Sustained open vent behaviour at Mt Michael, South Sandwich Islands

Abstract Mt Michael is a remote mafic open vent volcano in the South Sandwich arc that has sustained persistent thermal and gas emissions over decades, and yet its shallow magmatic system remains enigmatic. Here we combine in situ observations and geochemical measurements with multi-decadal satellite records of SO 2 flux and thermal emission to quantify temporal variability in open vent behaviour. Long-term activity is remarkably stable, but dynamic over weeks to months with large fluctuations in thermal output and gas release. Volcanic radiative power varies between 10 5 and 10⁸ W, indicating substantial changes in the size or temperature of the radiating surface, although affected by variable cloud cover. The number of active vents within the summit crater fluctuates, yet recurring positions support a stable shallow conduit structure. Gas emissions have a mean CO 2 /S T ratio of 3.8 ± 1.3. These compositions suggest gas–melt equilibration at moderate pressures during decompression and are interpreted to reflect energetic gas pulses that punctuate passive emissions. Variations in SO₂ flux are broadly coupled with thermal output, consistent with a convective regime modulated by volatile supply. We suggest that open vent behaviour at Mt Michael is transitional between an exposed magma column or dynamic small lava lake, where coupled gas and thermal emissions are linked to convection rate and magma column height, and a multi-vent system with spatial variation in eruptive style. These data highlight the value of integrating multi-parameter ground and satellite observations to ground-truth remotely sensed time series and constrain magmatic processes at volcanoes that are infrequently observed directly.