Yellowstone: geologists are monitoring ground deformation

Last week, park officials released Yellowstone’svital signs” report, documenting more than 24 natural resource indicators that affect the park’s ecological and environmental stability, from wildlife disease to climate change. The report also noted the park’s geological activity. The ground near the White Lake recording station has swelled 25 centimeters — more than 10 inches — since 2004, while more than 3,200 earthquakes rattled the park in 2010 — the largest concentration of tremors recorded since 1985. Knowing what it all means, however, remains something of a mystery. “Yellowstone seems to breathe,” said Yellowstone’s chief geologist, Hank Heasler. “That’s the best way to describe it. It goes through cycles of uplift and subsidence. That detailed pattern of ground deformation, well, we’re still in the process of figuring that out.”

Heasler attributed the increase in geological events to improving technology. Scientists can now detect earthquakes that passed unnoticed just 30 years ago. Deformations in the ground can be measured down to the millimeter. To say there are more earthquakes now than before, Heasler said, is akin to saying people get more phone calls now than they did 30 years ago. Technology makes the difference. “We’re finally getting good enough technology to suggest models over what’s causing the ground deformation,” Heasler said. “There are some very good ideas, and some scientists are very passionate about their theories. But we’re still in the debate phase, and that’s one of the more fascinating components of science.”

Yellowstone has bulged and shifted in various places over the years. Between 1996 and 2002, Heasler said, an area near Norris Junction lifted 12 centimeters as Yellowstone’s central caldera sank. “There might be a slow inhalation in one area and an exhalation in another,” Heasler said. “We need more data to really confirm the exact pattern and cause. But there are two great ideas out there that try to explain the deformation.” The deformation may be related to Yellowstone’s vast hydrothermal system, Heasler said. Like a blister under the skin, the park bulges and shifts under pressure.

Molten rock underlies the second theory. As the red-hot balloon of magma and gas moves toward the surface, Heasler said, it causes the ground to lift. “As an independent scientist, I can say both models have problems,” Heasler said. “There’s a lot of great work and scientific debate going on to understand what this ground deformation is really telling us.” The park is not only rising and falling, it’s also moving side to side. Over a four-month period in 2010, Yellowstone endured a swarm of 2,500 earthquakes — a swarm being “more earthquakes than normal in any period of time.” The temblors varied up to magnitude 3.8, which was recorded on Jan. 20. “People in this park can feel down to a magnitude 2.2 or so, depending on how sensitive they are and where they are,” Heasler said. “But if you put all the 2010 quakes into a single earthquake, it would only be equal to a magnitude 4.4.”

In comparison, the single strongest quake in the 1985 swarm measured 4.5. That swarm of quakes 26 years ago packed more energy than the latest swarm — so much so, Heasler said, people began leaving the West Yellowstone area. “They got tired of being rattled,” Heasler said. “With this 2010 swarm, we had 16 earthquakes felt in the Old Faithful area. Swarms are just a way of life in Yellowstone.” Yellowstone has experienced about 90 swarms since the mid-1990s alone. While some look at the figures and suggest that the world’s largest volcanic feature is beginning to stir, Heasler cautioned about jumping to such conclusions. “The seismometers have improved immensely,” Heasler said. “They’re able to sense an order of smaller magnitude earthquakes that seismographs in the early 1980s couldn’t.”

In the 1930s, park surveyors established benchmarks along Yellowstone’s interior roads noting their elevation. In the 1970s, as crews went back to relocate the benchmarks, they found the old readings off by as much as two feet. While they first believed that the earlier surveyors had taken sloppy readings, they soon realized that their readings hadn’t been wrong. Areas of the park had actually risen, something geologists are keenly aware of today. If a big volcanic eruption were coming, Heasler said, geologists would see it coming well in advance. And that’s not what the data is telling them. “Our monitoring not only allows us to see subtle changes, but it can also be used to predict a large eruption, or even a minor one. The bigger the eruption, the more indicators you’ll have and the farther in advance you’ll have them.”

Heasler said it’s not impossible that Yellowstone could experience a small eruption with little notice. The elements are there — earthquake swarms, ground deformations, thermal venting and volcanic gases. Yet the events aren’t occurring at the magnitude needed for something big, Heasler said, and they’re not occurring over the same spot. Yellowstone has seen 80 lava flows since the last giant eruption 640,000 years ago, Heasler said, and each of those technically classifies as an eruption. “Those areas of smaller eruptions are the most likely type that would occur,” Heasler said. “There’s always the possibility of a Hawaiian-type volcano that would only affect a small region of Yellowstone. But it wouldn’t have any regional catastrophic effects.