Crustal-scale degassing due to magma system destabilization and magma-gas decoupling at Soufriere Hills Volcano, Montserrat,

Abstract

Activity since 1995 at Soufrie`re Hills Volcano (SHV), Montserrat has alternated between andesite lava extrusion and quiescence, which are well correlated with seismicity and ground deformation cycles. Large variations in SO2 flux do not correlate with these alternations, but high and low HCl/SO2 characterize lava dome extrusion and quiescent periods respectively. Since lava extrusion ceased (February 2010) steady SO2 emissions have continued at an average rate of 374 tonnes/day (6 140 t/d), and incandescent fumaroles (temperatures up to 610oC) on the dome have not changed position or cooled. Occasional short bursts (over several hours) of higher (_ 10x) SO2 flux have been accompanied by swarms of volcano-tectonic earthquakes.