Is an uptick of rumblings under Mount Adams cause for seismic concern?

Mount Adams is the second-highest mountain in Washington state, after Mount Rainier. Known as an active stratovolcano, it's part of what scientists call the Cascade Volcanic Arc.

The last time it erupted was more than 1,000 years ago, but it's been making some noise lately. To find out more about these rumblings, KUOW’s Kevin Kniestedt spoke to University of Washington Earth and space sciences professor Harold Tobin, who directs the Pacific Northwest Seismic Network.

This interview has been edited for clarity.

Kevin Kniestedt: The US Geological Survey says they usually record about one earthquake at Mount Adams every few years, but they've clocked nine quakes so far in 2024, six in September alone. So, what's going on here?

Harold Tobin: That's absolutely right. In fact, it's up to 10 quakes. And, yeah, Mount Adams is very, very quiet, normally, seismically speaking. Earthquakes are a sign of either water, hot water, interacting with the rock in a volcano, a little bit of rumblings from that, and or the movement of magma. There's no evidence in this case that this is movement of magma yet, but certainly it is making a little more noise than it usually does, by a large margin right now.

I've read that there's only one seismometer on Mount Adams, but they're planning on more. First of all, why only one? And are they adding more because of the recent increase in earthquakes?

Yes, they're definitely adding more. In fact, there's now two seismometers as of some quick work by the Cascade Volcano Observatory folks late last week, and there's plans for, I think, two more stations to go in in the coming days. The reason there's only been one is a combination of the fact that it is so absolutely quiet, and also remote location, hard places to get to, hard places to maintain a 24/7 seismic station in that mountain environment.

With one station, I want to emphasize, we can detect earthquakes. So, we would know if there was more seismicity. In fact, that's exactly what happened in this case. But one station isn't enough for us to do a really precise job of detecting the very, very, small ones, or to measure the depth that the earthquakes occur. And we want better information on both of those now that it's making a little bit more seismic noise.

USGS researchers say they aren't alarmed by the string of quakes, but they are curious about what's going on. What's your take on this? Are you also not alarmed?

Yeah, that's exactly my take. I'm not alarmed. No, Mount Adams is certainly quiet, and for all we know, it might well just go right back to its slumbering, but on the other hand, any quakes like this are a sign of some kind of subsurface activity going on. And of course, we want to know what a volcano is doing. Unlike big earthquakes, volcanoes give us a lot of warning signs normally before any kind of eruption. So back in 1980, it was exactly seismic activity that was our warning signs for the Mount St Helens eruption, several months ahead of when it actually went off.

Now, the signs we're seeing at Mount Adams right now are not anything like what we saw in 1980 at St Helens, so I don't want people to be alarmed by that. But it is definitely interesting, and it will tell us more about how Mount Adams works and tell us what we need to know in case it does start rising above some threshold level of activity.

How would we know if Adams was going to do more? What kind of tells would we see?

There's a couple of different ones. Sticking to the seismic activity, one thing would be just increasing numbers, you know, by leaps and bounds, hundreds, thousands of times more small earthquakes, and especially if those earthquakes were showing a trend of rising from deeper to shallower in the volcano. But we also can see it through measurements we do with GPS and from satellites, whether the mountain is literally bulging, as Mount St Helens did in 1980, and even beyond that, monitoring for gas emissions, gasses that are coming out of the surface of the volcano, or high temperature measured from satellites or airplanes.

All of these are the kinds of things that show us that the magma is rising in the system and building up towards eruption. We don't see it at Mount Adams today, but that's certainly the stuff people are watching for.

How much advance notice would we have? How much more warning would we have?

It's really variable with volcanoes. I can't give you one number that just says this is it. Several months is what happened with Mount St Helens. Some volcanoes develop unrest for literally spans of years before a big eruption, or develop unrest and then never erupt. Other ones, it happens faster, days, probably not hours, in the case of at least what we've seen so far with the Cascades. But it's variable. I would generally expect some significant period of time, more than a few days, certainly.

We live in a region that has a number of earthquake risks, from the Cascadia Subduction Zone, from a number of faults. Whenever I hear about an earthquake somewhere in the region I wonder, is this more than just a small earthquake? Do I need to chill out a little bit? What's the answer here?

In general, small earthquakes are small earthquakes. We live in a seismically active place, and that's really all that they signify all by themselves. And certainly these earthquakes in the volcanoes are more about the potential for volcanic activity than for earthquake in the sense of much larger earthquake activity.

Earthquake faults in general, just don't do the thing of building up to a big earthquake, so that if we see a sprinkling of threes and fours that means, “Watch out, a big one is coming.” That's not the way earthquake faults work in general, whether it's here, California, Japan, or elsewhere. But there are certain kinds of signs that might cause us concern, like a large-ish earthquake offshore. But absent something like that, no, I don't think people should be concerned when there's a felt earthquake here and there in our region, except in the sense that we should always be prepared. We live in a seismically active place.

Listen to the interview by clicking the play button above.