CGRG Bibliography of Canadian Geomorphology
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Author : Allard, M.; Beaulieu, N.; Ruz, M.H.; Michaud, Y.#; Ménard, E.; An, W.; Caron, S. and Hequette, A.
Date : 1998
Title : Coastal changes along Manitounuk Strait, Hudson Bay, during the XIXth and XXth Centuries.
Publication : 28th Arctic Workshop, March 12 - 14, 1998. Institute of Arctic and Alpine Research University of Colorado, Boulder, CO USA
Issue :
Page(s) :
Abstract
Along the Hudson Bay coast, continuing and rapid isostatic uplift induces coastal progradation of shore sectors in bedrock and glacial deposits ; however, the shoreline sectors in post-glacial Tyrrell Sea clays have receded by tens of meters over the last 49 years. This retreat, normally unexpected along emerging coastlines, has provoked important losses of coastal marshes. Regional, large scale mapping of the discontinuous permafrost shows that it is almost exclusively concentrated in the clay deposits along the shoreline where it can reach thicknesses up to 16 m. Between the permafrost patches, the fine sediments of the low coastal terrace are affected by deep seasonal frost. The tidal flat itself is also affected by deep seasonal frost (3-4 m deep) as the ice-foot freezes to the bottom. The annual freezing induces the formation of ice lenses and of reticulated ice in those fine sediments. Both the degradation of permafrost and the thaw of the seasonnaly frozen sediments are responsible for widespread slope wasting and thermoerosion along the shoreline. Liquefaction and thaw weakening of the tidal flat sediments in early summer are relayed by wave erosion and transport by tidal currents. In fact, the clayey sectors of the coast evolve as an erosional platform and the shoreline actually retreats. A synthesis of our studies on coastal processes and regional permafrost history enables us to propose the following sequence for explaining the regional coastal dynamics : The permafrost aggraded rapidly under marshes from the years 1840 onward, as indicated by dendrochronology and by the computation of a mathematical model that simulates the growth of ice segregation mounds. At this time of documented cooler climatic conditions (Little Ice Age), the fast spatial expansion of permafrost patches and rapid frost heave (ca. 5 cm/a) locally added to isostatic uplift (ca. 1 cm/a) to accelerate the rate of coastal emergence and progradation. Conversely, permafrost degradation and increased freeze-thaw based erosion were responsible for localized retreat at a rate too fast to be balanced by isostatic uplift during the Xxth Century warming. In the coming decades, the inexorable isostatic uplift will end up dominating the coastal evolution over any variation in climate induced geomorphological processes, and the tidal marshes should start to expand again along Manitounuk Strait.
Bibliography of Canadian Geomorphology