New values for accumulation of unerupted magma inside Mt Etna volcano, determined from 42 years of ground deformation data

Abstract Volcanoes grow and change shape by eruption, magma intrusion and by spreading outwards under their own weight. To understand the workings of a volcano, the balance of these processes must be quantified, requiring decades of observation. Here, we measure displacement of 72 survey points on and around Mt Etna to millimetre accuracy for periods of up to 42 years. We find that Etna is increasing in volume by 2.68 million cubic metres a year due to the emplacement of unerupted magma. This is an order of magnitude smaller than previously thought and implies that Etna’s magma generation system is 8 times slower than generally accepted. We also find that outward east–west displacement is creating new land surface at the summit at the rate of 1640 m 2 per year and that Etna’s summit area is subsiding at rates exceeding 0.10 m per year in places.