WBBSE Chapter 1 Exogenetic Processes And Resultant Land Forms Short Question And Answers
Question 1. What is the snowline?
Answer:
Exogenetic processes landforms. Snowline:
- Huge snowfall occurs in high altitudes as well as polar regions
- The imaginary line above which the snow never melts totally or below which the snow starts melting is called the snowline.
- Snowline marks the beginning of the permafrost region
- . In low or middle latitudes, the snowline may exist j at S000-6000 m altitude But in polar, regions, it lies at the sea level itself.
Question 2. Classify the glaciers
Answer:
Glaciers can be generally classified into two categories —
1. mountain or valley glaciers and
2. continental glaciers H W. Ahlmann further classified glaciers into 3 broad categories and 11 subtypes based on their thermal and morphological characteristics
The three broad categories are-
- Mountain or valley glaciers
- Continental glaciers,
- Piedmont glaciers
Question 3. What Is a glacial erratic?
Answer:
Glacial erratic:
In a glacial region, when big rocks are carried too far away distances along with the snow and are deposited there after the glacier melts, the rocks are known as glacial erratics. These rocks are found to have no similarity with the local rocks. Example—Glacial erratics are seen in the high mountainous regions of Pahelgaon in Kashmir.
Question 4. What is a glacier? Name the glaciers that are sources of the river Ganga and Yamuna.
Answer:
Glacier:
Aglacierisamassorriveroficemovingslowly under the impact of gravity. In high altitudes and polar regions, where heavy snowfall occurs, glaciers are formed due to the accumulation of snow above the snowline. The river Ganga rises from the Gangotri glacier and the river Yamuna rises from the Yamunotri glacier.
Question 5. What do you mean by ‘basket of eggs topography’?
Answer:
Basket of eggs topography:
When the rocks, pebbles, sand and clay brought down by the glacier get deposited on the lowland like inverted boats, the topography looks like a number of eggs spread over the land. These are known as drumlins and the topography is known as ‘basket of eggs topography’. Example-Such groups of drumlins are seen in Ireland and Scotland.
Question 6. What do you mean by ice sheet?
Answer:
Ice sheet:
Glaciers are classified into valley glaciers, piedmont glaciers and continental glaciers. Out of these, the continental glaciers are in fact extensive ice sheets. In the polar regions, vast areas are covered with thick layers of ice like a sheet or cover. Thus, the area known as a narrow wall between them is known as an arete. Aretes are sharpened peaks resembling the shape of saw teeth
WBBSE Chapter 1Exogenetic Processes Landforms.
Question 7. What are paternoster lakes?
Answer:
Paternoster lakes:
In high mountainous areas, the glacial valleys seem to develop a number of steps or stairs through the processes of abrasion or plucking. Further, several depressions or hollows are created on these steps or stairs due to glacial erosion. These depressions later get filled with water when the glacier melts. These are known as paternoster lakes.
Question 8. What are knobs and kettles?
Answer:
Knobs: The rocks and pebbles brought down by glacial erosion flow down along with the rivers and spread on the outwash plains. If these materials accumulate like small domes on the plainlands, they are called knobs. Kettles: The big chunks of ice that flow down with the glacier-melt rivers, spread on the outwash plains and create hollows or depressions. These are called kettles. The hollows get filled with water as the ice chunks melt, and thus form kettle lakes.
Example: ‘Knob and Kettle’ topography is seen in many regions in northern Europe.
Question 9. What is the speed of glaciers?
Answer:
Speed of glaciers:
The glaciers move very slowly. The speed of the glaciers depends upon the slope of the land, the volume of ice, seasonal variations, gravitational pull, etc. Example—The glaciers of the Alps mountains move at an average speed of 5.5 cm per day. The Himalayan glaciers move at a speed of 2.5 7.5cm per day.
Question 10. Why does the end of a glacier look like a tongue?
