The CAVA (Carnegie Ambrym Volcano Analysis) Project - a Multidisciplinary Characterization of the Structure and Dynamics of Ambrym Volcano, Vanuatu

The CAVA (Carnegie Ambrym Volcano Analysis) Project aims to study the structure and dynamics of the magmatic system beneath Ambrym volcano in the Vanuatu archipelago using gravity, seismic, gas, and petrologic measurements. In December 2018 a fissure eruption occurred in the caldera, followed by the eruption of a lava flow and the propagation of a dike over more than 20 km towards the South East rift zone, as characterized by InSAR (Hamling et al., 2019; Shreve et al., submitted). During the eruptive crisis the two summit lava lakes at Benbow and Marum drained, and there is evidence of an eruption offshore of the SE coast. In May and September 2019 we conducted two field campaigns. We measured gravity at ~ 100 sites across the island using a Scintrex CG6 relative spring gravimeter together with decimetric GPS positions, and calculated the Bouguer gravity anomaly. The gravity anomaly is interpreted in terms of density contrast associated with local geology and the presence of magmatic fluids (water, gas, melt) in the upper crust. A network of 12 broadband seismometers was also deployed in the caldera and SE region of Ambrym to characterize the seismicity. The location, type, and depth of these earthquakes inform us about the dynamics of the system over the recent post-eruptive time interval, and includes earthquakes that may be associated with the new offshore vent. These results provide insight into the magma storage conditions at Ambrym, which are currently poorly known, and help to develop an understanding of the interplay between magmatic activity at the summit caldera and rift zone and regional tectonics at this large and complex basaltic shield volcano.