Fundamentals of Physical Geography
Chapter 7: Landforms and their Evolution Q. 1 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 Key Points: - Erosion in Humid Regions: -Areas which receive heavy rainfall running water is considered the most important of the geomorphic agents in bringing about the degradation of the land surface. 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 over steep gradients. With time, stream channels over steep gradients turn gentler due to continued erosion, and as a consequence, lose their velocity, facilitating active deposition. Erosion Over Slopes: -There may be more depositional forms associated with streams flowing over steep slopes as compared to rivers flowing over medium to gentle slopes. The gentler the river channels in gradient or slope, the greater is the deposition. When the stream beds turn.jpeg)
gentler due to continued erosion, downward cutting becomes less dominant and lateral erosion of banks increases and as a result the hills and valleys are reduced to plains. Erosion in Dry Regions: -In dry regions, most of the landforms are formed by the erosion and deposition of flood sheet. Although, in deserts, rain is scarce, it comes down speedily in a short period of time. The desert rocks lack of vegetation, exposed to mechanical and chemical.jpeg)
weathering processes due to drastic diurnal temperature changes, decay faster and the torrential rains help in removing the weathered materials easily. That means, the weathered debris in deserts is moved by not only wind but also by rain/sheet wash.
Q. 2 Explain the different stages of a river. Answer Key Points: -
A river passes through three stages like a human being: youth, mature and old. Youth Stage: -- 1) In youthful stage, streams flow in a shallow v-shaped valleys over the original slope.
- 2) In this stage down cutting and headward erosion are done by running water.
- 3) There are no floodplains but water divides are common.
- 4) George, canyon v-shaped valley, waterfall and rapids etc. are the main features created by river in the stage.
Mature Stage: -- 1) In the mature stage river flow in a large basin with a plenty of water.
- 2) In this stage lateral or side cutting is most common.
- 3) Waterfalls and rapids disappear. Flood plains and valley pains are formed.
- 4) River meandering, oxbow lakes and floodplains are the main features created by river.
Old Stage: -- 1) In the old stage river expands and flows at slow speed.
- 2) River does not do any erosional activity & deposition is the main work done by the river.
- 3) In this stage deltas and floodplains are formed.
- 4) Esturies, floodplains, deltas and natural levees etc. are the main features created by river.
Q. 3 Explain the erosional features made by rivers in their course. OrExplain the landforms that are seen in upper part of the river. Answer Key Points: - In upper part of the river, following landforms are formed: -1) V-Shaped Valleys: - Valleys start as small and narrow rills which gradually develop into long and wide gullies. Due to continue erosion these gullies further becomes deeper and wider to give rise to valleys. V shaped valley is formed in the areas of sufficient.jpeg)
rainfall where the rocks are not very hard down cutting and side cutting are done by river water and a v shaped valley is formed.2) Gorge: - A gorge is a deep valley with very steep to straight sides. A gorge is almost equal in width at its top as well as its bottom. The term “gorge” is often used to mean “canyon,” but a gorge is almost always steeper and narrower than a canyon..jpeg)
3) Canyon: - A canyon is a deep, narrow valley with steep sides. “Canyon” comes from the Spanish word cañon, which means “tube” or “pipe.” A canyon is characterised by steep step-like side slopes and may be as deep as a gorge. A canyon is wider at its top than at its bottom. In fact, a canyon is a variant of gorge..jpeg)
4) Waterfall: - When the river water falls down almost vertically form a sufficient height along the course of the river it forms a waterfall..jpeg)
5) Rapids: - Sometimes there is a band of hard rock along the base of the river which makes it jump over or fall downwards. This lead to formation of rapids at the river basin..jpeg)
6) Pothole and Plunge Pools: - Potholes are the large circular depressions on the base of the river or waterfall formed by (plucking up) erosion of running water. Due to continue erosion of the base level potholes grows in size and they are called plant poles..jpeg)
7) Incised or Entrenched Meanders: - They are very deep and wide menders cut in hard rocks by the action of river. They develop over original surface in the starting stages of a river due to erosion or uplift of land..jpeg)
8) River Terraces: - The step like formation on rivers walls are found on both side of the river valley and represent old valley floor levels. They may occur at the same elevation on the both side of the rivers in which they are called paired terraces but when terrace is present only one side of the stream it is called the unpaired terrace..jpeg)
Q. 4 How are river terrace formed? Answer Key Points: -River terrace are basically products of erosion as they result due to vertical erosion by the stream into its own depositional flood plains. The terraces may result due to: -.jpeg)
- 1) Seepage of water after a peak flow.
- 2) Change in hydrological regimes due to climatic changes.
- 3) Tectonic uplift of land.
- 4) Sea level changes in case of rivers closer to the sea.
Q. 5 Explain the depositional landforms made by rivers. Answer Key Points: -The transporting power of river decreases due to decrease in the speed and volume of its water so the river starts depositing its load which forms different types of depositional features. Some of them are: -1) Alluvial Fans: - An alluvial fan is a triangle-shaped deposit of alluvial sediments such as gravel, sand, and silt. Alluvial fans are formed when streams flowing from higher levels break into foot slope plains of low gradient..jpeg)
2) Deltas: - Delta is a triangular shaped deposition of sediments at the mouth of a river before it enters into any water body. This occurs where a river enters an ocean, sea, estuary, lake, reservoir, or another river that cannot carry away the supplied sediment..jpeg)
3) Floodplains: - Floodplain is a neighboring area of a river which gets flooded almost every year during the heavy rainfall. Most floodplains are formed by deposition of sediments like sand, silt and clay on the inside of river meanders and by overbank flow..jpeg)
4) Natural Levees: - Levees occur in the lower course of a river when there is an increase in the volume of water flowing downstream and flooding occurs. 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. It is formed when the movement of water pushes sediment to the side of rivers and creeks..jpeg)
5) Point Bars: - A point bar is a depositional feature made of alluvium that accumulates on the inside the bend of streams and rivers below the slip-off slope. Point bars are found in abundance in mature or meandering streams..jpeg)
6) Meander and Ox-bow Lake: - Meander is defined as the winding curve in the course of river. Meanders form when water in the river erodes the banks on the outside of the channel and deposits sediment on the inside of the channel. Meanders only occur on flat land where the river is large and established. An oxbow lake is a U-shaped lake that forms when a wide meander of a river is cut off, creating a free-standing body of water..jpeg)
7) Braided Channels / Streams: - It is a drainage network formed when river water is divided into number of converging and diverging channels separated by low sandbanks. These sandbanks are called braid bars or, in English usage, aits or eyots..jpeg)
Q. 6 Meander is not a landform but is only a type of channel pattern. Justify. OrWhat are the causes behind formation of river meander landform? Answer Key Points: -The formation of meanders is due to both deposition and erosion and meanders gradually migrate downstream. It is not a landform but is only a type of channel pattern because of: -- 1) Propensity of water flowing over very gentle gradients to work laterally on the banks.
- 2) Unconsolidated nature of alluvial deposits making up the banks with many irregularities which can be used by water exerting pressure.
