Mount Meager, 150 km north of Vancouver, British Columbia, is the youngest of four overlapping stratovolcanoes resting on a 400 m high ridge of nonvolcanic, crystalline and metamorphic rock. The complex comprises at least eight vents that have produced basaltic to more evolved andesitic, dacitic, and rhyolitic magmas. Andesite lava flows (500,000 to 1,000,000 years old) are the most abundant rock type and their maximum total flow thickness is over 1 km. The most recent volcanic activity started 2350 radiocarbon years ago from a vent on the northeast side of the mountain and consisted of a massive, dacitic, Plinian eruption.
The ash plume from this explosion travelled east across British Columbia into Alberta. The next stage of the eruption was marked by the production of hot, mobile, pyroclastic flows that travelled 7 km downstream from the vent. This early phase was followed by the extrusion of a lava flow that repeatedly collapsed on the steep slopes, producing a unique, dense, welded breccia thick enough and extensive enough to dam the Lillooet River valley, resulting in the formation of a lake upstream along the Lillooet River. One dam failure on the upper Lilloet River produced a cataclysmic outburst flood that sent small-house-sized boulders downvalley for several kilometres and destructive floodwaters even farther. The final stages of the eruption produced a short lava flow. Two peripheral clusters of hot springs are found within the complex and suggest that magmatic heat is still present. Canada's only producing pumice mine is on the northeast side of Mount Meager.
The explosive nature of past eruptions at Mount Meager suggests that this volcano poses a significant long-distance threat to communities across southern British Columbia and Alberta. It also poses a significant local threat to the town of Pemberton, British Columbia, about 50 km downstream from the volcano. The failure of natural dams formed on the upper Lillooet River by landslides not associated with volcanic activity could produce catastophic floods. In addition, volcano-generated debris flows (lahars) could travel as far as Pemberton. Another explosive eruption at Mount Meager would also have a significant impact on local mining and logging operations, as well as significant negative impacts on the Lillooet River fishery (the river has salmon runs at least to Lillooet Lake, if not farther west).
Volcanoes within the Mount Meager Volcanic Field | |
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Bridge River Vent | Mount Meager |
Mount Meager | Mount Meager |
Capricorn Mountain | Mount Meager |
Mosaic Assemblage | Mount Meager |
Mount Job | Mount Meager |
Devastation | Mount Meager |
Plinth Mountain | Mount Meager |
The Devastator | Mount Meager |