A volcano’s deep rumblings can help scientists to track the size of an eruption as it unfolds.

One of the many options for monitoring volcanoes is the measurement of infrasound, which consists of low-frequency sound waves below the range of human hearing. Instruments that detect infrasound can be used to monitor a volcano even when the weather is bad and volcano watchers can’t see the mountain.

In 2017, Alejandro Diaz-Moreno at the University of Liverpool, UK, and his colleagues placed 14 microphones around the summit of Mount Etna, a volcano on the Italian island of Sicily that erupts regularly and poses a threat to nearby towns. The team analysed the shape of the infrasound waves produced as gas and ash exploded in small bursts. This allowed the researchers to calculate how much material Etna was spitting into the atmosphere.

The installation of infrasound sensors at other volcanoes could help scientists to quickly collect accurate information about an eruption’s size and calculate how far its ash plumes might travel.