Geophysical Investigation of the Yellowstone Hydrothermal System

Yellowstone National Park hosts over 10,000 thermal features (e.g. geysers, fumaroles, mud pots, and hot springs), yet little is known about the hydrothermally active zones hundreds of meters beneath the features. Transient electromagnetic (TEM) soundings and 2D direct current (DC) resistivity profiles show that hydrothermal alteration at active sites have a higher electrical conductivity than the surrounding hydrothermally inactive areas. For that reason, airborne TEM is an effective method to characterize large areas and identify hydrothermally active and inactive zones using electrical conductivity. Here we present results from an airborne TEM survey acquired jointly by the U.S. Geological Survey and the University of Wyoming in November, 2016. We integrate resistivity from the airborne electromagnetic (EM) survey with research drillhole data and rock physics models to investigate the controls on electrical conductivity in the upper few hundreds of meters of the Yellowstone hydrothermal system. Resistivities in Yellowstone are the product of complex variations of lithology, temperature, salinity, clay content, and hydrothermal fluids. Results show that the main drivers in lowering the high resistivitiy of volcanic rocks are water saturation and hydrothermal alteration. Salinities are not significantly elevated in Yellowstone and temperature is not a first order affect.