together back to back, and forms narrow knife like ridges.
Pyramidal Peak
The pyramidal peaks formed when three or more cirques meet together (eg) Matterhorns.
U-Shaped Valley
When the glacier moves down along a river valley, the valley further gets eroded deep and wide to form a 'U' shaped valley.
Hanging Valley
These are valleys eroded by tributary glacier and that hangs over the main valley.
Fjord
Fjords are glacial valleys that are partly submerged in the sea.
Depositional Landforms of glacier
After getting eroded, fragments of rocks and boulders along with dirt form glacial debris. Glacial debris gets deposited in the low lying areas and form depositional features like moraines, drumlins, eskers, kames and outwash plains.
Moraine
1. Materials deposited by Glaciers is called Moraines.
2. Based on the location, they are classified into Ground moraine, Terminal moraine and Lateral moraine.
Drumlin (Basket of Egg Topography)
Drumlins are deposits of glacial moraines that resemble giant inverted teaspoons or half cut eggs.
Esker
Long narrow ridges composed of boulders gravel and sand deposited by streams of melting water which run parallel to a glacier are called eskers.
Outwash Plain
An outwash plain consists of glacial sediments deposited by the melting ice at the terminus of a glacier. It appears as an extensive accumulation of sand, gravel and silt.
Activity
Discuss in a small groups about the effects of global warming.
Wind
When air blows horizontally at or near the earth's surface is called wind. The erosional, transportational and depositional action of wind is predominant in arid regions. This is called as Aeolian Process.
Erosional Landforms of wind
Some of the erosional landforms of wind are mushroom rocks, Inselbergs and yardangs.
Mushroom Rock
Rocks are made up of hard and soft layers. When a rock's bottom is soft, the sand-laden winds blow against it and wear it down. By the constant wearing down action of the wind, the bottom gets eroded away to form a mushroom like structure. This is called a mushroom or pedestal rock. Such rocks are found near Jodhpur in Rajasthan.
Inselberg
Inselberg is a German term which means an island mountain. Certain hard rocks like igneous rocks are more resistant to wind action. Such isolated residual hills rising abruptly from their surroundings are termed as inselbergs. Example Uluru or Ayers Rock, Australia.
Yardang
In arid regions, certain rocks have hard and soft layers arranged vertically. When winds blow over these rocks, the soft layers get eroded leaving irregular crests. These are called yardangs.
Depositional Landforms of wind
Some of the depositional landforms are sand dunes, barchans and loess.
Sand Dune
In deserts, during sandstorms, wind carries loads of sand. When the speed of wind decreases, huge amount of sand gets deposited. These mounds or hills of sand are called sand dunes. There are different types of sand dunes.
Barchan
Barchan are isolated, crescent shaped sand dunes. They have gentle slopes on the windward side and steep slopes on the leeward side.
Transverse Dunes
Transverse dunes are asymmetrical in shape. They are formed by alternate slow and fast winds that blow from the same direction.
Longitudinal Dunes (Seif dunes)
Longitudinal dunes are long narrow ridges of sand, which extend in a direction parallel to the prevailing winds. These dunes are called Seifs in Sahara
Loess
The term loess refers to the deposits of fine silt and porous sand over a vast region. Extensive loess deposits are found in Northern and Western China, the Pampas of Argentina, in Ukraine and in the Mississippi Valley of the United States.
Do you know?
The thickest known deposit of loess is, 335 metre found in the loess plateau in China.
Wave
A steady up (crest) and down (trough) movement of surface water are called waves. Sea waves are the most powerful agents of gradation and their erosional, transportational and depositional processes are confined to a very narrow belt along coastal areas.
Erosional Land Forms of Waves
Some of the erosional landforms of sea waves are sea cliff, sea cave, arch, stack, beach, bar and spit and wave cut platform.
1. Sea Cliffs Sea cliffs are steep rock faces formed when sea waves dash against them. The rocks get eroded to form steep vertical walls.
2. Sea Cave Prolonged wave attack on the base of a cliff erodes rock materials, which result in the formation of caves.
3. Sea Arch When two caves approach one another from either side of a headland and unite, they form an arch. Example Neil Island, Andaman and Nicobar.
4. Sea Stack Further erosion by waves ultimately leads to the total collapse of the arch. The seaward portion of the headland will remain as a pillar of rock known as stack. Example the Old man of Hoy in Scotland.
5. Wave Cut Platforms Flat surface found at the foot of sea cliffs are called as wave cut platforms. Wave cut platform is also referred as wave cut benches terrace.
