Short Answer Type Questions:
Q1. What do incised meanders in rocks and meanders in plains of alluvium indicate?
Answer
The incised meanders in rocks and meanders in plains of alluvium indicates the status of original land surfaces over which streams have developed.
Q2. Explain the evolution of valley sinks or uvalas.
Answer
Generally, the surface run-off simply goes down swallow and sink holes and flow as underground streams and re-emerge at a distance downstream through a cave opening. When sink holes and dolines join together because of slumping of materials along their margins or due to roof collapse of caves, long, narrow to wide trenches called valley sinks or Uvalas form.
Q3.Underground flow of water is more common than surface run-off in limestone areas. Why?
Answer
Underground flow of water is more common than surface run-off in limestone areas because limestone is rich in calcium carbonate, the surface water as well as groundwater through the chemical process of solution and precipitation deposition, develop varieties of landforms. These two processes of solution and precipitation are active in limestones occurring either exclusively or interbedded with other rocks.
Q4.Glacial valleys show up many linear depositional forms. Give their locations and names.
Answer
Glacial valleys show up many linear depositional forms:
• Terminal moraines: formed at the end (toe) of the glaciers.
• Lateral moraines – formed along the sides parallel to the glacial valleys
• Ground moraines – many valley glaciers retreating rapidly leave an irregular sheet of till over their valley floors.
• Eskers – flow over the ground with ice forming its banks.
• Outwash Plains – The plains at the foot of the glacial mountains or beyond the limits of continental ice sheets.
• Drumlins – form beneath heavily loaded ice through fissures in the glacier.
Q5.How does wind perform its task in desert areas? Is it the only agent responsible for the erosional features in the deserts?
Answer
Winds also move along the desert floors with great speed and the obstructions in their path create turbulence. Winds cause deflation, abrasion and impact. Deflation includes lifting and removal of dust and smaller particles from the surface of rocks. In the transportation process sand and silt act as effective tools to abrade the land surface. The impact is simply sheer force of momentum which occurs when sand is blown into or against a rock surface. The wind action creates a number of interesting erosional and depositional features in the deserts. Winds are not the only agent responsible for the erosional features in the deserts. The rain or sheet wash is also important.
Q6. Running water is by far the most dominating geomorphic agent in shaping the earth’s surface in humid as well as in arid climates. Explain.
Answer
In humid regions, There are two components of running water. One is overland flow on general land surface as a sheet. Another is linear flow as streams and rivers in valleys. Most of the erosional landforms made by running water are associated with vigorous and youthful rivers flowing along gradients. With time, stream channels over steep gradients turn gentler due to continued erosion, and as a consequence, lose their velocity, facilitating active deposition. Overland flow causes sheet erosion. Depending upon irregularities of the land surface, the overland flow may concentrate into narrow to wide paths. In the early stages, down-cutting dominates during which irregularities such as waterfalls and cascades will be removed. In the middle stages, streams cut their beds slower, and lateral erosion of valley sides becomes severe. During their terminal stages, the running water makes deltas.In arid regions, though rain is scarce in deserts, it comes down torrentially in a short period oftime. The desert rocks devoid of vegetation, exposed to mechanical and chemical weathering processes due to drastic diurnal temperature changes, decay faster and the torrential rains help in removing the weathered materials easily. The weathered debris in deserts is moved by not only windbut also by rain/sheet wash.Thus, Running water is by far the most dominating geomorphic agent in shaping the earth’s surface in humid as well as in arid climates.
Q7. Limestones behave differently in humid and arid climates. Why? What is the dominant and almost exclusive geomorphic process in limestone areas and what are its results?
Answer
Limestones are permeable, thinly bedded and highly jointed and cracked therefore, the surface water
percolates well. After vertically going down to some depth, the water under the ground flows horizontally through the bedding planes, joints or through the materials themselves. This downward
and horizontal movement of water which causes the rocks to erode. Physical or mechanical removal of materials by moving groundwater is insignificant in developing landforms.
In arid climates, water table is below the surface therefore, there is less amount of surface water.
The amount of water differ in these two areas, therefore, limestones behave differently in humid and arid climates.
