GEOSCAN, résultats de la recherche


TitreSubannual erosion and retreat of cohesive till bluffs, McNab's Island, Halifax, Nova Scotia
AuteurManson, G K
SourceJournal of Coastal Research vol. 18, no. 3, 2002 p. 421-432
Séries alt.Commission géologique du Canada, Contributions aux publications extérieures 2000020
Documentpublication en série
Lat/Long OENS -64.0000 -63.5000 44.7500 44.5000
Sujetsérosion; glissements de pentes; resistance au cisaillement; tills; drumlins; études côtières; milieu côtièr; érosion côtière; géologie marine; sédimentologie
Illustrationslocation maps; cross-sections, stratigraphic; tables; formulae; photographs; graphs
ProgrammeCRSNG Conseil de recherches en sciences naturelles et en génie du Canada
Résumé(disponible en anglais seulement)
The roles of variable geotechnical properties and meteorologic and oceanographic conditions in contributing to the subannual variance in erosion, failure and retreat of cohesive till bluffs have been investigated by comparison of results of 18 months of observations and measurements of bluff erosion, retreat, water content and shear strength with wind speed and direction, water level, wave height, precipitation and temperature. Shear strength of the uncon- solidated cohesive till inversely depends on water content which is correlated to erosion and may be increased by precipitation and spray. In stepwise multiple regression, high winds from the direction of longest fetch, high water levels and high precipitation all significantly contribute to erosion. Failures and maximum rates of erosion tend to occur during storms when shear strength (resisting force) is low, and wave activity superimposed on elevated water levels results in increased incident energy (assailing force) at the bluff toe and over till exposures in the foreshore. The assailing and resisting forces are thus inversely related during storms such that thresholds of erosion can be easily exceeded. Erosion occurs at the bluff toe in response to both decreased resisting force and increased assailing force but, at the upper bluff edge, failures and retreat occur mainly due to decreased resisting force with only indirect impacts from increased wave activity. The relative importance of till properties and storms in contributing to subannual bluff erosion and retreat is therefore variable over the bluff profile which may contribute to longer term morphologic evolution of cohesive bluffs.