Insights into shallow magmatic processes at Kīlauea Volcano, Hawaiʻi, from a multiyear continuous gravity time series

Abstract

Continuous gravity data collected near the summit eruptive vent at Kīlauea Volcano, Hawaiʻi, during 2011–2015 show a strong correlation with summit‐area surface deformation and the level of the lava lake within the vent over periods of days to weeks, suggesting that changes in gravity reflect variations in volcanic activity. Joint analysis of gravity and lava level time series data indicates that over the entire time period studied, the average density of the lava within the upper tens to hundreds of meters of the summit eruptive vent remained low—approximately 1000–1500 kg/m3. The ratio of gravity change (adjusted for Earth tides and instrumental drift) to lava level change measured over 15 day windows rose gradually over the course of 2011–2015, probably reflecting either (1) a small increase in the density of lava within the eruptive vent or (2) an increase in the volume of lava within the vent due to gradual vent enlargement. Superimposed on the overall time series were transient spikes of mass change associated with inflation and deflation of Kīlauea's summit and coincident changes in lava level. The unexpectedly strong mass variations during these episodes suggest magma flux to and from the shallow magmatic system without commensurate deformation, perhaps indicating magma accumulation within, and withdrawal from, void space—a process that might not otherwise be apparent from lava level and deformation data alone. Continuous gravity data thus provide unique insights into magmatic processes, arguing for continued application of the method at other frequently active volcanoes.

Lava lake activity at the summit of Kīlauea Volcano in 2016

“…The summit eruption has provided new insights into lava lake dynamics and open-vent basaltic eruptions, including (1) the triggering of explosions by rockfalls (Orr and others, 2013), (2) the low density (and hence high gas content) of the lava lake (Carbone and others, 2013;Poland and Carbone, 2016), (3) the fact that the lake level acts as a piezometer of summit magma reservoir pressure (Patrick and others, 2015), (4) that gas pistoning in the lake is driven by shallow gas accumulation near the top of the lake (Patrick and others, 2016a), (5) the real-time modeling and forecasting of vog hazards (Businger and others, 2015), (6) the strong correlation between outgassing rates and seismic tremor (Kern and others, 2015;Nadeau and others, 2015;Patrick and others, 2016a), and (7) the recognition of slowly pulsing magma supply to the summit (Swanson and others, 2016).…”

Geophysics From Terrestrial Time‐Variable Gravity Measurements

“…Continuous measurements reduce these logistical issues, allow investigating high‐frequency or transient phenomena, improve dramatically the signal‐to‐noise ratio, and avoid aliasing (Van Camp et al, ). Continuous monitoring is important to monitor magma accumulation and withdrawal, revealing new physical properties of magmatic plumbing systems as the dynamics of intrusive sources (Battaglia et al, ; Poland & Carbone, ). This is especially true on persistently active volcanoes where significant variations on the daily and hour scales have been reported and are important for eruption forecasting (Branca et al, ; Gottsmann et al, ).…”

Continuous Gravity and Tilt Reveal Anomalous Pressure and Density Changes Associated With Gas Pistoning Within the Summit Lava Lake of Kīlauea Volcano, Hawai‘i

“…Gravity data used in this study were collected at a rate of 2 Hz from a site about 80 m above the floor of Halema‘uma‘u Crater and about 150 m east of the center of the eruptive vent (green dot in Figure ). Although gravity measurements are influenced by instrumental drift over time, changes that occur over minutes to a few days have been shown to mostly reflect volcanic processes (Poland & Carbone, ). No free‐air adjustments were applied to the data because the small amount of tilt associated with gas piston events (~0.1 μrad) measured at a site 2 km to the northwest of the summit vent suggests that the vertical deformation is negligible (previous studies have found that many tens of μrad of tilt at the same site correspond to only about 10 cm of vertical deformation; e.g., Lundgren et al, ; Poland et al, ).…”

“…This has not only allowed for tracking of eruptive activity through such manifestations as deformation and seismicity but also afforded the opportunity to deploy new instruments, like continuously recording gravimeters. Gravity has proven to be a particularly useful tool, suggesting that the upper ~100 m of the summit lava lake has a density of about 1,000 kg/m 3 and is thus extremely rich in bubbles (Carbone et al, ; Poland & Carbone, ) and also providing evidence for rapid convection in the subsurface magma reservoir that feeds the lava lake (Carbone & Poland, ).…”