Small quakes continue to rattle Yellowstone

Yellowstone National Park was jostled by small earthquakes for a third straight day Monday, and scientists watched closely to see whether the more than 250 tremors were a sign of something bigger.

Swarms of small earthquakes happen frequently in Yellowstone, but it is unusual for so many quakes to happen over several days, said Robert Smith, a professor of geophysics at the University of Utah.

“They’re certainly not normal,” Smith said. “We haven’t had earthquakes in this energy or extent in many years.”

Smith directs the Yellowstone Seismic Network, which operates seismic stations around the park.

He said the quakes ranged in strength from barely detectable to one of magnitude 3.8 on Saturday. A magnitude-4 quake is capable of producing moderate damage.

“This is an active volcanic and tectonic area, and these are the kinds of things we have to pay attention to,” Smith said. “We might be seeing something precursory.

“Could it develop into a bigger fault or something related to hydrothermal activity? We don’t know. That’s what we’re there to do, to monitor it for public safety.”

The strongest of dozens of quakes Monday was a magnitude 3.3 shortly after noon.

All the quakes were centered beneath the northwest end of Yellowstone Lake.

A park ranger based at the north end of the lake reported feeling nine quakes during a 24-hour period over the weekend, park spokeswoman Stacy Vallie said.

No damage was reported.

“There doesn’t seem to be anything to be alarmed about,” Vallie said.

Smith said it was difficult to say what might be causing the quakes.

He pointed out that Yellowstone was the caldera of a volcano that last erupted 70,000 years ago.

He said Yellowstone remained geologically active -- and its famous geysers and hot springs were a reminder that a pool of magma still existed underground.

“That’s just the surface manifestation of the enormous amount of heat that’s being released through the system,” he said.

In 1959, a magnitude-7.5 quake near Hebgen Lake just west of the park triggered a landslide that killed 28 people.