The dominant and almost exclusive geomorphic process in limestone is the processes of solution and deposition by the action of the groundwater. Many depositional forms develop within the
limestone caves. The depositional landforms in limestone areas by the action of ground water are stalctites, stalagmites and pillars.
Q8. How do glaciers accomplish the work of reducing high mountains into low hills and plains?
Answer
Masses of ice moving as sheets over the land or as linear flows down the slopes of mountains in broad trough-like valleys are called glaciers. The movement of glaciers is slow unlike water flow. The movement could be a few centimetres to a few metres a day or even less or more. Glaciers move basically because of the force of gravity.
Erosion by glaciers is tremendous because of friction caused by sheer weight of the ice. The material plucked from the land by glaciers get dragged along the floors or sides of the valleys and cause great damage through abrasion and plucking. Glaciers can cause significant damage to even un-weathered rocks and can reduce high mountains into low hills and plains.
As glaciers continue to move, debris gets removed, divides get lowered and eventually the slope is reduced to such an extent that glaciers will stop moving leaving only a mass of low hills and vast outwash plains along with other depositional features.
Long Answer Type Questions :
Q1.Explain the landforms that are seen in upper part of the river.
Answer:
In upper part of the river, many beautiful and attractive landforms are formed. Some of them are as follows:
- V-shaped valleys: Valleys start as small and narrow rills; the rills will gradually develop into long and wide gullies; the gullies will further deepen, widen and lengthen to give rise to valleys. Depending upon dimensions and shape, many types of valleys like V-shaped valley, gorge, canyon, etc. can be recognised.
- Gorge: A gorge is a deep valley with very steep to straight sides.
- Canyon: A canyon is characterised by steep step-like side slopes and may be as deep as a gorge. A gorge is almost equal in width at its top as well as its bottom. In contrast, a canyon is wider at its top than at its bottom. In fact, a canyon is a variant of gorge.
- Waterfall: When the rivers start falling in pits in mountainous regions, it makes waterfall.
- Plunge pools: Once a small and shallow depression forms, pebbles and boulders get collected in those depressions and get rotated by flowing water and consequently the depressions grow in dimensions. A series of such depressions eventually join and the stream valley gets deepened. At the foot of waterfalls also, large potholes, quite deep and wide, form because of the sheer impact of water and rotation of boulders. Such large and deep holes at the base of waterfalls are called plunge pools.
Q2.Explain the landforms made by erosion caused by groundwater.
Answer:
Important landforms made by erosion are as follows:
1. Pools: These are conical shaped pits whose depth is three to nine metres. The width of the mouth is more than one metre. Due to solubility in water, when cracks in limestone increase, then pools take birth.
2.Swallow holes: Small to medium sized round to sub-rounded shallow depressions called swallow holes form on the surface of limestones through soil.
3. Sinkholes: A sinkhole is an opening more or less circular at the top and funnel -shaped towards the bottom with sizes varying in area from a few square metre to a hectare and with depth from a less than half a metre to thirty metres or more.
4. Uvalas: When sinkholes and dolines join together because of slumping of materials along their margins or due to roof collapse of caves, long, narrow to wide trenches called uvalas are formed.
5. Collapse sinks: If the bottom of the sinkholes forms the roof of a void or cave underground it might collapse leaving a large hole opening into a cave or a collapse sinks.
6. Lapies: Gradually, most of the surface of the limestone is eaten away by these pits and trenches, leaving it extremely irregular with a maze of points, grooves and ridges or lapies. Especially, these
ridges or lapies form due to differential solution activity along parallel to sub¬parallel joints. The lapie field may eventually turn into somewhat smooth limestone pavements.
7. Caves: In areas where there are alternating beds of rocks (shales, sandstones, quartzites) with limestones or dolomites in between or in areas where limestones are dense, massive and occurring as thick beds, cave formation is prominent. Water percolates down either through the materials or through cracks and joints and moves horizontally along bedding planes. It is along these bedding planes that the limestone dissolves and long and narrow to wide gaps called caves result. There can be a maze of caves at different elevations depending upon the limestone beds and intervening rocks. Caves normally have an opening through which cave streams are discharged. Caves having openings at both the ends are called tunnels.
Q3.Explain the depositional landforms made by rivers.
