A new 40Ar/39Ar date from a pyroclastic density current deposit preserved on the northern slopes of the Lillooet River valley, British Columbia, indicates an explosive volcanic eruption of the Mount Meager Volcanic Complex (MMVC) at 24.3 ± 2.3 ka. The age of this pyroclastic deposit is a record of the second youngest explosive volcanic event for the MMVC and indicates that Mount Meager has erupted, explosively, at least twice in the past ∼25 000 years. The age of the volcanic eruption coincides with the early phase of growth of the late Wisconsin (Fraser) Cordilleran ice sheet. The deposit constrains the distribution and timing of glacier build-up in southwestern British Columbia over the last glacial cycle and suggests that the ice sheet was absent or thin in the upper Lillooet River valley at this time. Field evidence suggests the pyroclastic density current was sourced at high elevation near present-day Plinth Peak and was deposited and preserved on the adjoining Lillooet River valley wall. Coeval, proximal valley-filling glacial ice was up to ∼120 m thick.

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