Outwash Plain

An outwash plain, also known as a sandur, is a broad plain built from glaciofluvial sediment deposited by meltwater at the end of a glacier. As a glacier moves it grinds the rock beneath it and picks up debris, which meltwater then carries away from the glacier snout and spreads across the plain, sorting it so that larger boulders settle near the terminal moraine while finer silt is carried much farther. Outwash plains are often crossed by braided streams and pitted with kettle lakes, where blocks of buried ice slowly melted, and their drainage tends to be diffuse until it becomes more organized after the ice has retreated. The landform is especially well developed in Iceland, where volcanic heat beneath ice caps speeds up meltwater sediment deposition and can trigger sudden glacial outburst floods called jokulhlaups.