Mushy magma beneath Yellowstone

A recent prospective on the Yellowstone Caldera discounts its explosive potential based on inferences from tomographic studies which suggests a high degree of crystallization of the underlying magma body. In this study, we show that many of the first teleseismic P-wave arrivals observed at seismic stations on the edge of the caldera did not travel through the magma body but have taken longer but faster paths around the edge. After applying a number of waveform modeling tools, we obtain much lower seismic velocities than previous studies, 2.3 km/sec (V-p) and 1.1 km/sec (V-s). We estimate the physical state of the magma body by assuming a fluid-saturated porous material consisting of granite and a mixture of rhyolite melt and water and CO2 at a temperature of 800 degrees C and pressure at 5 km (0.1 GPa). We found that this relatively shallow magma body has a volume of over 4,300 km(3) and is about 32% melt saturated with about 8% water plus CO2 by volume. Citation: Chu, R., D. V. Helmberger, D. Sun, J. M. Jackson, and L. Zhu (2010), Mushy magma beneath Yellowstone, Geophys. Res. Lett., 37, L01306, doi: 10.1029/2009GL041656.