Landforms And Cycle Of Erosion

• Glacial landforms and Cycle of Erosion
• Marine landforms and Cycle of Erosion
• Arid landforms and Cycle of Erosion
• Karst landforms and Cycle of Erosion

Fluvial Landforms And Cycle Of Erosion

• The landforms created as a result of degradational action (erosion) or aggradational work (deposition) of running water are called fluvial landforms.
• The fluvial processes may be divided into three physical phases – erosion, transportation and deposition.

Fluvial Depositional Landforms

• The depositional action of a stream is influenced by stream velocity and the volume of river load.
• The decrease in stream velocity reduces the transporting power of the streams which are forced to leave some load to settle down.
• Increase in river load is effected through accelerated rate of erosion in the source catchment areas consequent upon deforestation.
• Various landforms resulting from fluvial deposition are as follows:

Alluvial Fans and Cones

• When a stream leaves the mountains and comes down to the plains, its velocity decreases due to a lower gradient.
• As a result, it sheds a lot of material, which it had been carrying from the mountains, at the foothills.
• This deposited material acquires a conical shape and appears as a series of continuous fans. These are called alluvial fans.
• Such fans appear throughout the Himalayan foothills in the north Indian plains.

Natural Levees

• These are narrow ridges of low height on both sides of a river, formed due to deposition action of the stream, appearing as natural embankments.
• These act as a natural protection against floods but a breach in a levee causes sudden floods in adjoining areas, as it happens in the case of the Hwang Ho river of China.

Delta

• A delta is a tract of alluvium at the mouth of a river where it deposits more material than can be carried away.
• The river gets divided into distributaries which may further divide and rejoin to form a network of channels.

A delta is formed by a combination of two processes:

1. load-bearing capacity of a river is reduced as a result of the check to its speed as it enters a sea or lake, and
2. clay particles carried in suspension in the river coagulate in the presence of salt water and are deposited.

• The finest particles are carried farthest to accumulate as bottom-set beds.
• Depending on the conditions under which they are formed, deltas can be of many types.

Glacial Landforms And Cycle Of Erosion

• A glacier is a moving mass of ice at speeds averaging few meters a day.
• Types of Glaciers: continental glaciers, ice caps, piedmont glaciers and valley glaciers.
• The continental glaciers are found in the Antarctica and in Greenland. The biggest continental ice sheet in
• Ice caps are the covers of snow and ice on mountains from which the valley or mountain glaciers originate.
• The piedmont glaciers form a continuous ice sheet at the base of mountains as in southern Alaska.
• The valley glaciers, also known as Alpine glaciers, are found in higher regions of the Himalayas in our country and all such high mountain ranges of the world.
• The largest of Indian glaciers occur in the Karakoram range, viz. Siachen (72 km), while Gangotri in Uttar Pradesh (Himalayas) is 25.5 km long.
• A glacier is charged with rock debris which are used for erosional activity by moving ice.
• A glacier during its lifetime creates various landforms which may be classified into erosional and depositional landforms.

Cirque/Corrie

• Hollow basin cut into a mountain ridge.
• It has steep sided slope on three sides, an open end on one side and a flat bottom.
• When the ice melts, the cirque may develop into a tarn lake.

Glacial Trough

• Original stream-cut valley, further modified by glacial action.
• It is a ‘U’ Shaped Valley. It at mature stage of valley formation.
• Since glacial mass is heavy and slow moving, erosional activity is uniform – horizontally as well as vertically.
• A steep sided and flat bottomed valley results, which has a ‘U’ shaped profile.

Hanging Valley

• Formed when smaller tributaries are unable to cut as deeply as bigger ones and remain ‘hanging’ at higher levels than the main valley as discordant tributaries.
• A valley carved out by a small tributary glacier that joins with a valley carved out by a much larger glacier.

• Steep-sided, sharp-tipped summit with the glacial activity cutting into it from two

Horn

• Ridge that acquires a ‘horn’ shape when the glacial activity cuts it from more than two sides.

