A little over 110 years ago, the remote wilderness of the Alaska Peninsula experienced what was likely the largest, more explosive eruption of the 20th century. This eruption covered the region with tens of meters of volcanic ash and debris, creating the aptly-named Valley of the 10,000 Smokes. Multiple volcanoes not eEven today, when the winds pick up during the late summer and fall, ash from this blast can be whipped up and lofted high into the air, sometimes even making people think an eruption has started.
Funny thing about the 1912 blast is that it came from a volcano that wasn't even on the map before the eruption. Not only that, but volcanoes that weren't even source of all this volcanic material collapsed during the eruption. Katmai saw a ~1.6 by 2.3 mile caldera form during June 1912 even though the eruption itself was coming from what would be named Novarupta, just to the west. If you want to read all about those fateful days in Alaska, I wrote about it during the 100th anniversary.
What's Happened Since 1912
Of the volcanoes in the vicinity of Novarupta (Katmai, Griggs, Mageik, Martin and Trident), only two have erupted since 1912. The furthest of the bunch -- Martin -- had two small eruptions in 1951 and 1953. Trident, the volcano closest to the Novarupta action, saw 14 eruptions between 1949 and 1974. Some of these have been relatively good sized, reaching VEI 3. However, it has been silent ever since.
Flash forward to August 2022. Since then, volcanologists at the Alaska Volcano Observatory have noticed earthquakes coming in swarms underneath Trident. Back during last summer, the earthquakes were numerous but started relatively deep, focused around 16 miles beneath the volcano. Over the course of a few days, those earthquakes became shallower and shallower, reaching as close to the surface as 3 miles.
Since the start of January, the earthquakes have remained at roughly that depth with dozens of earthquakes every week. Not only that, but there have been some earthquakes under the nearby volcanoes of Martin and Mageik. Things are definitely in a state of unrest in the Novarupta-Katmai area.
On February 22, the rate of earthquakes under Trident spiked, so the Alaska Volcano Observatory raised the alert status to Yellow (the second of four alerts). This was mostly to give people ample time to consider what might happen if Trident or one of the other volcanoes erupts again.
What's Going on at Trident?
The current evidence doesn't seem to point to an eruption in the immediate future, but whenever volcanologists see (1) an increase in earthquakes under a volcano, (2) those earthquakes persisting for months and (3) the depth of the earthquakes decreasing over time, then they know it is time to start watching closely. That's because this pattern is likely caused by magma rising from deep in the crust up into the volcano's shallow magmatic system. In a sense, the volcano is priming for ... something.
Now, whether then something is a new eruption or just a replenishment of magma without any blast is not known at this moment. Volcanologists would want some more signs, like deformation of the volcano or increased gas emissions or an even more intense earthquake swarm. None of that has happened yet at Trident.
If Trident does erupt, we're not likely talking about another enormous eruption like the 1912 Novarupta blast. When Trident was busy erupting in the 1940s-70s, most of its activity were moderate explosions that sent ash upwards 30,000 feet with accompanying lava and pyroclastic flows. Luckily, in such a remote location, the biggest hazard is for aircraft from all the potential ash.
So, Trident has joined Great Sitkin, Aniakchak, Semisopochnoi and Takawangha on elevated alert across the Aleutian volcanoes of Alaska. It wouldn't be shocking for something new to happen at Trident, especially after almost 50 years of quiet. The question will be whether this current unrest is a precursor to new eruptions.