NEW INSIGHTS INTO THE DEGLACIATION OF MONT MEGANTIC

Complex sequences of glacial deposits, including sub-glacial, ice-marginal, and post-glacial sediments, as well as associated ice marginal and sub-glacial erosional features were mapped in the late twentieth century near 1105-metre-high Mont Megantic in the Appalachian Mountains of Southern Quebec (Canada). Mont Megantic is the most southeasterly Monteregian Hills and consists of distinctive rocks (an outer, circular, syenitic ridge surrounding a central gabbroic/nordmarkitic cone), which stand 500 to 600 metres above the surrounding Chaudiere Hills. It was overridden during the last glaciation by Laurentide ice flowing at approximately ESE (110 degrees); because of its prominence, it caused a deflection of the regional flow. Very little of the earlier geomorphic mapping was carried out on the mountain, now part of the Mont-Megantic national park, or in the areas immediately adjacent to it. This study is based on the recent availability of LiDAR, GIS, and modern 3-D geomodelling techniques. Information has been derived from field observations, the Canada federal database, and data from private firms. The main output of the geomodelling is refinement of the understanding of the pattern and style of ice retreat inside, with the concomitant development of ice-dammed lakes, and around the outer ridge of the mountain.