This from AP:

Mount St. Helens shot a steam and ash plume at least 16,000 feet into the air Monday after a large rockfall from the lava dome in the Southwest Washington volcano's crater, scientists said.

Pilots reported the plume rose between 16,000 and 20,000 feet in the air, said scientists at the Cascades Volcano Observatory.

The rockfall coincided with a magnitude 3.1 earthquake shortly after 9 a.m. Monday at the mountain, scientists said, adding such events are expected during growth of the lava dome.

"There is no evidence of an explosion associated with this event," the observatory said in a statement.

Clouds obscured the crater at the time.

Lava has continued to push into the crater — most recently forming a sheer rock fin — since the 8,364-foot mountain reawakened with a drumfire of low-level seismic activity in September 2004. The crater was formed by the volcano's May 18, 1980, eruption.