As gateways to the seething-hot heart of our planet, volcanoes are feared for their occasionally cataclysmic behavior. From Vesuvius to Krakatau, some of the most devastating eruptions in human memory have one calamitous factor in common: caldera collapse.

Usually rapid and unannounced, only seven known collapses have occurred since the start of the 20th century, and scientists have been puzzling over the mechanism behind these events for more than a hundred years.

So when the massive Bárðarbunga volcano in Iceland’s remote southeastern interior started demonstrating caldera formation in slow motion, researchers had an unprecedented opportunity to better understand the process.

Reporting today in the journal Science, a team of 47 scientists and data modelers from nine countries, led by geophysicist Magnús