Mt St Helen's Rumbling & Grumbling: Explosion likely?
Seismologists believe there's an increased likelihood of a hazardous event at Mount St. Helens because of recent changes in the mountain's seismic activity, and on Sunday the U.S. Geological Survey issued a notice of volcanic unrest.
"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 office in Vancouver, Wash.