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Day 27: Geography - Geography (Day 26 to 36)

Landforms and its Evolution

Landforms and its Evolution

Work of River

  • Rivers or streams are of mainly two types: perennial and ephemeral. Perennial rivers hold water flow throughout the year which is permanent and are found in humid regions. Many of the major streams and most tributaries carry water occasionally during the wet season or during or after rainfall. These impermanent flows are called ephemeral streams, which are mostly found in arid climates.
  • The work of running water begins with the effect of precipitation. Rivers receive water primarily from rainfall, snow, hail or sleet, and the same water reaches finally to the sea after undergoing several processes. Due to gravitational force, the water flows downstream, and at the same time some forces, called frictional forces also resist the downstream flow. Water flow depends mainly on these two basic forces of gravitation and friction. Stream erosion is actively engaged in removing materials from its floor or bed, and sides of the channel. The capacity of eroding material generally depends on its energy.
  • The river erodes both vertical and lateral. The force of the flowing water sometimes can break the rocks of valley sides and erodes poorly consolidated alluvial materials such as sand, silt, clay and gravel due to the impact of currents of a channel. This erosion process may be called hydraulic action. It is the mechanical erosion, which helps to loosen and remove the materials of rocks by water alone. While removing the materials, the stream channel undergoes some type of chemical process of solution or acid reactions, which dissolute the soluble materials. This process is known as corrosion. For example, the river flowing in limestone region dissolves the rocks along the joints and forms cavities in them.
  • The pebbles and rock fragments strike against the rocks along the river bed and walls that results in weakening the rock to break down. The broken material moves down with the flowing water. In this type of abrasion process, the river makes its course deeper and wider. A cylindrical hole carved by the action of the swiftly moving river, termed as a pothole, is produced by the stream abrasion. Some other important features of abrasion are plunge pools, chutes and troughs. The rock fragments like boulders and cobbles collide against each other while moving with the water and are disintegrated into smaller grains of sand and silt. This process is termed as attrition. Because of the erosion, channel widening generally occurs where weathering and hill slope processes contribute to overall widening of the valley.

Processes involved in the river erosion

The Course of a River

Youth 

  • Streams are few during 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 fat with marshes, swamp and lakes. Meanders if present 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.

Mature 

  • 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 fat and broad inter stream areas and swamps and marshes of youth disappear and the stream divides turn sharp. Waterfalls and rapids disappear.

Old 

  • 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 fat with lakes, swamps and marshes. Most of the landscape is at or slightly above sea level.

Erosional Landforms

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 recognized.
  • A gorge is a deep valley with very steep to straight sides and 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.
  • Valley types depend upon the type and structure of rocks in which they form. For example, canyons commonly form in horizontal bedded sedimentary rocks and gorges form in hard rocks.

Potholes and Plunge Pools:

  • Over the rocky beds of hill-streams more or less circular depressions called potholes form because of stream erosion aided by the abrasion of rock fragments.
  • 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. These pools also help in the deepening of valleys.
  • Waterfalls are also transitory like any other landform and will recede gradually and bring the floor of the valley above waterfalls to the level below.

Incised or Entrenched Meanders

  • In streams that flow rapidly over steep gradients, normally erosion is concentrated on the bottom of the stream channel.
  • Also, in the case of steep gradient streams, lateral erosion on the sides of the valleys is not much when compared to the streams flowing on low and gentle slopes.
  • Because of active lateral erosion, streams flowing over gentle slopes develop sinuous or meandering courses.
  • It is common to find meandering courses over floodplains and delta plains where stream gradients are very gentle.
  • But very deep and wide meanders can also be found cut in hard rocks. Such meanders are called incised or entrenched meanders.
  • Meander loops develop over original gentle surfaces in the initial stages of development of streams and the same loops get entrenched into the rocks normally due to erosion or slow, continued uplift of the land over which they start.
  • They widen and deepen over time and can be found as deep gorges and canyons in hard rock areas.
  • They give an indication on the status of original land surfaces over which streams have developed.

River Terraces 

  • River terraces are surfaces marking old valley floor or floodplain levels.
  • They may be bedrock surfaces without any alluvial cover or alluvial terraces consisting of stream deposits. River terraces are basically products of erosion as they result due to vertical erosion by the stream into its own depositional floodplain.
  • There can be a number of such terraces at different heights indicating former river bed levels.
  • The river terraces may occur at the same elevation on either side of the rivers in which case they are called paired terraces.

