Its presence turns lake water aqua blue or brown, depending on its parent rock type. Coarser rocks may gouge scratches called striations . Retreat results when the glacier is ablating at a rate faster than its movement downvalley. Retreating termini are usually concave in shape. A glacier is a body of ice showing evidence of movement as reported by the presence of ice flowline, crevasses, and recent geologic evidence.
Glaciers exist where, over a period of years, snow remains after summer's end.
A sudden release of melt water from a glacier or glacier-dammed lake sometimes resulting in a catastrophic flood, formed by melting of a channel or by subglacial volcanic activity. Hydrothermal alteration is the alteration of rocks or minerals due to the reactions of geothermally heated water with minerals. The process weathers and weakens the rocks such that they may become unstable. Icefalls are somewhat analogous to waterfalls in rivers. The flow of the ice down a steep gradient often results in crevasses and seracs.