In this paper we measured changes in Earth’s gravity field derived from satellite measurements of the sea surface and used them to model the shape of the magma plumbing system under Hunga Volcano before and after the January 2022 eruption.

A component of this study was the repeat high resolution bathymetry that we used to account for the effect of large topographic changes that occurred during the eruption. We found that before the eruption magma was located in three discrete magma reservoirs, below, north and northwest of the volcano. After the eruption we found two of these reservoirs had become connected and their volume decreased by 30% due to the eruption, which may have contributed to the collapse of the inner part of the volcano. However, a large proportion of high melt content magma remains beneath the volcano.

Our approach is useful to identify understudied or new submarine magmatic systems with the potential to produce similar scale eruptions to that of 15 January 2022.