Mount St. Helens is a volcano in the Cascade Mountains, in the area called the Mt. St. Helens National Volcanic Monument. It is administered by the National Forest Service, not the National Park Service.
It is located in Washington state, about 55 miles northeast of Portland, Oregon, and 95 miles south of Seattle, Washington.
Over the last 500 years, Mount St. Helens has had at least four major explosive eruptions and many minor eruptions.
Mount St. Helens was named by Commander George Vancouver and the officers of H.M.S. Discovery for British diplomat Alleyne Fitzherbert (1753-1839). Fitzherbert's title was Baron St. Helens.
1792-1794 - The mountain was named while Commander Vancouver and H.M.S. Discovery officers were surveying the northern Pacific coast.
1835 - Mount St. Helens is first recognized as a volcano.
1857-1980 - Mount St. Helens is inactive.
May 18, 1980 - 8:32 am PDT - Mount St. Helens erupts!
The eruption blows off more than 1,000 feet from the top of the mountain, leaving a huge crater. The mountain had been known for its snow-capped peak, earning the nickname "the Fuji of America" for its resemblance to Japan's Mount Fuji.
Fifty-seven people are killed. Damage caused by the blast costs $1.1 billion (USGS).
Hot ash causes forest fires, and snow melt from the top of the mountain causes floods.
Volcanic ash spreads across the Northwest. More than 900,000 tons of ash are cleaned up from areas around Washington state.
The 1980 eruption is the first eruption in the continental United States outside of Alaska since 1917.
1980-1986 - Many small eruptions occur.
October 1986 - Sixteen "dome-building" eruptions build up the dome in the center of the crater.
Fall 2004 - Several days of unusual seismic activity lead seismologists to believe that an explosion resulting from steam buildup is likely to occur.
Oct. 1, 2004 - Mount St. Helens begins blowing a large cloud of smoke and steam on a Friday afternoon following a week in which scientists have closely monitored the volcano. Officials placed the region around the mountain on a volcanic advisory earlier in the week. The advisory issued is at the third of four levels -- with the fourth being eruption.
Oct. 4. 2004 - Huge plumes rise from Mount St. Helens, where geologists have been expecting a volcanic eruption. Officials with the U.S. Geological Survey say the volcano was likely having another steam eruption. A USGS official estimates the steam was rising about 10,000 feet from the top of the crater. Officials say some ash came out as well from the lava dome.
Oct. 11, 2004 - More steam erupts from Mount St. Helens. Earthquake activity declined after two days of increased activity. Mount St. Helens remains at a level two volcanic advisory.
Nov. 6, 2004 - A new lava dome formed inside Mount St. Helens' crater continues to grow, now sprouting a growth that extends upward by nearly 330 feet, officials said. The growth has taken place since Oct. 27, 2004.
March 8, 2005 - Mount St. Helens releases a column of smoke and ash nearly six miles high, leaving a plume visible for more than 50 miles.
September 11, 2005 - The U.S. Geological Survey raises the advisory for Mount St. Helens to "orange," which means that a high likelihood of volcanic activity exists, but it is not likely to threaten life.
May 2006 - A three hundred foot "fin" made of lava begins growing out of the crater.
January 2008 - Eruptions that have occured continously since October 2004 cease.
July 2014 - Final preparations begin for what geophysicists call the "equivalent of a combined ultrasound and CAT scan" of the inside of the volcano, a joint project by scientists at Rice University, the University of Washington, the University of Texas at El Paso and others that involves placing 3,500 seismic sensors around the volcano. The project will take four years in all and aims to improve volcanic monitoring and advance warning systems.