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Rivers of ice Glaciers are moving rivers of ice. They form high up in the mountains where layers of snow fall into a valley. As more snow falls, the ice becomes thicker. The ice is pressed down by the weight of the new snow. Then, the glacier slides slowly down the side of the mountain. Some glaciers end in the sea. Pieces break off and float away as icebergs. Not all mountains have glaciers on them. The Alps in France, Switzerland and Austria have glaciers. When the summer comes, the top layers of ice melt. Water flows over the ice in the form of a stream or as rills. Lakes often form in front of a mountain glacier. These also develop into rivers.
Rivers close to the Arctic often freeze in winter when the weather gets much colder. The River Ob in Siberia freezes in winter.
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