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Debris avalanche deposit with hummocky terrain resulting from the M...
January 13, 1984

Debris avalanche deposit with hummocky terrain resulting from the M...

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

Dome in Mount St. Helens crater; two USGS geologists (one in orange...
May 26, 1983

Dome in Mount St. Helens crater; two USGS geologists (one in orange...

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.

Early Warning Gage on Coldwater Lake at Mount St. Helens continuous...
October 1, 1982

Early Warning Gage on Coldwater Lake at Mount St. Helens continuous...

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. Gages, such as this Early Warning Gage on Coldwater Lake, were installed at lakes

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

Plume rises from Mount St. Helens' dome, Spirit Lake in foreground;...

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

Outlet channels were built at Castle Lake and Coldwater Lake (shown...
October 17, 1981

Outlet channels were built at Castle Lake and Coldwater Lake (shown...

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

Image shows two scientists on the slopes of Mount St. Helens with steam rising around them
September 24, 1981

Gas Sampling around the Mount St. Helens Dome

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.

Gas sampling around the Mount St. Helens dome. Analyzed results us...
September 24, 1981

Gas sampling around the Mount St. Helens dome. Analyzed results us...

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.

Lava dome in Mount St. Helens' crater, August 1981, viewed from a p...
August 22, 1981

Lava dome in Mount St. Helens' crater, Aug. 1981, viewed from a pho...

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.
August 4, 1981

Seismic station installation in Mount St. Helens's crater 1981 lava do

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.

Seismic station installation in Mount St. Helens's crater 1981 lava...
August 4, 1981

Seismic station installation in Mount St. Helens's crater 1982

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 de...
July 19, 1981

Lahars originating from Mount St. Helens after the 1980 eruption de...

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.

Dome within Mount St. Helens crater (aerial view) from June 1981 wi...
June 26, 1981

Dome within Mount St. Helens crater (aerial view) from June 1981 wi...

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).