23 Glacial and Periglacial Landscapes
Dr. Ramashray Prasad
Pre-requisites
Weathering, Slope Elements, Mass Wasting
Objectives
Total Six
Keywords
Periglacial , Ice Cap, Crevasses, Ablation, Moraine, Plucking And Abrasion, Cirque, Aretes, Col, Horn, Hanging Valley, Fjord, Moraine, Glacial Till, Glacio-Fluvial, Esker, Kettle, Kame, Roche Moutonnee, Drumlin, Patterned Ground, Blockfields, Pingos
Introduction
Glaciers and ice sheets are the world’s main storehouse of fresh water. They are the thick and large masses of slow moving ice under the influence of gravity. They are formed by compression of snow. The mass of ice is mostly confined in the areas where the temperature is below zero degrees Celsius. They are found in the high latitudes or high altitudes. In higher latitudes, glaciers are seen even on the flat ground. In low latitudes, the glaciers are found in the higher altitudes. Ice accumulation is possible when there is greater amount of snowfall in comparison to snowmelt. Glaciermoves downslope due to gravity. Therefore, slowly moving ice body known as glacier. Periglacial is referred to the areas at the periphery/edge of the glacier. It is characterized by low temperature. Its annual mean temperature is around zero degree Celsius. It summer season, the surface is free from ice but subsurface water is found in frozen state. Landscape is the surface of the earth as we observe while being in the field. It is basically the appearance of the land. The land itself is sculptured by many agents of erosion. Depending upon the processes of sculpturing, the landscapes are different. Glacial and periglacial landscapes refer to the land features developed due to the process of glaciations and periglaciation. In this module, we will discuss about these two processes as well as the sculptured features made by them.
Learning Objectives
After studying this module, you will be able to:
- explain the formation of glacier,
- distinguish between alpine and continental glaciation, describe the movement of an alpine glacier, explain various features formed by erosional work of glacier,
- explain various features formed by depositional work of glacier and identify the different types of moraine and their formation
Glacial and Periglacial Conditions
Glacial condition exists where the temperature is always less than zero degree Celsius. Mostly precipitation occurs in the form of snowfall in glacial areas. The annual amount of snowmelt is less than or equal to annual snowfall over the area. If snowfall is more, the glaciated area is on rise; but when it is equal to the snowfall, it is stagnant. When the snowfall is less than the snowmelt, the glaciated area is on decline. Glaciated areas always bear the ice on the surface. It is not so only when the slope is too high to sustain the ice. The accumulated ice is on slide downward. In this way, it develops a large number of features.
Periglacial condition exists in the peripheral areas of the glaciated regions. In this zone, the annual average temperature is around zero degree Celsius. In winter, there is thin layer of ice and snow accumulation but it is not the same during summer days. Even during summer days, the subsurface moisture content is found to be in a frozen condition. In the soil zone, the temperature is less than zero degree Celsius. Freezing and thawing is a normal condition which is main cause of weathering here. Both glacial and periglacial conditions are quite different from each other.
Glaciated Areas
Glaciers are found on all continents except Australia. Their widespread existence is in polar areas because of favorable conditions for the accumulation of ice. Since the Arctic is an ocean around the North Pole, the amount of glacial ice is widely variable with changing seasons, but the ice survives throughout the year. The land parts in the periphery of the Arctic Ocean like northern Canada, Alaska, Greenland and northern Eurasian region have sustaining glaciers. These landmasseshave glaciers throughout the year. The direction of the flow of ice is outward as per the slope of the area (Figure 1).
Figure 1: Ice Cover in Arctic Zone
Source: http://explanet.info/images/Ch08/08_62.jpg
Almost whole of the Antarctic continent is situated south of the Arctic Circle. Its 98 per cent area is covered with ice and only 2 per cent bare rocks are found. The Antarctica has ice sheet with an average thickness of about 2.16 Kilometers. The maximum thickness at Terre Adelie is recorded to be 4776 meter. Almost half of the coastal fringe areas is free from ice. Huge icebergs float on the ocean waters particularly in summer season (November to February) for the southern hemisphere. About 80 percent area of Greenland is under ice cover (Figure 2). The cross section drawn on the maps of Greenland and Antarctic has been drawn and the thickness of the ice over them is clearly seen.
