Microgravity Measurements Spanning 2019–2022 Indicate No Change in Magma Supply or Storage During Kīlauea's Reawakening

Abstract

After more than 2 years of quiescence following its major 2018 flank lava effusion and summit caldera collapse, Kīlauea, Hawaiʻi, returned to frequent eruptive activity in late 2020. Microgravity measurements from the summit region in 2019 and 2022 span this reawakening and indicate a gravity increase of up to hundreds of microgals near the center of the summit caldera. Much of this increase is caused by lava that partially filled the 2018 collapse pit. We accounted for this mass by differencing digital elevation models of the summit area to determine the geometry and amount of accumulated lava and its gravity contribution at each station in the network. The remaining gravity change is best approximated by a mass increase of 6.9 × 10 ¹⁰  kg (5.1–23.0 × 10 ¹⁰  kg at 95% credible interval) at a depth of 480 m (121–795 m at 95% credible interval) beneath the locus of the 2018 collapse. The modeled source depth reflects the combined impacts of magma accumulation in a reservoir known from previous geophysical studies to exist at about 1–2 km depth, intrusions between that reservoir and the surface, and mass accumulation in the heavily fractured caldera floor. The spatial and temporal patterns of subsurface mass accumulation during 2019–2022 imply that there were no significant changes in magma reservoir geometry or magma supply to the volcano in the years following the 2018 collapse.