Can. J. Fish. Aquat. Sci., Vol. 48(1991), 1503-1516

I. PETER MARTINI¹ and JOHN R. BOWLBY²

1Department of Land Resource Science, University of Guelph, Guelph, Ont. N1G 2Wl, Canada
²Geotechnical and Hydraulic Engineering Department, Ontario Hydro, 700 University Avenue, Toronto, Ont. M5G lX6, Canada

Lake Ontario, located at the northern margin of the Appalachian Basin, occupies a deep trough cut by rivers and glaciers into early to mid-Paleozoic limestones and shales. It is still being affected by movements along faults which have probably been active since late Precambrian (more than 600 million yr ago), as evidenced by small faults, "pop-ups" (small domes and anticlines) involving bedrock, Pleistocene drift (glacial and nonglacial deposits) and recent lacustrine sediments, and many small earthquakes (up to intensity V in the Mercalli scale). Infrequent large earthquakes may damage buildings and trigger slumps along coastal bluffs and subaqueous lacustrine slopes. Fractures generated by such crustal movements may become pathways for groundwater and leakage of stored dangerous substances. The lake receives sands from shore erosion of Pleistocene drift and silts and clays from rivers crossing vast Pleistocene lacustrine plains subjected to agricultural practices. Some of the nearshore, subaqueous sand deposits cannot be readily exploited for aggregates because shore erosion may be triggered and valuable ecosystems can be destroyed. Clays mop up pollutants, in part storing them in depocenters such as lagoons, marshes, and the deep lacustrine basins, and in part exporting them to the St. Lawrence River system.