LATE QUATERNARY GLACIAL DYNAMICS OF THE KEWEENAW PENINSULA

No detailed studies to map and interpret the glacial geology history of the Keweenaw Peninsula have been done since Hughes (1963). Hughes researched the “Physiography of a 6-Quadrangle Area” in the southern portion of the Peninsula for his doctoral dissertation, but that study only covered about 1/3 of the Keweenaw Peninsula. Earlier, Leverett (1910, 1929) did reconnaissance and made some interpretations, and Warren (1974) studied the bedrock topography, but no detailed studies of the northern 1/2 of the Peninsula have been undertaken. Thus, the glacial dynamics of the Keweenaw Peninsula are largely unknown.

In this study, field investigations over the summers of 2015 and 2016, coupled with remote sensing techniques (using TM and NED data) were the main tools used to interpret the ice movements. Till samples were collected at dozens of locations but most samples await processing (pebble lithology to assess provenance, and texture to differentiate till deposits…e.g. Part 2). Data from Hughes, Leverett, and others were combined with field and remote sensing data to create an ArcGIS coverage of glacial features, from which interpretations were made.

The glacial history of the Keweenaw Peninsula is one of two lobes moving southwestward through western Lake Superior, one on each side of the Peninsula. However, on the eastern side, (following the axis of Keweenaw Bay), the Keweenaw Lobe movements were more restricted due to rising elevations on the south, east, and west sides (200m+). Because forward motion was restricted, ice thickness increased more rapidly than the Duluth Lobe, which occupied the western arm of Lake Superior, allowing the Keweenaw Lobe to breach the crest of the southern Keweenaw Peninsula and move due westward and join the southwesterly moving Duluth Lobe. The transition from southwesterly moving ice on both sides of the Peninsula, to split movements took place in the vicinity of Ahmeek. There, striae, grooves, and other oriented features (such as whaleback forms and rôche moutonnée) reflect the change in ice dynamics. Additionally, an interlobate moraine with boulder till (up to 2m diameter) and significant accumulations of bouldery sand and gravel are found in the interlobate zone, for several kilometers around that area.