Mount St. Helens displayed a Memorial Day reminder of its might, shooting steam and an ash plume to an altitude of about 20,000 feet.
"We don't know how much steam and how much ash," said Cynthia Gardner, scientist in charge of the U.S. Geological Survey's Cascades Volcano Observatory said in a statement. "These are very short-lived events."
The event was not seen by many people, since clouds obscured the crater in southwest Washington state, the Vancouver (Wash.) Columbian reported.
Scientists said they believe the event was caused by a rockfall in the crater, corresponding with a magnitude 3.1 earthquake that occurred at 9:08 a.m. Monday about 1 mile west of the volcano. Mount St. Helens is about 45 miles from Vancouver.
"This is not unexpected activity when you have rock avalanches on the growing lava dome," Gardner told the Columbian. "These things happen fairly frequently."
A magnitude 3.1 earthquake is considered a minor event by the U.S. Geological Survey.
The volcano continues to grow at a rate of approximately 3 feet a day, the newspaper said.
Copyright 2006 by United Press International
Explore further: Bright points in Sun's atmosphere mark patterns deep in its interior