Preliminary Observations on Coastal Sediment Loss Through Ice Rafting in Lake Michigan
Keywords:Coastal erosion, sediment transport, ice transport, Great Lakes
Knowledge of sediment content in drifting coastal ice was combined with aerial observations ship-board ice sampling, and studies of LANDSAT images to show that ice rafting of sand is an Important mechanism influencing processes of coastal erosion and basin-deposition in southern Lake Michigan. During winter, the central lake usually remains open, while sand-charged ice formed In coastal waters is displaced lakeward from the western shore in long, sinuous bands by offshore winds. Under some conditions, these ice streamers are dissipated within 2 to 20 km from the coast. This occurred during offshore collection of ice-rafted sand and gravel, demonstrating a net loss of beach sand from the windward shore to deep water. Under other conditions, Ice streamers can cross the lake, leading to ice accumulations at the downwind or lee shore. Northwesterly winds dominate winter weather, so ice accumulations form mainly in the southeastern end of the lake, where they ultimately melt. Thus, ice rafting may be partly responsible for net sediment progradation at this southeastern, lee shore during the last few thousand years, and adds coarse grains to basin muds.