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  3. Mount Rainier, the highest mountain in Washington State, reaches to more than 14 410 feet (4 392 meters) above sea level. Though

Mount Rainier, the highest mountain in Washington State, reaches to more than 14 410 feet (4 392 meters) above sea level. Though

admin2012-01-14  13
问题     Mount Rainier, the highest mountain in Washington State, reaches to more than 14 410 feet (4 392 meters) above sea level. Though it is a dormant volcano (having last erupted 150 years ago) encased in over 35 square miles of snow and ice. steam vents in the summit craters suggest the volcano is not extinct. Even though it was built up to its towering height above the surrounding country by repeated eruptions and successive flows of hot lava, it is the slow and unstoppable power of glacial ice that is now reshaping it.
    Glaciers are essentially accumulations of snow that has not melted from year to year. As the snow accumulates, its weight presses the air out from between the crystals and packs the snow down tight, compressing it to a sponge-like, porous ice called firn or neve. Each year as a new layer of snow is added, the lower layers are compressed more and more, becoming harder and harder until finally the lower layers become as hard as ordinary ice. Then gravity pulls the ice down the mountainside, both scouring and smoothing the bedrock underneath it as it moves. The seasonal freezing and thawing breaks rocks from adjacent slopes, which then fail onto the glacier’s surface. The passing ice carries the debris away. Thus, what has been created by fire is destroyed by ice.
    A particularly amazing feature of Mount Rainier is the ice caves that are scattered along its flanks. They are formed when small grottos are melted out along the sides of the glacier. Rainier’s two ice-filled summit craters each support a network of ice caves which arc carved by heat and volcanic emissions from deep inside the mountain. This happens when the firn ice created from the continual accumulation of snow in the summit craters starts to melt from the heat that rises along the crater walls of the volcano. The currents of warm air melt chambers between the rock walls of the mountain and the firn ice. As the process continues, a complex network —a maze -of large caves and tunnels is created throughout the interior of the crater.
    This whole process depends on maintaining a rather delicate balance. In order for the process to continue, enough snow must fall each year to fill the craters and replace the ice that has melted underneath. But, if too little heat is emitted, and the snow steadily accumulates, then the ice will expand, pushing itself against the crater walls and filling the caverns with ice. On the other hand, if more steam is emitted than the amount of firn created, the ice pack will melt away, destroying the ice caves. It is in this manner that Mount Rainier s huge Paradise Ice Caves melted away in the 19th century. (459 words)
What causes the formation of firn ice?
选项 A、Gravity.
B、Continual accumulation of snow.
C、Volcanic emission.
D、Snow melting.
答案B
解析 参考第二段第二句。firn或neve是“冰原、粒雪”之意。
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