D-Fjord

• Steep-sided narrow entrance-like feature at the coast where the stream meets the coast.
• Fjords are common in Norway, Greenland and New Zealand.

Glacial Depositional Landforms

Outwash Plain

• When the glacier reaches its lowest point and melts, it leaves behind a stratified deposition material, consisting of rock debris, clay, sand, gravel etc. This layered surface is called till plain or an outwash plain.

Esker

• Winding ridge of un-assorted depositions of rock, gravel, clay etc. running along a glacier in a till plain.
• The eskers resemble the features of an embankment and are often used for making roads.

Kame Terraces

• Broken ridges or un-assorted depositions looking like hump in a till plain.

Drumlin

• Inverted boat-shaped deposition in a till plain caused by deposition.

Kettle Holes

• Formed when the deposited material in a till plain gets depressed locally and forms a basin.

Moraine

• General term applied to rock fragments, gravel, sand, etc. carried by a glacier.
• Depending on its position, the moraine can be ground moraine and end moraine.

Glacial Cycle Of Erosion

Youth

• The stage is marked by the inward cutting activity of ice in a cirque.
• Aretes and horns are emerging. The hanging valleys are not prominent at this stage.

Maturity

• Hanging valleys start emerging. The opposite cirques come closer and the glacial trough acquires a stepped profile which is regular and graded.

Old Age

• Emergence of a ‘U’-shaped valley marks the beginning of old age.
• An outwash plain with features such as eskers, kame terraces, drumlins, kettle holes etc. is a prominent development.

• Marine Landforms And Cycle Of Erosion

  • Sea waves, aided by winds, currents, tides and storms carry on the erosional and depositional processes.
  • The erosive work of the sea depends upon size and strength of waves, slope, height of the shore between low and high tides, shape of the coast, composition of rocks, depth of water, human activity etc.
  • The wave pressure compresses the air trapped inside rock fissures, joints, faults, etc. forcing it to expand and rupture the rocks along weak points. This is how rocks undergo weathering under wave action.
  • Waves also use rock debris as instruments of erosion (glaciers are quite good at this). These rock fragments carried by waves themselves get worn down by striking against the coast or against one another.
  • The solvent or chemical action of waves is another mode of erosion, but it is pronounced only in case of soluble rocks like limestone and chalk.

  Marine Erosional Landforms

  Chasms

  • These are narrow, deep indentations (a deep recess or notch on the edge or surface of something) carved due to headward erosion (downcutting) through vertical planes of weakness in the rocks by wave action.
  • With time, further headward erosion is hindered by lateral erosion of chasm mouth, which itself keeps widening till a bay is formed.

  

  Wave-Cut Platform

  • When the sea waves strike against a cliff, the cliff gets eroded (lateral erosion) gradually and retreats.
  • The waves level out the shore region to carve out a horizontal plane or a wave-cut platform.
  • The bottom of the cliff suffers the maximum intensive erosion by waves and, as a result, a notch appears at this position.

  

  Sea Cliff

  • Shoreline marked by a steep bank (escarpment, scarp).

  Sea Caves

  • Differential erosion by sea waves through a rock with varying resistance across its structure produces arched caves in rocks called sea caves.

  Sea Arches

  • When waves from opposite directions strike a narrow wall of rock, differential erosion of the rock leaves a bridge like structure called Sea arch.

  Stacks/Skarries/Chimney Rock

  • When a portion of the sea arch collapses, the remaining column-like structure is called a stack, skarry or chimney rock.

   

  Hanging Valleys

  • If the fluvial erosion of a stream at the shore doesn’t match the retreat of the sea, the rivers appear to be hanging over the sea. These river valleys are called hanging valleys.

  

  Blow Holes or Spouting Horns

  • The burst of water through a small hole on a sea cave due to the compression of air in the cave by strong waves. They make a peculiar noise.

