Investigating the Doublet Pool Thumping Cycle in Yellowstone National Park through temporal nodal deployments

Doublet Pool, which is located in the Upper Geyser Basin of Yellowstone National Park, is an active hydrothermal feature. Different from hot springs with a steady discharge, the pool produces distinctive thumps from collapsing steam bubbles about every half hour that can be heard and felt. To understand thermodynamic parameters that govern thumping and their sensitivity to external factors, we performed a recurring temporary multiple-year passive seismic experiment between 2015 and 2021. By linking recorded hydrothermal tremors with active thumping, we determine the onset, end, and interval of each thumping cycle. We observe both short-term and long-term thumping variations. On the time scale of minutes to hours, we find the silence interval between periods of thumping increases with increasing wind speed. On the time scale of months to years, the time between thumping episodes decreased from nearly 30 minutes before November 2016 to nearly 13 minutes in September 2018. This change followed unusual thermal activity on the surrounding Geyser Hill that featured a rare major eruption of Ear Spring on September 15, 2018, for the first time since the 1950s. By using an evaporative cooling model combined with temperature and pressure measurements in the pool, we determine the heating rate and heat needed to initiate the thumping. This study illustrates the value of continuous monitoring of active hydrothermal features through a multi-parameter approach. A better understanding of how internal and external factors control the surficial manifestations of the geothermal system could potentially lead to improved hazard mitigation associated with hydrothermal explosions.