Glaciers: Definition, Types and Mechanism of Glacial Erosion

Masses of ice moving as sheet over the land (continental glaciers or piedmont glacier if a vast sheet of ice is spread over the plains at the foot of mountains) or as linear flows down the slopes of mountains in broad through like valleys (mountain and valley Glaciers) are called glaciers.

Types of Glaciers:

Continental Glaciers: Continental glaciers are in fact, extensive ice sheets. These are called continental because they cover most part of a continent.

Extensive ice sheets radiate outward, from the center and more downslope. At present the biggest continental glaciers are Antarctic and Greenland ice sheets.

Piedmont Glaciers: The glaciers formed due to coalescence of several mountain or valley glaciers at the foothill zone are called piedmont glaciers. 

Such glaciers are found only in colder areas and not in the tropical or temperate regions because they melt when they reach the foothill zone.

Mountain or Valley Glaciers: The body of ice moving downslope under the impact of gravity through the valley bordered by rock valley walk in the mountain is called mountain glacier or valley glacier. The glaciers are located generally above the snow line as they are ablated while descending down the snowline.

Sometimes the term Alpine Glacier is used to describe glaciers that develop individually high in the mountains rather than as part of a broad icefield, usually at the heads of valleys.

Cirque Glaciers: Very small alpine glaciers confined to the basins where they originate are called Cirque Glaciers (because the basin is called a cirque.)

The ice occupying an armchair shaped cirque in the mountains is called Cirque Glaciers.

Normally, however alpine glaciers spill out of their originating basins and flow down valley as long, narrow valley glaciers. Occasionally they extend to the mouth of the valley and become piedmont glaciers.

Niche Glaciers: Represent a small upland ice mass which rests upon a sloping rock face.

Fjord Glaciers: Occupies a submerged coastal valley and its base lies below sea level. Many have steep terminus that recedes rapidly by frontal calving.

Ice Cap: A flattened, dome shaped mass of ice, similar to an ice sheet but under 50,000 square Km in area.

Ice Sheet: A continuous mass of glacier ice with an area over 50,000 square Km.

Ice Field: Extensive area of Ice in a mountainous region that consists of many inter-connected alpine glaciers.

Ice Shelf: It is a floating thick ice sheet or ice cap attached to the coasts.

Mechanism of Glacial Erosion:

Plucking: The glaciers freezes the joints and beds of the exposed rocks, tears out individual blocks and drag them away.

Abrasion: The grinding away of bedrock by fragments of rocks incorporated in ice. 

Ablation: Reduction of a glacier by melting, evaporation, iceberg calving or deflation.

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