Transcrustal magma ascent beneath Laguna del Maule, Chile

Arc volcanoes are fed by complex networks of storage zones that extend throughout the crust. Though the geometric details of these transcrustal magmatic systems are well resolved beneath several volcanic settings, the relationship between magma transport at depth and volcanic unrest at the surface remains poorly understood. At Laguna del Maule in central Chile, we show that seismically imaged magma reservoirs in the upper and lower crust are connected by a zone of deep crustal seismicity. A pronounced one-day seismic swarm in 2018 was followed approximately 3 months later by an increase in surface uplift rate. We infer that this swarm was driven by the injection of new melt, transported between lower to upper crust magma reservoirs. The lag time between melt transport and surface acceleration was perhaps governed by the hydraulic diffusivity within the upper crustal reservoir. These results indicate that volcanic unrest begins deep within the crust and months before observable signals of shallow reservoir pressurization.