Answer:
In a valley glacier, the middle part of the body of ice moves forward faster as it experiences friction solely from the valley base. On the other hand, the sides of the glacier experience friction from the base as well as the valley walls. Thus, the rate of movement of glacial ice decreases from the centre towards the edge. This causes the end
of the glacier to look like a tongue. This is also known as glacial snout.
Question 11. What is firn?
Answer:
Firn:
In cold regions, where temperatures drop below the freezing point, snowfall occurs instead of rainfall. The snow falls like the feathers of birds and spread over the ground to form an ice field. An increased volume of snow gets compacted under the pressure of the overlying snow. This partially compacted granular snow is known as firn, which is the intermediate stage between snow and glacial ice.
Question 12. What are Roche mountaineers?
Answer:
Roche mountaineers:
In a mountainous region, due to erosional works of glaciers, large asymmetrical domes with smooth and steep walls may be formed. These landforms are known as Roche mountaineers. Example—Several Roche mountaineers are seen in the glaciated valleys of the Kashmir Himalayas.
Question 13. Why is the degradation process called a destructive process?
Answer:
Degradation is the process by which the higher landforms are lowered by erosion, mass wasting and denudation so as to attain an equilibrium position or a graded profile. Since the original landforms are eroded and lowered by the process of degradation, it is considered a destructive process.
Question 14. Why is vertical erosion or downcutting of river valleys in the upper course more prominent compared to lateral erosion or side cutting?
Answer:
The level of downcutting or vertical erosion of river valleys in the upper course is more prominent compared to side cutting or lateral erosion because the river flows over a steep slope in the upper course, hence having high velocity. Also, the river carries a huge amount of rocks and pebbles in this stage, which act as tools of erosion. Thus, the valleys are deepened due to abrasion by the tools of erosion and the force of the flowing water.
WBBSE Chapter 1Exogenetic Processes Landforms.
Question 15. Why are islands and sand bars created in the middle and lower course of a river?
Answer:
Islands and sand bars are formed in the middle and lower course of the river because of the following reasons—
1. The speed of the river reduces in the middle course as it leaves the mountainous region and enters the plains. Owing to the gentle slope of the land and increased bed load the carrying capacity of the river reduces considerably.
2. Depositions start occurring on the river bed. As more and more depositions occur, the sand bars grow bigger in size and rise out of the water as islands
Question 16. What do you mean by a river?
Answer:
River:
A naturally flowing body of water from the uplands to the lowlands under the gravitational force following the slope is known as a river. It originates in the mountains, hills or plateaus and drains into seas, lakes or other water bodies. A river may be both snow-fed and rain-fed. E.g. rivers Ganga, Brahmaputra, Yamuna, etc.
Exogenetic processes landforms.
Question 17. What do you mean by tributaries and distributaries? Give examples.
Answer:
Tributaries:
The smaller streams of water from the nearby areas that join the main river are called tributaries. Tributaries contribute their water as well as eroded materials to the main flow. E.g. Yamuna is the most important tributary of the river Ganga.
Distributaries:
The small streams branching out from the main river near its mouth in order to distribute its excessive bedload are called distributaries. The load deposited by the distributaries over a vast region from the delta, e.g. Bhagirathi-Hooghli is an important distributary of the river Ganga.
Question 18. What is an ideal river? Give example.
Answer:
Ideal river:
The river which exhibits all three courses, i.e., the upper, middle, and lower courses prominently is called an ideal river. The river generally erodes in the upper or mountain course, transports in the middle course and deposits in the lower or delta course. The middle and the lower courses are spread over vast areas. An ideal river doesn’t change its course frequently. For example—River Ganga is an ideal river.
Question 19. How can the course of a river be divided based on the work done?
Answer:
A river performs three activities right from its source to its mouth. The river course can be divided into three parts based on its work. They are as follows—
1. Upper course, marked mostly by the erosional work of the river.
2. Middle course, marked mostly by the transportation work of the river.
3. Lower course, marked mostly by the depositional work of the river.
Question 20. What is the sixth power law?