Figure 2: Ice Cover over Antarctic and Greenland
Source: http://courses.missouristate.edu/emantei/creative/GndwGlaWnd/GreenAnt.jpg
We know that the effect of temperature is progressively reduced with increasing altitudes. It is the highest air temperature recorded at sea level and keeps on declining with increasing height. The distribution of temperature is also affected by the inclination of the sun rays. Due to this reason, the air temperature keeps on declining with increasing latitudes. That is why, the permanent snow line is different at different latitudes. Therefore, altitudes at various places where the ice cover is found is different with changing latitudes. In Polar Regions, it is available at the ground level. In equatorial zone, it is found five kilometers above the mean sea level whereas in temperate zone, it is one km to five kilometers (Figure 3). In central Africa at Kilimanjaro, it is found to be about 5500 meter, on Himalayas, it between 4500 to 6000 meter and on Alps, it is 2800 meter above mean sea level. Therefore, glaciers are found at the higher altitudes of the mountain ranges even in tropical and temperate region of the world.
Figure 3: Height of Snowline at Different Latitudes
The entire frozen water of the globe is termed as cryosphere. The cryosphere constitutes of ice and snow occupying the earth’s surface, mountains, rivers, lakes and oceans. The total amount of water stored in the cryosphere is about two percent of the total hydrosphere. Out of the total area under ice is 85.30 per cent on Antarctica and 13.27 per cent in Arctic region. Both constitutes 98.57 per cent of the glaciated area of the globe.Rest of about 1.5 per cent of the glaciated area is in other parts of the world. The details of the distribution of glaciers are given in the Table 1.
Table 1: Area and Approximate Volume of Present-day Glaciation
Source: Encyclopedia of Life Support System
Data Source: table 1
Glacier
Glacier is a creeping mass of ice. It moves very slowly. Immediate apparent movement of glacier is difficult to perceive. It takes a longer time to see the movement. The movement happens under the influence of gravity to the downslope direction. Since the glaciers are solid mass, they have enormous capacity to erode the rock and transport the rock fragments. In this process, they sculpture significant features creating distinct landscapes.But before coming to the landscapes, let us discuss about the types and their methods of erosion and transportation.
Types of Glaciers
Mountain Glacier: The accumulation of ice over the mountain slope covering large areas is called mountain glacier. It is the outward flow of ice from the icefields encompassing several peaks of the surrounding areas. It is, mostly, narrow and long because it occupies the preexisting river valley. In the higher altitude, the temperature is very low but as long as it comes down, the temperature keeps on increasing. This leads to ablation or breaking of glacier into ice pieces and ultimately melting. They are generally termed to that glaciers which are found on the mountains of tropical and temperate region. Glaciers are also found in the mountains of the polar region, but generally they are termed as polar glaciers because they occupy big continuous area of ice accumulation.
Valley Glacier: Valley glacier is a narrow strip of ice accumulation confined within the two walls of the preexisting river valley. Valley glaciers are also found on the mountain slopes. Sometimes, both of them are used as synonyms but they have slight difference. Mountain glaciers are huge in size whereas the valley glaciers are small in size and the ice is restricted within the two banks of the previously carved out river valleys. The downside terminating glacier is tongue shaped, i.e., smoothened round in appearance. Both of them are also known as Alpine glaciers. In fact, Alpine glaciers originate from the mountain summits and descend through the mountain valleys. Valley glaciers are very short in comparison to the continental glaciers. The longest of this type is less than 80km long (Table 2). The smallest may be of a few hundred meters.
