Whakaari/White Island is New Zealand’s largest active volcano. Its crater forms a huge natural amphitheater that opens to a bay.

In December 2019, a large group of tourists arrived for a day trip. They donned gas masks to watch fumaroles spew clouds of yellow steam.

Then, disaster struck. The volcano erupted suddenly, belching vapor and ash two miles into the sky. The cloud collapsed into the amphitheater, which funneled it directly at the tourists.

Half were killed and the other half suffered severe burns and lung damage from sulfuric acid fumes.

Scientists set out to analyze the eruption. Like most in the region, and many of the largest in the world, it was hydrothermal.

Water trapped in rock pores becomes superheated by shallow magma, increasing pressure. Then an external trigger, like a seismic tremor, destabilizes the system causing a huge instantaneous steam explosion.

Researchers used modern machine learning to analyze 40 years of eruption data at Whakaari. They found seismic patterns of magma movement in the subsurface, which superheated water and triggered the steam release.

Their new understanding could help predict future eruptions here. But the technique will have to be customized for other volcanoes and, for some, warning time may be very short.

If you’ve ever thought about visiting an active volcano, you should be aware that none are completely safe.