Answer:
Sixth power law:
The velocity of the stream(river) is one of the major factors on which its carrying or transportation capacity depends. A law to establish their relationship is known as the sixth power law, propounded by G.K. Gilbert. It states that the transportation power of the streams is proportional to the sixth power of its velocity. In other words, if the stream velocity is doubled, the transportation power of the stream increases 64 times. This law can be expressed in the following manner— Transportation power a (stream velocity)
Question 21. What is a water divide?
Answer:
Water divide:
The elevated land acting as a boundary between two river systems is known as a water divide. The water flowing from each side of the water divide flows into each separate body of water. The height of the water divide ranges from a slight elevation on plain land to a crest on a mountain range.
WBBSE Chapter 1Exogenetic Processes Landforms.
Question 22. What is a catchment area?
Answer:
Catchment area:
A catchment area or a drainage basin is an entire area that collects rainwater and contributes it to a channel. The shape of a drainage basin determines how rapidly will the run-off reach the main river and the outlet. In the case of circular basins, the run-off reaches quickly as compared to the elongated basins.
Question 23. What is a river valley?
Answer.
River valley:
The valley carved out by the river due to excessive downcutting and side-cutting along its course is known as a river valley. The shape and dimension of such valleys vary in each course of the river. V-shaped valleys are formed by the river in its youth stage or upper course while flat valleys are formed when the river reaches its mature stage in its middle course.
Question 24. What are gorges?
Answer:
Gorges:
The narrow steep-sided valleys formed in the mountainous regions due to heavy downcutting by the rivers are known as gorges. These valleys are V-shaped valleys. Here, vertical erosion by the rivers is more prevalent than lateral erosion. Example-Kali Gandaki gorge is a famous gorge in the Himalayas.
Question 25. What are potholes?
Answer:
Potholes:
In the upper course of the river, holes and depressions formed in the beds of the river valleys by the rock fragments and boulders brought down by the rivers are called potholes. Potholes are formed when the rocks get caught in the whirling water, moving in a circular manner and drilling the rocky beds of the valleys to form small holes. These holes gradually become bigger by the repetition of the same mechanism.
Question 26. What are meanders?
Answer:
Meanders:
The bends in the longitudinal course of the river are called meanders. Meanders have been named after the River Meander in Turkey because it flows through several bends. Once the river emerges onto the plains it loses speed due to the gentle slope of the land.
The slightest obstruction in the course forces the river to flow through various bends. Each of these bends has two types of slope. The side where the river strikes have a concave slope and are subjected to severe erosion. The other side is characterised by a convex slope where all the eroded materials are deposited. Thus, meanders are a result of both erosion and deposition.
Exogenetic processes landforms.
Question 27. What are interlocking spurs?
Answer:
Interlocking spurs:
In a mountainous region, the mountain ridges obstruct the flow of the river in such a way that the river has to erode the foothills and take frequent turns in order to avoid the ridges. From a distance, it appears that the ridges have been interwoven and the river has disappeared into the ridges. Such a series of mountain ridges are known as interlocking spurs.
Question 28. What is a cascade?
Answer:
Cascade:
A series of step-like waterfalls that originate when the river flows over an area with alternating bands of hard and soft rock beds is known as a cascade.
Example: Jonha waterfalls in Ranchi, Jharkhand
WBBSE Chapter 1Exogenetic Processes Landforms.
Question 29. What are endogenetic forces?
Answer:
Endogenetic forces:
The forces that act from within the earth are called endogenetic forces. These forces cause two types of movement in the earth, namely, vertical movement and horizontal movement. These movements give birth to various relief features such as plateaus, plains, lakes, folds, faults, etc. Volcanic eruptions and earthquakes are also a result of endogenetic forces.
Question 30. What are exogenetic forces?
