Guest Column by GeoT
Dateline: 06/13/00
The Pleistocene was the time of the great Ice Age of the world. The glaciers were most extensive in the Northern Hemisphere, but they also existed in the southern parts of South America, the mountains of southeastern Australia, and South Island New Zealand as well.
Global temperatures cooled an estimated 7 to 13 degrees Fahrenheit, resulting in an accumulation of ice in certain continental and mountain areas. The reason for the cooling is a subject of much debate, but this much we know: there were at least four and possibly as many as fourteen Ice Ages separated by times of warmer climate called interglacials - ancient global warming. During such times, glaciers melted, soils formed, and vegetation grew, only to be covered by subsequent glacial advances when the climate cooled again. All of this is known or suggested through the study of the glacial stratigraphy by the geological surveys of various Midwestern states.
It is also known that the glaciers were great modifiers of landscape. The ice accumulation centers in North America, near Hudson Bay, repeatedly sent ice outward in all directions, and severely eroded the Canadian Shield in the process. Additionally, the basins of the Great Lakes of North America were produced by the erosive action of the ice.
What the glaciers erode from one place comes to rest someplace else, and existing landscapes in the latter areas were modified too.
Prior to the glaciers, stream drainage was well established in the Central Lowland. One river, the Teays, (known in Illinois as the Mahomet or Mahomet-Teays) had produced a valley from the Blue Ridge of North Carolina to the southern part of Illinois, where it emptied into an extension of the Gulf of Mexico.
The ancestral Mississippi River entered Illinois from the northwest and flowed southeastward to meet the Teays. The two rivers joined southeast of present-day Peoria. That ancient Mississippi River was a tributary of the Teays. Subsequent deposition by various glaciers filled this part of the Mississippi valley and forced it to its present location along Illinois' western boundary.
Glacial deposits also filled the Teays valley system. (Some sections of the valley are still visible in the unglaciated areas of the Appalachians.) Floods of sediment-laden meltwater coursed down the Teays and its tributary valleys filling them with sand, gravel, and associated material. Later glaciers overrode the entire complex, covering it with layers of glacial drift, leaving end moraine and ground moraine as the surface. The pre-glacial system of valleys was totally obscured.
Today, the layers of sand and gravel in the Teays valley system are an important source of clean, abundant, groundwater. Many towns and cities along this preglacial valley use this resource as their municipal water supply.
As clean water becomes an increasingly precious resource, surely, places located above this preglacial feature will find it to be of utmost economic importance.
There may be hope for my small town in eastern Illinois yet!
