The eruption of Mount St. Helens on May 18, 1980 followed nearly two months of earthquakes and minor explosive eruptions. Collapse of the summit of the volcano on May 18 produced a large landslide that reduced the height of the volcano by 400 m (about 1300 feet). At the same time a laterally directed explosion blew down giant trees like matchsticks over a 600 square kilometer area and killed 57 persons. Mudflows reached as far as the Columbia River, sweeping away highway bridges and houses, and ashfall caused severe disruption over a several-state area.
Several other explosive eruptions, substantially smaller than on May 18, occurred in 1980, and episodic extrusion of lava in the new crater lasted until 1986, building a lava dome that reached a height of 270 meters.
