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Steamboat blows

Steamboat Geyser in the steam-phase of an eruption on June 4, 2018, in Norris Geyser Basin at Yellowstone National Park. In 2018 it erupted a record-setting 32 times. The previous record was 29 eruptions set in 1964.

Yellowstone Caldera Chronicles is a weekly column written by scientists and collaborators of the Yellowstone Volcano Observatory. This week's contribution is from Michael Poland, geophysicist with the U.S. Geological Survey and Scientist-in-Charge of the Yellowstone Volcano Observatory.

We're excited to be back. Even though core USGS and NPS staff remained at work to monitor volcanic activity in Yellowstone (and scientists at nonfederal institutions, like the University of Utah, remained at work throughout), our weekly article, Yellowstone Caldera Chronicles, was forced into a hiatus. Now that the lapse in appropriations is finally behind us, we can resume publishing.

Even though we missed the start of the new year, we'd like to provide you with a "2018 year in review" as our first Yellowstone Caldera Chronicles article of 2019. If you were a geyser watcher, it was surely one of the most memorable years in a long time.

Geysers were the story of 2018 — especially Steamboat geyser in the Norris Geyser Basin. Steamboat is the tallest active geyser in the world, but major water eruptions are usually rare, sometimes with years between events. In 2018, however, it erupted a record-setting 32 times! The previous record was 29 eruptions in 1964, and the geyser was quite active in the 1960s and early 1980s, so the recent activity is not unprecedented.

Most geysers in Yellowstone are like Steamboat — they do not erupt on regular schedules (Old Faithful is an exception). Certainly, the spate of activity was an exciting sight for the millions of visitors to Yellowstone National Park in 2018, and many tales of Steamboat eruptions graced social media this past summer.

The first Steamboat eruption of 2018 occurred on March 15. Following two additional eruptions in April and one on May 4, University of Utah and Yellowstone National Park scientists deployed seismic sensors around the geyser. The instruments recorded data through four eruptions before they were collected on June 4 (immediately following an eruption).

At Old Faithful, data like these have helped to map the plumbing system and eruptive patterns of that geyser in unprecedented detail. Hopefully, the data collected from Steamboat will similarly illuminate how that intermittent geyser works.

Steamboat wasn't the only Yellowstone geyser showing enhanced levels of activity in 2018. Giant geyser, in the Upper Geyser Basin (not far from Old Faithful), also erupted repeatedly (29 times, according to the GeyserTimes database). The last time Giant was so active was in 2007-2008, when it erupted several dozen times.

There was also a rare eruption of Ear Spring in the Upper Geyser Basin in September (an eruption that brought decades of human-generated garbage to the surface, like coins, a cinder block, and even a baby's pacifier), which was associated with the formation of a new thermal feature that forced the closure of a boardwalk. University of Utah scientists also responded to that event with a deployment of seismic sensors.

We don't know why intermittent geysers experience periods of heightened activity separated by months to years of dormancy or very infrequent eruptions. It is possible that the availability of water in the subsurface is a contributing factor — Yellowstone has experienced especially heavy precipitation in recent years.

In fact, recent research suggests that subsurface water plays a role in earthquake activity, as well. A comprehensive analysis of the Maple Creek earthquake swarm, which produced more than 2,400 located earthquakes a few miles north-northeast of West Yellowstone between June and September 2017, was completed in the past year. The results of the study, documented in a recent Yellowstone Caldera Chronicles article, suggest that water moving through the subsurface caused existing faults to rupture, which in turn resulted in more fluid movement, creating a feedback cycle. Water may actually be the cause of many earthquake swarms at Yellowstone.

Speaking of earthquakes, 2018 was a pretty average year for Yellowstone in that respect. The University of Utah Seismograph Station, which is responsible for the operation and analysis of the Yellowstone Seismic Network, located 2,007 earthquakes in Yellowstone during 2018. This is right on par with the average of 1,500-2,500 earthquakes per year for the region. The year did start quickly in terms of earthquakes, with a flare-up of 2017's Maple Creek swarm resulting in more than 700 located earthquakes in February 2018, but that was the only month with more than 200 located events.

The February seismicity was probably a continuation of the 2017 Maple Creek swarm, and that area is historically one of the most seismically active regions of the park. Overall in 2018, there were 21 seismic swarms accounting for 1,289 located earthquakes (64 percent of the total number of events).

The largest earthquakes of 2018 were a pair of 3.1 events that occurred during the February swarm. Only three events in the Yellowstone region were reported felt during the year.

There were no significant changes in ground deformation in and around Yellowstone during 2018. The area near Norris Geyser Basin continued to rise, while all stations in the caldera continued to subside, in both cases by about 2 centimeters (less than 1 inch) over the entire year. These patterns continue the trends that have been ongoing since 2015.

We hope that you all had a relaxing and pleasant holiday season and an enjoyable start to the new year. From all the members of the Yellowstone Volcano Observatory consortium, a belated Happy New Year.