Constraints on Absolute Magma Chamber Volume From Geodetic Measurements of Trapdoor Faulting at Sierra Negra Volcano, Galapagos

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