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Whakaari/White Island as it erupted this afternoon, in a still from footage provided to The Spinoff
Whakaari/White Island as it erupted this afternoon, in a still from footage provided to The Spinoff

ScienceDecember 10, 2019

Whakaari/White Island: The science of the eruption, and why there was no warning

Whakaari/White Island as it erupted this afternoon, in a still from footage provided to The Spinoff
Whakaari/White Island as it erupted this afternoon, in a still from footage provided to The Spinoff

We don’t normally see these eruptions coming, no matter how much we would like to. Many systems are already ‘primed’ for such events, but the triggers are poorly understood, writes Shane Cronin of the University of Auckland.

As of Monday night five people have been confirmed dead, 18 had been rescued and injured, some seriously, and several remained unaccounted for after a sudden volcanic eruption on Whakaari/White Island off the east coast of New Zealand.

The island is a tourist destination and around 50 people were on it when it erupted on Monday afternoon. Volcanologists at GeoNet, which operates a geological hazard monitoring system, described the eruption as impulsive and short-lived, with an ash plume that rose to more than three kilometres above the vent.

Volcanic hazards

White Island is one of several volcanoes in New Zealand that can produce sudden explosive eruptions at any time. In this case, magma is shallow, and the heat and gases affect surface and ground water to form vigorous hydrothermal systems.

In these, water is trapped in pores of rocks in a super-heated state. Any external process, such as an earthquake, gas input from below, or even a change in the lake water level can tip this delicate balance and release the pressure on the hot and trapped water.

The resulting steam-driven eruption, also called a hydrothermal or phreatic eruption, can happen suddenly and with little to no warning. The expansion of water into steam is supersonic in speed and the liquid can expand to 1,700 times its original volume. This produces catastrophic impacts.

The expansion energy is enough to shatter solid rock, excavate craters and eject rock fragments and ash out to hundreds of metres away from the vent. We know of sites in New Zealand where material has been blasted out over three kilometres from the vent by such eruptions.

The eruption on White Island sent sent huge amounts of steam and ash into the air in the blast. GeoNet, CC BY-ND

Potential for further eruptions

The hazards expected from steam-driven eruptions are violent ejections of hot blocks and ash, and the formation of “hurricane-like” currents of wet ash and coarse particles that radiate from the explosion vent. These can be deadly in terms of impact trauma, burns and respiratory injuries.

The eruptions are short-lived, but once one happens, there is a high chance for further, generally smaller ones as the system re-equilibrates. White Island is an acute location for such activity, but it is not the only location in New Zealand where this can happen.

Mount Ruapehu (crater lake), Mount Tongariro (Te Maari and Ketetahi) and geothermal areas of the central North Island all have the potential to cause such events. We know there have been more than 60 hydrothermal eruptions in the last 100 years in New Zealand. Some of these have caused loss of life.

No warning

Monitoring and warning for hydrothermal eruptions is a huge challenge. We don’t normally see these eruptions coming, no matter how much we would like to. Many systems are already “primed” for such events, but the triggers are poorly understood.

The warning periods, once an event gets under way, are likely in the order of seconds to minutes. Our only hope for anticipating these events is to track potential vapour and liquid pressure in hydrothermal systems and to learn from their long-term behaviour when they are at a super-critical state. Unfortunately there are no simple rules that can be followed and each hydrothermal system is different.

In this age of technology and instrumental monitoring, it seems irrational that there should be little or no warning for such eruptions. The eruption is not caused by magma, but by steam, and this is much harder to track in our current monitoring systems.

We have seen several other fatal hydrothermal catastrophies unfold in other parts of the world, such as the 2014 eruption of Mount Ontake in Japan. New Zealand has been luckier than many other parts of the world, until now.The Conversation

Shane Cronin is professor of Earth Sciences at the University of Auckland

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Keep going!
A photo of Whakaari/White Island from 2.30pm (Photo: Geonet)
A photo of Whakaari/White Island from 2.30pm (Photo: Geonet)

ScienceDecember 9, 2019

Whakaari/White Island eruption: What you need to know

A photo of Whakaari/White Island from 2.30pm (Photo: Geonet)
A photo of Whakaari/White Island from 2.30pm (Photo: Geonet)

Five people are dead, a number unaccounted for and up to 20 injured, some critically, after a volcano erupted in the Bay of Plenty this afternoon.

Update 9.16pm:

Police have confirmed that five people are dead following this afternoon’s Whakaari/White Island eruption. Deputy commissioner John Tims said it was too early to confirm nationalities but both New Zealanders and overseas tourists were involved. He told media the island was unstable and the physical environment was deemed too unsafe for police to return to and police did not know if there were still people alive on Whakaari/White Island tonight, reported RNZ. Police earlier said 23 people had been evacuated from the nearby area and up to 27 were still believed on the island.

Update 6.35pm:

National Operation Commander Deputy Commissioner John Tims has confirmed that there has been one fatality as a result of the eruption and that there is “likely to be more”. Around two dozen people are believed to still be on the island, but conditions are currently too dangerous for police and rescue services to attend.

