MOUNT ST. HELENS, Wash.  — Mount St. Helens released a towering white plume on Tuesday.

The volcano has periodically spewed ash and steam since last fall, when thousands of small earthquakes marked a seismic reawakening of the 9,677-foot mountain.

Late afternoon television footage showed the plume billowing thousands of feet into the air, then drifting slowly to the northeast.

MOUNT ST. HELENS, Wash. - Mount St. Helens released a towering plume of ash on Tuesday. The volcano has vented ash and steam since last fall, when thousands of small earthquakes marked a seismic reawakening of the 8,364-foot mountain.

Late afternoon television footage showed the plume billowing thousands of feet into the air, then drifting slowly to the northeast.

The ash explosion happened around 5:25 p.m., about an hour after a 2.0 magnitude quake rumbled on the east side of the mountain, said Bill Steele, coordinator of the Pacific Northwest Seismograph Network at the University of Washington.

Steele said he did not believe the explosion had increased the risk of a significant eruption and noted that recent flights over the volcano's crater did not reveal high levels of gases.

"We don't expect another explosion," said Peggy Johnson, a UW seismologist.

Steele said the ash burst may have been triggered by partial collapse of a lava dome in the crater, which has been growing steadily over the last several months.

"Until we get a better view in the crater we won't know," Steele said.

Johnson said there had been no increase in quake activity before the explosion.

"The seismicity had been continuing just as it had been," she said.

On May 18, 1980, the volcano 100 miles south of Seattle blew its top, killing 57 people and covering the region with gritty ash.

Mount St. Helens rumbled back to life Sept. 23, with shuddering seismic activity that peaked above magnitude 3 as hot magma broke through rocks in its path. Molten rock reached the surface Oct. 11, marking resumption of dome-building activity that had stopped in 1986.

Scientists have said a more explosive eruption, possibly dropping ash within a 10-mile radius of the crater, is possible at any time.

Mount St. Helens Information Statement, Tuesday, March 8, 2005, 6:00 P.M. PST

A small explosive event at Mount St. Helens volcano began at approximately 5:25 p.m. PST. Pilot reports indicate that the resulting steam-and-ash plume reached an altitude of about 36,000 feet above sea level within a few minutes and drifted downwind to the east-northeast. The principal event lasted about 30 minutes with intensity gradually declining throughout. The USGS Cascades Volcano Observatory lost radio signals from three monitoring stations in the crater soon after the event started. The cause of the outage won’t be known until scientists can visit the crater tomorrow to assess the situation, weather permitting. The event followed a few hours of slightly increased earthquake activity that was noted but not interpreted as precursory activity. There were no other indications of an imminent change in activity.

The current hazard assessment for the ongoing eruption mentions the possibility of such events occurring without warning, and the assessment remains unchanged. The eruption could intensify suddenly or with little warning and produce explosions that cause hazardous conditions within several miles of the crater and farther downwind. Small lahars could suddenly descend the Toutle River if triggered by heavy rain or by interaction of hot rocks with snow and ice. These lahars pose a negligible hazard below the Sediment Retention Structure (SRS) but could pose a hazard along the river channel upstream.