Evidence of rapid conduit sealing driving explosive activity at El Reventador (Ecuador) underpinned by a permanent SO2 camera installation.

El Reventador is a highly active stratovolcano located ≈90 km east of Quito (Ecuador). Since a paroxysmal eruption (VEI 4) in 2002, it has exhibited persistent open-vent degassing accompanied by frequent vulcanian-/strombolian-style explosions, as well as lava flows and small pyroclastic density currents. The relatively remote nature of this volcano, requiring 4-5 hours of arduous uphill hiking through thick jungle, hinders extensive research on this system. Furthermore, with changeable and often wet weather conditions in the region, reliable remote spectroscopic measurements of gas emissions can be particularly difficult to achieve. These complications highlight the importance of permanent instrument installations that can work autonomously, thus reducing the need for field campaigns and improving the chances of capturing high-quality data and/or interesting volcanic phenomena. Here, we present the first measurements from a permanent SO2 camera installation on El Reventador, focussed on a window of good measurement conditions lasting a few hours on 24th April 2022. During this period, explosions typically occurred at a sub-hourly rate, with varying sizes and repose periods. Prior to a number of the explosions we find a decrease in SO2 emissions suggestive of gas accumulating under a reduced-permeability magma seal in the upper conduit. Sealing appears to occur on the order of 10-20 minutes prior to explosions, although establishing a baseline emission rate for the freely degassing system is often precluded by the frequency of explosions. Indeed, we find periods where permeability in the upper conduit appears to begin reducing immediately after the previous explosion.