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Rock Glacier, Alaska

Visual Glossary of Glacial Features


Rock glaciers are rarer than ice glaciers, but they too owe their motion to the presence of ice. (more below)
The glacier's rugged cousin
U.S. Geological Survey photo by Bruce Molnia (fair use policy)
A rock glacier takes a combination of cold climate, a copious supply of rock debris, and just enough of a slope. Like ordinary glaciers, there is a large amount of ice present that allows the glacier to flow slowly downhill, but in a rock glacier the ice is hidden. Sometimes an ordinary glacier is simply covered by rockslides. But in many other rock glaciers, water enters a pile of rocks and freezes underground—that is, it forms permafrost between the rocks, and ice builds up until it mobilizes the rock mass. This rock glacier is in the valley of Metal Creek in the Chugach Mountains of Alaska.

Rock glaciers may move very slowly, only a meter or so per year. There is some disagreement over their significance: while some workers consider rock glaciers a kind of dying stage of ice glaciers, others hold that the two types are not necessarily related. Certainly there's more than one way to create them. For more photos of rock glaciers and a taste of current research, visit this page at Queen's University of Belfast.

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