The Mount Meager massif in the Garibaldi Volcanic Belt of southwestern British Columbia was the source for a massive ( VEI-5 ) Plinian eruption 2,350 years ago similar in character to the 1980 eruption of Mount St. Helens in the U.S. state of Washington . The eruption originated from a vent on the northeast flank of Plinth Peak , the highest and one of four overlapping stratovolcanoes which together form the Mount Meager massif . This activity produced a diverse sequence of volcanic deposits , well exposed in bluffs along the long Lillooet River , which are grouped as part of the Pebble Creek Formation . The explosive power associated with this Plinian eruption sent an ash column estimated to have risen at least above Meager , indicating it entered the second major layer of the Earth 's atmosphere . As prevailing winds sent ash and dust as far as to the east , it created the large Bridge River Ash deposit , extending from Mount Meager to central Alberta . Pyroclastic flows travelled downstream from the vent and buried trees along Meager 's forested slopes , which were burned in place . An unusual , thick apron of welded vitrophyric breccia may represent the explosive collapse of a former lava dome which deposited ash several meters in thickness near the vent area . This collapse blocked the Lillooet River to a height of at least , forming a lake . The lake reached a maximum elevation of and thus was at least deep . The pyroclastic deposits blocking the Lillooet River eventually eroded from water activity , causing a massive outburst flood that sent small house-sized boulders down the Lillooet River valley , and formed high Keyhole Falls . The final phase of activity produced a long glassy dacite lava flow that varies from thick . This is the largest known explosive eruption in Canada in the past 10,000 years . Two clusters of hot springs are found at the Mount Meager massif , suggesting magmatic heat is still present and volcanic activity continues
1980 eruption of Mount St. Helens
1980 eruption of Mount St. Helens
Volcanology of Canada