The 2004–2008 volcanic activity of Mount St. Helens in Washington, United States has been documented as a continuous eruption in the form of gradual extrusion of magma. Starting in October 2004 and ceasing in January 2008, a new lava dome was built up. The new dome did not rise above the rim of the crater created by the 1980 eruption of Mount St. Helens. 2004 activity On September 23, 2004, around 2:00 a.m. PDT, Mount St. Helens experienced an earthquake swarm, with about 200 small (less than magnitude 1) earthquakes occurring less than one-half mile (one kilometer) below the 1980s lava dome. Activity increased, and on September 26, the U.S. Geological Survey (USGS) and Pacific Northwest Seismograph Network issued a "notice of volcanic unrest", stating that a "hazardous event" was possible, and the U.S. Forest Service closed the mountain to all climbing. They also closed some trails in the area, due to the risk of debris flows from the possible melting of the Crater Glacier in the volcanic crater. Seismic activity continued to accelerate following the USGS advisory, with earthquakes approaching magnitude 2.5 occurring at a rate of about four per minute on September 29, prompting the USGS and Pacific Northwest Seismograph Network to issue a second advisory, increasing the "alert level" to the second of three levels, and warn of an increased likelihood of a steam explosion or eruption from the lava dome within the next few days. Such an event was expected to be relatively small and not pose a threat to regions beyond the immediate area of the mountain. However, the intensities and occurrences of the earthquakes continued to rise. The largest earthquake recorded was a magnitude 3.3. At 12:02p.m. PDT on October 1, 2004, the mountain erupted a plume of steam and volcanic ash about 9,700 feet (about 3 kilometers) into the air (according to pilot reports), from a vent in the then-unnamed Crater Glacier just southwest of the lava dome. The resulting ash plume was reported to have drifted south to Vancouver, Washington, Northern California and Wood Village, Oregon, dusting cars with a fine layer of black, sooty ash. Mount St. Helens vented another plume of steam the next day at 12:14p.m. PDT, which was stronger than the previous steam release. A low-frequency harmonic tremor followed the steam release, which led seismologists to raise the "alert level" to the third of three levels, indicating a