Yes, Alaska’s volcanoes still dominate in updated threat assessment

Augustine Volcano during its 2005-2006 eruption. (Photo by Cyrus Read, Alaska Volcano Observatory/USGS)

The US Geological Survey released an update this week to its volcano threat assessment, first published in 2005. It’s a look at every volcano in the United States and a ranking based on the hazards they pose.

This recent update has five Alaska volcanoes in the “very high threat” category, more than any other state.

Michelle Coombs, scientist in charge at the Alaska Volcano Observatory, said the level of threat depends on the type of volcano, and factors like proximity to people or flight paths, as well as the level of volcanic activity.

Coombs spoke with Alaska Public Media’s Casey Grove.

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COOMBS: Different volcanoes have different characters, or you could even say personalities. There are broad categories of volcanoes, though. The ones in Hawaii are hot spot volcanoes. They’re caused by a mantle plume that brings up really very hot, runny magma to the Earth’s surface that tends to make long-travel lava flows.

In Alaska, our volcanoes are caused by subduction of one of the Earth’s plates under another plate, and that tends to produce magmas that are wet and sticky and erupt very explosively. So produce many more ash clouds than what we see say at Kilauea other Hawaiian volcanoes.

So Redoubt is one that yeah, it erupts pretty often historically and it poses hazards to local populations primarily from both airborne ash clouds that can interact with aircraft or from ash fall.

GROVE: Looking at the list of volcanoes that are included here, it kind of looks like one of those BuzzFeed lists, like, “The Top 18 Volcanoes That Could Get You.”

So the top, you know, “very high threat level volcanoes are 1 through 18. What are the factors that lead to a volcano being included in one group as opposed to another, and why is it like 18 here and then 19 through 57 is the next group. Why is that?

COOMBS: So I mentioned there were 24 different kind of components to the threat number If you have volcanoes that tend to erupt explosively make lahars or mudflows other hazardous volcanic phenomena, those are going to get you higher scores in the hazard side of things. And then if those volcanoes tend to be near local populations, like Rainier is a great example. It’s got you know, several hundred thousand people downstream of it that could be affected by mudflows, so that gives you a high exposure ranking.

Kilauea Volcano in Hawaii is the top of the very high threat category. That’s because it has people living on it. In Alaska, we don’t have a lot of volcanoes like that. Most of our communities are away from volcanoes. Another hazard that plays into the ranking is aviation hazard and that’s one that in Alaska is a huge concern for us.

We have people flying over our volcanoes everyday, and as most of the listeners know volcanic ash and aircraft don’t mix very well.

GROVE: This report includes a piece about kind of a new volcano that’s been included, then a couple others that were sort of demoted from from the list, and I wonder if you could tell me about that. It made me feel a little bit like when Pluto got demoted from planet status.

COOMBS: Yeah, well the main players, so the very high threat volcanoes, those have stayed the same. We have five very high threat volcanoes in our state. Three are in the Cook Inlet and two are down Akutan and the cushioned down by Dutch Harbor and Akutan. Those haven’t changed in the vast majority of the high-threat ones didn’t change either partly.

That’s because they’re more active, more reported activity, and we already knew about about them and they’re better studied and better monitored. It’s the ones on the lower half of the list where there was some shuffling. Part of that is just we live in a big state. We have a ton of volcanoes many of them we know very little about.

And so the initial report in 2005 some some of the information we had to put into those metrics was pretty sparse and not very well documented. And so in the interim, better information came out in some cases and so I think we had six drop off the list altogether, and that’s because it was determined that they have not been active in the last 12,000 years ago, a period of time geologist call the Holocene, or post-glacial time. And that’s kind of our cutoff to be on the list, and so six of them got off the list and the final one I’ll mention is Four Peaked Volcano, which is down south of Augustine in lower Cook Inlet, and in 2006, out of the blue, that had an explosive eruption, just kind of a one-off, what we call a phreatic blast, and that caught our attention. We didn’t think that volcano was historically active or even potentially active but that put it on the radar so to speak.

GROVE: Do you have a favorite volcano? Like do you like the ones that are explosive and active and on the watch list or you more like into the slow roll beautiful-looking volcanoes?

COOMBS: Well, I’m a geologist, so I have a few favorite volcanoes. I’ve spent a lot of time working on Augustine Volcano and some of the ones in the Aleutians. Redoubt. I really like Redoubt.

But I would say the other ones that are fascinating, and part of the reason why I love living and working in Alaska is because there are these places we know almost nothing about. And so, to go out to the Western Aleutians and go to an island where maybe one or no other geologist has ever been and just sort of explore and be the first person to study and figure out what’s going on out there, that’s really fascinating as well. So I kind of like some of the obscure mysterious ones.