Grand Kankakee Marsh

The Kankakee Outwash Plain is a flat plain interspersed with sand dunes in the Kankakee River valley in northwestern Indiana and northeastern Illinois of the United States. It is just south of the Valparaiso Moraine and was formed during the Wisconsin Glaciation. As the glacier, stopped at the Valparaiso Moraine, melted, the meltwater was carried away to the outwash plain. On the south side of the moraine, where the elevation drops, the meltwaters eroded away valleys, carrying sand and mud with them. As the muddy meltwater reached the valley where the slope lessened, the water slowed down, depositing the sand on the outwash plain. This created a smooth, flat, and sandy plain. Before its draining, the Kankakee Marsh, located on the outwash plain, was one of the largest freshwater marshes in the United States.

The Grand Kankakee Marsh is the result of the last glacial age. The Wisconsin Glacial Episode began 70,000 years ago and removed all traces of the previous glacial topography. It wasn't until the last 3,000 years that the glaciers left the topography we know today. Beginning around 15,000 years ago, the Michigan lobe to the north and the Huron-Saginaw lobe to the east retreated back, leaving the area that was to become the Kankakee's valley clear of ice. Beginning 14,000 years ago, the head of the glacier stood along a line across the middle of Lake, Porter, and LaPorte counties. Melting ceased to outpace the arrival of new ice from the north. Over thousands of years, the glacier moved ground rock and soil southward, only to release along this edge of ice, building up a ridge that matched the front of the glacier. This formed the Valparaiso Moraine.

As soil built up along this front, the spring and summer melt was releasing large volumes of water, which moved and sorted the soils. South of the glacial front, water accumulated faster than it could drain, forming a glacial lake Kankakee. Today, the bedrock is hidden deep beneath the sediments left by the glaciers, but it still played a role in developing the lay of the land. At Momence, Illinois, a ridge of limestone was exposed at the surface. Here, all the water flowing off the front of the glacier had to pass westward, for south of glacial Lake Kankakee, the Iroquois Moraine blocked all drainage. Slight though it might be, it was higher than the limestone ridge. Between the Iroquois Moraine and the Momence Ridge, the waters from the glacier collected.

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Wikipedia