YELLOWSTONE NATIONAL PARK — For the currently dormant volcanoes that show no signs of stirring that make up Yellowstone National Park (YNP), predictions are based on the probability that an eruption will occur during a time frame rather than a specific date.
These “long-term weather forecasts,” as Deputy Scientist-in-Charge at the Yellowstone Volcano Observatory (YVO) Mark E. Stelten calls them in this week’s Caldera Chronicles, are similar to estimating the probability that an upcoming hurricane season will have more hurricanes than an average year. In other words, forecasts are based on the frequency at which eruptions occur for any given volcano over time, which geologists determine by combining geologic mapping with geochronology, or dating rock formations.
Also part of the forecast is whether or not a volcanic eruption has been a one-off, independent event or something that occurred as part of a bigger volcanic group event. YVO compares this type of trend with baseball, where it’s much more likely that baseballs will be hit into someone’s yard during baseball season instead of off-season.
“Recent research has shown that many volcanic systems, including Yellowstone, work in a similar way, with multiple eruptions occurring in rapid succession, separated by long periods with few to no eruptions,” YVO writes. “To accurately forecast volcanic eruptions, this ‘grouping’ of eruptions needs to be well-characterized.”
According to YVO, once the history of volcanic eruptions through time is understood, it’s necessary to understand where the volcano currently stands “in terms of its life cycle.” This is like trying to figure out if it’s currently baseball season or off-season.
Because YNP produces large but infrequent eruptions, with thousands to hundreds of thousands of years between eruptive episodes that could include one or more eruptions, YVO writes that there are few observations upon which to base a forecast; YVO confirms no eruptions have occurred in YNP during the past 70,000 years.
But, from 160,000 years ago to 70,000 years ago, rhyolite lava flows (or groups of lava flows) were erupting approximately every 20,000 years on average.
“Does this mean we are currently in the volcanic off-season?” YVO writes. “Or does it mean we are ‘due’ for an eruption (which, by the way, is never really true)? The reality is that we cannot say for sure based on statistical forecasting methods alone. Instead, we must combine these types of forecasts with real-time monitoring of the volcano to assess the state of the volcanic system.”
YVO confirms that current knowledge of YNP’s eruptive history, the annual probability of a volcanic eruption is 0.001%, which might even be an overestimate for the short term. There are currently no signs of an impending volcanic eruption based on monitoring data, and YVO writes that the magmatic system beneath YNP is mostly solid.
