THUMPING CYCLE VARIATIONS OF DOUBLET POOL IN YELLOWSTONE NATIONAL PARK, USA

Doublet Pool is an active hydrothermal feature in Yellowstone National Park, USA. Approximately every half hour, it thumps for about 10 min due to bubbles collapsing at the base of the pool. To understand its thermodynamics and sensitivity to external factors, we performed a recurring multiple-year passive seismic experiment complemented by visual, pressure, and temperature measurements in the pool. We link recorded hydrothermal tremor with active thumping, and are able determine the onset and end of thumping, and the duration of silence between each thumping cycle. This silence interval decreased from around 30 min prior to November 2016 to around 13 min in September 2018. This change followed unusual thermal activity on the surrounding Geyser Hill. In May 2023 we document a large change in the silence interval that recovers exponentially over a period of a few days. On a shorter time scale, evaporative cooling by wind can lengthen the pre-thumping silence interval. Based on a model for energy conservation, we find a heating rate of 3–7 MW and that the accumulated heat needed to initiate thumping is ∼6 GJ.