page_title: David A. Johnston
section_title: Final signs and primary blast
hierarchical_section_title: David A. Johnston / Eruption / Final signs and primary blast
caption_attribution_description: English: This slide shows Mount St. Helens, one day before the devastating eruption. The view is from Johnston Ridge, six miles (10 kilometers) northwest of the volcano. Italiano: Monte Sant'Elena il giorno prima dell'eruzione del 1980 Slovenčina: Sopka St. Helens pre erupciou v roku 1980.
context_page_description: David Alexander Johnston was an American United States Geological Survey volcanologist who was killed by the 1980 eruption of Mount St. Helens in the U.S. state of Washington. A principal scientist on the USGS monitoring team, Johnston was killed in the eruption while manning an observation post six miles away on the morning of May 18, 1980. He was the first to report the eruption, transmitting "Vancouver! Vancouver! This is it!" before he was swept away by a lateral blast. Despite a thorough search, Johnston's body was never found, but state highway workers discovered remnants of his USGS trailer in 1993.
  Johnston's career took him across the United States, where he studied the Augustine Volcano in Alaska, the San Juan volcanic field in Colorado, and long-extinct volcanoes in Michigan. Johnston was a meticulous and talented scientist, known for his analyses of volcanic gases and their relationship to eruptions. This, along with his enthusiasm and positive attitude, made him liked and respected by many co-workers. After his death, other scientists lauded his character, both verbally and in dedications and letters.
context_section_description: Given the increasing seismic and volcanic activity, Johnston and the other volcanologists working for the USGS in its Vancouver branch prepared to observe any impending eruption. Geologist Don Swanson and others placed reflectors on and around the growing domes, and established the Coldwater I and II observation posts to use laser ranging to measure how the distances to these reflectors changed over time as the domes deformed. Coldwater II, where Johnston died, was located just 6 miles (10 km) north of the mountain. To the astonishment of the USGS geologists, the bulge was growing at a rate of 5 to 8 feet (1.5 to 2.4 meters) per day.
  Tiltmeters installed on the volcano's north side displayed a northwest trending tilt for that side of the mountain, and a southwest trending tilt was observed on the south side. Worried that the amount of pressure on the magma underground was increasing, scientists analyzed gases by the crater, and found high traces of sulfur dioxide. After this discovery, they began to regularly check the fumarolic activity and monitor the volcano for dramatic changes, but none were observed. Disheartened, they instead opted to study the growing bulge and the threat an avalanche could have for humans relatively near the volcano.  An evaluation of the threat was carried out, concluding that a landslide or avalanche in the Toutle River could spawn lahars, or mudflows, downstream.
  At that point, the previously consistent phreatic activity had become intermittent. Between May 10 and May 17, the only change occurred on the volcano's north flank, as the bulge increased in size. On May 16 and 17, the mountain stopped its phreatic eruptions completely.
  The active Mount St. Helens was radically different from its dormant form, now featuring an enormous bulge and several craters. In the week preceding the eruption, cracks formed in the north sector of the volcano's summit, indicating a movement of magma.
  At 8:32 a.m. local time the next day (18 May), an earthquake measuring magnitude 5.1 rocked the area, triggering the landslide that started the main eruption. In a matter of seconds, vibrations from the earthquake loosened 2.7 cubic kilometers (0.6 cu mi) of rock on the mountain's north face and summit, creating a massive landslide. With the loss of the confining pressure of the overlying rock, Mount St. Helens began to rapidly emit steam and other volcanic gases. A few seconds later, it erupted laterally, sending swift pyroclastic flows down its flanks at near supersonic speeds. These flows were later joined by lahars. Before being struck by a series of flows that, at their fastest, would have taken less than a minute to reach his position, Johnston managed to radio his USGS co-workers with the message: "Vancouver! Vancouver! This is it!" Seconds later, the signal from the radio went silent, and all contact with the geologist was lost. Initially, there was some debate as to whether Johnston had survived; records soon showed a radio message from fellow eruption victim and amateur radio operator Gerry Martin, located near the Coldwater peak and farther north of Johnston's position, reporting his sighting of the eruption enveloping the Coldwater II observation post. As the blast overwhelmed Johnston's post, Martin declared solemnly that the camp and car sitting to his south were covered: "It's gonna get me, too," he said before his radio went silent.
  The extent, speed and direction of the avalanche and pyroclastic flows that overwhelmed Johnston, Martin, and others were later described in detail in a paper titled 'Chronology and Character of the 18 May 1980 Explosive Eruptions of Mount St. Helens', published in 1984 in a collection published by the National Research Council's Geophysics Study Committee. In this paper, the authors examined photographs and satellite images of the eruption to construct a chronology and description of the first few minutes. Included in the paper is figure 10.3, a series of timed photographs taken from Mount Adams, 33 miles (53 km) east of Mount St. Helens. These six photographs, taken side
caption: Mount St. Helens one day before the eruption, photographed by Harry Glicken from the ridge where the Coldwater II observation post manned by Johnston was located.
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