In the city of Catania, at the foot of the volcano, scientists are trying to explain its recent unusual behaviour

When his phone rang at 3.22am last Wednesday, 50-year-old Giuseppe Salerno, the head of volcanologists at Catania’s National Institute of Geophysics and Volcanology (INGV), was already up after a thundering rumble had awoken many of the city’s inhabitants. The call came from the headquarters of the INGV where, a few seconds before that disturbance, seismic waves on one of the 40 monitors in the operations room seemed to jump off the screen. For the 14th time in less than a month, Mount Etna had sent another reminder that it is one of the world’s most active volcanoes.

Etna, 3,300 (10,800ft) metres above sea level, has been in explosive form in recent weeks, spewing incandescent magma and a copious shower of ash that has reached as far as Catania. Since 16 February, with fastidious precision, every 48 hours the volcano has put on a firework display with lava fountains reaching as high as 2,000 metres.