Steamboat Geyser in Yellowstone National Park’s Norris Geyser Basin began a prolific sequence of eruptions in March 2018 after 34 y of sporadic activity. We analyze a wide range of datasets to explore triggering mechanisms for Steamboat’s reactivation and controls on eruption intervals and height. Prior to Steamboat’s renewed activity, Norris Geyser Basin experienced uplift, a slight increase in radiant temperature, and increased regional seismicity, which may indicate that magmatic processes promoted reactivation. However, because the geothermal reservoir temperature did not change, no other dormant geysers became active, and previous periods with greater seismic moment release did not reawaken Steamboat, the reason for reactivation remains ambiguous. Eruption intervals since 2018 (3.16 to 35.45 d) modulate seasonally, with shorter intervals in the summer. Abnormally long intervals coincide with weakening of a shallow seismic source in the geyser basin’s hydrothermal system. We find no relation between interval and erupted volume, implying unsteady heat and mass discharge. Finally, using data from geysers worldwide, we find a correlation between eruption height and inferred depth to the shallow reservoir supplying water to eruptions. Steamboat is taller because water is stored deeper there than at other geysers, and, hence, more energy is available to power the eruptions.

Geyser and volcano monitoring suffer from temporal, geographic, and instrumental biases. We present a recording bias identified through multiyear monitoring of Steamboat Geyser in Yellowstone National Park, USA. Eruptions of Steamboat are the tallest of any geyser in the world and they produce broadband signals at two nearby stations in the Yellowstone National Park Seismograph Network. In winter, we observe lower eruption signal amplitudes at these seismometers. Instead of a source effect, we find that environmental conditions affect the recorded signals. Lower amplitudes for 23–45 Hz frequencies are correlated with greater snow depths at the station 340 m away from Steamboat, and we calculate an energy attenuation coefficient of 0.21 ± 0.01 dB per cm of snow. More long‐term monitoring is needed at geysers to track changes over time and identify recording biases that may be missed during short, sporadic studies.

The active Yellowstone hydrothermal system results from shallow groundwater interacting with heat from a deeper magmatic system (Smith & Siegel, 2000). Variations in heating rate, conduit geometry, and water influx control the exact surface manifestation of each hydrothermal feature (e.g., Namiki et al., 2016;Rinehart, 1980;Toramaru & Maeda, 2013). An eruptive geyser is composed of a long narrow subsurface conduit with constrictions that inhibit effective fluid convection, keep the hydrostatic pressure high, and suppress the liquid-to-vapor phase transition. With continued heat accumulation, the system eventually reaches a critical condition where a perturbation in pressure initiates a phase transition between liquid and vapor, and the resulting volume expansion will vigorously eject a liquid-vapor mixture into the air (White, 1967). A hot spring, in contrast, is a steady-state system where both heat and water influx and outflux remain balanced. At least one hot spring in New Zealand (Iodine Pool; Legaz et al., 2009) and several features in Yellowstone, however, mysteriously "thump" either periodically or episodically suggesting their heat input and output are not completely balanced and thus that they share some similarities with geysers. Doublet Pool, a hot spring composed of a main and an auxiliary pool connected by a narrow channel at the surface, in the Upper Geyser Basin (Figure 1), is famous for its persistent, approximately periodic thumping cycle (Bryan, 2008). During active thumping, the water level in the main pool vibrates visibly, ground shaking can be felt, and thumping can be heard on a quiet day near the pool. While periodic thumping resembles a geyser's eruption pattern, the thumping at Doublet Pool never evolves into an active eruption.Many previous geophysical studies, including seismic investigations aimed at understanding the eruption dynamics of geysers, have recorded hydrothermal tremor connected to the liquid/vapor phase transition processes (Kedar et al., 1998(Kedar et al., , 1996Wu et al., 2017). The spatiotemporal distribution of the tremor sources has been used to illuminate the subsurface conduit system and infer the physical state of the geyser system during each stage of the eruption cycle (