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- 3) Coriolis force acting on the fluid water deflecting, it like it deflects the wind. When the gradient of the channel becomes extremely low, water flows leisurely and starts working laterally.
- 4) Normally, in meanders of large rivers, there is active deposition along the convex bank and undercutting along the concave bank.
- 5) The concave bank is known as cut-off bank which shows up as a steep scarp and the convex bank presents a long, gentle profile and is known as slip-off bank.
- 6) As meanders grow into deep loops, the same may get cut-off due to erosion at the inflection points and are left as Ox-bow.
Q. 7 Limestone behaves 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 Key Points: -- 1) Many depositional forms develop within the limestone caves. The chief chemical in limestone is calcium carbonate which is easily soluble in carbonated water i.e. carbon dioxide absorbed rainwater.
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- 2) This calcium carbonate is deposited when the water carrying it in solution evaporates or loses its carbon dioxide as it trickles over rough rock surfaces. Stalactites, Stalagmites and Pillars Stalactites hang as icicles of different diameters.
- 3) Normally they are broad at their bases and taper towards the free ends showing up in a variety of forms. Stalagmites rise up from the floor of the caves. In fact, stalagmites form due to dripping water from the surface or through the thin pipe, of the stalactite, immediately below it.
- 4) The results of the work of groundwater cannot be seen in all types of rocks. But in rocks like limestones or dolomites rich in calcium carbonate, the surface water as well as groundwater through the chemical process of solution and precipitation deposition develops varieties of landforms.
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- 5) These two processes of solution and precipitation are active in limestones or dolomites occurring either exclusively or interbedded with other rocks. Therefore, underground flow of water is more common than surface run off in limestone areas.
Q. 8 Explain the landforms made by erosion caused by Groundwater. Answer Key Points: - Important landforms made by erosion are as follows: -1) Pools: - These are conical shaped pits whose depth is three to nine meters. The width of the mouth is more than one meter. 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 limestone through soil..jpeg)
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 meters to a hectare and with depth from a less than half a meter to thirty meters or more..jpeg)
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..jpeg)
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..jpeg)
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..jpeg)
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 cave 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..jpeg)
Q. 9 Explain the depositional landforms formed by groundwater. Answer Key Points: - 
The depositional landform formed by the groundwater are: -- 1) Stalactites: - Stalactites hang as icicles of different diameter. Normally they are broad at their bases and taper towards the free ends showing up in variety of forms.
- 2) Stalagmites: - Stalagmites rise up from the floor of the caves. They are formed due to dripping water from the surface or through the thin pipe of stalactite. Stalagmite may take the shape of a column, a disc with either a smooth, rounded bulging end or a miniature crater like depression.
- 3) Pillars: - The stalagmite and stalactite eventually fuse to give rise to column and pillars.
Q. 10 How do glaciers accomplish the work of reducing high mountains into low hills and plains? Answer Key Points: -- 1) 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.
- 2) A glacier in its valley is slow unlike water flow. The movement could be a few centimeters to a few meters a day or even less or more. Glaciers move basically because of the force of gravity.
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- 3) 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.
- 4) Glaciers can cause significant damage to even un-weathered rocks and can reduce high mountains into low hills and plains.
- 5) 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.
Q. 11 Explain the erosional landforms made by Glaciers. Answer Key Points: -1) Cirque: - They are a bowl-shaped depression formed due to the erosional activity of glaciers on mountain and valley side walls at high elevations. Cirques are the most common of landforms in glaciated mountains. A lake of water can be seen quite often within the cirques after the glacier disappears. Such lakes are called cirque or tarn lakes..jpeg)
2) Horns and Serrated Ridges: - Horns form through head ward erosion of the cirque walls. If three or more radiating glaciers cut head-ward until their cirques meet, high, sharp pointed and steep sided peaks called horns form..jpeg)
3) Arete: - Arête, (French: “ridge”), in geology, a sharp-crested narrow ridge of rock which separates two valleys. It is typically formed when two glaciers erode parallel U-shaped valleys. Arêtes can also form when two glacial cirques erode head-wards towards one another, although frequently this results in a saddle-shaped pass, called a col..jpeg)
4) Glacial Valleys/Troughs: - Glacial troughs, or glaciated valleys, are long, U-shaped valleys formed by glaciers when a glacier travels across and down a slope. Troughs tend to have flat valley floors and steep, straight sides. Glaciers carve a set of distinctive, steep-walled, flat-bottomed valleys e.g. U-shaped valleys, fjords, and hanging valleys..jpeg)
A) U-shaped valley: - U-shaped valleys, trough valleys or glacial troughs, are formed by the process of glaciation (A glacial period within an ice age). Glaciation develops in established v-shaped river valleys where the ice erodes the surrounding rocks to create a “U” shaped valley with a flat bottom and steep sides. Glacier movement is driven by gravity..jpeg)
B) Fjords: - A fjords also spelled fiords are long, deep, narrow glaciated valleys with over-steepen walls around them which are filled with sea water. (sometimes called arm of the sea) Fjords are often set in a U-shaped valley. Fjords are found mainly in Norway, Chile, New Zealand, Canada, Greenland, and the U.S. state of Alaska..jpeg)
C) Hanging Valleys: - Hanging Valleys are found high up on the sides of larger U-shaped valleys. The ice has also melted in the hanging valleys, but because the land here is so much higher than in the larger U-shaped valley, water in the hanging valley forms waterfalls..jpeg)
Q. 12 Give the difference between Glacial Valleys/ Troughs and River Valleys. Answer Key Points: -Glacial Valley River Valley1. Definition- Glacial valley are formed when glaciers moves from a higher altitudes to a lower altitude due raise in temperature.
- River valley is caused by the flow of water in which soil erosion makes valley due to friction.
2. Area- The formation of glacial valleys does not depend on the gradient but only the volume of the glacier.
- The formation of the river valley is dependent on the gradient as they are formed due to the kinetic energy of rivers falling from a steep height.
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3. Shape- Glacial valleys are usually U-shaped. They are wide.
- River valleys are V- shaped. They are deeper.
4. Location- Glacial valleys are common near the North and South Poles and can also be seen near mountain ranges where the glaciers have receded (पुन: विकास).
- They are mainly found the near mountain ranges.
5. Origin- Most of the glacial valleys seen today were formed during ice age (Pleistocene era).
- River valleys are recent formations.
6. Examples- Yosemite (USA), The Frades Valley (Brazil), Glacier National Park, Montana (USA), Calchaquí Valleys (Argentina) etc. are the examples of glacial valleys.
- Indus Valley (Pakistan), Kashmir Valley (India), Doon Valley (India) etc. are the examples of river valleys.
Q. 13 Distinguish between till and alluvium. Answer Key Points: -1. Definition- It is the eroded material deposited by glaciers.
- It is the eroded material deposited on land by rivers.
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2. Origin- Till is glacial origin.
- Alluvium is fluvial origin.
3. Shape- Till has coarser sediments.
- Alluvium has non-coarser (fine particles) sediments.
