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In the past century, most eruptions of Steamboat Geyser in Yellowstone National Park's Norris Geyser Basin were mainly clustered in three episodes: 1961–1969, 1982–1984, and ongoing since 2018. These eruptive episodes resulted in extensive disturbance to surrounding trees. To characterize tree response over time as an indicator of geyser activity adjustments to climate variability, aerial and ground images were analyzed to document changes in tree coverage around the geyser since 1954. Radiocarbon dating of silicified tree remnants from within 14 m of the geyser vent was used to examine geyser response to possible variations in decadal to centennial precipitation patterns. We searched for atypical or absent growth rings in cores from live trees in years associated with large geyser eruptions. Photographs indicate that active eruptive phases have adversely affected trees up to 30 m from the vent, primarily in the dominant downwind direction. Radiocarbon dates indicate that the geyser formed before 1878, in contrast to the birthdate reported in historical documents. Further, the ages of the silicified trees cluster within three episodes that are temporally correlated with periods of relative drought in the Yellowstone region during the 15th–17th centuries. The discontinuous growth of trees around the geyser suggests that changes in eruptive patterns occur in response to decadal to multidecadal droughts. This inference is supported by the lack of silicified specimens with more than 20 annual rings and by the existence of atypical or missing rings in live trees during periods of extended geyser activity. Plain Language Summary: Steamboat Geyser, in Yellowstone National Park's Norris Geyser Basin, has the tallest eruptions among the world's active geysers. To examine whether eruptions impact trees in the vicinity of the geyser, we analyzed aerial photos acquired since 1954 which indicate that prior periods of frequent eruptions have adversely affected trees up to 30 m from the vent, primarily in the dominant wind direction. To examine if the limited availability of water may have caused the geyser to stop erupting in past centuries, we dated silicified tree remnants with radiocarbon. Results suggest that trees were growing near Steamboat during three periods when the geyser was not erupting because of prolonged droughts in the Yellowstone region during the 15th–17th centuries. This inference is supported by observations that none of the silicified tree specimens had more than 20 annual rings, implying that the trees did not grow for long periods, and by the presence of atypical or missing rings in live trees during periods of geyser activity. Key Points: Aerial photos indicate that recent eruptive phases of Steamboat Geyser have adversely impacted trees up to 30 m from the vent14C dates of silicified trees cluster in three periods that temporally correlate with regional droughts during the 15th–17th centuriesAtypical or absent tree‐rings suggest that prolonged eruption episodes impacted tree growth around Steamboat Geyser [ABSTRACT FROM AUTHOR]

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. Plain Language Summary: What we learn about geysers and volcanoes depends on when, where, and how we are able to monitor them. Here we present a case study of how seasonal changes affect data recorded on a seismometer, which is an instrument that measures ground motion. The world's tallest geyser, Steamboat Geyser in Yellowstone National Park, has intense eruptions that eject a mixture of water and steam. The eruptions are powerful enough to cause tiny ground motions from sound waves that begin in the air and then transfer into the ground. In the winter, we see smaller ground motions at two nearby seismometers. This might imply that Steamboat's eruptions are weaker in the winter; however, winter in Yellowstone comes with snow, and snow is good at absorbing sound wave energy. We find that smaller ground motions occur when snow depths are greater, and that the strength of ground motions should not be used to directly compare eruption intensity. Few geysers around the world are monitored with scientific equipment for long periods of time. Our result highlights the need for more of this type of monitoring so that we can identify biases that may be missed during shorter investigations. Key Points: Seismic signals from Steamboat Geyser eruptions contain ground‐coupled airwaves at distances up to 2.2 kmSnow dampens airwave arrivals leading to lower apparent signal amplitudes in winterInterpretation of eruption signals at both geysers and volcanoes should take changing environmental factors into account [ABSTRACT FROM AUTHOR]

