GRG 301C: Ch. 11, Glaciers
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nikkifahrenthold on April 10, 2012
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43 terms
Terms | Definitions |
|---|---|
 glacier | a thick ice mass that forms over hundreds or thousands of years; it originates on land from the accumulation, compaction, and recrystallization of snow. |
| valley (alpine) glacier | a glacier confined to a mountain valley, which in most instances had previously been a stream valley |
| ice sheet | a very large, thick mass of glacial ice flowing outward in all directions from one or more accumulation centers |
| ice cap | a mass of glacial ice covering a high upland or plateau and spreading out radially |
| outlet glacier | a tongue of ice normally flowing rapidly outward from an ice cap or ice sheet, usually through mountainous terrain to the sea |
| piedmont glacier | a glacier that forms when one or more valley glaciers emerge from the confining walls of mountain valleys and spread out to create a broad sheet in the lowlands at the base of the mountains |
| snowline | the lower limit of perennial snow |
| crevass | a deep crack in the brittle surface of a glacier |
| zone of accumulation | the part of a glacier characterized by snow accumulation and ice formation |
| calving | wastage of a glacier that occurs when large pieces of ice break off into water |
| glacial budget | the balance, or lack of balance, between accumulation at the upper end of a glacier and loss at the other end |
| ablation | a general term for the loss of ice and snow from a glacier |
| plucking | the process by which pieces of bedrock are lifted out of place by a glacier |
| abrasion | the grinding and scraping of a rock surface by the friction and impact of rock particles carried by water, wind, or ice |
| rock flour | ground-up rock produced by the grinding effect of a glacier |
| glacial striations | scratches and grooves on bedrock caused by glacial abrasion |
| glacial trough | a mountain valley that has been widened, deepened, and straightened by a glacier |
| hanging valley | a tributary valley that enters a glacial trough at a considerable height above the floor of the trough |
| pater noster lakes | a chain of small lakes in a glacial trough that occupy basins created by glacial erosion |
| cirque | an amphitheater-shaped basin at the head of a glaciated valley produced by frost wedging and plucking |
| tarn | a small lake in a cirque |
| fiord | a steep-sided inlet of the sea formed when a glacial trough was partially submerged |
| arete | a narrow, knife-like ridge separating two adjacent glaciated valleys |
| horn | a pyramid-like peak formed by glacial action in three or more cirques surrounding a mountain summit |
| glacial drift | an all-embracing term for sediments of glacial origin, no matter how, where, or in what shape they were deposited |
| till | unsorted sediment deposited directly by a glacier |
| stratified drift | sediments deposited by glacial meltwater |
| glacial erratic | an ice-transported boulder that was not derived from the bedrock near its present site |
| lateral moraine | a ridge of till along the sides of a valley glacier composed primarily of debris that fell to the glacier from the valley walls |
| medial moraine | a ridge of till formed when lateral moraines from two coalescing valley glaciers join |
| end moraine | a ridge of till marking a former position of the front of the glacier |
| ground moraine | an undulating layer of till deposited as the ice front retreats |
| outwash plain | a relatively flat, gently sloping plain consisting of materials deposited by meltwater streams in front of the margin of an ice sheet |
| valley train | a relatively narrow body of stratified drift deposited on a valley floor by meltwater streams that issue from the terminus of a valley glacier |
| kettle holes | depressions created when blocks of ice become lodged in glacial deposits and subsequently melt |
| drumlin | a streamlined asymmetrical hill composed of glacial till. the steep side of the hill faces the direction from which the ice advanced. |
| esker | sinuous ridge composed largely of sand gravel deposited by a stream flowing in a tunnel beneath a glacier near its terminus |
| kame | a steep-sided hill, composed of sand and gravel, originating when sediment collected in openings in stagnant glacial ice |
| pluvial lake | a lake formed during a period of increased rainfall |
| Pleistocene epoch | an epoch of the Quaternary Period beginning about 1.8 million years ago and ending about 10,000 years ago. Best known as a time of extensive continental ice sheets. |
| plastic | type of flow that occurs within the ice. Under pressure, ice behaves as a plastic material |
| basal slip | type of flow in which the entire ice mass slips along the ground; most glaciers are thought to move by this process |
| zone of fracture | zone that occurs in the uppermost 50 meters; tension causes crevasses to form in brittle ice |
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