Earth & Sky

Concentrated on some volcanoes in Oregon and Yellowstone National Park

The biggest, restless cauldera in the world is in Yellowstone National Park.

We’d like to thank the following person for today’s show:

Chuck Wicks
Research Geophysicist
U.S. Geological Survey
Menlo Park, CA
Earthquake and Volcano Hazards Program

ES: Thanks for talking with Earth and Sky today. Can you give me some background into the work that you’re doing at Three Sisters volcanoes?

CW: Basically what we are doing is a remote sensing study of volcanoes. Our goal is to study all the volcanoes in the U.S. And we do it with radar emitting satellites that bounce pulses off the earth. We come back the following summer and bounce pulses off the earth again, and we can compare, with some processing tricks on the computer, we can compare the two images. And we can measure very precisely, an image of deformation over an area. And this is much more cost-effective than trying to go out and put instruments in that we don’t have the money or manpower to do anyway.

By studying the Cascade Range, we found this one volcano that was inflating a couple of years ago. And it was doing it without any accompanying seismicity; there were no very small earthquakes that went along with it, which is usually fine. So it’s given us the opportunity to put instruments in and take measurements before magma actually came up through the crust, which it may not due. But we’ve had earthquakes swarm last March, the first swarm in that area in 30 years, has been instrumented seismically, that says that maybe the magma is starting to come up into the crust.

ES: Where and what was happening?

CW: Well, in particular, in the South Sisters volcanic field in Oregon, the find was that we could actually see an area of the Earth was bulging upwards, and it was coming up at a peak rate of about an inch a year. And because it was doing so aseismically, there’s no imminent danger, it also meant that we had no idea that it was going on. We’ve already been able to interface with the local authorities, and they’re aware of it, and they’re planning worst case scenarios if it does erupt in the future. So it gives us a big heads up on a possible eruption in this case.

ES: What’s the significance of the earthquakes?

CW: Well, before, when it was coming up aseismically, we were saying – okay, the magma is accumulating probably in the plastic part of the lithosphere, just beneath the brittle crust. And so we knew that it wasn’t a danger yet. And, we were telling the local authorities that if it starts having earthquakes associated with it, then that’s the first signs that that it’s gone to the next stage. The earthquakes are significant, it means the magma is actually coming up into the crust a little bit, whether it will erupt or not, we really don’t know. We’ve actually never seen a volcano deforming this way, that much before an eruption before. So this new technology is giving us new data that we’ve never had before, and we’ll just have to follow it through to the end.

ES: What would an eruption at Three Sisters be like, anything like Mt. St. Helens?

CW: Well, it’s hard to tell in this area. It’s what they call a big silicic system, so it could have a large explosive eruption. The last eruptions in that area were pretty small. It just oozed some very viscous, in one place viscous magma out to the surface in one place, and in another one it was a more Hawaii-type eruption. And these were more 1000-500 years ago. So we could have something pretty big, probably as isolated as it is, the ash would affect an area immediately in Eastern Oregon, the ash fall. A bigger danger would be if it erupted in the winter. it would cause a lot of snowmelt and mudflows, and probably end up plugging some of the Willamette river, maybe even up to the Columbia River by Portland.

The point is that we really don’t know. I would say from past eruptions in the area, in the past 20,000 years or so, it’s certainly given no indication that it’s going to produce an eruption like Mount St. Helens. Any ash that erupts out of it, if it’s an explosive type eruption, would be a hazard for airplanes and air traffic flying over the area. Or, people driving around in the ash after it falls, most likely east of the Cascades, which is not so heavily populated anyway. But the bigger problem would be the possibility of mudflows coming down the west side of the Cascades going towards a more populated areas like Eugene and up the Willamette River up towards Portland. Probably it would be an imminent danger for people in the drainage immediately west of the Cascades, but it would be more of a problem affecting shipping traffic, once it gets into the Willamette River in the Columbia, just by the increased sediment load.

ES: When did your lab start measuring the rise in the surface?

