Ash and gas discharge during open vent activity at El Reventador (Ecuador): explosion-style transitions driven by conduit capping

Since the VEI 4 eruption of November 2002, El Reventador volcano (Ecuador) has been the site of persistent open-vent activity characterized by frequent (hourly) Vulcanian—strombolian explosions and occasional (every few years) effusion of lava flows. The conduit processes that sustain this continuous eruptive activity are still poorly understood. Here, we combine high temporal resolution thermal infrared imaging with seismic recordings and DOAS-derived SO 2 fluxes focusing on a period of Vulcanian-style activity on 22–23 February 2017. Thermal imagery captured the emission and ascent dynamics of 26 plumes during the observation period, including those fed by explosions and degassing episodes. While most explosions have associated seismic signals, a few are marked by the absence of measurable seismic activity. Degassing episodes also show very few associated seismic signals. Explosions and degassing events seem to follow a sequence that can be explained by changes in the conduit permeability associated with rapid (over time scales of minutes) rheological stiffening of magma in the uppermost portion of the conduit to reduce degassing efficiency. Periods of open-vent outgassing alternate with periods of conduit capping resulting in system pressurization and leading to Vulcanian explosions that re-open the conduit allowing outgassing to resume.