YELLOWSTONE NATIONAL PARK, Wyo. - Sixteen small earthquakes with magnitudes up to 2.7 shook the park's Pitchstone Plateau last week.

The quakes were detected by seismographs operated by the University of Utah and partners.

They began Monday, 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.

Comment: This is incorrect. The Yellowstone volcano last erupted 640,00 years ago. From Wikipedia:
"The three eruptions happened 2.1 million years ago, 1.3 million years ago, and the most recent such eruption produced the Lava Creek Tuff 640,000 years ago and spread a layer of volcanic ash over most of the North American continent."

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.

No one likely felt the most recent quakes, Smith said.