From August 2018 to May 2019, Kīlauea’s summit exhibited unique, simultaneous, inflation and deflation, apparent in both GPS time series and cumulative InSAR displacement maps. This deformation pattern provides clear evidence that the Halema‘uma‘u (HMM) and South Caldera (SC) reservoirs are distinct. Post-collapse inflation of the East Rift Zone (ERZ), as captured by InSAR, indicates concurrent magma transfer from the summit reservoirs to the ERZ. We present a physics-based model that couples pressure-driven flow between these magma reservoirs to simulate time dependent summit deformation. We take a two-step approach to quantitatively constrain Kīlauea’s magmatic plumbing system. First, we jointly invert the InSAR displacement maps and GPS offsets for the location and geometry of the summit reservoirs, approximated as spheroidal chambers. We find that HMM reservoir has an aspect ratio of ~1.8 (prolate) and a depth of ~2.2 km (below surface). The SC reservoir has an aspect ratio of ~0.14 (oblate) and a depth of ~3.6 km. Second, we utilize the flux model to invert GPS time series from 8 summit stations. Results favor a shallow HMM-ERZ pathway an order of magnitude more hydraulically conductive than the deep SC-ERZ pathway. Further analysis shows that the HMM-ERZ pathway is required to explain the deformation time series. Given high-quality geodetic data, such an approach promises to quantify the connectivity of magmatic pathways between reservoirs in other similar volcanic systems.

Magma chamber volume is critical for volcano monitoring and forecasting. Standard geodetic methods cannot constrain the total volume, only the change in volume. Here, we show that stress perturbations associated with trapdoor faulting allow bounds to be placed on the total chamber volume at Sierra Negra volcano, in the Galapagos. The deformation response of the magma chamber to faulting depends on both the absolute chamber volume and the compressibility of the magma. Bubble-free magma provides the lower limit on compressibility, thus an upper bound on the chamber volume of 13.6 to 20.6 km3, depending on fault dip. We estimate an upper limit on compressibility using a conduit model relating volatile content to lava fountain height, which is compared with observations from the 2005 eruption, constrained by volatile content of olivine melt inclusions. This yields a lower bound on chamber volume of 0.5 times the upper bound.