Tracking Transcrustal Magma Ascent Beneath Laguna del Maule, Chile

There is abundant evidence that 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 constrained. At Laguna del Maule in central Chile, the site of several Holocene silicic eruptions and present-day surface uplift, 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 swarm of this seismicity in 2018 was followed 3 months later by an increase in the inflation rate observed at the surface. We infer that this earthquake swarm was driven by the injection of a new batch of melt, transported between lower to upper crust magma reservoirs. The lag time between melt transport and surface inflation was governed by the hydraulic diffusivity of the upper crustal reservoir. These results indicate that volcanic unrest at Laguna del Maule begins deep within the crust and months before observable signals of shallow magma reservoir pressurization and may be replicable for volcanic arcs worldwide.