Depressurization of a hydrothermal system following the August and November 2012 Te Maari eruptions of Tongariro, New Zealand

In 2012, two phreatic eruptions occurred at New Zealand's Tongariro volcano for the first time in over a century. Interferometric Synthetic Aperture Radar data collected by the Italian Space Agency's COSMO-SkyMed satellite constellation, indicates up to 20mm/yr of post eruptive subsidence focused across a 4km(2) region in the vicinity of the eruption site. Modeling of the deformation data indicates a shallow source at approximate to 500m depth (1100m asl) consistent with the depth of the hydrothermal system. We estimate an annual volume loss of 35,000m(3), leading to a pressure loss of approximate to 0.09MPa/yr. We suggest that fracturing associated with the eruptions has enabled the continued depressurization of the shallow hydrothermal system and that subsidence will continue until the fractures become resealed.