Green Icebergs

Toefl Practice Test 2 Reading

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Green Icebergs

​Icebergs are massive blocks of ice, irregular in shape; they float with only 12% of their Mass above the sea surface. They are formed by glaciers, large rivers of ice that begin in land in the snows of Greenland, Antarctica, and Alaska and they move slowly towards the sea. the forward movement, the melting at the base of the glacier where it meets the ocean, and waves and tidal action cause blocks of ice to break off and Float out into the sea. 

Icebergs are ordinarily  blue to white, although they sometimes appear to be dark or  opaque because they carry gravel and bits of rock. They may change color with changing light conditions and Cloud cover, glowing pink or gold in the morning or evening light, but this color change is generally related to the low angle of the sun above the horizon. however, travelers to Antarctica have repeatedly reported seeing green icebergs in the Weddell sea and, more commonly, close to the Amery ice shelf in East Antarctica 

​One explanation for green icebergs attributes their color to an optical illusion when blue ice is illuminated by a near horizon red sun, but green icebergs stand Out among white and blue icebergs under a great variety of light conditions. Another suggestion is that the color might be related to the ice with high levels of metallic compounds, including copper and iron. Recent Expeditions have taken ice samples from Green icebergs and ice cores, vertical, cylindrical ice samples reaching down to a great depths from the glacial ice shelves along the Antarctic continent. analysis of these cores and samples provide a different solution to the problem.

The ice shelf cores, with a total length of 215 m ( 705 ft), were long enough to penetrate through glacial ice, which is formed from the compaction of snow and contains air bubbles, and continue into clear, bubble free ice formed from seawater that freezes onto the bottom of the glacial ice. The properties of this clear sea ice were very similar to the ice from the green iceberg. The scientists concluded that green icebergs form when a two layer block of shelf ice breaks away and capsizes( Turns Upside Down), exposing the bubble free ice shelf that was formed from seawater. 

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A green iceberg that stranded just west of the Amery  ice shelf showed two distinct layers, bubbly blue white ice and bubble free green ice separated by a 1 meter long ice layer containing sediments. The green ice portion was textured by seawater erosion. wear cracks were present, the color was light green because of light scattering, where no cracks were present, the color was dark green. no apples were present in the green ice, suggesting that the ice was not formed from the compression of snow but instead from the freezing sea water. large concentrations of single-celled organisms with green pigments( coloring substances) occur along the edges of the ice shelves in this region; the sea water is rich in their decomposing organic material. The green Iceberg did not contain large amounts of particles from these organisms, but the ice had accumulated dissolved organic matter from the sea water. It appears that unlike salt, dissolved organic substances are not excluded from the ice in the freezing

​process. Analysis shows that the dissolved organic material absorbs enough blue wavelengths from solar light to make ice appear green. 

Chemical evidence shows that platelets( minute flat portions) of ice form in the water and then accrete  and stick to the bottom of the ice shelf to form a slush( partially melted snow). The slush is compacted by an unknown mechanism, and solid bubble free ice is formed from water high and soluble organic substances. When an iceberg separates from the ice shelf and capsizes, the green ice is exposed.

 The Amery  ice shelf appears to be uniquely suited to the production of green icebergs. Once detached from the ice shelf, these bugs drift in the currents and wind systems surrounding Antarctica and can be found scattered among Antarctica's less colorful icebergs.

Multiple Choice

According to paragraph 1, all of the following are true of icebergs Except:

• They do not have a regular shape

•  there are formed where glaciers meet the ocean

• most of their mass is above sea surface

•  waves and tides cause them to break off glaciers 

Multiple Choice

According to paragraph 2, what causes icebergs to sometimes appear dark or opaque?

• a heavy cloud cover

•  the presence of gravel or bits of rock

• the low angle of the sun above the horizon

• the presence of large cracks in their surface 

Multiple Choice

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. 

• One explanation notes that green icebergs stand out among other icebergs under a great variety of light conditions, but this is a attributed to an optical illusion 

• One explanation for the color of green icebergs a tributes their color to an optical illusion that occurs when light from a near Horizon Red Sun Shines on a blue iceberg 

• One explanation for green icebergs attributes their color to a great variety of light conditions, but green icebergs Stand Out best among other icebergs when illuminated by a near Horizon Red Sun 

• One explanation attributes the color of green icebergs to an optical illusion under special light conditions, but green icebergs appear distinct from other icebergs under a great variety of light conditions 

Multiple Choice

The word ‘penetrate’ in the passage is closest in meaning to 

• collect

• pierce

• melt

• endure

Multiple Choice

According to paragraph 4, how is glacial ice formed?

•  by the compaction of snow

•  By the freezing of seawater on the bottom of ice shelves

• By breaking away from the ice shelf

•  by  the capsizing of a two layer block of ice shelf

Multiple Choice

According to paragraph 4, ice  shelf cores  helped scientists explain the formation of green icebergs by showing that

•  the ice at the bottom of green icebergs is bubble free ice formed from Frozen seawater

•  bubble free ice is found at the top of the ice shelf

• glacial ice is lighter and floats better than sea ice

•  the clear sea ice at the bottom of the ice shelf is similar to ice from a green iceberg

Multiple Choice

Why does the author mention that ‘The  green ice portion was textured by sea water erosion’?

 

•  to explain why cracks in the iceberg appeared light green instead of dark green

•  to suggest that green ice is more easily eroded by seawater than white ice is

•  to support the idea that green ice had been at the bottom layer before capsizing

•  to explain how the air bubbles had been removed from the green ice

Multiple Choice

The word 'accumulated' is closest in meaning to

• collected

• frozen

• released

• covered

Multiple Choice

The word 'excluded' is closest in meaning to

• kept out

• compressed

• damaged

• gathered together

Multiple Choice

The word 'accrete' in the passage is closest in meaning to

• advance

• transfer

• flatten out

• come together

Multiple Choice

Which of the following is NOT  explained in the passage

 

•  why blocks of Ice Break wear glasses meet the ocean

•  why blocks of ice shelf sometimes capsize after breaking off

•  why green icebergs are commonly produced in some parts of Antarctica

• why green icebergs contain large amounts of dissolved organic pigments

Multiple Choice

The passage supports which of the following statements about the Amery  ice shelf?

•  The Amery  ice shelf produces on the green icebergs

•  The Amery  ice shelf produces green icebergs because it's ice contains high levels of metallic compounds such as copper and iron

•  The Amery  ice shelf produces green icebergs because the sea water is rich in a particular kind of soluble organic material

•  no green icebergs are found far from the Amery  ice shelf