Shallow magma dynamics at open-vent volcanoes tracked by coupled thermal and SO2 observations

Open-vent volcanic activity is typically sustained by ascent and degassing of shallow magma, in which the rate magma supply to upper feeding system largely exceeds eruption. Such unbalance between supplied (input) erupted (output) rates thought result from steady, degassing-driven, convective overturning a conduit/feeding dyke. Here, we characterize circulation at Stromboli volcano combining independent observations heat (Volcanic Radiative Power; via satellite images) gas (SO2, UV camera) output temporal interval (from August 1, 2018 April 30, 2020) encompassing summer 2019 effusive eruption two paroxysmal explosions (on July 3 28, 2019). We show that, during phase ordinary strombolian explosive that preceded eruption, average input (0.1-0.2 m3/s) (0.001-0.01 ∼2 orders magnitude. Conversely, converge an ∼0.4 m3/s summit effusion, implying overall suppression recycling back into system, hence excess degassing. find peak SO2 emissions lags behind thermal emission ∼27 days, suggesting output, lava flow field, initially dominates over conduit. propose this conduit mass unloading, produced initial leads decompression (of up 30 Pa/s) plumbing ultimately causing less-dense, volatile-rich batch(es) depth, enhanced activity, elevated fluxes culminating explosion on 28. Our results demonstrate combined analysis flux time-series paves way improved understanding magmatic dynamics open-vent volcanoes, transition regimes.