VANCOUVER, Wash. — A dome of lava that has been growing continuously for three years in the center of Mount St. Helens has stopped, U.S. Geological Survey scientists report. As a result of this pause in activity, scientists at the USGS Cascades Volcano Observatory lowered the Volcano Alert Level from Watch/Orange to Advisory/Yellow on Feb. 21. This alert level indicates that lava growth has ceased but renewed activity is possible.

Since late January 2008, seismic activity at Mount St. Helens has fallen to an extremely low level. The daily ground-tilt events have stopped, and images from field cameras show no evidence of recent lava-dome growth. A Global Positioning System instrument (spider) that USGS deployed via helicopter onto the lava dome on Feb. 15 is showing only subtle movements consistent with settling of the dome.

The new lava dome began growing rapidly in October 2004, and since then the rate of growth has been gradually slowing. "Considering the low rate of dome growth during the past several months, the current pause is not surprising," said Cynthia Gardner, scientist-in-charge at the observatory.

The new dome has grown to a volume similar to that of the dome that grew in the Mount St. Helens crater between 1980 and 1986.

During the 1980s, lava dome growth was episodic, with pauses in eruptive activity lasting from weeks to almost a year. Scientists have observed such episodic patterns at many other volcanoes worldwide. "We cannot determine at this time how long the current pause at Mount St. Helens will last or whether eruptive activity will cease for the foreseeable future," said Willie Scott, a research geologist with the observatory.

Despite the pause in dome growth, some hazards persist. The new lava dome remains hot in places and can still produce localized hot avalanches or small steam explosions that could cause hazardous conditions in and around the crater. Sudden melting of snow and ice or intense rainfall could send small lahars, mixtures of water and rock fragments, down the slopes of Mount St. Helens. Ash clouds from small explosions could affect aircraft.

The USGS and the University of Washington's Pacific Northwest Seismic Network will continue to monitor Mount St. Helens closely to watch for any sign of renewed lava-dome growth or other types of volcanic activity.

USGS scientists at the observatory will issue updates weekly, not daily, while Mount St. Helens is in Advisory/Yellow status.

For more information about the eruption and current activity reports, visit http://vulcan.wr.usgs.gov/Volcanoes/MSH/Eruption04/framework.html.

Alert level and aviation color code definitions may be found at http://pubs.usgs.gov/fs/2006/3139/fs2006-3139.pdf.

Additional information about volcanoes and volcano hazards is available at http://volcanoes.usgs.gov/.