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Summary of Events Leading Up to the
May 18, 1980 Eruption of Mount St. Helens

Mount St. Helens Precursory Activity - April 26 - May 2, 1980

The "bulge" as seen from Timberline on April 26, 1980. USGS Photo.

Explosions slowed, then ceased. The relatively serene appearance of the volcano made it difficult for officials to convince the public of the increasing hazards. According to a USFS spokesman, "I feel the general public really doesn't understand the danger."

Aerial and ground surveys confirmed a bulge about one mile long and one half mile wide on the north flank of the volcano.

Scientists were extremely concerned that large avalanches of rock, snow and ice from the bulge high on the volcano could reach Spirit Lake and State Route 504 within a few minutes.

April 26 - Steam and ash failed to rise above the crater rim. The tiltmeter at Timberline showed downward tilt to the north, but data from tiltmeters on the south and east flanks did not provide much useful information.

The Gifford Pinchot National Forest announced plans to set up tourist information centers at sites with a view of the mountain.

Weyerhaeuser considered blocking active logging roads to keep tourists out during the summer. They cited concerns over potential problems with congestion, fires, and accidents with logging trucks.

In late April small steam plumes barely rose above the crater rim. USGS photo courtesy of Dan Miller.

April 28 - Poor visibility hampered visual observations. No signs of explosion debris were noticed beyond the crater. When visible, the crater continued to emit small puffs of steam and ash. The Timberline tiltmeter data suggested continued deformation of the north flank.

According to a Longview Daily News article, USGS geologist Dave Johnston said the precise laser surveys revealed that the bulge is not confined to the Forsythe Glacier, but also included Goat Rocks dome. "It's very dramatic to see this much ground motion. It is unusual in a volcano and demands explanation. It can't be anything but some type of dramatic change going on inside the mountain." He added that even if the volcano quieted down, an extreme danger would persist until the north flank stabilized. The "only way it can stabilize is to come down."

Average rates of displacement for EDM targets on the north flank of Mount St. Helens. Red arrows indicate direction, length of arrows is proportional to rate of displacement. Dashed black line indicates outline of the bulge. Black circles are EDM stations. Figure modified from USGS Professinal Paper 1250, p. One meter equals 3.3 feet.

April 29 - Further studies of aerial photographs revealed that the bulge was about one mile long and one half mile wide. Ground surveys confirmed that between April 27 and 29 Goat Rocks dome shifted about 9 feet to the northwest. The Timberline tiltmeter continued to show downward tilt to the north, suggesting the bulge extended that far north.

Scientists believed the bulge represented the most serious potential hazard. The most serious concerns were about the likelihood of an avalanche into the North Fork Toutle River and Spirit Lake. An avalanche of snow, ice, and rock from the high part of the volcano could move downslope at more than 100 miles per hour.

Emergency services officials are frustrated because the public appeared to remain unaware of the danger. One official was quoted in the Seattle Post-Intelligencer as saying: "The mountain looks so serene, so people can't fathom 4,000 vertical feet of earth, rock and ice plunging into (Spirit Lake) in less than two minutes."

State officials asked the governor to close a large area around the volcano. The plan called for a Red Zone (no public access) and a Blue Zone (restricted access).

Aerial view of summit and highly fractured bulge high on the north flank. USGS photo courtesy of Dan Miller.

Aerial view of crater from the west. As the bulge continued to push outward, the large graben containing the crater was sinking. USGS photo courtesy of Dan Miller.

April 30 - The volcano remained quiet, but the bulge continued to expand northward. Only 15 earthquakes larger than magnitude 3.0 were recorded, including 6 larger than magnitude 4.0.

During the quiet, USGS geologist Dave Johnston sampled water from a small pond that had formed in the crater bottom. Concerned with the increasing instability of the bulge, USGS scientists issued an updated Hazards Warning.

Governor Ray and Forest Supervisor Robert Tokarczyk closed additional areas near the volcano based on this information. A Red Zone was established whose boundary ranged from 3 to 7 miles out from the peak. Access in this zone was restricted to scientists, law enforcement, and other officials. A Blue Zone was established. Access into this area was restricted during daylight hours to loggers and property owners with special permits.

David Johnston en route to sample ponded water inside the crater on April 30, 1980. USGS photo courtesy of Dan Miller.

May 1 - The mountain continued to steam continuosly without explosions. A small pool of water persisted in the crater. One survey target reportedly moved outward two feet in less than 12 hours. There were 26 earthquakes larger than magnitude 3.0, including 5 larger than 4.0.

A new seismic station was installed on Dogs Head to help detect earthquakes that might trigger a major avalanche and to improve the accuracy of earthquake location.

The USGS established a new observation post about 5 miles north of the summit. Dubbed "Coldwater II", the site housed time-lapse cameras and monitoring equipment from the previous site at Coldwater. A travel trailer has been placed on site to provide shelter for observers who are now located there around the clock.

According to the Longview Daily News two new gates were placed on State Route 504, one at Camp Baker and one at the Skamania County line. The paper also reported that although Cougar was inside the Blue Zone, residents had not yet been asked to evacuate. Also according to the same issue, at least three cabin owners in the Spirit Lake area refused to pay their annual property taxes because they were not allowed access to their property.

New gates closed State Route 504 at Camp Baker and at the Skamania County line. USGS photo.

May 2 - No explosions were reported. There were 30 earthquakes larger than magnitude 3.0, including 8 larger than 4.0. Five of these occurred within a twenty minute period, waking residents of Toutle. To date there have been 2,395 earthquakes larger than magnitude 3.0 recorded, including 258 larger than 4.0.

Thermal infrared surveys made by personnel from the US Naval Air Station at Whidbey Island revealed a previously unknown area of warm rock in the middle of the bulge. Ice continued to break up in this area, which was about 100 feet long and 50 feet wide.

Skamania County Sheriff Bill Closner accused television newsmen of practicing "one-upsmanship" by continuing to fly helicoters into the Red Zone. USFS spokesman Jim Unterwegner expressed concern that people did not seem to take the danger seriously: "One of the problems we're having ... is that people in the Northwest have never faced this kind of thing before ... I feel the general public really doesn't understand the danger." He referred to a man who recently telephoned to request a permit to climb the mountain. The man wanted to lodge a complaint when the permit was denied.

According to the Longview Daily News, Spirit Lake cabin owners became eligible for federally funded flood insurance. The insurance would not cover homes crushed by an avalanche, however.

Topographic map showing increases in elevation (blue) and decreases in elevation from April 12 to May 1, 1980. Contour interval is 40 feet. Solid black line indicates outline of the bulge. Dashed black line is outline of crater following May 18 eruption. Modified from USGS Professional Paper 1250, p. 126.

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