Study Guide for Exam 4 Ch 12-16

Study Guide for Exam 4 Ch 12-16 - Study Guide for Exam 4...

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Study Guide for Exam 4 Lutgens and Tarbuck Answers to the Review Questions Chapter 12 Deserts and Winds 1. A common misconception about deserts is that they are lifeless or nearly lifeless regions. A second misconception is that the world’s dry lands are always hot. Deserts are also commonly assumed to consist almost entirely of sand when in fact it generally represents only a small percentage of the total desert area. Finally, wind is thought to be the most important agent of erosion operating in desert regions. While wind is relatively more significant in deserts, most erosional landforms in deserts are created by running water. 2. Steppes are vast, slightly dry to semiarid plains and grasslands that are transitional between humid lands and much drier, true deserts. Steppes and deserts generally lie between 15 and 35 degrees north and south latitude; the Sahara Desert (Africa) and its bordering plains and semiarid grasslands are a good example. The desert and steppe regions of North America and central Asia extend to higher latitudes (40 to 45 degrees). Desert lands and steppes comprise about 30 percent of Earth’s land area. 3. Subtropical deserts coincide with zones of high air pressure called subtropical highs. These pressure systems are characterized by subsiding and warming air, conditions that are just the opposite of what are needed to produce clouds and precipitation. Middle-latitude deserts exist principally because of their positions in the deep interiors of large landmasses far removed from the ocean, which is the ultimate source of moisture for cloud formation and precipitation. 2. The Northern Hemisphere (Fig. 13.2) has, by far, larger areas of mountain-rimmed valleys and basins located in the interiors of the continents. Many of the middle-latitude deserts are in the western United States, Mexico, and central Asia. Thus deserts and dry lands at middle latitudes (35 to 45 degrees) are much more prevalent than in the Southern Hemisphere. 4. Middle-latitude deserts are more common in the Northern Hemisphere. 5. Mean annual precipitation alone is not a valid predictor of an area’s moisture balance. A significant fraction of the precipitation runs off or evaporates; a smaller fraction infiltrates, adding to the soil moisture and contributing to groundwater recharge and perennial stream flow. Water lost through evaporation and runoff is effectively eliminated from the soil moisture budget. 6. Weathering rates are accelerated by persistently high levels of moisture, because most of the reactions in chemical weathering involve water, both as a reactant and as a medium for ion transport. Dry conditions, as in a desert, result in very slow rates of chemical weathering and in slow, overall weathering rates. 7. Although wind erosion is more prominent than in humid environments and rainfall events are
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This note was uploaded on 07/17/2008 for the course GS 100 taught by Professor Leavell during the Spring '06 term at Ohio State.

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Study Guide for Exam 4 Ch 12-16 - Study Guide for Exam 4...

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