Old Faithful Geyser got its unique name in the 19th century because its eruptions were so regular and predictable. But during parts of the 13th and 14th centuries, the geyser did not erupt at all.
A time when Old Faithful wasn’t so faithful
Yellowstone Caldera Chronicles is a weekly column written by scientists and collaborators of the Yellowstone Volcano Observatory. This week's contribution is from Shaul Hurwitz, Research Hydrologist with the U.S. Geological Survey; John King, Tree Ring Scientist at Lone Pine Research; Greg Pederson and Justin Martin, Research Ecologists with the U.S. Geological Survey; David Damby, Research Chemist with the U.S. Geological Survey; Michael Manga, Professor at the University of California, Berkeley; Jeff Hungerford, Yellowstone National Park Geologist; and Sara Peek, Hydrologist at the U.S. Geological Survey.
Natural geysers are rare because they need special conditions to form: a supply of water, recent or active magmatism to supply heat, and the right geometry of fractures in subsurface rocks to permit episodic discharge. Because of the delicate balance between these controlling parameters, geysers have periods of activity and dormancy. Transitions between activity to dormancy and changes in the interval between eruptions are often caused by earthquakes that modify the geometry of fractures in subsurface rocks and by changes in the amount of regional precipitation that flows as groundwater to geyser reservoirs.
Many of the world’s geysers are concentrated in Yellowstone’s Upper Geyser Basin, including the most iconic, Old Faithful Geyser. In a journal paper published over 60 years ago, Yellowstone National Park naturalist George Marler described a mineralized wood sample from the mound of Old Faithful Geyser. In one of the first applications of the radiocarbon dating method, that wood was found to be about 730 years old, with an estimated uncertainty of 200 years.
Inspired by this observation, a team of scientists collected and studied 13 mineralized wood specimens from the Old Faithful geyser mound, collected under Yellowstone Research Permit YELL-SCI-8030 and published recently in the journal Geophysical Research Letters. Three specimens were identified as Lodgepole pine, which currently dominate nearly 80% of the total forested area in Yellowstone National Park. The species of the other samples could not be determined but are probably also remnants of lodgepole pine. The specimens were then split into 41 samples and dated with the radiocarbon method. To the surprise of the researchers, all wood samples had similar ages and implied that lodgepole pine trees grew on the geyser mound in the 13th and 14th centuries (1233-1362 CE). This range of dates is the same (within uncertainty) to the single date that George Marler determined more than six decades ago.
Because lodgepole pine trees do not grow on active geyser mounds, the study suggests that when these trees grew on the Old Faithful Geyser mound approximately 650 to 800 years ago, the geyser was not erupting. In the Yellowstone region, past climate reconstructions based on tree ring records reveal that a severe and sustained drought occurred in the mid-13th century, which coincides with the onset of tree growth on the Old Faithful Geyser mound. It would seem, then, that the pause in Old Faithful eruptions during the 13th and 14th centuries was related to diminished precipitation and groundwater supply to the geyser for several decades. The severe 13th century drought had significant effects well beyond Old Faithful Geyser. In fact, severe and persistent droughts impacted large parts of the USA and had a tremendous impact on indigenous peoples, including the Anasazi, Fremont, and Lovelock cultures.
It was quite a mystery as to why such old trees were preserved on the geyser mound, because in Yellowstone’s non-thermal areas, lodgepole pines usually decompose completely within 300 years. Wood from the lodgepole pines was preserved for over 650 years on the geyser mound because it was near-continuously wetted by the alkaline, silica-rich thermal waters erupted from geysers. These waters deposit the mineral opal on tree stems and wood tissues which prevents the disintegration of cellulose by fungi, bacteria, and insects—it causes silicification, or mineralization, of the wood! This silicification process can be rapid and take only days or weeks.
Because climate models forecast increasingly severe regional droughts by the mid-21st century, results from the new study suggest that geyser eruptions could become less frequent in the future. Indeed, periods of decreased precipitation have been shown in modern times to result in less frequent eruptions of Old Faithful, and the new research indicates that severe, long-duration droughts can terminate eruptions. For now, Old Faithful remains just that—faithful, with eruptions occurring about every 90 minutes. But this was not always the case in the past, as the new research demonstrates, and might continue to evolve in the future.