Canada has 21 active volcanoes. Of these, only one volcano has produced a deadly
eruption which caused loss of human life. The eruption in question was one of the deadliest
eruptions known on the planet, and killed about 2,000 people. However, few people have heard of
the small volcano which produced this deadly eruption. I am referring to the Tseax Cone,
which last erupted about 300 years ago in British Columbia. This video will discuss this volcano,
and mention what its future hazards are. The Tseax Cone Volcano can be found in
west central British Columbia, where it is 37 miles west-northwest of the town of Cedarvale.
This young volcano is not part of the Cascade range, but is rather part of a different volcanic
complex called the Northern Cordilleran Volcanic Province. Volcanoes in this section of British
Columbia exist due to tectonic forces in the region which are slowly stretching the crust.
This stretching of the crust creates a series of cracks, which then allows magma to travel
upwards and erupt onto the surface. The magma which erupts typically does not
have much silica, which means that the resulting eruptions are at worst only mildly explosive.
The Tseax cone represents the youngest of a set of several similar volcanoes in the region. 1,000
years ago, there was no trace of this volcano but instead a lush green forest with a river.
Then, in 1240 AD, the ground shook with numerous earthquakes as magma rose upwards through the
crust. Eventually, lava reached the surface, and erupted at a spot which offered the path
of least resistance. In this case, the path of least resistance was the edge of a local river.
Due to the amount of groundwater present in the region, the initial phase of the eruption was
characterized by a series of moderately sized explosions. As lava erupted in a fountain onto
the surface, ash ejected by these explosions fell in a several kilometer radius and coated
the ground. As these explosions continued, much of the ash fell close to the erupting vent. Along
with the erupted lava, this formed the beginnings of a cylindrical vent known as a cinder cone.
At the end of this small eruption, what remained was a 460 meter wide and 50 meter high cinder
cone with a circular depression in its center. In the subsequent period of several hundred
years, vegetation destroyed by heat and fires of the previous eruption regrew,
until the cone was unrecognizable. Then, on January 26th, 1700, the largest
earthquake in the last 1,000 years hit the region. This earthquake, measuring as a 9.1 on the Richter
scale, caused a large section of the nearby Juan de fuca tectonic plate to move. Although we aren't
exactly sure how, it appears that this earthquake caused the Tseax cone to erupt in the same year.
The eruption which it triggered was larger and far more destructive than the one in 1240,
as it erupted a much greater volume of lava. During the initial phase of the eruption,
a new SMALLER cinder cone was built on top of the existing one. From this cone, and a series
of two smaller vents to the north, erupted a vast volume of lava. This lava slowly flowed downhill,
which carried it to the west. Eventually, the lava turned north, and started flowing towards
three indigenous settlements. As the lava advanced at several kilometers per hour,
it emitted large amounts of carbon dioxide. Since carbon dioxide was heavier than air, it traveled
downhill ahead of the flows until it collected in a valley downstream. This toxic gas cloud caused
asphyxiation among those who had not already left the area. In the ensuing chaos, more than 2,000
people were killed by poison gasses, since it displaced breathable air. These people were never
recovered, as less than 24 hours later, the lava flow buried what remained of these three villages.
Although this volcano has not erupted since, it could erupt again. Typically, cinder cones only
erupt once. However, for an unknown reason, the Tseax cone did not follow this rule.
Even today, elevated concentrations of carbon dioxide are detected originating
from the volcano, suggesting that there is still magma not far beneath the surface.
If this volcano was to erupt again, it would likely create an almost identical course of
events which occurred due to the 1700 eruption. Such an eruption would require the immediate
evacuation of thousands of people up to 50 kilometers downriver of the volcano.
Overall, the 1700 AD Eruption of Tseax cone was not particularly large, rating as only a 2 on
the volcanic explosivity index. However, this eruption is a reminder that a large eruption is
not necessarily needed for it to be deadly. I hope that you enjoyed this video. If
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