TF阅读真题第885篇Periglacial Mounds

 

Periglacial Mounds

 

Periglacial regions are cold-climate areas that are located near the margins of glaciers-permanent ice sheets covering parts of the Arctic and other cold places. In some periglacial regions, huge mounds (hills) consisting of an outer layer of soil covering a core of solid ice may rise out of an otherwise flat landscape. These structures, called pingos, often develop over dried-out lake basins or along the sides of streams and rivers. Pingos become elevated by the growth of an ice core in the center of the mound, formed as a result of water pressure from below. Usually they develop in the sites where springs of water rise from the ground under pressure and feed the ice core, which freezes as it nears the surface of the ground. The upper part of the mound has a very different microclimate from the surrounding lowlands, and the southern slopes of the pingo mound may bear vegetation characteristic of a warmer climate, possibly even a tree cover. If the general climate becomes warmer, however, the ice core in the center of the pingo melts and the whole mass collapses to form a deep pool, surrounded by a circular rim or “rampart” formed from the soil and other organic material raised up by the mound. Circular ponds with ramparts can be found far to the south of the present-day Arctic regions, indicating the periglacial conditions that once prevailed there.

A similar type of structure is sometimes formed in those regions of the Arctic that are rich in peat (decomposed plant material), and this is termed a palsa. Palsas, like pingos, are large mounds that are formed by the development of ice beneath the surface of the ground. Generally smaller than pingos, palsas are only 2 to 3 meters in height and about 45 meters across. They often lie within wetland (water-saturated) areas, where they are interspersed with open pools and other palsas in various states of development. Palsas begin their formation as small irregularities on the surface of an area of low-lying land that is saturated in water. Even a very small elevation of a few centimeters can affect snow accumulation. The snow is blown from the slight mound and accumulates in the hollows between, so the more elevated spots have less snow cover in the winter. They therefore become cold, because snow acts as an insulating blanket, retaining some of the ground’s heat that it gained in the summer sun. By contrast, the cold penetrates any small raised areas of ground, causing an ice core to develop within them. As the ice forms, it expands, pushing the mound even higher so that even less snow is retained in the high winds. Palsa growth is thus a self-propagating process: the higher the palsa grows, the colder it becomes, and the colder it becomes, the more the ice core expands and pushes the palsa upward. The ice core survives through the summer, so its growth continues for many years, even centuries.

As the palsa grows in height, drainage (the ability of water to move down) improves and the vegetation on its surface becomes drier. The surface of the palsa may then develop a vegetation cover of lichens (small plantlike organisms). Many lichens are white or pale gray, and these reflect the sunlight, keeping the mound cool in summer. In the course of time, dwarf shrubs replace these lichens, but these have a darker color and absorb more heat from the summer sun. This, coupled with the increasing height of the dome, eventually leads to gradual removal of the surface soil, revealing the peat beneath. The dark-colored peat absorbs even more heat, and its exposure leads to the meltdown of the ice core. The core collapses quite quickly, leading to the formation of an open pool of water that is available for recolonization by wetland plants as the cycle begins again. Finnish scientists, working in the 1980s, demonstrated experimentally how this process operates. They spent a whole winter visiting an area of the Arctic wetland where, using a broom, they swept an area clear of snow and kept it clear through the winter. The result was the development of a permanent ice core beneath the ground, and within a few years the swept locality was developing into a palsa.

 

 

 

 

 

 

 

1

Periglacial regions are cold-climate areas that are located near the margins of glaciers-permanent ice sheets covering parts of the Arctic and other cold places. In some periglacial regions, huge mounds (hills) consisting of an outer layer of soil covering a core of solid ice may rise out of an otherwise flat landscape. These structures, called pingos, often develop over dried-out lake basins or along the sides of streams and rivers. Pingos become elevated by the growth of an ice core in the center of the mound, formed as a result of water pressure from below. Usually they develop in the sites where springs of water rise from the ground under pressure and feed the ice core, which freezes as it nears the surface of the ground. The upper part of the mound has a very different microclimate from the surrounding lowlands, and the southern slopes of the pingo mound may bear vegetation characteristic of a warmer climate, possibly even a tree cover. If the general climate becomes warmer, however, the ice core in the center of the pingo melts and the whole mass collapses to form a deep pool, surrounded by a circular rim or “rampart” formed from the soil and other organic material raised up by the mound. Circular ponds with ramparts can be found far to the south of the present-day Arctic regions, indicating the periglacial conditions that once prevailed there.

