In places high above the snow line, where more snow gathers than melts, it gets tightly packed. New snow falls and buries the old snow, which turns more dense and grainy. This is called firn and the process is called firnification. Layers of firn build up on top of each other and as they get thick and heavy, the grains of firn merge into huge mases of ice. Over time, the tightly compacted ice becomes so heavy and exerts so much pressure that the glacier slowly starts to move and slide downhill.

Glaciers are huge masses of ice that cover the basement rock. They are found only in regions where snow cover is permanent, that is, at the poles and at high altitude.

At low temperatures, snow does not melt. It accumulates and is compacted into ice. This gradual metamorphosis, which can take several decades, results in the formation of an enormous mass of ice, several dozen meters thick–a glacier.

Propelled by its own weight, a mountain glacier may become detached from the rock wall and slide downward. It slowly flows into the valley like a river of ice. As it descends, the glacier picks up rocks and debris, which accumulate in the form of mounds, called moraines.

If the climate warms, the glacier melts. We say that it recedes. It leaves behind a profoundly eroded landscape composed of wide, flat bottom valleys and many lakes.

Credit: Britannica

Picture Credit : Google 

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