Mafic magma feeds degassing unrest at Vulcano Island, Italy

The benign fuming activity of dormant volcanoes is punctuated by phases of escalating degassing activity that, on some occasions, ultimately prelude to eruption. However, understanding the drivers of such unrest is complicated by complex interplay between magmatic and hydrothermal processes. Some of the most comprehensively characterised degassing unrest have recently been observed at La Fossa cone on Vulcano Island, but whether or not these episodes involve new, volatile-rich ascending magma remains debated. Here, we use volcanic gas measurements, in combination with melt inclusion information, to propose that heightened sulphur dioxide flux during the intense fall 2021 La Fossa unrest is sourced by degassing of volatile-rich mafic magma. Calculations using a numerical model indicate observations are consistent with the unrest being triggered by the emplacement of similar to 3 center dot 10(6) m(3) of mafic magma at similar to 4-5 km depth. Degassing of mafic magma is argued as a recurrent driver of unrest at dormant volcanoes worldwide. Substantial volume and compositional changes in gas emissions from fumaroles on Vulcano island in late 2021 may reflect the degassing of fresh mafic magma, according to in situ and remote sensing measurements of gas emissions coupled with numerical modelling