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. By linking recorded hydrothermal tremor with active thumping, we determine the onset and end of thumping, and the duration of silence between each thumping cycle. The silence interval decreased from around 30 min before November 2016 to around 13 min in September 2018. This change followed unusual thermal activity on the surrounding Geyser Hill. On a shorter time scale, wind‐driven evaporative cooling can lengthen the pre‐thumping silence interval. Based on energy conservation, we determine the heating rate and heat needed to initiate thumping to be 3–7 MW and ∼6 GJ, respectively. Plain Language Summary: Doublet Pool is a hot spring in Yellowstone that has thumping cycles in which bubbles collapse underwater, producing vibrations that people can hear and feel. We placed two seismometers next to Doublet Pool to time its thumping cycles and analyze how they change over time. Strong winds lengthen the thumping interval by removing energy through the pool's surface. Over time scales of months to years, the duration of thumping cycles is controlled by changes in heating and pressurization from the hydrothermal system beneath Doublet Pool. Key Points: We observe short and long‐term variations in the thumping cycle recorded by two geophones deployed between 2015 and 2021On hourly to daily time scales, the time to initiate thumping correlates with the wind speedOn monthly to yearly time scales, cycle variations reflect changes in heating rate that vary by a factor of about 2 [ABSTRACT FROM AUTHOR]

To characterize eruption activity of the iconic Old Faithful Geyser in Yellowstone National Park over past centuries, we obtained 41 new radiocarbon dates of mineralized wood preserved in the mound of silica that precipitated from erupted waters. Trees do not grow on active geyser mounds, implying that trees grew on the Old Faithful Geyser mound during a protracted period of eruption quiescence. Rooted stumps and root crowns located on higher parts of the mound are evidence that at the time of tree growth, the geyser mound closely resembled its current appearance. The range of calibrated radiocarbon dates (1233–1362 CE) is coincident with a series of severe multidecadal regional droughts toward the end of the Medieval Climate Anomaly, prior to the onset of the Little Ice Age. Climate models project increasingly severe droughts by mid‐21st century, suggesting that geyser eruptions could become less frequent or completely cease. Plain Language Summary: The rarity of natural geysers reflects the special conditions needed for their formation, including an abundant supply of water. Therefore, severe droughts of extended duration could have led to large variations in the frequency and intensity of geyser eruptions. To characterize potential changes in eruption activity of the iconic Old Faithful Geyser in Yellowstone National Park over past centuries, we collected mineralized wood samples from its mound and used radiocarbon to date when these trees grew. Because trees do not live on active geyser mounds, we infer that the trees grew during a protracted period without eruptions. The dated fossil trees are from the thirteenth and fourteenth centuries during a time with severe multidecadal droughts in the region. Because climate models forecast increasingly severe droughts by mid‐21st century, geyser eruptions could become less frequent or completely cease. Key Points: Yellowstone's Old Faithful Geyser stopped erupting for many decades in response to severe multidecadal regional droughts in the thirteenth centuryWood is preserved for over 650 years because silica‐rich alkaline waters deposit amorphous opal on cellular filmsBecause climate models project increasingly severe droughts by mid‐21st century, eruptions could become less frequent or completely cease [ABSTRACT FROM AUTHOR]