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.

Sentence Simplification Questions句子简化题

AThe micro-climate and vegetation can differ significantly from one pingo to another, and some pingos even have a tree cover.

BThe slopes of the pingo share the same micro-climate as the surrounding lowlands, and both may bear vegetation, even tree cover, characteristic of warmer climates.

CThe vegetation and climate on some parts of the pingo may be characteristic of those of the surrounding lowlands

DThe climate and vegetation vary among parts of a pingo, and the micro-climate of its upper part differs from that of the surrounding lowlands.

 

2

Periglacial regions are cold-climate areas that are located near the margins of glaciers-permanent ice sheets covering parts of the Arctic and other cold places. In some periglacial regions, huge mounds (hills) consisting of an outer layer of soil covering a core of solid ice may rise out of an otherwise flat landscape. These structures, called pingos, often develop over dried-out lake basins or along the sides of streams and rivers. Pingos become elevated by the growth of an ice core in the center of the mound, formed as a result of water pressure from below. Usually they develop in the sites where springs of water rise from the ground under pressure and feed the ice core, which freezes as it nears the surface of the ground. The upper part of the mound has a very different microclimate from the surrounding lowlands, and the southern slopes of the pingo mound may bear vegetation characteristic of a warmer climate, possibly even a tree cover. If the general climate becomes warmer, however, the ice core in the center of the pingo melts and the whole mass collapses to form a deep pool, surrounded by a circular rim or “rampart” formed from the soil and other organic material raised up by the mound. Circular ponds with ramparts can be found far to the south of the present-day Arctic regions, indicating the periglacial conditions that once prevailed there.

According to paragraph 1, all of the following statements about pingos are true EXCEPT.

Negative Factual Information Questions否定事实信息题

AThey are formed by the small movements of nearby glaciers

BThey consist of an ice core covered by layer of soil

CThey are sometimes found in the place where a lake had existed earlier.

DTheir remains can be used to identify previous periglacial conditions in certain areas.

 

3

Periglacial regions are cold-climate areas that are located near the margins of glaciers-permanent ice sheets covering parts of the Arctic and other cold places. In some periglacial regions, huge mounds (hills) consisting of an outer layer of soil covering a core of solid ice may rise out of an otherwise flat landscape. These structures, called pingos, often develop over dried-out lake basins or along the sides of streams and rivers. Pingos become elevated by the growth of an ice core in the center of the mound, formed as a result of water pressure from below. Usually they develop in the sites where springs of water rise from the ground under pressure and feed the ice core, which freezes as it nears the surface of the ground. The upper part of the mound has a very different microclimate from the surrounding lowlands, and the southern slopes of the pingo mound may bear vegetation characteristic of a warmer climate, possibly even a tree cover. If the general climate becomes warmer, however, the ice core in the center of the pingo melts and the whole mass collapses to form a deep pool, surrounded by a circular rim or “rampart” formed from the soil and other organic material raised up by the mound. Circular ponds with ramparts can be found far to the south of the present-day Arctic regions, indicating the periglacial conditions that once prevailed there.

According to paragraph 1, a circular pond with a rampart forms when

Factual Information Questions事实信息题

Aice mixes with soil and other organic material

Ba pingo falls in because its core has melted

Cnew pingos begin to grow nearby

Dperiglacial conditions begin to prevail in the area of a pingo

 

4

A similar type of structure is sometimes formed in those regions of the Arctic that are rich in peat (decomposed plant material), and this is termed a palsa. Palsas, like pingos, are large mounds that are formed by the development of ice beneath the surface of the ground. Generally smaller than pingos, palsas are only 2 to 3 meters in height and about 45 meters across. They often lie within wetland (water-saturated) areas, where they are interspersed with open pools and other palsas in various states of development. Palsas begin their formation as small irregularities on the surface of an area of low-lying land that is saturated in water. Even a very small elevation of a few centimeters can affect snow accumulation. The snow is blown from the slight mound and accumulates in the hollows between, so the more elevated spots have less snow cover in the winter. They therefore become cold, because snow acts as an insulating blanket, retaining some of the ground’s heat that it gained in the summer sun. By contrast, the cold penetrates any small raised areas of ground, causing an ice core to develop within them. As the ice forms, it expands, pushing the mound even higher so that even less snow is retained in the high winds. Palsa growth is thus a self-propagating process: the higher the palsa grows, the colder it becomes, and the colder it becomes, the more the ice core expands and pushes the palsa upward. The ice core survives through the summer, so its growth continues for many years, even centuries.

