Rock Glacier
U.S. Geological Survey photo by Paul Carrara (fair use policy)
Rock glaciers like this one, in the San Juan Mountains of Colorado, are rarer than ice glaciers. 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. Below is another rock glacier from the valley of Metal Creek in the Chugach Mountains of Alaska.
U.S. Geological Survey photo by Bruce Molnia (fair use policy)
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.
Fossils
Geologic Features and Processes
Glaciers and Ice
Landforms
Minerals
Rocks
Geology and Society
