Unified Interior Regions

Landslide on the flank of a small drainage in northwest Seattle. Foundation of house on right edge of photograph and decks of neighboring houses were undermined.

Angle and distance measurements to the Mount St. Helens' flanks were taken periodically to monitor for deformation similar to the 1980 bulge. Station northeast of volcano.

Deformation measurements on the Mount St. Helens' dome; three geologists in middle bottom of this aerial photograph.

The last dome-building eruption of Mount St. Helens during the 1980s occurred in October 1986. A new lobe was extruded, increasing the dome's height to 925 feet (282 meters), making it taller than a 77-story building. In volume, the dome was nearly 40 times the size of Seattle's Kingdome stadium. The view is from Harry's Ridge, five miles (8 kilometers) north of the

View of the Spirit Lake outlet tunnel, built in 1985, that allows water to drain out of Spirit Lake safely and maintain the lake's water level 100 ft (30 m) below the estimated overtopping level.

The lava dome was taller than a 66-story building and almost as wide as the length of nine football fields. The dome completely fills the camera's field of view. Compare with image taken August 22, 1981 from the same location with the same camera.

Mount St. Helens four years after the May 18, 1980 eruption—lava dome in the crater and drainage channels development on flanks; view from Johnston Ridge.

Vegetation began reappearing as early as the summer of 1980 as many small trees and plants were protected by the snowpack on May 18. Seeds, carried by the wind or by animals, also entered the area and grew. By 1985, the ridges surrounding the volcano were covered with new growth.

The strength of the magnetic field increased as the dome cooled and magnetic minerals formed. During the eruptions the strength usually changed rapidly as magma heated and deformed the dome.

Harry's Ridge monitoring station, 8 km (5 mi) north of Mount St. Helens' crater.