LATE-GLACIAL AND POST-GLACIAL LANDSCAPE EVOLUTION OF BEAVER ISLAND, MICHIGAN

This paper presents the preliminary results of ongoing research into the late-glacial and post-glacial history of Beaver Island, in the northeastern part of Lake Michigan. Methods of study include landform analysis and mapping (1:24,000 based on the interpretation of aerial photographs and standard fieldwork. Previous maps of the island's geomorphic features have been at a scale of 1:500,000 (Farrand, 1982) and limited only to the most obvious shoreline features. Beaver Island's landforms are the result of glacial, coastal, and eolian processes. The most obvious glacial landforms are fluted hills located on the oldest part of the island, which was not fully submerged by high lake levels (Algonquin stage) following deglaciation. These drumlin-like features have 5 to 20 m of relief above the highest Lake Algonquin shoreline and are composed of till. Subtle fluted landforms also are preserved on the portion of the island that was submerged by Lake Algonquin. These features have lower relief (< 5 m) and are mantled by lake sediments. Well-developed shoreline landforms used to interpret lake levels are limited to wave-cut bluffs and beach strands, although spits, beach ridges, offshore bars and baymouth bars are locally present. We mapped beaches at the 224 m water elevation of the Main phase of Lake Algonquin. We have identified Algonquin strandlines at 220 m (Ardtrea phase) and 213 m (Wyebridge phase). Clear field evidence for the Payette phase (198 m) is indistinguishable from Nippissing shoreline features on much of Beaver Island. However, Nippissing strandlines are visible along Lakes Barney and Geneserath. Lake Algoma beaches lie at 180 m. Our work shows that all of the island's inland lakes were submerged during the Main phase of Lake Algonquin. The long axes of these lakes trend northwest to southeast, which is parallel to the glacially fluted landforms on the oldest part of the island. This orientation is parallel to offshore, submerged streamlined landforms visible in aerial photographs, which may be drumlins or flutes. We hypothesize that the lakes may occupy former glacial tunnel valleys or channels. Eolian landforms on the island are predominantly parabolic sand dunes and indicate strong winds from the west, west-southwest, and south and may obscure some Lake Nippissing shoreline features on the island's west side.