Old Faithful is a geyser in Yellowstone National Park, named after its regularity in erupting hot water and steam, fed by the geothermal activity of the Yellowstone supervolcano underneath.

In the last several decades, scientists have observed that Old Faithful’s interval between eruptions has changed considerably, stretching from about 60-65 minutes in the 1950s to about 90-94 minutes since 2001.

A geyser’s eruption is feed by a complex, underground vent system filled with water. As the magma in the underground heats up the groundwater, steam pressure will build up until it is sufficient to trigger a steam eruption on the surface. According to the scientists, no major changes have occurred in the thermal state of Yellowstone, excluding this factor as an explanation for the delay in Old Faithful’s eruptions. Another possible factor controlling geyser activity is the rising or falling groundwater table, drought periods reflecting a decrease in geyser activity. The precipitation itself does not directly feed the eruptions, but it recharges the groundwater body. In a new study, researchers from the US Geological Survey reconstructed Old Faithful’s long-term activity using wood fragments to test this hypothesis.

Today the mound surrounding the geyser is barren, as steam and the alkaline water will kill any seedlings. But partially mineralized wood fragments found near the vent suggest that once the geyser’s eruptions did relent for a while and trees grew in its location.

The USGS team used radiocarbon dating to identify the age of 13 wood samples they recovered from Old Faithful’s mound. The preserved remains suggest that trees grew for several decades on the site 800 years ago, around 1233 to 1362 CE. Using local tree ring data, the researchers matched the period of tree growth on Old Faithful’s mound with a pronounced megadrought in the 13th and 14th centuries across the region. At the time, the climate in Yellowstone was both warmer and drier. The upper tree line was higher up the slopes, and there is evidence of more fires during that period.

As the world gets increasingly hotter and drier, climate models project increasingly severe droughts in the coming 50 years in Yellowstone. Periods of decreased precipitation have been shown in modern observational records to result in less frequent eruptions of Old Faithful geyser, while the new dates of mineralised wood suggest that severe, long-duration drought events can lead to Old Faithful geyser eruption cessation.

Want to read more? Try:

Volcanoes: Global Perspective, by John Lockwood and Richard W. Hazlett (2010)

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