JEREMY WALKER / SCIENCE PHOTO LIBRARY JEREMY WALKER / SCIENCE PHOTO LIBRARY
Retreating glacier. A glacier is a huge mass of ice formed of compacted snow, moving slowly over a land mass. As it moves, the glacier erodes the rock beneath it, creating a U-shaped valley. The glacier carries rock debris that has fallen from the sides of the valley. As a glacier retreats, it leaves behind piles of such rocks, called glacial moraine. In this case, the moraine has been deposited along the sides of the glacier, forming lateral moraine. A glacier retreats when it melts faster than snow accumulates. Photographed in the Swiss Alps.
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