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Dr. Jake Jordan: A mechanism for enhancing long period eruptive precursors at silicic volcanoes

Wednesday, October 28, 2020, 11:30am - 12:30pm

We are pleased to be joined by Dr. Jake Jordan, a postdoctoral scientist at Rice University (http://jake-jordan.org). Dr. Jordan will be speaking on "A mechanism for enhancing long period eruptive precursors at silicic volcanoes". See summary below.

ABSTRACT: Simultaneous episodes of elevated seismic activity, degassing and ground deformation have been observed with remarkably regular frequency at a range of silicic volcanoes prior to periods of edifice growth and eruptions. For example, Mount Pinatubo in the Philippines and Soufriere Hills Volcano in Montserrat displayed such cyclical behavior close to major eruptive events in 1991 and 1996--1997, respectively, with periods of about ten hours at both volcanoes.  In this study, we explore the hypothesis that the frequency of the aforementioned eruptive precursors for elevated volcanic activity is set by pulses of bubbly, gas-rich magma.  We construct a theoretical model in which a bubbly, viscous magma rises and decompresses near the subsurface. During ascent, gas bubbles grow and water exsolves from the magma. Our theory predicts a range of growth rates for pulses of bubbly magma as a function of their wavelength. The fastest growing pulses form "porosity waves" which induce periodic behavior observed as eruptive precursors. The fastest growing porosity waves are determined by the balance between the forces arising from the growth of gas bubbles, exsolution of water and compaction from the magma overburden. Although gas exsolution decreases the growth rate of gas waves, a significant dissolved water content in the magma and a sluggish exsolution results in a filtering effect that favors long wavelength porosity waves.  The predicted wavelengths for these waves in numerical experiments and analysis are commensurate with the long period eruptive precursors observed at Mount Pinatubo and Soufriere Hills Volcano.