Answer:
Exogenetic forces:
The forces which act on the surface of the earth externally and cause changes in landforms, are called exogenetic forces. These forces are also known as denudational forces. Exogenetic forces are constantly engaged in the destruction of relief features which have been formed due to the endogenetic forces. Rivers, glaciers, winds, underground water, and sea waves, are some exogenetic forces that work to change the landforms on the earth’s surface.
Question 31. What do you mean by gradation?
Answer:
Gradation:
The process of acquiring a smooth and graded profile of landform that lies in equilibrium is called gradation. Gradation includes three processes. The higher landforms are eroded and smoothened in the first phase. In the second phase, the eroded materials are transported by the agents of erosion. In the third phase, the eroded materials are deposited in lowlands or depressions to obtain a graded profile. Thus, gradation helps to eliminate the vertical irregularities of relief on the surface of the earth.
Question 32. What is aggradation?
Answer:
Aggradation:
The process of increasing the height of a landform by deposition of materials eroded from elsewhere, is known as aggradation. It is a constructive process. Aggradation leads to the formation of alluvial fans and cones, flood plains, etc.
Question 33. Mention a few instances in which humans and animals act as agents of erosion.
Answer:
At times, human beings and animals also act as active agents of erosion. Mining, construction and agricultural activities cause widespread localised erosion. Burrowing animals such as rabbits, and beavers also act as agents of erosion.
Question 34. What are peneplains?
Answer:
Peneplains:
The featureless plains dotted with small undulations formed at the end of the cycle of erosion by rivers are known as peneplains. The river erodes the high landforms over a considerable period of time and lowers them. The soft rocks are eroded away faster and the hard rocks stand out on the surface as they are eroded less. These hard rocks standing out as highlands on a plain surface are known as monadnocks. E.g.-The Chotanagpur region is a peneplain, and the Pareshnath and Panchet hills lie as monadnocks.
Question 35. What is the middle course of a river?
Answer:
The middle course of a river:
The river emerges onto the plains from its mountainous or upper course and henceforth this course of the river on the plains is known as its middle course. All along this course, the speed of the river reduces comparatively but the volume of the water carried decreases. Transportation of the eroded materials from the upper course is the main activity of the river in this course. Deposition of the eroded materials is also partially seen along this course. Example-The course of the river Ganga between Haridwar and Rajmahal hills is its middle course.
Question 36. Which is the lower course or delta course of a river?
Answer:
The course of the river flowing through the plains when reaches its mouth is known as its lower course. The speed of the river in this course is vastly reduced due to the gentle slope of the land. The flow also becomes sluggish due to the huge amount of sediment that is carried with the water as a bed load. This leads to the deposition of the sediments near the mouth forming deltas. Example-The portion of the river Ganga, lying between Rajmahal hills to the mouth in the Bay of Bengal is known as the lower course of the river.
Exogenetic processes landforms.
Question 37. What is Plunge Pool?
Answer:
Plunge Pool:
In mountainous regions, waterfalls are created where the river drops from a considerable height with great velocity. Small depressions or hollows known as potholes are created at the base of the waterfalls due to the pounding of rock fragments brought down by the water. These potholes gradually grow bigger in size to form Plunge Pools.
Question 38. Why is the Lohachara island submerging?
Answer:
The Lohachara island at the mouth of the river Hooghly is gradually submerging because—
1. The sea level is rising.
2. Severe cyclonic storms are hitting the area frequently.
3. The mangrove forests are being cut down and thus the coasts are being exposed to erosion.
WBBSE Chapter 1Exogenetic Processes Landforms.
Question 39. What do you know about South Talpatti island?
Answer:
South Talpatti island:
The South Talpatti island also known as New Moore island existed 2 km away from the mouth of the river Hariyabhanga in the Sunderbans. The cardinal location of the island was 21°37’00″N and 89°08’30” S. The island emerged in the aftermath of the Bhola cyclone in 1970. According to satellite images, the island was about 2500 sq. km in area. The island is currently submerged due to the rise in the sea level as reasoned by scientists.
