SOURCE MATERIALS FOR LAKE MICHIGAN BEACHES

Abstract

The extensive wave erosion which has occurred in many parts of the Lake Michigan shoreline since I9I4.3 has centered interest on the materials composing the bluffs above the water line and on the amount and grain size of beach sediments yielded by wave erosion of these bluffs. The present study grew out of a preliminary mapping of the landform types and shore materials of the Lake Michigan basin carried out in 1952-53 for the Beach Erosion Board of the United States Army Corps of Engineers. The report prepared for the Beach Erosion Board summarized the geology of the Lake Michigan shoreline. Types of bedrock were indicated not only where such rocks form cliffs or reefs above water level but also beneath the unconsolidated materials which form three-quarters of the actual shoreline. Such unconsolidated materials were also mapped as to type and present form, and on these bases the shoreline was divided into physiographic units. These physiographic units and materials will be evaluated with respect to the total proportion of each type along the shoreline and the sediments yielded to the beach zone by wave erosion.