問題詳情

Question 30During most of their lives, surge glaciers behave like normal glaciers, traveling perhapsonly a couple of inches per day. However, at intervals of 10 to 100 years, these glaciersmove forward up to 100 times faster than usual. The surge often progresses along a glacierline like a great wave, proceeding from one section to another. Subglacial streams of meltwater(5)water pressure under the glacier might lift it off its bed, overcoming the friction between iceand rock, thus freeing the glacier, which rapidly sliders downhill Surge glaciers also mightbe influenced by the climate, volcanic heat, or earthquakes. However, many of theseglaciers exist in the same area as normal glaciers, often almost side by side.(10) Some 800 years ago, Alaska’s Hubbard Glacier advanced toward the sea, retreated, andadvanced again 500 years later. Since 1895, this secentry-mile-long river of ice has beenflowing steadily toward the Gulf of Alaska at a rate of approximately 200 feet per year. InJune 1986, however, the glacier surged ahead as much as 47 feet a day. Meanwhile, awestern tributary, called Valerie Glacier, advanced up to 112 feet a day. Hubbard’s surge(15) closed off Russell Fiord with a formidable ice dam, some 2,500 feet wide and up to 800feet high, whose caged waters threatened the town of Yakutat to the south.About 20 similar glaciers around the Gulf of Alaska are heading toward the sea. Ifenough surge glaciers reach the ocean and raise sea levels, West Antarctic ice shelves couldrise off the seafloor and become adrift. A flood of ice would then surge into the Southern(20) Sea. With the continued rise in sea level, more ice would plunge into the ocean, causing sealevels to rise even highter, which in turn would release more ice and set in motion a viciouscycle. The additional sea ice floating toward the tropics would increase Earth’s albedo andlower global temperatures, perhaps enough to initiate a new ice age. This situation appearsto have occurred at the end of the last warm interglacial (the time between glacations),(25)called the Sangamon, when sea ice cooled the ocean dramatically, spawning the beginningof the Ice Age.
30.What is the main topic of the passage?
(A) The classification of different types ofsurge glaciers
(B) The causes and consequences of surgeglaciers
(C) The definition of a surge glacier
(D) The history of a particular surge glacier

參考答案

答案：B
難度：適中0.625
統計：A(1),B(5),C(1),D(1),E(0)

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