Glaciers a powerful agents of erosion and leave characteristic land forms. Rock entrained in the ice will accumulate as moraines . Lateral moraines are those at the sides of the glacier, the terminal moraine marks the furthest advance of the ice. Recessional moraines mark intermediate advances. Medial moraines are rock entrained in ten middle of a glacier by the coalescing of lateral moraines where glaciers flow together.
Glacial valleys have a characteristic U-shape with very little alluvial fill.
They may have hanging tributaries. Where two cirques intersect the narrow ridge is called an arete . Aretes may intersect in a horn . Ice Ages Great continental ice sheets have covered much of the Northeastern US and most of Canada, as well as northern Europe and Asia during the Pleistocene. Each of the major advances lasted more than 100,000 years and the interglacial periods only about 20,000 years.