GEOL 1425 1st EditionFinal Exam Study Guide Lectures: 22-25Make sure you know about:1. Amount of ice present at the Wisconsin Glacial maximum-- Masses of ice 2 to 3.5 km thick built up over North America, Europe, and Asia. 2. Furthest southerly ice advance at the Wisconsin Glacial maximum-- Along the East Coast of the United States, the southernmost advance of this ice is recorded by the enormous sand and till deposits of the terminal moraines that form Long Island and Cape Cod. 3. Sea level change at the Wisconsin Glacial maximum-- the continents were slightly larger than they are today b/c the continental shelves surrounding them (some more than 100km wide) were exposed by a drop in sea level of about 130 m. This drop correspondsto an enormous growth in the volume of continental ice sheets (by about 70 million cubic kilometers) to three times the amount of ice on Earth today.4. Moraines-- A moraine is an accumulation of rocky, sandy, and clayey material carried by the ice or deposited as till. There are many types of moraines, each named for its position with respect to where it formed. Moraines of all kinds consist of till.5. Conditions for end moraine formation-- One of the most prominent in size and appearance is an END MORAINE, formed at the ice front. As the ice flows steadily downhill, it brings more and more sediment to its melting edge. The unsorted material accumulates there as a hilly ridge of till.6. **Alpine glaciers7. Drumlins-- Some continental glacier terrains display prominent landforms called drumlins—large, streamlined hills of till and bedrock that parallel the direction of ice movement. Drumlins, usually found in clusters, are shaped like long, inverted spoons or half eggs with the gentle slopes on the downstream sides. They may be 25 to 50 m high and a kilometer long. Geologists think that drumlins form under glaciers that move over a plastic mix of sub-glacial sediment and water. When the plastic mass encounters a bedrock knob or other obstacle, it is subjected to increased pressure. It then loses water and solidifies, forming a streamlined mass. An alternative hypothesis proposes that drumlins are formed by ice erosion of an earlier accumulation of till.8. Eskers-- Eskers are long, narrow, winding ridges of sand and gravel found in the middle ofground moraines. They run for kilometers in a direction roughly parallel to the direction of ice movement. Eskers were deposited by melt water streams flowing in tunnels along the bottom of a melting glacier.9. Northern Canadian permafrost-- The ground is always frozen in very cold regions, where the summer temperature never gets high enough to melt more than a thin surface layer. Perennially frozen soil, or permafrost, today covers as much as 25% of Earth’s total land area. Permafrost covers about 82 percent of Alaska and 50 percent of Canada, as well as great parts of Siberia. The oldest confirmed glaciation occurred during the Proterozoic, about 2.4 Ga. Its glacial deposits are preserved in Wyoming, along the Canadian portion of the Great Lakes, in northern Europe, and in South Africa.10. Kettle lakes-- Glaciated terrains are dotted with KETTLES, hollows or un-drained depressions that often have steep sides and may be occupied by ponds or lakes. Originate as isolated blocks of ice in outwash plains. A block of ice a kilometer in diameter could take 30 years or more to melt. By the time the block has melted completely, the margin of the glacier has retreated so far from the region that little outwash reaches the area. If the bottom of the kettle lies below the groundwater table, a lake will form.11. Varves-- Glaciers may deposit silts and clays on the bottom of a lake at the edge of the ice, in a series of alternating coarse and fine layers called VARVES. A varve is a pair of layers formed in one year by seasonal freezing of the lake surface.12. Cirques—at the head of the glacial valley, the plucking and tearing action of the ice tends to carve an amphitheater-like hollow called a CIRQUE (cwm, corrie). 13. Arêtes—with continued hard-warn erosion, cirques at the heads of adjacent valleys gradually meet at the mountaintops producing sharp, jagged crests called ARETES.14. Horns-- When several mountain glaciers erode head ward to a converging point a HORN,or pyramidal peak is formed15. Roche Moutonees-- Advancing glacier ice smooths small hills of bedrock—known as ROCHES MOUTONÉES (“sheep rocks”) for their resemblance to a sheep’s back—on their upstream side and plucks them to a rough, steep slope on their downstream side.16. Crevasses-- The upper parts of a glacier have little pressure on them. At low pressures, the ice behaves as a rigid, brittle solid, cracking as it is dragged along by the plastic flow of the ice below. These cracks, called CREVASSES, break up the ice near the surface. Crevasses are more likely to occur in places where glacier deformation is strong—such aswhere the ice drags against bedrock walls, at curves in the valley, and where the slope steepens sharply. 17. Firn-- A fresh snowfall is a light mass of loosely packed snowflakes. As the small, delicate crystals age on the. During this transformation, the mass of snowflakes compacts to form a dense, granular snow. As new snow falls and buries the older snow, the granular snow compacts further to an even denser form, called FIRN. 18. Glacial surge-- A sudden period of fast movement of a valley glacier, called a SURGE, sometimes occurs after a long period of little movement. Surges may last several years, and during that time the ice may speed along at more than 6 km/year—1000 times the normal velocity of a glacier. Surges appear to follow the buildup of water pressure in melt water tunnels at or near the base of the glacier. This pressurized water enhances basal slip. 19. Glacial plastic flow—movement by plastic flow forces within a glacier cause individual crystals of ice to slip tiny distances over short intervals of time. The sum of these movements within the enormous ice crystals that make up a glacier deforms the whole mass of ice in a process known as plastic flow. Plastic flow is most important in very coldregions, where the ice throughout the glacier, including its base, is well below the freezing. The basal ice is frozen to the ground, and most of the movement of these cold, dry glaciers takes place above the base by plastic deformation. 20. Glacial basal slip-- Basal slip is the sliding of a glacier