Mount Garibaldi, a supraglacial Pleistocene volcano in southwestern British Columbia

Abstract

Mount Garibaldi is an extinct volcano built for the most part by glowing avalanches during an almost uninterrupted series of Pelean eruptions. A dacite core and lava flows from a vent on the northern slope make up the remainder of th emountain. A large volume of debris from the western slope of the cone now lies in nearby Squamish Valley as fanglomerate and late Pleistocene to Recent alluvium. Despite the loss of enormous quantities of material from this side of the cone, part of the original upper surface persists in an adjoining sector. Tuff-breccias laid down by the glowing avalanches do not extend as far from the apex of the cone down two pre-existing valleys as they do on an intervening ridge. The cone was built during occupation of the valleys by Cordilleran ice of Wisconsin age and part of it was evidently deposited on the ice. Ice filling the old valleys may have prevented extension of the glowing avalanches beyond the limit reached on the intervening ridge which then protruded only a little above the ice surface. Melting of the ice in late Wisconsin time permitted extensive landsliding and transfer of debris from the cone to Squamish Valley.