6. Fluvioglacial processes - Erosion

Question 1

Explain what Proglacial Lakes and Overflows Channels are and their formation.

Answer 1

Glacial meltwater has great erosive power because of its volume and the large amount of debris it contains. During deglaciation, lakes develop on the edges of the ice, some occupying large areas. Overflows from these lakes (overflow channels) which cross the lowest points of watersheds will create new valleys. When the ice damming these meltwater lakes totally melts, many of the new valleys are left dry, as drainage patterns revert to the preglacial stage. In certain cases, however, the postglacial drainage adopts them, giving rise to new drainage patterns.

Large meltwater lakes of this kind (called Proglacial lakes) occurred in the English Midlands (Lake Harrison), the Vale of Pickering in North Yorkshire (Lake Pickering) and the Welsh borders (Lake Lapworth) at the end of the last glaciation.