Anatomy of Old Faithful
July 18 ” Anatomy Of Old Faithful And Yellowstone Volcano Plumbing” Presented by Bob Smith, Univ. of Utah, Dept Geology & Geophysics.
My presentation shows the culmination of more than a decade of research on the Yellowstone volcanic system employing seismic tomography, akin to CAT-scans, creating images from mantle depths of hundreds of km through the volcanic crust and evaluating the 3D structure and time-dependent properties of the Old Faithful geyser. Our results show that magma comes from deep in the earth’s Yellowstone mantle plume, ~1000 km deep, rising into two crustal magmatic bodies the shallowest, 5-16 km, drives Yellowstone’s extensive volcano and hydrothermal system. To extend these studies to high-resolution seismic imagery of the Upper Geyser Basin, we employed the recent availability of new arrays in November 2015 and 2016 of 133 seismographs inn collaboration with Yellowstone National Park and the University of Texas El Paso, and acquired over 5TB of data. This unprecedented dense seismic array provided a unique capability for recording environmental seismic signals, delineating in the 3D hydrothermal structure and time-dependent fluid flow. The seismic array recorded unexpected hydrothermal seismic signals attributed to fluid-flow through the hydrothermal body as well as those that do not appear to be related to any individual surface feature. Old Faithful geyser eruptions surprisingly have a very small seismic signal compared to large amplitude 45-minute pre-eruption harmonic tremor signals, likely due to collapsing gas bubbles associated with the subsurface plumbing system. We also discovered an absence of seismic signal for ray pays crossing west through the geyser which suggested a shallow subsurface low velocity body interpreted to be the unexpectedly large Old Faithful hydrothermal reservoir beneath the western part of the geyser apron and extending a kilometer or more westward beneath the Old Faithful Inn and surrounding developed area. Another of the more interesting results were signals consisting of regular spaced harmonic tremors every ~ 38 minutes on Geyser Hill that are interpreted to be associated with exsolution of CO2 and other gases rising in Doublet Pool. Interestingly our array of course also records humans walking around Old Faithful and we can track them coming and going before and after the eruptions. In addition I will show recently found old video footage of a TV camera lowered over 20 m into the throat of Old Faithful. Note that Old Faithful project is the beginning of University of Utah research and seismic monitoring of Yellowstone’s major hydrothermal systems.