Abstract

At some submarine volcanoes, the influx and output of magma vary over time producing years-to-decades-long cycles of inflation and deflation, which in turn cause pronounced physical changes in the overlying oceanic crust and the hydrothermal circulation hosted within. Permeability within the oceanic crust exerts primary control on seafloor fluid circulation and hence has important influences on the heat and chemical exchange between the earth's lithosphere and oceanic hydrosphere, as well as surface and subsurface biological communities. Despite its importance, permeability is one of the most poorly constrained hydrologic properties for most of the mid-ocean ridge system. In this study, harmonic analysis of a high-resolution, long-term time series of effluent temperature measured at a high-temperature hydrothermal vent on Axial Seamount yields time-varying estimates of the effective permeability within the hydrothermal upflow zone. Comparing the records of permeability and volcanic deformation during and after the April-May 2015 eruption at Axial suggests a decrease in upflow-zone permeability during co-eruptive deflation and an increase in permeability during post-eruption re-inflation from July 2015 to June 2019. Modeling of the three-dimensional strain field suggests that the temporal variations in effective upflow-zone permeability can be explained by closing and opening of hydrothermal pathways that accompany crustal compression and extension in relation to the volcano's deformation cycle.