The status of the Mt. Edgecumbe volcano near Sitka has changed from “dormant” to “historically active.”
The Alaska Volcano Observatory updated Edgecumbe’s status on May 9, but it doesn’t mean that the crater is any closer to an eruption – if at all.
A lot of people in Sitka have become used to calling Mt. Edgecumbe “dormant,” but that term really isn’t used by geologists.
“It’s a word that isn’t very well defined in volcanology,” says state geologist Cheryl Cameron. “It doesn’t have a lot of specific meaning to us. And instead, we tend to talk about volcanoes with how recent or long ago it’s been since they were active, or since they had an eruption.”
Cameron is a geologist with the Alaska Volcano Observatory in Fairbanks. Mt. Edgecumbe was formerly known as a “Holocene” volcano, since the geologic evidence of its last major eruption dates from the Holocene era, around 12,000 years ago.
However, the AVO now classifies Mt. Edgecumbe as “historically active.”
“For this flavor of active we don’t require that a volcano has had an eruption,” said Cameron. “So volcanoes can get put into this category through having had a recent eruption, or a suspected recent eruption, or they’ve got a period of deformation or seismic activity or fumarolic activity that we think reflects the accumulation of magma in the crust below the volcano.”
A “recent eruption” usually means within the last 300 years, but the AVO recognizes that Native oral histories indicate an eruption history that goes a few hundred years beyond that.
Nevertheless, being classified as “historically active” doesn’t mean that Mt. Edgecumbe is about to erupt. Rather, it’s going to get more attention now from the Alaska Volcano Observatory. Cameron says a geophysical team is on the ground in Sitka to do a temporary seismic installation on Kruzof Island that includes a global positioning system. The GPS can provide data in realtime about any deformation of the crust that might be happening, rather than waiting for a satellite to pass overhead, which happens only once every 12 days.
Not that the AVO wasn’t paying attention before, but there are over 50 “historically active” volcanoes in Alaska. Cameron actually grew up in Sitka, and the seismic “swarm” in April that got this ball rolling may have gone unnoticed – but it didn’t
“Because my brother sent me the earthquake location, and he said ‘Cheryl, what’s up with this?’ And I said, ‘Well, gosh, let me ask the seismologists,” said Cameron. “So the seismologist said, ‘you know, there’s a swarm.’ And of course, we still needed to do more work and further analysis to determine if the earthquakes were some sort of rather mundane tectonic processes or if they related to the volcano.”
Cameron says that the Alaska Volcano Observatory is making plans for a permanent seismic installation on Mt. Edgecumbe, and that any volcanic activity would likely come with plenty of advance warning.
“We don’t want people losing sleep over it,” she said.