Glacier surge

Mon 16 Mar 2015


During most of their lives, surge glaciers behave like normal glaciers, traveling perhaps only a couple of inches per day. However, at intervals of 10 to 100 years, these glaciers move forward up to 100 times faster than usual. The surge often progresses along a glacier like a great wave, proceeding from one section to another. Subglacial streams of meltwater water pressure under the glacier might lift it off its bed, overcoming the friction between ice and rock, thus freeing the glacier, which rapidly sliders downhill Surge glaciers also might be influenced by the climate, volcanic heat, or earthquakes. However, many of these glaciers exist in the same area 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 has been flowing steadily toward the Gulf of Alaska at a rate of approximately 200 feet per year. In June 1986, however, the glacier surged ahead as much as 47 feet a day. Meanwhile, a western tributary, called Valerie Glacier, advanced up to 112 feet a day. Hubbard’s surge closed off Russell Fiord with a formidable ice dam, some 2,500 feet wide and up to 800 feet 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. If enough surge glaciers reach the ocean and raise sea levels, West Antarctic ice shelves could rise off the seafloor 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 ocean, causing sea levels to rise even higher, which in turn would release more ice and set in motion a vicious cycle. The additional sea ice floating toward the tropics would increase Earth’s Albedo and lower global temperatures, perhaps enough to initiate a new ice age. This situation appears to have occurred at the end of the last warm interglacial (the time between glacations), called the Sangamon, when sea ice cooled the ocean dramatically, spawning the beginning of the Ice Age.

Questions:

1. What is the main topic of the passage?
(A) The classification of different types of surge glaciers
(B) The causes and consequences of surge glaciers
(C) The definition of a surge glacier
(D) The history of a particular surge glacier

2. The word “intervals” in line 2 is closest in meaning to
(A) records    
(B) speeds    
(C) distances    
(D) periods

3. The author compares the surging motion of a surge glacier to the movement of a 
(A) fish    
(B) wave    
(C) machine    
(D) boat

4. Which of the following does the author mention as a possible cause of surging glaciers?
(A) The decline in sea levels
(B) The occurrence of unusually large ocean waves
(C) The shifting Antarctic ice shelves
(D) The pressure of meltwater underneath the glacier

5. The word “freeing” in line 7 is closest in meaning to
(A) pushing    
(B) releasing    
(C) strengthening    
(D) draining

6. According to the passage, the Hubbard Glacier
(A) moves more often than the Valerie Glacier
(B) began movement toward the sea in 1895
(C) is 800 feet wide
(D) has moved as fast as 47 feet per day

7. Yakutat is the name of
(A) an Alaskan town        
(B) the last ice age
(C) a surge glacier        
(D) an Antarctic ice shelf

8. The word “plunge” in line 20 is closest in meaning to
(A) drop    
(B) extend    
(C) melt    
(D) drift

9. The term “vicious cycle” in lines 21-22 refers to the
(A) movement pattern of surge glaciers
(B) effect surge glaciers could have on the temperature of tropical areas
(C) effect that repeated rising sea levels might have on glacial ice
(D) constant threat surge glaciers could pose to the Gulf of Alaska

10. The author provides a definition for which of the following terms?
(A) Tributary (line 14)        
(B) Ice dam (line 15)
(C) Albedo (line 22)        
(D) Interglacial (line 24)

11. Which of the following statements is supported by the passage?
(A) The movement of surge glaciers can be prevented.
(B) The next ice age could be caused by surge glaciers.
(C) Surge glaciers help to support Antarctic ice shelves.
(D) Normal glaciers have little effect on Earth’s climate.

Answers:

1)B 2)D 3)B 4)D 5)B 6)D 7)A 8)A 9)A 10)D 11)B

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