Bedrock exposed along cliffs breaks away along joints Cliff retreat in a

Bedrock exposed along cliffs breaks away along joints

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Bedrock exposed along cliffs breaks away along joints. Cliff retreat in a plateau of flat-lying rocks evolves into: o Mesas large; top may be several square km o Buttes medium-sized features o Chimneys end result: height exceeds top surface area. Cliffs and mesas: rock layers and weathering determines appearance. Resistant layers form steep vertical cliffs. Weak layers weather to form rubble-covered slopes. Cliffs and mesas: structure governs landforms. Nonhorizontal bedding produces elongate linear ridges. o Cuesta steep, joint-controlled cliff; less steep dip slope. o Hogback steeply dipping beds create a symmetric ridge. o Inselberg eroded remnant of almost complete cliff retreat. Shape of inselbergs can vary depending on the rock type or the orientation of the stratification. Sharp-crested Plateau-like Loaf-shaped Desert Pavement Mosaic-like arrangement of surface stones. Originates by dust washing in between the stones. Surface stones progressively lifted, dust thickens beneath.
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Surface is often coated with desert varnish. Desert Landscapes Stony plains: gently sloping, gravelly alluvial fans. Pediments: ramp-like bedrock surfaces that slope up toward a mountain front. Sheetwash during floods carries sediment away from mountain front, erodes bedrock surface. Sand Dunes: windblown accumulations of sand. Sand carried by wind accumulates around an obstacle. Over time, a dune grows and begins to move downwind. o Sand saltates up windward side. o Sand tumbles down the slip face. Dunes generate enormous cross beds. Sand Dunes: windblown accumulations of sand. Many types; actual dune form depends on variation in: o Wind velocity and consistency of direction o Sediment supply is sand scarce or abundant? Desert Problems Desertification aridification of nondesert areas. Human activity aggravates natural processes. o Overpopulation o Overgrazing o Careless agricultural practices o Diversion of water supplies The semi-arid Sahel has become a desert. Desertification facilitates large dust storms that: Cross entire ocean basins. Carry diseased organisms. Destroy homes and land. Dust-bowl era of 1930s in the U.S. turned Great Plains farmland into wasteland.
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