Depositional Landforms of Waves
Beach
Sand and gravel are moved and deposited by waves along the shore to form beaches. This is the most dominant and constructive work of the sea. Example Juhu beach along Mumbai coast, Puri beach in Odisha and Marina beach in Chennai.
Bar
A bar is an elongated deposit of sand, shingle or mud found in the sea, almost parallel to the shoreline.
Spit
A spit is a ridge or embankment of sediment, attached to the land on one end and terminating in open water on the other end. Spits are common at the mouth of estuaries. Example Kakinada spit
Recap
Levelling of uneven landform is called gradation. Weathering is the breaking down of the rocks. Physical, chemical and biological are the three types of weathering. Running water, glacier, underground water, wind and waves are agents of weathering. Soil is the weathered materials covering the earth's surface insitu.
Exercise
Exercise 1. Choose the best answer:
1. The disintegration or decomposition of rocks is generally called as
a. weathering b. erosion c. transportation d. deposition
2. The process of the levelling up of land by means of natural agents.
a. aggradation b. degradation c. gradation d. none
3. DASH is seen in the lower course of the river.
a. Rapids b. Alluvial fan c. Delta d. Gorges
4. Karst topography is formed due to the action of
a. Glacier b. Wind c. Sea waves d. Ground water
5. Which one of the following is not a depositional feature of a glacier?
a. cirque b. Moraines c. Drumlins d. Eskers
6. Deposits of fine silt blown by wind is called as
a. Loess b. Barchans c. Hamada d. Ripples
7. Stacks are formed by DASH
a. Wave erosion b. River erosion c. Glacial erosion d. Wind deposion
8. DASH erosion is responsible for the formation of cirque.
a. wind b. glacial c. river d. underground water Exercise (2). Match the following:
| 1. Distributaries | |
| 2. Mushroom rock | |
| 3. Eskers | |
| 4. Stalactites | |
| 5. Cliff | |
Options: glacial action, action of sea wave, Lower course of river, Aeolian process, karst topography
Exercise (3). Consider the given statements and choose the right option given below
1. (1). 'I' Shaped valley is an erosional feature of the river. (2). 'U' Shaped valley is an erosional feature of the glacier. (3). 'V' Shaped valley is an erosional feature of the glacier.
a. 1, 2 & 3 are correct b. 1 & 2 are correct c. 1 & 3 are correct d. only 1 is correct
2. Statement 1: Running water is an important agent of gradation Statement 2: The work of the river depends on the slope of land on which it flows
a. Statement 1 is false and 2 is true b. Statement 1 and 2 are false c. Statement 1 is true and 2 is false d. Statement 1 and 2 are true
3. Statement: Limestone regions have less underground water. Reason: Water does not percolate through limestone
a. The statement is right reason is wrong b. The statement is wrong reason is right c. The statement and reason are wrong d. The statement and reason are right Exercise (4). Answer in brief:
1. Define weathering.
2. What do you mean by biological weathering?
3. Mention the three courses of a river with any two land forms associated to each course.
4. What are ox-bow lakes?
5. How does a sea cave differ from a sea arch?
6. List out any four karst topographical areas found in India.
7. What do you mean by a hanging valley?
8. Define: a) Moraine b) Drumlin c) Esker.
9. Mention the various features formed by wind erosion.
10. What is a wave cut platform?
Exercise (5). Give Reasons:
1. Chemical weathering is predominant in hot and humid zones.
2. Silt deposits are less at estuaries than deltas.
3. Wind can possibly erode the rocks from all sides.
Exercise (6). Distinguish between:
1. Physical and chemical weathering.
2. Delta and Estuary
3. Stalactite and stalagmite.
4. Longitudinal and Transverse sand dunes.
5. Inselbergs and yardangs
6. Spit and bar.
Exercise (7). Answer in Paragraph:
1. Write a note on weathering classify and explain.
2. Explain the erosional landforms formed by underground water.
3. What is a glacier? Explain its types.
4. Describe the depositional work of winds.
Exercise (8). Map Skill:
On the given outline map of the world, mark the following.
1. Any two deltas
2. A Karst region
3. Any two hot and cold deserts
Exercise 9. HOTS
1. Is wind the only gradational agent in the desert?
2. Underground water is more common in limestone areas than surface run off. Why?
3. The river channels in the lower course are wider than the upper course.
Exercise 10. Give geographical terms for the following:
a. Chemical alternation of carbonate rocks on lime stone region.
b. Flat surfaces near cliffs.
c. Erosion PLUS Transportation = Deposition
d. The bottom line of a snow field.
