For one scientist familiar with the New Zealand volcano that erupted on Monday and killed at least six people, it was “a disaster waiting to happen.”
“In 2003 when I stepped into the crater, I got this uncomfortable feeling that this is not a safe place to be,” Ray Cas, professor emeritus at Monash University in Melbourne, Australia, and a past president of the International Association for Volcanology, tells PEOPLE.
“You are immediately in this large amphitheater with very steep walls, it’s a very enclosed space, and if something happens there is almost nowhere you can go,” he says. “And on the floor of the crater there are volcanic gas vents making noxious sulfurous gases, and there are crater lakes filled with water almost at the boiling point.”
“The problem with that volcano, it can be highly unpredictable and erratic,” says Cas, who visited the volcano twice. “Even when the alert level [for an eruption] is relatively low, you can get unexpected explosions, which means it is just unacceptable to allow the general public to walk around the inside of the crater of a very active volcano that can explode at any time, as we witnessed on Monday.”
In 2014, Brad Scott, a volcano expert with New Zealand’s science institute GNS who visited White Island for almost 40 years, expressed his concerns about tourism at the volcano.
“We don’t visit but they still go,” he told the New Zealand Herald of tour operators taking visitors to the island despite conditions that made volcanologists “anxious.” GNS scientists also had “terse discussions” with the tour operators, according to the Herald.
And in a 2013 video, volcanologist Clive Oppenheimer of Cambridge University said there was concern “about the hazards” of the volcano’s heightened activity.
“You have to consider how important is it to collect the data. Is it worth risking your life for?” he asked.
Still, reported the New Zealand Herald, an estimated 10,000 to 15,000 tourists have visited White Island annually, “armed with gas masks and cameras, and a guide.”
Of the 47 people on the island at the time of the blast, nine were from the U.S., police said. Twenty-four people were from Australia, two from China, four from Germany, one from Malaysia, five from New Zealand and two from the U.K.
Some of the visitors came from Royal Caribbean’s cruise ship Ovation of the Seas. An archived version of the cruise line’s website from Dec. 4 features a description of an adventurous shore excursion where guests could partake in “a scenic boat ride along the picturesque Bay of Plenty to White Island for an unforgettable guided tour of New Zealand’s most active volcano.”
“Gas masks/breathing apparatus helps you get up close to roaring steam vents, bubbling pits of mud, hot volcanic streams and the amazing lake of steaming acid,” the page reads. “And the vivid hues of yellow and orange resulting from all sulfur on the island make for remarkable photos, so have your camera ready.”
Royal Caribbean has not returned PEOPLE’s request for comment.
“I don’t know what advice is given to the people who go on the tours,” says Cas, “whether they say you are entering into an environment where there is a risk of dying.”
For the last month, GeoNet, which monitors volcanic activity on White Island, issued weekly bulletins on volcanic unrest, and in a Dec. 3 bulletin wrote: “Volcanic gas emission and seismic activity continue to remain elevated.”
“There has to be more respect for nature. We can’t assume we can access anything we want,” Jozua van Otterloo, a volcanologist at Monash University, told the New York Times.
“This is something policymakers and the public need to consider. Even though this is such a great place, should we be allowing people to go in such large numbers?”