Mount St. Helens Precursory Activity

Phreatic explosion on March 30, 1980. USGS Photo courtesy of Dan Miller.

Explosions, Tremor and Traffic - This week's activity at Mount St. Helens was characterized by intense seismic swarms and frequent phreatic explosions. The average daily amount of energy released by earthquake activity reached its highest level on April 2. The first harmonic tremor detected on April 1 suggested that magma was on the move beneath the volcano. Phreatic explosions created a second crater which quickly merged with the first, and the north flank showed the first signs of significant deformation. Continued closures taxed law enforcement budgets and the patience of those interested in accessing restricted areas.

Earthquake Activity Peaks

The number of earthquakes reached its highest level about the same time that explosions began. Over the next few days the number of earthquakes dropped but the average magnitudes increased (see plot below). The result was an increase in the amount of seismic energy released. Both the number of earthquakes and energy release reached their highest values within the first two weeks of volcanic unrest. Over the next two months the number of earthquakes steadily declined, while the amount of energy released fluctuated but did not surpass previous peaks.

Number of earthquakes > magnitude 2.5 per 6 hour period (plotted as black line) and daily energy release (red line, shaded area). The earthquake counts reached their highest point prior to the May 18 eruption on March 27th, but the daily energy release did not peak until a few days later (Modified from USGS Professional Paper 1250, p.101).

During the first week of April a different type of seismic signature was showing up on seismograms from Mount St. Helens. On April 1 the first weak harmonic tremor was detected. Stronger bursts of harmonic tremor were recorded on the 2nd. The seismogram to the right is an example of harmonic tremor recorded at seismic station RAN on April 2.

Seismogram of harmonic tremor recorded on seismic station RAN on April 2, 1980. Click here or on the image above to see more of this April 2 seismogram.

Earthquake activity during the week was accompanied by frequent explosions that drew crowds of scientists and tourists on the ground and in the air alike. During periods when the mountain was covered by clouds, USGS observers flying above the volcano documented explosions that were large enough to penetrate the cloud layer. The series of five photographs below records an explosion that occurred on the afternoon of April 2. USGS photos courtesy of Dan Miller.

Daily Log

March 29 - A second crater formed to the west of the first and was visible on the morning of the 29th. Steam and ash mainly vented from this new crater. There were 86 earthquakes larger than magnitude 3.0 and 39 earthquakes between magnitude 3.5 and 4.4 recorded. USGS hydrologists have detected no unusual increase in streamflow, but noted a slight acidification of surface waters in areas contaminated with ash from earlier explosions. Throughout the night a blue flame was observed intermittently in the older crater or jumping between the old and new craters. According to USGS Geologist David Johnston, the flame was likely a result of the emission of a flammable gas, probably hydrogen sulfide.

A second crater (foreground) on the summit of Mount St. Helens was visible on the morning of March 29. USGS photo courtesy of Don Swanson.

March 30 - Ninety three explosions of steam and ash were observed. Ash from some of these reached the towns of Cougar and Stevenson to the southeast and was detected as far away as Mount Jefferson. Light ashfall in the Bull Run Watershed near Mount Hood prompted official concern at the Portland Water Bureau over possible acidification of the city's water supply. There were 58 earthquakes larger than magnitude 3.0, including 6 larger than magnitude 4.0. A group from Dartmouth College began remote measurements of sulfur dioxide (SO₂). Early results showed the volcano emitted about 0.3 tons per day, which verified the identification of sulfur dioxide detected on the 28th. USGS scientists installed a tiltmeter near the volcano.

A carnival-like atmosphere prevailed around Mount St. Helens. By afternoon as many as 70 aircraft were reportedly flying around the volcano at the same time. At the Yale Reservoir boat launch over 300 cars were parked as sightseers sought a good view of the mountain. From Interstate 5 to the roadblock at mile 35 on State Route 504, vehicles lined both sides of the road at vantage points such as Silver Lake.

One of ninety three explosions that occurred on March 30. USGS photo courtesy of Rick Hoblitt.

March 31 - Both craters enlarged as explosions continued. A change in wind direction brought ash to the Kelso-Longview area by noon. To date none of the ash from these explosions has come from new magma, but rather pulverized bits of older rocks that make up the summit. The frequency of earthquakes has decreased but the number of larger earthquakes has increased, so the total energy release remained about the same. Among these were two earthquakes of magnitude 4.6. Explosions and earthquakes triggered two avalanches of snow and rock near the Goat Rocks dome.

