page_title: Mount St. Helens
section_title: General
hierarchical_section_title: Mount St. Helens / Geographic setting and description / General
caption_attribution_description: English: 35 years later after the May 18, 1980 eruption. The image shows a three-dimensional view of the mountain, looking toward the southeast, as it appeared on April 30, 2015. The image was assembled from data acquired by the Operational Land Imager on Landsat 8 and the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) on Terra.
context_page_description: Mount St. Helens is an active stratovolcano located in Skamania County, Washington, in the Pacific Northwest region of the United States. It is 50 miles northeast of Portland, Oregon and 96 miles south of Seattle, Washington. Mount St. Helens takes its English name from the British diplomat Lord St Helens, a friend of explorer George Vancouver who made a survey of the area in the late 18th century. The volcano is located in the Cascade Range and is part of the Cascade Volcanic Arc, a segment of the Pacific Ring of Fire that includes over 160 active volcanoes. This volcano is well known for its ash explosions and pyroclastic flows.
  Mount St. Helens is most notorious for its major eruption on May 18, 1980, the deadliest and most economically destructive volcanic event in US history. Fifty-seven people were killed; 250 homes, 47 bridges, 15 miles of railways, and 185 miles of highway were destroyed. A massive debris avalanche, triggered by an earthquake of magnitude 5.1, caused a lateral eruption that reduced the elevation of the mountain's summit from 9,677 ft to 8,363 ft, leaving a 1 mile wide horseshoe-shaped crater. The debris avalanche was up to 0.7 cubic miles in volume.
context_section_description: Mount St. Helens is 34 miles (55 km) west of Mount Adams, in the western part of the Cascade Range. These "sister and brother" volcanic mountains are approximately 50 miles (80 km) from Mount Rainier, the highest of Cascade volcanoes. Mount Hood, the nearest major volcanic peak in Oregon, is 60 miles (100 km) southeast of Mount St. Helens.
  Mount St. Helens is geologically young compared with the other major Cascade volcanoes. It formed only within the past 40,000 years, and the pre-1980 summit cone began rising about 2,200 years ago. The volcano is considered the most active in the Cascades within the Holocene epoch (the last 10,000 or so years).
  Prior to the 1980 eruption, Mount St. Helens was the fifth-highest peak in Washington. It stood out prominently from surrounding hills because of the symmetry and extensive snow and ice cover of the pre-1980 summit cone, earning it the nickname, by some, "Fuji-san of America". The peak rose more than 5,000 feet (1,500 m) above its base, where the lower flanks merge with adjacent ridges. The mountain is 6 miles (9.7 km) across at its base, which is at an elevation of 4,400 feet (1,300 m) on the northeastern side and 4,000 feet (1,200 m) elsewhere. At the pre-eruption tree line, the width of the cone was 4 miles (6.4 km).
  Streams that originate on the volcano enter three main river systems: The Toutle River on the north and northwest, the Kalama River on the west, and the Lewis River on the south and east. The streams are fed by abundant rain and snow. The average annual rainfall is 140 inches (3,600 mm), and the snow pack on the mountain's upper slopes can reach 16 feet (4.9 m). The Lewis River is impounded by three dams for hydroelectric power generation. The southern and eastern sides of the volcano drain into an upstream impoundment, the Swift Reservoir, which is directly south of the volcano's peak.
  Although Mount St. Helens is in Skamania County, Washington, access routes to the mountain run through Cowlitz County to the west, and Lewis County to the north. State Route 504, locally known as the Spirit Lake Memorial Highway, connects with Interstate 5 at Exit 49, 34 miles (55 km) to the west of the mountain. That north–south highway skirts the low-lying cities of Castle Rock, Longview and Kelso along the Cowlitz River, and passes through the Vancouver, Washington–Portland, Oregon metropolitan area less than 50 miles (80 km) to the southwest. The community nearest the volcano is Cougar, Washington, in the Lewis River valley 11 miles (18 km) south-southwest of the peak. Gifford Pinchot National Forest surrounds Mount St. Helens.
caption: April 30, 2015, Mount St. Helens[9]
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