GNS learns how earthquakes can trigger eruptions

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A chance discovery by researchers at GNS Science has shed light on why it is possible for an earthquake, in rare conditions, to trigger a volcanic eruption.  

In a paper published this week in Science Advances, authors Ian Hamling and Geoff Kilgour of GNS Science describe their study of an eruption at Ambrym volcano in Vanuatu in 2015, during which they discovered, almost by accident, that it was very likely triggered by a magnitude 6.4 earthquake near the volcano the day before.

“While looking back at a sequence of satellite images over the volcano, we discovered that a fairly large volume of magma had pushed its way towards the surface prior to the eruption,” Ian says.

“After a bit more digging, we noticed there had been a magnitude 6.4 earthquake about 10km south of the volcano 30 hours before the eruption.”

Geoff says because of the close timing of the two events, the pair used their understanding of how magmas behave to model the reaction of the magma to the earthquake.

“We found that Ambrym’s magma must have been both water-saturated and within a narrow temperature range for it to respond to the earthquake.”  

“These conditions help trigger an eruption by causing gas bubbles to grow in the volcano’s magma reservoir.

“We can think of these as ‘Goldilocks conditions’: if the magma is too hot, gas bubbles will not form and if it is too cold, the magma will lock up and it cannot flow to generate an eruption.”

Supplied image.

Using satellite interferometry data showing surface deformation within the volcano’s caldera, the pair’s modelling indicated that stress changes caused by the M6.4 quake likely induced gas bubbles in the volcano’s shallow magma prompting it to expand and erupt.

Each year there are 150-200 magnitude 6 and larger earthquakes worldwide, but very few trigger volcanic eruptions, Ian says.

“This study shows that magma has to be in a primed condition before an earthquake can trigger an eruption.”

He says the findings have implications for management of volcanic hazards.

“If you could get good estimates of the properties of magmas at different volcanoes, you could provide an additional advisory that a volcanic system was currently more susceptible to eruption.

“We’d now like to study a wider range of magmas to see if the same pattern holds for different magma compositions.”

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