Too close for comfort?
Boulder lies more than 400 miles from Yellowstone. Would we actually be affected by such an eruption?
By Terri Cook
The movie opens with a dark and wintry Colorado scene: a group of snowmobilers, bundled into fur-edged parkas, frantically racing through several feet of soft powder in the middle of a raging blizzard. The understated subtitles announce the location: Colorado, and then the date: August 9. Powder in August? In this instant, viewers of the 2005 BBC docudrama Supervolcano realize that something is terribly amiss—the falling flakes aren’t snow; they’re ash. The Yellowstone supervolcano is erupting, with clearly catastrophic results.
This scene may be great for ratings, but how realistic is it? As the crow flies, Boulder lies more than 400 miles from Yellowstone. Would we actually be affected by such an eruption? The short answer, says U.S. Geological Survey (USGS) volcanologist and Boulder Councilwoman Lisa Morgan Morzel, is “most likely.”
Yellowstone, the world’s first national park, is a natural wonderland of gushing geysers, gurgling mudpots, steaming vents and hot springs that collectively comprise half the geothermal features on the planet. Their presence near Wyoming’s northwestern corner is related to the underground circulation of scorching-hot water, which is heated by the presence of a vast supply of magma, some of it perched just a few miles beneath the surface.
The magma is believed to be associated with a steady plume of hot, spongy material rising from a source deep within the Earth, perhaps as far down as 1,800 miles at the core/mantle boundary, Morzel says. This so-called “hotspot,” which has been active in the Yellowstone area for the last few million years, is responsible for forging much of the region’s landscape, including several enormous bowl-shaped depressions, called calderas, located in and west of the park.
Products of the most violent type of volcanic eruptions, calderas form when enormous pressures empty an entire magma chamber in a matter of a couple of days, creating a yawning void into which the overlying land catastrophically collapses.
Three caldera eruptions have rocked the Yellowstone region in the geologically recent past. The two largest, which occurred 2.1 million and 640,000 years ago, respectively expelled 585 cubic miles and 240 cubic miles of ash and lava, qualifying them as “supereruptions.” About 1.3 million years ago, a third caldera eruption ejected 67 cubic miles of material—a drop in the bucket compared to the others, but still 670 times more than the devastating 0.1 cubic mile of ash ejected by Mount St. Helens in 1980.
New Model Yields Answers to a Persistent Question
Could a caldera eruption happen again in Yellowstone? In Supervolcano, the chief geologist blithely tells reporters that the odds of another supereruption are 1 in 600,000—half as likely as the chance that an airplane will crash in their backyards, he jokes. In reality, Yellowstone hasn’t experienced any eruptions in the last 70,000 years, and experts at the USGS Volcano Hazards Program estimate the chances of another supereruption as 1 in 730,000—about the same odds that you’ll be struck by lightning or killed by an asteroid impact this year.
But what would happen if nature defied the odds and a massive eruption did occur? From painstaking mapping, geologists know that large volumes of lava as well as pyroclastic flows—raging torrents of hot gas and rock fragments—poured from Yellowstone during past supereruptions. In addition, huge amounts of ash, blasted high into the atmosphere, drifted as far as Iowa and Louisiana before settling, like snowflakes, to the ground. But much of this ash has since been carted off by rivers or shifted by gusts of wind, so its thickness—and hence the associated hazard level—has been difficult for scientists to gauge.
Last year a group of USGS geologists, tired of being unable to answer the interminable questions about how much ash would fall in a given area, applied a new model of ash dispersion to the Yellowstone region. The results show that under current weather patterns, a supereruption comparable in size to the one that occurred 640,000 years ago would blanket nearly the entire nation with ash, contaminating water supplies and farmland and almost completely shutting down communications and air travel.
While local impacts would depend upon how long the eruption lasted, as well as the winds at that time of year, the average of all the model simulations indicates that Boulder would be coated with 2.5 to 5.2 inches of ash—enough to create treacherous driving conditions, short out transformers, cause respiratory problems, and clog the engines of the Supervolcano snowmobiles, but probably not enough to block water and sewer lines or cause buildings to collapse. Those conditions would more likely occur in Casper, Wyo., or Billings, Mont., which would be buried beneath 3 to 6 feet of ash.
The injection of so much volcanic gas and ash into the atmosphere would also drastically cool the global climate. Given the sixfold greater volume of erupted material, the conditions following a Yellowstone supereruption would almost surely be worse than the “year without a summer” that followed the 1815 eruption of Indonesia’s Mount Tambora. The resulting crop failures led to the worst famine in the 19th century.
Fortunately, the Yellowstone system shows little indication that it’s headed toward such an eruption. Any renewed activity, according to Morzel, would most likely take the form of a lava flow or a hydrothermal explosion. And while that could create issues in and near the park, she says, Boulder would not likely be affected.
Terri Cook is a Boulder-based science writer whose career has focused on exploring and explaining the history of our amazing planet. She is the co-author of three books, including Geology Underfoot Along Colorado’s Front Range. Follow her adventures at www.down2earthscience.com.