The eruption took place with little warning early Monday afternoon local time while dozens of tourists from nearby cruise ship Ovation of the Seas were touring the volcano.

New Zealand is located in one of the world’s most tectonically-volatile regions. Vulcanologists said that while the eruption was relatively small compared to other past disasters, anyone close to the site would have been in serious danger.

Raymond Cas, emeritus professor at Monash University’s school of earth, atmosphere and environment said, “White Island has been a disaster waiting to happen for many years. Having visited it twice, I have always felt that it was too dangerous to allow the daily tour groups that visit the uninhabited island volcano by boat and helicopter,”

Associate professor Derek Wyman, a geoscientist at Sydney University, said he was surprised tourists were allowed so close to the site, given its recent history.