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  3. In Death Valley, California, one of the hottest, most arid places in North America, there is much salt, and salt can damage rock

In Death Valley, California, one of the hottest, most arid places in North America, there is much salt, and salt can damage rock

admin2014-01-13  63
问题     In Death Valley, California, one of the hottest, most arid places in North America, there is much salt, and salt can damage rocks impressively. Inhabitants of areas elsewhere, where streets and highways are salted to control ice, are familiar with the resulting rust and deterioration on cars. That attests to the chemically corrosive nature of salt, but it is not the way salt destroys rocks. Salt breaks rocks apart principally by a process called crystal prying and wedging. This happens not by soaking the rocks in salt water, but by moistening their bottoms with salt water. Such conditions exist in many areas along the eastern edge of central Death Valley. There, salty water rises from the groundwater table by capillary action through tiny spaces in sediment until it reaches the surface.
    Most stones have capillary passages that suck salt water from the wet ground. Death Valley provides an ultra-dry atmosphere and high daily temperatures, which promote evaporation and the formation of salt crystals along the cracks or other opening within stones. These crystals grow as long as salt water is available. Like tree roots breaking up a sidewalk, the growing crystals exert pressure on the rock and eventually pry the rock apart along planes of weakness, such as banding in metamorphic rocks, bedding in sedimentary rocks, or preexisting or incipient fractions, and along boundaries between individual mineral crystals or grains. Besides crystal growth, the expansion of halite crystals(the same as everyday table salt)by heating and of sulfates and similar salts by hydration can contribute additional stresses. A rock durable enough to have withstood natural conditions for a very long time in other areas could probably be shattered into small pieces by salt weathering within a few generations.
    The dominant salt in Death Valley is halite, or sodium chloride, but other salts, mostly carbonates and sulfates, also cause prying and wedging, as does ordinary ice. Weathering by a variety of salts, though often subtle, is a worldwide phenomenon. Not restricted to arid regions, intense salt weathering occurs mostly in salt-rich places like the seashore, near the large saline lakes in the Dry Valleys of Antarctica, and in desert sections of Australia, New Zealand, and central Asia.
Which of the following can be inferred from the passage about rocks that are found in areas where ice is common?
选项 A、They are protected from weathering.
B、They do not allow capillary action of water.
C、They show similar kinds of damage as rocks in Death Valley.
D、They contain more carbonates than sulfates.
答案C
解析 根据文章最后一段最后一句“Not restricted to arid regions，intense saltweathering occurs mostly in salt—rich places like the seashore，near the large saline lakes in theDry Valleys of Antarctica，and in desert sections of Australia，New Zealand，and central Asia．”可知，激烈的盐风化不仅存在于干旱地区，发生在含盐丰富的地方，如海边、在南极洲的干谷大盐湖附近，还有澳大利亚、新西兰和中亚的沙漠地段。南极洲就是冰天雪地的地方。据此判断，答案是C。
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