GUY RAZ, host:

A few little earthquakes here or there - that's just a part of everyday life when you live on top of the largest supervolcano in North America. That volcanic system is what powers Yellowstone National Park. But in the last eight days, there have been more than 400 earthquakes at Yellowstone. So should we be worried? It's this week's "Science Out of the Box."

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RAZ: Hank Heasler is a Park Service geologist, and he's on the line with us from his office at Yellowstone. Mr. Heasler, welcome to the show.

Mr. HANK HEASLER (National Park Service Geologist, Yellowstone Park): My pleasure.

RAZ: At least 400 earthquakes in a little more than a week. Is the ground still shaking there?

Mr. HEASLER: It definitely is. The earthquake swarm is continuing.

RAZ: And is it a little odd? Is it a little creepy?

Mr. HEASLER: Well, for the individuals who are within a few miles of the earthquakes, and that includes the Park Service settlement we have there called Lake(ph), they have commented to me that they would appreciate it if the earthquakes would stop so that they could get a good night's sleep.

RAZ: I mean, is this normal? I mean, how common is it to have so many earthquakes at Yellowstone?

Mr. HEASLER: It's not normal. This is an unusual sequence of having this many earthquakes in as short a time period. But having a lot of earthquakes over a short time period in the same area is the definition of an earthquake swarm. And we've had much larger earthquake swarms in Yellowstone in the past. Back in 1985, there was an earthquake swarm that lasted for three months and had a magnitude 4.7 earthquake associated with it. The current swarm has had a maximum earthquake of only 3.9 and that did not cause any structural damage. However, it was felt as far away as Old Faithful, which is about 30 miles away. Most of the earthquakes have only been felt quite locally within a few miles of the earthquakes.

RAZ: Now, Yellowstone actually sits on top of a supervolcano. What is a supervolcano? And how is it different from a normal volcano?

Mr. HEASLER: The difference between a supervolcano and a regular volcano is simply the difference between a super-sized drink and a regular drink. The supervolcano just means it has the potential for a very large catastrophic eruption.

RAZ: And is that why there are so many geysers at Yellowstone?

Mr. HEASLER: Correct. The reason Yellowstone was created as the world's first national park is because of all the hot water features: the geysers, the mud pots, the steam vents, the hot springs. And all those thermal features are fueled by the molten rock which is just a few miles below the surface at Yellowstone.

RAZ: With all of these earthquakes happening, the swarm, should we start panicking? I mean, does it mean that there could be a volcanic eruption under Yellowstone National Park?

Mr. HEASLER: This particular earthquake swarm is not indicating an imminent volcanic eruption at this time. The earthquake energy associated with this swarm and the number of quakes and magnitude is well within the historic earthquake activity for Yellowstone. So right now we are not concerned about this indicating any sort of volcanic activity. However, we are very closely monitoring this earthquake swarm with all the new tools at hand that seismologists and scientists have. And there will be many months of work after the swarm stops in order to try to figure out the precise cause of these earthquakes.

RAZ: Hank Heasler is a geologist who works at Yellowstone National Park. We spoke with him via phone from his office. Mr. Heasler, thanks for joining us.

Mr. HEASLER: Thank you.

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