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Glacio-isostatic adjustment modelling of improved relative sea-level observations in southwestern British Columbia, Canada

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dc.contributor.author Gowan, Evan James
dc.date.accessioned 2007-12-06T00:40:48Z
dc.date.available 2007-12-06T00:40:48Z
dc.date.copyright 2007 en_US
dc.date.issued 2007-12-06T00:40:48Z
dc.identifier.uri http://hdl.handle.net/1828/263
dc.description.abstract In the late Pleistocene, most of British Columbia and northern Washington was covered by the Cordilleran ice sheet. The weight of the ice sheet caused up to several hundred metres of depression of the Earth’s crust. This caused relative sea level to be higher in southwestern British Columbia despite lower global eustatic sea level. After deglaciation, postglacial rebound of the crust caused sea level to quickly drop to below present levels. The rate of sea-level fall is used here to determine the rheology of the mantle in southwestern British Columbia. The first section of this study deals with determination of the postglacial sea-level history in the Victoria area. Constraints on sea-level position come from isolation basin cores collected in 2000 and 2001, as well as from previously published data from the past 45 years. The position of sea-level is well constrained at elevations greater than -4 m, and there are only loose constraints below that. The highstand position in the Victoria area is between 75-80 m. Sea level fell rapidly from the highstand position to below 0 m between 14.3 and 13.2 thousand calendar years before present (cal kyr BP). The magnitude of the lowstand position was between -11 and -40 m. Though there are few constraints on the lowstand position, analysis of the crustal response favours larger lowstand. Well constrained sea-level histories from Victoria, central Strait of Georgia and northern Strait of Georgia are used to model the rheology of the mantle in southwestern British Columbia. A new ice sheet model for the southwestern Cordillera was developed as older models systematically underpredicted the magnitude of sea level in late glacial times. Radiocarbon dates are compiled to provide constraints on ice sheet advance and retreat. The Cordillera ice sheet reached maximum extent between 17 and 15.4 cal kyr BP. After 15.4 cal kyr, the ice sheet retreated, and by 13.7 cal kyr BP Puget Sound, Juan de Fuca Strait and Strait of Georgia were ice free. By 10.7 cal kyr BP, ice was restricted to mountain glaciers at levels similar to present. With the new ice model, and using an Earth model with a 60 km lithosphere, asthenosphere with variable viscosity and thickness, and transitional and lower mantle viscosity based on the VM2 Earth model, predicted sea level matches the observed sea level constraints in southwestern British Columbia. Nearly identical predicted sea-level curves are found using asthenosphere thicknesses between 140-380 km with viscosity values between 3x10^18 and 4x10^19 Pa s. Predicted sea level is almost completely insensitive to the mantle below the asthenosphere. Modeled present day postglacial uplift rates are less than 0.5 mm yr^-1. Despite the tight fit of the predicted sea level to observed late-glacial sea level observations, the modelling was not able to fit the early Holocene rise of sea level to present levels in the central and northern Strait of Georgia. en_US
dc.language English eng
dc.language.iso en en_US
dc.rights Available to the World Wide Web en_US
dc.subject sea level en_US
dc.subject glacio-isostatic adjustment en_US
dc.subject mantle viscosity en_US
dc.subject Cordilleran ice sheet en_US
dc.subject Cascadia subduction zone en_US
dc.subject Wisconsin glaciation en_US
dc.subject.lcsh UVic Subject Index::Sciences and Engineering::Earth and Ocean Sciences::Geophysics en_US
dc.subject.lcsh UVic Subject Index::Sciences and Engineering::Earth and Ocean Sciences::Geodesy en_US
dc.subject.lcsh UVic Subject Index::Sciences and Engineering::Earth and Ocean Sciences::Geology en_US
dc.title Glacio-isostatic adjustment modelling of improved relative sea-level observations in southwestern British Columbia, Canada en_US
dc.type Thesis en_US
dc.contributor.supervisor James, Thomas S.
dc.contributor.supervisor Spence, George D.
dc.degree.department School of Earth and Ocean Sciences en_US
dc.degree.level Master of Science M.Sc. en_US


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