The volcano in New Zealand that killed an estimated 14 people when it erupted with little warning is notoriously difficult to predict, making it one of the most dangerous in the world, according to scientists.
The volcano on White Island is New Zealand’s largest and a major tourist attraction. And while some warning signs were reported, scientists familiar with the area say they were not enough to halt public tours.
“It’s not the first time this volcano has behaved like that, where there was an explosion with no warning,” said David Phillips, head of the School of Earth Sciences at the University of Melbourne in Australia. “This time, it was terrible because the explosion happened when people were visiting the crater.”
Beginning several months ago, researchers at GeoNet, an organization founded in 2001 that monitors activity at all of New Zealand’s volcanoes, observed an uptick in activity at White Island. The scientists reported “small, muddy, geyser-like explosions” in the volcano’s active crater, but kept their alert to Level 1, their lowest designation which signals minor volcanic unrest.
On Nov. 18, that warning was raised to Level 2 after GeoNet recorded stronger volcanic tremors at White Island and an increase in toxic sulfur dioxide coming from the volcano. Level 2 is categorized as “moderate to heightened volcanic unrest,” but tour companies typically stick to a business-as-usual approach under this designation, according to Richard Arculus, a volcanologist at the Australian National University.
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“With a Level 2, it’s standard practice for tour operators to keep operating,” Arculus said. “There might be more activity like mud or water being thrown out of the crater lake, but tour operators would not cancel tours on a Level 2 alert.”
This is because it’s not unusual to see fluctuating patterns of activity at White Island, according to Phillips.
“It’s one of the most active volcanic systems and it’s very difficult to predict,” he said. “This sort of activity waxes and wanes all the time, and alert levels go from 1 to 2, and in most cases nothing happens.”
White Island is known as a stratovolcano, characterized by continuous small-to-moderate eruptions over the past 150,000 years. About 70 percent of the volcano is submerged in the Bay of Plenty, and eruptions at White Island typically occur when water comes into contact with magma.
“There’s water in the crater at the top and it filters down fractures, and at some point, that water came into contact with the magma,” Phillips said. “But, this is taking place underground, so it’s hard to know the exact location of fractures and where the water and magma systems may be.”
When the volcano erupted this week, 47 tourists were visiting White Island, which is located roughly 30 miles off the coast of New Zealand’s North Island.
New Zealand Police said they intend to open an investigation into the events surrounding the eruption, including an inquest into health and safety issues for tourists and tour companies. But Phillips said White Island is a major attraction that boosts the local economy, and New Zealand, in particular, is known for its adventure tourism industry.
“No matter what it is, adventure tourism is not without risk, so where do you draw the line?” Phillips said. “If you have tourists going to that island just about every day, there’s always going to be a finite risk.”
But speaking for himself, Phillips said any kind of heightened activity would be enough to make him think twice.
“I’m fairly risk-averse,” he said. “Despite the fact that volcanoes are of great interest to me, if the warning went from Level 1 to Level 2, I wouldn’t go. I would much prefer to visit when things are quiet.”
Denise Chow is a reporter for NBC News Science focused on the environment and space.