Mount St. Helens is the most historically active volcano in the Cascade range, having produced four major explosive eruptions since 1479, and dozens more smaller eruptions, including pyroclastic flows, lava flows and domes, and lahars. It is located approximately 80 km NE of Portland, OR.
Mount St. Helens is best known for its large explosive eruption, summit collapse and directed blast of May 18, 1980, which was the most expensive and deadly volcanic event in United States history. The volcano continued erupting during 1981-1986, producing a lava dome within the 1980 crater. Mount St. Helens last erupted in 2004-2008, when it produced a series of spectacular lava spines with a cumulative volume of almost 100 million cubic meters. Tremor and millions of small earthquakes accompanied both of the recent eruptions. Source: Mount St. Helens.