GEO 101-007 Chapter 18 Notes
GEO 101-007 Chapter 18 Notes GEO 101-007
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This 4 page Class Notes was uploaded by Jennifer Gintovt on Thursday November 5, 2015. The Class Notes belongs to GEO 101-007 at University of Alabama - Tuscaloosa taught by Dr. William Lambert in Summer 2015. Since its upload, it has received 21 views. For similar materials see The Dynamic Earth in Geology at University of Alabama - Tuscaloosa.
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Date Created: 11/05/15
GEO 101007 11415 Chapter 18 Amazing Ice Glaciers and Ice Ages Louis Agassiz Geologist from Switzerland Proposed that places in Europe that had random rocks showing up must have been a result of a glacier dropping the rocks as it melted Glacial Erratic Erratic o A boulder or cobble that was picked up by a glacier and deposited hundreds of kilometers away from the outcrop from which it was detached Ice frozen water is a mineral naturally occurring inorganic solid with a de nite chemical composition and regular crystal structure Layers of Snowfall Layers of snowfall are very much like layers of loose sediment With time and pressure from snow above snow akes recrystallize into solid ice Snow to solid ice Loose snow Granular snow Fim Finegrained ice Coarsegrained ice m o Compacted granular ice derived from snow that forms where snow is deeply buried if buried more deeply fim turns into glacial ice Glacier A river or sheet of ice that slowly ows across the land surface and lasts all year long movement caused by gravity Formation of Glaciers Three criteria for glacier formation 1 Local climate must be cold enough that winter snow does not melt entirely away during the summer 2 There must be sufficient snowfall for a large amount of snow to accumulate 3 Slope of the surface must be gentle enough that the snow does not slide away in avalanches Types of Glaciers Two categories of glaciers 1 Mountain alpine shape controlled by topography of mountains ow from high to low elevation I Cirque GEO 101007 11415 II Valley III Ice caps IV Piedmont 2 Continental vast ice sheets that cover thousands of square kilometers of continental crust today the only eXists in Antarctica and Greenland How exactly do glaciers move Plastic deformation 1 Only occurs below 60 m 2 Grains change shape very slowly as new grains form while old grains disappear Basal sliding 1 Must be warm enough for water to build up at base of glacier 2 Water along base on glacier acts as a lubricant on which the glacier can move water decreases friction The rate of ice movement varies with time and within the glacier friction slows down movement where ice contacts rock sediment Crevasse Formation A large crack that develops by brittle deformation in the top 60 m of a glacier FIGURE 18 a a 1 ml Li iiw H mm 0 Oligin Glaciers are similar to bank accounts I Deposits snowfall 5 x Glacial Equilibrium Withdrawals ablation lti 1if A snowfall ablation Zone of accumulation x dePOSitS Withdrawals Equilibrium line 39 Zone of ablation Glacial Advance Terminus toe i snowfall gt ablation Ablation includes 39 i deposits gt withdrawals o Sublimation evaporation of ice into water vapor o Melting ice melts and liquid water ows away 0 Calving breaking off of chunks of ice Glacial Retreat snowfall lt ablation deposits lt withdrawals Icebergs Ice is grounded in shallow water but oats in deep water 1 Sea Ice also contribute icebergs to ocean i Ice formed by the freezing of the 7 Q k3 surface of the sea V V f Plucking and Abrasion 39 39 bluei mg y l l r4 V I Roche d i j I 39 v 3 3 39 HWOUIOH lCL a Aliimam waits quot2e JIMWed a e i plid Mg pres w GEO 101007 11415 Plucking is chunks of bedrock being plucked out by the moving ice Abrasion is chunks of rock that has already been plucked up into the glacier that move against the bedrock as the glacier moves and cause abrasions Glaciers move sediment clasts of all sizes Moraine a sediment pile composed of till glacial sediment deposited by a glacier Lateral moraine a strip of till along the side margins of a glacier Medial moraine a strip of till in the interior of a glacier parallel to the ow direction of the glacier formed by the lateral moraines of two merging glaciers Six Types of Glacial Deposits 1 m unsorted sediment carried by ice deposited beneath at the side or at the toe of a glacier 2 Erratics cobble to boulder size clasts of rock found within till or random places where the glacier was once owing 3 Glacial marine sediment deposited at sea by melting 4 Glacial outwash till from the glacier toe that is transported and sorted by braided streams 5 Loess silt and clay size sediment transported away from glacier s toe and deposited some distance away from the glacier 6 Glacial Lake Bed ne grained sediments deposited in glacial lakes varves are common alternating thin layers of clay and silt Glacial lakebed sediments Varve a pair of thin layers of glacial lakebed sediment one consisting of silt brought in during the spring oods and the other of clay deposited during the winter when the lake s surface freezes over and the water is still Kettle Hole a circular depression in the ground made when a block of ice calves off the toe of a glacier becomes buried by till and later melts Drumlin a streamlined elongated hill formed when a glacier overrides glacial till Glacial Subsidence and Rebound Glacial Subsidence the sinking of the surface of a continent caused by the weight of an overlying glacial ice sheet Glacial Rebound the process by which the surface of a continent rises back up after an overlying continental ice sheet melts away and the weight of the ice is removed still happening today in some areas Pleistocene Epoch 26 mya to 11000 ya Laurentide Ice Sheet an ice sheet that spread over northeastern Canada during the Pleistocene ice ages Glaciation glacial period A portion of an ice age during which huge glaciers grew and covered substantial areas of the continents GEO 101007 11415 Interglacia a period of time between two glaciations Holocene a period of geologic time since the last ice glaciation