Mount St. Helens
3,000 ft (900 m) high steam plume on May 19, 1982, two years and a day after the 1980 major eruption that created the visible gap on the north side of the mountain
Highest point
Elevation	8,363 ft (2,549 m)
Prominence	4,605 ft (1,404 m)
Listing	Washington prominent peaks 11th Washington isolated peaks 11th Washington highest peaks 35th
Coordinates	46°11′28″N 122°11′40″W / 46.1912000°N 122.1944000°W / 46.1912000; -122.1944000[1]
Naming
Etymology	Alleyne FitzHerbert, 1st Baron St Helens
Native name	Lawetlat'la (Cowlitz) Loowit (Klickitat) Louwala-Clough (Klickitat)
Geography
Mount St. Helens Location in Washington state
Parent range	Cascade Range
Topo map	USGS Mount St. Helens
Geology
Formed by	Subduction zone volcanism
Rock age	Less than 40,000 years old
Mountain type	Stratovolcano
Volcanic arc	Cascade Volcanic Arc
Last eruption	2004–2008
Climbing
First ascent	1853 by Thomas J. Dryer
Easiest route	Hike via south slope of volcano (closest area near eruption site)

Mount St. Helens (known as Lawetlat'la to the local Cowlitz people, and Loowit or Louwala-Clough to the Klickitat) is an active stratovolcano located in Skamania County, Washington,^[1] in the Pacific Northwest region of the United States. It lies 52 miles (83 km) northeast of Portland, Oregon,^[2] and 98 miles (158 km) south of Seattle.^[3] Mount St. Helens takes its English name from that of the British diplomat Alleyne FitzHerbert, 1st Baron St Helens, a friend of explorer George Vancouver who surveyed the area in the late 18th century.^[1] The volcano is part of the Cascade Volcanic Arc, a segment of the Pacific Ring of Fire.

The Mount St. Helens major eruption of May 18, 1980, is currently the most economically destructive volcanic event in U.S. history.^[4] 57 people were killed and 200 homes, 47 bridges, 15 miles (24 km) of railways, and 185 miles (298 km) of highway were destroyed.^[5] A massive debris avalanche, triggered by a magnitude 5.1 earthquake, caused a lateral eruption^[6] that reduced the elevation of the mountain's summit from 9,677 to 8,363 ft (2,950 to 2,549 m), leaving a 1-mile-wide (1.6 km) horseshoe-shaped crater.^[7] The debris avalanche was 0.6 cubic miles (2.5 km³) in volume.^[8] The 1980 eruption disrupted terrestrial ecosystems near the volcano. By contrast, aquatic ecosystems in the area greatly benefited from the amounts of ash, allowing life to multiply rapidly. Six years after the eruption, most lakes in the area had returned to their normal state.^[9]

After its 1980 eruption, the volcano experienced continuous volcanic activity until 2008. Geologists predict that future eruptions will be more destructive, as the configuration of the lava domes requires more pressure to erupt.^[10] However, Mount St. Helens is a popular hiking spot and it is climbed year-round. In 1982, the Mount St. Helens National Volcanic Monument was established by Congress.