A swarm of earthquakes continued to rattle Yellowstone National Park on Monday. Over the past two days, more than 37 temblors have shaken the earth below Yellowstone Lake, causing scientists to speculate on the cause and field questions on whether the quakes were a prelude to an eruption of the park's super volcano.

"It's an energetic earthquake swarm," said Mike Stickney, director of the earthquake studies office for the Montana Bureau of Mines and Geology. "I'm hearing reports that people in the park have been feeling some of them."

Stickney said Monday that mild earthquakes swarms are relatively common for the Yellowstone region. This round of quakes, however, may be more vigorous than in recent years, though the cause is just as puzzling.

"There have been two other swarms this fall that come to mind," said Stickney. "But they weren't as many and they weren't as large as what we're seeing now."