4. Composition- Tills are generally unmixed coarse and fine rock fragments angular to sub angular in shape.
- Alluvium is loose, unconsolidated sediments of clay, silt and sand.
Q. 14 Glacial valleys show up many linear depositional forms. Give their locations and names. OrExplain the depositional landforms made by Glaciers. Answer Key Points: - The depositional landforms formed by glaciers are: -1) Moraines: - A moraine is material left (called till) behind by a moving glacier. This material is usually soil and rock. Just as rivers carry along all types of debris and silt that builds up to form deltas, glaciers transport all types of dirt and rock masses that build up to form moraines..jpeg)
2) Eskers: - Eskers are ridges made of sands and gravels, deposited by glacial melt-water flowing through tunnels within and underneath glaciers, or through melt-water channels on top of glaciers..jpeg)
3) Outwash Plains: - Outwash plains are expansive, generally flat areas formed by deposition of eroded materials such as gravel, silt, sand and clay. Outwash plains are formed in front of a glacier and are where material is deposited over a wide area, carried out from the glacier by meltwater. They are dominated by braided rivers when the glacier is actively melting..jpeg)
4) Drumlins: - Drumlins are smooth oval shaped ridge-like features composed mainly of glacial till with some masses of gravel and sand. They may measure up to 1 km in length and 30 m or so in height and 500 m wide. A drumlin, from the Irish word droimnín ("littlest ridge"), first recorded in 1833. Drumlins may comprise layers of clay, silt, sand, gravel and boulders in various proportions. (In geology, a boulder is a rock fragment with size greater than 256 millimeters in diameter. Smaller pieces are called cobbles and pebbles.).jpeg)
Q. 15 Explain different types of Moraines with diagram. Answer Key Points: - Different types of moraines are: -1) Terminal Moraine: - A terminal moraine is also sometimes called an end moraine. It forms at the very end of a glacier. At a terminal moraine, all the debris that was scooped up and pushed to the front of the glacier is deposited as a large clump of rocks, soil, and sediment. Scientists study terminal moraines to see where the glacier flowed and how quickly it moved..jpeg)
2) The Lateral Moraines: - They form along the sides parallel to glacial valleys. These moraines partly or fully owe their origin to glacio- fluvial waters pushing up materials to the sides of glaciers. The glacier pushes material up the sides of the valley at about the same time, so lateral moraines usually have similar heights.3) Supraglacial Moraine: - A supraglacial moraine is material on the surface of a glacier. Lateral and medial moraines can be supraglacial moraines. Supraglacial moraines are made up of rocks and Earth that have fallen on the glacier from the surrounding landscape. Dust and dirt left by wind and rain become part of supraglacial moraines. Sometimes the supraglacial moraine is so heavy; it blocks the view of the ice river underneath.4) Medial Moraines: - A medial moraine is found on top of and inside an existing glacier. Medial moraines are formed when two glaciers meet. Two lateral moraines from the different glaciers are pushed together. This material forms one line of rocks and dirt in the middle of the new, bigger glacier..jpeg)
5) Ground Moraines: - Many valley glaciers retreating rapidly leave an irregular sheet of till over their valley floors. Such deposits varying greatly in thickness and in surface topography are called Ground moraines. Ground moraines are the most common type of moraine and can be found on every continent.
Q. 16 Distinguish between river Alluvial Plains and Glacial Outwash Plains. Answer Key Points: -1. Definition- The alluvial plains are caused by the weathering that is caused by the water currents in the seas, river or lakes or the water flows from higher lands to low lands.
- An outwash plain is a plain formed by the sedimentary deposits by a glacier when it melts.
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2. Composition- These landforms are made up of the deposition of sediment over a long period of time from the fluvial movement to form alluvial soil.
- Slow and continuous glacial movement takes place over time to cause sizable erosive work to produce a glacial plain.
3. Specialty- They are more fertile plains as they are composed of fine particles.
- They are less fertile plains as they are composed of coarse particles.
Q. 17 What are the various differences between a high rocky coast and a low sedimentary coast in terms of processes and landforms? Answer Key Points: -1. Definition- They are shores that do not show any depositional landform initially.
- They are the shores where rivers appears extends their length by building coastal plains and deltas.
2. Shape- At high rocky coasts waves break with great force, against the land shaping the hill sides into cliffs.
- Here cost line became smooth due to occasional incursions of water in the form of lagoons and tidal creeks.
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3. Specialty- Erosion features dominant on high rocky coasts.
- Depositional features dominant on low sedimentary coasts.
4. Landforms- Bars are formed due to materials which fall off and removed from sea cliffs.
- Marshes and Swamps may abound along the coasts.
5. Examples- West coast of India is the example of a high rocky coast.
- East coast of India is the example of a low sedimentary coast.
Q. 18 Explain the erosional landforms created by waves and currents. Answer Key Points: -1) Wave-Cut Cliffs: - A wave-cut platform, shore platform, coastal bench, or wave-cut cliff is the narrow flat area often found at the base of a sea cliff or along the shoreline of a lake, bay, or sea that was created by erosion..jpeg)
2) Terraces: - Marine terraces are formed by coastal erosion and reflect the history of the rise and fall of sea level over time. However, marine terraces are only found along coastlines where the land is rising. In areas where the land is sinking they are submerged or buried by younger sediments..jpeg)
3) Sea stacks: - A stack or sea stack is a geological landform consisting of a steep and often vertical column or columns of rock in the sea near a coast, formed by wave erosion. Stacks are formed over time by wind and water, processes of coastal geomorphology..jpeg)
4) Sea Cave: - A sea cave, also known as a littoral cave, is a type of cave formed mainly by the wave action of the sea, ocean or lake. Sea caves occur on almost every cliffed coast where the waves break directly on a rock cliff and are formed by mechanical erosion that is responsible for the majority of inland caves..jpeg)
5) Sea Arc: - Sea Arch also known as Marine Arch, Marine Bridge or Sea Bridge is an opening through a headland, formed by wave erosion or solution which leaves a bridge of rock over the water..jpeg)
Q. 19 What are different depositional landforms created by Oceans or Waves? Answer Key Points: -Sea waves also deposit their eroded materials. It gives birth to following landforms.1) Beaches: - A beach is a narrow, gently sloping strip of land that lies along the edge of an ocean, lake, or river dominated by deposition. Materials such as sand, pebbles, rocks, and seashell fragments cover beaches. Most of the sediment making up the beaches comes from land carried by the streams and rivers or from wave erosion. Beaches are temporary features..jpeg)
2) Dunes: - Coastal dunes are a ridge, or a series of ridges, that form at the back of a beach and differ from most other constructional coastal landforms in that they are formed by the movement of air (Aeolian transport) rather than by tidal, wave, or current action. Beaches are characteristic of shorelines that may occur as patches along even the rugged shores..jpeg)
3) Bars: - A ridge of sand and shingle formed in the sea in the off-shore lying approximately parallel to the coast is called an off-shore bar. A bar is created when there is a gap in the coastland with water in it. They form sandy banks with the sea on one side and lagoons on the other side..jpeg)
4) Barriers: - Barrier also known as Barrier Beaches are long, narrow islands of sediments that run parallel to the shore and are detached from it..jpeg)
5) Spits: - A spit is an extended stretch of beach material that projects out to sea and is joined to the mainland at one end. Spits are also created by deposition. Spits are formed where the prevailing wind blows at an angle to the coastline, resulting in long shore drift..jpeg)
Q. 20 How does wind perform its task in desert areas? Is it the only agent responsible for the erosional features in the deserts? Answer Key Points: -- 1) The desert floors get heated up too much and too quickly because of being dry and barren.
