| Term: | Glacial drift |
| Definition: |
Glacial drift is the loose and unsorted rock debris distributed by glaciers and glacial meltwaters. As glaciers melt, their remaining load of rocks is distributed in several ways. Rocks may be dropped in place by the melting ice; they may be rolled to the ice margins, or they may be deposited by meltwater streams. Collectively, these deposits are called 'glacial drift'. 'Till' refers to the debris deposited directly by the glacier. Rock debris rolls off the glacier edges and builds piles of loose unconsolidated rocks called 'glacier moraine'. 'Lateral moraines' form along the side of a glacier and curl into a 'terminal moraine' at the glacier's downvalley end. Drift and moraines are valuable to geologists because they outline the boundaries of past glaciations.
All rock material in transport by glacial ice, and all deposits predominantly of glacial origin made in the sea or in bodies of glacial meltwater, including rocks rafted by icebergs. "Glacial drift occurs as scattered rock fragments, as till [rocks mixed with finer material], and as outwash [fine material with no rocks]. Contrast with angular drift."(from Glossary of Arctic and Subarctic Terms 1955). AMSglossary A generic term applied to all glacial and glaciofluvial deposits. PhysicalGeography GCW |