Proglacial Lake

A proglacial lake is a lake formed at the edge of a glacier, either by a moraine or an ice dam left behind as the glacier retreats, or by meltwater trapped against an ice sheet in land that the weight of the ice had pressed downward. Moraine dammed lakes form when the ridges of rock and sediment a retreating glacier leaves behind naturally block meltwater, while smaller versions called tarns can fill bowl shaped hollows called cirques that mountain glaciers carve out. Ice dammed lakes form where the glacier itself acts as the barrier, holding back river flow until the water eventually breaks through in a sudden, sometimes catastrophic flood known as a jokulhlaup. Larger proglacial lakes can also form across whole regions where land depressed by the weight of a retreating ice sheet holds meltwater against the remaining ice, a pattern that was widespread roughly ten thousand years ago at the end of the last ice age and continues today in places such as Greenland.