Glaciers - Reading Comprehension Test (Page 2 of 4) in pdf

5. What general direction did the ice sheet

move? Why do you think this is?

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6. What do you think the “terminal Moraine” is

and what does it tell us about the glacier that

once covered New York State?

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How do Glaciers Cause Erosion?

When a glacier advances down a valley or over

a continent, the ice pushes, carries, and drags

great quantities of soil and sediment. These

loose materials have little chance of

remaining in place when a mass of ice

hundreds or even thousands of meters thick moves over them. Ridges and knobs of bedrock are pried loose or

rounded by the moving ice. Although ice is much softer than most bedrock, the rocks and sediment dragged along

the bottom of a glacier scrape and scour the bedrock over which the glacier passes.

7. How can glacial striations (scratches) tell you the direction the glacier moved?

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Valleys

In mountainous or hilly terrain, advancing glaciers seek the lowest passages and move through valleys ﬁrst. Stream

valleys often have a V-shape in proﬁle, especially in mountain areas. Streams and the sediment they carry occupy only

the bottom of the valley and do not erode the sides of the valley. The sides of a

stream valley in mountainous terrain collapse under the inﬂuence of weathering

and gravity, which often give them a steep but uniform slope of the V-proﬁle.

When a glacier moves down a mountain valley ﬁlling it with ice,the erosive action

of the glacier and its load of sediment pluck, scrape, and scour the sides of the

valley changing its proﬁle to a broader U-shape. U-shaped valleys are strong

evidence of glacial erosion.

8. Why do rivers create V-shaped valleys while glaciers create U-shaped valleys?

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How Can we Recognize Deposition Caused by Glaciers?

Sediment transported by glaciers must also be deposited. There are several

differences between sediments deposited by ice and sediments deposited by

water or wind. Water and wind sort sediments. Moving ice transports and deposits

sediment without regard to particle sizes. Therefore, sediments deposited directly

by glaciers are unsorted and do not show layering. This unsorted glacial debris is sometimes called till. Stream

sediments are deposited where streams ﬂow, usually in the bottom of a valley. But a glacier can move its debris

anywhere that the ice covers, even to the highest parts of New York State. Glacial sediments often cover

the whole land surface with an uneven blanket of till composed of mixed particle sizes. Water and wind

usually deposit the larger particles of their load relatively close to its source. On the other hand,

glaciers carried their load of sediments, including boulders of granite and gneiss from Canada,

hundreds of kilometers southward into New York State. In western New York State where the local

bedrock is sedimentary,most often shale, siltstone, and limestone, these foreign rock types are

especially noticeable. New York soils have a greater variety of minerals and they are more fertile than

Unsorted Glacial

Sediment

they would have been if they contained only local rocks. Large rocks that were transported from one

area to another by glaciers are known as erratics.

Glaciers - Reading Comprehension Test Page 2

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