White Island eruption thought to be caused by natural buildup of gases

Monday, 9 December 2019

Prime Minister Jacinda Ardern and police national operation commander Deputy Commissioner John Tims addressed the media about the Whakaari/White Island eruption.

An eruption on White Island most likely occurred after rocks and minerals gradually clogged up geothermal vents until it literally 'popped like a balloon',

GeoNet vulcanologist Geoff Kilgour said while they will not know for certain until it is safe enough to visit the island, this seemed to be the most likely scenario.

The Island, off the coast of Whakatāne in the Bay of Plenty, erupted around 2.30pm on Monday spewing ash 12,000 feet into the air.

At least one person was critically injured in the eruption, with many more injured.

The moment White Island erupted from the west Crater rim.

'What happens is that a seal starts to form - a shroud of minerals take up all of the space within the rocks - the pressure builds up, it's a bit like a balloon and it keeps blowing until the balloon can't hold it back,' Kilgour said.

'Essentially, that's what's happened here.'

* White Island: A stark, dangerous and wondrous place

* Injuries reported as White Island volcano erupts in the Bay of Plenty**

He said the eruption was similar to those seen on the Island in 2012, 2013 and 2016.

Injured tourists on White Island evacuated after eruption.

'Initial signs from the eruption are that it was essentially a big burst event. It wasn't a whole series of bursts, it was basically one very large pop.'

When asked if he thought people should have been travelling to the island, he said the best they can do is provide people with the best information they can and for them to make that decision.

'Even for our own staff we would have limited our time on the island, we do that generally, it's an active volcano. The unfortunate part of this is that these eruptions occur from going from nothing to something within a couple of seconds and then the eruption is over.

'It's a bit like a lightening strike, sure they happen and they're quite rare, but they happen in a short instance. It's very unfortunate for people to be on the island during an eruption in general, especially if they don't go to the island all the time. For a tourist, they are there once in their life and it's a very rare occasion.

White Island as seen from Whakatane at 2.30pm.

'It's impossible to predict these eruptions and all we can do is try to provide as much information as we can for people to make their own decisions.'

This burst fragmented all of the rocks around where the gas is able to escape, generating ash.

Some of this ash was too dense to travel in the air and flows down the crater floor while the ash that was airborne rose to 12,000 feet into the air, based on information given to GeoNet from MetService.

Those gases are mixture of magma gases - mainly carbon dioxide and sulphur dioxide, he said.

'The gas that's in the plume, there's pretty much every nasty gas you can think of.'

Kilgour said activity had dropped quite substantially since the eruption. This was expected if it was a gas-driven eruption caused by a seal.

'It's by no means the only scenario, but this was essentially a one-off burst and then everything starts to die down gradually and that's what happened in the April 2016 eruption.'

'The difficulty for us is that there's a lot of uncertainty in what happens next and every vulcanologist around the world will tell you that sometimes these events lead to something else, but most of the time they don't. Our best guess is that things will start to quieten down.'