Question 40. What is the current condition of Ghoramara island?
Answer:
The current condition of Ghoramara island:
The Ghoramara island lies 92 km south of Kolkata, north of the Sagar islands at the mouth of river Hooghly and east of the mouth of river Haldi in the Bay of Bengal. This is an island in the Sundarban region. In 1951, the size of the island was 38.23sq. km, but by 2011, the size reduced to a mere 4.37sq.km. Experts predict that the island will totally disappear due to submergence in the near future.
Question 41. What do you mean by rejuvenation?
Answer:
Rejuvenation:
Rejuvenation means acceleration of the erosive work of the rivers due to various factors. This lengthens the period for the cycle of erosion of the rivers. A river may be rejuvenated due to earth movements that cause upliftment or depression of land, substantial fall in the sea level, river capture, etc. Landforms created due to the rejuvenation of rivers include knick points, valley-in-valley topography, incised meanders, paired terraces, etc.
Question 42. What are wadis?
Answer:
Wadis:
The small, shallow dry river valleys found in the deserts are called wadis. The wadis remain dry for most of the time and get filled at times of sudden rain in the desert. They often shift from one position to another or get lost in the sand.
Example: Wadi Al-Batin of Saudi Arabia is a famous wadi.
Question 43. What do you mean by a pediment?
Answer:
Pediment:
In desert regions, the winds are the strongest agent of erosion. The small rocks, pebbles, sand particles etc., that blow with the wind help in eroding large boulders or mountains to low landforms. A pediment is a plain formed at the foothills of mountains in a desert by the joint action of erosion and deposition by the wind as well as flowing water. It remains covered with rocks and boulders.
WBBSE Chapter 1Exogenetic Processes Landforms.
Question 44. What are dunes?
Answer:
Dunes:
In deserts, the winds are very strong and can lift and carry large amounts of sand as they blow. But if the winds are obstructed by trees, rocks, boulders, bushes, hillocks, etc., they lose speed and drop the sand at the place of obstruction. Thus, the sand gets accumulated as high dumps over long stretches of land. These landforms are known as sand dunes. Dunes also form due to the presence of a dominant direction in which the wind blows.
Question 45. What is a barchan?
Answer:
Barchan:
The barchan is a transfer sand dune that is found in the desert region. It stands across the direction of the wind. It looks like a crescent moon. The middle part of the barchan can be 15-30m high. It has two horns on either side which move forward as the wind blows
Question 46. What is a garage?
Answer:
Garage:
In a desert region, the wind is the most active agent of erosion. The wind erodes mainly by the process of abrasion, where the rocks and pebbles carried by the wind collide against the lower parts or base of a high boulder or a hill. The soft rocks at the base get eroded faster and the hard rocks on the top remain as it is. Thus, the landform develops a narrow base and a broad top. This looks like a mushroom and thus is known as a mushroom rock. Such mushroom rocks are known as gara in the Sahara region.
Question 47. What is loess? Or, Define Loess.
Answer:
Loess:
Loess are the yellowish soil particles that are blown by the wind from the deserts and deposited elsewhere. Loess contains particles that are very fine textured and rich in quartz silt, clay and carbonate minerals. The soil particles do not have any similarity with the rocks and soil present in the region where they have been deposited. The plains formed of the loess deposits are called loess plains.
Question 48. What is an oasis?
Answer:
Oasis:
In desert regions, a huge depression may be created due to the blowing away of sand by the wind regularly. The depression becomes so deep that the surface of the region reaches the level of the underground water table. Thus, water is easily available here, and the soil remains moist. This region is known as the oasis, as the availability of water helps in the growth of trees around the depression and makes this region look green. An oasis is like a garden in the desert region.
Question 49. What are ventifact and dreikanter?
Answer:
Ventifact: In a desert region, if the wind blows from one direction, the large rocks are polished on one side (the side facing the wind) by the process of abrasion, while the other sides remain uneven and rough. Such a rock is known as a ventifact.