  

  Plane of Marine Erosion/Peneplain

  • The eroded plain left behind by marine action is called a plain of marine erosion. If the level difference between this plain and the sea level is not much, the agents of weathering convert it into a peneplain.

  Marine Depositional Landforms

  

  Beach

  • This is the temporary covering of rock debris on or along a wave-cut platform.

  Bar

  • Currents and tidal currents deposit rock debris and sand along the coast at a distance from the shoreline.
  • The resultant landforms which remain submerged are called bars.
  • The enclosed water body so created is called a

  Barrier

  • It is the overwater counterpart of a bar.

  Spit and Hook

  • A spit is a projected deposition joined at one end to the headland, with the other end free in the sea.
  • The mode of formation is similar to a bar or barrier.
  • A shorter spit with one end curved towards the land is called a

  Tombolos

  • Sometimes, islands are connected to each other by a bar called tombolo.

  Marine Cycle Of Erosion

  Youth

  • The waves are very active.
  • Sea caves, arches and stalks begin to develop.
  • Cliff undercutting is pronounced and wavecut platform begins to emerge due to wave erosion.
  • By the end of youth, an irregular coastline remains.

  Maturity

  • The cliff and wave-cut platform are conspicuous.
  • Stream deposition is taking place. These valleys may be normal or of the hanging type.
  • Various landforms indicating continuous deposition are visible, such as bars, barriers and spits.

  Old Age

  • Irregularities, such as caves and arches disappear.

  Coastlines

  • The boundary between the coast (the part of the land adjoining or near the sea) and the shore (the land along the edge of a sea) is known as the coastline.

  Coastlines can be divided into the following classes:

  1. Coastline of Emergence
  2. Coastline of Submergence
  3. Neutral coastline
  4. Compound coastline
  5. Fault coastline
  • Coastline are modified either due to rise or fall in sea levels or upliftment or subsidence of land, or both.

  

  Coastlines of Emergence

  • These are formed either by an uplift of the land or by the lowering of the sea level.
  • Bars, spits, lagoons, salt marshes, beaches, sea cliffs and arches are the typical features.
  • The east coast of India, especially its south-eastern part (Tamil Nadu coast), appears to be a coast of emergence.
  • The west coast of India, on the other hand, is both emergent and submergent. The northern portion of the coast is submerged as a result of faulting and the southern portion, that is the Kerala coast, is an example of an emergent coast.
  • Coramandal coast == Tamil Nadu Coast == Coastline of emergence
  • Malabar coast == Kerala Coast == Coastline of emergence
  • Konkan coast == Maharashtra and Goa Coast == Coastline of submergence.

  Coastlines of Submergence

  • A submerged coast is produced either by subsidence of land or by a rise in sea level.
  • Ria, fjord, Dalmatian and drowned lowlands are its typical features.

  Ria

  • When a region is dissected by streams into a system of valleys and divides, submergence produces a highly irregular shoreline called ria coastline.
  • The coast of south-west Ireland is a typical example of ria coastline.

  Fjord

  • Some coastal regions have been heavily eroded by glacial action and the valley glacier troughs have been excavated below sea level.
  • After the glaciers have disappeared, a fjord coastline emerges.
  • These coasts have long and narrow inlets with very steep sides.
  • The fjord coasts of Norway are a typical example.

  

  Dalmatian

  • The Dalmatian coasts result by submergence of mountain ridges with alternating crests and troughs which run parallel to the sea coast.
  • The Dalmatian coast of Yugoslavia is a typical example.

  

  Drowned lowland

  • A drowned lowland coast is low and free from indentations, as it is formed by the submergence of a low-lying area.
  • It is characterized by a series of bars running parallel to the coast, enclosing lagoons.
  • The Baltic coast of eastern Germany is an example of this type of coastline.

  Neutral Coastlines

  • These are coastlines formed as a result of new materials being built out into the water.
  • The word ‘neutral’ implies that there need be no relative change between the level of sea and the coastal region of the continent.
  • Neutral coastlines include the alluvial fan shaped coastline, delta coastline, volcano coastline and the coral reef coastline.

