Mt St. Helens 27 years Ago Today

[Christina]

The following is taken from the link at Wikipedia:"On March 20, 1980, Mount St. Helens experienced a magnitude 4.2 earthquake. Steam venting started on March 27. By the end of April, the north side of the mountain started to bulge. With little warning, a second earthquake of magnitude 5.1 May 18 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). On the Volcanic Explosivity Index scale, the eruption was rated a five (a Plinian eruption).""The collapse of the northern flank of St. Helens mixed with ice, snow, and water to create lahars (volcanic mudflows). The lahars flowed many miles down the Toutle and Cowlitz Rivers, destroying bridges and lumber camps. A total of 3.9 million cubic yards (3.0 million m³) of material was transported 17 miles (27 km) south into the Columbia River by the mudflows.""For more than nine hours, a vigorous plume of ash erupted, eventually reaching 12 to 16 miles (20 to 27 km) above sea level. The plume moved eastward at an average speed of 60 miles per hour (95 km/h), with ash reaching Idaho by noon.""By about 5:30 p.m. on May 18, the vertical ash column declined in stature, and less severe outbursts continued through the night and for the next several days. In all, St. Helens released energy equivalent to 350 megatons of TNT; or 27,000 atomic blasts over Hiroshima; or seven times more than the strongest atomic bomb ever built and tested, the Tsar Bomba. It ejected more than 0.67 cubic miles (2.8 cubic km) of material. The removal of the north side of the mountain reduced St. Helens' height by about 1,300 feet (400 m) and left a crater one to two miles (1.6 to 3.2 km) wide and 0.5 mile (800 m) deep, with its north end open in a huge breach. The eruption killed 57 people, nearly 7,000 big game animals (deer, elk, and bear), and an estimated 12 million fish from a hatchery. It destroyed or extensively damaged over 200 homes, 185 miles (300 km) of highway and 15 miles of railways."

 

[tomwebster]

These are some interesting pics of Mt St Hellens from 1980 to 2004:http://vulcan.wr.usgs.gov/Volcanoes/MSH/Im.../framework.html