Answer:
Depositional Landfoi, made by rivers:
1. Alluvial Fans: Alluvia ms are formed when streams flowing from higher levels break into foot slope plains of low gradient. Normally very coarse load is carried by streams flowing over mountain slopes. This load becomes too heavy for the streams to be carried over gentler gradients and gets dumped and spread as a broad low to high cone shaped deposit called alluvial fan. Usually, the streams which flow over fans are not confined to their original channels for long and shift their position across the fan forming many channels called distributaries. Alluvial fans in humid areas show normally low cones with gentle slope from head to toe.
2. Deltas: Delta is like alluvial fans but develop at a different location. The load carried by the rivers is dumped and spread into the sea. If this load is not carried away far into the sea or distributed along the coast, it spreads and accumulates. Such areas over flood plains built up by abandoned or cut-off channels contain coarse deposits. The flood deposits of spilled waters carry relatively finer materials like silt and clay. The flood plains in a delta are called delta plains.
3. Floodplains: Floodplain is a major landform of river deposition. Large sized materials are deposited first when stream channel breaks into a gentle slope. Thus, normally, fine sized materials like sand, silt and clay are carried by relatively slow moving waters in gentler channels usually found in the plains and deposited over the bed and when the waters spill over the banks during flooding above the bed.
4. Natural Levees: Natural levees are found along the banks of large rivers. They are low, linear and parallel ridges of coarse deposits along the banks of rivers, quite often cut into individual mounds. During flooding as the water spills over the bank, the velocity of the water comes down and large sized and high specific gravity materials get dumped in the immediate vicinity of the bank as ridges. They are high nearer the banks and slope gently away from the river. The levee deposits are coarser than the deposits spread by flood waters away from the river. When rivers shift laterally, a series of natural levees can form.
5. Point Bars: Point bars are also known as meander bars. They are found on the convex side of meanders of large rivers and are sediments deposited in a linear fashion by flowing waters along the bank. They are almost uniform in profile and in width and contain mixed sizes of sediments. If there more than one ridge, narrow and elongated depressions are found in between the point bars.
Q4.Explain the erosional landforms created by waves and currents.
Answer:
Cliffs, Terraces, Caves and Stacks are important landforms created by erosion caused by waves and currents.
- Wave-cut cliffs: Almost all sea cliffs are steep and may range from a few m to 30 m or even more. At the foot of such cliffs there may be a flat or gently sloping platform covered by rock debris derived from the sea cliff behind. Such platforms occurring at elevations above the average height of waves is called a wave-cut terrace.
- Terraces: The lashing of waves against the base of the cliff and the rock debris that gets smashed against the cliff along with lashing waves create hollows and these hollows get widened and deepened to form sea caves. The roofs of caves collapse and the sea cliffs recede further inland.
- Sea stacks: Retreat of the cliff may leave some remnants of rock standing isolated as small islands just off the shore. Such resistant masses of rock, originally parts of a cliff or hill are called sea stacks.
Like all other features, sea stacks are also temporary and eventually coastal hills and cliffs will disappear because of wave erosion giving rise to narrow coastal plains, and with onrush of deposits from over the land behind m ay get covered up by alluvium or may get covered up by shingle or sand to form a wide beach.
Q5.Explain the different stages of a river.
Answer:
A river passes through three stages like a human being: youth, mature and old.
1. Youth Stage: Youth streams are less in number. In this stage with poor integration and flow over original slopes showing shallow V-shaped valleys with no floodplains or with very narrow floodplains along trunk streams. Streams divides are broad and flat with marshes, swrnmp and lakes. If meanders are present, they develop over these broad upland surfaces. These meanders may eventually entrench themselves into the uplands. Waterfalls and rapids may exist where local hard rock bodies are exposed.
2. Mature Stage: During this stage streams are plenty with good integration. The valleys are still V-shaped but deep; trunk streams are broad enough to have wider floodplains within which streams may flow in meanders confined within the valley. The flat and broad inter stream areas and swamps and marshes of youth disappear and the stream divides turn sharp. Waterfalls and rapids disappear.
3. Old Stage: Smaller tributaries during old age are few with gentle gradients. Streams meander freely over vast floodplains showing natural levees, oxbow lakes, etc. Divides are broad and flat with lakes, swamps and marshes. Most of the landscape is at or slightly above sea level.
