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Transcript: Chat with state Department of Natural Resources geologist Pat Pringle

Moderator: Welcome to The Olympian's Capitol Chat, I'm your moderator, environment reporter John Dodge. Our guest today is Pat Pringle, a geologist with the state Department of Natural Resources and author of a book on the geology of Mount St. Helens, which erupted 20 years ago Wednesday in the most powerful volcanic explosion in recent U.S. history.

Moderator: Pat, could you begin by telling us a little about your background?

Pringle: I'm a geologist and I have a bachelors and masters in geology. My experience over last two decades has been eight years with USGS at the Cascades observatory in the volcanic hazards assessment program there, and I was also PIO during the last eruption in 1986 before this current activity started. Since 1990 I've been with Washington Division of Geology and Earth Resources, which is in the Washington Department of Natural Resources.

Rob, Olympia: What's the likelihood of a major eruption in the next 5 years?

Pringle: Well I think to forecast the likelihood of such a thing geologists mainly look at the past hstory of a volcano, and we're fortunate -- for St. Helens we have excellent studies of its history. The eruption in 1980 gave us a lot of this info. For example, the study of tree rings in the buried forest have determined the age of the eruptions of Mount St. Helens in the last five centuries, some of which were larger than the 1980 eruption.

The 1479 eruption was one of those. 1482, a little more than two years later was another large eruption. Both of those were larger than 1980 erupton. Another eruption occurred around 1500. The volcano was very active for the next two centuries into the 1700s, then there was a hiatus of several decades until 1800, when there was a very large eruption and lava flow, and then continued sporadic activity culminating with the goat rocks lava dome in the early 1840s.

Based on that we know it could produce an eruption closely spaced in time to another major eruption. There's an idea it would have to completely build up its summit before another big eruption, but that's not the case -- there is plenty of magma below the mountain to supply a large eruption. But we think there's very low probability of that.

Moderator: What are the chances that the volcano will remain in a dome-building mode long enough to rebuild the symmetrical peak that it had before the 1980 eruption?

Pringle: I don't know the answer to that. I don't know that we've seen this kind of activity within our lifetime to see how likely that is. There was a 1956 eruption in Kamchatka that produced a similar dome, but we are in a waiting mode here and we'll see how long this continues. The estimate is based on how long the discharge rate takes.

Randy, Centralia: Can you estimate the amount of chlorine in emissions from Mt. St. Helens?

Pringle: I haven't heard the data on how much cholorine is in emissions -- water vapor is most abundant, so I would imagine low concentrations, parts per million of chlorine. We know there are salts produced, so there must be some chlorine. It's not an uncommon volcanic gas.

Moderator: How did the eruption of Mount St. Helens change scientific thinking about volcanic hazards within the Cascade Range?

Pringle: Where do I start? There are so many ways. For starters I think it changed how much we know about the different volcanic processes like lava flows and debris avalanches. It got us to focus on these processes which, for a first time, we could see up close and go to other volanoes and try to see if there were the same kind of results. It's had a huge payoff for assessing other volcanoes.

Moderator: The more you look the more you find?

Pringle: Yes, because there's a lot you don't see because it's buried or eroded away. So for example, when we see a layer of lahars, we're seeing a minimum number because of vegetation coverage and other elements. So that focuses on the processes. Also we've learned a lot about monitoring the volcanoes -- looking at earthquakes, gas discharges, the deformation of volcanoes -- and the ability to practice that on Mount St. Helens.

Moderator: Are we better at predicting eruptions today than in 1980?

Pringle: I think we are, and also we can do it more safely because of GPS and other technological changes. I think knowing about the processes at the volcanoes, like the lahars, helps, and we've also learned to educate ourselves and the public better about those processes because we understand what the scale of those events can be and what causes them. You can have different types of lahars, so other geologic studies have looked at decomposition going on in a voclano, like at Rainier, to see why we have lahars.

A lahar is a debris flow from a volcano, a concentrated slurry about 60 percent to 70 percent sediment -- rock, soil and vegetation -- that flows along river beds. It's been compared to flowing concrete. When you're at Mount St. Helens and the layers are exposed in it, you see the lahars are due to the mountain being a big pile of rubble.

