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 crus
