- Old Faithful geyser in Wyoming's Yellowstone National Park erupts regularly every 90 minutes or so.
- A new study found that its eruption frequency has changed over time, and stopped completely for a few decades 800 years ago.
- The pause came during a period of global warming that resulted in long droughts in Yellowstone.
- Such droughts are likely to happen again, so could once again interfere with Old Faithful's cycle.
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Old Faithful, the famed geyser in Yellowstone National Park, erupts with captivating regularity.
Phenomenal bursts of hot water and steam — fed by the geothermal activity of the Yellowstone supervolcano underneath — spurt up with such punctuality they can be predicted, giving the geyser the nickname Eternity's Timepiece.
But Old Faithful wasn't always so faithful, and long ago, Eternity's Timepiece stopped ticking entirely.
Trees surrounding the geyser can tell us about its past eruption cycle
In the last several decades, scientists observed that Old Faithful's interval between eruptions (IBEs) has changed considerably, stretching from about 60 to 65 minutes in the 1950s to about 90 to 94 minutes starting in 2001.
To investigate why — and probe the links between Old Faithful's IBE variations and long-term drought variability in the region — researchers from the US Geological Survey (USGS) collected several remnants of mineralized wood found around the mound Old Faithful sits on. Their study results were published October 7.
Today, the mound is barren and empty of trees. Trees don't grow on active geyser mounds, as the constant deluge and splatter of the scalding, alkaline-rich discharge are incompatible with germination and seedling growth.
Nonetheless, a 1956 study was able to analyze an ancient wood sample recovered from Old Faithful. The study suggested that, once upon a time, the geyser's eruptions stopped for some time and trees grew in its location.
Inspired to learn more, the USGS team analysed 13 mineralized wood samples they recovered from Old Faithful's mound. Radiocarbon dating suggested these trees grew in Yellowstone several centuries ago, between 1233 to 1362.
"When I submitted the samples for radiocarbon dating, I didn't know whether they would be hundreds or thousands of years old," lead study author and USGS geologist Shaul Hurwitz told Science, adding, "it was an 'aha!' moment when they all clustered within a 100-year period in the 13th and 14th centuries."
Drought stopped Old Faithful 800 years ago
To figure out why and how these trees were able to live during this relatively brief, decades-long window in which Old Faithful stopped erupting, the researchers looked for historical data that could explain whether there were drought conditions at the time.
The reduced precipitation and lower groundwater supply during droughts would have turned off the taps for the iconic geyser.
They didn't have to look far. Previously collected local tree-ring data indicated pronounced megadroughts across the region and in other parts of the world too. This resulted from severe conditions during an episode known as the Medieval Climate Anomaly (or the Medieval Warm Period) that ended roughly 800 years ago.
"It's the time when we have things like grapes growing in Northern England and a loss of sea ice that allowed people to discover Greenland," palaeoclimatologist Cathy Whitlock from Montana State University, who wasn't involved in the study, told Inside Science.
She added: "We know in Yellowstone it was both warmer and drier. The upper tree line was higher up the slopes and there is evidence of more fires during that period."
Old Faithful could stop erupting in the future
The links Hurwitz's team found don't just fill in gaps about Old Faithful's historical time-keeping. They may also point to geyser eruption variations in the near future — as soon as the mid-21st century — as the world gets increasingly hotter and drier due to climate change.
That's something Hurwitz foreshadowed over a decade ago, and even though Eternity's Timepiece has shown it can be a bit unreliable sometimes, the real clock never stops.
"Climate models project increasingly severe droughts and large fires by mid-century leading to a major transformation of Yellowstone's ecosystems," the study authors wrote.
"Periods of decreased precipitation have been shown in modern observational records to result in less frequent eruptions of Old Faithful Geyser, while the new 14C dates of mineralized wood suggest that severe, long-duration drought events can lead to Old Faithful Geyser eruption cessation," they added.