Remembering Mt. St. Helens: Interview with Don Swanson
Among the team of geologists monitoring Mt. St. Helens at the time of its violent eruption 30 years ago, Don Swanson recounts his experience with poignant clarity.
The Scoop: Don Swanson was one of the geologists monitoring Mount St. Helens leading up the 1980 eruption (pictured, right). He was in Vancouver at the time of eruption and witnessed a majority of the eruption by air, hovering near the erupting volcano. After the eruption, the Cascades Volcano Observatory (CVO) was formed and he was brought on as lead geologist. Even though he is no longer based in the Cascades and the Mt. St. Helen's eruption was 30 years ago, he remembers the event and the months leading up to it as clear as day.
Hirji: So how did you get involved with monitoring with Mt. St. Helens in the first place?
Don Swanson: I had set up a instrumental network in 1972 to measure deformation around Mt. St. Helens. I was asked to be in charge of the St. Helens study should something happen. When there were earthquake swarms in March of 1980, a team was set up and I was put in charge of the deformation team, working alongside James (Jim) Moore and Peter (Pete) Lipman.
Hirji: What did your initial observations involve?
Don Swanson: We put targets on the north side of the volcano around the volume, or the growing bulge. We made angle measurements of the deformation and there were huge changes: 1.5 meters (5 feet) of movement a day! The deformation was shallow and limited to the north. We determined this after using Spirit Lake as a giant tiltmeter (an instrument used to measure changes in the inclination of a surface) and determined that there was little change on the east side.
Hirji: The fact that you used the lake as a tiltmeter is impressive. How exactly did that work?
Don Swanson: During the winter months, the lake iced over. This means that there was no wave action to change the water distribution. We could see down to a microradian of tilt. We estimated points around the margin of the lake. Then we scouted around to a lumber yard in Vancouver for yardsticks to measure the lake level. By measuring the elevation of the lake levels over days and weeks with yardsticks that were nailed to piers and trees, we found that the shoreline was not tilting.
Hirji: Was the deformation at Mt. St. Helens large in comparison to other volcanoes you had monitored?
Don Swanson: This was actually the first time I was involved with monitoring a stratovolcano where you could see deformation. Before, I had monitored Soufrière volcano on St. Vincent Island in the West Indies. At the time a dome was growing in a crater lake. It was aseismic, meaning there was no seismic activity associated with the volcanism, with no measurable deformation. So I was initially skeptical when I started at Mt. St. Helens, but then I saw the huge deformation and was convinced.
Hirji: Since you were coming and going throughout the spring, it was lucky you ended up being there for the main eruption.
Don Swanson: I happened to be the one on the scene when May 18 rolled around. I arrived May 15, or maybe a couple days earlier.
I was in the field on May 17. I had a visitor, a graduate student from Germany. I had talked with David (Dave) Johnston about who would be at the post on Saturday night. Dave agreed to go and I was supposed to replace him Sunday morning.
We made the usual measurements on Saturday. The day was so nice and warm that the helicopter pilot landed on the crater and got out. We looked into the crater. Dave actually went into the crater for samples to determine gas levels.
Hirji: Sounds like the calm before the storm.
Don Swanson: On Sunday morning, I was in the forest service building looking at the equipment when we saw a big signal. I ran upstairs and called Dave. Apparently he had already made his famous words ("Vancouver! Vancouver! This is it!"). There was no answer.
We had a spotter airplane go immediately. We could see the tall eruption column and we flew up there. As we approached, we noticed the volcano didn't look the way it had before. It had lost it's top.
Hirji: As the world has seen with the recent Iceland volcano eruption, flying near an eruption column isn't the safest thing.
Don Swanson: We avoided the north part of the volcano, flying east to west in figure eights. We flew from 9:30 am to 12:30 pm. Then we had to refuel.
We saw a big change in the plume after noon. I think I wrote 12:17 pm in my notes. The plume became more violent. This is when the pyroclastic flows (a horizontal eruption column) started. Though we couldn't see the flows, we could infer from the big gap in the mountain side. Also, earlier we had seen tinier pyroclastic flows from the southern rim downslope. There were lots of mud flows. Nearly all the valleys had fresh debris. Mud flows had wiped out all the snow.
Hirji: What was it like watching from the helicopter?
Don Swanson: It was silent to us. The drone of the helicopter engine overwhelmed our hearing. It was like watching a silent film with no subscripts or organist playing in the theater.
Looking to the west, we could see fires from the fallout and blast. And there was lightning in the ash cloud. It was quite striking and dramatic.
Hirji: How did the eruption compare with what you expected?
Don Swanson: We thought the eruption would be vertical like a normal (or more common) volcanic eruption. Although we knew there was a possibility that there could be a flank failure (when the side of the volcano collapses, creating a landslide and triggering the volcanic blasts). But we thought these things were rare. We didn't know much about it.
Hirji: What were some of the lessons learned from the eruption?
Don Swanson: A big lesson was that indeed there can be a massive failure of volcano flank. The result of the failure is a debris avalanche. People started recognizing debris avalanches around the world, like at Mt. Shasta in California. A lightbulb came on. Within 1-2 years roughly 100 avalanches were recognized around the world. It was a marvelous kind of awakening.
Hirji: In addition to identifying debris avalanches, what role did Mt. St. Helens play in global volcano monitoring?
Don Swanson: Mt. St. Helens eruption was important because it was so well observed. It provided a kind of model for jump-starting volcano monitoring around the world. Existing observatories got increased funding and people learned how to respond. It is important to note that we are always learning and improving how we respond, but it was certainly a major step along the way.
The Cascades Volcano Observatory was established after the eruption. Before we were located in a rented office in an insurance building. After CVO, the Alaska Volcano Observatory was formed, followed by Long Valley and Yellowstone. Things really happened after the eruption.
Hirji: I had no idea the eruption played such a critical role in building our volcano observatory programs. Thanks for taking the time to share your story!
Don Swanson: Thanks for talking with me.