Continental Glacition Essay, Research Paper
Continental Glaciers The Action of Ice on Land As glaciers become extremely large, they eventually reach the lowlands, which isessentially more gentle terrain. As these huge glaciers reach the lowlands, they travel muchmore slowly, because they no longer have the steep mountian sides to push the ice downfaster. Once on the lowlands, the glacier spreads out for they are no longer restricted byvalleys, and become known as Ice Sheets . As long more snow falls than ice melts, IceSheets will continue to expand. Ice Sheets NEVER move backwards- although theyappear to do this when the melting process exceeds the accumulation process. Ice Sheets move by being pushed from up above by masses of ice accumulating in thehigher valleys. These ice sheets are capable of a lot of erosion, seen in the picture below. Erosional Features As seen in the above the picture, the land is fairly smooth, due to the continentalgalciers. The thick, heavy ice has cut some edges into the ground, but there are no highmountains, just a bit of rough topography. Ice Sheets often carry debris within their layers,due to erosion. In fact, the Canadian Prairies were largely formed by the deposition ofsediment from these continental glaciers as they moved outwards from the centres of theice accumulations. The more debris that an ice sheet carries, however, the slower itmoves. The reason for this is that in order to carry millions of tons of solid material, suchas dirt and rock, a lot of energy must be consumed, and these massive sheets don’t have alot of energy to begin with. If the glacier runs out of energy, the erosion stops, and thedebris is dropped off in dropping zones called drumlins. An example of a drumlin is shownin the photograph above. The diagram above shows the features of glacial deposition in Denmark, and northGermany. The terminal moraine marks the place where the ice sheet melted as fast as itarrived. Here the debris piled up into a hill because the ice was no longer able to carry italong. Instead, some of the lighter material floats down with the water, and the finematerial is sorted from the coarse at the outwash plain. Notice how the original land wasflat and featureless, but after the continental glacier, some rough topography was formed.These ice sheets, however, due to their erosion capabilities, can also work to smooth someareas. Factors Affecting Ice-ages The Ice-age’s biggest enemy is the climate’s warming. Glaciers have proven to beresilient, however, for they have returned and retreated three times in the past half amillion years. Most of the Continental Glaciers that have melted are now higher up, andare known as Alpine Glaciers. As the weather warms, there is less snow, and much of theice sheet melts into lakes rivers, and even oceans. One example of ice sheets melting isBritain’s sheets that melted from the lowlands in just a couple thousand years. This mayseem like a long time, but considering the magnitude of the glaciers (some get toapporximately 200m deep), this is extremely rapid. The Continental Glaciers in NorthAmerica dissappeared within about 8000 years, but once they melted back to the base ofmountains, their retreat slowed down because of the steep ascent of the mountains. Manyglaciers stopped moving when they came to mountains, and instead deposited recessionalmoraines(to find out more about this, search under “Alpine Glaciers”). These morainesblock valleys, such as the maraines in Penticton, southern British Columbia. Most morains,
however, are washed away by rivers. According to Milutin Milankovitvh, the variation in the Earth’s orbit through timehas caused changes in the amount and the distribution of sunlight and other solar radiationreaching the Earth’s surface. The Illinois State Museum says that the Earth’s orbit changesapproximately every 100,000 years. In the orbit’s more elliptical shape, there is greatseasonal contrast in the nothern and southern hemispheres. For example, one hemispherewill have hot summers and cold winters, whereas the other hemisphere will be the reverse.When the orbit is in its more circular shape, however, both hemispheres will have similarseasonal contrasts in temperature. This change in radiation, although small(0.2%), isextreme enough to expand and melt ice sheets. The tilt of the Earth aslo affects radiation,and so therefore galciers in the same way as the orbit. End Of A Glacier Ice moves very slowly , but over millins of years a glacier can move a greatdistance and grow to a great size . Glaciers , being composed genrally of water , have theability to move across land and pick land up for a slow motion ride. Ice moves from it’ssource by the pressure of pushing form the back of a glacier causeing the front to moveforward and take over more land . When the pressure from the back is no more then theice stops moving and genrally starts to cool down . Streams of water begin nearly ten kmback from the front of the glacier and slowly run and move there way down into theglacier until the are flowing across the ground , here they lay sediment and carve thereway into the earth . The carves in the earth form gravel beds and are called eskers . Whenthe front of a glacier is really warm and melting very fast the water pours out from allsorts of holes and caves onto whatever plain is out front . This deposits lots of gravel intothe plian and a forest soon grows over and the land is hard to recognize . Kinds Of Movement There are three main ways that glaciers move ; they are internal deformation , basalsliding , and deforming substrate . With internal deformation the ice deforms under it’sown weight because of gravity . Temp. , thickness of the ice , and pressure all effect therate at which the glacier will move . Movement here is slow and around ten to twentymeters per year . Basal sliding is when the base of an ice sheet is near the pressure meltingpoint and water is being made present . The larger the ice sheet the less likly this willhappen because at the bases of huge ice sheets the temp. for melting is -1.6 deegreescelcius . Water reduces friction and allows the ice to move faster in response to gravity .Basal sliding can move an ice sheetup to a few hundred meters a year and it erodeslandscapes very badly . Water is not the only thing that induces sliding or movement . Thesediment under the glacier (if it’s weak) can give way to the big weight . If the sedimenthas a little water in it than the glacier might tend to use it as a water slide . Depositional Features Millions and millions of tonnes of ice pushed , crushed , and carved their waythrough all the geographical features of yesterday and made them what they look liketoday . Along the way the ice picks up rock and dirt of all sorts , in small and bigquantities moving it around and setting it down in a different place . When a glacierbecomes saturated with rocks and can no longer move it begins to melt leaving drumlinsand eskers , and from the eskers : stream plains. The glaciers , due to the enormousamount of pressure within , could shove anything in it’s way easily to the side . Deeptrenches where rivers now rule are foot prints of glaciers as well as drumlins liningthemselves across Canada .