Ice-Walled Lake Plain

Turtle Lake, Wisconsin

Here is map showing the Location of Turtle Lake Wi, the area where ice-walled lake plains are found, and the area where you can find till outwash plains from the last glaciers.

What Is an Ice-Walled Lake Plain ?

Ice-walled-lake plains form in the stagnant marginal zone of glacial Ice Sheets. They are conspicuous, but little-known, landforms within the broad bands of hummocky glacial topography extending from the Great Lakes to Alberta. They are flat-topped hills up to 50 m high and up to a few kilometers wide. Laminated offshore sediment up to tens of meters thick underlies the middle part of many of these features, and coarser shore sediment are typically present around their edges. These lake plains provide evidence of the final disintegration of the ice and the distribution of debris from the melting ice.
Some of the ice-walled lakes persisted in debris-covered ice through hundreds and thousands of years during which the climate was cold enough for permafrost to exist and for the margin of the ice sheet to retreat. Some may have persisted into the earliest Holocene, when they were inhabited by plants and animals in a climate only slightly cooler and wetter than today, indicating surrounding ice was well insulated by rock debris. Many smaller ice-walled-lake plains, especially those in Alberta, Minnesota, and Wisconsin seem to have been walled by ice but contain more till-like material than lake sediment, indicating a variety from ice-walled-lake plains with abundant lake sediment to similar features with abundant till-like sediment to collapse hummocks. In some areas hummocks surrounding ice-walled-lake plains are composed mostly of collapsed lake sediment.
Ice-walled-lake plains are important in evaluating the possible subglacial or supraglacial origin of glacial hummocks. Ice-walled-lake plains and hummocks formed where supraglacial debris slumped down ice slopes. Some debris was reworked by supraglacial streams, or in ice-walled lakes. There is no evidence that any substantial amount of subglacial material was squeezed up into the hummocks or the ice-walled lakes. Compressive flow near the ice margin, enhanced by permafrost or re-advances of ice into areas of stagnant ice, most likely contributed to the accumulation of thick masses of debris-rich ice that yielded thick supraglacial debris as they melted. The hummocky moraine surrounding the ice-walled-lake plains formed when the supraglacial debris was let down as the last ice melted.

 

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Ice-Walled Lake Plain

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Figure 1 is a photo taken outside of Turtle Lake Wisconsin, note that you can see the hummocky terrain with a small kettle lake formed into the middle.

Chris Below
belowcs@uwec.edu

University Wisconsin Eau Claire

 

 

 

 

This figure explains how an Ice Walled Lake Plain is formed.