ABSTRACT: A descriptive model of shoreline development showing nearshore control of coastal landform change: Late Wisconsinan to Present, Lake Huron, Canada

CGRG Bibliography of Canadian Geomorphology
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Abstract

The 12900 year 14C history of nearshore morphological change for glacial and post-glacial lakes at the eastern shore of the Huron Basin is investigated in order to formulate a descriptive model of the development of past and present shores, to determine the control exerted by the subaqueous shoreface on the maturation of coastal landforms, and to provide shore recession information for the purpose of land-use set-backs. The reach examined, from Goderich to Point Clark, Ontario, Canada includes: glacial till shorebluffs, with bedrock, a lower stony till, or a finer till exposed in the surf zone; an extensive foreland with the relict backshore bluffs fronted by a series of dunes and ridges, at Point Clark; a fillet beach updrift of the Goderich harbour structures; and smaller headlands. Relict Lakes Warren, Algonquin, and Nipissing shorebluffs and nearshore zones are compared to the bluffs and nearshore of Lake Huron. Accurate historical and current erosion rates are established for Lake Huron, as well as the composition of the coast and nearshore profile. Since parts of the past shorelines were truncated by subsequent bluff recession at lower water levels, the exposed profile at existing relict bluffs and the subaqueous profile now at Lake Huron are used, along with other available data, to recreate the location and sequence of shorelines since Lake Warren times. Examination of these past and present coastal landforms shows that erosion of the concave-upward profile of the surf zone allowed continuous recession of the onshore bluffs due to erosion at the bluff toe. No submarine platform or ramp or subaqueous debris terrace forms to protect the bluff. The debris from this erosion is removed downdrift or offshore. Only when the littoral drift is trapped by an obstruction does it accumulate sufficiently to protect the bluff. However, if the composition in the surf zone changes to a more resistant material, such as bedrock or a stony till, a bedrock or boulder-covered shelf may form. The shelf dissipates wave energy and thereby protects the onshore bluff. These shelves can trap littoral drift, allowing the formation of onshore dunes and ridges. These variations of the subaqueous shoreface control the geomorphological development of the coastal landform.

Bibliography of Canadian Geomorphology