Valparaiso Moraine
The Valparaiso Moraine is a recessional moraine that forms an immense U around the southern Lake Michigan basin in North America. It is a band of hilly terrain composed of glacial till and sand. The Valparaiso Moraine defines part of the continental divide known as the Saint Lawrence River Divide, bounding the Great Lakes Basin. It begins near the border of Wisconsin and Illinois and extends south through Lake, McHenry, Cook, DuPage and Will counties in Illinois, and then turns southeast, going through northwestern Indiana. From this point, the moraine curves northeast through Lake, Porter, and LaPorte counties of Indiana into Michigan. It continues into Michigan as far as Montcalm County.
The moraine was formed during the Crown Point Phase of the Wisconsin glaciation. At this time the glacier covering the area had grown thin, so it was restrained by dolomite rock layers in the Lake Michigan basin. Where the glacier stopped, glacial till and sand was deposited, creating the hills of the moraine. After the Valparaiso Moraine was formed, the glacier retreated and formed the Tinley Moraine.
Several place names in the region are named after these moraines. The moraine itself was named after the city of Valparaiso in Indiana where the moraine is at its highest and the city lies on the moraine.
As part of the continental divide, many creeks or rivulets have their origin source in the Valparaiso Moraine. Water on one side of the moraine flows into Lake Michigan, through the Great Lakes, and eventually into the Atlantic Ocean via the Saint Lawrence River, while water run-off on the other side of the moraine flows into tributaries of the Mississippi River, which eventually flows into the Gulf of Mexico. The moraine divide was breached at the Chicago Portage gap by a canal beginning in the mid-19th century.
History
The Valparaiso Moraine formed as the first major moraine of the Cary substage of the Wisconsin Glacial period. There are three minor moraines that have been identified in northeastern Illinois, the Minooka, Rockdale, and Manhattan. Within the arc created by the Valparaiso Moraine are two younger Cary substage moraines of the Tinley Moraine and the Lake Border Moraine. Younger still is the Port Huron system, which occurs in the northern portion of the Lake Michigan Basin. The Cary substage dates to around 30,000 years before present.Location
The Valparaiso system includes five moraines north of Chicago. The most northerly reach is to the headwaters of the Fox River in Waukesha County, west of Milwaukee. The moraine angles to the south and east, reaching the headwaters of the Des Plaines River west of Kenosha, Wisconsin, in the county of the same name. The moraine forms a major portion of the eastern divide of the Fox River Basin and then the western bank of the Des Plaines River. The moraine continues southward along the Des Plaines River following the route of the modern Tri-State Tollway around the west side of Chicago. Where the Des Plaines River bends to the west and forms the Illinois River, the moraine angles south and east, continuing along I-294 towards Chicago Heights. In this area, the moraine has widened out towards the south and east, becoming a broad plain covering large portions of Will and Kankakee counties.Turning eastward, the moraine enters Indiana. The moraine is wide as it passes through Lake County, Indiana, covering nearly half of the county's midsection. As it passes through Porter County, Indiana, it is under the city of Valparaiso, from which it derives its name. Through Indiana, the moraine forms a "continental divide" between the drainage of the Great Lakes and the Gulf of Mexico by the Mississippi River.
The moraine then turns northeast, passing just north of La Porte, Indiana, through the county of the same name. Upon entering Michigan the moraine forms much of the shoreline of Lake Michigan northward through St. Joseph. From here northward the moraine angles more eastward, missing Holland and passing through Grand Rapids, finally ending in a mingling of inter-lobe moraines about northwest of Grand Rapids in Montcalm County.
Distribution
The inner border is less than and at its closest approach is only about from Lake Michigan. The system is from or up to nearly . It is narrowest in LaPorte County, Indiana and widest in Lake County, Indiana. In northern Illinois the moraines merge into a composite moraine, including parts of earlier stages..The Valparaiso morainic system in Michigan includes the morainic belt along Lake Michigan, from the Grand River Valley south. In places it consists of two or more ridges. These ridges coalesce and separate repeatedly. In northern Van Buren County it becomes associated with the Saginaw moraine.