White Island. Source: Wikimedia Commons.

Whakaari/White Island eruption – Expert Reaction

Steam and gas jets are still coming out of the active vent on Whakaari / White Island, following the eruption on Monday afternoon.

In GeoNet’s latest alert, available here, duty volcanologist Geoff Kilgour states seismic activity has dropped to low levels and there has been no further eruptive activity. The Volcanic Alert Level remains at Level 3 (out of a possible 5).

Police are leading the search and rescue operation. Safety advice is available via the National Emergency Management Agency (Civil Defence).

The SMC asked experts to comment on the eruption.

Dr Marco Brenna, lecturer, Department of Geology, University of Otago, comments:

“This was likely an eruption caused by overpressurisation of the shallow hydrothermal system under the crater of White Island. Basically, input of fresh magma over the past month or so, indicated by increased seismicity and gas emissions recorded by GeoNet, provided heat and energy into the system (like switching on the heat under a pressure cooker). At some point, the shallow crust under the crater could not contain the increased pressure, and that caused the explosion.

“I understand that ash fall was largely local and there should not be wide dispersal over the mainland apart for possibly portions of northeastern North Island. Possibly some of the concern with accessing the island for rescue missions is linked to the presence of fine ash all over the crater area, which could cause respiratory issues or problems with landing. As far as I read, monitoring by GeoNet is not giving any signs of further activity. Overall I can’t comment on decisions by emergency responders to access or not access the island.

“A similar eruption occurred at Mount Tongariro’s Te Maari crater in 2012. There a first (larger) explosion in August caused by an overpressurised system sent out ash over large parts of eastern North Island. This was followed by a second explosion in November, likely due to further pressurisation caused by sealing of cracks by hydrothermal fluids. The second eruption there (you can find videos on Youtube) was rather comparable what happened on White Island, and it is just because the Tongariro Crossing goes past at some distance that no harm was done to tourists.”

Declared conflict of interest: None

Dr Cristian Montanaro, Postdoctoral Researcher, Dept of Earth and Environmental Sciences, University of Munchen, Germany, and honorary academic, University of Auckland, comments:

Note: Cristian is currently based in Germany. He was a post-doctoral researcher at the University of Auckland from 2016 to 2018 and is currently involved with a MBIE Smart Idea project with Shane Cronin.

“Whakaari (White Island) is New Zealand’s most active volcano and is characterised primarily by steam-driven ‘phreatic’ eruptions (more than 30 explosive events in the last century). Sudden flashing of super-heated water at shallow depths may result in large craters excavation, formation of highly energetic steam-rich density currents and wet jets of poorly sorted rock debris, as well as launching of m-sized ballistic clasts – generally among the most frequent causes of volcanic incidents and infrastructure disruption.”

Declared conflict of interest: None

Professor Shane Cronin, Volcanologist, University of Auckland, comments:

“Sudden, unheralded eruptions from volcanoes such as White Island can be expected at any time. 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.”

Declared conflict of interest: None

Our friends from the Australian and UK Science Media Centres collected the following comments, feel free to use these in your reporting. 

Emeritus Professor Ray Cas, School of Earth, Atmosphere and Environment, Monash University, comments:

“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. White Island lies almost 50 kms offshore from Whakatāne, and experiences significant explosive eruptions every 3 to 5 years. It has a very active geothermal system with many steaming gas vents and varying numbers of hot water-filled crater lakes in the floor of an amphitheatre shaped large crater.

“The volcano is a marine stratovolcano. In the late 1800’s a sulphur mine was established on the island, with a small settlement for the workers. This was destroyed in 1914 when a rock avalanche of hydrothermally weakened rock collapsed from the crater walls and inundated the mining buildings, most of which were destroyed with significant loss of life.

“Many of the explosions are hydrothermal, resulting from superheating of the geothermal waters by molten rock or magma within the volcano. Most of the material that is explosively ejected is hydrothermally altered country rock for around the geothermal vents, but sometimes the ejected materail includes fragments of fresh magma. In addition to the hot rock fragments and fragments of magma, large volumes of volcanic gas and superheated steam are released which produce a hot plume of gas and rock that rises above the vent, sometimes to heights of thousands of metres. The temperature of the erupting mass can the several hundred degrees Celsius. Hazards include rock projectiles, noxious gases and burns from the hot gas cloud.

“In the lead up to major eruptions there can be elevated levels of steam release, small explosions and increased seismicity, as occurred on this occasion in the last two weeks.”

Declared conflict of interest: None

Dr Jessica Johnson, Lecturer in Geophysics, University of East Anglia, UK, comments:

“The eruption was unfortunate but not completely unexpected. Levels of activity at White Island/Whakaari have been relatively high since September, and even more elevated over the last couple of weeks, with increased numbers of small earthquakes and more volcanic gas detected than usual. As a consequence, the volcanic alert level was raised. Similar eruptions have happened over the last 100 years or so.

“Even though the alert level was raised, it is still very difficult to forecast exactly what will happen at volcanoes. White Island/Whakaari is an andesitic stratovolcano, which means that it can have lots of different types of eruptions. It also has a water-filled crater lake. When water reacts with hot rock or magma, it can create explosions, and therefore, can make eruptions even more difficult to forecast.

“Depending on the prevailing wind, residents near the coast of the North Island may experience some ashfall and may be able to smell volcanic gases. This can be hazardous for people with breathing difficulties. The ash and volcanic gases could also affect the local environment such as the marine reserve. However, on a global scale, this was quite a small eruption and so it is unlikely to affect the environment on a larger scale.

“It is very difficult to say whether there will be more eruptions like this one, but GeoNet (part of GNS Science) are closely monitoring the situation and will communicate any changes in activity to the authorities.

“White Island/Whakaari is a very beautiful and interesting destination that naturally attracts tourism. It is very difficult to say whether tourism should be allowed there. The volcano has displayed similar unrest in the past with no major eruptions. The most that the scientists can do is continue to monitor the volcano and issue information when it is available.”

Declared conflict of interest: None

Prof David Rothery, Professor of Planetary Geosciences, Open University, UK, comments:

“White Island (Whakaari) had 5 separate eruptive events between the year 2000 and now, with the 9 Dec eruption being the 6th and biggest.

“Background activity on White Island had been increasing over recent days, as reported by GeoNet (which has scientific oversight of volcanic activity New Zealand). I understand that White Island is privately owned, and that the state has no control over access. In view of this unforecast (and possibly unforecastable), sudden moderately large and fatal eruption, questions will be raised about the duty of White Island Tours in allowing their clients to go ashore – but thousands have done so previously to experience the sights and sounds of an active (but not usually erupting) volcano. I was in New Zealand three years ago, and had an earthquake not prevented my travelling from the South Island I would probably have visited White Island myself.

“My guess is that this explosive eruption was steam-driven, as a consequence of seawater interacting with magma below the active crater. Hot rock fragments and steam were blasted upwards, and part of this cloud fell back and surged along the ground. A repeat on the same scale in the next few hours or days is unlikely, but cannot be ruled out.

“White Island volcano is a consequence of the Pacific Ocean floor being subducted below the North Island of New Zealand – a process that supplies magma to volcanoes onshore on North Island that allows geothermal power generation.  This is not a major eruption in the grand scheme of things, and is extremely unlikely to presage increased volcanic activity elsewhere.”

Declared conflict of interest: None