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CHAPTER 15 Glaciers and Glaciation

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CHAPTER 15 Glaciers and Glaciation Page 53 CHAPTER 15 Glaciers and Glaciation 1. Glaciers are masses of ice on land that move by plastic flow and basal slip. Glaciers currently cover about 10% of the land surface and contain 2% of all water on Earth. 2. How does glacial ice form, and why is it considered to be a rock? 3. Valley glaciers are confined to mountain valleys and flow from higher to lower elevations, whereas continental glaciers cover vast areas and flow outward in all directions from a zone of accumulation. 4. Other than size, how do valley glaciers differ from continental glaciers? 5. A glacier forms when winter snowfall in an area exceeds summer melt and therefore accumulates year after year. Snow is compacted and converted to glacial ice, and when the ice is about 40 m thick, pressure causes it to flow. 6. Firn is: a. freshly fallen snow; b. a granular type of ice; c. a valley train; d. another name for the zone of wastage; e. a type of glacial groove. 7. Pressure on ice at depth in a glacier causes it to move by: a. rock creep; b. fracture; c. basal slip; d. surging; e. plastic flow. 8. Crevasses in glaciers extend down to: a. about 300 in; b. the base of the glacier; c. the zone of plastic flow; d. variable depths depending on how thick the ice is; e. the outwash layer. 9. The behavior of a glacier depends on its budget, which is the relationship between accumulation and wastage. If a glacier possesses a balanced budget, its terminus remains stationary; a positive or negative budget results in advance or retreat of the terminus, respectively. 10. Explain in terms of the glacial budget how a once active glacier becomes a stagnant glacier. 11. If a glacier has a negative budget: a. the terminus will retreat; b. its accumulation rate is greater than its wastage rate; c. all flow ceases; d. the glacier's length increases; e. crevasses will no longer form. 12. Glaciers move at varying rates depending on the slope, discharge, and season. Valley glaciers tend to flow more rapidly than continental glaciers. 13. What is the relative importance of plastic flow and basal slip for glaciers at high and low latitudes? 14. What is a glacial surge and what are the probable causes of surges? Page 54 15. Glaciers are powerful agents of erosion and transport because they are solids in motion. They are particularly effective at eroding soil and unconsolidated sediment, and they can transport any size sediment supplied to them. 16. Explain how glaciers erode by abrasion and plucking. 17. Why are glaciers more effective agents of erosion and transport than running water? 18. Rocks abraded by glaciers may develop a smooth surface that shines in reflected light. Such a surface is called glacial: a. grooves; b. polish; c. flour; d. striations; e. till. 19. Which of the following is a glacial erratic? a. deposit of unsorted, unstratified till; b. glacially transported boulder far from its source; c. sand and gravel deposited in a depression on a glacier; d. U-shaped glacial trough; e. deposits consisting of light and dark layers. 20. Continental glaciers transport most of their sediment in the lower part of the ice, whereas valley glaciers may carry sediment in all parts of the ice. 21. Erosion of mountains by valley glaciers yields several sharp, angular landforms including cirques, arêtes, horns, U-shaped glacial troughs, fiords, and hanging valleys. 22. Describe the processes responsible for the origin of a cirque, U-shaped glacial trough, and hanging valley. 23. The bowl-shaped depression at the upper end of a glacial trough is a(an): a. inselberg; b. cirque; c. lateral moraine; d. drumlin; e. till. 24. A small take in a cirque is a: a. pluvial lake; b. proglacial lake; c. tarn; d. salt lake; e. glacial trough lake. 25. What is an arête and how does one form? 26. Which of the following is not an erosional landform? a. horn; b. arête; c. lateral moraine; d. U-shaped glacial trough, e. roche moutonnée. 27. A knifelike ridge separating glaciers in adjacent valleys is a(an): a. fiord; b. horn; c. arête; d. cirque; e. lateral moraine. 28. Headward erosion of a group of cirques on the flanks of a mountain may produce a(an): a. tarn; b. varve; c. drumlin, d. kettle; e. horn. 29. A pyramid-shaped peak formed by glacial erosion is a: a. fiord; b. medial moraine; c. horn; d. cirque; e. hanging valley. Page 55 30. Continental glaciers abrade and bevel high areas, producing a smooth, rounded landscape. 31. How do the erosional landforms of continental glaciers differ from those of valley glaciers? 32. Depositional landforms include moraines, which are ridgelike accumulations of till. Several types of moraines are recognized, including terminal, recessional, lateral, and medial moraines. 33. Discuss the processes whereby terminal, recessional, and lateral moraines form. 34. How does a medial moraine form, and how can one determine the number of tributaries a valley glacier has by its medial moraines? 35. Glacial drift is a general term for: a. the erosional landforms of continental glaciers; b. all the deposits of glaciers; c. icebergs floating at sea; d. the movement of glaciers by plastic flow and basal slip; e. the annual wastage rate of a glacier. 36. The number of medial moraines on a glacier generally indicates the number of its a. tributary glaciers; b. terminal moraines; c. eskers; d. outwash plains; e. valley trains. 37. Drumlins are composed of till reshaped into streamlined hills by continental glaciers. 38. Describe drumlins, and explain how they form. 39. Stratified drift consists of sediments deposited in or by meltwater streams issuing from glaciers; it is found in outwash plains and valley trains. Ridges called eskers and conical hills called kames are also composed of stratified drift. 40. What are outwash plains and valley trains? 41. In a roadside outcrop, you observe a deposit of alternating light and dark laminated mud containing a few large boulders. Explain the sequence of events responsible for its deposition. 42. During the Pleistocene Epoch, glaciers covered about 30% of the land surface. Several intervals of widespread glaciation, separated by interglacial periods, occurred in North America. The other Northern Hemisphere continents were also affected by widespread Pleistocene glaciation. 43. The most recent ice age occurred during the: a. Archean Eon; b. Pleistocene Epoch; c. Mesozoic Era, d. Cambrian Period; e. Tertiary Period. 44. Areas far beyond the ice were affected by Pleistocene glaciation; climate belts were compressed toward the equator, large pluvial lakes existed in what are now and regions, and sea level was as much as 130 m lower than at present. Page 56 45. How do pluvial lakes differ from proglacial lakes? Give an example of each of these types of lakes. 46. Loading of the Earth's crust by Pleistocene glaciers caused isostatic subsidence. When the glaciers disappeared, isostatic rebound began and continues in some areas. 47. We can be sure that the ancient shorelines of the Great Lakes were horizontal when they were formed, yet now they are not only elevated above their former level but they also tilt toward the south. How can you account for these observations? 48. Major glacial intervals separated by tens or hundreds of millions of years probably occur as a consequence of the changing positions of tectonic plates, which in turn cause changes in oceanic and atmospheric circulation patterns. 49. Currently, the Milankovitch theory is widely accepted as the explanation for glacial- interglacial intervals. 50. The reasons for short-term climatic changes, such as the Little Ice Age, are not understood. Two proposed causes for such events are changes in the amount of solar energy received by Earth and volcanism. abrasion glacier arête ground moraine basal slip hanging valley cirque horn continental glacier lateral moraine drumlin medial moraine end moraine Milankovitch theory esker outwash plain fiord plastic flow firn recessional moraine firn limit stratified drift glacial budget terminal moraine glacial drift till glacial erratic U-shaped glacial trough glacial groove valley glacier glacial ice valley train glacial polish zone of accumulation glacial striation zone of wastage.
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