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

Vocabulary Questions词汇题

Aenters and spreads through

Bmaintains direct contact with

Caffects

Dfreezes

 

5

A similar type of structure is sometimes formed in those regions of the Arctic that are rich in peat (decomposed plant material), and this is termed a palsa. Palsas, like pingos, are large mounds that are formed by the development of ice beneath the surface of the ground. Generally smaller than pingos, palsas are only 2 to 3 meters in height and about 45 meters across. They often lie within wetland (water-saturated) areas, where they are interspersed with open pools and other palsas in various states of development. Palsas begin their formation as small irregularities on the surface of an area of low-lying land that is saturated in water. Even a very small elevation of a few centimeters can affect snow accumulation. The snow is blown from the slight mound and accumulates in the hollows between, so the more elevated spots have less snow cover in the winter. They therefore become cold, because snow acts as an insulating blanket, retaining some of the ground’s heat that it gained in the summer sun. By contrast, the cold penetrates any small raised areas of ground, causing an ice core to develop within them. As the ice forms, it expands, pushing the mound even higher so that even less snow is retained in the high winds. Palsa growth is thus a self-propagating process: the higher the palsa grows, the colder it becomes, and the colder it becomes, the more the ice core expands and pushes the palsa upward. The ice core survives through the summer, so its growth continues for many years, even centuries.

According to paragraph 2, in areas where palsas form, why is there a temperature difference in the winter between the slightly higher spots and the slightly lower spots that are in between?

Factual Information Questions事实信息题

AThe higher spots are warmer because they receive and retain more heat from the summer sun

BThe higher spots are colder because they lose heat through the hollows that appear in them.

CThe lower spots are warmer because they retain insulating snow.

DThe lower spots are colder because they remain saturated with water.

 

6

A similar type of structure is sometimes formed in those regions of the Arctic that are rich in peat (decomposed plant material), and this is termed a palsa. Palsas, like pingos, are large mounds that are formed by the development of ice beneath the surface of the ground. Generally smaller than pingos, palsas are only 2 to 3 meters in height and about 45 meters across. They often lie within wetland (water-saturated) areas, where they are interspersed with open pools and other palsas in various states of development. Palsas begin their formation as small irregularities on the surface of an area of low-lying land that is saturated in water. Even a very small elevation of a few centimeters can affect snow accumulation. The snow is blown from the slight mound and accumulates in the hollows between, so the more elevated spots have less snow cover in the winter. They therefore become cold, because snow acts as an insulating blanket, retaining some of the ground’s heat that it gained in the summer sun. By contrast, the cold penetrates any small raised areas of ground, causing an ice core to develop within them. As the ice forms, it expands, pushing the mound even higher so that even less snow is retained in the high winds. Palsa growth is thus a self-propagating process: the higher the palsa grows, the colder it becomes, and the colder it becomes, the more the ice core expands and pushes the palsa upward. The ice core survives through the summer, so its growth continues for many years, even centuries.

According to paragraph 2, which of the following statements about palsa growth is true?

Factual Information Questions事实信息题

AIt occurs when the palsa becomes colder causing the ice inside to expand

BIt occurs most rapidly during the summer.

CIt causes surrounding areas to become colder.

DIt is eventually stopped by wind when the palsa reaches a certain height.

 

7

As the palsa grows in height, drainage (the ability of water to move down) improves and the vegetation on its surface becomes drier. The surface of the palsa may then develop a vegetation cover of lichens (small plantlike organisms). Many lichens are white or pale gray, and these reflect the sunlight, keeping the mound cool in summer. In the course of time, dwarf shrubs replace these lichens, but these have a darker color and absorb more heat from the summer sun. This, coupled with the increasing height of the dome, eventually leads to gradual removal of the surface soil, revealing the peat beneath. The dark-colored peat absorbs even more heat, and its exposure leads to the meltdown of the ice core. The core collapses quite quickly, leading to the formation of an open pool of water that is available for recolonization by wetland plants as the cycle begins again. Finnish scientists, working in the 1980s, demonstrated experimentally how this process operates. They spent a whole winter visiting an area of the Arctic wetland where, using a broom, they swept an area clear of snow and kept it clear through the winter. The result was the development of a permanent ice core beneath the ground, and within a few years the swept locality was developing into a palsa.