INTERNET RESOURCES
1. www.usgs.gov.in
2. www.nasa.gov.in
3. https://www.isro.gov.in
4. https://www.india.gov.in
ICT Corner
Karst Topography
Steps
Use the URL to reach 'Karst Topography' page.
Allow flash player to play, if it asks.
Click 'Next' button in the bottom of the page to proceed to the next page and explore the animation.
Select 'Dissolution' option from the left and explore.
Use the arrow keys to move forward and backward to the animation.
Website URL: http://folk.uio.no/hanakrem/svalex/E-learning/Karst/
Book-back Exercises — Questions & Answers
Answers generated strictly from the Samacheer Kalvi textbook content. Attempt each question first, then click "Show Answer" to check.
I. Choose the Correct Answer
1. The disintegration or decomposition of rocks is generally called as
a) weathering b) erosion c) transportation d) deposition
Answer: a) weathering
Explanation: Weathering is the breaking, disintegration and decomposition of materials of the earth's crust by their exposure to atmosphere.
2. The process of the levelling up of land by means of natural agents.
a) aggradation b) degradation c) gradation d) none
Answer: c) gradation
Explanation: Gradation is the process of levelling of the land by means of natural agents like rivers, ground water, winds, glaciers, and sea waves.
3. _____ is seen in the lower course of the river.
a) Rapids b) Alluvial fan c) Delta d) Gorges
Answer: c) Delta
Explanation: In the lower course, the main work of the river is deposition and it develops typical landforms like delta and estuary.
4. Karst topography is formed due to the action of
a) Glacier b) Wind c) Sea waves d) Ground water
Answer: d) Ground water
Explanation: As an agent of gradation, underground water creates distinct landforms in limestone regions called Karst Topography.
5. Which one of the following is not a depositional feature of a glacier?
a) cirque b) Moraines c) Drumlins d) Eskers
Answer: a) cirque
Explanation: Cirque is an erosional landform where the glacier erodes the steep side walls of the mountain and forms a bowl-shaped armchair like depression.
6. Deposits of fine silt blown by wind is called as
a) Loess b) Barchans c) Hamada d) Ripples
Answer: a) Loess
Explanation: The term loess refers to the deposits of fine silt and porous sand over a vast region.
7. Stacks are formed by _____
a) Wave erosion b) River erosion c) Glacial erosion d) Wind deposition
Answer: a) Wave erosion
Explanation: Further erosion by waves ultimately leads to the total collapse of the arch. The seaward portion of the headland will remain as a pillar of rock known as stack.
8. _____ erosion is responsible for the formation of cirque.
a) wind b) glacial c) river d) underground water
Answer: b) glacial
Explanation: The glacier erodes the steep side walls of the mountain and forms a bowl-shaped armchair like depression, it is termed as Cirque.
II. Match the Following
1. Match the Following
| 1. Distributaries | a) glacial action |
| 2. Mushroom rock | b) action of sea wave |
| 3. Eskers | c) Lower course of river |
| 4. Stalactites | d) Aeolian process |
| 5. Cliff | e) karst topography |
Answers: 1-c, 2-d, 3-a, 4-e, 5-b
III. Consider the Given Statements
1. Consider the given statements and choose the right option given below (1). 'I' Shaped valley is an erosional feature of the river. (2). 'U' Shaped valley is an erosional feature of the glacier. (3). 'V' Shaped valley is an erosional feature of the glacier.
a) 1, 2 & 3 are correct b) 1 & 2 are correct c) 1 & 3 are correct d) only 1 is correct
Answer: b) 1 & 2 are correct
Explanation: V-shaped valley is formed by vertical erosion of the river, U-shaped valley is formed when the glacier moves down along a river valley.
2. Statement 1: Running water is an important agent of gradation Statement 2: The work of the river depends on the slope of land on which it flows
a) Statement 1 is false and 2 is true b) Statement 1 and 2 are false c) Statement 1 is true and 2 is false d) Statement 1 and 2 are true
Answer: d) Statement 1 and 2 are true
Explanation: The work of running water (rivers) is the most extensive among all the other agents of gradation. The steep gradient increases the velocity and the river channel performs erosion with great force.
