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(L20)Glaciers_and_Glacial_Erosion_E10

(L20)Glaciers_and_Glacial_Erosion_E10 - Glaciers and...

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1 Glaciers and Glacial Erosion – GLY 2010- Summer 2010 -Lecture 20 Ice Margin, Commonwealth Glacier, Antarctica
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2 Glacier Moving mass of ice that forms when snowfall exceeds snowmelt over a long period of time Movement is downhill, due to gravity Form at or above the snowline, the lowest altitude at which snow commonly forms in the mountains As climates warm, the snowlines are expected to move higher in elevation, and glaciers to retreat
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3 Types of Glaciers
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4 Continental Ice Sheet Large ice masses that blanket a sizable part of a continent Ice may be kilometers thick, and movement is limited, occurring mainly in local areas or very slowly over time
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5 Present Day Continental Ice Sheets Greenland and Antarctica currently are occupied by continental ice sheets
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6 Snowfield and Ice Cap Large mass of snow and ice on a flat surface, topped by recent snow Ice caps show little movement They occupy the tops of mountains Outlet glaciers may flow downward from the ice cap
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7 Snowfield and Icecap Above Byrd Glacier, Antarctica Snow blankets and fills the valleys between the nunataks in the foreground
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8 Fox Glacier, New Zealand Outlet glacier fed by Ice Cap
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9 Mountain Valleys High in the mountains, snow may accumulate Glaciers are formed in stages Snow Firn Glacial Ice
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10 Snow Snow occurs in many forms, for example wet or dry Snow accumulates with a great deal of air trapped inside (you need to pack snow to make a decent snowball)
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11 Firn During the first summer following snowfall, some of the snow melts Meltwaters trickles downward, helping to compact the snow As winter approaches, resulting mass freezes together to form firn
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12 Formation of Glacier Ice
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13 Glacial Ice Repeated years of thaw/freeze cycles, and the weight of accumulated firn and snow, transform the lower layers to ice There are ten known structural forms of water ice, at least half of which occur in nature
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14 Cirque Glacier Ice movement erodes a depression near the head of the glacier Glacier occupies the hole for a prolonged period, creating a bowl-shaped depression under the glacier After the cirque glacier melts, the depression remains Cirque may be filled with water, and is called a tarn lake, or it may be dry
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15 Cirque Glacier Photo
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16 Cirque Photo by Dr. Michael Hambrey
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17 Alpine or Valley Glacier Confined by surrounding bedrock highlands Generally move down steep to very steep surfaces As cirque glaciers expand, they flow into pre-existing stream cut channels, enlarging and changing the shape of these valleys Stream valleys have V-shaped profiles, whereas glacial valleys are U-shaped
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18 Valley Glacier Photo Valley glacier flowing through mountains in Alaska
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19 Piedmont Glaciers One or more valley glaciers flowing from the confines of valley walls and spread out to form broad sheets Piedmont literally means foot of the mountain Malaspina Galcier (Alaska) is a classic large piedmont glacier that descends to tidewater from several mountain sources
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20 Tidewater Glacier, Alaska Tidewater glaciers flow into the sea, calving icebergs
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