ICE-WALLED LAKE PLAIN DISTRIBUTION IN MICHIGAN

Before the availability of LiDAR in Michigan, Ice-Walled Lake Plains (IWLP) were rarely recognized. IWLPs in Michigan are generally subtle and typically not distinguishable on 7.5 minute topographic maps, aerial photos or county soils surveys. They are often unrecognizable even when standing in the middle of one. Recent surficial geological mapping and the availability of LiDAR has made their identification possible. These supraglacial ice stagnation features appear as relatively flat to slightly bowl shaped plateaus slightly elevated above the surrounding morainal uplands. They have steeper outward facing ice-contact slopes down to the surrounding land surface. Most occur on hummocky uplands, end moraines, with some on till plains. They are not found in outwash plains, glacial drainage-ways or lowlands.

They most commonly occur in clusters but occasionally are seen as a single isolated IWLP. Some are clearly distinct features and others appear as a compound IWLP made up of a number of coalesced IWLPs or as smaller satellite IWLPs within larger one. They come in a wide variety of sizes, averaging 43 acres (17.3 hectares) and shapes but are commonly rounded. They are thought to have formed as short-lived lakes in depressions on a stagnating ice surface, where generally fine grained materials are deposited from the surrounding higher stagnating ice. Overtime as the glacier melts and as more sediment is deposited in the lake, eventually the lake sediments are deposited on the land surface resulting the elevated low relief plateaus above the surrounding land surface.

The IWLPs were digitized from LiDAR DEMs, hillshades, shaded relief, and slope maps and using machine learning. Hand augered borings, coring and road cuts reveal textures widely ranging from clay to fine sand to coarse sand. The Saginaw Lobe has significantly more IWLPs than the Lake Michigan and Huron Erie Lobes. Certain moraines or portions of moraines have IWLPs while others have none. They can be cored to find fossils and OSL samples collected for age dating. Since IWLPs often occur on morainal ridges, the dates can be used as a minimum age for an ice advance. Because they occur in a distinct depositional environment, mapping their distribution assists in interpreting the glacial history of an area and in differentiating subtle moraines and ice margins from others.