Fig. 3. Storage pressures estimated by the rhyolite-MELTS geobarometer (circles) and by the H₂O-CO₂ content of quartz-hosted MIs (squares).

Each circle represents the equilibration pressure calculated by rhyolite-MELTS using the average glass composition of one pumice clast, and different shades indicate statistically distinct compositional groups within some units. Note that, if the gray pumice from Osumi were not quartz saturated, the pressures are maxima. The ±1σ error bar on the left side shows the 38-MPa uncertainty in pressure due to analytical uncertainty alone, as calculated by Pitcher et al. (13) using the same instrument and procedure. Each square represents the saturation pressure of one MI, calculated using MagmaSat (31). Error bars are 1σ propagated from uncertainty in thickness and in the terms of the equations used to calculate H₂O and CO₂ contents from FTIR spectra. Approximate depth is shown on the right, assuming a crustal density of 2.7 g cm⁻¹.