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发信人: bonjovi (bonjovi), 信区: Flyingoverseas
标  题: TOEFL2000�.5真题6
发信站: 哈工大紫丁香 (2001年05月01日16:19:35 星期二), 站内信件

Questions 30 - 40
510152025   During most of their lives, surge glaciers behave like normal glac
iers, traveling perhapsonly a couple of inches per day. However, at interval
s of 10 to 100 years, these glaciersmove forward up to 100 times faster than
usual. The surge often progress along a glacierlike a great wave, proceedin
g from one section to another. Subglacial streams of meltwatermight act as a
lubricant, allowing the glacier to flow rapidly toward the sea. The increas
ingwater pressure under the glacier might lift it off its bed, overcoming th
e friction between ice and rock, thus freeing the glacier, which rapidly sli
des downhill. Surge glaciers alsomight be influenced by the climate, volcani
c heat, or earthquakes. However, many of theseglaciers exist in the same are
as as normal glaciers, often almost side by side.Some 800 years ago, Alaska'
s Hubbard Glacier advanced toward the sea, retreated,and advanced again 500
years later. Since 1895, this seventy-mile-long river of ice hasbeen flowing
steadily toward the Gulf of Alaska at a rate of approximately 200 feet pery
ear. In June 1986, however, the glacier surged ahead as much as 47 feet a da
y. Meanwhile, a western tributary, called Valerie Glacier, advanced up to 11
2 feet per day. Hubbard'ssurge closed off Russell Fiord with a formidable ic
e dam, some 2,500 feet wide and up to800 feet high, whose caged waters threa
tened 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 could rise off the s
eafloor and become adrift. A flood of ice would then surge into the Southern
Sea. With the continued rise in sea level, more ice would plunge into the o
cean,causing sea levels to rise even higher, which in turn would release mor
e ice and set in motiona vicious cycle. The additional sea ice floating towa
rd the tropics would increase. Earth's albedo and lower global temperatures,
perhaps enough to initiate a new ice age. Thissituation appears to have occ
urred at the end of the last warm interglacial (the time betweenglaciations)
, called the Sangamon, when sea ice cooled the ocean dramatically, spawningt
he beginning of the Ice Age.
30. What is the main topic of thepassage?(A)    The classification of different
types of surge glaciers.(B)    The causes and consequencesof surge glaciers.(C
)   The definition of a surge glacier.(D)   The history of a particular surgeGla
cier.
31. The word "intervals" in line 2 is closest in meaning to(A)  records(B)  sp
eeds(C) distances(D)    periods
32. The author compares the surging motion of a surge glacier to themovement
of a (A)   fish(B) wave(C) machine(D)  boat
33. Which of the following does the another mention as possible cause of sur
ging glaciers?(A)   The decline in sea levels.(B)   The occurrence of unusuallyl
arge ocean waves.(C)    The shifting Antarctic iceshelves.(D)   The pressure of m
eltwaterUnderneath the glacier.
34. The word "freeing" in line 7 is   closest in meaning to(A)  pushing(B)  re
leasing(C)  strengthening(D)    draining
40.Which of the following statementsis supported by the passage?(A) The move
ment of surgeglaciers can be prevented.(B)  The next ice age could be Cause b
y surge glaciers.(C)    Surge glaciers help to supportAntarctic ice shelves.(D)
    Normal glaciers have littleeffect on Earth's climate.
    35. According to the passage, the   Hubbard Glacier(A)  moves more often tha
n theValerie Glacier.(B)    began movement toward thesea in 1895(C) is 800 feet
wide.(D)   has moved as fast as 47 feetper day.
36. Yahutat is the name of(A)   an Alaskan town(B)  the last ice age(C) a surge
glacier(D) an Antarctic ice shelf
37. The word "plunge" in line 20 is closest in meaning to(A)    drop(B) extent(
C)  melt(D) drift
38. The term "vicious cycle" in line 22 refers to the(A)    movement pattern of
surgeglaciers(B)   effect surge glaciers could haveon the temperature of trop
ical    areas(C)    effect that repeated rising sealevels might have onglacial
ice(D)  constant threat surge glaciers could pose to the Gulf of Alaska
39.The author provides a definition for    which of the following terms?(A)
Tributary (line 14)(B)  Ice dam(line 15)(C) Albedo (line 23)(D) Interglacial
(line 24)

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