Glaciers - Reading Comprehension Test printable pdf download

Name: __________________________________________________ Date: _______________ Period: _________

GLACIERS

What is a glacier?

Snow falls and accumulates on the ground everywhere in New York State. In the highest parts of the

Adirondack Mountains, winter snow often lasts into early summer before it is completely melted. If the mountains

were 1000 or 2000 meters higher, the reduced warmth of summer would not be able to melt winter snow. Each year

more snow would accumulate and exert pressure on the underlying snow. This pressure would change the snow to ice

and gravity would make the ice begin to ﬂow downhill. This is how glaciers form. The reason that no glaciers exist

today in New York State is that there are no places where the snow does not completely melt before the following

winter.

Snow and ice exist as crystals. When snow falls,the ﬂakes are usually light and feathery. After the ﬂakes reach

the ground and are buried under fresh snow,the delicate crystals gradually change to solid ice over a period of time

that depends on such factors as speed of burial and temperature. Is ice a solid or a liquid? Ice is composed of water in

the crystalline solid form. It ﬁts the deﬁnition of a solid. Under short-term stress, ice behaves as a solid. An ice cube

in an environment below freezing has a ﬁxed shape. Hit it with a hammer and it breaks into smaller pieces. Yet, ice in

a glacier ﬂows. Glaciers do not ﬂow because the ice is melting. They ﬂow because solid ice responds to long-term

stress by bending and deforming.

1. Brieﬂy describe how glaciers form.

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2. Why are there currently no glaciers in New York State?

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3. What causes ice, a solid material, to be able to ﬂow downhill like a liquid?

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Types of Glaciers

C ont i nent al Gl ac i ers

Val l ey Gl ac i ers

A continental glacier ﬂows outward from a zone of

Once permanent ice has formed atop mountains, it

accumulation to cover a large part of a continent. If the

begins to ﬂow downhill under the inﬂuence of gravity.

process could be speeded up, it might resemble what

Valley glaciers, which begin high in mountain areas,

pancake batter looks like as it is poured onto a griddle.

ﬂow from the high ice ﬁelds through valleys to lower

Ice sheets that are several kilometers thick now cover

elevations. Most valley glaciers descend to an elevation

most of Greenland and Antarctica. Scientists have

where it is warm enough to melt the ice as quickly as it

studied both regions to gain an understanding of ice

advances. If the ice in the glacier is moving forward at a

caps and how they ﬂow outward and down to the

rate of 1 meter/day, but the ice is also melting back 1

oceans. Ice ﬂowing into an ocean breaks away from the

meter/day, the front of the glacier will not appear to

main body of the glacier to ﬂoat away as icebergs.

move. This is known as a dynamic equilibrium because

Because ice is less dense than water, icebergs do not

the rate of ﬂow and the rate of melting are in balance.

sink. Icebergs from Greenland and Antarctica are large

Even though the end of the glacier may be in the same

enough to pose a threat to the shipping industry. A

place from year to year, the ice is, in fact, constantly

number of vessels, for example the Titanic, have sunk

moving downhill. Ice in a small glacier may advance

due to damage from collisions with icebergs.

only a few millimeters a day while larger ones may

Fortunately, icebergs break up and melt before they

advance a few centimeters a day. As gradient and

can invade most ocean areas.

volume affect the speed of water in rivers, they also

inﬂuence the speed of ice ﬂow in glaciers. Also, like the

water in most rivers, ice moves fastest near the center

and near the surface of a glacier.

4. What is the main difference between a continental glacier and a valley glacier?

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The diagram on the left shows the extent to which the last continental ice sheet extended during the last ice age,

approximately 20,000 years ago.

Glaciers - Reading Comprehension Test

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