Typical landforms formed by the work of river

Depositional Landforms

Alluvial fans 

  • Alluvial fans 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 and they appear as high cones with steep slope in arid and semi-arid climates.

Deltas

  • Deltas are 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 as a low cone.
  • Unlike in alluvial fans, the deposits making up deltas are very well sorted with clear stratification.
  • The coarsest materials settle out first and the finer fractions like silts and clays are carried out into the sea.
  • As the delta grows, the river distributaries continue to increase in length and delta continues to build up into the sea

Floodplains

  • Deposition develops a floodplain just as erosion makes valleys.
  • 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.
  • A river bed made of river deposits is the active floodplain. The floodplain above the bank is inactive floodplain.
  • Inactive floodplain above the banks basically contain two types of deposits — flood deposits and channel deposits.
  • In plains, channels shift laterally and change their courses occasionally leaving cut-of courses which get filled up gradually.
  • Such areas over flood plains built up by abandoned or cut-of 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.

Meanders 

  • In large flood and delta plains, rivers rarely flow in straight courses.
  • Loop-like channel patterns called meanders develop over food and delta plains.
  • Meander is not a landform but is only a type of channel pattern.
  • This is because of (i) propensity of water flowing over very gentle gradients to work laterally on the banks; (ii) unconsolidated nature of alluvial deposits making up the banks with many irregularities which can be used by water exerting pressure laterally; (iii) coriolis force acting on the fluid water defecting it like it defects the wind.
  • When the gradient of the channel becomes extremely low, water flows leisurely and starts working laterally.
  • Slight irregularities along the banks slowly get transformed into a small curvature in the banks; the curvature deepens due to deposition on the inside of the curve and erosion along the bank on the outside.
  • If there is no deposition and no erosion or undercutting, the tendency to meander is reduced. Normally, in meanders of large rivers, there is active deposition along the concave bank and undercutting along the convex bank.
  • The concave bank is known as cut-of bank which shows up as a steep scarp and the convex bank present a long, gentle profile. As meanders grow into deep loops, the same may get cut-of due to erosion at the infection points and are left as ox-bow lakes.              

Work of Groundwater

  • The work of groundwater involves chemical processes of rock weathering at the surface or below the surface by the movement of groundwater. The corrosion or solution process is one of the most effective ways of erosion process in the erosional work of groundwater. Dissolution is a process by which rock or water combines with a solution or a group of solutes. Solubility depends on the mineral content of rock, for example halite is more soluble compared to gibbsite. Most of the rocks are soluble to some extent in water. The work of groundwater particularly in limestone, dolomite, and chalk areas produces distinctive assemblage of landforms at the surface which is termed as karst topography. Limestone is composed of calcium carbonate which reacts strongly with carbonic acid solution to produce calcium bicarbonate. This calcium bicarbonate compound tends to be dissolved in water.
  • Carbon dioxide (CO2 ) gas is present in the atmosphere, and is dissolved on rainwater, lakes and oceans. The rainwater mixed with carbon dioxide becomes an active solvent. When this solvent percolates into the rocks, it dissolves and disintegrates the rock particles by solution. CO2 when dissolved in water forms weak carbonic acid (H2O + CO2 ®H2CO3 ). Carbonic acid is the main solvent in karst landscape.
  • Dolomite rock is calcium magnesium carbonate rock that seems to be slightly less soluble than limestone under normal conditions, but characteristically behaves as limestone in natural waters. Solution along joints and cracks in limestone beneath the surface are slowly widened which results into the formation of underground gullies and caverns.
  • These are formedboth horizontally and vertically. Caves are excellent traps for sediments, and they allow the water flowing from a sink or percolation point to a spring or a seepage point. Calcite precipitation produces fashionable and decorative landforms inside caves are called speleothems. Speleothems are mainly made up of carbonate deposits and are formed by water through dripping and/ or flow. When water and CO2 leaves from the solution, the calcite compound is deposited. Much of the deposition occurs on the sides of the cavern, and also from the roof and the floor.
  • Stalagmites and stalactites are the most common types of speleothems. Stalagmites grow from the floor by the water flow towards the sides and the roof, whereas stalactites form from the water which drips from the ceilings. The largest cave system in the world is Mammoth Cave, USA that occupies more than 560 kms of known passages and particularly one passage at vertical depth of 110 m.
  • The term karst denotes both a set of processes and an assemblage of landforms. A variety of small scale solutional features and sculptures like grooves or holes are found on limestone and dolomite surfaces on the ground or in caves known as karren. These are also called lapies in French and lapiaz in Spanish. These features widely occur in groups and are called karren fields. Karren is resulted from the surface dissolution of limestone and is notably not developed on chalk because of its high porous nature.
  • The most common surface features of karst landscapes are sinkholes or dolines. These are simply closed depressions formed in circular or ellipsoidal in shape. These range from less than a meter to several hundred meters diameter and from a few meters to over a hundred meters of depth. The combination of processes namely dissolution of surface carbonate rocks, cave collapse, subsidence, and piping are involved in creating several types of sinkholes.
  • Uvalas are formed by the connection of more than one sinkhole, and consist of flat floors. They are generally larger than small dolines.
  • Due to the decalcification of impure limestone, there is an accumulation of material inside sinkholes called Terra Rossa. A polje is a large closed depression with flattened floors that is predominantly observed in temperate regions.
  • The word polje in Slavic language means a cultivable field. These are also named as campo or piano in Italy, plans in France, hojos in Cuba, pla in Spain and wangs in Malaysia.
  • More porous material contains large space due to which it can hold more water. The high permeability materials are able to transmit underground water through these interconnected openings.

