Mount St. Helens - 28 Years After Catastrophic Eruption

Prior to the 1980 eruption, Mount St. Helens was the fifth-highest peak in Washington.

At 8:32 AM Sunday morning, May 18, 1980, Mount St. Helens erupted causing catastrophic devastation which was the deadliest and most economically destructive volcanic event in the history of the United States.

(COUGAR, Washington) - At 8:32 AM Sunday morning, May 18, 1980, Mount St. Helens erupted causing catastrophic devastation which was the deadliest and most economically destructive volcanic event in the history of the United States.

Shaken by an earthquake measuring 5.1 on the Richter scale, the north face of this tall symmetrical mountain collapsed in a massive rock debris avalanche. Nearly 230 square miles of forest was blown down or buried beneath volcanic deposits. At the same time a mushroom-shaped column of ash rose thousands of feet skyward and drifted downwind, turning day into night as dark, gray ash fell over eastern Washington and beyond. The eruption lasted 9 hours, but Mount St. Helens and the surrounding landscape were dramatically changed within moments.

Fifty-seven people were killed; 250 homes, 47 bridges, 15 miles of railways, and 185 miles of highway were destroyed. The eruption caused a massive debris avalanche, reducing the elevation of the mountain's summit from 9,677 feet to 8,365 feet and replacing it with a mile-wide horseshoe-shaped crater. The debris avalanche was up to 0.7 cubic miles in volume. The collapse of the northern flank of St. Helens mixed with ice, snow, and water to create volcanic mudflows. They flowed many miles down the Toutle and Cowlitz Rivers, destroying bridges and lumber camps. A total of 3.9 million cubic yards of material was transported 17 miles south into the Columbia River by the mudflows.

During the lead-up to the 1980 eruption of Mount St. Helens, 83-year-old Harry R. Truman, who had lived near the mountain for 54 years, became famous when he decided not to evacuate before the impending eruption, despite repeated pleas by local authorities. His body was never found after the eruption. Had the eruption occurred one day later, when loggers would have been at work, rather than on a Sunday, the death toll would almost certainly have been much higher. Also among the victims of the 1980 eruption was 30-year-old volcanologist David A. Johnston, who was stationed on the nearby Coldwater Ridge. Moments before his position was hit by the hot ash cloud, Johnston uttered his famous last words: "Vancouver! Vancouver! This is it!" Johnston's body was never found. In 1982, President Ronald Reagan and Congress created the 110,000-acre National Volcanic Monument for research, recreation, and education. Inside the Monument, the environment is left to respond naturally to the disturbance.

Magma reached the surface of the volcano about October 11, 2004, resulting in the building of a new lava dome on the existing dome's south side. This new dome continued to grow throughout 2005 and into 2006. Several transient features were observed, such as the "whaleback," which comprised long shafts of solidified magma being extruded by the pressure of magma beneath. These features are fragile and break down soon after they are formed. On July 2, 2005, the tip of the whaleback broke off, causing a rockfall that sent ash and dust several hundred meters into the air.

Mount St. Helens showed significant activity on March 8, 2005, when a 36,000-foot plume of steam and ash emerged — visible from Seattle. This relatively minor eruption was a release of pressure consistent with ongoing dome building. The release was accompanied by a magnitude 2.5 earthquake.

Another feature to emerge from the dome is called the "fin" or "slab." Approximately half the size of a football field, the large, cooled volcanic rock was being forced upward as quickly as 6 feet per day. In mid-June 2006, the slab was crumbling in frequent rockfalls, although it was still being extruded. The height of the dome was 7,550 feet, still below the height reached in July 2005 when the whaleback collapsed.

On January 16, 2008, steam has begun seeping from a fracture atop the lava dome. Associated seismic activity is the most noteworthy since 2004. Scientists have suspended activities in the crater and the mountain flanks, but the risk of a major eruption is deemed low.

Sources: USGS and Wikipedia