Cas’ colleague, Associate Professor Oliver Nebel, says volcanoes are categorised into extinct, dormant and active.
“White Island belongs to the latter category, as part of the Pacific Ring of Fire - a network of volcanoes along the boundaries of the plates that make up Earth's outer shell,” Nebel says.
There were 47 people exploring the country's most active volcano at the time of the eruption. Five have been confirmed dead and eight are still missing, feared dead, police confirmed. Three Australians are likely to be among the five dead, said Prime Minister Scott Morrison, with more bad news feared still to come.
A number of reconnaissance flights have flown over the island and no signs of life have been seen since the eruption. GNS Science, New Zealand's geoscience agency, warned there was a 50/50 chance of another eruption in the coming 24 hours, as the volcano vent continued to emit "steam and mud jetting".
Hayden Marshall-Inman, an experienced guide for White Island Tours, was the first to be named among the dead.
According to Associate Professor Nebel, Monday’s event appeared to be a phreatic eruption.
“These types have less molten rock involved and more gas/vapour. This causes white smoke as opposed to the regular black smoke. The gas that erupted would have ejected very fast (supersonic), is extremely hot and toxic. Because there is little lava involved, however, many of the regular warning systems that work on other, larger volcanoes may not have been triggered.”
White Island is about 50 km from the east coast of North Island and huge plumes were visible from the mainland. Volcanologists said the ash plume shot 3,658 metres into the air.
A crater rim camera owned and operated by New Zealand science agency GeoNet showed groups of people walking toward and away from the rim inside the crater, from which white vapour constantly billows, in the hour leading up to the eruption.
Michael Schade, an engineering manager from San Francisco, was one of the tourists who made it off the island just before the eruption.
"This is so hard to believe," Schade said in a video posted on Twitter as he sped away from the island by boat. "Our whole tour group were literally standing at the edge of the main crater not 30 minutes before."
New Zealand Prime Minister Jacinda Ardern praised the bravery of pilots who made the decision to rush to the island in the blast’s aftermath.
"I want to acknowledge the courageous decision made by first responders and those pilots who in the immediate rescue effort made an incredibly brave decision under extraordinarily dangerous circumstances in an attempt to get people out," she Ardern.
"As a result of their efforts a number of people were rescued from the island."
The volcano's last fatal eruption was in 1914, when it killed 12 sulphur miners. There was a short-lived eruption in April 2016. Daily tours allow more than 10,000 people to visit the volcano every year.
'Whakaari', as it is known in the Maori language, is New Zealand’s most active cone volcano, built up by continuous volcanic activity over the past 150,000 years.
About 70 per cent is under the sea, making the massive volcanic structure the largest in New Zealand.
Lead Image: Volcanic eruption at Whakaari/White Island.
Image Credit: GeoNet (GNS Science)