3. Statement: Limestone regions have less underground water. Reason: Water does not percolate through limestone
a) The statement is right reason is wrong b) The statement is wrong reason is right c) The statement and reason are wrong d) The statement and reason are right
Answer: c) The statement and reason are wrong
Explanation: Ground water is an active agent in limestone regions. When rain water mixes with carbon-di-oxide and enters into a limestone region, it dissolves and destroys much of the limestone.
IV. Answer Briefly
1. Define weathering.
Answer: Weathering is the breaking, disintegration and decomposition of materials of the earth's crust by their exposure to atmosphere.
2. What do you mean by biological weathering?
Answer: Biological weathering occurs due to the penetration and expansion of plant roots, earthworms, burrowing animals (rabbits, rats) and some human activities.
3. Mention the three courses of a river with any two land forms associated to each course.
Answer: The three courses are: (1) Upper course - V-shaped valleys, gorges, canyons, waterfalls (2) Middle course - flood plains, meanders, ox-bow lakes (3) Lower course - delta and estuary.
4. What are ox-bow lakes?
Answer: Meanders in due course of time become almost a complete circle with narrow necks. This in turn gets abandoned and forms a lake. This is called an Ox-bow lake.
5. How does a sea cave differ from a sea arch?
Answer: Sea cave is formed by prolonged wave attack on the base of a cliff which erodes rock materials. Sea arch is formed when two caves approach one another from either side of a headland and unite.
6. List out any four karst topographical areas found in India.
Answer: Western Bihar - Guptadham caves; Uttarakhand - Robert cave and Tapkeshwar temple; Madhya Pradesh - Pandav caves Pachmari hills; Bastar district in Chattisgarh - Kutumsar; Andhra Pradesh (Visakhapatnam) - Borra caves.
7. What do you mean by a hanging valley?
Answer: These are valleys eroded by tributary glacier and that hangs over the main valley.
8. Define: a) Moraine b) Drumlin c) Esker.
Answer: a) Moraine: Materials deposited by Glaciers is called Moraines. b) Drumlin: Drumlins are deposits of glacial moraines that resemble giant inverted teaspoons or half cut eggs. c) Esker: Long narrow ridges composed of boulders gravel and sand deposited by streams of melting water which run parallel to a glacier.
9. Mention the various features formed by wind erosion.
Answer: Some of the erosional landforms of wind are mushroom rocks, Inselbergs and yardangs.
10. What is a wave cut platform?
Answer: Flat surface found at the foot of sea cliffs are called as wave cut platforms. Wave cut platform is also referred as wave cut benches terrace.
V. Give Reasons
1. Chemical weathering is predominant in hot and humid zones.
Answer: Chemical weathering involves disintegration and decomposition of rocks due to chemical reactions. This is predominantly high in the hot and humid regions such as the equatorial, tropical and sub tropical zones because high temperature and moisture accelerate chemical reactions.
2. Silt deposits are less at estuaries than deltas.
Answer: Estuary is formed where the river meets the sea. Deposition of silt by the river is not possible here in the estuaries like delta as the waves keep on eroding the deposits.
3. Wind can possibly erode the rocks from all sides.
Answer: The erosional, transportational and depositional action of wind is predominant in arid regions. Wind can blow from different directions and carry sand particles that can erode rock surfaces from multiple angles, creating features like mushroom rocks and yardangs.
VI. Distinguish Between
1. Physical and chemical weathering.
Answer: Physical weathering is the breakdown of rocks without changing their chemical composition, through the action of physical forces. Chemical weathering involves disintegration and decomposition of rocks due to chemical reactions and is predominantly high in hot and humid regions.
2. Delta and Estuary
Answer: Delta is a triangular shaped low lying area formed by the river at its mouth with fine deposits of sediments enriched with minerals. Estuary is formed where the river meets the sea and deposition of silt is not possible as waves keep eroding the deposits.
3. Stalactite and stalagmite.
Answer: Stalactites are formed when water containing dissolved calcite gradually drips from the ceiling of caves, water evaporates and the remaining calcite hangs from the ceiling. Stalagmites are formed when the calcite deposits rises upward like a pillar from the floor.
4. Longitudinal and Transverse sand dunes.
Answer: Longitudinal dunes are long narrow ridges of sand, which extend in a direction parallel to the prevailing winds. Transverse dunes are asymmetrical in shape and are formed by alternate slow and fast winds that blow from the same direction.
5. Inselbergs and yardangs
Answer: Inselbergs are isolated residual hills rising abruptly from their surroundings formed by hard rocks like igneous rocks that are more resistant to wind action. Yardangs are formed when winds blow over rocks with hard and soft layers arranged vertically, the soft layers get eroded leaving irregular crests.
