Ice marginal valley

known also as Urstromtal (from German) it is a broad, flat valley formed on permafrost before the front of a retreating ice sheet. The water outflowing from the melting ice sheet (proglacial water) and water flowing from areas already deglaciated (extra glacial water) erodes the surface and accumulates the material in front of a glacier. On ice marginal valley terraces, dunes were formed (for example in Warsaw-Berlin glacial valley, currently Kampinos Forest, in the river Narew valley).