Glaciers are ice masses that form from snow accumulated and compressed over years. They appear as permanent features of the landscape, but they are always in motion. Ice is a solid, rather than a liquid, and ice flow is through the deformation( change in arrangement)of ice crystals, the glaciers tiny building blocks. Glacier motion resulting from this slow internal deformation is typically a few meters per year. The ice flows downslope under the influence of gravity. However, ice flow is controlled mainly by the slope of the ice surface rather than the bed(the ground surface below), and for this reason ice near the base of a glacier can flow uphill over obstructing bedrock ridges.
Observations of the speed of glaciers, made both by field surveys and from satellite measurements show that ice flows at rates ranging from less than a meter to several kilometers per year. A number of large fast-flowing glaciers drain the interior of then Greenland Ice Sheet, and the Jakobshavns Isbrae glacier in West Greenland has a flow rate of 7 kilometers per year, the fastest observed anywhere in the world. Speeds such as this are not produced by crystal deformation alone. It is the presence of liquid water, and sometimes water-saturated sediments(settled matter at the glacier bed that provides the necessary lubrication for fast flow.
But, how can the temperature beneath hundreds and sometimes thousands, of meters of ice reach the melting point to allow water flow? The coldest place on a glacier or Ice sheet is close to the surface, because the ice is in contact With the cold atmosphere. With increasing depth through the ice, the temperature actually increases This is because heat from Earth’s interior called geothermal heat, and heat generated by ice crystal deformation, ac o warm the ice. Friction(rubbing), caused by the glacier sliding over the bed, also plays a role in warming the ice at depth. The further from the cold surface, the higher the temperature, a phenomenon observed in drill holes several kilometers deep through the Greenland Ice Sheet. Where the melting point is reached at the glacier bed, water may be located in several places. It can be in channels cut into the bedrock of the overlying ice, in a thin film, or held within soft sediments immediately beneath the ice. In each case, friction at the glacier bed is reduced and ice can then move at speeds much faster than through ice deformation alone.
In addition to being important components of the landscape and modifiers of the local climate, glaciers receive attention because of their sometimes unpredictable behavior. Many Arctic glaciers undergo catastrophic advances known as surges, sometimes o several kilometers in a few months, which are unrelated to any climatic changes. Surge-type glaciers remain inactive for many decades, punctuated by much shorter periods of fast flow. The shift from stagnation to rapid flow and advance of the end of the glacier s thought to be associated with the buildup of water to lubricate the glacier bed or With a change In the state of subglacial sediment from frozen to wet Surging glaciers may dam major rivers or even fiords temporarily. Many other glaciers trap water in the form of internal reservoirs or ice-dammed lakes the sudden release of which causes catastrophic flooding.
The surface of a glacier bears witness to the forces generated during ice flow, the way in which debris is transported, and the role played by meltwater. When ice is stretched, as it goes round a bend, over a rock bump or step in the bed, or on entering the sea, it fractures in brittle fashion, producing large cracks called crevasses. Crevasses are a major hazard to traveling on glaciers, especially in the accumulation area, where they may lurk largely hidden beneath snow. Crevasses are commonly several meters wide and a few tens of meters deep. although few direct measurements have been made. They usually form distinct geometrical sets and where several intersect, travel is usually impossible. The most intense crevassing occurs when glaciers surge At such times, the whole glacier surface may break up.
1
Glaciers are ice masses that form from snow accumulated and compressed over years. They appear as permanent features of the landscape, but they are always in motion. Ice is a solid, rather than a liquid, and ice flow is through the deformation( change in arrangement)of ice crystals, the glaciers tiny building blocks. Glacier motion resulting from this slow internal deformation is typically a few meters per year. The ice flows downslope under the influence of gravity. However, ice flow is controlled mainly by the slope of the ice surface rather than the bed(the ground surface below), and for this reason ice near the base of a glacier can flow uphill over obstructing bedrock ridges.
