Images

Lava fountains erupt from fissures during the first week of the Pu‘u ‘Ō‘ō eruption south of Pu‘u Kahaualea, approximately 2.4 km (1.5 miles) northeast of where subsequent eruptions built the Pu‘u ‘Ō‘ō cone. The early fissures cut through old forested lava flows in a remote section of Kīlauea's east rift zone.

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.

The September 25, 1982, Kaluapele eruption was a brief but vigorous event that followed nearly two hours of seismic unrest and rapid summit inflation. Lava erupted from a 1,150-foot-long fissure near the southern end of the caldera, producing fountains up to 220 feet high.

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

Plumes of steam, gas, and ash often occured at Mount St. Helens in the early 1980s. On clear days they could be seen from Portland, Oregon, 50 miles (81 kilometers) to the south.

The April 30, 1982, Kaluapele eruption was a short-lived summit event that lasted about 19 hours. Lava erupted from a 3,200-foot-long fissure northeast of Halemaʻumaʻu crater, producing low fountains 15–30 feet high, with bursts up to 160 feet.

The lahar flowed from the crater into the North Fork Toutle River valley and eventually reached the Cowlitz River 80 km (50 mi) downstream. The lahar also entered Spirit Lake, which can be seen in the lower left corner.

People living adjacent to streams and rivers that flow away from the volcano are continually impacted by the upstream erosion and downstream sedimentation of the large volume of material erupted in 1980. The decrease in carrying capacity in downstream channels increases the chance for flooding.

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.

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.

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.

These pyroclastic-flow deposits of the climactic eruption of Mount Mazama, during which Crater Lake caldera formed, are eroded into spectacular spires at The Pinnacles on Wheeler Creek.

Pinnacles left by erosion of fumaroles that formed as layered pyroclastic flow deposit released gas and solidified into chimneys that eventually eroded, Crater Lake, Oregon.

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).

These measurements were used to study the erosion processes and to estimate the severity of the sedimentation problem. Rod person (lower left) and instrument persons (upper right) give scale.

Photo 15 of 15: Water level in sinkhole chimney stabilized since the previous day. View to south across the sinhole.