Why can’t we predict when a volcano will erupt?

We started 2016 with a bang. Both Chile and Indonesia saw a clutch of volcanoes erupting after laying dormant for a decade or more. This followed an eruption in April 2015, when Calbuco volcano in Chile burst back to life after more than 40 years of silence, with experts giving less than two hours of warning. In an era of global satellite monitoring with proliferating networks of instruments on the ground, why can we still not accurately predict volcanic eruptions?

Volcano scientists have an unprecedented array of tools with which to keep an eye on the world’s many restless and active volcanoes. In many cases, we can watch emerging events from the safe distance of an volcano observatory. Or, once an eruption has begun, we can observe it in near-real time using satellite feeds and social media. But this isn’t matched by our ability to anticipate what might happen next at a restless but dormant volcano. New research, however, is providing clues about the best way to look for signals of future volcanic behaviour.

Like medicine, volcanologists can get a clearer sense of the state of a volcano using observations from many other examples around the world. But if we don’t know the prior history of a particular volcano, and with no way of taking the equivalent of a biopsy from it, our capacity to work out what is going on is always going to be limited. For example, some volcanoes stay completely quiet and then erupt violently without warning, while others are noisy but have a moment of calm before they erupt. Without prior knowledge, how would we know?

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