White Island: Better eruption predictions
A study of rocks ejected from Whakaari/White Island in 2016 – during an ‘‘incredibly active’’ period for the volcano since 2011 – could point the way to better eruption forecasting.
The volcano off the Bay of Plenty coast, which has been active for at least 150,000 years, erupted on December 9, 2019 leading to the deaths of 21 people who were visiting the island.
For the new research, University of Canterbury scientists and visiting students from US colleges, along with GNS Science and international researchers, tested rocks from the island to see, among other things, how easily they cracked and how gas travelled through them.
The team discovered that cracked rocks can act like valves – opening and closing – to allow gas to escape.
Lead researcher Dr Ben Kennedy, UC Associate Professor of physical volcanology in the School of Earth Sciences, said the findings were ‘‘remarkable’’ and would help scientists better understand the behaviour of the volcano and interpret its sounds and tremors.
‘‘We hope our research will ultimately lead to more accurate volcanic monitoring and forecasting of future eruptions,’’ he said.
‘‘The research team found evidence that these valve-like cracks can become clogged by minerals.
‘‘If these valves become clogged, the gas cannot escape. If gas cannot escape, pressure builds, leading toward an explosive eruption.’’
It was the first time researchers had carried out
experiments that showed rocks behaved in that way, Kennedy said. Because the rocks came from inside the volcano, they had provided a unique look at what went on inside.
Cracked rocks provided a ‘‘pipe’’ that connected magma at depth to the lake on the crater floor.
‘‘The pipe has crack valves along its length, some of which are open and some of which are closed by the weight of the volcano or blocked by minerals,’’ Kennedy said.
‘‘If you can imagine a series of kind of branching pipes. They are all full of rubble effectively. The gas is basically moving along the cracks. Then occasionally the cracks block up and blast out all that rubble.’’
The research has been published in the journal Geosciences. The paper said Whakaari had been in an extended period of unrest and minor eruption since 2011.
During recent unrest there were a range of surface phenomena, with several episodes of lake draining, mud fountaining, ash venting, directed ballistic bursts – where rocks are ejected – and surges, and the appearance of a lava dome. There was also star bursting, which Kennedy described as a huge bubble maybe 6 metres across bursting spectacularly in a very muddy lake.
Whakaari had been ‘‘incredibly active’’ since 2011 with all sorts of different types of activity, Kennedy said.
In 2016 some of the pipes that material erupted from were pointing down the crater almost toward the area where visitors came ashore. The ejected rocks were between about bowling ball and marble size, travelling at maybe 50-100m per second.
There were thought to have been at least three ‘‘cannon shots’’, with an estimated 400,000 particles in total coming out, the furthest going about 200m, Kennedy said.
It was comparatively a ‘‘very small’’ event with most of the ejected material found close to the crater.