Figure 4: Valley Glacier
Source: https://upload.wikimedia.org/wikipedia/commons/thumb/f/fa/Upper_Tasman_Glacier.jpg/1200px-Upper_Tasman_Glacier.jpg
Table 2: Five Longest Non-Polar Glaciers in the world
Source: http://www.worldatlas.com/articles/the-longest-non-polar-glaciers-in-the-world.html
Piedmont Glacier: When the ice mass moving through the steep surface of the mountain reaches at the foothills or the plain area, it creates piedmont glacier. Piedmont means an area from the foothills to the flat plain land. The confined ice of the valley glacier is forced to spread over a larger area because of lowering of the slope. It takes the shape of bulb-like lobes (Figure 5).
Source: http://www.atuttaneve.it/public/foto_atuttaneve/ghiacciaio-QUTTINIRPAAQ-NATIONA-%20PAR-Canada.jpg
Continental Glacier: A continuous sheet of ice occupying a very large areais known as continental glacier. The movement of the continental glacier is, normally, from the center to outward all directions (Figure 1 and 2). Relatively small sized continental glaciers are known as ice fields. Similarly, a big sized continental mass of glaciers covering enormous area is called ice sheets. Almost whole of the Antarctic and Greenland are covered with ice sheets. A thick mass of ice and snow (Figure 5) forming a glacier over a great deal of area is termed as ice cap. It may develop over the continental or on mountain glacier. Continental glaciers are very long and large in comparison to the valley glaciers. The longest continental polar glacier is more than 500 km long (Table 3).
Table 3: Five Longest Continental Polar Glaciers in the world
Source: https://top5ofanything.com/list/1adf90d1/Longest-Glaciers
Anatomy of Alpine/Valley Glaciers
Alpine glacier is concerned with mountain glacier found in different continents at varying altitudes. Uppermost section is characterized by zone of accumulation of ice due to extreme cold condition. Intermediaries is characterized by greater rock plucking from the glacial valley and abrasion (Figure 6). Steep slope is associated with crack in ice blocks called crevasses. Lowermost zone is accompanied by melting of the ice due to increase in temperature. This is known as zone of ablation. In this zone, the load carried by the glacier is deposited popularly known as moraine. Over the years, a sort of equilibrium of ice accumulation is maintained.
Figure 6: Anatomy of Alpine Glaciers
Work of Glaciers
The glaciers perform their works in three different ways – erosion, transportation and deposition.
Erosion: Glacier perform its erosional works primarily in two ways –plucking and abrasion. When any sort of irregularity is found in the way of a glacier, the solid mass of ice exerts enormous pressure. The pressure plucks and crushes the rock in the way. It becomes easier when the jointed rocks are found. This process is termed as plucking or quarrying. The plucked rocks or the fragmented rocks materials available keep on moving along with the moving ice. Once that material moves along the side or the bed of the glacier, they erode the surface. This leads to the scratching of the bed as well as the reduction of the moving materials in their size. This process is termed as abrasion. Both plucking and abrasion is very clear from the Figure 7.
Figure 7: Plucking and Abrasion by Glacier
Factors Affecting the Rate of Glacial Erosion
There are several factors affecting the glacial erosion like – thickness of ice, topography, geology of the area, temperature, velocity of the glacier, slope amount of ice accumulation and ablation etc. (Figure 8).
Figure 8: Factors Affecting the Rate of Glacial Erosion
Transportation:The work of transportation by glacier is performed in three ways. When the weathered rock materials falls on the glaciers, they are transport on the ice surface. Slowly and slowly, a part of the materials fall below the ice surface and are transported for a considerable distance. Some of the rock fragments moves further downward and reaches to the bottom of the glacier. Based on the position of the rock fragments they are categorized into three. The first one is said to be surface (supraglacial), the second to be internal (englacial) and the third to be basal (subglacial). They are shown in Figure 7.
Figure 7: Three Methods of Glacial Transportation
Deposition: The eroded and transported load of the glacier is deposited when the carrying capacity is reduced. The carrying capacity is reduced due to slope reduction or melt of ice and further lowering of the mass of ice. In both the cases, the deposition is evident. The deposition by glacier is very distinct because it is unsorted and ungraded deposits of the load of the glacier. Depending upon the place and material of deposits, they may be categorized in to several groups about which, it will be dealt while dealing with landforms.
