Mount St. Helens is a active stratovolcano located in Skamania County, Washington in the Pacific Northwest part of the United States. Mount St. Helens is 154 km south of Seattle, Washington and 80 km northeast of Portland, Oregon. The volcano is located in the Cascade Range and is a part of the Cascade Volcanic Arc. A segment of the Pacific Ring Of Fire. Mount St. Helens is also known as Louwala Clough or "Lawetlat's" to the Cowlitz people and "Loowit" to the Klackitat people. This volcano is known for its ash explosions and pyroclastic flows.
As with many other volcanos in the Cascade Range, Mount St. Helens is a large eruptive cone containing of lava rock inter layered with ash, pumice, and other deposits. The mountain includes layers of Basalt and andesite through which several domes of dacite lava have erupted. The largest of the dacite domes formed the previous summit, and off the northern flank sat the smaller Goat Rocks dome. Both were destroyed in the 1980 eruption.
Mount St. Helens is most notorious for its major 1980 eruption, the deadliest and economically destructive volcanic event in the history of the United States. Fifty seven people were killed, 250 houses destroyed, 47 bridges, 24 km of railway, and 298 km of highway were destroyed. A massive debris avalanche triggered by a earthquake measuring a 5.1 on the Richter scale caused an eruption that reduced the elevation of the mountains summit from 9,667 ft to 8,363 ft leaving a 1.6 km wide horseshoe-shaped crater. The debris avalanche was up to 2.9 km in volume. The Mount St. Helens National Volcanic Monument was created to preserve the volcano and its aftermath to be scientifically studied.