The word “obstructing” in the passage is closest in meaning to
Arising
Bchanging
Cdeveloping
Dblocking
2
Observations of the speed of glaciers, made both by field surveys and from satellite measurements show that ice flows at rates ranging from less than a meter to several kilometers per year. A number of large fast-flowing glaciers drain the interior of then Greenland Ice Sheet, and the Jakobshavns Isbrae glacier in West Greenland has a flow rate of 7 kilometers per year, the fastest observed anywhere in the world. Speeds such as this are not produced by crystal deformation alone. It is the presence of liquid water, and sometimes water-saturated sediments(settled matter at the glacier bed that provides the necessary lubrication for fast flow.
Which of the following can be inferred from paragraph 2 about the Jakobshavns Isbrae glacier in West Greenland?
AIt sits on a layer of liquid water or on very wet sediments
BIt flows at a rate of less than a meter to several kilometers a year
CIt is the first to have its speed measured from a satellite
DIts speed is mainly the result of crystal deformation
3
But, how can the temperature beneath hundreds and sometimes thousands, of meters of ice reach the melting point to allow water flow? The coldest place on a glacier or Ice sheet is close to the surface, because the ice is in contact With the cold atmosphere. With increasing depth through the ice, the temperature actually increases This is because heat from Earth’s interior called geothermal heat, and heat generated by ice crystal deformation, ac o warm the ice. Friction(rubbing), caused by the glacier sliding over the bed, also plays a role in warming the ice at depth. The further from the cold surface, the higher the temperature, a phenomenon observed in drill holes several kilometers deep through the Greenland Ice Sheet. Where the melting point is reached at the glacier bed, water may be located in several places. It can be in channels cut into the bedrock of the overlying ice, in a thin film, or held within soft sediments immediately beneath the ice. In each case, friction at the glacier bed is reduced and ice can then move at speeds much faster than through ice deformation alone.
According to paragraph 3, all of the following contribute to the melting of the ice at the bottom of glaciers EXCEPT
Aheat drawn from the atmosphere through the surface of the glacier
Bheat produced within Earth
Cheat produced when ice crystals within the glacier deform
Dheat generated by the movement of the glacier over the bed
4
In addition to being important components of the landscape and modifiers of the local climate, glaciers receive attention because of their sometimes unpredictable behavior. Many Arctic glaciers undergo catastrophic advances known as surges, sometimes o several kilometers in a few months, which are unrelated to any climatic changes. Surge-type glaciers remain inactive for many decades, punctuated by much shorter periods of fast flow. The shift from stagnation to rapid flow and advance of the end of the glacier s thought to be associated with the buildup of water to lubricate the glacier bed or With a change In the state of subglacial sediment from frozen to wet Surging glaciers may dam major rivers or even fiords temporarily. Many other glaciers trap water in the form of internal reservoirs or ice-dammed lakes the sudden release of which causes catastrophic flooding.
Why does the author point out that glacier surges are “unrelated to any climatic changes”?
ATo explain why glacier surges can become catastrophic
BTo contrast the effects on fjords of slow-moving glaciers with those of surging glaciers
CTo argue against the claim that glaciers are modifiers of the local climate
DTo support the claim that glaciers sometimes behave unpredictably
5
In addition to being important components of the landscape and modifiers of the local climate, glaciers receive attention because of their sometimes unpredictable behavior. Many Arctic glaciers undergo catastrophic advances known as surges, sometimes o several kilometers in a few months, which are unrelated to any climatic changes. Surge-type glaciers remain inactive for many decades, punctuated by much shorter periods of fast flow. The shift from stagnation to rapid flow and advance of the end of the glacier s thought to be associated with the buildup of water to lubricate the glacier bed or With a change In the state of subglacial sediment from frozen to wet Surging glaciers may dam major rivers or even fiords temporarily. Many other glaciers trap water in the form of internal reservoirs or ice-dammed lakes the sudden release of which causes catastrophic flooding.
According to paragraph 4, which of the following is true of surge-type glaciers?
AThey occur as a result of changes in the water content of the glacier bed.
BThey affect the climate more rapidly than do other types of glaciers
CThey are more active near major rivers than near fjords
DThey cause subglacial sediment to change from frozen to wet in a short period
6
In addition to being important components of the landscape and modifiers of the local climate, glaciers receive attention because of their sometimes unpredictable behavior. Many Arctic glaciers undergo catastrophic advances known as surges, sometimes o several kilometers in a few months, which are unrelated to any climatic changes. Surge-type glaciers remain inactive for many decades, punctuated by much shorter periods of fast flow. The shift from stagnation to rapid flow and advance of the end of the glacier s thought to be associated with the buildup of water to lubricate the glacier bed or With a change In the state of subglacial sediment from frozen to wet Surging glaciers may dam major rivers or even fiords temporarily. Many other glaciers trap water in the form of internal reservoirs or ice-dammed lakes the sudden release of which causes catastrophic flooding.