Erosional Landforms
A number of landforms are created due to erosion by glaciers. Important among then are the followings:
Cirque:The shape of the cirque is just like an armchair and it is being made by glacial erosion. When the glacier descends from the mountain slope, it moves faster due to very steep slope. Later when the slope lowers, the excessive accumulation of ice exerts enormous pressure and the base is eroded by ice rotation, plucking and abrasion. In due course of time the base is further eroded and a depression is created (Figure 8A and 8B). It is called cirque which is a French term and meant for a circle or bowl shaped. It is also known as Corrie in Scottish.
Figure 8A: Formation of Cirque or Corrie
Figure 8B: Successive Development of Cirque or Corrie
Aretes: When several cirques or corries are developed on different sides of a mountain peak, their separating boundaries are further narrowed and sharpened. The sharp knife or blade edged boundaries are called arêtes. It is shown in a diagrammatic presentation in Figure 9A and the real feature in Figure 9B. Mountain climbers generally follow aretes for scaling the peak.
Figure 9A: Diagrammatic Presentation of Aretes
Figure 9B: Arete in Real Field
Col: Col is a depression like feature made between two peaks. Generally, col is made by the erosive action of glacier. This depression is created by the moving glacier. It helps in passing the mountain from one side to another. Col is also known as pass or saddle. Saddle is a seat fastened on the back of a horse for sitting and riding the horse. It is depressed at the center but raised in the front and rear and hence, it is called so (Figure 10).
Figure 10: Appearance of Col or Saddle
Horn or Pyramidal Peak: When the glaciers are developed from different sides of a peak, they erode the preexisting surface of the peak successively (Figure 11A) and make it a sharp and pointed peak with very steep slope. This gives a rise of a pyramidal peak which is also termed as horn as it is very pointed (Figure 11B).
Figure 11A: Successive Development of Pyramidal Peak
Source: http://www.mountainprofessor.com/images/matterhorn-3-b.jpg
Hanging Valley: Hanging valley is a tributary glacial valley of a main glacier. Main glacier has huge amount of ice, hence, erode the base greater. Therefore, the main glacial valley is much deeper. The tributary glacier has lesser amount of ice, hence, less erosion. Therefore, the base of the tributary glacier remains above the main glacier valley (Figure 12). When the glaciation is over, the tributary valley is seen above the main valley. That is why, it is called hanging valley.
Figure 12: Hanging Valley and Truncated Spur
Truncated Spur: Spur is a long tongue shaped ridge dropping down in an inverted ‘V’ separating the two adjacent valleys. The valleys confluence with another main river. When the same area comes under the influence of glacier (due to climate change), the main river turns into main glacier. Volume of ice in the main glacier is very large, it erodes its valley greater. Since, the glacier is the moving solid ice, it erodes not only the bed but side also. The dropped down spur is eroded and the slope of the spur is interrupted. This interrupted/ broken spur is called truncated spur (Figure 12).
‘U’ Shaped Valley: Glacial ice movement erodes its sides and make the trough much wider. The bed of the glacier is flat and both sides are almost vertical. This elongated wider trough is called ‘U’ shaped valley (Figure 12). When the glaciation period is over and ice is melted, the valley is exposed.
Fjord: Fjords are submerged glacial valleys under the sea water along the coast. The bottom of the valley is cut down because of heavy accumulated ice movement even below the sea level. With the culmination of ice age, the sea level also rises and down cut glaciated valleys along the sea coast are drowned under the sea water. Because of this process, the coast is greatly dissected (Figure 13A and 13B). This sort of coasts are found in the high latitudes and near polar areas.
