LAKEFLOOR GEOMORPHOLOGY OF WESTERN LAKE ERIE

Bathymetry of western Lake Erie, exceeding in detail any previous bath ymetry, is an early result of a project conducted jointly by the U.S. National Oceanic and Atmospheric Administration and the Canadian Hydro graphic Service. This bathymetry utilizes the entire archive of histor ic hydrographic data assembled since 1903 in the U.S. and Canada. Deta ils of bottom configuration for the shallow (<12 m) western portions o f Lake Erie are highlighted using a 1-meter contour interval. The isla nds and reefs bordering and lying within the western basin have bedroc k cores which are erosional remnants of the more resistant upper Silur ian and lower Devonian dolomites and limestones. Overdeepened channels between the islands have been sites of postglacial nondeposition, and probably erosion, due to intense wind-driven water circulation throug h these restricted passages. The Pelee-Lorain Ridge is interpreted as a late Wisconsinan end moraine upon which sand deposits have been conc entrated. The point Pelee Ridge is apparently a morainic ridge, capped by sand deposits transported in part by longshore drift converging on Point Pelee. A fan-shaped feature with a surface depth of 10-15 m, wh ich extends to the east of Point Pelee Ridge, may be a former shorelin e delta of the Detroit River. This fan-shaped feature may have formed following opening of the Port Huron outlet about 4000 yr bp when the n ew River was actively eroding its channel and bringing a heavy load of sediment into Lake Erie-although subaqueous deposition of fan sedimen ts is a possible alternate explanation. Sculptured drift-like features interpreted as relict spits extend northwestward and southeastward fr om the bedrock reefs in the western basin off Locust Point. Channels o n the floor of the western Lake Erie basin underlying the main shippin g lanes have been excavated by propeller wash where ship traffic incre ases speed, resulting in resuspension of bottom sediments. Dumpsites f or dredge spoils excavated from channels are expressed in the bathymet ry by a distinctive hummocky pattern in two areas.