A MARTÍNEZ, HOST:
A part of Yellowstone National Park is closed after a hydrothermal explosion spewed boiling water and steam high in the air. No one was injured, but in a video posted on social media, park visitors are seen running away from the blast.
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UNIDENTIFIED PERSON: (Yelling) Run, run, run. Run. Run.
MARTÍNEZ: I spoke with Mike Poland, a scientist with the Yellowstone Volcano Observatory, about what caused this explosion.
MIKE POLAND: This is an event where water flashes to steam in the shallow hot water pumping system beneath a geyser or hot spring. That rapid expansion when it goes from the water to the steam phase can create a big explosion if it occurs in a confined space, and that's effectively what happened here.
MARTÍNEZ: All right. So just to be clear, though, this wasn't a volcano eruption.
POLAND: That's exactly right. If this had been triggered, for example, by magma that was rising in contacted groundwater, we would see much, much different signs. There would be ground deformation, the ground rising up really dramatically. We would have seen geyser activity that was longer-lasting and much broader over a much larger area than this single event in Biscuit Basin.
MARTÍNEZ: OK. And you mentioned the place where it happened, Biscuit Basin. By the way, great name. Great name for anything if you put biscuit in the title. But what is this part of the park known for?
POLAND: Biscuit Basin is sort of a sub-basin in the Upper Geyser Basin, and that's where Old Faithful is located. So you've got the densest concentration of geysers really in the world. But then Biscuit Basin has a number of these beautiful pools, like Sapphire Pool. And there's a lot of really vivid colors due to the bacteria that are growing in these hot water pools. Really gorgeous place. But obviously changed a bit now.
MARTÍNEZ: So what does it look like now?
POLAND: Well, the pool that exploded and some nearby pools are really just sort of dark and mucky at this point from all of the material that was stirred up by the explosion. And it's a bit difficult to say now how it's going to evolve in the future. So it's possible that we'll see a change in activity of the features. Maybe they will have small eruptions going into the future. Maybe they'll come back as these placid pools. Something to keep an eye on because the plumbing system clearly is different now than it was just a couple of days ago.
MARTÍNEZ: Yeah. Is this unusual what happened?
POLAND: This sort of explosion was on the big side, as these explosions go for ones that are sort of historic. But not an unusual process. Water is flashing to steam all the time under Yellowstone. And there are explosions pretty often in the park, maybe a few times a year, often in the backcountry, so you may not see them or perhaps during a season when there's no one really out and about. There have been other explosions in heavily visited tourist areas. Porkchop Geyser in Norris Geyser Basin blew up in 1989. Excelsior Geyser in the 1880s had some very large explosive events.
MARTÍNEZ: Biscuit Basin, Porkchop Geyser. I mean, you've got to be hungry to work at Yellowstone, I would assume. It sounds like it, at least.
POLAND: (Laughter).
MARTÍNEZ: Now, one of the things we saw in the video is that there were people standing on boardwalks right by where this happened. How does the park plan out where the boardwalk should be? I mean, is there a science to it, a math to it to just make sure that they're safely at a safe distance?
POLAND: It's a real challenge because the activity in these geyser basins is always changing. So there can be areas of ground that heat up and cool down over time. And when that happens, the park does have to move boardwalks to safer locations. At the same time, you want to allow visitors to be able to see some of these really beautiful features. So the park is sort of always having to weigh the stability of the ground with the visitors' experience, I think, but safety is paramount on their mind. So I don't think we're going to see this area reopen until there's a really thorough assessment of how the features here might have changed.
MARTÍNEZ: That's Mike Poland, scientist with the Yellowstone Volcano Observatory. Mike, thanks.
POLAND: Thanks very much.
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