Chapter 12: Glaciers and Glaciation


1. A glacier is a thick ice mass that originates on land from the accumulation, compaction, and recrystallization of snow. The circumstances that glacial ice forms is when temperatures remain below freezing following a snowfall. Glaciers are created where more snow falls in winter than melts during the summer.

2. a) The term continental is often used to describe this type of glacier-ice sheets. b) The type of glacier that is also called an alpine glacier are piedmont glaciers. c) This is a stream of ice leading from the margin of an ice sheet through the mountains to the sea is an outlet glacier. d) This is a glacier formed when one or more valley glaciers spreads out at the base of a steep mountain front are piedmont glaciers. e) Greenland is the only example in the Northern Hemisphere of an ice sheet.

3. Glaciers are found today in Greenland and Antarctica, The percentage of the Earth’s land area that glaciers cover are 10 percent. The area covered by glaciers during the Pleistocene is 2/3 more than it was today.

4. Glacial flow is the name given to movement of glacial ice. One mechanism of flow involves the internal movement within the ice. The ice behaves as a brittle solid until the pressure or load is equal to the weight of 50 to 60 meters of the ice. Once the load is surpassed, the ice acts as a plastic material continuously flowing. The other mechanism is the whole ice mass slipping along the ground. In a valley glacier all the ice does not move at the same rate. The ice moves faster in the center due to the sides being slowed down by friction. Also, due to frictional drag with the bedrock floor, the lower portion moves slower than the top.

5. Crevasses form in the upper portion of a glacier but not below 50 meters because below 50 meters the plastic flow seals up the crevasses.

6. Whether a glacier is advancing, retreating, r stationary depend upon the economy of a glacier. The circumstance where a glacial front will advance is when ice accumulation exceeds ablation (balance or lack of balance between accumulation and wastage). When ice accumulation and ablation balance out the glacier is stationary and when ablation exceeds accumulation the ice front will retreat.

7. The processes of glacial erosion are plucking and abrasion. Plucking occurs when a glacier flows over a fractured bedrock surface loosening and lifting blocks of ice and incorporating them into the ice and carrying them off. Abrasion occurs when ice with its load of rock fragments moves along acting as a giant rasp or file and grinds the surface below as well as the rocks within the ice. The pulverized rock produced is called rock flour and glaciers also produce long scratches and grooves on large fragments called glacial striation.

8. A glaciated mountain valley differs from a mountain valley that was not glaciated by prior to being glaciated, a mountain valley is typically narrow and V-shaped. During glaciation, a valley glacier widens, deepens, and straightens the valley, creating a U-shaped glacial trough.

9. The erosional features that you might expect in an area where valley glaciers exist or have recently existed are U-shaped glacial troughs, hanging valleys, cirques, fiords, aretes, and horns. A glacial trough is a youthful V-shaped valley that was transformed into a U-shaped by a glacier. Hanging valleys are tributary valleys that stand high above the main trough after a glacier has receded. A cirque is a hollowed out, bowl shaped depression having precipitous walls on three sides but are open on the down valley side. Fiords are deep, steep sided inlets of the sea that exist in many high latitude areas of the world where mountains are adjacent to the oceans. Aretes are sinuous, sharp edged ridges and horns are sharp, pyramid like peaks.

10. A glacial drift is a term for all sediments of glacial origin, no matter how, where, or in what form they were deposited. The difference between till and stratified drift is that till is unsorted directly by the glacier and stratified drift is sorted and stratified and not deposited by a glacier but by glacial melt water. The general effect that glacial deposits have on the landscape is that the glacial deposits level the landscape.

11. Four basic moraine types are lateral, medial, end (terminal), and ground (recessional) moraines. All moraines are created by the deposition of glaciers which form these layers or ridges of till. The significance of terminal and recessional moraines is that an terminal moraine marks the farthest advance of a glacier and recessional moraines are formed as the ice front periodically became stationary during retreat.

12. They type of moraine that may be used to evaluate the mineral resource potential in regions occupied by valley glaciers is medial moraines.

13. Kettle form when a block of stagnant ice becomes wholly or partially buried in drift and ultimately melts, leaving a pit in the glacial sediment.

14. The ice sheet that affected the area was moving south. I was able to determine this by the steep side of the hills was to the north and the gentle side faced the south.

15. Ice-contact deposits are deposits that formed in a opening within the glacier. Kames are steep-sided hills that are composed of sand and gravel. They are believed to have originated when sediments collected in openings in stagnant ice. Eskers are ridges that are deposits made by streams flowing in tunnels beneath the ice, near the terminus of a glacier.

16. The development of the glacial theory is a good example of applying the principle of uniformitarianism. This is because scientists discovered that an extrusive ice age instead of catastrophism floods were responsible for the deposits and the many features existed. It is a good example of applying the principle of uniformitarianism since it shows an example of a large changes that occurred over a long period of time.

17. In North America four major stages of glaciation have been recognized. In the order the occurred is the Nebrashen glacial, Kansan glacial, Illinoian glacial, and Wisconsin glacial stages.

18. During the Pleistocene epoch the amount of glacial ice in the Northern Hemisphere was about twice as great as in the Southern Hemisphere. This was because the southern polar ice could not spread far beyond the margins of Antarctica while North America and Eurasia provided great expanses of land for the ice sheets to spread out on.

19. Three indirect effects of Ice Age glaciers were the forced migrations of plants and animals, many river courses have little resemblance to their preglacial routes, and land has slowly been rising because the added weight from the ice had down warped the Earth’s crust. Also, the present sea level is 130 meters higher than it was then. The growth of ice sheets had caused a worldwide drop in sea level.

20. Plate tectonics help explain the cause of ice ages by the Earth’s shifting crustal plates have carried the continents from tropical latitudes to more poleward locations causing ice ages to occur. No, the plate tectonics cannot explain the alternation between interglacial and glacial climates during the Pleistocene since climatic changes brought by moving plates are extremely gradual.

Chapter 13: Deserts and Winds(Next)
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