Cowlitz County Commisioners declared a state of emergency in an attempt to obtain assistance from the Washington National Guard in staffing roadblocks. According to a report in the Longview Daily News, Colonel Val E. McCreary (commander of the WA National Guard) announced that 300 troops, 50 trucks and 3 helicopters were on standby in case Governor Ray ordered evacuations. The Washington Department of Emergency Services (WADES) pressed the Clark County Amateur Radio Club into service as a backup communications network should the primary network maintained by the USFS fail.

Public response to the activity varied. The Vancouver Columbian reported that USFS personnel had fielded calls from frustrated citizens who could not access their cabins within closed areas while members of the press had been allowed in. Other calls ranged from gamblers requesting the number of explosions in the previous 24 hours to those blaming the volcano's restlessness on the desecration of Indian graves in the area.

Harry Truman began his climb to media folk-hero status due to extensive coverage in newspapers and television. He is the only person who has refused to leave his home on the south shore of Spirit Lake. A Longview Daily News article quoted Harry as saying, "I think the whole damn thing is overexaggerated...Spirit Lake and Mount St. Helens are my life...You couldn't pull me out with a mule team."

Continued explosive activity enlarged the two craters and ate away at the narrow bridge separating them. USGS photo courtesy of Rick Hoblitt.

April 1 - Several plumes from explosions reached altitudes of 20,000 feet. Ashfall was reported south of the mountain in Cougar and as far away as the outskirts of Vancouver. Some observers claimed these were the strongest explosions to date. Ongoing explosive activity has caused the two craters to merge into one single crater over 600 feet across. A block of the summit bounded by two crack systems has sunk at least 200 feet. The settling has caused noticeable outward displacement, or bulging, of the rocks and ice north of the crater. Two earthquakes of magnitude 4.7 occurred, as well as the first weak harmonic tremor.

Large cracks crossing the summit bounded a wedge of rock and ice that included the crater. This block, or graben, had sunk at least 200 feet by April 1. USGS photo courtesy of Richard Waitt.

The occurrence of larger earthquakes accompanied by harmonic tremor, more vigorous explosions, and presence of sulfur dioxide led scientists to suggest that there is an increased possibility of an eruption involving magma. Attempts to obtain aerial photographs of the mountain were unsuccessful due to poor weather. Scientists would like photos to compare with similar ones taken in 1979 to help determine the physical changes that have occurred.

Cowlitz and Skamania County officials decided to ask the Washington National Guard for assistance. The two counties have been maintaining six roadblocks around the clock since March 27. They estimate that because of the extensive network of logging roads, they would need as many as 29 roadblocks and 175 officers to completely block off access. Nolan Lewis, Director of Cowlitz County Emergency Services, was quoted in the Tacoma News Tribune,"I just can't fathom it, people are swarming in from all over, putting their lives in danger... Sunday when the weather was clear, the road up to the mountain looked like downtown Seattle at rush hour."

Federal Aviation Administration (FAA) officials transferred control of air traffic operations around Mount St. Helens to their Seattle center. In a Vancouver Columbian article, an FAA spokesman said that an estimated 100 planes were in the controlled area at times. Aircraft have maintained radio silence and illegally entered the restricted area from all directions and altitudes. According to a Longview Daily News article, one pilot reported,"It was like a dog fight over the crater last Thursday (March 27) before the Forest Service started its air control."

About 300 loggers returned to work in areas northwest of the volcano.

Cars lined State Route 504 approaching the roadblock. Clear weather drew crowds of volcano watchers closer to the mountain. USGS photo courtesy of Lyn Topinka.

April 2 - At least 12 plumes of steam and ash were observed above the mountain. One reached an altitude of 20,000 feet. Light ashfall was reported in Portland and Vancouver. At least one explosion threw out chunks of ice that fell to the west of Spirit Lake. There were 63 earthquakes larger than magnitude 3.0, including 5 larger than 4.0 (the largest was magnitude 4.8). A stronger burst of harmonic tremor was recorded between about 7:35 and 7:50 AM. The 2nd would turn out to be the most active day for earthquakes with magnitudes greater than 3.0 for the entire month of April.

Ashfall from the continuing explosions caused concern for US Fish and Wildlife Officials at the Wind River and Carson National Salmon Hatchery. According to an article in the Longview Daily News, water normally a pH of 6.8 had decreased to 6.1 in the river and to 5.8 in the hatchery water. Water with a pH of 5.5 would begin to cause extreme stress to the fish. Fish would begin to die in water with at a pH of 5. Operators said they plan to release the hatchlings if the water reaches a pH of 5.5.

