Within British Columbia are a number of active volcanoes that are not very well known, such
as the Iskut Unuk River cones, and this is despite the fact that it erupted a 20 kilometer
long lava flow in 1904 which crossed the international border into Alaska.
In fact, the reason why many of these regional volcanoes are not well known is due to their
remoteness.
However, one of these volcanic systems is well known, at least among volcanologists.
What I am referring to is the type locality for the origin of a name of a feature used
to widely describe a type of subglacial volcanic vent, as the feature shown on screen was the
site of the first analysis of this landform in geologic literature.
What you are looking at is called a tuya, which is a flat topped and steep sided type
of subglacial volcano.
Tuyas forms underneath thick ice sheets in a peculiar process which forms its unusual
shape.
This tuya is one of more than a dozen tuyas which are part of a much larger volcanic complex
of said landforms in addition to other similar subglacial landforms and even a cinder cone,
being known as the Tuya Volcanic Field.
It has erupted at least once in the last 11,700 years, and will certainly erupt again.
The youngest landform is known as Gabrielse cone, which probably erupted around 7000 BCE.
The Tuya volcanic field is located in far northwest British Columbia, near the border
with Yukon.
The closest town, Jade City, lies 50 kilometers to the east.
The abundant jade mined in the area is unrelated to the volcanic complex, as it formed in much
older layers of rock.
This volcanic field contains more than a dozen vents via a combination of tuyas, subglacial
mounds, and cinder cones spread across an area of 4,700 square kilometers, which is
just slightly larger than the U.S. state of Rhode Island.
These scattered vents are present rather than a single massive volcano, as the magma which
supplies the volcanism in this section of Canada is intermittent and thus new intrusions
of magma which reach the surface occur in different sections of the overall volcanic
field.
No vents seemingly erupt more than a few times.
The exact age of when the first vent in the Tuya Volcanic Field erupted is unclear, although
its oldest currently known vent dates to 1.8 million years old.
This age was when a tuya known as Kima 'Kho formed, as when an initial intrusion of magma
erupted onto the surface, overlying it was an extensive and thick ice sheet which covered
the landscape, measuring more than a kilometer thick.
As lava erupted into the bottom of a thick glacier, it 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
termed a tuya.
Over the next 1.79 million years, the area remained glaciated although the thickness
of glacial ice varied.
During this time, numerous other tuyas formed such as Mathew's Tuya, the famous Tuya Butte,
and several unnamed tuya vents.
However, some eruptions underneath the ice sheet did not produce a sufficient volume
of molten rock and tephra to melt the entirety of the overlying glacier above an eruption,
and as a result formed a different volcanic feature which is termed a subglacial mound.
One of these subglacial mounds is the dark colored Ash Mountain, which is 580 meters
or 1,900 feet tall.
It is covered in layers of rounded lava called pillow basalt, which is often seen in volcanoes
underneath the ocean's surface.
The youngest subglacial vent in the overall volcanic field erupted 20,000 years ago and
is known as Caribou Tuya.
The most recent eruption from this volcanic field occurred sometime between 5,000 and
10,000 years ago, only after the overlying ice sheets had retreated.
It formed a small red cinder cone called the Gabrielse Cone, which created a lava flow
that traveled 5 kilometers to the northeast.
Luckily, eruptions from this volcanic field are almost in my opinion always only moderately
explosive or purely effusive.
Future eruptions cannot form more tuyas, as an ice sheet is no longer present.
Any future eruption would either form a new cinder cone or small shield volcano, whose
worst effects would be causing wildfires in this sparsely populated region of Canada and
perhaps sending volcanic gasses including carbon dioxide into regional low points and
valleys.
Using a US Geological Survey method of rating volcanoes, the Tuya Volcanic Field would be
classified as a very low threat volcano.
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