HIGH-RESOLUTION GIS ANALYSIS OF PALIMPSEST GLACIAL FEATURES IN A MARGINAL GLACIAL ENVIRONMENT, COASTAL MAINE

Multiple, overlapping or ‘palimpsest' glacial features are typically interpreted over large scale study areas (Kleman 1997), however high resolution mapping using GIS techniques reveals similar complex ice-flow patterns at the local scale (<1:5000). Damariscove Island, mid-coast Maine is examined by combining small scale field measurements of glacial striations with data from 1:24,000 topographic maps, published digital elevation models (DEM's), and available NOAA bathymetry. The Damariscove Island terrain is dominated by a 0.5 kilometer long cove running ~north/south, parallel to the long axis of the island. GPS-positioned field measurements of striations and cove orientation yield a consistent trend of ~190 degrees, implying a glacial origin for the cove. This contrasts with the more regional southeastern glacial flow patterns evident from the state map. DEM's based on available elevation data show a distinct stoss and lee topography on the island that is aligned with this regional southeast flow direction. A significant portion (58%) of the land surface of the island can be classified as northwest facing stoss slopes to this southeast glacial flow direction rather than the SSW glacial striations common on the island. Extending this analysis to the surrounding islands also yields evidence of both the regionally interpreted southeastern flow regime (1), as well as the measured 190 degree SSW flow regime (2). Flow regime 1 is consistent with a topographically independent flow driven by a distal ice center. Flow regime 2 is consistent with the waning phase of glaciation when topographic control is reinstated (McCaiug 2002) and lithologic influence becomes important. Upright bedding of host rock on Damariscove strikes 10 / 190 ° which allows for preferential glacial erosion (Glasser 2004) and subsequently formation of the cove of the same orientation. It is hypothesized that as this phase continued to wane, localized topography further influenced flow producing small scale striation variation, which was resolved within the island data set as glacial striations were found to diverge around a local topographic high.