Glaciers of India and the World: Notes for Exams

A glacier is a thick mass of ice formed on land from compacted snow that moves slowly downhill under its own weight. Glaciers hold the greater part of the fresh water of the earth, carve the sharpest mountain scenery, and feed the three great river systems of northern India through the summer. Examiners ask the names of individual glaciers and their locations, the rivers that rise from them, and the landforms that glacial erosion and deposition leave behind.

How a glacier forms and moves

Above the snow line, more snow falls in winter than melts in summer. The buried snow is compressed into grainy ice called firn or neve, and under greater pressure into solid glacial ice. The upper part of a glacier, where snow is added, is the zone of accumulation; the lower part, where ice is lost by melting and evaporation, is the zone of ablation, and the line between them is the equilibrium line. The lower end of the ice is the snout. Movement is slow, often a few centimetres to a few metres a day, by sliding over the bed and by plastic flow within the ice; where the ice passes over a steepening of the bed it cracks into deep fissures called crevasses, and the great crack at the head of a valley glacier is the bergschrund. Glaciers are grouped as continental ice sheets, which bury whole landmasses as in Antarctica and Greenland, ice caps on plateaus and highlands, valley or alpine glaciers that move down existing valleys, piedmont glaciers formed where valley glaciers spread out on a plain, and small cirque or hanging glaciers. About a tenth of the land surface of the earth is under ice, and Antarctica alone holds the greater part of it.

Landforms of glacial erosion and deposition

A glacier erodes by plucking blocks out of its bed and by abrasion with the rock fragments frozen into its base. The hollow it scoops at the head of a valley is a cirque or corrie, and a lake left in that hollow is a tarn. Where cirques cut back on two sides, the sharp ridge between them is an arete, and where three or more meet, the sharp pyramidal peak is a horn, of which the Matterhorn of the Alps is the standard example. A valley occupied by a glacier is widened and deepened into a U-shaped valley or glacial trough, in contrast with the V-shaped valley of a river; a tributary glacier that cuts less deeply is left as a hanging valley, from which a waterfall drops. A trough drowned by the sea after the ice melts is a fjord, as on the coasts of Norway. Resistant rock smoothed on the up-glacier side and jagged on the down-glacier side is a roche moutonnee.

Deposition gives gentler forms. Unsorted debris dropped by ice is till or boulder clay, and the ridges of such debris are moraines: lateral along the sides, medial where two glaciers join and their lateral moraines merge, terminal or end moraine across the snout, and ground moraine spread beneath. A smooth oval mound of till shaped like an inverted spoon is a drumlin, and a field of them gives basket-of-eggs topography. Meltwater streams within or under the ice leave long winding ridges of sand and gravel called eskers, mounds called kames, and a flat outwash plain of sorted sand beyond the terminal moraine. A large boulder carried far from its parent rock is an erratic, and a hollow left by a melting ice block becomes a kettle lake.

Important glaciers of India

Because these glaciers feed the Indus, the Ganga and the Brahmaputra, the Himalaya and the Karakoram together are often called the Third Pole. Their retreat is studied by the Geological Survey of India and other agencies, and the sudden bursting of a lake dammed by moraine, known as a glacial lake outburst flood, is a recognised mountain hazard. India runs its polar research through the National Centre for Polar and Ocean Research at Goa, with the stations Maitri and Bharati in Antarctica, the earlier Dakshin Gangotri having been buried in ice, and Himadri at Svalbard in the Arctic.

Important glaciers of the world

The Lambert glacier of East Antarctica is the largest and longest glacier in the world, draining a vast interior basin into the Amery ice shelf. The Fedchenko glacier in the Pamir mountains of Tajikistan is the longest glacier outside the polar regions. In the Karakoram, Baltoro, Biafo and Hispar are among the longest valley glaciers in the world. Aletsch in Switzerland is the largest glacier of the Alps, and Mer de Glace in France and Pasterze in Austria are other well-known Alpine glaciers. Vatnajokull in Iceland is the largest ice cap of Europe. Sermeq Kujalleq, long called Jakobshavn, in Greenland is among the fastest moving glaciers, while Malaspina in Alaska is the textbook piedmont glacier and Perito Moreno in Patagonia and Franz Josef in New Zealand are the best known glaciers of the southern hemisphere. Khumbu glacier lies on the usual climbing route to Mount Everest.