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An outwash plain is the area where stream action has built stratified deposits of gravel, sand, silt, or clay beyond the glacier itself. The sediment is characteristically coarse grained and well sorted. The bedding (if present) is usually thin and truncated by younger beds. Grain size variations are sharp and numerous in both the vertical and horizontal direction. The major components of the sediment vary depending on the location of outwash relative to the glacier. Close to the glacier boulders, gravel, and sand predominate which indicate continual deposition of the bed load. Further from the glacier the grain size decreases with more silt and clay present; filling of glacial lakes is also a type of outwash (see filled lakes).
The surface of the outwash plain can be either pitted or nonpitted. In areas where the outwash deposited over an unglaciated area or area not recently glaciated, the surface will tend to be nonpitted. If, however, buried ice blocks are included in the outwash, the ablated blocks will result in a pitted surface marked by numerous kettles. This pitting will be extremely developed in areas of deposition on a stagnant ice mass of irregular thickness.
An outwash confined to a valley is called a valley train; braided streams are also very common.
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