The eruption of some of the largest volcanoes on the planet could be predicted several decades before the event, according to researchers.
Analysis of rock crystals from the Greek island of Santorini suggests eruptions are preceded by a fast build-up of magma underground, which might be detected using modern instrumentation.
Such volcanoes can produce enough ash and gas to temporarily change the global climate.
The research is in the journal Nature.
Volcanologists refer to history's largest volcanoes as "caldera-forming eruptions", as the magma ejected is so voluminous that it leaves a massive depression on the Earth's surface and a crater-like structure known as a caldera.
The largest of these volcanoes have been dubbed "supervolcanoes" and their eruptions can trigger devastation with global impacts.
Such volcanoes can lie dormant for hundreds of thousands of years before blowing. But while researchers believe seismic data and other readings would give us a few month's notice of such an eruption, the new study suggests we might anticipate these events much earlier.
"When volcanoes awaken and when the magma starts to ascend to the surface, cracking rock as it does, it sends out signals," Prof Tim Druitt of France's Blaise Pascal University and lead researcher told BBC News.
"You get seismic signals, you get deformation of the surface, increasing gas emission at the surface - and this can be detected.
"The question we're addressing here is what's going on at depth prior to these big eruptions. The classical view was that during long repose periods over thousands of years, magma slowly accumulates a few kilometres below the volcano and finally it blows.
"What we're finding is that there's an acceleration phase of magma build-up on a time scale of a few decades, and that's surprisingly short given the thousands of years of repose that have preceded that eruption."
The evidence comes from analysis of crystals in pumice rock from the Santorini site, which the researchers in France, Switzerland and Singapore analysed using modern instrumentation including electron and ion microprobes.
"The changes in composition of the crystals with time provide little histories of how the magma itself has evolved," said Prof Druitt.
"What we found was that all the crystals in the magma grew within a few decades of the eruption."
BBC
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