Glacial Landforms and Cycle of Erosion

Relevance: Prelims/Mains: G.S paper I: Geography: Geomorphology: Glacial Landforms: Erosional and Depositional

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.

Arete

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.

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

Drumlin

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.

Why are world’s highest mountains at the equator?

Ice and glacier coverage at lower altitudes in cold climates is more important than collision of tectonic plates. [Glacial erosion is very strong because of huge boulders of rocks carried by the glacial ice that graze the surface. Though ice moves only few meters a day, it can take along it huge rocks that can peal the outer layers.]
Scientists have solved the mystery of why the world’s highest mountains sit near the equator.
Colder climates are better at eroding peaks. In colder climates, the snowline on mountains starts lower down, and erosion takes place at lower altitudes.
In general, mountains only rise to around 1,500m above their snow lines, so it is the altitude of these lines — which depends on climate and latitude — which ultimately decides their height.
At low latitudes, the atmosphere is warm and the snowline is high. Around the equator, the snowline is about 5,500m at its highest so mountains get up to 7,000m.
There are a few exceptions [that are higher], such as Everest, but extremely few.
When you then go to Canada or Chile, the snowline altitude is around 1,000m, so the mountains are around 2.5km.

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