Linking Geophysical Properties to Dynamic and Structural Components of Spouter Geyser

Abstract:

Understanding geophysical properties within and surrounding geyser systems is essential in translating the measured geophysical response to a geological image. Our goal is to correlate measured geophysical responses to subsurface sinter, vapor movement, and water content to help spatially and temporally constrain geyser systems. To correlate the response to a geologic image, 2D time-lapse DC resistivity, 2D seismic refraction, time-lapse transient electromagnetics (TEM), and time-lapse surface nuclear magnetic resonance (sNMR) datasets were collected at Spouter Geyser in Black Sand Basin in Yellowstone National Park. These data provide insight into various physical properties that can be correlated to structural components through a comprehensive interpretation.

The subsurface geyser structure is formed as amorphous silica sinter precipitates out of the supersaturated hydrothermal waters. The silica precipitate decreases the porosity and volume of the electrically conductive hydrothermal water in the pores. This increases the resistivity response measured by the DC resistivity and TEM in areas of the geyser structure. The sinter precipitate correlating to the increased electrical resistivity response cements the glacial till, expecting to increase the seismic velocity response as a more coherent structure is formed. In addition, electrically resistive vapor (CO₂, H₂O_(g), N₂) moving through the system further increases the resistivity response and illuminates the structure in the time-lapse DC resistivity and time-lapse TEM images. The sensitivity of the electrical resistivity to the sinter deposits and vapor flux is established through a 2D DC resistivity forward modeling exercise validating the interpretations outlined above.

Time-lapse sNMR also provides information about the subsurface structure by imaging the water content with depth. Water content changes highlight areas of the structure as water is expelled from the system during the eruption. Additionally, the percent water content change through the eruption cycle along with a measure of the volume of water erupted provides an estimate of the total volume of water in the geyser structure.