Moderator: What changes did the eruption cause in terms of public awareness?

Pringle: Because the volcanic eruption was televised, there was a public interest in learning about it. They began looking at other volcanoes and began understanding what they could do, like Hood or Rainier. So it's changed the public perception of what they do and it's made it necessary for better dialogue between scientists and the public about how to think about those hazardous processes to live comfortably around volcanoes. Which I think we can.

Moderator: If Mount St. Helens started to form a bulge on its north flank today, how would scientists and emergency management officials respond in terms of a restricted zone, compared to 1980?

Pringle: I think first of all it's important to note they are monitoring the volcano for just such an eruption, and 1980 was a lesson learned for the possibilty and scale of a lateral blast. If there was evidence of such bulging, they would take the appropirate mesasures to have zones set up for public safty. Volcanologists take that very seriously; emergency managers do as well.

Moderator: Compare the relative dangers posed by Mount St. Helens, compared to Mount Rainier.

Pringle: I think Mount Rainier can erupt the same way. St. Helens in its history has produced many more explosive eruptison than Rainier, so the hazards of volcanic ash to aviation and public health are imporatant and Helens is a serious consideration in that. Particularly today with tech tools, very tiny ash particles can be troublesome, so it's not just a health problem but an environmental nuisance of major proportions.

Lahars are also major concern, but they are a major concern at Rainier because of all the lahars you can find radiating out from the voclnao, and it's got a cubic mile of of snow and ice that can produce future lahars. The age and size of the mountain do play a role in its susceptibilty to collapse. There are areas of Mount Rainier that have undergone a great deal of hydrothermal alteration, meaning parts of the mountain have chemically decayed, getting old and brittle.

Moderator: What would be the affect on Rainier of a major earthquake, like the one that triggered the lateral blast at St. Helens?

Pringle: We have no evidence from the past of that but there are other voclanoes, like one in Japan that just flowed a chunk of it back in 1984.

Moderator: What current data at the volcano provides the U.S. Forest Service confidence that it can reopen Johnston Ridge Observatory without undue risk to the public?

Pringle: I think that the reason they can let them back into that specific area is twofold. One, it's an area where you can commmunicate with people rapidly and there's a major transport route to move them away, and secondly, the scientists have the volcano monitored very well and think they can tell when the mountain would be building up to large-scale eruption.

Moderator: What signals from the volcano are telling them that?

Pringle: That would be the nature of the earthquakes they can sense under the mountain, the amount of swelling they can sense on GPS, and the gases too. All those three combined.

Moderator: How would you describe the current status of volcano-monitoring activity in the Cascades Range? Is the monitoring network in place adequate to protect public safety, especially for river valley residents living downstream of volcanoes?

Pringle: I know the usgs released a serious report recently saying we need to do more to monitor the volcanoes. Right now we have just one gas crew in the Cascasde range so we have to share that with Alaska. Some volcanos need additional study, for example Glacier Peak volcano, and the staffing for such studies is not there, so those studies are in the planning stages but haven't been done yet.

We do have basic monitoring equipment in place at the Pacifc Northwest Seismic Network that would give us clues, early warning that a volcano like Glacier Peak was ready to erupt, and in that case crews could be sent to monitor that volcano's heightened activity. There's monitoring and then there's hazard assessments about the history of the mountain, and both of those need to be better-funded in the future.

Moderator: As you go around and talk to the public about St. Helens and volcanic hazards in our region, what is on the public's mind?

Pringle: It's exciting. The interest of people is just mindboggling to me. They are really excited out there over this. They want to know what the expectations are for the future, and so do we. They're fascinated by the potential scale of the events and at the same time they are very interested in this steady state of eruption happening. They are all marveling at the new dome, in part because they've seen pictures taken of it, like the aerial pics and the Web cam. So many people tell me they check the Web cam every morning.

The USGS Web site (link) and the Washington Division of Earth Resources and Geology Web site (link) both have lots of info. Some other good Web sites are the DNR's page on St. Helens (link), the USGS Washington update (link) and the Pacific Northwest Seismograph Network (link) .

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