High-cadence SO2 camera observations of persistent explosive activity at El Reventador (Ecuador)

Frequent explosive activity at intermediate volcanoes is somewhat enigmatic and has been attributed to a number of driving mechanisms (e.g., slug flow, gas accumulation beneath a low-permeability seal). Here, we use high-temporal resolution SO2 camera data to investigate links between passive gas emissions and explosive activity at El Reventador (Ecuador), a system which has exhibited persistent and frequent explosive activity for over 2 decades. Across 16 days of data between 2022 and 2024, we find that SO2 emissions were elevated in April 2022 (6.1 ± 2.0 kg/s), relative to all later periods (0.69 ± 0.67 kg/s), and suggest this may relate to more vigorous magma convection following an effusive event which likely ended in late 2021 or early 2022. Overall, we capture 107 explosions, finding, perhaps counterintuitively, that there is no clear link between explosion rate and passive gas emission rates. 20 explosions are preceded by a considerable decrease in SO2 emissions 10s of minutes before the event, which we attribute to sealing of the upper conduit causing gas accumulation and eventual explosive failure of the seal. In 5 of these cases, we identify small increases in emissions 10s of seconds prior to the explosive failure, suggesting that pressure build-up begins to open gas pathways through the seal before explosive fragmentation commences. The majority of explosions may be caused by slug flow, as previously proposed (Vásconez et al. 2022); however, we do not rule out rapid conduit sealing or partial seal failures as other potential driving mechanisms. By exploiting high-cadence data from a permanent SO2 camera installation, this work makes a step towards understanding the fundamental processes that govern persistent explosive activity at intermediate volcanoes.