Sea level rise reduces volcanic eruptions

Sea levels have affected volcanic eruptions on the Greek island of Santorini over the past 360,000 years, according to research published in Nature Geoscience.

The research finds that lower sea levels, which happen during ice ages, were linked to higher rates of eruption. The researchers believe this result likely holds true for other island volcanoes.

“The mechanism is quite simple,” says Dr Christopher Satow, senior lecturer in physical geography at Oxford Brookes University, UK, and lead author on the paper.

“Falling sea levels remove mass from the Earth’s crust, and the crust fractures as a result. These fractures allow magma to rise and feed eruptions at the surface.”

This animation shows the effect of sea levels on volcanic eruptions. Credit: Oxford Brookes University

This mechanism has been proposed by researchers before, but the Santorini caldera volcano provided a useful record for Satow and colleagues to firm up the theory.

“A huge eruption 3600 years ago caused the centre of what was then a conical island to sink into the sea, revealing an extraordinarily detailed history of over 200 volcanic eruptions preserved within the remaining circle of cliffs,” says Satow.

Photo of boats beside santorini's cliffs, showing layers deposited by past eruptions
Santorini cliffs, showing layers deposited by past eruptions. Credit: Ralf Gertisser (Keele University)

“Comparing this eruption history to a sea-level record allowed us to show for the first time that the sea level has had an important role in determining the timing of eruptions at Santorini, and probably at many other island volcanoes around the world.”

The researchers determined that 208 of the 211 eruptions that had occurred on Santorini over the past 360,000 years had happened when sea levels were at least 40 metres below their current levels.

They backed this result up with numerical modelling to show that when sea levels drop 40 metres or more below current levels, there’s enough stress at the top of the magma chamber on Santorini for the Earth’s crust to fracture, allowing magma to move upwards in dykes.

While we know that volcanic activity can have short-term effects on the Earth’s climate, Satow says this research demonstrates that the reverse is also true.

“What is less well known is that on long timescales, the climate can also affect volcanoes,” he says. “As ice sheets retreated across volcanic landscapes after the last ice age, the removal of mass changed the stress conditions in the Earth’s crust, allowing the fractures which feed volcanic eruptions to form more easily.

“As these ice sheets melted, the global sea level rose rapidly, by around 100 meters, adding a significant mass to the crust around many volcanic islands which, in theory, should alter their eruptive activity.”

With 57% of the world’s volcanoes either on islands or in coastal areas facing sea-level rise from global warming, the researchers say this effect needs to keep being investigated.

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