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Unformatted text preview: This page last updated on 18-Apr-2011 EENS 1110 Physical Geology Tulane University Prof. Stephen A. Nelson Glaciers and Glaciation Glaciers constitute much of the Earth that makes up the cryosphere, the part of the Earth that remains below the freezing point of water. Most glacial ice today is found in the polar regions, above the Arctic and Antarctic Circles. While glaciers are of relatively minor importance today, covering only about 10% of the surface, evidence exists that the Earth's climate has undergone fluctuations in the past, and that the amount of the Earth's surface covered by glaciers has been as much as 30% in the past. In fact, much of the topography in the northern part of North America, as well as in the high mountain regions of the west, owe their form to erosional and depositional processes of glaciers. The latest glaciation ended only 10,000 years ago. The Earth has experienced numerous glaciations, the most recent during the Pleistocene Epoch between 1.8 million years ago and 11,000 years ago. Other episodes occurred in the Permian, Ordovician, and Late Precambrian. Definition of a glacier A glacier is a permanent (on a human time scale, because nothing on the Earth is really permanent) body of ice, consisting largely of recrystallized snow, that shows evidence of downslope or outward movement due to the pull of gravity. Types of Glaciers (note: images of these features are shown in your textbook and will be shown in class.) Mountain Glaciers- Relatively small glaciers which occur at higher elevations in mountainous regions. Smallest of these occupy hollows or bowl-shaped depressions on sides of mountains ( cirque glaciers ). As cirque glaciers grow larger they may spread into valleys and flow down the valleys as valley glaciers . Paths these valley glaciers take are controlled by existing topography. If a valley glacier extends down to sea level, it may carve a narrow valley into the coastline. These are called fjord glaciers , and the narrow valleys they carve and later become filled with seawater after the ice has melted are fjords . If a valley glacier extends down a valley and then covers a gentle slope beyond the mountain range, it is called a piedmont glacier . If all of the valleys in a mountain range become filled with glaciers, and the glaciers cover then entire mountain range, they are called ice caps . Glaciers and Glaciation 4/18/2011 Page 1 of 9 Ice Sheets (Continental glaciers)- are the largest types of glaciers on Earth. They cover large areas of the land surface, including mountain areas. Modern ice sheets cover Greenland and Antarctica. These two ice sheets comprise about 95% of all glacial ice currently on Earth. They have an estimated volume of about 24 million km 3 . If melted, they contain enough water to raise sea level about 66m (216 ft.). This would cause serious problems for coastal cities (L.A., NY, Washington DC, New Orleans, Miami, SF etc). The Greenland ice sheet is in some places over 3000 m (9800 ft) thick and the weight of ice has depressed much of the crust of Greenland...
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