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冰川是缓慢移动的大量的冰，这些冰是在每年降雪多于融化的地区积累起来的。

Glaciers are slowly moving masses of ice that have accumulated on land in areas where more snow falls during a year than melts.

雪以六角形晶体的形式落下，但一旦落到地面，雪很快就会变成一团更小、圆形的颗粒。

Snow falls as hexagonal crystals, but once on the ground, snow is soon transformed into a compacted mass of smaller, rounded grains.

由于它们周围的空气空间由于被压实和消散而减少，颗粒变得更密集。

As the air space around them is lessened by compaction and melting, the grains become denser.

随着进一步的融化，再冻结，以及新下的雪增加了重量，雪达到了一个颗粒状的再结晶阶段，介于雪花和冰之间，被称为粒雪。

With further melting, refreezing, and increased weight from newer snowfall above, the snow reaches a granular recrystallized stage intermediate between flakes and ice known as firn.

随着时间的推移，压力的增加，再加上从上方重新冻结的融水，小粒雪颗粒变得更大，成为蓝色冰川冰的相互锁结的晶体。

With additional time, pressure, and refrozen meltwater from above, the small firn granules become larger, interlocked crystals of blue glacial ice.

当冰足够厚时，通常超过30米，雪和粒雪的重量会使底部的冰晶变得有塑性，并从积雪区域向外或向下流动。

When the ice is thick enough, usually over 30 meters, the weight of the snow and firn will cause the ice crystals toward the bottom to become plastic and to flow outward or downward from the area of snow accumulation.

冰川是开放系统，雪是系统的输入，融水是系统的主要输出。

Glaciers are open systems, with snow as the system’s input and meltwater as the system’s main output.

冰川系统由两个基本的气候变量控制：降水和温度。

The glacial system is governed by two basic climatic variables: precipitation and temperature.

为了使冰川生长或保持其质量，必须有足够的降雪量来弥补或超过冰川融化、蒸发和崩解造成的年度损失。这些现象是指冰川的一大块消失于海洋或大型湖泊中。

For a glacier to grow or maintain its mass, there must be sufficient snowfall to match or exceed the annual loss through melting, evaporation, and calving, which occurs when the glacier loses solid chunks as icebergs to the sea or to large lakes.

如果夏季的高温持续时间过长，那么上一年冬天的降雪就会融化。

If summer temperatures are high for too long, then all the snowfall from the previous winter will melt.

过剩的降雪是冰川形成的必要条件。

Surplus snowfall is essential for a glacier to develop.

过剩的雪会堆积起来，多年积累的雪的压力会把埋在地下的雪变成冰川冰，其深度足以让冰流动。

A surplus allows snow to accumulate and for the pressure of snow accumulated over the years to transform buried snow into glacial ice with a depth great enough for the ice to flow.

冰川有时按温度分为流动较快的温带冰川或流动较慢的极地冰川。

Glaciers are sometimes classified by temperature as faster-flowing temperate glaciers or as slower-flowing polar glaciers.

冰川是地球水文循环的一部分，在总水量上仅次于海洋。

Glaciers are part of Earth’s hydrologic cycle and are second only to the oceans in the total amount of water contained.

目前地球上大约2%的水以冰的形式冻结。

About 2 percent of Earth’s water is currently frozen as ice.

然而，2%可能是一个具有欺骗性的数字，因为世界上超过80%的淡水是以冰的形式存在于冰川中，其中大部分在南极洲。

Two percent may be a deceiving figure, however, since over 80 percent of the world’s fresh water is locked up as ice in glaciers, with the majority of it in Antarctica.

如果我们估算一下假设世界冰川融化时所释放的水，那么冰的总量就更惊人了。

The total amount of ice is even more awesome if we estimate the water released upon the hypothetical melting of the world’s glaciers.

This would change the geography of the planet considerably.

相反，如果另一个冰河时代来临，海平面会急剧下降。

In contrast, should another ice age occur, sea level would drop drastically.

在最后一个冰河时代，海平面下降了大约120米。

During the last ice age, sea level dropped about 120 meters.

当雪落在高山或极地地区，它可能成为冰川系统的一部分。

When snow falls on high mountains or in polar regions, it may become part of the glacial system.

与迅速返回海洋或大气的雨水不同，成为冰川一部分的雪参与了一个慢得多的循环系统。

Unlike rain, which returns rapidly to the sea or atmosphere, the snow that becomes part of a glacier is involved in a much more slowly cycling system.

在这里，水可能以冰的形式储存数百年甚至数十万年，然后再以融水的形式释放到液态水系统中。

Here water may be stored in ice form for hundreds or even hundreds of thousands of years before being released again into the liquid water system as meltwater.

然而，与此同时，这种冰并不是静止的。

In the meantime, however, this ice is not static.

冰川以巨大的能量在陆地上缓慢移动，即使是坚硬的岩层也被雕刻，冰川从而在吞没、推动、拖动的过程中重塑地貌，并最终在远离原始位置的地方使岩屑沉积。

Glaciers move slowly across the land with tremendous energy, carving into even the hardest rock formations and thereby reshaping the landscape as they engulf, push, drag, and finally deposit rock debris in places far from its original location.

