یخشار

thumb|right|The icefall (center) in the Roosevelt Glacier, Mount Baker, Washington, U.S. An icefall is a portion of certain glaciers characterized by relatively rapid flow and chaotic crevassed surface, caused in part by gravity. The term icefall is formed by analogy with the word waterfall, which is a similar phenomenon of the liquid phase but at a more spectacular speed. When ice movement of a glacier is faster than elsewhere, because the glacier bed steepens or narrows, and the flow cannot be accommodated by plastic deformation, the ice fractures, forming crevasses. Where two fractures meet