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(l)John Lemker/Earth Scenes, (r)Francois Gohier/Photo Researchers, (b)Paul A. Souders/CORBISFigure 12 Many high-altitude areas owetheir distinctive appearance to glacial erosion.Mountain glaciers can carve bowl-shaped depressionscalled cirques.Glaciers can widen valleys, giving them a U-shapedprofile.Effects of Glacial Erosion Glacial erosion of rock can be apowerful force shaping Earth’s surface. In mountains, valley glacierscan remove rock from the mountaintops to form largebowls, called cirques (SURKS), and steep peaks. When a glaciermoves into a stream valley, it erodes rock along the valley sides,producing a wider, U-shaped valley. These features are shown inFigure 12. Continental glaciers also shape Earth’s surface. Theseglaciers can scour large lakes and completely remove rock layersfrom the land’s surface.Glacial Deposition Glaciers also can deposit sediments.When stagnant glacier ice melts or when ice melts at the bottomof a flowing glacier or along its edges, the sediment theice was carrying gets left behind on Earth’s surface. This sediment,deposited directly from glacier ice, is called till. Till is amixture of different-sized particles, ranging from clay to largeboulders.As you can imagine, a lot ofmelting occurs around glaciers,especially during summer. Somuch water can be producedthat streams often flow away fromthe glacier. These streams carryand deposit sediment. Sand andgravel deposits laid down by thesestreams, shown in Figure 13, arecalled outwash. Unlike till, outwashusually consists of particlesthat are all about the same size.Figure 13 This valley in NewZealand has been filled withoutwash.Explain how you could distinguishoutwash from till.327