Erosion by ice/glacier

  • A glacier is a large mass of ice that is persistently moving under its own weight over the land or as linear flows down the slopes of mountains in broad trough-like valleys.
  • Glaciers are formed in the areas where the accumulation of snow exceeds its ablation (melting and sublimation) over many years, often centuries.
  • Glaciers move under the influence of the force of gravity.
  • Glaciers are of four types, viz. 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 Iceland, for example, has an area of 8,450 square kilometres, and the thickness of its ice is 1,000 metres.
  • 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.
  • While the continental ice masses covering thousands of square kilometres and thousands of metres thick move outward in all directions from their central portions, the valley glaciers move down the mountain slope towards lower regions.
  • Glaciation generally gives rise to erosional features in the highlandsand depositional features on the lowlands, though these processes are not mutually exclusive because a glacier plays a combined role of erosion, transportation and deposition throughout its course.
  • It erodes its valley by two processes viz. plucking & abrasion.

Plucking → Glacier freezes the joints & beds of underlying rocks, tears out individual blocks & drags them away.

Abrasion → Glacier scratches, scrapes, polishes & scours the valley floor with the debris frozen into it.