In January 1991 I visited White Island volcano in the Bay of Plenty with my parents. It was an awesome yet surreal place, completely hostile to everything except a colony of birds living on its flanks and broken scrub in which they had made their homes. It helped to fuel a long standing interest in volcanoes and a desire to work on them. But nearly 29 years later in an eruption in broad daylight it has shown New Zealand and the world why volcanoes command respect.
The eruption at 1411 hours New Zealand time 09 December 2019 was tiny by global standards. It only lasted a few minutes, but in that time it has killed one person, injured 23 and left another 27 unaccounted for.
So, how did one small eruption that would probably have been forgotten by many by the end of the year except for the fact that it was lethal, manage to cause such grief? And how can this be prevented from happening again?
White Island is a volcano with a crater lake covering the main vent. Between the water and the magma below there is a layer of sediment that changes in chemical composition to almost crystallize and bound the debris covering the vent together. If the magma is at depth then fumarole activity will be lesser because the sealed vent provides less routes for the vapours to escape. As it rises the fumarole activity increases. Directly above the magma a mass of volcanic vapours rises towards the surface and as it pushes its way through the fluid saturated debris steam pressure builds. When the overhead mixture can no longer sustain the pressure it explodes.
Unfortunately eruptions through lakes tend to happen with quite short notice – only a few minutes in some cases, though the warning signs might be overt: seismic activity, a disturbance in the crater lake and increased venting. In the case of White Island where the boat/helicopter is some several hundred metres from the vent, even if they ran back, they might not make it before the explosion.
The explosion in a confined space can be devastating. A cloud of superheated rocks, mud and steam will expand at several hundred metres per second in all directions. If conditions permit a ground surge of falling debris will move across the crater floor and immediate surrounds at possibly over 100km/h. Whilst there are instances of people surviving such conditions, their injuries are likely to be acute. Based on the available footage of yesterday, that is what appears to have happened.
White Island, like New Zealand’s other volcanoes is monitored 24 hours a day 7 days a week by GeoNet, which has a network of seismometers, camera’s and other instruments in place. They provide real time seismic, photographic and other coverage of the volcanoes. Yesterday, just before the eruption, the GeoNet camera on White Island’s flank took an image that showed people on the crater floor perhaps 50-100 metres from the crater rim. The seismometer showed elevated activity that had been continuing for about three weeks was still happening. Last week a GeoNet statement said that it had entered a phase where an eruption should be considered possible.
Duty volcanologist for Institute of Geological and Nuclear Sciences (G.N.S.), which operate GeoNet, Brad Scott, has said that it is up to individual tour groups whether or not they operate from one day to the next. They operate through various alert levels. Hard hats, fully enclosed shoes and breathing masks are compulsory.
Over the next few days as the authorities piece together what happened, New Zealand will learn the story of how White Island caught authorities, tourist operators and locals alike off guard. But for now we focus on the survivors, those that are missing and those that were injured.