Process of underground water forming various features

  • Rivers flowing through karst landscape involved in erosion process leads to the formation of various types of valleys. They particularly form gorges more frequently by the cavern collapse. The river flow gradually decreases its water at a particular point leading to the creation of a blind valley, where the river’s total load flows into the interior of the karst mass. Dry valleys are more or less like normal river valleys that lack fluvial channels in their beds and are found mainly at the head waters of the channel system. They are common in karst landscapes and characteristically have steep slopes and flat floors in limestone regions.

Work of Wind

  • Wind is a geomorphic agent in all terrestrial environments. It is a potent agent only in dry areas with fine-grained soils and sediments and little or no vegetation. It is limited by a protective cover of vegetation and moist soil, which helps to bind soil particles together. Winds may erode, transport, and deposit materials, and are effective agents in regions with sparse vegetation and a large supply of unconsolidated sediments. Although water is a much more powerful eroding force than wind, Aeolian processes are important in arid environments such as deserts.
  • Wind can erode desert rocks in two ways:
  • Deflation: the removal of fine, loose particles from the surface of rocks.
  • Abrasion: small particles being carried by the wind scrape of particles from the rock surface. It then transports the eroded material by three processes:
  • Suspension: very small particles (<0.15mm) are picked up and carried by the wind.
  • Saltation: small particles (0.15-0.25mm) are temporarily lifted from the ground and bounce along the surface.
  • Surface Creep: larger particles (>0.25mm) are hit and pushed along the ground by particles being moved by saltation.

Erosional Landforms

Yardangs

Yardangs are narrow, streamlined ridges that are usually three to four times longer than they are wide.  They are made up of long ridges of hard resistant rocks alternating with narrow furrows of soft rocks. Here, both the bands of hard and soft rocks aligned vertically to the direction of the blowing prevailing winds. The process of abrasion is accelerated in the course of the blowing prevailing winds, assisting in wearing the soft bands of rocks into narrow corridors between the hard layers. Eventually, the bands of hard rocks remain standing high above the soft bands that have been worn into narrow corridors.

Zeugen

A zeugen is a tabular mass of resistant rock, standing prominently in the desert. It is usually composed of alternating layers of hard and soft rocks. These alternating bands of rock usually lie horizontal on top of one and another. The softer rock layer usually lies beneath a surface layer of more resistant rock. The sculpturing effects of wind abrasion wear them into a furrow and ridge looking landscape. Insolation weathering enhances this activity.

Playas

Playas are by far the most prominent landforms in the deserts. In basins with mountains and hills around and along, the drainage is towards the centre of the basin and due to gradual deposition of sediment from basin margins, a nearly level plain forms at the centre of the basin. In times of sufficient water, this plain is covered up by a shallow water body. Such types of shallow lakes are called as playas where water is retained only for short duration due to evaporation and quite often the playas contain good deposition of salts. The playa plain covered up by salts is called alkali fiats.

