Periglacial Shoreline Erosion of a Rocky Coast: George River Estuary, Northern Quebec
Keywords:Erosion, frost-riving, sea ice, rock benches, raised shorelines, Ungava Bay
Shore erosion landforms in bedrock were observed along the estuary of George River in a macrotidal periglacial environment. Quarrying of cavities in gneissic bedrock is largely dependent on geological structure, principally on joints and foliations. Frost-riving operating in the jointed rock loosens preconfigured blocks that are thereafter mobilized by waves and sea ice. Gelifraction and frost shattering along the shore are more effective at places where streamlets flow to the shore and where fresh water seeps throughout the structure. Measurements of erosion profiles were made relative to initially glacial-sculptured intertidal outcrops. Erosional landforms were observed along the whole shoreline length of the study area which was also classified into segments according to slope angle, geographic orientation and fetch. Observations indicate that erosion is more intensive in sectors having low and medium slope angles that allow shore ice to override and where the large fetches favour wave pounding and sea-ice thrusting. The erosion takes place preferentially around the mean high tide level. The knowledge of the acting erosional processes and the resulting landforms allow the recognition of raised bedrock shoreline features associated with post-glacial, uplifted shorelines. These raised bedrock shoreline landforms correspond very well in elevation with the more conspicuous raised shorelines in Quaternary sediments in the region. Some age correlations with major dated Holocene shorelines in the eastern Canadian Arctic are suggested.