Picking Up Steam

The renewed activity of the world’s tallest geyser, Steamboat Geyser (Yellowstone National Park) in 2018, offers the opportunity to utilize long-term continuous infrasound and low-frequency acoustic monitoring to quantify eruptive behaviors. Eruption parameters including onset timing, duration, phase transitions between steam and water, instantaneous sound intensity, eruptive power, energy content, and spectral character, may be used to characterize individual eruption styles and reveal eruption trends. I interpret the character of the acoustic radiation through corroboration of first-hand observations and time-lapse video. I find that infrasound (acoustic energy below 20 Hz) is a particularly effective tool for tracking the evolving eruption style of Steamboat and complements other monitoring techniques data streams including seismicity, outflow temperature, and eyewitness observations. Our experiment produced a 13-month acoustic chronology of Steamboat Geyser, consisting of 23 major eruptions and weeks of precursory minor activity. I identify common trends in Steamboat’s eruptive behaviors. Typically, a major eruption starts with a short (< 1 hour) water-dominated phase, during which jetting of water reaches maximum elevations of 120m. Following the water phase, the eruption transitions to a steam-dominated phase that persists for over 12 hours post-eruption onset. Signal structure in the low infrasound bands (0.5 to 2 Hz) may be used to identify water-to-steam phase transitions in the eruption column. The long-term infrasound record is useful for statistical analysis of eruptions and their timing. Although median major eruption intervals are about 10 days there are some outliers. Unlike other fountain-type geysers whose plumbing system is more isolated, there does not appear to be a relationship between event duration and inter-event timing.