Andrew Perkins

Andrew Perkins (2015)

Refining the pattern and style of deglaciation on the southern Fraser Plateau and environs [PhD thesis]


The Cordilleran Ice Sheet (CIS) represents an ideal paleo-analogue for studying the pattern and style of deglaciation across an area of moderate relief. Hypotheses tested on the CIS landscape may be applied to our understanding of the processes involved in modern deglaciation. This thesis addresses current shortcomings in our understanding of the pattern and style of CIS deglaciation over the southern Fraser Plateau in south-central British Columbia (BC). During the last glacial buildup, ice advancing from mountain ranges in the east and west met somewhere over the southern Fraser Plateau (Tipper 1971a), forming an area of significant ice accumulation, according to models of glacioisostatic rebound (Fulton and Walcott 1975, Johnsen and Brennand 2004), and potentially increasing in thickness to form an ice divide during glacial maximum (Wilson et al. 1958). Deglaciation through ice stagnation and downwasting has been hypothesized for the plateau (Fulton 1967, 1976, 1991). This thesis tests the hypothesis that the lateglacial landform and sediment record supports the large-scale regional stagnation of the CIS over south-central BC.

Through the integration of aerial photographs, digital elevation models, field observations of landform morphology, stratigraphy and sedimentology, and shallow geophysics (electrical resistivity tomography, ground-penetrating radar) a map of lateglacial landforms and lakes associated with deglaciation of the last CIS is produced. Ice-marginal indicators, including ice-marginal lake systems and moraines are used to reconstruct ice-marginal positions, demonstrating retreat from southeast to northwest across the southern Fraser Plateau. Fields of pristine glaciotectonic moraines indicate active retreat rather than passive melting of plateau ice. Analysis of morphosedimentary relationships of esker systems and associated glacier hydrology demonstrates ice retreat was characterized by low-sloping thin ice where ice-dammed lakes were important for meltwater storage. Crevasse-fill ridges and eskers formed in ice-walled canyons record areas of localized ice stagnation.

Full thesis PDF (63 MB)