CW: Well we actually started measuring it in 2001, as we got our interferomtry lab running here, the data go back as far as 1992, when the first European satellites were sent up. We use all European data to date and monitor it. And by looking back at the data in 1992 we could see that the uplift itself probably began in 1997-1998.

ES: How would you characterize the uplift; is it happening fast, slow, big, small?

CW: I would say that it’s dramatic in terms of what you can see with the radar data. If you went out there in the field and tried to see a difference in one year to the next, or even from the beginning of the uplift to the end, you wouldn’t see any difference with your eye. But looking at the interferograms we produced from the satellite data, it’s probably one of the fastest deforming areas in the Western U.S., so it’s significant, yeah.

ES: Can you give me a little history of the volcano, eruptions, etc…?

CW: The eruptions, a little less than 2000 years ago, there was one that was silicic. And if you go out in the field and look at it, it just looks like this huge pile of rhyolite. It’s so viscous that it couldn’t move very far. It made it to the surface and didn’t move laterally much at all. And the other eruption that occurred almost contemporaneously with that was a basaltic eruption like you see in Hawaii right now, and that was five miles to the north of the silicic one. It was very low viscosity, so it was able to run quite a distance; it ran down some of the upper watersheds and things like that. If you drive up today, it looks like a large area of blocky basalt.

ES: Can you talk a little bit more about how you actually get information about these uplifts; what is it that you’re measuring?

CW: Well, we get our data by tasking the European Space Agency satellite to acquire data over an area. They’ve got a limited amount of power with their satellite, so they have to decide where they’re going to gather data and where they’re not. Ideally, they’ll gather data where we want it, in this case at the Three Sisters Volcano, and because the snow kind of destroys the signal, we can only use signal that was acquired June through early October in the best case. And when we get the data, we’ll process it and compare it with data that was gathered the previous summer, and see how much the Earth has moved, in this 100 km by about 100 km swath. We’ll end up with an image, or a picture of deformation, rather than what you get from most field methods, which are points of deformation.

ES: How is this different than what’s been done in the past to gather information about surface changes?

CW: It’s different in that we have an instrument that will give us a picture of deformation, so it will give us a picture of a broad area on the Earth’s surface, what’s going on, what’s deforming and what’s not. And the other thing that’s significant is, because it’s remote sensing, we don’t actually have to have anybody in the field to do this. We just wait for the DVD to come in with the data on it, and process it on our computer and look at it. And the benefit also is that it’s a radar satellite, it’s not sensitive to clouds, and it can see through the clouds, which is important in the Northwest. Even if it’s a cloudy day in June, we can get data from it.

ES: How are you sure that the pictures you’re making from satellite data are correct, that they should be trusted?

CW: Well, in some cases you don’t. Usually, if you have one interferogram and a small signal, you might question it. And the way to do that is through redundancy, and get different interferograms from different time intervals that show the same thing. And in this case we actually have ground truthing about a month after we discovered that this was going up, the folks at Cascade Volcano Observatory flew out with a helicopter and installed a continuous GPS, and that was in May, so they had to dig through the snow, but the following summer, they surveyed some old geodetic monuments they had surveyed in it in 1985, and established a bunch of new ones with GPS that were optimized to fit the area we saw deforming. And, follow-ups on that are very much in agreement with what we’re seeing with the interferometry. So we do have good ground truth on it. And the resurvey of the 1985 instruments showed that there was nothing the happened between 1985 and 1997-98 when we thought it started. So we’re pretty sure that we’re seeing the whole episode from the beginning, and we have a good idea of the accuracy of it.

ES: And I understand that the earthquakes signal a significant change in volcanic activity.

CW: Yeah, the thresholds would be determined by the seismicity. Once we have persistent earthquake activity, and then we see migration of the earthquake activity at shallow depths. And then we start becoming more alarmed and have a more active monitoring capability established. The logistics are pretty difficult, because it’s right smack in the middle of the wilderness. Whenever we go in to do campaign GPS surveys, we have to have everything packed in by a mule train. It’s averaging about an inch a year – it has been pretty steadily since it began, so it’s probably on the order of seven inches of peak uplift by now.

ES: So there apparently was a swarm of small earthquakes in March of 2004.