6. Spit and bar.
Answer: A spit is a ridge or embankment of sediment, attached to the land on one end and terminating in open water on the other end. A bar is an elongated deposit of sand, shingle or mud found in the sea, almost parallel to the shoreline.
VII. Answer in Paragraph
1. Write a note on weathering classify and explain.
Answer: Weathering is the breaking, disintegration and decomposition of materials of the earth's crust by their exposure to atmosphere. There are three types of weathering: Physical weathering is the breakdown of rocks without changing their chemical composition through physical forces. Chemical weathering involves disintegration and decomposition of rocks due to chemical reactions and is predominant in hot and humid regions. Biological weathering occurs due to the penetration and expansion of plant roots, earthworms, burrowing animals and human activities.
2. Explain the erosional landforms formed by underground water.
Answer: Most erosion takes place due to the process of solution in karst topography. When rain water mixes with carbon-di-oxide and enters limestone regions, it dissolves and destroys limestone creating various landforms. Terra rossa is red clay soil deposited due to dissolution of limestone. Lappies are long furrows formed when joints of limestone rocks are corrugated by groundwater. Sinkholes are funnel shaped depressions formed due to dissolution of limestone rock. Caves and caverns are subterranean features formed by dissolution of limestone rocks when carbon dioxide reacts with water to form carbonic acid.
3. What is a glacier? Explain its types.
Answer: A Glacier is a large mass of ice that moves slowly over the land, from its place of accumulation. It is also known as 'River of ice'. The place of accumulation is called snowfield. The height above which there is permanent snow cover in higher altitude or latitude is called snowline. The gradual transformation of snow into granular ice is called 'firn' or 'neve' and finally it becomes solid glacial ice. Glaciers are powerful erosive agents that create various erosional and depositional landforms in mountainous regions.
4. Describe the depositional work of winds.
Answer: Wind deposits various landforms in arid regions. Sand dunes are mounds or hills of sand formed when wind speed decreases and huge amounts of sand get deposited during sandstorms. Barchans are isolated, crescent shaped sand dunes with gentle slopes on windward side and steep slopes on leeward side. Transverse dunes are asymmetrical in shape formed by alternate slow and fast winds from same direction. Longitudinal dunes are long narrow ridges of sand extending parallel to prevailing winds. Loess refers to deposits of fine silt and porous sand over vast regions found in Northern China, Argentina, Ukraine and Mississippi Valley.
VIII. HOTS
1. Is wind the only gradational agent in the desert?
Answer: No, wind is not the only gradational agent in deserts. Though the erosional, transportational and depositional action of wind is predominant in arid regions, running water during occasional rainfall and underground water also act as agents of gradation in desert regions.
2. Underground water is more common in limestone areas than surface run off. Why?
Answer: Ground water is an active agent in limestone regions. When rain water mixes with carbon-di-oxide and enters into a limestone region, it easily percolates through the joints and cracks of limestone rocks and dissolves the limestone, creating underground channels and caverns, making underground water flow more common than surface runoff.
3. The river channels in the lower course are wider than the upper course.
Answer: In the upper course, erosion is the dominant action with steep gradients creating V-shaped valleys. In the lower course, the river moves across broad, level plains loaded with debris, and large deposits of sediments are found at the level bed. The river splits into distributaries and the main work is deposition, making the channels wider.
IX. Give Geographical Terms
1. Give geographical terms for the following: a. Chemical alternation of carbonate rocks on limestone region. b. Flat surfaces near cliffs. c. Erosion PLUS Transportation = Deposition d. The bottom line of a snow field.
Answer: a. Carbonation b. Wave cut platform c. Gradation d. Snowline
📝 Summary
- External processes on Earth are driven by solar energy and gravitational forces, constantly shaping the Earth's surface through weathering and gradation.
- Weathering breaks down rocks through three main types: physical weathering (without chemical change), chemical weathering (through reactions like oxidation and carbonation), and biological weathering (by plant roots and burrowing animals).
- Physical weathering includes exfoliation (layer-by-layer peeling), granular disintegration (loose grains falling out), and block disintegration (stress on rock joints from temperature changes).
- Chemical weathering is most active in hot and humid regions through processes of oxidation, carbonation, solution, and hydration, with agents including oxygen, carbon-dioxide, hydrogen and water.
- Gradation is the natural levelling process carried out by rivers, groundwater, winds, glaciers, and sea waves that transport weathered materials and create various landforms.