Can you explain in layman’s terms how scientists determine when geological signs warrant a public watch or warning of an impending eruption?

I’d like to say that there is an exact formula that tells us all of this, but there isn’t. The patterns differ with time, and they shift as you approach an eruption as well. So it is having the instruments necessary to kind of monitor the pulse or take the pulse of the volcano.

And primarily we’re looking at seismicity — the kind of sounds that rocks make when they break or get stressed. And also there’s a different kind of seismicity when magma is moving or approaching the surface.

The other thing we look at is the change in shape of the volcano. As magma comes in, it causes the volcano to grow and expand. … So the shape-changing part, we use GPS instruments a lot — but ours are accurate to millimeters instead of many meters. …

We particularly look for the correlation between the change in shape and increased earthquake activity. … We knew that when it continued to inflate and continued to show activity, that sooner or later it would get to the point where the pressure inside the volcano is greater than the strength of the rocks holding it in there.

How would you describe the geological activity at Mauna Loa at this point? And the chances of another major event in the near future?

That’s an excellent question, and it’s one that we’re asking ourselves. … Mauna Loa went (quiet) from 1950 to 1975, 25 years till a summit eruption. Then from 1975 to 1984, nine years. And then from ’84 — that’s like 38 years, right? The 38-year period between eruptions, we don’t have a historical analog for it, right?

So we don’t know. Are we shifting back into a time now where Kilauea is going to be more at the summit, and Mauna Loa becomes more active? We can’t tell you that right now. We’re not sure ourselves. … Having another big rift-zone eruption seems very unlikely, but maybe going to a summit eruption, or something like that, in fairly short order is more possible. That’s historically what’s happened. …

We are in a transition period, possibly, so it’s going to be kind of wait and see. So that’s why we pay attention to the instruments all the time.

Was it unusual to have both Mauna Loa and Kilauea erupting at once?

For some reason it’s kind of gotten in the lore that it is unusual, but the fact of the matter is that it’s really not that unusual.

So in 1984, we were in the middle of the (Kilauea) Pu‘u ‘O‘o (vent) sequence of eruptions where it erupted about once a month for about a day. And 1984, Mauna Loa lasted three weeks. In the middle of that there was a Pu‘u ‘O‘o eruption that behaved just like it would’ve, whether or not Mauna Loa was erupting, didn’t seem to be impacted. …

But there may be a relationship between total volume — one of them is producing more eruptions, the other one kind of quiets down, and then they switch back and forth, maybe. But we’ve only seen that switch once. … So there’s the hint of a correlation there. We just don’t know if that’s something that will hold up over time or not.

Haleakala on Maui is considered dormant. How does it compare with Mauna Loa?

Both Mauna Loa and Kilauea right now sit on top of the Hawaiian hotspot, and they’re in their active phase where they have very high supply rates. … They get a lot more lava to them than any other volcanoes that we know of. …

So we have this kind of continual throughput of magma, which makes these things, they erupt quite frequently. As you move off of the hotspot, you don’t have that throughput, so you can’t keep the shallow magma chamber alive, they start to solidify. … When you move off of there too, sometimes they get what’s been called the rejuvenated phase. And it’s a very different composition of material. It’s very unusual kind of melts that come up.

But some volcanoes rejuvenate and others don’t. … Haleakala really just sort of passed through all those phases, moved off the hotspot and just sort of slowed down its eruption rate. … That magma chamber, because the amount of melting is so much smaller, has to be a lot deeper in the Earth to stay warm … on the order of probably 40 miles down.

Certainly Haleakala is not considered extinct. Dormant. Dormant is fine for it. It means that it’s not showing any signs of restlessness at the moment.

What is the work ahead on the samples that have been collected?

There’s a lot of analysis of what all the things were, how they correlate with each other, how they compare to past events and stuff. … The samples we collected to look at changes in the melt over time … seem to be quite a bit different than it was in 1984. …

As you noticed it, it really roared down the steep part of the hill and then it got to the bottom and it just piled up, and basically just turned into this big creeping mass, right? So we want to improve our models to capture that kind of change better.

And so that’s going to take a lot of analyzing of those samples — and we actually count all the crystals — and then you can back-calculate a lot of the things about the strength and viscosity of the material from that.

THE BIO FILE

>> Title: Scientist-in-charge, Hawaiian Volcano Observatory, U.S. Geological Survey.

>> Career history:Studied tundra ecology in home state of Colorado as well as in the Canadian Arctic before switching to the geology path. Taught at the University of Hawaii at Hilo for 20 years.

>> Personal:Moved to Hawaii with his wife (also a geologist); two children, one studying lunar geology and one “more interested in studying human beings and things like that.”

>> One more thing: I liked volcanoes when I was a kid, but it was a surprise to me, too, that I ended up here! I found out that I really loved them, and originally you love them because you’re fascinated by the process and the beauty of it. I came here in the 1980s, when Kalapana was being overrun. The impact of trying to use science to help people in their day-to-day lives became real important to me. So I think that’s the most satisfying thing at this point in my career.