At 8,364 feet (9,677 feet before May 18, 1980), Mount St. Helens is located in South West Washington about 50 miles North East of Portland, Oregon.  It is one of several lofty volcanic peaks that dominate the Cascade Range of the Pacific Northwest.  The 1980 eruption marked the re-awakening of a relatively young (40,000 years) volcano that had been dormant since 1857.  A magnitude 5.1 earthquake struck beneath the volcano setting in motion the devastating eruption.  Snow and ice melted, forming torrents of water and rock debris; within minutes, a massive plume of ash thrust 19 km into the sky, where the prevailing wind carried about 490 tons of ash across 57,000 sq.km. of the Western United States.