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Whakaari/White Island eruption: What lies beneath the active volcano

Wednesday, 11 December 2019

  Whakaari/White Island, a volcano that has been active for at least 150,000 years, is much bigger than it first appears.

On Monday afternoon, it erupted while 47 people, including tourists and tour guides, were still on the island. At least six people had died since, dozens were injured and recovering in hospital, and many were still missing.

On the surface, New Zealand's most active volcano is a rugged piece of land, measuring around 2 kilometres in diameter and mostly occupied by the Main Crater. It peaks at 321 metres with the crater floor sitting less than 30m above sea level, according to GNS Science.

But beneath the surface is almost 1000m of marine mountain - making up around 70 per cent of the cone.

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On the surface, Whakaari/White Island measures around 2 kilometres in diameter. But beneath the surface is almost 1000m of marine mountain.
On the surface, Whakaari/White Island measures around 2 kilometres in diameter. But beneath the surface is almost 1000m of marine mountain.

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Whakaari/White Island peaks at 321metres high with the crater floor sitting less than 30m above sea level, according to GNS Science.
Whakaari/White Island peaks at 321metres high with the crater floor sitting less than 30m above sea level, according to GNS Science.

* Whakaari / White Island eruption: What scientists say about the volcano

Whakaari/White Island, a volcano that has been active for at least 150,000 years, is much bigger than it first appears.
Whakaari/White Island, a volcano that has been active for at least 150,000 years, is much bigger than it first appears.

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White Island Flights operations manager George Walker captured these images of White Island about two hours after the volcanic eruption.
White Island Flights operations manager George Walker captured these images of White Island about two hours after the volcanic eruption.

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'The cone rises about 900m above the local sea floor, but most of the cone is below sea level,' GNS Science volcanologist Brad Scott explained.

The part of the volcano beneath the surface - known as a composite cone or stratovolcano - was made up of layers of ash and lava flow.

Between 1976 and 2000, it was in a state of almost continuous eruption, with explosive eruptions changing the crater floor.

'Whakaari/White Island is a cone volcano and has built up a typical-looking volcanic cone from many small but locally significant eruptions over a long period.'

Sitting around 50km from the mainland, Scott said in a statement on the GNS Science website there was an 'extremely low likelihood' of an eruption having an effect on the mainland.

'If there were any effects, the most likely are fine ash falls (like pollen) and the smell of volcanic gas, which are more likely to just be a nuisance.'

There was previous activity in the year 2000 from March to September, and again in 2012. A larger eruption following Monday's wasn't likely, but GNS estimated an equal likelihood of either no eruption or a smaller, or similar-sized, eruption to impact the Main Crater floor.

'There is a high level of uncertainty associated with this estimate.'

The exact cause of Monday's eruption wasn't yet known, but experts assumed it was a phreatic eruption caused by an explosion of steam pressure.