Deflation Hollows and Caves

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. Deflation also creates numerous small pits or cavities over rock surfaces. The rock faces suffer impact and abrasion 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.

Mushroom, Table and Pedestal Rocks: Many rock-outcrops in the deserts easily susceptible to wind deflation and abrasion are worn out quickly leaving some remnants of resistant rocks polished beautifully in the shape of mushroom with a slender stalk and a broad and rounded pear shaped cap above. Sometimes, the top surface is broad like a table top and quite often, the remnants stand out like pedestals.

Depositional Landforms

Wind is a good sorting agent. 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 sorted. When the wind slows or begins to die down, depending upon sizes of grains and their critical velocities, the grains will begin to settle. So, in depositional landforms made by wind, good sorting of grains can be found. Sand accumulations come in a range of sizes and forms. Deposition may occur as sheets of sand (dune fields and sand seas) or loess or as characteristic dunes.

Ripples: Wind ripples are the smallest Aeolian bed form. They are regular, wave like undulations lying at right-angles to the prevailing wind direction.

Loess: Loess is terrestrial sediment composed largely of windblown silt particles made of quartz. It covers some 5-10 per cent of the Earth’s land surface, much of it forming a blanket over pre-existing topography that may be up to 400 m thick. Loess requires three things:

  • a source of silt;
  • wind to transport the silt; and
  • a suitable site for deposition and accumulation

Dunes: Dunes are collections of loose sand built piece meal by the wind. They usually range from a few metres across and a few centimetres high to 2 km across and 400m high. Sand dunes form where there is a source of sand. Dune sand is usually composed of quartz, which is extremely hard and doesn’t easily decay. Dune sand grains are beautifully rounded by abrasion.

Crescent shaped dunes called barchans with the points or wings directed away from wind direction i.e., downwind, form where the wind direction is constant and moderate and where the original surface over which sand is moving is almost uniform. Parabolic dunes form when sandy surfaces are partially covered with vegetation. That means parabolic dunes are reversed barchans with wind direction being the same.

Seif also called linear dunesis similar to barchans with a small difference. 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. Longitudinal dunes form when supply of sand is poor and wind direction is constant. They appear as long ridges of considerable length but low in height.

Transverse dunes 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. Most of the dunes in the deserts shift and a few of them will get stabilised especially near human.

Work of Sea Waves

  • Waves and currents of oceans create a special and spectacular landscape in coastal terrain. Let us understand the process of moving water by waves and ocean currents. In specific terms, waves are agents of erosion and currents are responsible for transportation and deposition. Waves are important agents involved in the activity of shoreline changes and it is to remember that waves are formed by wind blowing over a water surface. The wind action near the surface is comparatively high than the deep water. Wind waves operate on all shorelines, from small ponds, lakes, to the larger ocean basins. Waves are formed in water in orbital motion that decreases towards bottom called as wave of oscillation.