Figure 13A: Close-up View of Fjord along the Sea Coast in High Latitude
http://www.landscapeplaces.com/wordpress/wp-content/uploads/2016/03/Dollarphotoclub_87784887.jpg
Figure 13B: Panoramic View of Fjord Coast in Norway
Source:https://www.fjordnorway.com/imageresizer/?image=%2Fdmsimgs%2F8B7BEC653B4E7AE9CF 19D3D1E44FF982D480AEC6.jpg&action=ProductDetailFullWidth
Depositional Landforms
Numerous landforms are created due to deposition of glacial loads when its capacity to carry is reduced. Important among then are the followings:
Moraine:The materials carried by the glacial ice is deposited in an ideal condition when the carrying capacity is reduced. These deposits are generally unsorted and un-stratified as it is deposited as and when the material reaches and dropped. Most of them are boulders of different sizes. Depending upon the place of deposits, the moraines are classed into different groups. They are:
Lateral Moraine: The two sides of the glacier is generally have exposed rocks. The weathered materials are dropped at the side of the glacier and are transported along. Materials are also supplied due to landslide as well. Carried materials also erode the side of the glacier and further more loads are generated. These materials are deposited along the side of the glacier and hence, they are called lateral moraine (Figure 14).
Medial Moraine: When tributary glacier or two glaciers meet with each other, the meeting side’s lateral moraines also joins together and moves further downward. Slowly and slowly the joined lateral moraine reaches towards the middle/ near middle. When the ice melts, the joined lateral moraine is deposited and is called medial moraine (Figure 14).
Figure 14: Different Types of Moraines
Source: https://classconnection.s3.amazonaws.com/221/flashcards/2900221/jpg/moraine2-13E6C383B0176BF468A.jpg
Terminal Moraine: The deposits which occur at the down end of the glacier in a ridge-like accumulation. These debris are pushed forward by advancing glacial tongue and dropped at the end. The terminal moraine spreads from one side or bank of the glacier to another covering the entire width. It appears like a belt of small hilly ground with knobs and joints (Figure 14)
Recessional Moraine:Recessional moraine is a sort of terminal moraine. After the formation of terminal moraine, when the glacier retreats, a new terminal moraine is formed at upstream. The previous terminal is, later, called as recessional (down) moraine (Figure 14).
Ground Moraine: Irregular blanket of glacial loads deposited on the floor in a rolling to flat landscape after glacial melt/ retreat is called ground moraine. As the term itself explains, it is the whole of the ground down side the existing glacier where the glacial load is deposited (Figure 14). It is formed in both the cases – continental glacier and valley glacier. Ground moraine is also known as till plain.
Glacial Till and Till Plain:The glacier carries huge amount of loads with it. When the glacier melts/ retreats, the transported loads are deposited. This deposition is undulating to flat in look.
The deposition of such materials at a certain location at small scale is till (Figure 15A) and the widespread area containing till is termed as till plain (Figure 15B). This type of till plain is very extensive in continental glacier but confined in the valley glacier.
Figure 15A: Glacial Till
http://www.albertawow.com/hikes/Saskatchewan_Glacier/Saskatchewan%20Glacier%20Till%20Plains.JPG
Outwash Plain:Down side from the glacial melt, water associated with smaller pieces of ice floats below. Gravels, sands, silts and clays are carried downward by the melted water and deposited far away. It forms a sloppy but relative flat plain known as outwash (material washed/ carried by water) plain. It is different from till plain. Till plain has unsorted materials directly deposited by melt of ice and, hence, dropped without ordering of the size of materials. Outwash plain has sorted deposits as it is deposited by glacio-fluvial (small ice pieces of ice and flowing water) action.
Figure 16: Outwash Plain
Source: http://www.coolgeography.co.uk/A-level/AQA/Year%2012/Cold%20environs/Fluvioglacial/outwash-plain-axel.jpg
Esker:Esker is a long, narrow and zigzag ridge like structure generally made up of stratified sediments deposited by subglacial meltwater (Figure 17). Its height varies from 5 meter to 50 meter and width is 50 meter to 500 meter whereas the length many as 500 meter to many kilometers. Esker is not necessarily a continuous feature, but it may be a detached or broken. Literally, it is deposited by the meltwater of the glacier and hence, they are sorted.
