White Island should be a no-go zone when the volcanic alert level reaches two because of the unpredictability of the volcano, an Australian expert says.
Professor Ray Cas, from Monash University’s School of Earth, Atmosphere and Environment, said White Island is particularly dangerous because it is a marine volcano, making evacuations particularly difficult.
I think that particularly when the alert level reaches two on that particular island it should be a no-go zone,” he said.
“The alert level was raised several weeks ago from one to two - now that tells us there is increased activity under the volcano, something is happening under the volcano.
“The important thing about that volcano is that unpredictability. We know from past events which may happen every few years, you can have these unexpected explosions even when the alert level is as low as two.
“The big danger there is you can get these unexpected, unpredictable explosions with very terrible consequences we saw yesterday.”
The nature of the White Island volcano also adds to the danger, Mr Cas said.
During a hydrothermal explosion like the one that occurred yesterday, hot water which often sits in the crater can mix with rock debris and ash to create a hot mixture.
“You walk into this great amphitheatre-like crater which is scattered with gas vents releasing all kind of noxious gases and also craters which ,depending, are invariably filled with extremely hot water which is close to boiling temperature,” he said.
“Each of those represents a hazard. The gases can actually pond in that big crater and become really poisonous, the crater lake can overspill which it has done in the past. You get this flood of water and mud at nearly boiling temperature.
“If there is an explosive eruption, that hot water gets mixed into the ejected solid material and produces this really hot mixture of gas, rock debris and ash.”
A hydrothermal explosion occurs when the pressure in the geothermal system builds up.
“The explosive eruption is what we call a hydrothermal explosion, so underneath the volcano there is a body of magma, a body of molten lava, if you like, which is transmitting heat to the rock but also to the groundwater that is in cracks and fractures in the edifice.
“That groundwater consists of gases released by the magma and also sea water which is circulating into and through the volcanic edifice through those cracks and fissures.
“That is an inexhaustible source of external water, so White Island has a constantly active and high-temperature geothermal system.”
“Now sometimes those cracks or fractures block up with minerals which are precipitated into them and therefore the pressure builds up the geothermal system builds up and needs to be released with a very significant explosion, which we saw yesterday.”