(L22)Deserts_and_Wind_Erosion_E10

(L22)Deserts_and_Wind_Erosion_E10 - 1 Deserts and Wind...

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Unformatted text preview: 1 Deserts and Wind Erosion GLY 2010 – Summer 2010 Lecture 22 Photo by Bruce R. Thomas. copyright © 2005 - 7 2 What Is a Desert? • May be hot, warm, or cold • Vegetation is generally sparse • Must be arid or semi-arid 3 Desert and Steppes • Deserts are arid, steppes are semi-arid Wind Circulation 4 Wind Circulation 4 Map of desert regions Rain Shadow effect Aridity Index Global Atmospheric Circulation Model 5 Rain Shadow Deserts • On the leeward side of mountains, particularly those near the coast, there is often an arid region 5 6 Pacific Northwest 7 Rain Shadow on the Olympic Peninsula 7 Return to Wind Circulation 8 Aridity Index • Aridity Index = area’s potential annual evaporation divided by recorded average annual precipitation Humid - up to 1.5 Semi-arid 1.5 to 4.0 Arid greater than 4.0 Hyper-arid - no exact definition - numbers over 100 - Eastern Sahara and Atacama Deserts can reach 200 9 Physical Weathering Dominates • With little available moisture, chemical weathering rates quickly slow to near zero • Physical weathering also slows, but not to zero • Therefore, physical weathering becomes the dominant process 10 10 Evaporite Deposits in Basins • Interior drainage possible Streams run into a basin, which may accumulate some water Evaporation rates are so high, the lake never gets deep enough to spill over the lowest point in its rim Rather, the water simply becomes more saline, or dries up entirely Salt deposits (evaporites) form 11 Playa Lake • A playa lake is a naturally occurring wetland that contains water only seasonally • Playas often form when water collects in a natural depression • Over time, a chemical reaction dissolves the underlying caliche layer, the land surface subsides (sinks), and a playa is created • Ten’s of thousands of these lake exist on the western edge of the Great Plains 11 12 What Are Playas? 12 13 Playas and the Ogallala Aquifer 13 14 14 Salina • A salina is an ephemeral lake, created by interior drainage and evaporation • Near Shiprock, New Mexico 15 15 Bonneville Salt Flats • The area west of Salt Lake Utah to near the Nevada border is a large, flat expanse of evaporite salt • It supports almost no vegetation • The salt flats are a remnant of Pleistocene glacial Lake Bonneville, which covered a much larger area • As the glacial lake evaporated, salts began to accumulate, and are still accumulating today 16 16 Glacial Lake Bonneville • Glacial Lake Bonneville was one of several large Pleistocene lakes • Great Salt Lake and the Bonneville Salt Flats are remnants 17 17 Erosional Landforms • Physical weathering dominates, so...
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This note was uploaded on 07/13/2011 for the course GLY 2010 taught by Professor Warburton during the Summer '07 term at FAU.

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(L22)Deserts_and_Wind_Erosion_E10 - 1 Deserts and Wind...

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