CHAPTER 13 Arid Environments

CHAPTER 13 Arid Environments - 2009 Allan Ludman and...

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1 CHAPTER 13 PROCESSES AND LANDFORMS IN ARID ENVIRONMENTS PURPOSE • To understand how erosion and deposition in arid regions differ from those in humid regions. • To recognize how those differences make arid landscapes different from those of humid environments. • To become familiar with landforms and landscapes of arid regions. MATERIALS NEEDED Colored pencils 13.1 INTRODUCTION Arid regions are defined as those that receive less than 25 cm (10 inches) of rain per year –very little water for stream and groundwater erosion or for chemical and physical weathering. Weathering, mass wasting, wind and stream erosion are still the major shapes of arid landscapes but because they are applied in very different proportions than in humid regions, the results are strikingly different from humid area landscapes (Figure 13.1). Figure 13.1 Arid landforms from the southwestern United States a. Erosional remnants, Monument Valley b. Hoodoo panorama, Bryce National Park c. Delicate Arch, Arches National Park Movies and television portray arid regions with camels resting at oases amid mountainous sand dunes. Some like parts of the Sahara and Mojave deserts, do look like that (minus camels in the Mojave), but some have more rock than sand, others lie next to shorelines where there is no shortage of water, and the North and South Poles are among Earth’s most arid regions (Figure 13.2). © 2009 Allan Ludman and Stephen Marshak W.W. Norton & Company
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2 Figure 13.2 Types of arid regions a.Sandy desert (Sahara) b. Polar desert, Norway c. Rocky desert, Utah EXERCISE 13.1: COMPARING ARID AND HUMID LANDSCAPES Compare arid landscapes in a part of Canyonlands National Park and the Grand Canyon, located in Utah and Arizona, respectively, (Figure 13.3a, b) with humid landscapes of the Delaware Water Gap at the New Jersey/Pennsylvania border (Figure 13.3c), and an area in Utah (Figure 13.3d). Figure 13.3: Comparison of arid and humid landscapes a. Canyonlands National Park, Utah b. Grand Canyon National Park, Arizona c. Delaware Water Gap, New Jersey/Pennsylvania d. Humid region in Utah (from EPOP)
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3 a)In which areas are the landforms more angular? In which are they more rounded? Suggest an explanation for the difference. b)In which areas do you think landscape changes are more rapid? Are slower? Explain your answer. c) What other differences do you see between the arid and humid regions? d) What type of erosion appears to be dominant in the arid regions? In the humid regions? How is this possible? 13.2 PROCESSES IN ARID REGIONS Now let’s examine the underlying causes for the different evolution of landscapes arid and humid areas. Features tend to survive longer in arid areas than in humid ones because weathering, erosion, and deposition are slowed by the scarcity of water needed to abrade, dissolve, and carry debris away. In the absence of water, soluble rocks like limestone, dolostone, and marble – easily weathered and eroded in humid regions to form valleys –
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CHAPTER 13 Arid Environments - 2009 Allan Ludman and...

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