Contents

J. Great Lakes Res. 21(1)
Internat. Assoc. Great Lakes Res., 1995
Thomas J. Murphy, ed.

J. Great Lakes Res. 21(1):3-16.
Internat. Assoc. Great Lakes Res., 1995
Type: Article

Relationship of Lithology and Geomorphology to Erosion of the Western Lake Superior Coast

Beth L. Johnson and Carol A. Johnston, Natural Resources Research Institute, University of Minnesota, 5013 Miller Trunk Highway, Duluth, Minnesota, 55811

ABSTRACT: Coastal erosion/accretion rates measured from aerial photos taken in the 1930s and 1960s-1970s were compared with lithologic and geomorphic properties of the northern and southern coasts of western Lake Superior. The coasts were divided into four lithologic types based on Quaternary geology: bedrock, clay, sandy till, and water-laid sand and gravel. Average erosion of the southern coast was significantly higher than that of the northern coast for clay (0.78 vs. 0.14 m/yr), and for water-laid sand and gravel (1.89 vs. 0.16 m/yr). Sandy till on the southern coast eroded an average of 0.12 m/yr; till units were negligible along the northern coast. Bedrock constitutes 57% of the northern coast and has eroded at an average rate of 0.08 m/yr; bedrock exposures are rare along the southern coast. Clay coasts facing north or northwest eroded significantly faster than those facing south, and water-laid sand and gravel coasts facing north eroded significantly faster than those facing southeast. This is probably because major storm winds and waves come from the northeast, with a greater impact on the north- and northeast-facing shores. Offshore slope and bluff slope were not significantly related to erosion rates.

KEYWORDS: Coastal erosion, lithology, geomorphology.

[Full Text (PDF) - Subscribers Only]