According to paragraph 4, glaciers may cause damage by doing which of the following?
AChanging the course of major rivers
BCreating temporary fjords
CTrapping water inside themselves and then suddenly releasing it
DFilling lakes with a great amount of ice
7
The surface of a glacier bears witness to the forces generated during ice flow, the way in which debris is transported, and the role played by meltwater. When ice is stretched, as it goes round a bend, over a rock bump or step in the bed, or on entering the sea, it fractures in brittle fashion, producing large cracks called crevasses. Crevasses are a major hazard to traveling on glaciers, especially in the accumulation area, where they may lurk largely hidden beneath snow. Crevasses are commonly several meters wide and a few tens of meters deep. although few direct measurements have been made. They usually form distinct geometrical sets and where several intersect, travel is usually impossible. The most intense crevassing occurs when glaciers surge At such times, the whole glacier surface may break up.
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
AAlthough ice is often brittle, it can be stretched to go around and over bends, rock bumps, or steps
BAs ice travels it may become stretched, causing the formation of large cracks.
CIce that forms in a brittle fashion will crack easily into crevasses
DIce must stretch as it goes around bends and rock bumps before entering the sea
8
The surface of a glacier bears witness to the forces generated during ice flow, the way in which debris is transported, and the role played by meltwater. When ice is stretched, as it goes round a bend, over a rock bump or step in the bed, or on entering the sea, it fractures in brittle fashion, producing large cracks called crevasses. Crevasses are a major hazard to traveling on glaciers, especially in the accumulation area, where they may lurk largely hidden beneath snow. Crevasses are commonly several meters wide and a few tens of meters deep. although few direct measurements have been made. They usually form distinct geometrical sets and where several intersect, travel is usually impossible. The most intense crevassing occurs when glaciers surge At such times, the whole glacier surface may break up.
Paragraph 5 mentions all of the following about crevasses EXCEPT:
AThey result from ice stretching as it encounters obstacles or enters the sea.
BThey are much wider and deeper in accumulation areas than in others
CThey are sometimes invisible.
DTheir production is most extreme when glaciers advance rapidly.
9
In addition to being important components of the landscape and modifiers of the local climate, glaciers receive attention because of their sometimes unpredictable behavior. ■ Many Arctic glaciers undergo catastrophic advances known as surges, sometimes o several kilometers in a few months, which are unrelated to any climatic changes.■ Surge-type glaciers remain inactive for many decades, punctuated by much shorter periods of fast flow.■The shift from stagnation to rapid flow and advance of the end of the glacier s thought to be associated with the buildup of water to lubricate the glacier bed or With a change In the state of subglacial sediment from frozen to wet Surging glaciers may dam major rivers or even fiords temporarily. ■Many other glaciers trap water in the form of internal reservoirs or ice-dammed lakes the sudden release of which causes catastrophic flooding.
Look at the four squaresthat indicate where the following sentence could be added to the passage
But what causes the sudden movement of these glaciers?
Where would the sentence best fit？Click on a square sentence to the passage.
10
Glaciers are large masses of ice that move slowly across the landscape.
AUntil field surveys and satellite observations revealed that they are always in motion, glaciers were thought to be permanent features of the landscape.
BSurges are sudden. unexpected and very rapid movements, sometimes of several kilometers in a few months which occur after long periods of inactivity and may cause flooding and other problems
CThe difference in temperature between the surface and depth of a glacier has been used to explain the rate at which ice flow occurs
DIce flow, resulting from the internal deformation of ice crystals typically results in movement of a few meters per year, but glaciers can move much faster over liquid water or wet sediments.
ECrevasses are deep cracks in the glaciers surface that appear when the glacier surges or moves over uneven ground, and which can make it difficult or impossible to cross the glacier.
FGlaciers undergo changes both on the surface and in the interior as they move, and these changes affect the landscape in different ways.