Cowlitz County deputies abandoned roadblocks as the day ended. According to an article in The Oregonian, the State Department of Emergency Services (WADES) claimed the counties had not supplied all the information needed in order to offer assistance. Officials from both Cowlitz and Skamania County were critical of the state's response. The State Patrol took over manning the roadblock on State Route 504 while Skamania County continued to man roadblocks on State Route 503 and road N73 north of Carson.

The USFS sent 30 moving vans to the St. Helens Ranger District compound to remove the personal possessions of 37 Forest Service employees who had been evacuated March 27.

A Boston television producer was fired after airing an April Fool's Day story about a popular ski resort that had turned into a raging volcano. It included video footage of explosions from St. Helens.

One of at least twelve explosions that were observed on April 2. USGS photo courtesy of Richard Waitt.

Ash blown downwind carried with it sulfurous compounds. Over time continued ashfall in some areas led to a slight acidification of waters at the Wind River and Carson National Salmon Hatchery. USGS photo courtesy of Richard Waitt.

Moving vans remove personal possessions from the St. Helens Ranger District compound. Forest Service employess and their families had been evacuated on March 27 following the first explosion. USFS photo courtesy of Jim Hughes.

April 3 - Explosions sent plumes upwards from the crater almost hourly. Ash was reported in and near Tacoma, 70 miles to the north. Some plumes reached altitudes of 16 to 17,000 feet. The crater is now approximately 1500 feet wide and 300 feet deep. Seismometers recorded 6 earthquakes equal to or larger than magnitude 4.0, including one of magnitude 4.6. Two bursts of harmonic tremor were also recorded.

Governor Dixie Lee Ray declared a State of Emergency and set up a "Mount St. Helens Watch Group." Local officials in Oregon and Washington issued pamphlets prepared by the Federal Emergency Management Agency on "What to do during a volcano ashfall."

Tourists continue to flock to Mount St. Helens. Milepost 33 on State Route 504 has turned into a popular area with volcano watchers. According to a report in The Oregonian, a Weyerhaeuser logging supervisor said his employees were just as curious as the tourists,"...our attendance record (on the job) has been better than ever since the mountain blew. They may be nervous, but this way they can come and gawk." According to later reports in several local newspapers, a Skykomish, WA, man apparently evaded roadblocks and reached the summit of St. Helens on foot. The FAA reported 109 planes inside the restricted zone.

By April 3 the crater had expanded to 1500 feet across and 300 feet deep. USGS photo courtesy of Richard Waitt.

The "Hula Hut" near the roadblock on State Route 504 offered barbecued Hawaiian food and hot dogs for the many sightseers that congregated in the area. USGS photo courtesy of Lyn Topinka.

April 4 - Explosions continued with some plumes reaching altitudes of 16,000 feet. Two more episodes of harmonic tremor and 5 earthquakes with magnitudes larger than 4.0 were recorded. Approximately two to three earthquakes of magnitude 3 or 4 were recorded each hour. USGS hydrologist David Frank set up a time-lapse camera at a location 8.4 miles northwest of the volcano. The site overlooks the North Fork Toutle River and has an unobstructed view of St. Helens. It is considered to be high enough to provide safety from even the largest expected mudflow. Additional instruments are slated to be installed over the next few days. The scientists refer to the observation post as "Coldwater" (later referred to as "Coldwater I," following the establishment of a second observation post 4 miles north of the crater called "Coldwater II"). Scientists considered the greatest hazards from an eruption to be flash floods or mudflows, particularly those that might cause Swift Reservoir to overflow.

Washington State Department of Transportation established a volcano viewing area near Ridgefield off of Interstate 5 and made plans to secure another viewing site near Centralia-Chehalis. State officials moved the roadblock on State Route 504 about 20 miles further from the volcano. The roadblock at milepost 34 remained in place, but was unmanned. Officials also considered changes to the roadblock on State Route 503 near Cougar. Governor Dixie Lee Ray called out the National Guard to assist deputies at roadblocks. According to articles in the Vancouver Columbian, overtime for Skamania County law enforcement maintenance of roadblocks ran $6,000 (out of an annual budget of $11,000) for the three days following the first explosions. Loggers met with scientists and public officials in Vancouver to push for more access to restricted areas. According to a Vancouver Columbian article, one company claimed that 50% of their workers have been laid off and operations reduced by 80% due to closures.

Map showing distribution of hazards (47Kb) from a possible eruption of Mount St. Helens for April 1, 1980. Modified from Crandell and Mullineaux, 1978: "Potential Hazards From Future Eruptions of Mount St. Helens Volcano, Washington." Graphic by Lisa Faust, USGS.