On April 11th, 2022, a swarm of earthquakes began underneath the prominent Mount Edgecumbe
stratovolcano in far eastern Alaska.
This earthquake swarm would go on to produce several hundred earthquakes over the next
11 days before ending on April 22nd.
Although the largest of these earthquakes was a mere magnitude 2.8, they were not tectonic
in origin.
Rather, they occurred due to a new intrusion of magma underneath the Mount Edgecumbe volcanic
complex.
Although the volume of this ongoing intrusion is unknown, it is centered at a depth of 3.1
miles or 5 kilometers below sea level.
This intrusion pushed up the overlying ground much like a mole digging a tunnel in a grass
yard.
As a result, large sections of Kruzof Island have been uplifted, with the maximum deformation
totaling approximately 27 centimeters or 11 inches.
This uplift is not a new phenomenon as it has been ongoing since August of 2018.
Each year, a wide swath of the island is uplifted at a maximum rate of up to 8.7 centimeters
or 3.4 inches which is quite significant for a volcano in this area of Alaska.
For comparison, the rate of uplift is quite similar to the current uplift at Campi Flegrei
in Italy, which is being uplifted by a maximum of 9 centimeters a year.
In both cases, it can be assumed that a large volume of shallow magma is present which is
causing seismic unrest.
Although the magmatic intrusion seemingly started in 2018, an increased number of volcanic
earthquakes were not detected until 2020.
The earthquake swarm on April 11th simply represented the greatest number of earthquakes
in a day on the volcano so far.
This area of uplift is centered about 1.5 miles east of the summit of Mount Edgecumbe,
where it overlies one of the area's mainly silica rich lava flows.
My interpretation of this location suggests that in the event an eruption was to eventually
occur, the most likely spot would be on the eastern end of the Crater Ridge caldera.
Along with a 1.6 kilometer wide and 240 meter deep caldera, Crater Ridge consists of a series
of large rhyolite lava domes.
This area produced two eruptions since the end of the last ice age, in both 7220 BC and
3810 BC.
Thus, although it is unconfirmed, I am assuming that the ongoing intrusion of magma is dacitic
or rhyolitic.
Although magma is clearly moving at depth, it is still quite deep and is at least for
the immediate future unlikely to generate an eruption.
Depending on the quoted source, Mount Edgecumbe has not erupted for either 800 or 4,200 years.
The younger figure relies on oral history of the Tlingit people, which has so far not
been conclusively linked to any eruption deposit.
Although, it is possible that a small phreatic eruption occurred then.
Regardless, Mount Edgecumbe has not erupted for a rather long time.
Thus, no easy path exists for fresh molten rock to reach the surface.
This is both good and bad.
The good news is the intrusion of magma is less likely to produce an eventual eruption
than a volcano with a number of recent eruptions such as Mount Saint Helens if a similar scenario
was witnessed there.
The bad news is that because there is a lot of hard ground overlying the magma, any future
eruption would be highly explosive, potentially forming a large explosion crater.
With this being said, because there is no dominant pathway for magma to reach the surface,
any further advance of molten rock in the crust would generate hundreds if not thousands
of earthquakes, many of which would be large enough to feel in the town of Sitka.
So far, this situation has not occurred.
9 times out of 10 an intrusion of magma does not result in a new volcanic eruption.
However, an eruption of Mount Edgecumbe is certainly more likely in the next decade than
it was 10 years ago.
This video is not a lake April Fools joke, unlike the fake eruption a prankster pulled
off in 1974.
Thanks for watching.
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