Whenever glaciers impede drainage, topographic closure may occur, resulting in the ponding ofrunoff. The term 'proglacial lake' has been used for lakes that owe their existence to the presence of a confining glacier margin (ice-marginal lakes), and for lakes that were strongly influenced by glacial meltwater, but which lay in a closed depression not directly in contact with the ice. In some ways this distinction is academic, and it is also arbitrary as to when a meltwater-fed lake not bounded by a glacier evolved from proglacial to non-glacial. However, ice-marginal lake basins commonly have a distinctive morphology and contain sediments with unique characteristics that reflect both their close proximity to the ice and the rapid changes that typically occur in that environment. As ice advanced and retreated, the distribution ofthese lakes changed; many eventually drained as the ice barrier disappeared, as isostatic rebound altered basin closure, and as outlets eroded.
During the last period of continental deglaciation, some large lakes remained ice marginal throughout their history. Other lakes, such as the glacial Great Lakes in North America, which occupied previously existing basins, were ice-marginal for only part of their history, progressively evolving to more distal meltwater-dominated proglacial lakes, and then to residual non-glacial bodies of water.
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