Insight into the May 2015 inflation event at Kīlauea volcano, Hawai'i

Abstract

We use ground and space geodetic data to study surface deformation and gravity change at Kīlauea volcano from January to September 2015. This period includes an episode of heightened activity in May 2015, which we refer to as ’the May 2015 event’. The data set consists of Global Navigation Satellite System (GNSS), tilt, visual and seismic time series along with 25 descending and 15 ascending acquisitions of the Sentinel-1a satellite in Interferometric Wide swath mode and microgravity surveys taken a few years before and just after the May 2015 event. We identify four different stages of surface deformation and volcanic activity during the May 2015 event which we attribute to the movement of magma and pressure changes in response to a magma supply and withdrawal imbalance in the shallow plumbing system. In particular, we model the deformation sources attributed to the Halema’uma’u reservoir (HMMR) and South caldera reservoir (SCR). The SCR was best described by inflation of a spheroidal at 2.8 (2.65-3.07) km depth below the Southern caldera region. The HMMR source was modelled by a point source deflation located East of the Halema’uma’u crater at 1.5 (0.95- 2.62) km depth. The surface microgravity changes which would result from changes in these reservoirs are significantly lower than the actually observed microgravity changes. We attribute this to the lack of complexity of the single point source model used. Mechanisms that add/remove mass from the subsurface without accompanying surface deformation, which are not part of the point source model, played a significant role. More frequent microgravity campaign surveys, if needed with a smaller network, are the only way to improve our understanding of these processes and help to quantify them.