Mass accumulation beneath the summit of Kilauea Volcano, Hawai’i (2008-2012): new constraints from micro-gravity and deformation measurements

Kilauea Volcano, Hawai’i, is currently erupting at two locations: from vents on the volcano’s east rift zone (ERZ) since 1983 and at the summit, within Halema’uma’u Crater, since March 2008. A previous study that combined micro-gravity and deformation measurements acquired between 1975 and January 2008 revealed shallow magma accumulation ~1 km beneath the southeastern rim of Halema’uma’u Crater, near where the new eruptive vent opened. This vent is now occupied by a > 100 m diameter lava lake whose surface fluctuates between 60 and 150 meters below the vent rim. New gravity surveys of about 50 stations in the summit area of Kilauea have been performed since the start of the summit eruption. The measurements span a sequence of important volcanic events: (i) long-term deflation across the summit until March 2010, (ii) re-inflation until March 5, 2011, when (iii) an eruptive fissure opened along the ERZ causing rapid deflation at the summit of the volcano and, (iv) re-inflation from the end of the fissure eruption on March 9, 2011, through 2012. Microgravity measurements were performed using two Scintrex CG-5 gravimeters and following a double-looping procedure. GPS data and InSAR measurements from both the German Space Agency (DLR) TerraSAR-X satellite and the Italian Space Agency (ASI) satellite-constellation Cosmo-SkyMed are used to adjust the gravity measurements for the free-air effect and to constrain magmatic sources. Preliminary results show that, while no significant residual gravity changes are recorded from 2008 to March 2011, following the March 2011 eruption a positive gravity anomaly (> 100 ± 25 μGal) is present in the same area that showed signs of mass accumulation during 1975-2008. The positive residual gravity change is also accompanied by inflation of the summit (maximum uplift was about 0.12 m). We investigate the nature of this mass accumulation through the combined analysis of deformation and micro-gravity data.