Steamboat Geyser erupting on May, 23, 2022. Dead and downed trees can be seen in the foreground/Mara Reed, UC Berkeley

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 Mara H. Reed, PhD candidate at the University of California, Berkeley.

What can trees tell us about Steamboat Geyser’s history? Why do Steamboat’s seismic eruption signals vary seasonally? 

The behemoth of Norris Geyser Basin, Steamboat Geyser, has drawn the attention of scientists and park visitors alike since it began an active phase in March 2018. At its peak in 2019–2020, major eruptions were occurring almost weekly. The prolonged activity gave researchers an opportunity to understand what influences eruption timing, map the plumbing system with the help of densely deployed seismometers, search for eruption precursors in gas emissions, and listen to water and steam jetting with specialized microphones. Even though Steamboat’s eruptive pace has slowed (only a few eruptions so far this year), research on the geyser continues in earnest.

Something you might notice while walking around a geyser basin is that trees and thermal features don’t get along. As thermal areas form and change, hot ground and silica-laden, boiling water kill existing trees and prevent new growth. Portions of these trees can be preserved through silica precipitation on and within the wood, which prevents normal decay of plant matter. Because it is possible to date these trees using a variety of techniques, preserved trees may hold the key to tracking historical changes in thermal activity. For example, a few years ago scientists were able to date wood samples embedded in Old Faithful Geyser’s sinter mound and inferred that Old Faithful must have been dormant in the 13th and 14th centuries!

A study just published in the journal Geochemistry, Geophysics, Geosystems takes a close look at Steamboat’s current and past impact on the surrounding lodgepole pine trees. Most trees 14–24 meters (46–79 feet) from the vent show significant signs of stress, including dead branches and canopy tops. The researchers compared aerial and ground-based photos taken since 1954 to establish that all three of Steamboat’s recorded more active phases (1961–1969, 1982–1984, and 2018–present) adversely affected nearby trees. But only the recent active phase was associated with distant tree death up to 250 meters (820 feet) away along the dominant wind direction, perhaps meaning eruptions occurred frequently enough in the most recent active phase, compared to those in the 1960s and 1980s, for falling spray to kill trees that far away. However, there is also evidence for increased ground temperatures in the tree kill area, so other factors might be at play.

Several partially mineralized wood samples were found on the sinter shelf immediately southeast of Steamboat Geyser’s vents. Dating these samples revealed that they most likely came from three sets of trees that grew for periods of less than 20 years during the late 15th century, mid-17th century, and late 18th century. Philetus Norris, second superintendent of Yellowstone and namesake of Norris Geyser Basin, believed that he witnessed Steamboat’s formation in August 1878. The wood sample ages provide evidence that Steamboat was active in the centuries prior and that Norris may have just seen a particularly violent major eruption. The three age clusters line up with periods of regional drought, suggesting that Steamboat (like Old Faithful) may be susceptible to variations in climate—when there is less rainfall, geyser activity diminishes and trees can grow closer to the geyser vents.

Another recent study, published in Geophysical Research Letters, delves into a mystery surrounding Steamboat’s seismic signature. Steamboat is one of just two geysers that are powerful enough to produce repeated eruption signals at a station in the Yellowstone Seismic Network (the other is Giantess Geyser in the Upper Geyser Basin). This is due to both eruptive intensity and distance from seismometers—the network was designed to detect small earthquakes, so seismometers were typically placed far away from geyser basins to avoid unwanted noise related to hydrothermal activity.

When analyzing data from station YNM, located in the Norris Museum building just 340 meters (~1/4 mile) north of Steamboat Geyser, researchers noticed that wintertime eruption signals were generally much weaker than summer signals. The straightforward explanation would be that eruption intensity is weaker in the winter, but visual observations did not support this. The next most likely explanation is that some environmental factor affects how the seismometer records the geyser eruption. In this case, snow turned out to be the culprit—strength of shaking recorded at YNM decreased as snow depth increased.

Four examples of vertical ground shaking during Steamboat Geyser eruptions as recorded by seismic station YNM. The vertical scale is the same for each seismogram. At deeper snow depths, the shaking appears weaker. This is because snow suppresses the amount of energy that is transmitted into the ground by the geyser’s eruption/Figure adapted from Reed and Manga, 2023.

Why does snow dampen Steamboat’s seismic signals? Anyone who lives in a snowy climate is familiar with how quiet the world seems to be after a fresh snowfall. Snow is a good absorber of sound because acoustic waves don’t travel well through porous materials. It turns out that the shaking YNM records during Steamboat eruptions originates as noise produced by water and steam jetting. These acoustic waves then transmit some energy into the ground; if snow is present, less energy is transferred. The findings highlight the benefits of long-term monitoring and also have implications for interpretation of the sounds produced at active snow-covered volcanoes like Mount Etna in Italy and Villarrica in Chile.

What will Steamboat teach us next? Only time will tell. You can keep up with Steamboat’s activity through crowdsourced observations posted to GeyserTimes, by viewing runoff temperature data updated daily, or observing spikes in water flow at the streamgage through which all water from Norris Geyser Basin flows.