Magma chamber volume is critical for volcano hazards assessment and forecasting. Standard geodetic methods constrain volume change, not the total volume. Here, we show that the deformation response of the magma chamber to trapdoor faulting events at Sierra Negra volcano, Galapagos, depends on the product of the absolute chamber volume and the magma compressibility. Bubble‐free magma provides the lower limit on compressibility, thus an upper bound on the chamber volume of 13.6–20.6 km3, depending on fault dip. We estimate an upper limit on compressibility using a conduit model relating volatile content to lava fountain height, compared with observations from the 2005 eruption, constrained by volatile content of olivine melt inclusions. This yields a lower bound on chamber volume roughly half the upper bound. We find that the best fitting trapdoor fault is near‐vertical; reverse dips are slightly favored (88°).

The supply, storage, and subsurface transport of magma are some of the most fundamental, yet least understood volcanic processes (Poland et al., 2014). These processes, along with eruptive dynamics, are modulated by the geometry and nature of the pathways connecting magmatic reservoirs (Keating et al., 2008). The geometry and dimensions of individual pathways can be constrained by inverting surface deformation with continuum mechanics based models (e.g., Owen et al., 2000;Montagna & Gonnermann, 2013). However, with multiple reservoirs and a network of magmatic pathways, estimating the dimensions of each pathway directly from deformation can be challenging. Because magma flux is proportional to the hydraulic conductivity of the pathway, and pressure change in a reservoir depends on magma flux, time dependent deformation associated with each reservoir may reveal the connectivity of a multi-reservoir system (e.g., Bato et al., 2018;Le Mével et al., 2016;Reverso et al., 2014). Here we demonstrate that, physics-based models, coupled with Bayesian inversion, can synthesize multi-reservoir conceptual models with geodetic measurements to quantitatively constrain the hydraulic connectivity of magmatic systems.Despite decades of research, the nature of Kīlauea's summit reservoirs and their connectivity to the East Rift Zone remains enigmatic (we reserve "East Rift Zone" for the geographic location and "ERZ" for the reservoir active in the observation period). Efforts to interpret summit deformation in terms of simple reservoir models yielded diverse reservoir locations and geometries (e.g., Baker & Amelung, 2012;Fiske & Kinoshita, 1969). Although modeled reservoirs cluster into two groups -a shallow Halema'uma'u (HMM) and a deeper South Caldera (SC) reservoir (e.g., Cervelli & Miklius, 2003;Poland et al., 2014), it has been suggested that the summit system represents a single irregularly shaped reservoir (Dieterich & Decker, 1975;Ryan, 1988). This ambiguity arises because deformation signals associated with these reservoirs are almost always of the same sign. The configuration of magmatic pathways connecting Kīlauea's summit reservoirs and ERZ is also elusive. Cervelli and Miklius (2003) argue that an "Γ shaped" pathway connecting the deeper SC reservoir to the shallower HMM reservoir, and then to ERZ, is required to explain the drainage Abstract 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. ...

In this article, we investigate the link between closure phase and the observed systematic bias in deformation modeling with multi-looked SAR interferometry. Multi-looking or spatial averaging is commonly used to reduce stochastic noise over a neighborhood of distributed scatterers in InSAR measurements. However, multi-looking may break consistency among a triplet of interferometric phases formed from three acquisitions leading to a residual phase error called closure phase. Understanding the cause of closure phase in multi-looked InSAR measurements and the impact of closure phase errors on the performance of InSAR time-series algorithms is crucial for quantifying the uncertainty of ground displacement time-series derived from InSAR measurements. We develop a model that consistently explains both closure phase and systematic bias in multi-looked interferometric measurements. We show that nonzero closure phase can be an indicator of temporally inconsistent physical processes that alter both phase and amplitude of interferometric measurements. We propose a method to estimate the systematic bias in the InSAR time-series with generalized closure phase measurements. We validate our model with a case study in Barstow-Bristol trough, California. We find systematic differences on the order of cm/year between InSAR time-series results using subsets of varying maximum temporal baseline. We show that these biases can be identified and accounted for.