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1. Origin and Properties of Hydrothermal Tremor at Lone Star Geyser, Yellowstone National Park, USA

   https://doi.org/10.1029/2020JB019711  

   Nayak, Avinash ; Manga, Michael ; Hurwitz, Shaul ; Namiki, Atsuko ; Dawson, Phillip B. ( December 2020 , Journal of Geophysical Research: Solid Earth)

   Geysers are rare geologic features that intermittently discharge liquid water and steam driven by heating and decompression boiling. The cause of variability in eruptive styles and the associated seismic signals are not well understood. Data collected from five broadband seismometers at Lone Star Geyser, Yellowstone National Park are used to determine the properties, location, and temporal patterns of hydrothermal tremor. The tremor is harmonic at some stages of the eruption cycle and is caused by near‐periodic repetition of discrete seismic events. Using the polarization of ground motion, we identify the location of tremor sources throughout several eruption cycles. During preplay episodes (smaller eruptions preceding the more vigorous major eruption), tremor occurs at depths of 7–10 m and is laterally offset from the geyser's cone by ~5 m. At the onset of the main eruption, tremor sources migrate laterally and become shallower. As the eruption progresses, tremor sources migrate along the same path but in the opposite direction, ending where preplay tremor originates. The upward and then downward migration of tremor sources during eruptions are consistent with warming of the conduit followed by evacuation of water during the main eruption. We identify systematic relations among the two types of preplays, discharge, and the main eruption. A point‐source moment tensor fit to low‐frequency waveforms of an individual tremor event using half‐space velocity models indicates averageV_S ≳ 0.8 km/s, source depths ~4–20 m, and moment tensors with primarily positive isotropic and compensated linear vector dipole moments.

    

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2. The 2018 reawakening and eruption dynamics of Steamboat Geyser, the world’s tallest active geyser

   https://doi.org/10.1073/pnas.2020943118  

   Reed, Mara H. ; Munoz-Saez, Carolina ; Hajimirza, Sahand ; Wu, Sin-Mei ; Barth, Anna ; Girona, Társilo ; Rasht-Behesht, Majid ; White, Erin B. ; Karplus, Marianne S. ; Hurwitz, Shaul ; et al ( January 2021 , Proceedings of the National Academy of Sciences)

   null (Ed.)

   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. 

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3. Imaging the Deep Subsurface Plumbing of Old Faithful Geyser From Low‐Frequency Hydrothermal Tremor Migration

   https://doi.org/10.1029/2018GL081771  

   Wu, Sin‐Mei ; Lin, Fan‐Chi ; Farrell, Jamie ; Allam, Amir ( July 2019 , Geophysical Research Letters)

   Old Faithful Geyser in Yellowstone is one of the most well‐known hydrothermal features in the world. Despite abundant geophysical studies, the structure of Old Faithful's plumbing system beneath ~20‐m depth remained largely elusive. By deploying a temporary dense three‐component geophone array, we observe 1–5 Hz low‐frequency hydrothermal tremor originating from Old Faithful's deeper conduit. By applying seismic interferometry and polarization analyses, we track seismic tremor source migration throughout the eruption/recharge cycle. The tremor source drops rapidly to ~80‐m depth right after the eruption and gradually ascends vertically back to ~20‐m depth, coinciding with the previously inferred bubble trap location. Likely excited by the liquid/steam phase transition, the observed tremor source migration can provide new constraints on the recharge process and deeper conduit geometry. Combined with the shallow conduit structure from previous studies, these results provide constraints on the major fluid pathway down to 80‐m depth.

    

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4. Bayesian nonparametric inference for panel count data with an informative observation process

   https://doi.org/10.1002/bimj.201700176  

   Liang, Ye ; Li, Yang ; Zhang, Bin ( February 2018 , Biometrical Journal)

   In this paper, the panel count data analysis for recurrent events is considered. Such analysis is useful for studying tumor or infection recurrences in both clinical trial and observational studies. A bivariate Gaussian Cox process model is proposed to jointly model the observation process and the recurrent event process. Bayesian nonparametric inference is proposed for simultaneously estimating regression parameters, bivariate frailty effects, and baseline intensity functions. Inference is done through Markov chain Monte Carlo, with fully developed computational techniques. Predictive inference is also discussed under the Bayesian setting. The proposed method is shown to be efficient via simulation studies. A clinical trial dataset on skin cancer patients is analyzed to illustrate the proposed approach.

    

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5. Yellowstone's Old Faithful Geyser Shut Down by a Severe Thirteenth Century Drought

   https://doi.org/10.1029/2020GL089871  

   Hurwitz, Shaul ; King, John C. ; Pederson, Gregory T. ; Martin, Justin T. ; Damby, David E. ; Manga, Michael ; Hungerford, Jefferson D. G. ; Peek, Sara ( October 2020 , Geophysical Research Letters)

   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.

    

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