Glaciers and Glaciation

We live today in the twilight of a great episode of refrigeration, when much of the Northern Hemisphere was covered by continental ice sheets, like those that still cover Antarctica and Greenland. Although the ice itself has now retreated from most of Europe, Asia, and North America, it has left traces of its influence across the whole face of the landscape in jagged mountain peaks, gouged-out upland valleys, swamps, changed river courses, and boulder-strewn, table-flat prairies in the lowlands.

Glaciers are thick masses of slow-moving ice. In the higher lands and polar regions, the annual winter snowfall usually exceeds the summer loss by melting. Permanent snow fields build up, and their lowest boundary is the snow line, the actual height of which varies with latitude and climate. Buried snow recrystallizes to form ice, which moves slowly under its own weight. It moves most rapidly in the middle of the glacier.

Exercise 3. Read the text above once again and decide true or false are the following statements:

1. The episode of refrigeration is at its height.

2. Antarctica and Greenland are still covered by ice sheets.

3. Jagged mountain peaks, gouged-out upland valleys, swamps, changed river courses, and boulder-strewn, table-flat prairies in the lowlands are the traces of glaciation.

4. Glaciers usually move quickly.

5. The snow doesn’t fall in the higher lands.

6. In the polar regions the snow melts in summers.

7. The actual height of the lowest boundary of the snow line depends on latitude and climate.

8. In the top layer snow recrystallizes to form ice.

9. The central part of the glacier is the most rapid.

Exercise 4. Read the following text “Glacial Erosion” and fill in the gaps with the words given below:

Glacial Erosion

Glacial erosion has a powerful 1 … upon land that has been buried by ice and has done much to shape the 2 … ranges of our present world. Both valley and continental glaciers acquire many 3 … of boulders and rock fragments, which, frozen into the sole of the glacier, gouge and rasp the rocks over which the glaciers pass. The rocks are slowly 4 … down to a smooth, fluted, grooved surface. Glacial meltwater, from periods of daylight or 5 … thaw, seeps into rock fissures and joints. When it 6 … again, it helps to shatter the rocks, some of which may become frozen into the body of the glacier and be 7 … away as the glacier moves down-slope. Avalanches and undercutting of 8 … sides add to the rock debris.

1. – abraded

2. – carried

3. – mountain

4. – freezes

5. – summer

6. – thousands

7. – valley

8. – effect

Exercise 5. Look through the texts above once again and answer the following questions:

1. How far are we today from the great episode of refrigeration?

2. Which parts of the Earth are still covered with the ice sheet?

3. What trace has glaciation left on the other parts of the world?

4. Why does the snow in the higher lands and polar regions stay permanently?

5. When does snow recrystallize to form ice?

6. How does the glacier move?

7. How have mountain ranges appeared on the surface of our present world?

8. How does the surface of the rocks become smooth, fluted or grooved?

Exercise 6. Read, write down, and translate the secret information about mountains’ changing:

Before During After

A. Copy separating words and sentences: