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Glaciers

Glaciers are large sheets of ice that flow down very high mountains and are often the source of snow-fed rivers. Glaciers, found mainly in places such as Antarctica and Greenland, cover almost 10% of the earth's landmass, varying in size. A glacier begins life as snowflakes. As more snow falls and gathers, the weight of the snow on top compresses the lower layers to form ice. The pile of snow and ice becomes thicker and heavier till the point when the layer of ice at the very bottom melts under the pressure. It re-freezes almost at once; but the process is repeated over and over, and as a result the entire mass begins to slide downhill slowly along the rock surface. A glacier has an enormous impact on the topography of the area, pushing aside boulders, cutting through rocks, and denting its path as it moves.
Most of the world's glaciers are found at the Poles, but they exist on all of the world's continents, even Africa. Australia doesn't have any glaciers; however, it is considered part of Oceania, which includes several Pacific island chains and the large islands of Papua New Guinea and New Zealand. Both of these islands have glaciers. Glaciers require very specific geographical and climatic conditions. Most are found in regions of high snowfall in winter and cool temperatures in summer. The amount of precipitation (whether in the form of snowfall, freezing rain, avalanches, or wind-drifted snow) is important to glacier survival. In areas such as Siberia and parts of Antarctica, the lack of adequate precipitation prevents glacier development.

Some facts
At presently, about 10% of the world's land area is covered with glaciers.
Glaciers store about 75% of the world's freshwater.
Glacierized areas cover over 15,000,000 square kilometres.
In the United States, glaciers cover over 75,000 square kilometres, with most of the glaciers located in Alaska.
During the last Ice Age, glaciers covered 32% of the total land area.
If all land ice melted, the sea level would rise approximately 70 metres worldwide.
North America's longest glacier is the Bering Glacier in Alaska, measuring 204 kilometres long.
The Malaspina Glacier in Alaska is the world's largest piedmont glacier, covering over 8,000 square kilometres and measuring over 193 kilometers across at its widest point.

In India, glaciers are found in the Himalayas. There are about 15,000 glaciers flowing through these mountains, covering about 17% of the mountain area and supporting numerous perennial rivers such as the Ganga, Indus, and Brahmaputra. Some well-known glaciers are described below.

Dokriyani
This glacier is believed to be as old as the Himalayan Mountains. Dokriani 'Bamak' is a well-developed medium sized glacier of the Bhagirathi basin. The glacier is 5 km long and flows in a northwest direction terminating at an elevation of 3,800 m. It originates at an altitude of 13 000 feet in Uttaranchal's Garhwal district. It is one of the most studied glaciers in the world. A recent study says that it has been shrinking by a few metres every year.

Gangotri
This is located in Uttaranchal's Tehri Garhwal. One of the oldest glaciers in the Chaukhamba range, it is where the river Ganga originates. The Gangotri is not a single valley glacier, but a combination of several other glaciers that are fed to it and form a huge mass of ice. The glacier covers 28km and terminates at Gaumukh (4,000m).

Pindari
This is one of the most beautiful glaciers in the Kumaon hills and is known as the Jewel of Kumaon. iIt is located at a height of 13 000 feet above sea level between the Nanda Devi and Nandakot peaks and terminates at an altitude of 3,627 m. It is 5 km long, the snout is about 6 m high and 2.5 m wide and above the snout, the glacier extends for about 3m. The Pinder River that emerges from the Pindari glacier drains the valley.

Zemu
The Zemu glacier is the largest and most famous glacier in the eastern Himalayas, with a length of about 26 km. It is located in northwestern Sikkim in a U-shaped valley at the base of the Kanchenjunga massif. The Teesta river has its source in this glacier.
Many tributary glaciers feed the trunk glacier.

Siachen
This is the largest glacier in the world outside the Polar regions, stretching over a length of about 72 km. It lies in the extreme north- central part of Jammu and Kashmir near the border of India and Tibet, on the north-facing slopes of the Karakoram Range, and feeds the Shaksgam river that flows into Tibet. The glacier can be approached from Skardu in Ladakh. To the east of the Siachen lies a group of three glaciers known as the Rimo North, Central, and South. Between them, these glaciers have almost 700 square km of ice, which, at places, is 100 m deep. Altogether, the glaciers contain about 200 cubic kilometres of ice.