- 2) The heated floors heat up the air directly above them and result in upward movements in the hot lighter air with turbulence, and any obstructions in its path sets up eddies, whirlwinds, updrafts and downdrafts.
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- 3) Winds also move along the desert floors with great speed and the obstructions in their path create turbulence.
- 4) There are storm winds as well which are very destructive. Winds cause deflation, abrasion and impact.
- 5) Deflation includes lifting and removal of dust and smaller particles from the surface of rocks.
- 6) In the transportation process sand and silt act as effective tools to abrade the land surface.
- 7) The impact is simply sheer force of momentum which occurs when sand is blown into or against a rock surface. It is similar to sand- blasting operation.
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- 8) The wind action creates a number of interesting erosional and depositional features in the deserts.
No, wind is not the only agent responsible for the erosional features in the deserts. Wind is one of the two dominant agents in hot deserts. The other one is rain or sheet-wash.
Q. 21 Explain the landforms created by erosion through wind. Answer Key Points: -Important erosional landforms created by wind are as follows: -1) Pediments: - Gently inclined rocky floors close to the mountains at their foot with or without a thin cover of debris are called pediments. Such rocky floors form through the erosion of mountain front through a combination of lateral erosion by streams and sheet flooding. A pediment is a gently sloping erosion surface or plain of low relief formed by running water in arid or semiarid region at the base of a receding mountain front..jpeg)
2) Pediplains: - The term is used in geology and Geomorphology, and it is derived from the Latin words pes, which means "genitive case," and pedis, which means "foot." Pediment. A pediplain is an extensive plain or low featureless plains formed by wind erosion. The processes through which pediplains forms is known as pediplanation. Theformation of a pediplain relies on erosion, which is the force behind the creation of a pediment..jpeg)
3) Playas: - Playa, (Spanish: shore or beach) also called pan, flat, or dry lake, flat-bottom depression found in interior desert basins within arid and semiarid regions. These depressions periodically covered by water that slowly filtrates into the ground water system or evaporates into the atmosphere and due to gradual deposition of sediment (salt, sand, and mud) from basin margins, a nearly level plain called ‘Playa Plains’ forms at the centre of the basin. Such types of shallow lakes are called as playa lakes..jpeg)
4) Deflation Hollows: - Weathered mantle from over the rocks or bare soil, gets blown out by persistent movement of wind currents in one direction. This process may create shallow depressions called deflation hollows..jpeg)
5) Caves: - Deflation also creates numerous small pits or cavities over rock surfaces. The rock faces suffer impact and erosion of wind-borne sand and first shallow depressions called blow outs are created, and some of the blow outs become deeper and wider fit to be called caves..jpeg)
6) Mushroom, Table and Pedestal Rocks: - Mushroom Tables / Mushroom rocks also known as pedestal rocks or a rock pedestal are Ventifacts (a stone shaped by the erosive action of windblown) in the shape of a mushroom. In deserts, a greater amount of sand and rock particles are transported close to the ground by the winds which cause more bottom erosion in overlying rocks than the top. Sometimes, the top surface is broad like a table top and remained lower portion stand out like pedestals..jpeg)
Q. 22 Explain the depositional landforms made by wind. Answer Key Points: -Wind is the most powerful agent of erosion and deposition in the desert areas. Depending upon the velocity of wind, different sizes of grains are moved along the floors by rolling or saltation and carried in suspension and in this process of transportation itself, the materials get moved.1) Barchans: - A barchan or barkhan dune is a crescent-shaped dune. Barchans are formed when the top of the crescent faces the wind direction. The term was introduced in 1881 by Russian naturalist Alexander von Middendorf, for crescent-shaped sand dunes in Turkestan and other inland desert regions..jpeg)
2) Parabolic: - Parabolic dunes form when sandy surfaces are partially covered with vegetation. That means parabolic dunes are reversed barchans with wind direction being the same..jpeg)
3) Seif: - Seif is a long, narrow sand dune or chain of dunes, generally oriented in a direction parallel to the prevailing wind. Seif is similar to barchan but Seif has only one wing or point. This happens when there is shift in wind conditions. The lone wings of seifs can grow very long and high..jpeg)
4) Longitudinal Dunes: - Large, elongated dunes lying parallel to the prevailing wind direction are called longitudinal dunes. Longitudinal dunes usually have symmetrical cross sections. They generally form in areas that are located behind an obstacle where sand is abundant and the wind is constant and strong. They appear as long ridges of considerable length but low in height..jpeg)
5) Transverse Dunes: - They are aligned perpendicular to wind direction. These dunes form when the wind direction is constant and the source of sand is an elongated feature at right angles to the wind direction. They may be very long and low in height. When sand is plenty, quite often, the regular shaped dunes coalesce and lose their individual characteristics..jpeg)
Q. 23 Give the difference between different types of sand dunes. Answer Key Points: - There are two types of sand dunes: -1) Sand Dunes in Deserts: - Dry hot deserts are good places for sand dune formation. Obstacles to initiate dune formation are equally important. There can be a great variety of dune forms. Crescent shaped dunes or barchans, parabolic dunes, longitudinal dunes and Transverse dunes etc..jpeg)
2) Sand Dunes formed by Waves: - The sandy beach which appears so permanent may be reduced to a very narrow strip of coarse pebbles in some other season. Most of the beaches are made up of sand sized materials. Beaches called shingle beaches contain excessively small pebbles and even cobbles. Sand dunes forming long ridges parallel to the coastline are very common along low sedimentary coasts..jpeg)
Question Bank
Q1. Explain the main two landform forming factors with example.Q2. Discuss about the main three controlling factors which can upset the normal landform developmental processes?Q3. Write a short note on monadnocks.Q4. Explain the formation of peneplain.Q5. Explain the main features of several stages of river.Q6. Differentiate between gorge and canyon.Q7. Distinguish between potholes and plunge pools.Q8. Differentiate between entrench meander and meander over floodplains.Q9. What is river terraces? What are the factors of the formation of river terraces?Q10. Explain the process of formation of alluvial fans or delta or floodplains or natural levees or point bars or meanders or ox-bow lakes or braided channels.Q11. Discuss about erosional and depositional landforms by rivers.Q12. Explain the erosional landforms created on the karst topography OR erosional landforms created by ground water.Q13. Discuss about the deposional landforms created by ground water OR deposional landfroms created within the limestone cave.Q14. What are the erosional and deposional landforms created by glacier? - Briefly explain each landforms with diagram.Q15. What is wave-cut platform?Q16. What are the erosional and deposional features of ocean wave? - Explain with diagram.Q17. Discuss about erosional and depositional landforms created by wind with diagram.Q18. Explain the main three factors which can upset the systematic and sequential stages in the development and evolution of landforms.
