Ring of Fire

Should scientists be concerned about what lurks beneath our first national park?

By John Dvorak

Standing at the edge of Old Faithful, you can feel the tension mount as the crowd anticipates the next explosion of boiling water and steam. People are checking their watches. A few are armed with notebooks and pencils, prepared to record whatever they see. Others steady their cameras.

And then it happens. It begins as a small spurt that grows rapidly into a tower of pulsating sprays, jetting more than a hundred feet into the air. No one is disappointed. Every display is different. A few people leave, but most stay and are joined by newcomers eager to see the next burst of the world’s most famous geyser. The eruption of Old Faithful is one of the iconic scenes from our national parks, and millions of visitors travel to Yellowstone National Park each year to witness it. But few are aware that each burst is only a subtle part of the immense volcanic system that lies beneath their feet. And only now are scientists beginning to unravel how this complex system works.

First, consider this phenomenon: Yellowstone’s surface rises, then falls, then rises again in a cycle that takes years to complete. Although changes are measured in mere inches per year—imperceptible to visitors—there’s no doubt that Yellowstone is in constant motion.

Scientists aren’t sure what’s causing the ups and downs, but Jake Lowenstern, head of the Yellowstone Volcano Observatory, has a hunch: magma. Several miles beneath Yellowstone’s surface lies a chamber of molten rock, or magma, that powers the world’s largest collection of geysers and hydrothermal features, including Old Faithful. As that magma cools and crystallizes, it releases gases and hot fluids that get trapped in pockets as they rise toward the surface. Lowenstern believes that the accumulation of fluids in these pockets could be pushing the surface upward.

Sinking grounds, on the other hand, could be triggered by one of the thousands of earthquakes that occur each year in Yellowstone (don’t worry—few are strong enough to be felt by visitors). Earthquakes can rupture those sulfur-rich pockets, releasing the fluids and causing the ground to drop.

But a shifting ground isn’t the only mystery. Heat flows out of Yellowstone’s surface 30 times faster than at any other place on the continent, thanks to the layer of magma just below. But does that mean the park is getting hotter or cooling off? That question is the main focus of the park’s geology studies, according to Yellowstone geologist Hank Heasler. And rightfully so: If the park is getting hotter, the magma chamber might be expanding, and the volcano would likely become more active. If the magma chamber is cooling off, it could signal a period of relative calm.

Answers to that question could help explain an incident in July 2003, when the temperatures of normally cool soils within the Norris Geyser Basin rose to an alarming 200 degrees Fahrenheit. Hot-water pools boiled away, new mud pots formed, and the extreme jump in temperature killed several trees. Park Superintendent Suzanne Lewis closed the area to visitors for three months, until temperatures dropped to safe levels again. Fast-forward to March 10, 2004, when park staff stumbled on five bison carcasses near Norris Geyser Basin. The three adults and two calves were lying on their sides, legs rigid and pointing away from their bodies—unusual positions that led park biologists to believe the bison had died quickly and as a group. Further investigation suggested that the animals had inhaled lethal concentrations of gases common in volcanic areas.

While extremely cold weather and still air might have been partly to blame (normally, wind disperses these gases before they can accumulate to deadly concentrations), what followed also raised eyebrows: Four months later, after nearly a decade of slow subsidence, the ground surface began to rise again. And in early 2010, when the rate of uplift slowed, Yellowstone experienced the largest swarm of earthquakes in 20 years.

So how does all this ground movement relate to the death of bison and trees, if at all? Are all of these events simply unpredictable coincidences, or is there something bigger going on?

Such correlations are difficult to make because scientists haven’t been studying these processes for long. What they do know is this: Although future eruptions are possible, there is little indication that one will happen anytime soon. Serious volcanic activity would follow “a considerable amount of [ground] deformation, intense earthquake swarms, and steam explosions,” Lowenstern says. Yellowstone’s recent activity pales in comparison.

We’re a long way from knowing exactly what’s going on beneath the surface of one of our most beloved national parks, but that’s just part of its charm. “Before I started working here, I had no idea how special Yellowstone was,” says Heasler. “It’s hard to find the right superlative to describe this place.”

John Dvorak is a volcanologist and science writer living near Hilo, Hawai’i.


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