Mount St. Helens

Inside the crater of Mount St. Helens, a lava dome was built between October 1980 and 1986 by seventeen eruptions of viscous dacite lava. Each eruption added between 1 and 22 million m3 of new lava to the dome; most of the growth occurred when magma extruded onto the surface of the dome to form lava flows as thick as 40 m and as large as 400 m in diameter. The repeated rise of magma into the dome before the eruptions produced an exceptional pattern of ground tilt on the crater floor that began 2 to 4 weeks before magma extruded onto the dome. This repeated pattern of ground tilt was one of the most reliable measurements of deformation that we used to accurately predict when the Mount St. Helens lava dome would erupt.

At 8,365 feet, the rim of Mount St. Helens provides outstanding views of the crater, lava dome, blast area, and surrounding volcanic peaks. The most popular route to the summit is Monitor Ridge, starting at Climber's Bivouac. Most climbers complete the round trip in 7 to 12 hours. The route begins on the Ptarmigan Trail #216A which gently climbs for about 2 miles to timberline. Above timberline, the route travels over steep, blocky lava flows on the lower slopes and loose, sandy volcanic ash on the upper slopes. In early summer, snow is commonly encounted, especially in gully bottoms.