Q. 1 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 Key Points: -
Erosion in Humid Regions: -
Areas which receive heavy rainfall running water is considered the most important of the geomorphic agents in bringing about the degradation of the land surface. 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 over steep gradients. With time, stream channels over steep gradients turn gentler due to continued erosion, and as a consequence, lose their velocity, facilitating active deposition.
Erosion Over Slopes: -
There may be more depositional forms associated with streams flowing over steep slopes as compared to rivers flowing over medium to gentle slopes. The gentler the river channels in gradient or slope, the greater is the deposition. When the stream beds turn
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gentler due to continued erosion, downward cutting becomes less dominant and lateral erosion of banks increases and as a result the hills and valleys are reduced to plains.
Erosion in Dry Regions: -
In dry regions, most of the landforms are formed by the erosion and deposition of flood sheet. Although, in deserts, rain is scarce, it comes down speedily in a short period of time. The desert rocks lack of vegetation, exposed to mechanical and chemical
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weathering processes due to drastic diurnal temperature changes, decay faster and the torrential rains help in removing the weathered materials easily. That means, the weathered debris in deserts is moved by not only wind but also by rain/sheet wash.
Q. 2 Explain the different stages of a river.
Answer Key Points: -
A river passes through three stages like a human being: youth, mature and old.
Youth Stage: -
- 1) In youthful stage, streams flow in a shallow v-shaped valleys over the original slope.
- 2) In this stage down cutting and headward erosion are done by running water.
- 3) There are no floodplains but water divides are common.
- 4) George, canyon v-shaped valley, waterfall and rapids etc. are the main features created by river in the stage.
Mature Stage: -
- 1) In the mature stage river flow in a large basin with a plenty of water.
- 2) In this stage lateral or side cutting is most common.
- 3) Waterfalls and rapids disappear. Flood plains and valley pains are formed.
- 4) River meandering, oxbow lakes and floodplains are the main features created by river.
Old Stage: -
- 1) In the old stage river expands and flows at slow speed.
- 2) River does not do any erosional activity & deposition is the main work done by the river.
- 3) In this stage deltas and floodplains are formed.
- 4) Esturies, floodplains, deltas and natural levees etc. are the main features created by river.
Q. 3 Explain the erosional features made by rivers in their course. Or
Explain the landforms that are seen in upper part of the river.
Answer Key Points: - In upper part of the river, following landforms are formed: -
1) V-Shaped Valleys: - Valleys start as small and narrow rills which gradually develop into long and wide gullies. Due to continue erosion these gullies further becomes deeper and wider to give rise to valleys. V shaped valley is formed in the areas of sufficient
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rainfall where the rocks are not very hard down cutting and side cutting are done by river water and a v shaped valley is formed.
2) Gorge: - A gorge is a deep valley with very steep to straight sides. A gorge is almost equal in width at its top as well as its bottom. The term “gorge” is often used to mean “canyon,” but a gorge is almost always steeper and narrower than a canyon.
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3) Canyon: - A canyon is a deep, narrow valley with steep sides. “Canyon” comes from the Spanish word cañon, which means “tube” or “pipe.” A canyon is characterised by steep step-like side slopes and may be as deep as a gorge. A canyon is wider at its top than at its bottom. In fact, a canyon is a variant of gorge.
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4) Waterfall: - When the river water falls down almost vertically form a sufficient height along the course of the river it forms a waterfall.
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5) Rapids: - Sometimes there is a band of hard rock along the base of the river which makes it jump over or fall downwards. This lead to formation of rapids at the river basin.
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6) Pothole and Plunge Pools: - Potholes are the large circular depressions on the base of the river or waterfall formed by (plucking up) erosion of running water. Due to continue erosion of the base level potholes grows in size and they are called plant poles.
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7) Incised or Entrenched Meanders: - They are very deep and wide menders cut in hard rocks by the action of river. They develop over original surface in the starting stages of a river due to erosion or uplift of land.
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8) River Terraces: - The step like formation on rivers walls are found on both side of the river valley and represent old valley floor levels. They may occur at the same elevation on the both side of the rivers in which they are called paired terraces but when terrace is present only one side of the stream it is called the unpaired terrace.
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Q. 4 How are river terrace formed?
Answer Key Points: -
River terrace are basically products of erosion as they result due to vertical erosion by the stream into its own depositional flood plains. The terraces may result due to: -
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- 1) Seepage of water after a peak flow.
- 2) Change in hydrological regimes due to climatic changes.
- 3) Tectonic uplift of land.
- 4) Sea level changes in case of rivers closer to the sea.
Q. 5 Explain the depositional landforms made by rivers.
Answer Key Points: -
The transporting power of river decreases due to decrease in the speed and volume of its water so the river starts depositing its load which forms different types of depositional features. Some of them are: -
1) Alluvial Fans: - An alluvial fan is a triangle-shaped deposit of alluvial sediments such as gravel, sand, and silt. Alluvial fans are formed when streams flowing from higher levels break into foot slope plains of low gradient.
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2) Deltas: - Delta is a triangular shaped deposition of sediments at the mouth of a river before it enters into any water body. This occurs where a river enters an ocean, sea, estuary, lake, reservoir, or another river that cannot carry away the supplied sediment.
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3) Floodplains: - Floodplain is a neighboring area of a river which gets flooded almost every year during the heavy rainfall. Most floodplains are formed by deposition of sediments like sand, silt and clay on the inside of river meanders and by overbank flow.
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4) Natural Levees: - Levees occur in the lower course of a river when there is an increase in the volume of water flowing downstream and flooding occurs. 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. It is formed when the movement of water pushes sediment to the side of rivers and creeks.
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5) Point Bars: - A point bar is a depositional feature made of alluvium that accumulates on the inside the bend of streams and rivers below the slip-off slope. Point bars are found in abundance in mature or meandering streams.
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6) Meander and Ox-bow Lake: - Meander is defined as the winding curve in the course of river. Meanders form when water in the river erodes the banks on the outside of the channel and deposits sediment on the inside of the channel. Meanders only occur on flat land where the river is large and established. An oxbow lake is a U-shaped lake that forms when a wide meander of a river is cut off, creating a free-standing body of water.
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7) Braided Channels / Streams: - It is a drainage network formed when river water is divided into number of converging and diverging channels separated by low sandbanks. These sandbanks are called braid bars or, in English usage, aits or eyots.
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Q. 6 Meander is not a landform but is only a type of channel pattern. Justify. Or
What are the causes behind formation of river meander landform?
Answer Key Points: -
The formation of meanders is due to both deposition and erosion and meanders gradually migrate downstream. It is not a landform but is only a type of channel pattern because of: -
- 1) Propensity of water flowing over very gentle gradients to work laterally on the banks.
- 2) Unconsolidated nature of alluvial deposits making up the banks with many irregularities which can be used by water exerting pressure.