Figure 17: Formation of Esker
Kettle:A kettle is a shallow and small pothole or depression area in which glacial brought sediment is deposited and remaining hollow part covers the water. It is formed and appear on the surface by retreating glacier. Probably, this depression is created by the plucking, but later deposition of sediment and water accumulation give the birth of kettle. This water-filled body is known as Kettle Lake (Figure 18).
Figure 18: Kettle and Kettle Lake
Source: http://slideplayer.com/slide/4908488/16/images/41/Kame+and+kettle+topography,+Alaska.jpg
Kame:Kame is the accumulation in a mound like shape made up of poorly sorted sand, boulders and gravels brought by glacier at its terminus. A number of kames a formed when the glacier melts and terminates or recedes. A group of closely formed kames are termed as kame complex. Several kettle lakes are seen in a kame complex.
Roche Mountonnee: It is a French word meant for woolly rock, but in English it means sheep-back or sheep-rock. Roche Moutonnee (Figure 19) is a smoothened bedrock of a glaciated region byabrasion in the upstream side and rough and steep surface to the downstream due to plucking/ scouring. Once the area is free from glacier, the same feature appearances to the surface.
Figure 19: Formation of Roche Mountonnee
Source: http://web.gccaz.edu/~lnewman/gph111/topic_units/glacial/19_16.jpg
Drumlin: Drumlin is an elongated oval-shaped deposited mound of small hill-like feature formed by glacier (Figure 20). It is made up of glacial till containing boulder, gravels and sand transported by glacier and finally deposited in the above mentioned shape. They are seen in the plain and are many in number. They vary in dimension like one to two kilometers in length, 400 to 600 meter in width and 15 to 30 meter in height.
Figure 20: Longitudinal and Cross-Sectional View of Drumlin
Source: http://www.geography-site.co.uk/pages/physical/glaciers/images/drum.jpg
An Overview of Erosional Features
The important erosional (Figure 21A) and Depositional (Figure 21B) landforms made by glacier is represented below.
Figure 21A: Erosional Landforms Made by Glacier
Source: https://www.pmfias.com/wp-content/uploads/2015/12/Glacial-Erosional-Landforms-glaciated-topography.jpg
Figure 21A: Depositional Landforms Made by Glacier
Periglacial refers to the area in the periphery of the glaciated region. During summer, the region is almost free from ice on the surface but the subsoil is still frozen throughout the year.This is very clearly be seen from Figure No. 22A and thin layer of snow and ice accumulation in Figure No. 22B. The seasonal freezing and thawing of subsoil is regular feature of the region. During winter, the surface witnesses heavy snowfall and ice accumulation. In another words, the area is almost permanently frozen condition but without permanent ice cover on the surface. The mean monthly temperature is between minus one degree to minus 15 degree Celsius. The periglacial areas changes with the change in the climatic condition prevailing on the planet.
Figure 22A: Frozen Subsoil Water in Permafrost Area
Source: http://www.avilagtitkai.com/uploads/article/permafroszt-2-2bd603159d.jpg
Figure 22B: Thin Layer of Frost/ Snow in Permafrost Area
Source: http://www.dewereldmorgen.be/images/cache/xl/2011/02/18/permafrost.jpg
Based on the extent of freezing condition, the permafrost areas are classified into three groups – continuously permafrost, discontinuously permafrost, sporadic permafrost and isolated permafrost. The surface layer, where freezing and thawing is seen, is known as active layer.
The periglacial areas witness several processes important among are frost action, frost heave, frost shattering indirectly leading to rock-fall, earthflow and debris flow.
Frost Action: It is quite obvious that the volume of ice is greater than that of water. Freezing and thawing is a natural process. The water laying in the pores/ cracks or opening expands and breaks the rocks when it turns into ice. Therefore, weathering process is amplified by this process.
Frost Heave:When the subsoil water freezes, it leads to upward swelling of top soil. This process is repeated time and again with changing seasons. Upper soil is loosened and subject to removal easily.
Frost Shattering: Freezing and thawing process is known as frost shattering. The water laying in the cracks of exposed rocks in cold climates leads to breaking it.
