Insights on Recent Ground Deformation of Taal Volcano based on continuous GPS Measurements

Six Global Positioning System stations around the active Taal Volcano caldera complex on Volcano Island (Philippines) detected an uplift event between December 2014 and May 2015. The greatest deformation was measured south of Main Crater Lake (MCL). The event preceded swarms of volcano-tectonic earthquakes (VTs) beneath Volcano Island. Along with seismicity, flux rates of CO2 dissolved in the waters of MCL rose gradually, reaching saturation point by March 2015. Taal Lake’s water level similarly increased. According to GPS observation data, Taal Volcano has slowly deflated since June 2015. Likewise, seismicity and water levels decreased to baseline levels by October 2015. Volcano deformation during this period of unrest is most consistent with pressurization of Taal Volcano’s hydrothermal system rather than direct magma processes, in agreement with seismicity and gas monitoring. We modeled the continuous GPS deformation velocities to estimate the location, depth and volume change of the deformation source before and after the episode of unrest. We inverted the deformation velocities using an analytical model that assumes an elastic, homogeneous and isotropic crust