  Compound Coastlines

  • Such coastlines show the forms of two of the previous classes combined, for example, submergence followed by emergence or vice versa.
  • The coastlines of Norway and Sweden are examples of compound coastlines.

  Fault Coastlines

  • Such coastlines are unusual features and result from the submergence of a downthrown block along a fault, such that the uplifted block has its steep side (or the faultline) standing against the sea forming a fault coastline.

  

  • A gully is a landform created by running water. Gullies resemble large ditches or small valleys, but are metres to tens of metres in depth and width.
    

    Arid Landforms And Cycle Of Erosion

    • Arid regions are regions with scanty rainfall. Deserts and Semi-arid regions fall under arid landforms.

    Erosional Arid Landforms

    Water Eroded Arid Landforms

    

    Rill

    • In hill slope geomorphology, a rill is a narrow and shallow channel cut into soil by the erosive action of flowing water.

  • Ravine

  • A ravine is a landform narrower than a canyon and is often the product of stream cutting erosion. Ravines are typically classified as larger in scale than gullies, although smaller than valleys.

• Badland Topography

  • In arid regions occasional rainstorms produce numerous rills and channels which extensively erode weak sedimentary formations.
  • Ravines and gullies are developed by linear fluvial erosion leading to the formation of badland topography.
  • Example: Chambal Ravines.

  

  Bolsons

  • The intermontane basins in dry regions are generally known as bolsons.

  

  Playas

  • Three unique landforms viz. pediments, bajadas and playas are typically found in bolsons.
  • Small streams flow into bolsons, where water is accumulated. These temporary lakes are called playas.
  • After the evaporation of water, salt-covered playas are called salinas.

  

  Pediments

  • In form and function there is no difference between a pediment and an alluvial fan; however, pediment is an erosional landform while a fan is a constructional one.
  • A true pediment is a rock cut surface at the foot of mountains.

  Bajada

  • Bajadas are moderately sloping depositional plains located between pediments and playa.
  • Several alluvial fans coalesce to form a bajada.

  Wind Eroded Arid Landforms

  • The wind or Aeolian erosion takes place in the following ways, viz. deflation, abrasion, and attrition.
  • Deflation == removing, lifting and carrying away dry, unsorted dust particles by winds. It causes depressions known as blow outs.
  • Abrasion == When wind loaded with sand grains erodes the rock by grinding against its walls is called abrasion or sandblasting.
  • Attrition == Attrition refers to wear and tear of the sand particles while they are being transported.

  Following are the major landforms produced by wind erosion.

  

  Deflation basins

  • Deflation basins, called blowouts, are hollows formed by the removal of particles by wind. Blowouts are generally small, but may be up to several kilometers in diameter.

  Mushroom rocks

  • A mushroom rock, also called rock pedestal or a pedestal rock, is a naturally occurring rock whose shape, as its name implies, resembles a mushroom.
  • The rocks are deformed in a number of different ways: by erosion and weathering, glacial action, or from a sudden disturbance. Mushroom rocks are related to, but different from, yardang.

  Inselbergs

  • A monadnock or inselberg is an isolated hill, knob, ridge, outcrop, or small mountain that rises abruptly from a gently sloping or virtually level surrounding plain.

  

  Demoiselles

  • These are rock pillars which stand as resistant rocks above soft rocks as a result of differential erosion of hard and soft rocks.

  Zeugen

  • A table-shaped area of rock found in arid and semi-arid areas formed when more resistant rock is reduced at a slower rate than softer rocks around it.

  Yardangs

  • Ridge of rock, formed by the action of the wind, usually parallel to the prevailing wind direction.

  Wind bridges and windows

  • Powerful wind continuously abrades stone lattices, creating holes. Sometimes the holes are gradually widened to reach the other end of the rocks to create the effect of a window—thus forming a wind window. Window bridges, are formed when the holes are further widened to form an arch-like feature.

