GEODETIC, SEISMIC AND ACOUSTIC MEASUREMENTS OF ERUPTIONS AT LONE STAR GEYSER, YELLOWSTONE NATIONAL PARK, USA

Geysers are intermittently discharging hot springs that are driven by steam and non-condensable gas. They are excellent analogues to volcanoes because both systems are characterized by cyclic phenomena triggered by phase changes. Thus, an investigation of geyser dynamics provides unique opportunities to study a wide range multiphase eruption processes and the geophysical signals they induce in the near field. In September 2010 we carried out a four-day experiment at Lone Star Geyser, about 5 km SSE of Old Faithful Geyser in Yellowstone National Park. Lone Star was selected for the experiment because it is isolated from other geysers, its eruptions are vigorous and voluminous, and its eruption intervals are relatively constant and predictable, occurring approximately every 3 hours. We made geodetic, seismic and acoustic measurements during 32 eruption cycles using a broadband seismometer, a microphone, 5 platform tiltmeters, 3 collimating InfraRed sensors, 2 gravimeters, 2 Light Detection And Ranging (LiDAR) scanners, a Forward Looking InfraRed (FLIR) camera, and high-speed video cameras. The myriad of subsurface processes recorded during the experiment include spatially and temporally variable tilt transients, Long Period (LP) events (seconds), Very-Long-Period (VLP) events (about 2 minute period) that occur at approximately 22 minute intervals, impulsive bubble collapse events (0.25 second duration) with nearly monochromatic frequencies of 20-25 Hz, and pulsating flow instabilities that increase substantially with the onset of ground deformation. These signals provide constraints on shallow hydrothermal processes and allow comparison with signals recorded in more complex volcanic systems where gas-driven and magma-driven processes are often hard to distinguish.