Mount St. Helens

Mount St. Helens
3,000-foot (910 m) steam "plume" on May 19, 1982, two years after its major eruption
Highest point
Elevation	8,365 ft (2,550 m)
Prominence	4,605 ft (1,404 m)
Coordinates	46°11′28″N 122°11′40″W / 46.1912000°N 122.1944000°W / 46.1912000; -122.1944000[1]
Geography
Location	Skamania County, Washington, U.S.
Parent range	Cascade Range
Topo map	USGS Mount St. Helens
Geology
Age of rock	< 40,000 yrs
Mountain type	Active stratovolcano
Volcanic arc	Cascade Volcanic Arc
Last eruption	2004 – July 10, 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 is a volcano in the U.S. state of Washington. It is 96 miles (154 km) south of Seattle and 53 miles (85 km) northeast of Portland, Oregon. The volcano is in Cascade Range of mountains. It is part of the Cascade Volcanic Arc in the Pacific Ring of Fire that includes over 160 active volcanos. This is a deadly volcano.

Mount St. Helens was first called Louwala-Clough, which means "smoking" or "fire mountain" in the language of the Native American Klickitat people. This volcano is well known for its explosions and flows of lava. Its most famous volcanic eruption was on May 18, 1980.^[2] In 1982, U.S. President Ronald Reagan and the United States Congress made the Mount St. Helens National Volcanic Monument, a 110,000-acre (45,000 ha) area around the volcano that is also a part of the Gifford Pinchot National Forest.

The 1980 eruption was the deadliest and most economically destructive volcanic event in the history of the United States. 57 people were killed;^[3] 250 homes, 47 bridges, 15 miles (24 km) of railways, and 185 miles (298 km) of highway were destroyed.^[4] A massive debris avalanche was triggered by an earthquake measuring 5.1 on the Richter scale. This caused the eruption, which reduced the height 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.^[5] The debris avalanche was up to 0.7 cubic miles (2.9 km³) in volume.

1. ↑ "Mount Saint Helens". Geographic Names Information System. United States Geological Survey.
2. ↑ "Mount St. Helens National Volcanic Monument". USDA Forest Service. (accessed 26 November 2006)
3. ↑ "The eruption of Mount St Helens", How it Works, no. 42, Imagine Publishing, p. 60, 2012-12-27
4. ↑ Cite error: The named reference Tilling1990 was used but no text was provided for refs named (see the help page).
5. ↑ "May 18, 1980 Eruption of Mount St. Helens". USDA Forest Service. Archived from the original on 2009-05-29.