“I know that there will be a huge amount of anxiety for those who had loved ones on the island at the time,” said prime minister Jacinda Ardern, who will be travelling to Whakatāne tonight with minister of defence Peeni Henare. There is not expected to be significant impact to the rest of the North island, and ash fall should remain confined to Whakaari.

Residents in the area are being urged to continue to follow local authorities.
Steam emitting from Whakaari/White Island following the eruption this afternoon (Photo: John Boren/Getty Images)

Update 5.58pm:

GeoNet’s webcam images show volcanic ash has covered the main crater floor.

“Ash fall appears to be confined to the island, although there may be a small amount reaching East Cape in the coming hours,” GNS Science duty volcanologist Geoff Kilgour says.

“Our monitoring equipment is still operating, and while we have seen a steady decline in activity, there remains significant uncertainty.

“Currently there are no signs of further eruptions, but we will continue to closely monitor Whakaari/White Island for further signs of activity.”

Update 5.44pm: 

University of Auckland professor and volcanologist Shane Cronin says sudden eruptions like the one that took place today can happen at any time on a volcano like White Island.

“Magma is close to the surface, and the heat and gases from this heat the surface and ground waters to form vigorous hydrothermal systems. We know hydrothermal and so-called ‘phreatic’ eruptions can occur suddenly and with little or no warning because they are driven by the expansion of super-heated water into steam.

“The hazards expected from such events are the violent ejection of hot blocks and ash, and formation of ‘hurricane-like’ currents of wet ash and coarse particles that radiate from the explosion vent. These can be deadly in terms of causing impact trauma, burns and respiratory problems. The eruptions are short-lived, but once one occurs, there are high chances for further, generally smaller ones as the system re-equilibrates.”

Update 5.41pm:

Update 5.12pm: 

A revised estimate from the police is that there were fewer than 50 people on or near the island at the time of the eruption. An unknown number of people on the island are still unaccounted for. One person transported to shore has been critically injured in the eruption.

Update 5.03pm

An update from Geonet says the eruption occurred at 2.11pm and generated an ash plume of around 12,000ft (3658 metres) above the vent. Ash fall appeared to be confined to the island and they were not expecting more than a minor amount to reach East Cape in the coming hours. “Our monitoring equipment is still operating, and we have seen a steady decline in activity since the eruption. There remains significant uncertainty as to future changes but currently, there are no signs of escalation.”

The Herald is reporting that the majority of people visiting Whakaari today were from cruise ship Ovation of the Seas, which is berthed at Port of Tauranga. Port company chief executive Mark Cairns was quoted as saying he understood the majority of those injured in the eruption were from the ship.

Update 4.13pm

Prime minister Jacinda Ardern has addressed the media, describing the eruption as an “evolving situation” and advising that people in the area avoid Whakatāne Heads and Muriwai Road. “We believe that 100 people were around or on the island at the time,” said Ardern. “All our thoughts are with those affected at this stage.” Several people believed to be on the island are still unaccounted for. Civil Defence and NZ Police are expected to hold a press conference at 5.30 pm.

What’s going on?

Whakaari/White Island, New Zealand’s most active cone volcano, located 48km off the eastern coast of the Bay of Plenty, is erupting. Large plumes of steam can be seen from the volcano and GNS volcanologist Steven Sherburn confirmed the eruption began about 2.15pm. 

Is anyone hurt?

Stuff reports that up to 100 people may have been on the island at the time, and St John told Newstalk ZB up to 20 people may have been injured. Some are believed to be critical and several rescue helicopters are on the way. An image from a GNS camera appears to show people on the island. The Herald reports an emergency operation centre has been set up at Whakatāne Hospital to work alongside Civil Defence.

The moment of eruption captured on Geonet’s live cameras (Photo: Geonet)

Is it still dangerous?

Civil Defence says the immediate vicinity of the volcano is hazardous. GNS Sciene Te Pū Ao has set the Volcanic Alert Level to four (danger on volcanic cone and all island, possibility of very large eruption) and the Aviation Colour Code to orange. RNZ reports that people living in or near the area have been warned to close all windows and doors and wear a dust mask or handkerchief because of falling ash, and the public has been urged to avoid Whakatāne Heads and Muriwai Drive.

Was there any warning?

RNZ reported there has been moderate volcanic unrest on the island for the past few weeks, prompting GNS to say it appeared the volcano was possibly entering a period where eruptive activity is more likely than normal. At the end of October, Stuff reported that sulphur dioxide gas output and volcanic tremor levels were at the highest levels since 2016.

The crater floor before and after the eruption (Photo: Geonet)

Has this happened before?

There was a short-lived eruption on Whakaari/White Island in 2016. Before that, a series of small eruptions took place between 2012 and 2013. The longest historic eruption period on Whakaari/White Island was between from December 1975 to September 2000. According to Geonet, the last major eruption of this episode was in late July 2000 and covered the crater floor area in scoria, also displacing a crater lake and forming a new explosion crater 150m across. Major eruptions from 1981 to 1983 altered much of the island’s landscape and destroyed the extensive pōhutukawa forest. In 1914, several sulphur miners were killed in an eruption. 

More details will be added as they come in.