The state of Washington has several volcanoes which are classified as active. Of these,
most recent volcanic eruption occurred from Mount Saint Helens between 2004 and 2008. However,
this is not the only volcano which could erupt again in the near future. In northern Washington,
a very tall volcano could be responsible for the next eruption within the state.
After all, it last erupted only 300 years ago. The volcano I am referring to is Glacier Peak,
which is part of the Cascade Mountain range.
This video will discuss this high risk active volcano, and mention what its future hazards are.
Within Washington, the vast majority of active volcanoes are stratovolcanoes, such as Mount
Adams, or Mount Rainier. As indicated by its steep slopes and massive size, Glacier Peak is
also a stratovolcano. Stratovolcanoes contain alternating layers of both cooled lava, and ash.
This type of volcano produces very slow moving lava in eruptions, which does not
move very far and thus creates steep slopes. If you look at this volcano from satellite,
you will note that it has an incredibly rugged appearance. Although this is partially due to
explosive volcanic activity, it is primarily due to numerous glaciers which have carved out large
portions of this mountain. Today, eleven significant glaciers are present on Glacier Peak,
which is how the volcano was originally named. Due to the numerous glaciations on th`is volcano,
much of its early geologic record is not known. What we do know is that this volcano began forming
sometime between 600,000 and 200,000 years ago, due to a radiometrically dated ancient
lava flow. In the last fifty thousand years, at least three cinder cones formed on the volcano
after a series of strombolian eruptions. One of these, named Dishpan Gap cone,
is 10 miles south of the main summit. The closest cinder cone to the summit is White Chunk Cone,
which is believed to have formed sometime between 17,000 and 2,000 years ago. Due to the glacial
scarring seen on its surface, I am leaning towards the older of these two estimated dates.
Glacier Peak is primarily made of dacite rock. This is important, as this rock type contains
more silica than a rock found at a typical stratovolcano. The more silica a rock has,
the more explosive the eruptions it produces are. As a result, the eruptions from Glacier Peak are
far more energetic than a typical stratovolcano. For example, one eruption 13,000 years ago was
five times larger than the 1980 eruption of Mount Saint Helens. This eruption deposited an inch or
more of ash as far away as Missoula in Montana. Within Washington, several areas received more
than a foot of ashfall. This eruption created a pyroclastic flow and generated a very large
lahar which travelled all the way to Puget Sound. Over the last 7,000 years, Glacier Peak has had a
rather predictable style of volcanic activity. At first, a series of eruptions creates a lava
dome due to high silica magma. Eventually, part or all of a lava dome would collapse
and trigger a pyroclastic flow and lahar in an explosive eruption. This cycle repeated
itself at least five times during this period. The largest of these eruptions occurred 2200
years ago. Although it was an order of magnitude smaller than the eruption 13,000 years ago,
it produced a large lahar which made it all the way to the ocean.
The most recent eruption from Glacier peak occurred about 300 years ago, although there is
a 100 year margin of error. This eruption did not produce any lava, at it was a phreatic eruption.
The US Geological Survey recently designated Glacier Peak as a very high threat volcano.
Why is this the case? Simply put, Mount Saint Helens and Glacier Peak are the only volcanoes
in Washington State that have generated large, explosive eruptions in the past
15,000 years. Although very few people live near Glacier Peak, a future explosive eruption could
pose a hazard to people that live fifty or more miles away. I am not referring to the potential
threat of ashfall. Rather, I am talking about lahars. Due to the amount of snow always present
on the summit, any type of magmatic eruption will generate a lahar. A lahar is a very large
debris flow with the viscosity of concrete that travels through riverbeds and low lying areas.
A map shown on screen shows that a number of towns could be effected by a future lahar. Such
an eruption occurs about once every 1,000 years. I hope that you enjoyed this video! If
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