Wave action in deep and shallow water

  • Movement of the water in this process is very weak at a depth approximately equal to half of their wavelength (L/2). As the wave passes, the water moves upward and downward called wave crest and wave trough. The horizontal distance from trough to trough or from crest to crest is called wavelength (L), which is proportional to the wind velocity. The vertical distance from crest to trough is known as wave height. Water moves faster on the crest than in the trough. Sea waves move through the sea in the direction of the wind, and its height depends on wind speed, wind duration and distance of the wind. When the wave reaches to shallow water, it will tilt forward then the wave breaks abruptly. After breaking of the wave, the force of the wave translates up thebeach and creates a swash. The resultant wave return flow forms backwash, which creates a rip-current. This rip current is a localized current which causes unexpected danger for bath takers. In shallow water, inshore parts of a wave crest moves more slowly than the offshore parts. When a wave approaches the coast, its crest tends to run parallel to the topographic contours of the seafloor. This process is called wave refraction.
  • Another important action of ocean water is called tide, which has a regular and predictable pattern. The tides rise and fall in a cycle that produces two high tides and two low tides in a day. Tides are movements of the ocean water formed due to the gravitational attraction of the Sun and the Moon. They bring changes in water levels along the coasts. Almost all coasts experience rising tide and falling tides.
  • They are two types a) high spring tides are higher than normal high tides that occur when the Earth, the Moon and the Sun are in the same alignment, b) low neap tides, alternate with spring tides, occur when the Moon and the Sun are perpendicular to one another with respect to the Earth. Tides control the vertical ranges of wave action. A large tidal range is able to produce a broad shore zone whereas a small tidal range may create small wave energy at constant level. Ocean currents also play an important role in the circulation of sediment supply. Ocean currents may be described as mass movement of water circulated by wind in the open sea.
  • Waves are responsible for erosion along the coastline. Because of corrosion, the soluble rocks to some extent get dissolved in sea water by wave action. But this process is less significant in the work of waves as solution is slow due to high calcium carbonate distribution in the ocean water. Abrasion plays an important part in shoreline processes.
  • Waves mobilize the smooth rounded stones, sand, pebbles, and small boulders to hit against rocky cliffs and shore that lead to the intense erosion. The resultant debris is broken, smoothened, and made smaller by further wave action, and most of it is transported towards the sea due to artillery force of the waves. An enormous amount of pressure is mounted on rock joints and cracks of the coastal rocks leading to the formation of cleavages.
  • Unlike corrosion or abrasion, the rock materials are disintegrated into finer or very small fragments, and are easily transported by under-tow and rip-currents towards the sea. This process is called attrition.

Various coastal landforms

  • Waves form a variety of landscape features. Steep slope or vertical wall of the rock or sediment formed in the shore of the sea due to the undercutting process of the waves is called a cliff. The steepness of the cliff generally depends on bedrock lithology and geological structure, and weathering process. Cliffs are considered to be the transition zone between the continent and the sea. Along the joints and bedding planes, the waves put pressure and actively cut at the base of the cliff which leads to the formation of a concave shape. This type of concave cut is termed as notch or nip. Due to further under cutting, the upper part of the cliff looks hanging and it may collapse at some point of time. Wave cut platform or terraces are formed during the cliff recession process at cliff’s face. When softer part of the platform gets slow erosion, while the harder part remains uneroded, the feature is known as rock reef.
  • Gorge, sea cave, sea arch, sea stack, bay, bar, spits, etc. are commonly formed due to the intense erosion occurring at the structural weakness of the rocks. Gorge is one type of erosional feature formed by the wave action along weak fault lines or joints in rock with a low dip. Gorges are also called as geos or yawns in Scotland and zawns in South-West England. When waves forcefully strike against the closely spaced jointed rocks, the soft rock part getscut down and eroded away, which results in the formation of sea caves.
  • Sea archs form when two caves on opposite sides of top portion are united. When the arch falls in and the remnant part remains standing on wave cut platform, the resultant feature is called sea stack. When the material is eroded easily than the surrounding composed material of the coast, bay is formed.
  • Bars are formed in inter-tidal and sub-tidal zones. They are in various shapes like linear, sinuous or crescent, and are generally parallel or oblique to the coast. When sand and/or gravel gets accumulated by waves, tides and wind action, a barrier is formed.
  • Spits are sub-aerial outcrops of sediments consisting of sand and gravel which are deposited as a result of longshore drift currents. Barrier spits are formed at the mouths of estuaries. A strand of beach sand that connects islands to islands or islands to the mainland forms a tombolo.
  • Sediment is accumulated along the landward margins of the ocean is known as a beach. Beaches are generally composed of various locally available abundant materials and also by the sediment derived from cliffs and mountains and rivers. Some beaches are pebble beaches commonly observed in the middle and high latitudes, and some are sandy in nature occurring along tropical coasts. The materials are transported from one place to another due to wave action on the coast.
  • During storms, the force of the wave is higher which causes to dismantling of rocks and widening of the fractures. In the beach, accumulation and loss of sand depend mainly on the level of wave activity. Low energetic waves can move the sand towards the beach face because of reducing backwash.
  • Due to high energetic waves, beaches tend to affect erosion because of the movement of sand towards open water by strong backwash.
  • Estuaries are long and narrow tidal inlets and are partially enclosed but connected to the open sea.

