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MELTING THE MYSTERY OF THE GREAT ICE AGE MELTING MYSTERY THE GREAT AGE ICE THE Research into glaciation began in the mid-19th century, but scientists are still uncertain about why ice ages occur or when the next glaciation period will emerge. hose of us who live in the Midwest United States seem to have the worst of both worlds: hot, humid summers where the temperature often reaches 95 degrees Fahrenheit, and cold winters where the mercury can plummet to zero. Despite these seemingly unbearable extremes, we live in a land of plenty because of the most fertile soil in the world—courtesy of the Great Ice Age. According to scientists, over the course of the last two million years at least four (possibly six) periods of glaciation ploughed out an assortment of rock from Canada, moved it south in a 100-foot-high floe of ice and snow, pulverised it against bedrock and deposited it on the Midwest plain. The ice sheet produced large quantities of gravel, sand and silt. A mixture of these materials, called till, forms much of the soil in the Ohio and Upper Mississippi river valleys. Remnants of these vast sheets of ice can still be seen today in the form of numerous lakes that pepper the northern regions of the Midwest. Retreating glaciers left large depressions in the Earth's crust which filled with melt-water, the most magnificent of which are the Great Lakes. Other larger lakes, such as Winnipeg, Reindeer, Athabasca, Great Slave and Great Bear in Canada, existed at one time but have since drained off and disappeared.' Glaciers reached as far south as the current locations of the Ohio and Missouri rivers, although the Wisconsin ice sheet, the most recent glacier, stopped midway across the extent of Illinois about 18,000 years ago and began to retreat some time between then and 16,000 years ago. Local legend has it that the glacier stopped 20 miles north of Springfield, the state capital. There is a grand mound there named Elkhart Hill, more than a mile in circumference. According to History of Logan County, Illinois , Elkhart Hill is "the most conspicuous physical feature that adorns the landscape of Logan County ... with virgin timber on its summit and every side, it entrances the vision of the passerby as it towers above" the surrounding landscape.” Glacial advances and retreats also had dramatic effects upon areas south of the glaciers. An advance in the ice sheet in the northern hemisphere 30,000 years ago caused sea levels to fall approximately 425 feet. With so much water diverted from the natural cycle to form the ice, the flat continental shelves were exposed as dry land. This caused the same effect as raising the land, which caused rivers to erode deeply into the valleys—in the Lower Mississippi, Tombigbee-Alabama and Red river systems, for example. As the Wisconsin ice sheet began to melt, these valleys were filled with sediment carried by melt-water in swollen rivers. Most of the water south of the glaciers flowed into the Upper Mississippi, Ohio and Missouri river basins. Sediment-loaded water spilled into the Lower Mississippi River, forming a huge flood plain that stretched over 500 miles long and 200 miles wide. At the leading edge of the glaciers, ice cliffs were up to 200 feet high, with cold dry winds sweeping down from their frozen crowns. The harshest of climatic conditions occurred in this zone next to the ice. Cold temperatures and strong winds created an Arctic-like desert, a wasteland littered with rock debris and fine sediment. Strong winds gathered this sediment from the glaciers and deposited it in sometimes thick, extensive layers called loess. These deposits cover much of the Midwest and extend south into Louisiana and M ppi. Loess deposits form many of the present-day bluffs along the Lower Mississippi River and are the source of the Midwest's rich farmland that we enjoy today. by Edward F. Malkowski © 2004, 2007 Website: http://www.sonsofgod- daughtersofmen.com © 2004, 2007 Website: http://www.sonsofgod- daughtersofmen.com JUNE — JULY 2007 NEXUS + 41 Walls of Snow and Ice by Edward F. Malkowski www.nexusmagazine.com