Yellowstone National Park's caldera, which covers a 25- by 37-mile (40- by 60-kilometer) swath of Wyoming, is an ancient crater formed after the last big blast, some 640,000 years ago. The simmering volcano has produced major eruptions—each a thousand times more powerful than Mount St. Helens's 1980 eruption—three times in the past 2.1 million years. The supervolcano has recently caused miles of ground to rise dramatically, scientists report beginning in 2004, which saw the ground above the caldera rise upward at rates as high as 2.8 inches (7 centimeters) a year. Recent earthquakes on the west side of Yellowstone caldera were part of the intense January/February 2010 earthquake swarm of ~2,350 earthquakes.
"If that geothermal development outside of the park begins, we need to know whether that's going to cause Old Faithful to suddenly stop spewing," says Rick Lawrence of Montana State University.
Geothermal energy development is here to stay, says Yellowstone Park geologist Cheryl Jaworowski, but it has also raised some big questions for the National Park Service, which is tasked by Congress to monitor and protect Yellowstone's unique landscape.
Their project is part of a new monitoring plan the park implemented in 2005. The plan uses remote sensing and airborne reconnaissance to observe geothermal changes across all of Yellowstone in a systematic and scientific manner. In the past, scientific studies on the ground tended to focus on individual features, and the only park wide estimate of Yellowstone's heat was derived from a chemical product of geothermal systems that appears in the river system. But with different technology available today, says Jaworowski, the park wants to expand its monitoring options.
To understand Yellowstone's geothermal system, "we need to start looking at the forest rather than the individual trees," says Jawrorski. And one way to see Yellowstone's geothermal "forest" is to get a view from space.
Circling Earth from a height of 438 miles, the Landsat satellites have been gathering for decades a huge amount of data about the land surface. A single scene can take in the entirety of Yellowstone National Park, and the data it gathers is much more than a pretty picture. In addition to measuring the visible light in the electromagnetic spectrum -- what we can see -- the Landsat satellites each have an instrument that detects waves in the thermal band -- heat energy.
Earth radiates heat all the time because it is warmed by the sun. Like a sponge, the ground absorbs solar energy, and like when you squeeze off excess water, the Earth reemits some of that solar energy at a longer wavelength back into space. But in Yellowstone, the total energy picked up by the satellite includes energy produced by the Earth itself, geothermal energy. The amount of solar energy reemitted depends on air temperature, vegetation cover, and soil moisture among other variables, and geothermal energy is only a small fraction of the total.
Some 600,000 years ago there was a colossal cauldron of magma, a supervolcano, that exploded with such violence that it left an ash layer almost ten feet deep a thousand miles away in eastern Nebraska killing all plant life and covering almost all of the United States west of the Mississippi. Modern geological surveys have shown that this supervolcano erupts catastrophically every 600,000 years, and the land that supervolcano is trapped in was called by Blackfoot Indians 'the land of evil spirits' -what we call today, Yellowstone National Park.
A report from scientists at the University of Utah shows that the “supervolcano” underneath Yellowstone has risen at a record rate since mid 2004. Apparently, a “pancake-shaped blob” of molten rock he size of Los Angeles was pressed in to the slumbering volcano, some six miles down.
“There is no evidence of an imminent volcanic eruption or hydrothermal explosion. That’s the bottom line,” says seismologist Robert B. Smith, lead author of the study and professor of geophysics at the University of Utah. “A lot of calderas [giant volcanic craters] worldwide go up and down over decades without erupting.”
The journal Science however reported that the caldera floor of the massive volcano has risen 3 inches, per year, for the past three years. This is a rate of growth three times more rapid than ever observed, since records were first kept back in 1923.
“Our best evidence is that the crustal magma chamber is filling with molten rock,” Smith says. “But we have no idea how long this process goes on before there either is an eruption or the inflow of molten rock stops and the caldera deflates again,” he adds.
If you were traveling Yellowstone's pristine backcountry peaks and alpine valleys, you would never realize that you're traveling atop of the world's most massive active volcano. Only when you got down to the boiling thermals of Firehole River and the Geyser Basin whould you realize that you're a stranger in a strange land.
A brief history lesson on Yellowstone shows us an area that crosses over the Wyoming border in to Montana and Idaho, and holds North America’s record as being the largest volcanic field. Produced by a “hotspot” 400 miles beneath the Earth’s surface, it rises to 30 miles underground, at which point it widens in to an area about 300 miles across.
At this point, blobs of magma which have been channeled up from the hotspot – a gigantic plume of hot and molten rock – break off from the top of the plume, and rise in to the magma chamber beneath the Yellowstone caldera.
It is this magma – that is believed to exist between 5 and 10 miles beneath the surface of Yellowstone – that heats the geysers and hot springs that have made Yellowstone National Park one of America’s foremost attractions.