Dreikanter: If the wind blows from different directions, all the faces of the rocks standing out are polished by the process of abrasion. Thus, a landform with three polished faces is formed. This is known as dreikanter.
Question 50. What are seif dunes?
Answer:
Seif dunes:
‘Seif’ means sword in Arabic. The long and narrow dunes like swords formed in the deserts are called seif dunes.
The seif dunes are formed in sandy deserts parallel to the direction of the wind. These are practically the longitudinal dunes. According to scientist Bagnold, the barchans in the desert region get gradually converted to seif dunes.
Question 51. What are blowouts or deflation hollows? Or, How are the “deflation hollows” formed?
Answer:
Blowouts or deflation hollows are sandy depressions found in desert regions. They are formed by the removal of sand from a region by the wind. They are commonly found in arid regions or coastal regions where there is the sufficient sand cover. Example—Qattara Depression, Egypt.
Exogenetic processes landforms.
Question 52. What do you mean by playa lakes?
Answer:
Playa lakes:
The saltwater lakes found in desert regions are called playa lakes. They are known as ‘hands’ in Rajasthan and ‘shafts’ in Sahara. The ephemeral streams that originate from the surrounding mountains drain into these lakes. The non-perennial rivers of the desert region may also drain into these playa lakes.
Question 53. What is a bajada?
Answer:
Bajada:
The gently sloping plain land lying between the pediment and the playa in a desert region is called a bajada. It may be formed at the foothills of mountains by the accumulation of clay, silt and pebbles. The alluvial cones formed at the foothills of mountains in a fluvial aeolian environment may join with each other and form a bajada.
WBBSE Chapter 1Exogenetic Processes Landforms.
Question 54. Why does abrasion occur at a height of a few metres above the earth’s surface?
Answer:
Abrasion is the process in which the rock pieces, pebbles and sand blown by the wind rub against or collide against the rocky hills or walls on the earth’s surface and thus erode them. Abrasion occurs only till a few metres above the ground because the large rock pieces cannot be lifted too high above the ground by the winds. The presence of erosive tools carried by the wind is maximum at the lower columns of air than at a height.
Question 55. What are star dunes?
Answer:
Star dunes:
In desert regions, winds blow from different directions during different times of the year. Thus, dunes are formed in different directions. Star dunes are formed by variable winds. They grow vertically and do not migrate laterally. A star dune has multiple slip faces, a central peak and three or more arms extending radially.
Question 56. What do you mean by Agassi?
Answer:
Agassi:
The seif dunes lie parallel to one another and the gap or passage between two adjacent seif dunes is called a corridor. These corridors are devoid of sand and lie as pavements or vast stony plains in the desert. These are called reg. Such reg or corridors between parallel dunes are known as gassy in Sahara, Africa. These corridors are used as caravan paths for travelling through the deserts.
Question 57. What do you mean by erg?
Answer:
Erg:
The vast stretches in the desert made up of sand accumulations are known as ergs. Ergs are formed where the wind is most active and the amount of sand present is huge. These depressions of wind accumulations were formerly filled with alluvium.
Question 58. Name some deserts of the mid-latitudes.
Answer:
Some deserts of the mid-latitudes are— Gobi, Taklamakan and the desert of Turkestan in Asia, the Colorado desert in North America, etc. The number of deserts in mid-latitudes is more than the number of deserts in low latitudes.
Question 59. Name some deserts of the low latitudes.
Answer:
The low-latitude deserts are found within 20°-30° latitudes in both hemispheres. These deserts have developed on the western margins of the continents. E.g.— Sahara, and Kalahari in Africa; the Arabian desert, the Baluchistan desert and Thar desert in Asia; Soneran in North America, the Great Australian desert in Australia, etc.
Question 60. What is adobe?