因此，冰川形成了各种各样的地貌，这些地貌在地表脱离冰雪覆盖后很长一段时间内仍然存在。

As a result, glaciers create a great variety of landforms that remain long after the surface is released from its icy covering.

纵观地球的大部分历史，冰川并不存在，但目前地球表面约有10%被冰川覆盖。

Throughout most of Earth’s history, glaciers did not exist, but at the present time about 10 percent of Earth’s land surface is covered by glaciers.

现在的冰川在南极洲、格陵兰岛和除澳大利亚以外的所有大陆的高海拔地区都有发现。

Present-day glaciers are found in Antarctica, in Greenland, and at high elevations on all the continents except Australia.

在不远的过去，距今大约240万年前到大约1万年前，地球上近三分之一的陆地面积周期性地被数千米厚的冰覆盖。

In the recent past, from about 2.4 million to about 10,000 years ago, nearly a third of Earth’s land area was periodically covered by ice thousands of meters thick.

在更遥远的过去，其他冰河时代也曾发生过。

In the much more distant past, other ice ages have occurred.

The word “interlocked” in the passage is closest in meaning to

According to paragraph 1, which of the following does NOT describe a stage in the development of firn?

According to paragraph 2, surplus snow affects a glacier in all the following ways EXCEPT:

Paragraph 2 implies that which of the following conditions produces the fastest moving glaciers?

Why does the author consider the hypothetical melting of the world’s glaciers?

The discussion in paragraph 3 answers all the following questions EXCEPT:

Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.

According to paragraph 5, in what way is the present time unusual in the history of Earth?

Look at the four squares  that indicate where the following sentence could be added to the passage. Firn has the appearance of wet sugar, but it is almost as hard as ice.  Where would the sentence best fit? Click on a square  to add the sentence to the passage.

Directions: An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. Some sentences do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points.

Glacier Formation Glaciers are slowly moving masses of ice that have accumulated on land in areas where more snow falls during a year than melts. Snow falls as hexagonal crystals, but once on the ground, snow is soon transformed into a compacted mass of smaller, rounded grains.  As the air space around them is lessened by compaction and melting, the grains become denser.  With further melting, refreezing, and increased weight from newer snowfall above, the snow reaches a granular recrystallized stage intermediate between flakes and ice known as firn.  With additional time, pressure, and refrozen meltwater from above, the small firn granules become larger, interlocked crystals of blue glacial ice.  When the ice is thick enough, usually over 30 meters, the weight of the snow and firn will cause the ice crystals toward the bottom to become plastic and to flow outward or downward from the area of snow accumulation. Glaciers are open systems, with snow as the system’s input and meltwater as the system’s main output. The glacial system is governed by two basic climatic variables: precipitation and temperature. For a glacier to grow or maintain its mass, there must be sufficient snowfall to match or exceed the annual loss through melting, evaporation, and calving, which occurs when the glacier loses solid chunks as icebergs to the sea or to large lakes. If summer temperatures are high for too long, then all the snowfall from the previous winter will melt. Surplus snowfall is essential for a glacier to develop. A surplus allows snow to accumulate and for the pressure of snow accumulated over the years to transform buried snow into glacial ice with a depth great enough for the ice to flow. Glaciers are sometimes classified by temperature as faster-flowing temperate glaciers or as slower-flowing polar glaciers. Glaciers are part of Earth’s hydrologic cycle and are second only to the oceans in the total amount of water contained. About 2 percent of Earth’s water is currently frozen as ice. Two percent may be a deceiving figure, however, since over 80 percent of the world’s fresh water is locked up as ice in glaciers, with the majority of it in Antarctica. The total amount of ice is even more awesome if we estimate the water released upon the hypothetical melting of the world’s glaciers. Sea level would rise about 60 meters. This would change the geography of the planet considerably. In contrast, should another ice age occur, sea level would drop drastically. During the last ice age, sea level dropped about 120 meters. When snow falls on high mountains or in polar regions, it may become part of the glacial system. Unlike rain, which returns rapidly to the sea or atmosphere, the snow that becomes part of a glacier is involved in a much more slowly cycling system. Here water may be stored in ice form for hundreds or even hundreds of thousands of years before being released again into the liquid water system as meltwater. In the meantime, however, this ice is not static. Glaciers move slowly across the land with tremendous energy, carving into even the hardest rock formations and thereby reshaping the landscape as they engulf, push, drag, and finally deposit rock debris in places far from its original location. As a result, glaciers create a great variety of landforms that remain long after the surface is released from its icy covering. Throughout most of Earth’s history, glaciers did not exist, but at the present time about 10 percent of Earth’s land surface is covered by glaciers. Present-day glaciers are found in Antarctica, in Greenland, and at high elevations on all the continents except Australia. In the recent past, from about 2.4 million to about 10,000 years ago, nearly a third of Earth’s land area was periodically covered by ice thousands of meters thick. In the much more distant past, other ice ages have occurred.