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Glaciovolcanism in the Garibaldi volcanic belt Wilson, Alexander M.

Abstract

This thesis investigates glaciovolcanism in the Garibaldi volcanic belt (GVB) of southwestern British Columbia (SWBC), Canada. Field observations and modelling are used to investigate: i) the paleoenvironmental implications of glaciovolcanism in SWBC, ii) volcanic eruption processes in glaciovolcanic environments, and iii) causal linkages between the volcanic eruptions and the growth and decay of terrestrial ice masses. Throughout the Pleistocene, the GVB has experienced multiple alpine and continental glaciations. The GVB comprises >100 Quaternary volcanoes and much of the character of this volcanism is ascribed to the range of magma compositions (alkaline basalt to rhyolite), to the extreme relief of the landscape, and to interactions with ice. The three key findings are: i) The GVB volcanoes are established as a powerful proxy for the local paleoenvironment. The volcanic deposits are used in conjunction with a geometric model for mountain glacier growth and retreat to inform on the presence, thickness, and transient properties of the Cordilleran Ice Sheet over the last 1 Ma. ii) Studies of two effusive glaciovolcanoes (the Lillooet Glacier basalts, and the Table) show that eruption style and deposit morphology are strongly influenced by the nature of heat exchange between the erupted lava and the ice. Specifically, meltwater drainage attending eruptions exerts a critical control on eruptive behaviour (i.e., dictating the ephemeral presence of an englacial lake). Lava-dominated tuyas, may be constructed from eruptions involving within-ice dike injection, steep, well-drained bedrock topography and endogenous, englacial inflation of the massif. iii) Transient growth and decay of terrestrial ice masses can influence the timing, size and distribution of eruptions. Specifically, glacier-induced deformation of topography may impart local, shallow crustal stresses which influence eruption frequency, eruption size and vent distribution, depending on the rheology of the bedrock and the geometry of the topography. At the scale of the crust, transient loading and unloading of ice sheets may act as a glacial pump, bending the crust downwards during loading (causing a suppression in eruptions) and allowing the crust to rebound during unloading (causing an increase in eruptions). Supplementary materials available at: http://hdl.handle.net/2429/73440.

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