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

• Main Author: Gowan, Evan James
• Other Authors: James, Thomas S., Spence, George D.
• Format: Thesis
• Language: English
• Published: 2007
• Subjects: sea level; glacio-isostatic adjustment; mantle viscosity; Cordilleran ice sheet; Cascadia subduction zone; Wisconsin glaciation; UVic Subject Index::Sciences and Engineering::Earth and Ocean Sciences::Geophysics; UVic Subject Index::Sciences and Engineering::Earth and Ocean Sciences::Geodesy; UVic Subject Index::Sciences and Engineering::Earth and Ocean Sciences::Geology; British Columbia; Canada; Ice Sheet
• Online Access: http://hdl.handle.net/1828/263

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 ...