Magma Supply Dynamics at Mt. Etna (Italy) Inferred from Peripheral Soil CO2 Emissions: Insights into the 2018 Flank Eruption and the 2021 Paroxysmal Activity

Abstract

Open-conduit volcanoes are characterized by continuous magma supply and persistent degassing, whereas eruptive activity occurs intermittently and is controlled by magma transfer and accumulation processes within the feeding system. At Mt. Etna, temporal variations in peripheral soil CO2 emissions provide a sensitive tracer of deep magma intrusions and can be used to quantify magma inputs into the feeding system. Here, we analyze soil CO2 flux measurements between 2016 and 2021 to reconstruct the evolution of magma supply dynamics, focusing on two major eruptive activities: the December 2018 flank eruption and the exceptional paroxysmal activity of 2021. The reconstructed history reveals contrasting magma supply dynamics associated with the two crises. The December 2018 eruption was preceded by several deep magma input episodes and subsequent upward magma transfer during the preceding months, whereas the 2021 crisis followed the largest magma supply anomaly recorded over the last two decades, which developed between May 2020 and February 2021. This exceptional input preceded the February‑April 2021 lava-fountain sequence, one of Etna’s most energetic eruptive episodes in recent decades. The reconstructed magma dynamics show remarkable agreement with deformation-derived volume changes and independent geodetic, seismological, geophysical and petrological evidence, supporting the effectiveness of peripheral soil CO2 emissions in tracking magma input and transfer processes within Etna’s plumbing system.