North of Vancouver are three closely spaced active volcanoes.
Although the last eruption from these peaks was several thousand years ago, they all have
the potential to and will erupt again.
The most famous of these peaks is Mount Garibaldi, whose last eruption sent a thick lava flow
into the city of Squamish along with damaging lahars around 10,000 years ago.
To the north of Mount Garibaldi is a larger volcanic field which surrounds the scenic
Garibaldi Lake.
This volcanic field contains a number of explosively formed lava domes, and beautiful flat peaked
featured termed tuyas.
The third volcano to the north is often forgotten about, but is proven to still be active due
to its associated hot springs and earthquake swarms meaning an underground magma chamber
is still present.
I am referring to Mount Cayley, which erupted at least twice since the end of the last ice
age.
This video will discuss this little known volcano, and what its future hazards are.
For some additional context as to where this volcanic complex is, it is centered 20 kilometers
west of the city of Whistler.
The Mount Cayley volcanic field consists of a dozen recent vents spread out over an area
of 450 square kilometers.
These vents almost perfectly form a northward trending straight line of activity, which
represent their origin as part of the Cascade Mountain Range.
Around the landscape, beautiful towering flat topped tuyas can be found such as the scenic
Ring Mountain Tuya.
Although its true age is unknown, it is almost certainly less than 1 million years old.
At the time, the ice age had been ongoing for more than 1 million years, and a 2000
meter thick glacier towered above all of the peaks in the vicinity.
Soon, lava erupted into a glacier, but could not travel very far and slowly built up into
a steep sided hill.
Eventually, a large section of the overlying glacier was melted by its proximity to the
lava, forming a small subglacial lake.
As subsequent eruptions continued, the volcanic cone eventually reached the height of the
lake.
Lavas then slowly deposited along the level of the lake water, forming a flat top.
By the time the eruptive series had ended, what remained was a unique subglacial volcano.
Around the volcanic field, numerous other tuyas and subglacial mounds can be found which
formed during the same ice age.
Another notable feature of this field is a particular eruption which occurred 50,000
years ago during an interglacial period.
It sent a thick basalt lava flow through a valley which traveled more than 20 kilometers
to the south before reaching Daisy Lake.
However, the vast majority of volcanic activity occurred around Mount Cayley itself.
This highly eroded stratovolcano was constructed in intervals during the last 4 million years
during incredibly explosive eruptions.
The lava it erupted had a composition of dacite, so it primarily formed large overlapping lava
domes.
On occasion, these lava domes would collapse, creating massive pyroclastic flows.
These lava dome forming eruptions have continued after the end of the last ice age.
One feature, known as Slag Hill, formed around 11,000 years ago.
The most recent eruption to occur within this volcanic complex occurred around 6,500 years
ago, which formed the 440 meter wide and 1 kilometer long fresh looking West Pali lava
dome.
Remnants of the recent eruption which formed this feature can be found in the layers of
ash imbedded in the river to the west.
Although the history of this volcanic field is not truly well understood, it is a dangerous
volcanic complex.
Due to the type of lava it erupts, any future eruption would be very explosive.
Such an eruption would include pyroclastic flows which could reach populated areas and
travel up to 8 kilometers away.
However, the main danger would be long distance lahars.
Lahars are the volcanic equivalent of flash floods, which can result in a wall of water
more than 100 meters in height.
Due to the nature of this complex, a number of towns up to 50 kilometers away would be
put at risk during any future eruption which I have labeled on screen.
Using the US Geological Survey method of rating volcanoes, Mount Cayley would be classified
as a high threat volcano.
I hope that you enjoyed this video!
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