Which of the following can be inferred from paragraph 3 about new palsas that have not yet grown much in height?

Inference Questions推理题

AThey have not yet developed any kind of ice core.

BThey are too wet to support a cover of lichens

CThey have better drainage than taller palsas do

DThey support more wetland plants than the surrounding low- lying land does

 

8

As the palsa grows in height, drainage (the ability of water to move down) improves and the vegetation on its surface becomes drier. The surface of the palsa may then develop a vegetation cover of lichens (small plantlike organisms). Many lichens are white or pale gray, and these reflect the sunlight, keeping the mound cool in summer. In the course of time, dwarf shrubs replace these lichens, but these have a darker color and absorb more heat from the summer sun. This, coupled with the increasing height of the dome, eventually leads to gradual removal of the surface soil, revealing the peat beneath. The dark-colored peat absorbs even more heat, and its exposure leads to the meltdown of the ice core. The core collapses quite quickly, leading to the formation of an open pool of water that is available for recolonization by wetland plants as the cycle begins again. Finnish scientists, working in the 1980s, demonstrated experimentally how this process operates. They spent a whole winter visiting an area of the Arctic wetland where, using a broom, they swept an area clear of snow and kept it clear through the winter. The result was the development of a permanent ice core beneath the ground, and within a few years the swept locality was developing into a palsa.

In paragraph 3, the author discusses experiments conducted in an area of the Arctic in order to

Rhetorical Purpose Questions修辞目的题

Aprovide evidence supporting the explanation of how palsas begin to form

Bshow how wetland plants recolonize an open pool of water

Cdemonstrate the role of erosion in the collapse of fully formed palsas

Dexplain how the scientific understanding of the growth and collapse of palsas changed after the 1980s

 

9

As the palsa grows in height, drainage (the ability of water to move down) improves and the vegetation on its surface becomes drier. ⬛ The surface of the palsa may then develop a vegetation cover of lichens (small plantlike organisms). ⬛ Many lichens are white or pale gray, and these reflect the sunlight, keeping the mound cool in summer. ⬛ In the course of time, dwarf shrubs replace these lichens, but these have a darker color and absorb more heat from the summer sun. ⬛ This, coupled with the increasing height of the dome, eventually leads to gradual removal of the surface soil, revealing the peat beneath. The dark-colored peat absorbs even more heat, and its exposure leads to the meltdown of the ice core. The core collapses quite quickly, leading to the formation of an open pool of water that is available for recolonization by wetland plants as the cycle begins again. Finnish scientists, working in the 1980s, demonstrated experimentally how this process operates. They spent a whole winter visiting an area of the Arctic wetland where, using a broom, they swept an area clear of snow and kept it clear through the winter. The result was the development of a permanent ice core beneath the ground, and within a few years the swept locality was developing into a palsa.

Look at the four squaresthat indicate where the following sentence could be added to the passage

As a result, this type of vegetation helps preserve the palsa’s ice core.Insert Text Questions句子插入题

Where would the sentence best fit？Click on a square  sentence to the passage.

10

Pingos and palsas are two types of mounds that develop in periglacial regions.

Prose Summary Questions概要小结题

Select 3 answers

APalsas form where wetland water freezes into an ice core, while pingos, which are generally larger than palsas, have an ice core fed by underground water rising under pressure.

BA palsa may eventually become a pingo if the conditions remain cold enough for the palsa to continue to expand in height and width.

CPingos and palsas grow in size as snow builds up in the winter and does not completely melt in the summer, refreezing into ice sheets when the winter returns

DMelting of the ice core due to warmer conditions results in the collapse of pingos and palsas, leading to the formation of a pool of water where the mound once was.

EAs a palsa grows, its vegetation may change first to lichens and later to shrubs that absorb heat and thus destroy the palsa, allowing wetland plants to grow in its place again.

FAs palsa’s shrubs die, their decomposition leads to the formation of large amounts of peat on the palsa’s surface, and this process may continue for many years.