Yellowstone’s most famous geyser, Old Faithful, has erupted with an unusual degree of regularity since records were first taken, in the 1870s, discharging thousands of gallons of boiling, silica-rich water over 30 meters into the air an average of 16 times a day.
Scientists studying fossilized wood samples buried and preserved by the geyser have now confirmed that Old Faithful is likely thousands of years old, according to a new study by Hurwitz et al. They also found that the famous geyser was dormant for several decades during the 13th century due to a megadrought that gripped much of western North America. Finally, with warmer temperatures and extended droughts now expected to increase in the region due to climate change, researchers expect longer intervals between Old Faithful’s eruptions.
Old Faithful’s Medieval Forest
Despite its being one of the most popular and recognizable geologic features on Earth, scientists know surprisingly little about Old Faithful, such as how old it is or what its eruption patterns looked like through prerecorded history.
As geysers erupt over the course of hundreds to thousands of years, dissolved silicate minerals in the discharged water slowly build up around their bases, forming a slightly elevated landscape known as a sinter mound. Plant growth is conspicuously absent near these mounds due to high soil temperatures, an alkaline pH, and a high concentration of silica—so any fossilized plants found buried within the mound likely grew at a time when the geyser was inactive.
Scientists have known there was fossilized plant material buried near Old Faithful since at least the early 1950s, when a geologist working for the U.S. Geological Survey (USGS) used what was then the newly developed method of radiocarbon dating on a single wood sample retrieved from Old Faithful’s sinter mound in an attempt to determine the geyser’s age.
Radiocarbon dating indicated the wood was about 730 years old with an estimated error of 200 years. This meant that sometime in around the 12th or 13th century, Old Faithful ran dry.
A Sudden Disappearance
Now, for the first time in over 50 years, scientists have collected additional fossil wood samples from the geyser’s sinter mound in an attempt to determine what may have caused Old Faithful’s dry spell. Their radiocarbon results matched almost perfectly with the date obtained more than a half century ago.
“The radiocarbon dating methods we have today are nothing close to what they had back in the early 50s, so when we got back our first batch of results, I thought it was almost too good to believe,” said Shaul Hurwitz, a research hydrologist with the USGS at the California Volcano Observatory and lead author of the new study.
The new study found that the wood fossils were 750 years old. They were located near the top of the mound, which, according to Hurwitz, indicates that Old Faithful was already hundreds, if not thousands, of years old by the time the trees grew there.
By taking radiocarbon dates from the oldest and youngest parts of a single wood sample, Hurwitz and his team determined that trees grew on Old Faithful’s sinter mound for about 100 years during the 13th and 14th centuries, which coincides with the tail end of what’s become known as the Medieval Climate Anomaly.
The Medieval Climate Anomaly
During the Medieval Climate Anomaly, which started at about 900 CE and ended some 400 years later, Earth underwent a slight warming period that resulted in severe droughts in western North America.
By using tree ring data taken from long-lived juniper trees—some of which are more than 1,400 years old—in the northern part of Yellowstone National Park, scientists can infer approximately how much water was available during a given year.
During the 13th century, Yellowstone was experiencing a prolonged period of severe drought. By combining this information with the radiocarbon dates obtained from the geyser’s sinter mound, scientists concluded that without enough rain to recharge groundwater reserves, Old Faithful—likely along with many of the surrounding geysers—went dry.
“We know from paleoclimate studies that this was a time of more fires in Yellowstone, which is usually associated with warm temperatures and drought,” said Cathy Whitlock, a paleoecologist at Montana State University in Bozeman who was not involved in the new study.
Looking to the Future
This isn’t the first time environmental conditions have been shown to affect the timing of Old Faithful’s eruptions. A series of earthquakes in the area starting in 1959 caused the intervals between eruptions to increase by several minutes. The timing between intervals was further increased by the Turn of the Century Drought that struck the western United States between the years 2000 and 2010, the worst dry spell in the region since the Medieval Climate Anomaly.
“This pattern could play out again in the future as global warming creates drier conditions,” Whitlock said. “Old Faithful already seems to be going off less frequently, which suggests that climate is affecting the water and underground plumbing.” (Geophysical Research Letters, https://doi.org/10.1029/2020GL089871, 2020)
—Jerald Pinson (@jerald_pinson), Science Writer