Images

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

Low fountain, approximately 50 meters high, from Pu'u 'O'o on Hawai'i Island's Kilauea Volcano (viewed from the north). Lava issuing from the breach in the northeast rim of the crater produced an 'a'a flow that extended more than 4 kilometers. Eruption episode 8.

Pu'u 'O'o fountain approximately 100 meters high during eruption episode 8 on Hawai'i Island's Kilauea Volcano. Dark clots of spatter land near the base of the fountain, contributing to the growth of the cone. Less dense cinder, visible in the upper right, is carried downwind of the cone.

Accretionary lava ball comes to rest on the grass after rolling off the top of an 'a'a flow in Royal Gardens subdivision on Hawai'i Island's Kilauea Volcano. Accretionary lava balls form as viscous lava is molded around a core of already-soldified lava.

View at dusk of the young Pu'u 'O'o cinder-and-spatter cone, with fountain 40 meters high, on Hawai'i Island's Kilauea Volcano (episode 5).

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.

The April 1983 landslide at Thistle, Utah, created a 200-ft-high (60-m-high) blockage of Spanish Fork canyon that caused disastrous flooding of the Thistle creek and Soldier Creek valleys upstream.  The flooding caused by the landslide required relocation of a major highway and railway.  An emergency spillway and diversion tunnels were constructed to drain

Arching fountain of lava approximately 10 meters high issuing from the western end of the 0740 vents, a series of spatter cones 170 meters long, south of Pu'u Kahaualea on Hawai'i Island's Kilauea Volcano (episode 2). Episodes 2 and 3 were characterized by spatter and cinder cones, such as Pu'u Halulu, which was 60 meters high by episode 3.

Forest of lava trees resulting from eruption of a 1-km-line of vents east of Pu'u Kahaulea on Hawai'i Island's Kilauea Volcano. The bulbous top of each lava tree marks the high stand of the lava flow as it spread through the trees.

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.