When engineers began drilling into an Icelandic volcano named Krafla, things took a turn for the weird. The team’s objective was to approach the boundary of a magma reservoir 2.5 miles below the surface, tapping into superheated fluids that could produce geothermal energy. But when the drill was just over a mile down, molten rock began creeping up the drill.

On that brisk spring day in 2009, the engineers had accidentally hit a pocket of magma sitting right below the surface that no one knew was there.

Krafla is “one of the best studied volcanoes on the planet,” says Hugh Tuffen, a volcanologist at Lancaster University in the United Kingdom who wasn’t involved with the research. It has been repeatedly