Tseax Volcano, Canada


North America’s largest recent earthquake may have triggered a volcanic eruption in British Columbia

The Cascadia megathrust earthquake of 1700 CE affected the whole Pacific coast of North America and may have rejuvenated a basaltic volcano in central British Columbia, Canada.
Megathrust earthquakes are some of the most impressive and dangerous geologic events: the shaking itself, as well as the possibility of tsunamis make these events very destructive. There is now growing evidence that volcanic eruptions can be triggered by these earthquakes, adding to the list of dangers. Most megathrust earthquakes occur in regions like the west coast of South America. However, 309 years ago such an earthquake struck the Pacific Northwest of the US and Canada. The Cascadia earthquake was recognised from tsunami records in Japan and changes in sea level along 1000 km of the coastline of British Columbia, Washington and Oregon. The earthquake was not recorded in written documents, but information on the event was preserved in the oral traditions of the First Peoples (Indians).
Although the province of British Columbia has many volcanoes, volcanic activity is much less than in the states to the south. One of the largest eruptions in the last 1000 years was from Tseax volcano. The 30-km-long basalt flow killed 2000 people when it engulfed two villages, making it Canada’s worst natural disaster. The traditional date for the eruption was 1780, based on an anthropologist’s and a missionary’s interpretation of oral traditions. However, a geologist at the Université du Quebec ŕ Chicoutimi, Canada, has shown that it must be earlier. A comparison of existing magnetic data from the flow with marine magnetic measurements made by the navigators James Cook and George Vancouver suggests that it actually erupted around 1700, close to the date of the Cascadia earthquake. Indeed, tradition holds that the eruption was preceded by ground shaking, which may have been the Cascadia earthquake itself.
The Tseax volcano may have been particularly sensitive to triggering because it had already erupted in the 12th century. Study of crystals in the rocks suggests that the magma may have been kept molten since that time by a stream of hot CO2 gas from a deeper magma chamber. This magma could have then easily erupted in response to stresses produced by a distant earthquake.
If this mechanism is important then many other dormant or inactive volcanoes may be reactivated by major earthquakes. Nature hazard planning must then be enlarged to include this possibility.

‘Large Earthquakes Trigger A Surge In Volcanic Eruptions’ http://www.sciencedaily.com/releases/2009/01/090110084653.htm