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, Shaul Hurwitz and Blaine McCleskey, research hydrologists with the U.S. Geological Survey, and Erin White, Park Hydrologist at Yellowstone National Park.

During June 10–13, 2022, an “atmospheric river” event—a system of warm and extremely wet air that usually originates in the tropics—struck the Yellowstone National Park region. More than 2–3 inches of rain, combined with warm overnight temperatures, melted a large amount of snow that had not previously melted because of a cool and snowy spring. The result was historic flooding.

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News channels and social media are full of images and videos showing the devastating impacts of these floods. Some communities adjacent to Yellowstone National Park, like Gardiner and the area of Cooke City in southern Montana, were completely isolated by floodwaters and damage to roads. Power was lost in many places, as was access to clean drinking water. The north and northeast entrance roads in Yellowstone are closed indefinitely, and Yellowstone National Park was completely closed while the threat to visitor safety was evaluated (current plans are for the southern half of the park to reopen on June 22). Recovery will probably take years, with new roads and bridges needed in several places.  Portions of the northern part of Yellowstone National Park, which was most heavily impacted, may be closed for months.

The level of flooding in the northern part of Yellowstone National Park and in southern Montana was literally unprecedented (see the USGS press release at https://www.usgs.gov/news/state-news-release/usgs-media-alert-usgs-crews-continue-measure-and-assess-yellowstone-river)—a fact that we know thanks to a long record of instrumental river monitoring.  The USGS has developed accurate ways of determining how much water is flowing in a river, and in Yellowstone the USGS operates streamgages on several of the rivers that flow out of the park.  The streamgage on the Yellowstone River at Corwin Springs, just north of Yellowstone National Park, contains records that extend back to 1892!  These long-term data are vital to understanding the impacts of events like last week’s flood and how often such events occur, and monitoring the river systems is critical to forecast and warn of flood conditions.  In addition to the streamgages, the US Department of Agriculture’s National Water and Climate Center administers an automated snow-monitoring program—the SNOwpack TELemetry (SNOTEL) Network—and data from these stations indicate that there was a considerable amount of snow on the ground when the heavy rain in the region began.

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On Monday, June 13, 2022, the height of the water in the Yellowstone River at the Corwin Springs gage reached almost 14 feet—about 2.5 feet higher than the previous record flood event in June 1918.  Discharge peaked at approximately 50,000 CFS (a provisional estimate that is subject to revision), which was much greater than the previous peak flow of about 32,000 CFS from 1918 and in the late 1990s.  These data indicate that the amount of water that was flowing through the gage in the four days between June 11th and June 15th (more than 70 billion gallons) would fill more than one hundred thousand Olympic swimming pools!  If a football field would have walls on all sides, those walls would have to be three miles high to hold all that water.

Monitoring networks operated by the Yellowstone Volcano Observatory are largely intact, despite the catastrophic damage to other infrastructure. Some of the major impacts of heavy rainfall are landslides, and following the unprecedented rain and flooding, many small landslides occurred in different areas of the park. Power outages resulted in a temporary loss of data access from Norris Geyser Basin, but power was restored after a few days.  Other seismic and ground deformation monitoring stations remained fully functional because they are well above river valleys and run on solar and battery power, and they send data out via radio links. River-monitoring stations, including those that measure hot-spring inputs, will need maintenance once the floodwaters recede, as the sensors may have been damaged or buried in sediment.

Will the historic flooding cause any changes in seismic, hydrothermal, or volcanic activity in Yellowstone National Park?  Probably not immediately, and possibly not at all. Most of the rainfall and snowmelt from the recent flooding ended up in rivers draining the area, but some of the water percolated into the ground. There are general correlations across the western USA between seasonal precipitation and small earthquakes caused by changes in surface loading (from snow and water) and groundwater recharge, but analysis of overall seismicity in Yellowstone does not show a strong connection between heavy rainfall and strong earthquakes or earthquake swarms.  Earthquake activity that is related to increasing subsurface pore pressure is mostly related to water that ascends from depth, rather than percolating downward from the surface.  For example, the 2017 Maple Creek earthquake swarm—the second-largest ever recorded in Yellowstone National Park—was probably driven by water rising from deep reservoirs, increasing pore pressure and causing slip on existing faults.

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Hydrothermal explosions are another hazard in Yellowstone and occur when groundwater flashes to steam beneath the surface.  Such explosions are also unlikely to result from the recent flooding.  Flood events by themselves do not provide the trigger needed to cause groundwater to flash to steam.  Rather, it might require an event like a large local earthquake to rupture a hydrothermal system.

Changes in geyser activity, however, can result from variations in groundwater pressure. Based on data recorded between 1998 and 2006 it was proposed that years with lots of rain or snow result in higher groundwater pressures that shortened the eruption cycles of Old Faithful Geyser by a few minutes.  When there is less precipitation, geyser activity may be reduced—recent research found that Old Faithful went dormant during a prolonged period of drought, for example. But not all geysers respond to rainfall.  At Steamboat Geyser, no correlation was found between rainfall and the geyser’s reactivation in 2018.

Last week’s flooding in Yellowstone was truly unprecedented, and YVO offers our heartfelt sympathy to those that have been impacted by the devastating event—especially people who live and work in the north part of Yellowstone National Park and in nearby communities.  While we don’t expect that the flooding will have an immediate or dramatic impact on seismic or hydrothermal activity in Yellowstone, and YVO monitoring systems remain operational, the consequences of the flooding on residents, park employees, and visitors will be felt for years to come. You can learn more about what causes floods, how often extreme floods occur, and how peak flow is determined at https://www.usgs.gov/special-topics/water-science-school/science/floods-things-know.