- 2017年12月07日16:48 来源：小站整理
- 参与（0） 阅读（349）
Glaciers are large masses of ice on land that show evidence of past or present movement. They
grow by the gradual transformation of snow into glacier ice.
A fresh snowfall is a fluffy mass of loosely packed snowflakes, small delicate ice crystals
grown in the atmosphere. As the snow ages on the ground for weeks or months, the crystals shrink
and become more compact, and the whole mass becomes squeezed together into a more dense
form, granular snow. As new snow falls and buries the older snow, the layers of granular snow
further compact to form firm, a much denser kind of snow, usually a year or more old, which has
little pore space. Further burial and slow cementation — a process by which crystals become
bound together in a mosaic of intergrown ice crystals — finally produce solid glacial ice. In this
process of recrystallization, the growth of new crystals at the expense of old ones, the percentage
of air is reduced from about 90 percent for snowflakes to less than 20 percent for glacier ice. The
whole process may take as little as a few years, but more likely ten or twenty years or longer. The
snow is usually many meters deep by the time the lower layers are converted into ice.
In cold glaciers those formed in the coldest regions of the Earth, the entire mass of ice is at
temperatures below the melting point and no free water exists. In temperate glaciers, the ice is at
the melting point at every pressure level within the glacier, and free water is present as small drops
or as larger accumulations in tunnels within or beneath the ice.
Formation of a glacier is complete when ice has accumulated to a thickness (and thus weight)
sufficient to make it move slowly under pressure, in much the same way that solid rock deep
within the Earth can change shape without breaking. Once that point is reached, the ice flows
downhill, either as a tongue of ice filling a valley or as thick ice cap that flows out in directions
from the highest central area where the most snow accumulates. The trip down leads to the
eventual melting of ice.
1. Which of the following does the passage mainly discuss?
(A) The effect of glaciers on climate
(B) Damage from glaciers
(C) Glacier formation
(D) The location of glaciers
2. Which of the following will cause density within the glacier to increase?
(A) Increased water and air content
(B) Pressure from the weight of new snow
(C) Long periods of darkness and temperature variations
(D) Movement of the glacier
3. The word "bound" in line 9 is closest in meaning to
4. Which of the following will be lost is a glacier forms?
5. According to the passage , which of the following is the LEAST amount of time necessary for
glacial ice to form?
(A) several months
(B) several years
(C) at least fifty years
(D) a century
6. The word "converted" in line 15 is closest in meaning to
7. What is the purpose of the material in paragraph three?
(A) To define two types of glaciers
(B) To contrast glacier ice with non-glacier ice
(C) To present theories of glacier formation
(D) To discuss the similarities between glacial types
8. In temperate glaciers, where is water found?
(A) Only near the surface
(B) In pools of various depths
(C) In a thin layer below the firm
(D) In tunnels
9. The word "it" in line 21 refers to
10. It can be inferred from the last paragraph that a glacier
(A) can revert to a fluffy mass
(B) maintains the same shape throughout the glacial process
(C) is too cold to be thoroughly studied
(D) can contribute water to lakes, rivers, or oceans