  

  Arid Depositional Landforms

  • Landforms are also created by the depositional force of wind. These are as follows.

  Ripple Marks

  • These are depositional features on a small scale formed by saltation (he transport of hard particles over an uneven surface in a turbulent flow of air or water).

  

  Sand dunes

  • Sand dunes are heaps or mounds of sand found in deserts. Generally their heights vary from a few metres to 20 metres but in some cases dunes are several hundred metres high and 5 to 6 km long.

  Some of the forms are discussed below:

  

  Longitudinal dunes

  • Formed parallel to the wind movement. The windward slope of the dune is gentle whereas the leeward side is steep. These dunes are commonly found at the heart of trade-wind deserts like the Sahara, Australian, Libyan, South African and Thar deserts.

  Transverse dunes

  • Dunes deposited perpendicular (transverse) to the prevailing wind direction.

  Barchans

  • Crescent shaped dunes. The windward side is convex whereas the leeward side is concave and steep.

  Parabolic dunes

  • They are U-shaped and are much longer and narrower than barchans.

  Star dunes

  • Have a high central peak, radically extending three or more arms.

  Loess

  • In some parts of the world, windblown dust and silt blanket the land. This layer of fine, mineral-rich material is called loess.
  • Extensive loess deposits are found in northern China, the Great Plains of North America, central Europe, and parts of Russia and Kazakhstan.
  • The thickest loess deposits are near the Missouri River in the U.S. state of Iowa and along the Yellow River in China.
  • Loess accumulates, or builds up, at the edges of deserts. For example, as wind blows across the Gobi, a desert in Asia, it picks up and carries fine particles. These particles include sand crystals made of quartz or mica. It may also contain organic material, such as the dusty remains of skeletons from desert animals.
  • Loess often develops into extremely fertile agricultural soil. It is full of minerals and drains water very well. It is easily tilled, or broken up, for planting seeds.
  • Loess usually erodes very slowly – Chinese farmers have been working the loess around the Yellow River for more than a thousand years.

  

• Karst Landforms And Cycle Of Erosion

  • Karst is a landscape which is underlain by limestone which has been eroded by dissolution, producing towers, fissures, sinkholes, etc.
  • It is so named after a province of Yugoslavia on the Adriatic sea coast where such formations are most noticeable.
  • Karst topography is a landscape formed from the dissolution of soluble rocks such as limestone, dolomite, and gypsum.
  • It is characterized by underground drainage systems with sinkholes, caves etc..

  Conditions Essential for Full Development of Karst Topography

  • Presence of soluble rocks, preferably limestone at the surface or sub-surface level.
  • These rocks should be dense, highly jointed and thinly bedded.

  Cavern

  • This is an underground cave formed by water action by various methods in a limestone or chalk area.

  

  Arch/Natural Bridge

  • When a part of the cavern collapses the portion which keeps standing forms an arch.

  Sink Hole/Swallow Hole

  • Sink holes are funnel-shaped depressions having an average depth of three to nine metres.
  • These holes are developed by enlargement of the cracks found in such rocks, as a result of continuous solvent action of the rainwater.
  • The surface streams which sink disappear underground through swallow holes.

  

  Karst Window
  • When a number of adjoining sink holes collapse, they form an open, broad area called a karst window.

  

  Sinking Creeks/Bogas

  • In a valley, the water often gets lost through cracks and fissures in the bed. These are called sinking creeks, and if their tops are open, they are called bogas.

  

  Stalactite and Stalagmite

  • The water containing limestone in solution, seeps through the roof in the form of a continuous chain of drops.
  • A portion of the roof hangs on the roof and on evaporation of water, a small deposit of limestone is left behind contributing to the formation of a stalactite, growing downwards from the roof.
  • The remaining portion of the drop falls to the floor. This also evaporates, leaving behind a small deposit of limestone aiding the formation of a stalagmite, thicker and flatter, rising upwards from the floor.
  • Sometimes, stalactite and stalagmite join together to form a complete pillar known as the column.