KARST FEATURES OF THE HIAWATHA NATIONAL FOREST, UPPER PENINSULA, MICHIGAN

The Upper Peninsula of Michigan is made up in part of Silurian carbonate sequences. These carbonate sequences make up the northern edge of the Michigan Basin and part of the Niagara Escarpment, which runs from eastern New York, through Ontario, Canada, across the Upper Peninsula in Michigan, and back south through the Door Peninsula in Wisconsin. The group which makes up the largest areal extent and upon which nearly all the karst is found in the Upper Peninsula is the Engadine group, which is a dolostone of middle Silurian age.

Karst features have been mapped in this area for the last few years, including: alvar, boulder fields, caves, cliffs, fissures, ledges, outcrops, sinkholes, and springs. With the addition of this year’s (2011) field data and the data from Larson et al. (2010) further karst - paleo-lake level relationships can be made. Our data suggest that the karst features on the Hiawatha are related to the Algonquin (~250m) and the Nippising (~200m) high lake level stages. We believe that these surficial karst exposures are due to wave action, which eroded away the overburden leaving the bedrock and subsequent karst features exposed with the ensuing lake level drops.

We also present a model for the formation of the dolostone boulder fields on the Hiawatha that invokes the association between the boulder fields and outcrops. We suggest that the boulder fields found surrounding the outcrops are formed by the freeze-thaw cycles of northern Michigan, which bring the upper part of the bedrock to the surface in the form of boulders.

This project was made possible by the GeoCorps America Program which is sponsored by the Geological Society of America and the United States Forest Service.