The spectacular eruptions of the Kīlauea volcano in Hawaii in 2018 were triggered by extreme rainfall in the preceding months, research suggests.
Scientists say the finding raises the possibility that climate breakdown, which is causing more extreme weather, could lead to an increase in eruptions around the world.
The 2018 Kīlauea eruptions were one of the most extraordinary sequences in at least 200 years, according to the scientists, with rifts opening, summit explosions and collapses, and a magnitude 6.9 earthquake. But the trigger was not known.
However, several months of unusually high rainfall preceded the eruption, with one 24-hour period setting a record for the entire US. This flood of water would have percolated down into fissures and pores in the rocks of the volcano, as far as 1.8 miles (2.9km) below the surface.
The scientists calculated this pushed up the pore pressure inside the rocks to the highest level in almost 50 years, weakening them and allowing magma to push up from below.
The scientists also looked at eruptions of Kīlauea since 1790 and found that these historical events were twice as likely to happen in the rainy season. Such a link has long been thought possible – JD Dana, one of the first geologists to visit Hawaii in the late 1800s, suggested the idea.
They also ruled out magma pressure from below triggering the eruption, because the surface had barely deformed, and the gravitational pull of the sun and moon, which can trigger eruptions.
“All the circumstantial evidence points in the same direction,” said Jamie Farquharson, at the University of Miami, whose research is published in the journal Nature. Rain has been linked to shallow eruptions in the past, such as at Mount St Helens in 1980, but this is the first time an impact at depth has been found.
“Critically, as our climate continues to change, the occurrence of prolonged periods of extreme rainfall is predicted to increase in many parts of the world, increasing the potential for rainfall-triggered volcanic phenomena,” said Farquharson, adding that research on the phenomenon was needed on other volcanoes. Other scientists have warned that the melting of ice on volcanic peaks may also cause eruptions.
Farquharson said rainfall could now be an additional factor taken into account when assessing the risk of a volcano erupting.
Michael Manga, at the University of California, Berkeley, who was not part of the study, said: “Volcanoes are part of a dynamic Earth system. Volcanic eruptions influence all surface environments, including climate and weather. Changes in those surface environments, such as heavy rainfall, might also influence eruptions. We are only just beginning to understand these interactions.”
