Editor's note: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.

The year 2024 will rightly be remembered for the well-documented explosion at Biscuit Basin. But that wasn’t the only geological activity of note that occurred in the Yellowstone region during the year…

In Yellowstone, 2024 will probably be remembered as the year of the hydrothermal explosion. There were two noteworthy such events, each important for different reasons.

First came the hydrothermal explosion in Norris Geyser Basin. That occurred on a terrace overlooking Porcelain Basin on April 15. The area had been a site of abundant thermal activity over the past few years, with water cascading into Nuphar Lake since 2021–2022 and causing the lake to change to a blue-green color and the level to rise.

The activity culminated with the April 15 explosion, which left a crater about 10 feet (3 meters) across along with an area of disrupted ground. The explosion was not witnessed because few people were in the park during the seasonal closure, but it was detected in acoustic and seismic monitoring, including new sensors that had been installed in September 2023. This event has the distinction of being the first hydrothermal explosion in Yellowstone to have been detected by monitoring instruments.

Of course, with no witnesses, the April 15 explosion went mostly unnoticed by the public. The same cannot be said about the July 23 explosion of Black Diamond Pool at Biscuit Basin. This event occurred just before 10 AM local time on a bright, sunny day, when dozens of people were in the area. They had to run for safety as an unheralded explosion hurled rocks, mud, liquid water, and steam hundreds of feet into the air.

Fortunately, there were no injuries, even though geologists later mapped over 1,400 rocks with a long dimension greater than a foot that were ejected by the event. Much of the debris was thrown in the direction of the Firehole River, although the boardwalk adjacent to Black Diamond Pool was severely damaged. Smaller explosive events, reaching a few tens of feet in height, and surges of water continued to occur from the pool into the fall and winter months.

Aerial view of Biscuit Basin, Yellowstone National Park, showing debris deposited by the July 23, 2024, hydrothermal explosion from Black Diamond Pool. Major features are labeled. The main debris field (within dashed yellow line) has a gray appearance. Photo taken by Joe Bueter, Yellowstone National Park, on July 23, 2024.

As usual, there were also interesting changes at thermal features throughout the park during 2024. For example, Economic Geyser, in Upper Geyser Basin, experienced a series of eruptions for the first time since 1999. In West Thumb Geyser Basin, Abyss Pool began to heat up and overflow, and its color changed from dark and somewhat murky to a deep blue as the summer progressed. And near Nymph Lake, a few miles north of Norris Geyser Basin, a new steam vent appeared at the base of a hill in August. This sort of activity is typical in Yellowstone, where the only constant is change.

New steam vent at the base of a hill north of Nymph Lake, west of the highway and between Norris Geyser Basin and Roaring Mountain. USGS photo by Mike Poland, September 1, 2024.

Steamboat Geyser—the tallest geyser in the world—also continued to be active, although with many fewer eruptions than in previous years. The geyser erupted 6 times in 2024 compared to 32 in 2018 (the year that the current episode of activity began), 48 each in 2019 and 2020, 20 in 2021, 11 in 2022, and 9 in 2023.

In contrast to the interesting hydrothermal activity, the year was seismically calm. There were 1,173 earthquakes located in the Yellowstone region during 2024, which is at the low end of the typical annual seismicity—usually about 1,500–2,500 located earthquakes each year. The largest event was a M3.3 that occurred on January 3, 2024, as part of a swarm of 112 located earthquakes that took place during January 1–6. Ironically, this swarm right at the start of 2024 was also the largest of the year. As is typical, about half of all the earthquakes during 2024 occurred as part of swarms (defined as sequences of earthquakes that occur in roughly the same place in rapid succession), and 7 earthquakes during the year were reported to be felt.

Map of seismicity (red circles) in the Yellowstone region during 2024. Gray lines are roads, black dashed line shows the caldera boundary, Yellowstone National Park is outlined by black dot-dashed line, and gray dashed lines denote state boundaries/USGS

There were no changes in ground deformation in 2024. Yellowstone Caldera continued to subside at a rate of a few centimeters (1–2 inches) per year, temporarily interrupted during the summer months by a pause or slight uplift due to changes in snowmelt and groundwater conditions. There were no significant changes in ground motion in the vicinity of Norris Geyser Basin.

Yellowstone Volcano Observatory scientists conducted a variety of field work during the year. In addition to of geological studies, upgrades were made to a number of monitoring sites—improvements that were targeted in the monitoring plan that was published in 2022. YVO scientists also gathered in May to discuss new research and monitoring results, and to plan new work for the coming years—including an expansion of hydrothermal monitoring at Norris and Upper Geyser Basins.

YVO is optimistic that 2025 will include new research results, sensor upgrades, and station installations, so stay tuned to future editions of Yellowstone Caldera Chronicles for updates! From everyone at YVO, stay safe, be healthy, and have a Happy New Year!