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- 3) Coriolis force acting on the fluid water deflecting, it like it deflects the wind. When the gradient of the channel becomes extremely low, water flows leisurely and starts working laterally.
- 4) Normally, in meanders of large rivers, there is active deposition along the convex bank and undercutting along the concave bank.
- 5) The concave bank is known as cut-off bank which shows up as a steep scarp and the convex bank presents a long, gentle profile and is known as slip-off bank.
- 6) As meanders grow into deep loops, the same may get cut-off due to erosion at the inflection points and are left as Ox-bow.
Q. 7 Limestone behaves 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 Key Points: -
- 1) Many depositional forms develop within the limestone caves. The chief chemical in limestone is calcium carbonate which is easily soluble in carbonated water i.e. carbon dioxide absorbed rainwater.
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- 2) This calcium carbonate is deposited when the water carrying it in solution evaporates or loses its carbon dioxide as it trickles over rough rock surfaces. Stalactites, Stalagmites and Pillars Stalactites hang as icicles of different diameters.
- 3) Normally they are broad at their bases and taper towards the free ends showing up in a variety of forms. Stalagmites rise up from the floor of the caves. In fact, stalagmites form due to dripping water from the surface or through the thin pipe, of the stalactite, immediately below it.
- 4) The results of the work of groundwater cannot be seen in all types of rocks. But in rocks like limestones or dolomites rich in calcium carbonate, the surface water as well as groundwater through the chemical process of solution and precipitation deposition develops varieties of landforms.
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- 5) These two processes of solution and precipitation are active in limestones or dolomites occurring either exclusively or interbedded with other rocks. Therefore, underground flow of water is more common than surface run off in limestone areas.
Q. 8 Explain the landforms made by erosion caused by Groundwater.
Answer Key Points: -
Important landforms made by erosion are as follows: -
1) Pools: - These are conical shaped pits whose depth is three to nine meters. The width of the mouth is more than one meter. 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 limestone through soil.
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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 meters to a hectare and with depth from a less than half a meter to thirty meters or more.
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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.
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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.
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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.
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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 cave 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.
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Q. 9 Explain the depositional landforms formed by groundwater.
Answer Key Points: -
The depositional landform formed by the groundwater are: -
- 1) Stalactites: - Stalactites hang as icicles of different diameter. Normally they are broad at their bases and taper towards the free ends showing up in variety of forms.
- 2) Stalagmites: - Stalagmites rise up from the floor of the caves. They are formed due to dripping water from the surface or through the thin pipe of stalactite. Stalagmite may take the shape of a column, a disc with either a smooth, rounded bulging end or a miniature crater like depression.
- 3) Pillars: - The stalagmite and stalactite eventually fuse to give rise to column and pillars.
Q. 10 How do glaciers accomplish the work of reducing high mountains into low hills and plains?
Answer Key Points: -
- 1) 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.
- 2) A glacier in its valley is slow unlike water flow. The movement could be a few centimeters to a few meters a day or even less or more. Glaciers move basically because of the force of gravity.
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- 3) 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.
- 4) Glaciers can cause significant damage to even un-weathered rocks and can reduce high mountains into low hills and plains.
- 5) 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.
Q. 11 Explain the erosional landforms made by Glaciers.
Answer Key Points: -
1) Cirque: - They are a bowl-shaped depression formed due to the erosional activity of glaciers on mountain and valley side walls at high elevations. Cirques are the most common of landforms in glaciated mountains. A lake of water can be seen quite often within the cirques after the glacier disappears. Such lakes are called cirque or tarn lakes.
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2) Horns and Serrated Ridges: - Horns form through head ward erosion of the cirque walls. If three or more radiating glaciers cut head-ward until their cirques meet, high, sharp pointed and steep sided peaks called horns form.
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3) Arete: - Arête, (French: “ridge”), in geology, a sharp-crested narrow ridge of rock which separates two valleys. It is typically formed when two glaciers erode parallel U-shaped valleys. Arêtes can also form when two glacial cirques erode head-wards towards one another, although frequently this results in a saddle-shaped pass, called a col.
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4) Glacial Valleys/Troughs: - Glacial troughs, or glaciated valleys, are long, U-shaped valleys formed by glaciers when a glacier travels across and down a slope. Troughs tend to have flat valley floors and steep, straight sides. Glaciers carve a set of distinctive, steep-walled, flat-bottomed valleys e.g. U-shaped valleys, fjords, and hanging valleys.
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A) U-shaped valley: - U-shaped valleys, trough valleys or glacial troughs, are formed by the process of glaciation (A glacial period within an ice age). Glaciation develops in established v-shaped river valleys where the ice erodes the surrounding rocks to create a “U” shaped valley with a flat bottom and steep sides. Glacier movement is driven by gravity.
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B) Fjords: - A fjords also spelled fiords are long, deep, narrow glaciated valleys with over-steepen walls around them which are filled with sea water. (sometimes called arm of the sea) Fjords are often set in a U-shaped valley. Fjords are found mainly in Norway, Chile, New Zealand, Canada, Greenland, and the U.S. state of Alaska.
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C) Hanging Valleys: - Hanging Valleys are found high up on the sides of larger U-shaped valleys. The ice has also melted in the hanging valleys, but because the land here is so much higher than in the larger U-shaped valley, water in the hanging valley forms waterfalls.
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Q. 12 Give the difference between Glacial Valleys/ Troughs and River Valleys.
Answer Key Points: -
Glacial Valley River Valley
1. Definition
- Glacial valley are formed when glaciers moves from a higher altitudes to a lower altitude due raise in temperature.
- River valley is caused by the flow of water in which soil erosion makes valley due to friction.
2. Area
- The formation of glacial valleys does not depend on the gradient but only the volume of the glacier.
- The formation of the river valley is dependent on the gradient as they are formed due to the kinetic energy of rivers falling from a steep height.
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3. Shape
- Glacial valleys are usually U-shaped. They are wide.
- River valleys are V- shaped. They are deeper.
4. Location
- Glacial valleys are common near the North and South Poles and can also be seen near mountain ranges where the glaciers have receded (पुन: विकास).
- They are mainly found the near mountain ranges.
5. Origin
- Most of the glacial valleys seen today were formed during ice age (Pleistocene era).
- River valleys are recent formations.
6. Examples
- Yosemite (USA), The Frades Valley (Brazil), Glacier National Park, Montana (USA), Calchaquí Valleys (Argentina) etc. are the examples of glacial valleys.
- Indus Valley (Pakistan), Kashmir Valley (India), Doon Valley (India) etc. are the examples of river valleys.
Q. 13 Distinguish between till and alluvium.
Answer Key Points: -
1. Definition
- It is the eroded material deposited by glaciers.
- It is the eroded material deposited on land by rivers.
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2. Origin
- Till is glacial origin.
- Alluvium is fluvial origin.
3. Shape
- Till has coarser sediments.
- Alluvium has non-coarser (fine particles) sediments.
4. Composition
- Tills are generally unmixed coarse and fine rock fragments angular to sub angular in shape.
