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The Valley Palimpsest: Relicts of compounding volcanic, glacial and fluvial processes in valley systems of the Garibaldi Volcanic Belt, Canada

Annie Borch 1, James K. Russell1, Rene W Barendregt2

  • Affiliations: 1Earth, Ocean, and Atmospheric Sciences Department, University of British Columbia, Vancouver, Canada. 2Department of Geography and Environment, University of Lethbridge, Lethbridge, Canada.

  • Presentation type: Poster

  • Presentation time: Tuesday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 162

  • Programme No: 3.5.21

  • Theme 3 > Session 5

Abstract

The Coast Mountains of southwestern B.C. host the Garibaldi Volcanic Belt (GVB), which has an eruptive history spanning the multiple glacial, periglacial, and non-glacial periods of the Quaternary. The geomorphology of the area is heavily controlled by Quaternary period processes. The timing and magnitude of volcanic-glacial-fluvial interactions are chronicled by the landscape, especially in drainage systems that have a history of volcanism. The Cheakamus valley is one such drainage system, and is host to the Cheakamus basalts (CB), a Late Quaternary set of voluminous (1.65 km3, ~31 km long) basalt lavas. These lavas preserve striking evidence of syn- and post-eruptive interaction with a myriad of paleoenvironments (subaerial, fluvial and/or glacio-volcanic). Previous research on the CB leave fundamental questions unanswered, including the age, source, duration and number of eruptions responsible for the Cheakamus basalts, as well as the nature of the environment of their emplacement. We combine detailed field mapping, geochemistry, textural analysis, Ar/Ar dating and paleomagnetic analysis to determine the basalt's eruptive history, and to clarify the timing and interaction of lava, glaciers and fluvial systems. Our results indicate the CB were emplaced by a single eruption of short duration, into multiple environmental conditions captured by the lava's morphology. Additional geomorphologic mapping indicates the valley system has been further and fundamentally impacted by post-glacial processes, including a previously unknown glacial lake outburst flood. The valley's mixture of primary eruptive morphologies and secondary erosive features provide a snapshot of a rapidly changing Quaternary landscape.