Work of Glaciers

  • The subject of glaciology deals with the behaviour of glacial ice. Glacier is formed due to the accumulation of huge volume of ice above snow line, which is the zone between permanent and seasonal snow, under extreme cold climatic conditions.
  • There are two types of glaciers namely valley glaciers (mountain or Alpine glaciers) and continental glaciers. Valley glaciers can be long or short, narrow or wide, single or multiple branches of tributaries like rivers. Their width is small compared to their length that varies from a fraction of kilometer to few kilometers.
  • Each glacier is a stream of ice that flows down the valley from snow accumulation center near its head. On the other hand, continental glaciers exist in the form of large scale ice sheets in nonmountainous areas of the continents. These enormous ice masses flow out in all directions from one or more accumulation centers. The poles receive very low total annual solar energy which results in the large scale accumulation of ice.
  • Example of this category is Greenland in the Northern Hemisphere and Antarctica in the Southern Hemisphere.

Various landforms formed by glacial action

Erosional Landforms

  • Cirques are bowl shaped features at the head of a glacial valley. They have steep headwalls and a low threshold of rock or moraine. A tarn (lake) may  fill a cirque after the glacier is gone. Cirques may begin in nivation basins where freeze thaw beneath a snow bank breaks up rock which is then removed by creep, solifluction, and rill wash, thereby hollowing out a depression. Bergschrund are large, very deep glacial crevasses near the headwall of a cirque- between the ice and headwall. Cirques are more common on north and east facing slopes in northern hemisphere because these sides remain cooler with less afternoon sunlight to melt the snow.
  • Horns are steep faceted mountain peaks, sculpted and surrounded by three or more cirques and their steep headwalls.
  • Arêtes are high, pinnacled ridges formed by cirques eroding each side of the ridge.
  • Cols are low areas between higher stretches of a ridge (arête) where opposing cirques have started to cut through the ridge.
  • Glacial Valleys have a characteristic parabolic shape, which vary from the prototypical deep, steep-sided, fat bottomed, U-shape valley, which forms in resistant bedrock, to wide shallow troughs, which form in less resistant bedrock.

Depositional Landforms

Glaciers are capable of carrying a huge amount of rock debris over considerable distances. Glacial deposition is mainly of two types: deposition directly from the ice after melting; and by melt water flowing from a glacier.

Moraines

  • The material deposited from the ice is known as till, and the landforms created by such deposits are called moraines.
  • Till is a glacial deposit composed of various sizes of boulders or stones in combination of smooth mixture of clay, silt or sand.
  • The large bulk of this unsorted debris eroded by glacial melt water streams are redeposited at the low layers of ice in the form of moraines. The transportational work of glaciers generally involves when rock debris are transported on its surface are called as supraglacial or along its bed known as subglacial or somewhere in between the two are termed as englacial.
  • The glacier carries frost shattered material from the valley walls and once it is fallen onto the ice surface forming a long ridge of material at the sides of the glacier are called lateral moraines. Medial moraines are formed by the merger of two lateral moraines where two valley glaciers flow together. The rock fragments also accumulate as thin layer of sediments on the surface through upward shearing of the ice and by down wasting which releases the englacial materials.
  • Englacial debris is found in the main body of the glacier and is covered from subsequent snow fall. Some of the supraglacial material may fall into crevasses and become englacial.
  • Overtime some materials moves downward through the ice due to ice melting and is also buried by overriding ice. Much of the materials deposited beneath the glacier is termed as ground moraines.

Drumlins

  • Drumlins are egg shaped features composed of till that are formed in the shape of streamlined asymmetrical hills. They form parallel to the direction of the ice movement.

Eskers

  • Eskers are long narrow ridges composed largely of sand and gravel deposited by stream flowing tunnels within or beneath the ice tunnels.

Kames

  • Kames are steep mounds and conical hills commonly formed with eskers. These are individual mounds or hills composed of stratified drift. They may represent former crevasse filling, which comprises of stratified debris that enters crevasses though supraglacial streams.

Outwash Plains

  • At the end of the glaciation on land, the vast quantity of sediment is deposited as flat alluvial aprons that lead the stream channel to become braided. This type of broad accumulation of stratified material is said to be outwash plains.

Kettels

  • Kettels form as a block of stagnant ice, which is decayed and buried. These water filled irregular depression or pits are called kettel lakes.

GK through MAP (Snippets)

Physical Division in Utter Pradesh

Physical Division in Utter Pradesh

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