Within Canada, there are 21 active and potentially active volcanoes.
Of these, the most well known is Mount Meager, which produced a catastrophic eruption approximately
2,500 years ago which ejected 1.3 cubic kilometers of volcanic rock.
For comparison, this was 30% larger than the 1980 eruption of Mount St. Helens!
However, within the country there is a volcano which produced a far larger eruption.
The eruption in question was about 150 times the size of the aforementioned eruption of
Mount Meager, and caused more than 400 square kilometers of ground to collapse, forming
a massive caldera.
The volcano which produced this eruption is also the tallest volcano within Canada, and
is known as the Silverthrone Caldera.
Today, we know that this volcano is still active as it produces occasional swarms of
earthquakes.
This video will discuss this volcano, its large eruption, and mention what its future
hazards are.
The Silverthrone Caldera can be found in west central British Columbia near Vancouver Island.
Specifically, it is 325 kilometers northwest of the city of Vancouver.
From satellite, we can see that much of this large volcanic complex is covered in thick
glaciers, so its features are difficult to see.
However, there is a massive caldera rim buried under much of this ice.
On screen, I have outlined the calder's edge.
It measures an impressive 30 kilometers long and 20 kilometers wide.
This caldera formed in what may have been the largest volcanic eruption within Canada
of the last 1 million years.
It originated approximately 650,000 years ago, when a large eruption drained much of
the underlying volcano's magma chamber.
This caused the top of the volcano to collapse downwards by at least 200 meters, much like
a sinkhole, to fill this empty space in the magma chamber.
This massive collapse occurred over an area of 473 square kilometers.
The associated eruption created a 50 kilometer high ash plume, and produced pyroclastic flows
which likely traveled more than 50 kilometers away.
Thick beds of ash were deposited, totaling more than 100 meters in some locations.
Thus, after this eruption ended, what remained was a crater in the ground, much like Crater
Lake in Oregon, but much shallower and more broad.
In the aftermath of this massive eruption, a volume of magma erupted onto the caldera
floor.
Since this magma was highly viscous, it began growing into a glowing gray lava dome of a
rock type called dacite.
Over time, similar eruptions built a complex of overlapping lava domes which were spread
across the caldera floor.
During these eruptions, intermittent lava dome collapses would occur.
This triggered pyroclastic flows, which raced downhill for several kilometers.
This lava dome forming eruptive activity largely ceased around 100,000 years ago.
Eventually, thick glaciers covered the caldera, which was now almost completely unrecognizable
due to the numerous lava domes and volcanic cones which had grown in it.
Within the last 100,000 years, at least 4 medium sized eruptions occurred, which created
flat topped volcanic features called tuyas.
Here is an example near the caldera wall.
After the glaciers retreated, one additional eruption occurred.
A new eruptive vent erupted bombs of lava and emitted a small lava flow which traveled
a kilometer.
This eruption occurred sometime around 6,600 years ago, but the margin of error on this
date is high.
If this volcano was to erupt again, even a small eruption could be catastrophic.
The main threat a future eruption could pose are lahars associated with the rapid melting
of glaciers on this volcano.
This would send a wall of water up to 200 meters high downstream, effecting towns up
to 100 kilometers away.
On screen, I have labeled 3 towns at risk in the event of a future eruption.
They should be evacuated when the next eruption occurs.
Luckily, this volcano should not erupt for some time, as it appears to be in the waning
stages of its overall lifespan.
Using the US Geological Survey method of rating volcanoes, Silverthrone Caldera would be classified
as a high threat volcano.
I hope that you enjoyed this video!
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