Siliceous sinter is formed by biogenic and abiogenic opal deposition around hot springs and geysers. Using Structure-from-Motion photogrammetry we generated three-dimensional models of Giant and Castle Geysers from the Upper Geyser Basin of Yellowstone National Park. We use these models to calculate an approximate mass of sinter for each (~2 and ~ 5 kton, respectively) and estimate a range of plausible long-term deposition rates for Castle Geyser (470 to 940 kg·yr−1). We estimate ~2% of the silica discharged from Castle Geyser is deposited as sinter in the cone and proximal terraces. We collected 15 sinter samples following the stratigraphy of each geyser from the older terrace to the younger cone and examined them using a variety of analytical methods. We find that young opaline sinter with high water content (<12 wt% from loss on ignition) contains higher concentrations of major and trace elements, notably As, Sb, Rb, Ga and Cs, relative to older dehydrated sinter. Rare earth element (REE) concentrations in sinter are 2–3 orders of magnitude higher than in the thermal water from which they are deposited. Sinter deposits are enriched in light REE, Gd and Yb when normalized to concentrations in thermal water and enriched in Eu, Tm, and Yb when normalized to the underlying rhyolite. Sinter samples with the highest REE concentrations are also enriched in organic material, implying either microbial uptake of REE, or that organic molecules are efficient ligands that form metal complexes. • We generated 3-D models of geysers in Yellowstone and calculate their volumes. • Dehydration and mineralogy change with increasing silica sinter (geyserite) age. • Large chemical variations in geyserite with increasing age. • Sinters are enriched in antimony, cesium, gallium and rare earth elements (REE). • REE concentrations are 2–3 orders of magnitude higher than in thermal water. [ABSTRACT FROM AUTHOR]

We describe a new effort to date hydrothermal silica sinter deposits (geyserite) from the Upper Geyser Basin of Yellowstone National Park using 14C of co-deposited organic matter, U-series and cosmogenic 10Be methods. A majority of the samples were collected from stratigraphic sections, mainly at Riverside, Giant, and Castle Geysers. Ages obtained from 41 14C analyses range from modern to 12.1 cal ka BP. Nearly all the 14C ages show inconsistencies with their stratigraphic positions, and several replicate 14C analyses from the same sample result in significantly different ages. The δ13C values of the organic material in the sinter range from −26.6‰ to −12.7‰. The more enriched values are attributed to microbial fixation of dissolved inorganic carbon (DIC), which has heavier δ13C values and is 14C-depleted relative to atmospheric CO 2 , leading to an apparent older age. U-series analyses on 4 samples yielded ages between 2.2 and 7.4 ka. Large 230Th/U age uncertainties in the sinter, due to low uranium concentrations along with elevated 232Th and associated initial 230Th, make these ages imprecise for use on Holocene deposits. A single cosmogenic 10Be exposure age of 596 ± 18 ka is considerably older than the age of underlying rhyolite and is thus unreliable. This apparent old age results from contamination by meteoric 10Be trapped in the opal that overprints the very small amount of cosmogenic 10Be. By presenting the problems we encountered and discussing their probable cause, this paper highlights the difficulty in obtaining reliable, high-precision geochronological data necessary to use sinter deposits as paleoenvironmental and paleo-hydrothermal archives. • We identify challenges in determining reliable ages of hydrothermal sinter deposits. • We apply radiocarbon, uranium-series and cosmogenic beryllium dating methods. • Radiocarbon ages can be biased by microbial fixation of dissolved inorganic carbon. • Uranium-series uncertainties are too large for precise dating of Holocene sinter. • Beryllium-10 exposure ages cannot be used for dating sinter from the Holocene. [ABSTRACT FROM AUTHOR]

Hydration fronts penetrate 50-135 µm into glassy rhyolite embayments hosted in quartz crystals from the Mesa Falls Tuff in the Yellowstone Plateau volcanic field. The hydration fronts occur as steep enrichments that reach 2.4 ± 0.6 wt% H2O at the embayment opening, representing much higher values than interior concentrations of 0.9 ± 0.2 wt% H2O. Molecular water accounts for most of the water enrichment. Water speciation indicates the hydration fronts comprise absorbed meteoric water that modified the original magmatic composition of the rhyolitic glass. We used finite difference diffusion models to demonstrate that glass rehydration was likely produced over a few decades as the ignimbrite cooled. Such temperatures and time scales are consistent with rare firsthand observations of decadal hydrothermal systems associated with cooling ignimbrites at Mount Pinatubo (Philippines) and the Valley of Ten Thousand Smokes (Alaska). [ABSTRACT FROM AUTHOR]