CW: Yeah, that’s right. We just had one earthquake swarm in March, and it pretty much ended in 2 1/2 days. And there have been a few scattered earthquakes since. We don’t have the persistent earthquake activity that usually precedes an eruption by months to years.

ES: Could you talk a little bit about what causes those earthquakes?

CW: What’s causing the earthquakes most likely is that the rocks in the lower crust are just being flexed beyond their elastic limits; they’re starting to break. And, usually the magma can’t come up to the surface unless it goes through this brittle rock and breaking and providing some fractures for the magma to start up as kind of the first part of an eruption.

ES: How likely is it that there will be an eruption at Three Sisters anytime soon?

CW: Well I guess that’s the $64 dollar question. We know the cascades are actually – if you look at them in historical terms, speaking geologically – they’re in sort of an active cycle. Active means, maybe an eruption 2000-5000 years, so it doesn’t mean like Kilauea that’s erupting continuously for 20 years.

So, we’re pretty sure that there’s going to be an eruption again somewhere in the Cascades. It is almost a certainty. But as far as having an idea, the only ideas we have are to look where places are deforming. And right now, in the Cascades, the only volcano we know that’s inflating is South Sister.

ES: Furthering the course of your research, what was something that really surprised you?

CW: The surprising thing to me was, when I initially discovered it, was that it was inflating at all. Because I had hiked through there numerous times and the only reason I tried that as a starting point for the Cascades is because I knew that it had a lot of good rock exposure that would give me good back scatter and make a good interferogram. And when I actually processed the first interferogram and saw that it was inflating aseismically, I was pretty surprised.

ES: I imagine that not everyone was convinced about that.

CW: Well, there are people in the interferometry community who are excited, and accepted it right away. But there are some old-school geologists who thought, “oh, maybe it’s mislocated, or maybe it’s an artifact, and they didn’t tend to believe it until we actually had some field measurements that showed the same thing.

ES: Does this imaging work extend beyond just for people tracking volcanic activity?

CW: One of the guys that I worked with in the beginning here, he came through as a post-doc and I trained him, he’s using it for water resources. So he’s looking at where areas are subsiding over aquifers when they are being over pumped, something like that, so for aquifer monitoring. So there’s limited numbers of people applying the technique right now to looking at oilfield monitoring, there’s probably a lot of legal ramifications involved to knowing where the oil is actually coming from. But you can track the deformation of the surface and model where the oil’s actually moving from. And, of course we’re actually using it for earthquakes to see what’s moved after an earthquake, and to see how the earth moves during an earthquake

And we’re seeing some interesting little things, like in the San Simeon earthquake, I just started looking at some co-seismic data from that, and I could see an area around Pasaroble where there’s actually some side effects that gave me a signal of about 20 mm, a little less than an inch. But it also corresponds with where the actual damage happened during the earthquake, which is fairly far from the actual epicenter. And it seems like it’s just side effects that we can see, soft sediments there, or something like that.

ES: Are there other volcanoes that you’re studying with interferometry?

CW: We’ve applied this to a lot of aleutian volcanoes as well, which is a pretty remote, and again, that’s about the only way that’s cost-effective to monitor any of these Aleutian volcanoes. There’s 40 active volcanoes up there that erupt every 10 years or so. So it’s really been a blessing for monitoring them.

ES: Where would you say is the most likely place for a volcanic eruption to happen?

CW: Well, in North America it would have to be Alaska, just because of the sheer number of volcanoes there. But also, Yellowstone is very important, because of the size of it. And also, there’s a caldera in California that’s called Long Valley Caldera that’s also very large, and very active, with a lot of seismicity and degassing events that make it very dangerous. And not to mention the skiing community that’s right on top of it.

ES:

CW: The first area that we looked at was Yellowstone, and then after we had some success there we tried in the Cascades. When I was at the University of Oregon I did part of my field camp in the area of Three Sisters wilderness. And I knew that it had the right ground conditions to make some good interferograms, and it turned out to be a good one. I also knew that there was recent volcanism in the area, so that there would be a chance that there should be some magma-related deformation.