Man's physical universe

xanabras

166 THK EARTH AS MAN'S ABODE

STUDY QUESTIONS

1. What processes offset the results of degradation?

2. What is isostasy?

3. What is an earthquake?

4. Recent data suggest the possibility that some earthquakes occur at depths

of five hundred miles, but this depth does not seem likely to be a region of

fractures. Two views arise: (1) the earthquakes are caused by fractures, and

fractures occur at greater depths than is commonly thought; or else (2) (Suggest

another possible alternative.)

5. All the known ice ages occurred either during or soon after continental uplifts

and mountain-building. Thus the earth may be said to manufacture its own

ages. Volcanic activity was also very great during these mountain-building

periods. Is there any evidence in this section that would support this idea

that the earth manufactures its own ice ages?

6. Why do earthquakes often occur along certain seacoasts?

7. What is a fault, and how is it produced?

8. Why have the eroding and transporting action of the various degrading

factors not brought all land areas below sea level?

9. What processes bring about a shift in weight and pressure on the earth's

surface?

10. E.xplain the present gradual elevation in the Great Lakes region.

11. Explain how earthquake centers may be located.

12. Explain the principle of the seismograph.

13. Differentiate between the behavior and nature of the two types of volcanoes.

14. What is the cause of volcanoes?

15. Of what kinds of tremors do earthquakes consist?

16. Is there any reason why earthquake regions should also be volcanic regions?

17. What are the causes of earthquakes?

18. Are there any evidences of present volcanic activity in the United States?

19. What are dikes, sills, and laccoliths?

20. Mention some well-known topographic features that are volcanic in origin.

21. What is diastrophism?

22. Why do earthquakes occur more often in California than in the Mississippi

Basin?

23. Give several examples of very destructive explosive \'olcanoes.

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