Images

The May 18, 1980 debris avalanche from Mount St. Helens covered over 24 square miles (62 square kilometers) of the upper Toutle River valley and blocked tributaries of the North Fork Toutle River. New lakes such as Castle Lake (pictured here) and Coldwater Lake were created.

Debris avalanche deposit with hummocky terrain resulting from the May 18, 1980 eruption of Mount St. Helens. View to the east toward Coldwater Lake.

By 1987, the dome had replaced only three percent of the volume removed by the May 18, 1980 eruption. If that rate of growth had continued it would have taken over 200 years to rebuild Mount St. Helens to its pre-1980 size. Instead, Mount St. Helens entered a quiet period which continued until 2004.

One major concern to people living downstream of Mount St. Helens was a breakout of any of the impounded lakes, such as Coldwater or Castle Lakes, due to the instability of the debris dams blocking them. Flood waters from a breakout could be more catastrophic than the lahars of May 18, 1980.

Plume rises from Mount St. Helens' dome, Spirit Lake in foreground; view from the north. May 19, 1982.

Glacier extent maps on Mount St. Helens from before and after the May 18, 1980 eruption.

Outlet channels were built at Castle Lake and Coldwater Lake (shown here) to stabilize water levels and prevent overtopping of the debris dams.

USGS geologists gathered samples by hand from vents on the dome and crater floor. Additionally, sulfur dioxide gas was measured from a specially equipped airplane before, during, and after eruptions to determine "emission rates" for the volcano.

USGS geologists gathered samples by hand from vents on the dome and crater floor. Additionally, sulfur dioxide gas was measured from a specially-equipped airplane before, during, and after eruptions to determine "emission rates" for the volcano. During eruptions, emission rates typically increased to 5 to 10 times their pre-eruptive value.

In this view the dome is 535 feet (163 meters) high and nearly 1/4 mile (0.4 kilometers) wide, making it taller than a 44-story building (or, nearly the height of the Washington Monument) and wider than the length of four football fields. Compare with image taken August 12, 1985 from the same location with the same camera.

Seismic station installation in Mount St. Helens's crater 1981 lava dome. USGS, in conjunction with the University of Washington, maintain seismic stations at Mount St. Helens. An increase in seismicity (earthquakes) is often the first precursor to an approaching eruption.

The U.S. Geological Survey, in conjunction with the University of Washington, maintain seismic stations at Mount St. Helens. An increase in seismicity (earthquakes) is often the first precursor to an approaching eruption.

Lahars originating from Mount St. Helens after the 1980 eruption destroyed more than 200 homes and over 185 miles (300 kilometers) of roads. Pictured here is a damaged home along the South Fork Toutle River.

Between 1980 and 1986, Mount St. Helens' dome grew in different ways. From 1980 through 1982 the dome grew in periodic extrusions of stubby lava flows, called lobes. During this time frame Mount St. Helens' lobes grew at a rate of 3 to 10 feet per hour (1-3 meters/hour).

U.S. Army Corps of Engineers preformed dredging projects on the Toutle, Cowlitz, and Columbia Rivers and by 1987 enough material had been removed to build a 12 lane highway, one-foot thick from New York, NY to San Francisco, CA.

Small phreatic eruption of Mount St. Helens in the spring of 1980, before the May 18, 1980 blast.

This October dome was taller than a nine-story building and wider than the length of three football fields. This dome was not the first dome to grow in the crater. In June and August 1980, two domes formed, only to be blasted away by the explosive events of July 22 and October 16.

Nearly 135 miles (220 kilometers) of river channels surrounding the volcano were affected by the lahars of May 18, 1980. A mudline left behind on trees shows depths reached by the mud.

Many smaller animals, such as gophers, mice, frogs, fish, and insects were hibernating below ground or under water on May 18, 1980, and they survived the blast. Larger animals such as bear (whose tracks are shown here), elk, deer, and coyotes have been moving back into the area as their food supplies increase.

This lake was once surrounded by lush forest and is within the area devastated by the directed blast, covered by ash and tephra, then inundated by pyroclastic flows. Remnants of the forest float on the surface of the lake. Mount Rainier (4,392 m or 14,410 ft) is in the distance. The view is from the south.

The direction of the blast, shown here from left to right, is apparent in the alignment of the downed trees. Over four billion board feet of usable timber, enough to build 150,000 homes, was damaged or destroyed.