- Alluvium is loose, unconsolidated sediments of clay, silt and sand.
Q. 14 Glacial valleys show up many linear depositional forms. Give their locations and names. Or
Explain the depositional landforms made by Glaciers.
Answer Key Points: -
The depositional landforms formed by glaciers are: -
1) Moraines: - A moraine is material left (called till) behind by a moving glacier. This material is usually soil and rock. Just as rivers carry along all types of debris and silt that builds up to form deltas, glaciers transport all types of dirt and rock masses that build up to form moraines.
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2) Eskers: - Eskers are ridges made of sands and gravels, deposited by glacial melt-water flowing through tunnels within and underneath glaciers, or through melt-water channels on top of glaciers.
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3) Outwash Plains: - Outwash plains are expansive, generally flat areas formed by deposition of eroded materials such as gravel, silt, sand and clay. Outwash plains are formed in front of a glacier and are where material is deposited over a wide area, carried out from the glacier by meltwater. They are dominated by braided rivers when the glacier is actively melting.
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4) Drumlins: - Drumlins are smooth oval shaped ridge-like features composed mainly of glacial till with some masses of gravel and sand. They may measure up to 1 km in length and 30 m or so in height and 500 m wide. A drumlin, from the Irish word droimnín ("littlest ridge"), first recorded in 1833. Drumlins may comprise layers of clay, silt, sand, gravel and boulders in various proportions. (In geology, a boulder is a rock fragment with size greater than 256 millimeters in diameter. Smaller pieces are called cobbles and pebbles.)
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Q. 15 Explain different types of Moraines with diagram.
Answer Key Points: -
Different types of moraines are: -
1) Terminal Moraine: - A terminal moraine is also sometimes called an end moraine. It forms at the very end of a glacier. At a terminal moraine, all the debris that was scooped up and pushed to the front of the glacier is deposited as a large clump of rocks, soil, and sediment. Scientists study terminal moraines to see where the glacier flowed and how quickly it moved.
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2) The Lateral Moraines: - They form along the sides parallel to glacial valleys. These moraines partly or fully owe their origin to glacio- fluvial waters pushing up materials to the sides of glaciers. The glacier pushes material up the sides of the valley at about the same time, so lateral moraines usually have similar heights.
3) Supraglacial Moraine: - A supraglacial moraine is material on the surface of a glacier. Lateral and medial moraines can be supraglacial moraines. Supraglacial moraines are made up of rocks and Earth that have fallen on the glacier from the surrounding landscape. Dust and dirt left by wind and rain become part of supraglacial moraines. Sometimes the supraglacial moraine is so heavy; it blocks the view of the ice river underneath.
4) Medial Moraines: - A medial moraine is found on top of and inside an existing glacier. Medial moraines are formed when two glaciers meet. Two lateral moraines from the different glaciers are pushed together. This material forms one line of rocks and dirt in the middle of the new, bigger glacier.
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5) Ground Moraines: - Many valley glaciers retreating rapidly leave an irregular sheet of till over their valley floors. Such deposits varying greatly in thickness and in surface topography are called Ground moraines. Ground moraines are the most common type of moraine and can be found on every continent.
Q. 16 Distinguish between river Alluvial Plains and Glacial Outwash Plains.
Answer Key Points: -
1. Definition
- The alluvial plains are caused by the weathering that is caused by the water currents in the seas, river or lakes or the water flows from higher lands to low lands.
- An outwash plain is a plain formed by the sedimentary deposits by a glacier when it melts.
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2. Composition
- These landforms are made up of the deposition of sediment over a long period of time from the fluvial movement to form alluvial soil.
- Slow and continuous glacial movement takes place over time to cause sizable erosive work to produce a glacial plain.
3. Specialty
- They are more fertile plains as they are composed of fine particles.
- They are less fertile plains as they are composed of coarse particles.
Q. 17 What are the various differences between a high rocky coast and a low sedimentary coast in terms of processes and landforms?
Answer Key Points: -
1. Definition
- They are shores that do not show any depositional landform initially.
- They are the shores where rivers appears extends their length by building coastal plains and deltas.
2. Shape
- At high rocky coasts waves break with great force, against the land shaping the hill sides into cliffs.
- Here cost line became smooth due to occasional incursions of water in the form of lagoons and tidal creeks.
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3. Specialty
- Erosion features dominant on high rocky coasts.
- Depositional features dominant on low sedimentary coasts.
4. Landforms
- Bars are formed due to materials which fall off and removed from sea cliffs.
- Marshes and Swamps may abound along the coasts.
5. Examples
- West coast of India is the example of a high rocky coast.
- East coast of India is the example of a low sedimentary coast.
Q. 18 Explain the erosional landforms created by waves and currents.
Answer Key Points: -
1) Wave-Cut Cliffs: - A wave-cut platform, shore platform, coastal bench, or wave-cut cliff is the narrow flat area often found at the base of a sea cliff or along the shoreline of a lake, bay, or sea that was created by erosion.
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2) Terraces: - Marine terraces are formed by coastal erosion and reflect the history of the rise and fall of sea level over time. However, marine terraces are only found along coastlines where the land is rising. In areas where the land is sinking they are submerged or buried by younger sediments.
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3) Sea stacks: - A stack or sea stack is a geological landform consisting of a steep and often vertical column or columns of rock in the sea near a coast, formed by wave erosion. Stacks are formed over time by wind and water, processes of coastal geomorphology.
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4) Sea Cave: - A sea cave, also known as a littoral cave, is a type of cave formed mainly by the wave action of the sea, ocean or lake. Sea caves occur on almost every cliffed coast where the waves break directly on a rock cliff and are formed by mechanical erosion that is responsible for the majority of inland caves.
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5) Sea Arc: - Sea Arch also known as Marine Arch, Marine Bridge or Sea Bridge is an opening through a headland, formed by wave erosion or solution which leaves a bridge of rock over the water.
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Q. 19 What are different depositional landforms created by Oceans or Waves?
Answer Key Points: -
Sea waves also deposit their eroded materials. It gives birth to following landforms.
1) Beaches: - A beach is a narrow, gently sloping strip of land that lies along the edge of an ocean, lake, or river dominated by deposition. Materials such as sand, pebbles, rocks, and seashell fragments cover beaches. Most of the sediment making up the beaches comes from land carried by the streams and rivers or from wave erosion. Beaches are temporary features.
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2) Dunes: - Coastal dunes are a ridge, or a series of ridges, that form at the back of a beach and differ from most other constructional coastal landforms in that they are formed by the movement of air (Aeolian transport) rather than by tidal, wave, or current action. Beaches are characteristic of shorelines that may occur as patches along even the rugged shores.
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3) Bars: - A ridge of sand and shingle formed in the sea in the off-shore lying approximately parallel to the coast is called an off-shore bar. A bar is created when there is a gap in the coastland with water in it. They form sandy banks with the sea on one side and lagoons on the other side.
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4) Barriers: - Barrier also known as Barrier Beaches are long, narrow islands of sediments that run parallel to the shore and are detached from it.