Answer:
Adobe:
In North America, loess deposits are found in the valleys of the Mississippi and Missouri rivers. Scientists believe that this landform had been formed in the Pleistocene Age when sand from the moraines and outwash plains was blown off and deposited here. These loess deposits are known as adobe in North America. Loess is extensively found in Nebraska, Illinois, Iowa, etc.
Question 61. Why do valleys rivers while carving glaciers out T carve or out’V’ ‘U’ shaped valleys?
Answer:
Case Studies on Exogenetic Landforms
- The rivers have great speed in the mountainous region.
- The intensity of downcutting is more than the intensity of side cutting. regions the valley carved out are ‘I’ shaped and while flowing through the wet regions the shape of the valleys resembles the letter V.
- In the case of glaciers, the intensity of side-cutting of valleys is similar to that of downcutting. Rocks are broken and removed by the process of plucking and abrasion.
- Thus, the shape of the valley resembles the letter ‘U’.
WBBSE Chapter 1Exogenetic Processes Landforms.
Question 62. Mention the importance of glaciers as a source of sweet and fresh drinking water.
Answer:
- A glacier is not only a frozen river of ice but also influences the landform and climate. the environment of the glacial region.
- It can be considered as a reserve for freshwater pres in the frozen form. About 97.20% of the water present on the earth’s surface is salty and unfit for use. The rest 2.80% of the water is fresh.
- Out of this share, about 0.0001% of the water flows through rivers, 0.9999% lies as underground water, and 1% remains frozen as ice.
- This means that about 75% of usable fresh water is trapped in the glaciers. Out of this about 90% or more lie in Antarctica.
- Rivers like Ganga, Yamuna, Indus and Brahmaputra rise from the glaciers. Thus, the glaciers in the high mountains are important in being reserves of freshwater in frozen form.
Question 63. Why are the roches moutonnees smooth on one side and rough on the other?
Answer:
- In a glaciated region, if a large boulder, or rock comes in the way of the glacier, the side over which the glacier moves forward is smoothened and polished by the process of abrasion.
- The opposite side over which the glacier descends is plucked and eroded and weathered.
- Thus, one slope of the Roches moutonnees is smooth while the opposite side is rough, uneven and plucked.
Question 64. How are glacial stairways formed?
Answer:
When the glaciers descend from very high mountains into valleys, they develop steps or stairs along the walls of the valleys through the processes of abrasion and plucking. The steps may develop due to unequal distribution of load in the glacier or alternate alignment of hard and soft rock beds. These steps are known as glacial stairways.
Question 65. What do you mean by abrasion?
Answer:
Abrasion:
Abrasion or corrasion is a type of erosion. The natural agents of erosion like rivers, glaciers and wind bring down rock fragments, pebbles, sand and stones that rub against the rock beds on the surface of the earth. This is known as the process of abrasion. Thus, the surface is polished and eroded fast by the removal of loosened materials.
Question 66. What are eskers?
Answer:
Eskers:
Eskers are depositional landforms found in the lowlands or foothills of mountains or valley glaciers. When the debris (rocks, pebbles, stone, etc.) brought down by glaciers gets deposited like low-lying ridges (about 15 m in height) with branches, they are called eskers.
Exogenetic processes landforms.
Question 67. Where is the erosional action of wind most predominant?
Answer:
In arid regions of the world where the rainfall received is less than 25cm, growth of natural vegetation is negligible or almost absent the erosional action of the wind is most predominant. The land surface remains open and uncovered. There are almost no obstructions to the blowing wind. Hence the winds blow at a great speed. Also, the high diurnal range of temperature leads to the disintegration of rocks. These rock fragments are carried with the wind further eroding the landscape by the process of abrasion.
Question 68. How is sand formed in the deserts?
Answer:
In the desert regions, the diurnal and annual ranges of temperature are very high. This enhances weathering by mechanical methods, where the large rocks are gradually broken down into small rock fragments. Also, abrasion of rocks leads to further breakdown of rocks into sand particles. Lack of rainfall helps to speed up the whole process. Thus, sand is formed in the deserts.