Mount St. Helens reawakened in late September 2004. Small magnitude earthquakes beneath the 1980-1986 lava dome increased in frequency and size, and a growing welt formed on the southeast margin of the previous lava dome and nearby portions of Crater Glacier.
On October 1, 2004, the first of several explosions shot a plume of volcanic ash and gases from a vent on the growing welt, followed by the slow extrusion of lava. For the next three years, a series of hot, solid, smooth-sided lava spines rose from the vent, bulldozed their way across the crater floor and piled up to form a new dome 460 m (1,500 ft) high. The growing lava dome pushed Crater Glacier aside, causing it to flow rapidly toward the front of the 1980 breach; flow continues today.
Scientists used a variety of monitoring techniques during the 2004-2008 eruption, such as tracking ground deformation, measuring the temperature of lava spines, interpreting earthquakes, sampling groundwater, observing changes to water quality, deploying temporary remote monitoring stations (spiders), collecting and analyzing lava samples, producing time-lapse videos of dome growth and glacier advance, and digital elevation models of surficial changes in the crater.
By monitoring Mount St. Helens, scientists are better able to understand the volcano’s behavior, to assess hazards and potential impacts, and to provide timely warnings of future events.
The video was produced for a public event commemorating the 10th anniversary of the beginning of the 2004-2008 eruption.
Video courtesy: USGS