YELLOWSTONE NAT'L PARK - Sixteen small earthquakes -- with magnitudes up to 2.7 -- shook Yellowstone National Park last week, around the edge of a volcano that has not erupted in more than 70,000 years.

The tremors shook the park's Pitchstone Plateau, and were detected by seismographs operated by the University of Utah.

The earthquakes began on April 30, just before midnight. The largest occurred at 3:09 a.m. Tuesday and the quakes continued until Wednesday, according to Bob Smith, a University of Utah professor.

"I was up working and watching these, saying 'Whoa, what does this all mean?"' he said. "It kept my interest quite high."

The quakes occurred on the southern edge of a volcano caldera at the center of Yellowstone. The volcano last erupted 70,000 years ago and some experts believe it has the potential to erupt again. If that happened, a large portion of the western United States could be affected.

Smith said earthquake swarms are common in Yellowstone. As many as 70 swarms of small earthquakes have occurred in the region between 1983 and 2006.

Probably no one felt the most recent quakes, Smith said.

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