SEATTLE - A strengthening series of earthquakes at Mount St. Helens prompted seismologists Sunday to warn that the once-devastating volcano may see a small explosion soon.
The U.S. Geological Survey (news - web sites) issued a notice of volcanic unrest in response to the swarm of hundreds of earthquakes that began Thursday.
"The key issue is a small explosion without warning. That would be the major event that we're worried about right now," said Willie Scott, a geologist with the USGS (news - web sites) office in Vancouver.
The quakes were tiny at first, but on Saturday and Sunday there were more than 10 temblors of magnitude 2.0 to 2.8, the most in a 24-hour period since the last dome-building eruption in October 1986, Scott said.
In the event of an explosion, Scott said the concern would be focused on the area within the crater and the flanks of the volcano. It's possible that a five-mile area primarily north of the volcano could receive flows of mud and rock debris.