The problem that the seismologists are facing is that they simply have not enough data to make an educated guess as to what will happen next. We know of three supervolcanic eruptions that happened before our time on Earth, but nothing more. Is Yellowstone nearing an explosion, or is this just part of the supervolcano’s normal processes?
Since the most recent blast 640,000 years ago, about 30 smaller eruptions—including one as recent as 70,000 years ago—have filled the caldera with lava and ash, producing the relatively flat landscape of the Yellowstone plateau we see today. According to the US Geological Survey, the rate slowed between 2007 and 2010 to a centimeter a year or less. However, since the start of the 2004 swelling, ground levels over the volcano have been raised by as much as 10 inches (25 centimeters) in places.
"It's an extraordinary uplift, because it covers such a large area and the rates are so high," said the University of Utah's Bob Smith, a longtime expert in Yellowstone's volcanism in an interview with National Geographic.
Scientists believe a growing magma reservoir four to six miles (seven to ten kilometers) below the surface is the culprit, driving the uplift. The surge doesn't seem to herald an imminent catastrophe, Smith said.
"At the beginning we were concerned it could be leading up to an eruption," said Smith, who co-authored a paper on the surge published in the December 3, 2010, edition of Geophysical Research Letters. "But once we saw [the magma] was at a depth of ten kilometers, we weren't so concerned. If it had been at depths of two or three kilometers [one or two miles], we'd have been a lot more concerned."
Studies of the surge, he added, may offer clues about what's going on in the volcano's subterranean activity, which may eventually help scientists predict when Yellowstone's next volcanic eruption will break out.
Smith and colleagues at the U.S. Geological Survey (USGS) Yellowstone Volcano Observatory have been mapping the caldera's rise and fall using tools such as global positioning systems (GPS) and interferometric synthetic aperture radar (InSAR), which gives ground-deformation measurements.
Ground deformation can suggest that magma is moving toward the surface before an eruption: The flanks of Mount St. Helens, for example, swelled dramatically in the months before its 1980 explosion.
There are also many examples, including the Yellowstone supervolcano, where it appears the ground has risen and fallen for thousands of years without an eruption.
According to current theory, Yellowstone's magma reservoir is fed by a plume of hot rock surging upward from Earth's mantle. As the amount of magma flowing into the chamber increases, the reservoir swells like a lung and the surface above expands upward. Models suggest that during the recent uplift, the reservoir was filling with 0.02 cubic miles (0.1 cubic kilometer) of magma a year. When the rate of increase slows, the theory goes, the magma likely moves off horizontally to solidify and cool, allowing the surface to settle back down.
"These calderas tend to go up and down, up and down," he said. "But every once in a while they burp, creating hydrothermal explosions, earthquakes, or—ultimately—they can produce volcanic eruptions."
Predicting when an eruption might occur is extremely difficult, in part because the fine details of what's going on under Yellowstone are still undetermined. What's more, continuous records of Yellowstone's activity have been made only since the 1970s—a tiny slice of geologic time—making it hard to draw conclusions.
"Clearly some deep source of magma feeds Yellowstone, and since Yellowstone has erupted in the recent geological past, we know that there is magma at shallower depths too," said Dan Dzurisin, a Yellowstone expert with the USGS Cascades Volcano Observatory in Washington State.
"There has to be magma in the crust, or we wouldn't have all the hydrothermal activity that we have," Dzurisin added. "There is so much heat coming out of Yellowstone right now that if it wasn't being reheated by magma, the whole system would have gone stone cold since the time of the last eruption 70,000 years ago."
The large hydrothermal system just below Yellowstone's surface, which produces many of the park's top tourist attractions, may also play a role in ground swelling, Dzurisin said, though no one is sure to what extent. "Could it be that some uplift is caused not by new magma coming in but by the hydrothermal system sealing itself up and pressurizing?" he asked. "And then it subsides when it springs a leak and depressurizes? These details are difficult."
The roughly 3,000 earthquakes in Yellowstone each year may offer even more clues about the relationship between ground uplift and the magma chamber.
For example, between December 26, 2008, and January 8, 2009, some 900 earthquakes occurred in the area around Yellowstone Lake, which may have helped to release pressure on the magma reservoir by allowing fluids to escape, and this may have slowed the rate of uplift, the University of Utah's Smith said.
"Big quakes [can have] a relationship to uplift and deformations caused by the intrusion of magma," he said. "How those intrusions stress the adjacent faults, or how the faults might transmit stress to the magma system, is a really important new area of study."
Overall, USGS's Dzurisin added, "the story of Yellowstone deformation has gotten more complex as we've had better and better technologies to study it."
Thankfully, our ability to use our planets past to predict its future continues to grow, to a point where, maybe someday, we will be able to predict what Yellowstone is up to.
To monitor Yellowstone's potenial hazard, the Yellowstone Volcano Observatory was formed in 2000, administered by the University of Utah, the Park Service, and the U.S. Geological Survey.