Rock-fall:Rock-fall is a type of mass movement in which the fragmented rocks tumble down almost freely. In the cold climates, the exposed rocks are fragmented by freezing and thawing action and hence, the credit of rock-fall is credited to permafrost action.
Earthflow and Debris Flow: The availability of water content liquefies the soil and if it is on the slope, it flows quickly. This action is seen in the periglacial areas as the melt water of ice triggers it. Debris flow includes the unconsolidated soil, rock fragments and remnants of biotic life along with water. When these are associated with on the slope, it leads to debris flow and it is also triggered by water made available by snow melt in periglacial areas.
Landforms in Periglacial Areas
Several types of landforms are found in the periglacial areas. Some of them are:
Patterned Ground: Patterned ground is termed to that ground surface when the laying materials are distributed in a certain pattern. The pattern may be of any kind like stripes, ovals, circles, polygons particularly in the periglacial areas. They are made by frost heave action (Figure 23).
Figure 23: Patterned Ground
Source: https://nsidc.org/sites/nsidc.org/files/images//Patterned_Ground.jpg
Ice Wedges: The wedges mean pieces or slice or blocks. When the rocks are broken into pieces due to ice action, it is termed as ice wedges. In this situation, the water or ice penetrates vertically into surface for several meters. In cold climates(periglacial areas) the seasonal freezing and thawing cause the rock to break and penetrate further down during summer. In winter, it freezes and further the space is widened leading to rock breaking.
Blockfields: Blockfields are areas of huge expanse constituting the freeze-thaw weathered angular rock blocks in periglacial areas. Rock blocks get disintegrated into smaller pieces and thus, angular rocks are seen on the surface (Figure 24).
Figure 24: Angular Rocks Covered Blockfield
Source:
http://www.liguriaheritage.it/heritage/download/fstore/1383731394614/Blockfield_pianFretto.jpg
Pingos: Pingos are hills of earth and gravel in a dome-shaped formed in the periglacial areas under which the subsoil water freezing and tends to push the upper part upward. Its height may vary from 5 meter to 70 meter and the diameter from 30 meter to one km. most of the pingos are circular in shape.
Figure 24: Formation of Pingos
Source: https://www.britannica.com/science/pingo
Summary and Conclusion
Glacier is a flowing body of ice moving slowly as it a solid mass of water. Glaciers are found where the temperature is less than zero degree Celsius throughout the year. Based on the location and situation, glaciers are grouped broadly into two – continental and valley glacier. Continental glaciers are found in the polar region occupying very large areas as well as huge accumulation of ice. Valley glaciers are located on the mountain slopes of tropical and temperate region on high altitudes occupying very small areas with little ice. Moving ice erode the underlying rocks by
plucking and abrasion. The generated loads are transported along the glacier. Later on, the same is deposited in certain conditions. Due to both erosion and deposition several types of landforms are created. Important among the erosional landforms are cirque, arête, col, horn, hanging valley, truncated spur, U-shaped valley, fjord etc. Some depositional landforms are moraine, till, till plain, outwash plain, esker, kettle, kettle lake, rochemoutonnee, drumlin etc. The peripheral areas of the glaciers areas are known as periglacial areas where the freezing and thawing action is very prominent. This area witness the frost action and frost heave. Several types of landforms are also developed in this area.
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References
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Web links
- http://geology.com/articles/glaciers/
- http://nsidc.org/glims/glaciermelt/
- http://vancouverhiatus.com/hikingterms/valley-glacier.html
- http://www.3dgeography.co.uk/glacier-diagrams
- http://www.antarctica.gov.au/about-antarctica/environment/icebergs-and-ice/ice-sheet
- http://www.bbc.co.uk/education/guides/zf64jxs/revision
- http://www.onegeology.org/extra/kids/earthprocesses/continentalGlaciers.html
- https://www.asf.alaska.edu/blog/how-do-glaciers-move/
- www.cengage.com/resource_uploads/downloads/0495555061_137189.pdf
- www.grid.unep.ch/glaciers/pdfs/glaciers.pdf