Competitive Exams: Glaciers: Glaciated Topography

About 10% of the earth's surface is covered by glaciers. Glaciers are formed due to accumulation of ice. Snowline is generally defined as a zone between permanent and seasonal snow and that height above which there is permanent snow cover, The snowline is at he lowest height sealevel in the polar region and increases equatorward where it tends to occur between 50006000 mt. The areas of accumulation of huge volume of ice are called snowfields. The glaciers grow by gradual transformation of snow into granular snow and then into firn and neve and finally into solid glacial ice (granular snowfirn/nevesolid ice).

Types of glaciers: They are basically of three types:

  • Mountain glaciers

  • Continental glaciers

  • Icecaps. Glaciers. Icecaps: The biggest is called as icecap. It is broad domes with flattened cross section covering thousands glaciers. There is one difference between icesheets and jcecaps. Icesheets: Eg. Antarctic and Greenland.

Continental glaciers

It is also a kind of icesheet but since it is spread oyer the continents, hence are known as continental glaciers.

Examples are: Antarctic average thickness is 4000 m; Greenland average thickness is 3000m. Other examples are Arctic, Canada, Iceland, Norway.

Valley/Mountain/Alpine glaciers:

  1. Examples are:

    1. Himalayan region: Roopal glacier (16 km), Punma glacier (27 km), Rjmu glacier (40 km), Himarche glacier, Barche and Milaspin glacier (all in Kashmir Himalaya).

    2. Hispar glacier, Baifo glacier (62 km), Baltorp glacier (58 km), Siachen (72 km), Batura glacier (58 km), Sasaini glacier (158 km), all in Karakoram range.

Cirque glacier

The armchair shaped or amphitheatre cirque or corrie is a horse shoe shaped, steep wall depression representing a glaciated valley hill. It is known by different names at different places. It is known as:

  • CWN at Wales

  • CORRIE at Scotland

  • KAR at Germany

  • Cirque lake is called ‘Tarn’

Col/Aretes and Horns

  • When it becomes pyramidal called as col and peak

  • When the peak looks like teeth, it is called ‘aretes’ Nunatak: The higher peaks and mounds surrounded J>y_ice from all sides are called Nunatak&

  • Milan glacier (19 km), Kedarnath (14 km), Gangotri glacier (25 km), Kosa (11 km) all in Kumaon Himalayas. Zemu glacier (25 km), Kanchenjunga (16 km) all in Sikkim.

Other subtypes of glaciers

  1. Piedmont glacier: These are found in colder areas and not in the tropical or temperate regions. If is to coalescence of several mountains and valleys or glaciers at the foothill zone for eg. Melaspina of Alaska (USA)!

  2. Iceshelf: Floating thick icesheet/icecap attached to the coast. Eg. Ross iceshelf, Ronne iceshelf, Filchner iceshelf all in Atlantic coast.

  3. Niche glacier: It represents a small upland icemass which rests upon a sloping rockface.

  4. ‘U’ shaped valley: They are ‘U’ shaped and are associated with the tributary valleys called hanging valleys. The main glacial valleys of much greater depth are called hanging valleys.

  5. Crag and Tail: A peculiar landform having vertical eroded steep side up glacial side and taillike appearance with lower height, down glacial side is called crag and tail.

  6. Roches mountains: They are all covered by ice andlakes are formed at the foothills and are called Beaded lakes and the smaller lakes are called Paternoster lake.

  7. Morraines: They are ridgelike depositional features of glaciers. They are long but narrow ridges with height more than 30 m

  8. Drumlins: They look like inverted elliptical or avoid hills.

  9. Eskers: They are long narrow and sinuous ridges of sands and gravels and are situated in the middle of ground moraines.

  10. Kames: These are small hills or irregular mounds of bedded sands and graves which are deposited by melt of the water near or at the edge of the retreating icesheets.

  11. Kettles and Hummocks: Kettles are depressions in the outwash plains. Large kettles are dotted with numerous low mounds and are called hummocks.

  12. Outwash: The melt water caused due to ablation of glaciers at its snout descents through the terminal morraine and spreads like sheet water. It is also known as ‘sander’ and ‘braids’

Landforms Made By Glaciers

Features of Erosion:

  1. Cirques; These are circular depressions formed by plucking and grinding on the upper parts of the mountainslopes. Also known as Corries or Amphitheatre.

  2. Arete: This. Name is applied to the sharp ridges produced by glacial erosion. Where two cirquewalls intersect from opposite sides, a jagged, knifelike ridge, called arete results, also known as comb or serrateridge.

  3. Horn: Where three or more cirques grow together, a sharppointed peak is formed by the intersection of the aretes.

  4. Col: Where opposed cirques have intersected deeply, a pass or notch called a col is formed.

  5. Glacialtrough: Glacier flow constantly deepens and widens its channel so that after the ice has finally disappeared, there remains a deep, steep walled, ‘U’ shaped valley, known as glacial trough.

  6. Hanging valley: Tributary glaciers also carve ‘U’ shaped troughs. But they are smaller in crosssection, with floors lying high above the floorlevel of the main trough, i.e.. main glacial valley.

  7. Fiords; When the floor of a glacial trough open to the sea lies below sea level, the seawater will enter as the icefronts recedes, producing a narrow estuary, known as a ‘fiord’

  8. Tarns: The bedrock is not always evenly excavated under a glacier, so that floors of troughs and cirques may contain rockbasin and rocksteps. Cirques and upper parts of troughs thus are occupied by small lakes called tarns.

GlacioFluvial Deposits

  1. Outwash plain: It is also known as overwash plain. Glacial streams carry a huge quantity of rockdebris and then form fanlike plains beyond the terminus of glaciers. These are stratified, when they occur on valley floors, such outwash plains are called valley trains.

  2. Karnes or kame terraces: These are formed on the top surface of a glacier where the surficial meltwaters wash sediments from the top in to depressions. As the ice melts the material that formerly filled depressions on top of the glacier is dropped and makes small hills, which are more or less flattopped and are known as kames. Terraces, called kame terraces, are built in this way.

  3. Eskers: These are winding steepsided ridgelike features built of stream borne drift, these are also known as Osser or Oss.

  4. Erratics: These are stray boulders of rocks which have undergone a prolonged glacial transport and have subsequently been deposited in an area, where the country rocks are of distinctly different types. At times they are delicately balanced upon glaciated bedrock, and are called poking or loggingstone.

  5. Kettles: Drifts occurring in the vicinity of a glacier and particularly those lying near about the iceterminus are ordinarily found to contain a number of depressions, some of which may give rise to lakes or swamps. Such hollows are known as kettles.

  6. Varves; These are layered clays alternating with coarser and finer sediments.

Other ImportantProcesses and Features Associated with Glacier

  1. Niviation: It is the process of quarrying of rocks mostly by frostaction.

  2. Ablation. Includes processes both evaporation and the melting of snow and ice.

  3. Calving: Within fiords, glaciers come in contact with marine water and blocks of ice are found to breakoff from the mass of the glacier. This process of wastage of glacier is known as calving.

  4. Serace: Similar to a waterfall in a river, in a steeper section of the valley, the glacier is brokenup into rugged icepinnacles and is known as serace.

  5. Iceberg: These are floating icehill on the sea water.

  6. Crevasses: These are cracks formed due to differential movement within the mass of glacier. In German, they are known as Bergschrund.

  7. Nunatak: A rockmass which projects through an icesheet, generally found at the margins of a sheet where the ice is thinnest, is known as nunatak.