Mount Saint Helens, Gifford Pinchot National Forest, Washington

I plan to go Mount St. Helens last week!

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 south of Seattle, Washington and 50 miles northeast of Portland, Oregon.

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.

Mount St. Helens, is the most active volcano in the Cascade Range. Its most recent series of eruptions began in 1980 when a large landslide and powerful explosive eruption created a large crater, and ended 6 years later after more than a dozen extrusions of lava built a dome in the crater This volcano is well known for its ash explosions and pyroclastic flows.

Larger, longer lasting eruptions have occurred in the volcano's past and are likely to occur in the future. Although the volcano seems to have returned to a period of quiet, scientists with the U.S. Geological Survey and University of Washington Geophysics Program continue to closely monitor Mount St. Helens for signs of renewed activity.

Mount St. Helens is most notorious for its catastrophic eruption on May 18, 1980, at 8:32 am PDT, the deadliest and most economically destructive volcanic event in the history of the United States. After hundreds of additional earthquakes, steam explosions on March 27 blasted a crater through the volcano's summit ice cap. Within a week the crater had grown to about 1,300 feet in diameter and two giant crack systems crossed the entire summit area. By May 17, more than 10,000 earthquakes had shaken the volcano and the north flank had grown outward at least 450 feet to form a noticeable bulge. Such dramatic deformation of the volcano was strong evidence that molten rock (magma) had risen high into the volcano.

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 measuring 5.1 on the Richter scale, caused an eruption, reducing the elevation of the mountain's summit from 9,677 ft to 8,365 ft and replacing it with a 1 mile wide horseshoe-shaped crater. The debris avalanche was up to 0.7 cubic miles in volume.

As with most other volcanoes in the Cascade Range, Mount St. Helens is a large eruptive cone consisting of lava rock interlayered with ash, pumice, and other deposits. The mountain includes layers of basalt and andesite through which several domes of dacite lava have erupted. The largest of the dacite domes formed the previous summit, and off its northern flank sat the smaller Goat Rocks dome. Both were destroyed in the 1980 eruption.