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68954-Ch18_IM

68954-Ch18_IM - Chapter 18 The Topography of Arid Lands...

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Chapter 18: The Topography of Arid Lands TOPICS A Specialized Environment Special Conditions in Deserts Running Water in Waterless Regions Surface Water in the Desert Fluvial Erosion in Arid Lands Fluvial Deposition in Arid Lands Characteristic Desert Surfaces—Ergs, Regs, and Hamadas Erg –A Sea of Sand Reg – Stony Deserts Hamadas – Barren Bedrock The Work of the Wind Aeolian Erosion Aeolian Transportation Aeolian Deposition Two Characteristic Desert Landform Assemblages Basin-and-Range Terrain Mesa-and-Scarp Terrain People and the Environment: Desertification KEY TERMS aeolian processes (p. 539) alluvial fan (p. 545) badlands (p. 550) bajada (p. 546) barchan dune (p. 541) blowout (p. 539) bornhardt (p. 533) butte (p. 550) deflation (p. 539) desert pavement (p. 538) desert varnish (p. 538) differential erosion (p. 533) ephemeral stream (p. 532) erg (p. 536) exotic stream (p. 531) hamada (p. 538) inselberg (p. 533) loess (p. 542) mesa (p. 549) pediment (p. 533) piedmont (p. 536) pinnacle (p. 550) plateau (p. 549) playa (p. 532) reg (p. 538) salina (p. 532) saline lake (p. 532) sand dune (p. 540) sapping (p. 549) scarp (p. 549) seif dune (p. 541) slip face (p. 540) transverse dune (p. 541) 244
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CHAPTER OUTLINE I. A Specialized Environment A. Most of the terrain-forming processes shaping humid regions also apply to desert, but a variety of factors are different: B. Special Conditions in Deserts 1. Weathering, creep, soil and regolith, impermeable surfaces, sand, rainfall, drainage, wind, basins of interior drainage, vegetation. a) Weathering : mechanical weathering is dominant. (1) Produces lower rate of weathering and angular particles of rock. b) Soil and regolith : thin or absent. (1) Contributes to stark, rugged, rocky terrain. c) Soil Creep : minor influence (lack of soil and lack of water). (1) Helps produce angular desert slopes. d) Impermeable surfaces : Caprock and hardpans. (1) Little moistures seeps into ground. e) Sand : (1) Inhibits streamflow and overland flow (2) Readily moved by heavy rains (3) Influenced by wind f) Rainfall : Usually intense when it happens. (1) Flooding is rule, so fluvial erosion and deposition are effective and conspicuous, even though rain is sporadic and rare. g) Fluvial deposition : Almost all streams are ephemeral (and effective agents of erosion). (1) Transportation usually short distance, so depositional features are unusually common. h) Wind : Their landforms are NOT produced largely by wind action. i) Basins of interior drainage : Most desert drainages have no hope of reaching ocean. j) Vegetation : Lack of vegetation is the single most significant feature of dry lands. (1) Provides little protection from raindrops or inadequately binds surface with roots. II. Running Water in Waterless Regions A. Despite it being a dry climate, running water is still the most important external agent for landform development in deserts. 1. Though rare, the precipitation is intense in its effect on the lightly vegetated cover, producing abrupt runoff.
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