Many people within Canada are well aware of the famous 1980 Eruption of Mount Saint Helens.
This eruption was not only famous due to its size and destructive power, but also because
it destroyed much of Mount Saint Helens, reducing the volcano's overall height.
In Canada there is a different volcano which produced an almost carbon copy of this eruption
2400 years ago.
The volcano which produced this eruption is known as Mount Meager.
This volcano is still very much active, as evidenced by its active fumaroles and hot
springs.
This video will discuss this powerful volcano, and mention what its future hazards are.
Mount Meager is located in the southwest portion of British Columbia, where it is 150 kilometers
north of Vancouver.
Meager is one of the very northernmost active volcanoes in the Cascade Range, and exists
due to the collision of two tectonic plates off the western coast of Canada.
There, the Juan de fuca tectonic plate is being subducted underneath the North American
plate.
The melted crust from this collision then melts and migrates upwards, until it erupts
on the surface, thus forming a volcano.
The first eruption from Mount Meager occurred 2.6 million years ago, when andesitic lava
reached the surface.
This eruption created a series of lava flows and ash, forming a gray basement rock in the
south of the volcanic complex.
Although several other eruptions occurred in the next 1 million years, the next major
eruptive period began 1.6 million years ago.
Over the span of the next 200,000 years, numerous explosive eruptions built a 500 meter thick
layer of rock out of both andesite and dacite rock.
Subsequent eruptions in the area built a tall volcanic cone known as devastator peak, or
the devastator.
The series of eruptions which built this volcanic cone were the most voluminous of the entire
eruptive history of Mount Meager.
These eruptions occurred over a vast area and involved a number of cones, leaving a
permanent mark on the area's topography.
The volcanic cone which is the basis for the name of this volcano, Meager, formed about
100,000 years ago.
The most recent eruptive center is centered around Plinth Peak, which was built by a series
of eruptions which deposits andesite and dacite.
By 5,000 years ago, Plinth peak had a satellite cone to the northeast which stood several
thousand meters above the surrounding landscape.
So, why isn't this cone still visible?
The answer is that this satellite cone was mostly destroyed during a catastrophically
large eruption from Mount Meager in 410 BC.
This eruption began with a massive explosion.
The explosion caused a large portion of the satellite cone to slide off to the northeast,
forming a 1.5 kilometer wide crater.
From this crater emerged a tall eruption column which shot more than 20 kilometers into the
atmosphere.
Pyroclastic flows during this phase of the eruption swept down a series of rivers adjacent
to the volcano, as material was funneled into a low point.
Remnants of this pyroclastic flow can still be seen today, through numerous dead and darkened
trees petrified by the eruption.
Ash from this phase of the eruption was subsequently carried hundreds of kilometers, and fell throughout
British Columbia and Alberta.
Afterwards, a series of lava domes began forming in the remnants of the exposed crater, much
like what occurred at Mount Saint Helens.
These lava domes experienced a cycle of building and collapse, which created additional series
of landslides and pyroclastic flows.
One of these landslides dammed Lillooet River, causing a large lake to build.
However, since this dam was primarily built out of ash, it was structurally unstable.
Eventually, the dam failed, and released a torrential 100 meter flood downstream.
The eruption which had just taken place was the largest to occur within Canada of the
last 10,000 years.
On the volcanic explosivity index, this eruption rated as a 5, placing it on par with the 1980
eruption of Mount Saint Helens.
Although Mount Meager has not erupted since, it will erupt again.
Today, Meager has at least two active hot springs, and occasionally vents volcanic gas
at its summit.
This activity hints at a shallow magma chamber at depth, which could erupt with rather little
notice.
Any future eruption would likely be an order of magnitude smaller than the 410 BC Eruption,
and create a series of similar hazards.
As such, the main hazard outside of the immediate vicinity would be lahars, which could travel
more than 100 kilometers downstream and wash away homes, roads, and bridges.
However, this volcano does not need to erupt to cause problems downstream.
In both 1975, and then again in 2010, large landslides occurred on the flanks of the volcano.
These landslides are likely becoming more frequent due to the rate of melting glaciers.
I hope that you enjoyed this video.
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