Volcano! ~

Mount St. Helens---
Stratovolcano

Mount St. Helens is an active stratovolcano located in Skamania County, Washington, in the Pacific Northwest region of the United States. It is 96 miles (154 km) south of Seattle, Washington and 50 miles (80 km) northeast of Portland, Oregon. Portland, Oregon is the nearest major city from Mount St. Helens. It is 50 miles (80 km) northeast of Mount St. Helens with a population of 582,130

This 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.
(Date of most destructive eruption) Mount St. Helens is most famous for its catastrophic eruption on May 18, 1980, at 8:32 am PDT[2] which was the deadliest and most economically destructive volcanic event in the history of the United States. Fifty-seven people were killed; 250 homes, 47 bridges, 15 miles (24 km) of railways, and 185 miles (298 km) of highway were destroyed. A massive debris avalanchetriggered by an earthquake measuring 5.0 on the Richter scale, caused an eruption, reducing the elevation 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.[3] The debris avalanche was up to 0.7 cubic miles (2.9 km3) in volume.
(Date of most recent eruption) On January 16, 2008, steam began seeping from a fracture on top of the lava dome. Associated seismic activity was the most noteworthy since 2004. Scientists suspended activities in the crater and the mountain flanks, but the risk of a major eruption was deemed low.[37] By the end of January, the eruption paused; no more lava was being extruded from the lava dome. On July 10, 2008, it was determined that the eruption had ended after more than six months of no volcanic activity.[38]
(Other events associated with the last eruption) On May 18, with little warning, a second earthquake, of magnitude 5.1, triggered a massive collapse of the north face of the mountain. It was the largest known debris avalanche in recorded history. The magma inside of St. Helens burst forth into a large-scale pyroclastic flow that flattened vegetation and buildings over 230 square miles (600 km2). More than 1.5 million metric tons of sulfur dioxide were released into the atmosphere.[25] On the Volcanic Explosivity Index scale, the eruption was rated a five (a Plinian eruption).
http://en.wikipedia.org/wiki/Mount_St._Helens


(Major hazards to humans) Volcanic gases were directly responsible for approximately 3% of all volcano-related deaths of humans between 1900 and 1986.[1] Some volcanic gases kill by acidic corrosion; others kill by asphyxiation. The greenhouse gas, carbon dioxide, is emitted from volcanoes, although volcanic emissions account for less than 1% of the annual global total.[3] Some volcanic gases including sulfur dioxide, hydrogen chloride, hydrogen sulfide and hydrogen fluoride react with other atmospheric particles to form aerosols. [1]
http://en.wikipedia.org/wiki/Volcanic_gas

Volcanic eruptions are one of Earth's most dramatic and violent agents of change. Not only can powerful explosive eruptions drastically alter land and water for tens of kilometers around a volcano, but tiny liquid droplets of sulfuric acid erupted into the stratosphere can change our planet's climate temporarily. Eruptions often force people living near volcanoes to abandon their land and homes, sometimes forever. Those living farther away are likely to avoid complete destruction, but their cities and towns, crops, industrial plants, transportation systems, and electrical grids can still be damaged by tephra, ash, lahars, and flooding.
http://volcanoes.usgs.gov/hazards/index.php

(Minimising risk to the population)
• participates in volcano-emergency planning workshops and emergency-response exercises
• convenes international, regional, and local workshops focused on volcano-hazard issues
• prepares educational materials with partners, including exhibits, fact sheets, booklets, video programs, and maps
• collaborates with emergency-management specialists to develop effective warning schemes
• meets with community leaders and residents wanting information about potentially dangerous volcanoes in their area
• works with the news media and media producers
• leads educational field trips to active and potentially dangerous volcanoes for the public, officials, local residents, educators, and students
• helps educators and students with classroom presentations, teacher workshops, field trips, and activities

http://volcanoes.usgs.gov/hazards/planning.php