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5) Spits: - A spit is an extended stretch of beach material that projects out to sea and is joined to the mainland at one end. Spits are also created by deposition. Spits are formed where the prevailing wind blows at an angle to the coastline, resulting in long shore drift.
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Q. 20 How does wind perform its task in desert areas? Is it the only agent responsible for the erosional features in the deserts?
Answer Key Points: -
- 1) The desert floors get heated up too much and too quickly because of being dry and barren.
- 2) The heated floors heat up the air directly above them and result in upward movements in the hot lighter air with turbulence, and any obstructions in its path sets up eddies, whirlwinds, updrafts and downdrafts.
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- 3) Winds also move along the desert floors with great speed and the obstructions in their path create turbulence.
- 4) There are storm winds as well which are very destructive. Winds cause deflation, abrasion and impact.
- 5) Deflation includes lifting and removal of dust and smaller particles from the surface of rocks.
- 6) In the transportation process sand and silt act as effective tools to abrade the land surface.
- 7) The impact is simply sheer force of momentum which occurs when sand is blown into or against a rock surface. It is similar to sand- blasting operation.
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- 8) The wind action creates a number of interesting erosional and depositional features in the deserts.
No, wind is not the only agent responsible for the erosional features in the deserts. Wind is one of the two dominant agents in hot deserts. The other one is rain or sheet-wash.
Q. 21 Explain the landforms created by erosion through wind.
Answer Key Points: -
Important erosional landforms created by wind are as follows: -
1) Pediments: - Gently inclined rocky floors close to the mountains at their foot with or without a thin cover of debris are called pediments. Such rocky floors form through the erosion of mountain front through a combination of lateral erosion by streams and sheet flooding. A pediment is a gently sloping erosion surface or plain of low relief formed by running water in arid or semiarid region at the base of a receding mountain front.
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2) Pediplains: - The term is used in geology and Geomorphology, and it is derived from the Latin words pes, which means "genitive case," and pedis, which means "foot." Pediment. A pediplain is an extensive plain or low featureless plains formed by wind erosion. The processes through which pediplains forms is known as pediplanation. The
formation of a pediplain relies on erosion, which is the force behind the creation of a pediment.
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3) Playas: - Playa, (Spanish: shore or beach) also called pan, flat, or dry lake, flat-bottom depression found in interior desert basins within arid and semiarid regions. These depressions periodically covered by water that slowly filtrates into the ground water system or evaporates into the atmosphere and due to gradual deposition of sediment (salt, sand, and mud) from basin margins, a nearly level plain called ‘Playa Plains’ forms at the centre of the basin. Such types of shallow lakes are called as playa lakes.
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4) Deflation Hollows: - Weathered mantle from over the rocks or bare soil, gets blown out by persistent movement of wind currents in one direction. This process may create shallow depressions called deflation hollows.
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5) Caves: - Deflation also creates numerous small pits or cavities over rock surfaces. The rock faces suffer impact and erosion of wind-borne sand and first shallow depressions called blow outs are created, and some of the blow outs become deeper and wider fit to be called caves.
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6) Mushroom, Table and Pedestal Rocks: - Mushroom Tables / Mushroom rocks also known as pedestal rocks or a rock pedestal are Ventifacts (a stone shaped by the erosive action of windblown) in the shape of a mushroom. In deserts, a greater amount of sand and rock particles are transported close to the ground by the winds which cause more bottom erosion in overlying rocks than the top. Sometimes, the top surface is broad like a table top and remained lower portion stand out like pedestals.
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Q. 22 Explain the depositional landforms made by wind.
Answer Key Points: -
Wind is the most powerful agent of erosion and deposition in the desert areas. Depending upon the velocity of wind, different sizes of grains are moved along the floors by rolling or saltation and carried in suspension and in this process of transportation itself, the materials get moved.
1) Barchans: - A barchan or barkhan dune is a crescent-shaped dune. Barchans are formed when the top of the crescent faces the wind direction. The term was introduced in 1881 by Russian naturalist Alexander von Middendorf, for crescent-shaped sand dunes in Turkestan and other inland desert regions.
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2) Parabolic: - Parabolic dunes form when sandy surfaces are partially covered with vegetation. That means parabolic dunes are reversed barchans with wind direction being the same.
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3) Seif: - Seif is a long, narrow sand dune or chain of dunes, generally oriented in a direction parallel to the prevailing wind. Seif is similar to barchan but Seif has only one wing or point. This happens when there is shift in wind conditions. The lone wings of seifs can grow very long and high.
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4) Longitudinal Dunes: - Large, elongated dunes lying parallel to the prevailing wind direction are called longitudinal dunes. Longitudinal dunes usually have symmetrical cross sections. They generally form in areas that are located behind an obstacle where sand is abundant and the wind is constant and strong. They appear as long ridges of considerable length but low in height.
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5) Transverse Dunes: - They are aligned perpendicular to wind direction. These dunes form when the wind direction is constant and the source of sand is an elongated feature at right angles to the wind direction. They may be very long and low in height. When sand is plenty, quite often, the regular shaped dunes coalesce and lose their individual characteristics.
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Q. 23 Give the difference between different types of sand dunes.
Answer Key Points: -
There are two types of sand dunes: -
1) Sand Dunes in Deserts: - Dry hot deserts are good places for sand dune formation. Obstacles to initiate dune formation are equally important. There can be a great variety of dune forms. Crescent shaped dunes or barchans, parabolic dunes, longitudinal dunes and Transverse dunes etc.
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2) Sand Dunes formed by Waves: - The sandy beach which appears so permanent may be reduced to a very narrow strip of coarse pebbles in some other season. Most of the beaches are made up of sand sized materials. Beaches called shingle beaches contain excessively small pebbles and even cobbles. Sand dunes forming long ridges parallel to the coastline are very common along low sedimentary coasts.
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Question Bank
Q1. Explain the main two landform forming factors with example.
Q2. Discuss about the main three controlling factors which can upset the normal landform developmental processes?
Q3. Write a short note on monadnocks.
Q4. Explain the formation of peneplain.
Q5. Explain the main features of several stages of river.
Q6. Differentiate between gorge and canyon.
Q7. Distinguish between potholes and plunge pools.
Q8. Differentiate between entrench meander and meander over floodplains.
Q9. What is river terraces? What are the factors of the formation of river terraces?
Q10. Explain the process of formation of alluvial fans or delta or floodplains or natural levees or point bars or meanders or ox-bow lakes or braided channels.
Q11. Discuss about erosional and depositional landforms by rivers.
Q12. Explain the erosional landforms created on the karst topography OR erosional landforms created by ground water.
Q13. Discuss about the deposional landforms created by ground water OR deposional landfroms created within the limestone cave.
Q14. What are the erosional and deposional landforms created by glacier? - Briefly explain each landforms with diagram.
Q15. What is wave-cut platform?
Q16. What are the erosional and deposional features of ocean wave? - Explain with diagram.
Q17. Discuss about erosional and depositional landforms created by wind with diagram.
Q18. Explain the main three factors which can upset the systematic and sequential stages in the development and evolution of landforms.
