On April 11th, 2022, a swarm of earthquakes began underneath the prominent Mount Edgecumbe
stratovolcano in far eastern Alaska.
This earthquake swarm began at 2 am local time, and went on to produce several hundred
earthquakes over the next several days, and is still continuing at the present.
Although earthquakes are quite common at volcanoes within Alaska, the context of Mount Edgecumbe
makes their sudden appearance be a bit worrying.
You see, Mount Edgecumbe falls under a group of volcanoes which lie dormant on the orders
of hundreds to thousands of years, only to suddenly reawaken and produce a truly catastrophic
eruption, comparable in size to the 1980 eruption of Mount Saint Helens.
Other volcanoes in this group include El Chichon in Mexico, Mount Parker in the Philippines,
and Apoyeque in Nicaragua.
During long stretches of dormancy between major eruptions, these volcanoes display next
to zero levels of volcanic unrest.
Thus, the appearance of any form of seismic activity if confirmed to be volcanic in origin
falls within a waking up cycle which lasts anywhere from several weeks to several years.
In other words, if Alaskan scientists witnessed a similar series of earthquakes underneath
other volcanoes such as Mount Redoubt or the Fisher Caldera, it would not be a cause for
concern as these peaks have a history of frequent earthquake swarms and erupt quite frequently.
Mount Edgecumbe on the other hand, does not have a history of earthquake swarms, and retrospective
analysis revealed that this volcano only began to produce small earthquakes in 2020.
The ongoing quake swarm represents the highest seismic unrest recorded since sensors were
emplaced on the volcano, and could theoretically signal a new eventual eruptive period which
would begin sometime in the next decade.
For context, Mount Edgecumbe is located in far eastern Alaska where it is 15 miles west
of the city of Sitka, covering the southern half of the Kruzof Island, consisting of an
area of approximately 100 square miles.
This volcano is located adjacent to the major Queen Charlotte-Fairweather Fault, where its
vents are primarily situated on an apparent fissure which trends perpendicular to it.
Over 600,000 years this fissure has produced lava domes, cinder cones, volcanic explosion
craters, two stratovolcanoes, and a large caldera.
While these vents have been active at varying times throughout the lifespan of the overall
volcanic complex, recent eruptions have been confined to the Crater Ridge caldera and the
summit of Mount Edgecumbe.
These occurred via powerful explosive eruptions 11,250, 9,000, 5,760, and 4,310 years ago,
the latter of which represents Edgecumbe's last known eruption.
The largest of these eruptions 11,250 years ago ejected 7.0 cubic kilometers of volcanic
rock, causing 3 feet of ash to fall on what is now the town of Sitka and up to 98 feet
thick closer to the eruption site.
The ongoing earthquake swarm is centered around and to the northeast of Crater Ridge, which
is a worrying sign as the quakes have an apparent northeast trend that matches what an expected
magmatic intrusion would look like.
With this being said, we are still unsure of what is causing these earthquakes as Mount
Edgecumbe is not heavily monitored and does not have sufficient equipment on it to determine
the origin of these quakes.
This insufficient monitoring is why Mount Edgecumbe is given a white alert level, roughly
translating to unassigned aka not sufficiently monitored to give it a proper designation
such as green, yellow, or red.
The ongoing earthquakes have a potentially magmatic signature to them, as they are seemingly
too numerous to have all originated from small fault lines in the area.
I used satellite data to check for uplift indicating the intrusion of magma, but sadly
the latest dataset only included data until April 8th before the earthquake swarm began.
Although these earthquakes are concerning, by far the most likely outcome is that they
will decline over time before completely stopping, thus not resulting in any form of eruption.
However, this activity is truly unusual so only time will tell what will occur next.
Thanks for watching!
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