SEATTLE (Reuters) - A rock fall at Mount Saint Helens caused a large gray cloud of dust to appear above the volcano on Tuesday, but there was no sign of increased seismic activity.
Seismic levels at Mount Saint Helens, which came back to life last year by emitting steam and ash, are "amazingly regular," said Seth Moran, a seismologist at the U.S. Geological Survey.
Mount St. Helens erupted in 1980 and killed 57 people and was mostly dormant until September 2004, when new magma activity pushed up a lava dome in the crater of the volcano that also emitted steam and ash for weeks.
"This is the first rock fall that we've seen in a while," said Moran, who added that rock falls are a common occurrence when a volcano builds a lava dome.
Moran said that clear weather and calm winds kept the dust cloud hanging over the volcano Tuesday afternoon, making it visible for miles.
Mount St. Helens is located in southwestern Washington state, about 100 miles south of Seattle, and 50 miles north of a busy airport at Portland, Oregon.
The U.S. Geological Survey, which monitors Mount Saint Helens from its Cascades Volcano Observatory in Vancouver, Washington, kept its alert status at its second-highest level. No major eruptions are expected to be imminent.