Mount St. Helens, located in Southwest Washington State, blasted its way into the history books on Sunday, May 18, 1980 in a spectacular eruption . In March 1980, it began rumbling, attracting the attention of volcanologists worldwide. A dome began swelling on the mountain’s north slopes.
The most catastrophic eruption on May 18, 1980, at 8:32 was the deadliest and most economically destructive volcanic event in the history of the United States. The damage caused was huge . 57 people were killed , 250 homes, 47 bridges, 15 miles (24 km) of railways, and 185 miles (298 km) of highway were destroyed. A massive debris avalanche triggered by a earthquake measuring 5.0 on the Richter scale, caused an eruption, reducing the elevation of the mountain’s summit from 9,677 ft (2,950 m) to 8,365 ft (2,550 m) and replacing it with a 1 mile (1.6 km) wide horseshoe-shaped crater .The earthquake was caused by a sudden surge of magma from the Earth’s mantle.
For more than nine hours, a vigorous plume of ash erupted, eventually reaching 12 to 16 miles (20 to 27 km) above sea level. The plume moved eastward at an average speed of 60 miles per hour (100 km/h) with ash reaching Idaho by noon. Ashes from the eruption were found collecting on top of cars and roofs next morning, as
far as the city of Edmonton in Alberta, Canada
The Mount St. Helens National Volcanic Monument was then created after this catastrophic event in order to preserve the volcano and allow to be scientifically studied.
Mount St. Helens also showed significant activity on March 8, 2005, when a 36,000-foot (11,000 m) plume of steam and ash emerged . this event was visible from Seattle .This relatively minor eruption was a release of pressure consistent with ongoing dome building. The release was accompanied by a magnitude 2.5 earthquake.
On October 22, 2006, at 3:13 p.m. a magnitude 3.5 earthquake broke loose Spine 7. The collapse and avalanche of the lava dome sent an ash plume 2,000 feet (600 m) over the western rim of the crater. The ash plume then rapidly dissipated.
On December 19, 2006, a large white plume of condensing steam was observed, leading some media people to assume there had been a small eruption. The volcano was in continuous eruption from October 2004, but this eruption consisted in large part of a gradual extrusion of lava forming a dome in the crater.
On January 16, 2008, steam began seeping from a fracture on top of the lava dome. Associated seismic activity was the most noteworthy since 2004. Scientists suspended activities in the crater and the mountain flanks. By the end of January, the eruption paused , no more lava was being extruded from the lava dome. On July 10, 2008, it was determined that the eruption had ended after more than six months of no volcanic activity.
Mount St. Helens taught scientists a great deal about how volcanoes work and for the moment there is no danger of an imminent eruption.