Sediment Load of Shore Ice and Ice Rafting Potential, Upper St. Lawrence Estuary, Quebec, Canada
Keywords:Ice processes, ice cover, ice floes, sediment-laden ice, coarse debris, sedimentary budget, importance of ice rafting
The annual shore ice in the upper St. Lawrence estuary, Quebec, is heavily loaded with terrigenous debris of all grain sizes (from clay to boulders exceeding 1 m in diameter). Our estimate of sediment load is based on the amount of debris observed at the surface, at the base and in the ice cover fastened to the shore, in grounded ice floes, and on debris freshly released by ice floes upon melting in intertidal zones. Observations and measurements extended from 1982 to 1992. They were made on both shores in the area between Quebec City and Grondines, with emphasis on two particular sites (Neuville and Grondines). The mean load of the ice cover is approximately 25,000 tons per km. Considering the area covered, it is estimated that about one million tons of rock debris, of which 70-75% is coarse, is displaced by ice annually over various distances. Ice rafting is thus a major process in the sedimentary budget of the study area.