Washington’s Mount Adams is seeing unusual earthquake activity

Mount Adams, about 70 miles north of Portland, is one of the sleepiest active volcanoes in the Cascade Range. A small earthquake every few years is typical. But it’s shaken up expectations recently — with six small quakes in September alone.

Jon Major, scientist in charge with the U.S. Geological Survey in Vancouver, said there’s no cause for alarm. He recently joined OPB environment editor Courtney Sherwood to discuss the latest seismic readings, how they’re opening the door to new research into Mount Adams — and why scientists are confident there’s no connection between the Cascade Volcano chain and a strange odor that drifted down the Interstate 5 corridor.

Their conversation has been edited for length and clarity.

Courtney Sherwood: Could you give us a high-level recap — what’s been observed at Mount Adams over the last month and how’s that different from what would be normal there?

Jon Major: At Mount Adams we typically will see one locatable earthquake maybe every couple of years. And this year we’ve had nine earthquakes that we’ve actually been able to locate at Mount Adams. During the month of September, we actually had six earthquakes that were located at Mount Adams.

Sherwood: Do we know what causes these quakes? Is this magma moving? Is this plate tectonics?

Major: It’s a little mysterious. One of our challenges is that there’s only one seismic station within about seven miles of the volcano. So it makes it really difficult to get very accurate locations and depths. In response to that, we are putting out some seismic stations to be able to gather some more data and try to get better constraints on location, size, and depth of these earthquakes.

Sherwood: The info USGS has posted online says there’s no cause for concern. Can you explain how is it that we know?

Major: We can put this in perspective a little bit. At Mount St. Helens and Mount Rainier, we’ll get somewhere between 10 and 20 earthquakes a month.

The volcanoes in the Cascades talk to us all the time. Mount Adams generally is fairly quiet. This time, it’s decided to perk up a little bit and talk to us a little bit more. Exactly why it’s talking to us, we don’t know for sure.

These earthquakes are pretty small. The ones that we’ve actually been able to locate range in size from just under Magnitude 1 to about a Magnitude 2. If a person was standing out at Mount Adams, they would not have felt those earthquakes.

And we have no other signs that anything is going on at the volcano.

We don’t have a dedicated gas sensing station there. But there’s no indication right now that the volcano seems to be degassing in any way.

We don’t have any GPS stations out there right now. We don’t have any on-the-ground instruments capable of detecting ground deformation. But we do have satellite imagery that is capable of detecting some ground deformation. And at least in the limited windows that satellite imagery can get accurate data, it’s not picking up any ground deformation right now.

Sherwood: Do we know why Mount Adams is usually quiet compared to some of the other Cascades volcanoes?

Major: If we just look at the history of Mount Adams a little bit, Mount Adams is largely a volcano that erupts lava flows. We call that effusive volcanism versus explosive volcanism. Mount Adams has been seldom explosive in its history.

The last time it had an eruption from the summit of the volcano was probably more than 10,000 years ago. And over the last 10,000 years, the eruptions that have occurred at Mount Adams have been around the lower flank of the volcano. They’ve been these cinder cone-type eruptions and small lava flows that have traveled maybe a few miles from the base of the volcano, a bit more like the volcanism we might see over in Indian Heaven or down in Central Oregon.

It’s not a volcano that’s been highly active.

That’s not to diminish the risks that Mount Adams poses. There are communities downstream of Mount Adams — Trout Lake — and one of the hazards that Mount Adams does pose to the communities is, we call them lahars, these volcanic mudflows.

In the past 6,000 years, Mount Adams has had a couple of large volcanic mudflows that have made it down to and beyond Trout Lake, so it’s something we take seriously. With these earthquakes going on, it’s a good opportunity for us to learn a bit more about this volcano. There’s no indication that this is portending any eruption, but we’re keeping an eye on it and just trying to gather more information.

Sherwood: If it starts looking like something’s going to happen here, do you feel pretty confident that there’ll be plenty of warning and opportunities to let people know? It sounds like you’re not saying that would happen, but if things change.

Major: Sure. If magma pushes its way to the surface, it’s going to do a few things. It’s got to break rock to be able to get up to the surface. And when it breaks rock, it’s going to generate earthquakes. Those earthquakes will increase in frequency, they’ll increase in size, and over time they’ll get shallower.

So that’s one thing we watch for at any of our volcanoes. What’s the nature and style of the earthquakes? Are they changing? Are they getting bigger? Are they getting more frequent?

The second thing magma does when it pushes its way up to the surface is, it causes the ground to deform. Think of a water balloon that you’re inflating with water, right? The more water you pump into it, that balloon tends to expand. Well, the same thing happens with volcanoes.

If we start to see obvious ground deformation, if we start to see releases of gasses, that’s going to tell us something.

Any eruption in any of our volcanoes in the Cascades is going to broadcast pretty loud that things are moving within the volcano. And the evolution of technologies that we have over the past 40 years, since Mount St. Helens erupted, gives us a much greater capability of getting the earliest detection of any of those types of things.

Sherwood: OK, I just have one last question, and I know this is a little strange. There was news about a week ago about this mysterious smell drifting from Southwest Washington, moving south along the I-5 corridor. Some people thought it smelled sulfuric. There was online speculation. Is there any chance that this is related?

Major: No, I think we can rule this out pretty confidently for a couple of reasons.

First, let’s start with Mount St. Helens. So the obvious suspect, volcano-wise, is probably Mount St. Helens, and we have a gas-sensing station up in the crater. At the time that those smells were reported, our gas-sensing station showed that there was virtually no emission of any kind of sulfuric gasses, either sulfur dioxide or hydrogen sulfide, the one that gives you the rotten egg smell.

Related: Strange odor reportedly wafting south along I-5 corridor toward Portland

Over at Mount Adams, right now, there’s no kind of fumarole vent where gasses would obviously be emitted.

As gasses get emitted from volcanoes and they drift down wind, they’re going to dilute in the atmosphere. And so being so far from this area — I don’t know what the distance is as the crow flies, but it’s a pretty far distance from the Portland-Vancouver area — in order for that strong an odor to be coming from Mount Adams, you’d really have to be putting out quite a bit of gas emission.

And then, gasses are trapped in magma. If magma was pushing its way up to the surface, where gasses could be emitted, we’d be seeing earthquakes that are indicative that magma was pushing its way up, and we’re not seeing that. So I think we can pretty confidently rule Mount Adams out as well.