At 2:11 P.M. local time on Monday, New Zealand’s White Island volcano (also called Whakaari) erupted, with clouds of gas and ash filling the air. The volcanic island, which resides in the Bay of Plenty off the country’s North Island, is a popular tourist destination; several dozen people were on and around it when the blast occurred. As of publication time, at least six people were confirmed killed, and several more are missing.

Exactly what caused the eruption and what killed those present will take time to investigate, because researchers will need to examine the volcanic debris. The island is currently unsafe for people to set foot on, though, which has also hampered rescue efforts. The disaster highlights the inherent risk in visiting some of the planet’s most volatile spots, where conditions can change rapidly, and scientists have a limited ability to predict danger even at well-monitored volcanoes such as this one.

Janine Krippner, a New Zealander who works as a volcanologist at the Smithsonian Institution’s Global Volcanism Program, is no stranger to these risks—including at White Island, which she has visited. Scientific American spoke with her about the island’s eruptive history, how scientists will investigate the latest eruption and the constraints on science’s ability to limit risks around volcanoes. [An edited transcript of the interview follows.]

What type of volcano is White Island, and how active has it been historically?

New Zealand is in a subduction zone—the North Island is—so this is a subduction zone volcano, and it’s actually growing from beneath the sea. Sixty percent of the cone is below the sea surface. We’re only seeing the very top, and the highest point is around 320 meters above the water. So when people visit the volcano, they’re actually walking up into the crater. And this is New Zealand’s most active volcano—it’s been active for at least 150,000 years. So, being an incredibly active volcano, that does mean that we will get explosions like this every now and again. In the grand [geologic] scheme of things, this is actually a very small event. But when you have people who are up around the crater, it doesn’t take a big event to be devastating. And that is what's happened here.

This is a volcano where it is an amazing place to go see nature face-to-face, but that does mean that people are taking the risk of something happening when they do. And it’s heartbreaking. I’m heartbroken for everyone who’s been hurt and who’s involved and who has lost someone.

While we don’t know precisely what happened in this eruption, how do the steam eruptions that this volcano can produce work?

You have a volcano that is in the ocean, so you have a lot of seawater percolating through. You also have rainwater, so there’s a lot of water in that system. And because it’s an active volcano, there’s also a very active heat source as well. This means that you have water turning into steam. Now you can often see that steam coming out [of the crater] as gases. But if something traps that gas—and that gas has the ability to build up pressure for any reason—then it can build to the point where that pressure has to go somewhere, and it causes an explosion. That explosion can rip apart rock within the volcano, and that rock can be hot as well. And that rock can go flying, at incredible speeds, out of the crater.

How will scientists determine what type of eruption this was?

The definitive way to tell is to look at the actual rocks and volcanic material that came out, so they’ll be able to tell if it was all the material that has been sitting there for a while or if it is fresh magma that has come up recently.

You’ve been to White Island. What was the experience like, and did you have any safety concerns?

Being a volcanologist, any active volcano you go to—even if you can’t see the activity—you have to have some level of concern and respect for what might happen. So I went in knowing the risks, and it was an amazing experience. The people who ran the tour were great, and they were very safety-conscious. I thought they did a great job. And the volcano itself is an amazing place to visit, but there is a risk every time you go to any active volcano—not just this one that is more visibly active. There’s always a risk of something happening, with or without magma coming up.

What does this event tell us about the risk of allowing people around active volcanoes?

There was the Ontake eruption in 2014 in Japan, and it was a similar situation. It’s a volcano where a lot of people go hiking, and there’s a lot of tourism, and there were people up around the crater. A small explosion happened, and they were at the wrong place at the wrong time. This has happened so many times, and it will continue to happen. And it’s not just the active ones that have these plumes of gas coming out—they’re all inherently dangerous, whether it’s even because of the wildlife or the weather or rockfalls. And we’ve got to lessen that or mitigate that as much as we can. But we can’t eliminate it, and we can’t keep people off every volcano on the planet.

This kind of stuff is volcanologists’ worst nightmare—people getting hurt on volcanoes. This is what we strive to prevent. But, you know, it’s not just the science. We have people whose livelihoods depend on volcanoes for tourism or farming or other kinds of things around the world. We get a lot of benefits from volcanoes, too. And it’s the more rare scenario where something goes wrong, and people get hurt.