|
David Alexander Johnston (December 18, 1949 – May 18, 1980) was an American USGS volcanologist who died during the 1980 eruption of Mount St. Helens in Washington. A principal scientist on the monitoring team, Johnston perished while manning an observation post 6 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. Johnston's remains were 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 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. Johnston felt scientists must do what is necessary, including taking risks, to help protect the public from natural disasters. His work, and that of fellow USGS scientists convinced authorities to close Mount St. Helens to the public before the 1980 eruption. They maintained the closure despite heavy pressure to re-open the area; their work saved thousands of lives. His story became intertwined within the popular image of volcanic eruptions and their threat to society, and a part of volcanology's history. To date, Johnston, along with Harry Glicken, is one of two American volcanologists known to have died in volcanic eruption. Following his death, Johnston was commemorated in several ways, including a memorial fund established in his name at the University of Washington to fund graduate-level research. Two volcano observatories were established and named after him: one in Vancouver, Washington, and another on the ridge where he died. Johnston's life and death are featured in several documentaries, films, docudramas and books. Along with others who died during the eruption, Johnston's name is inscribed on memorials dedicated to their memory. == Life and career == Johnston was born at the University of Chicago Hospital on December 18, 1949, to Thomas and Alice Johnston. They originally lived in Hometown, Illinois but moved to Oak Lawn shortly after Johnston's birth.〔 Johnston grew up with one sister. His father worked as an engineer at a local company and his mother as a newspaper editor. Johnston often took photographs for his mother's newspaper and contributed articles to his school's newspaper. He never married.〔 After graduating from high school, Johnston attended the University of Illinois at Urbana-Champaign. He planned to study journalism, but became discouraged after a poor grade in a large lecture class. He was intrigued by an introductory geology class, and changed his major.〔 His first geologic project was a study of the Precambrian rock that forms Michigan's Upper Peninsula. There he investigated the remains of an ancient volcano: a suite of metamorphosed basalts, a gabbroic sill, and volcanic roots in the form of a dioritic and gabbroic intrusion. The experience planted the seed of Johnston's passion for volcanoes. After working hard to learn the subject,〔 he graduated with "Highest Honors and Distinction" in 1971. Johnston spent the summer after college in the San Juan volcanic field of Colorado working with volcanologist Pete Lipman in his study of two extinct calderas.〔〔 This work became the inspiration for the first phase of his graduate work at the University of Washington in Seattle, in which he focused on the Oligocene Cimarron andesitic volcanic complex in the western San Juans.〔 Johnston's reconstruction of the eruptive history of the extinct volcanoes prepared him to study active volcanoes.〔 Johnston's first experience with active volcanoes was a geophysical survey of Mount Augustine in Alaska in 1975. When Mount Augustine erupted in 1976, Johnston raced back to Alaska, shunting his former work on the Cimmaron Volcano into a master's thesis, and making Mount Augustine the focus of his Ph.D. work. He graduated in 1978 with his Ph.D., having shown that (1) the emplacement mechanism of the pyroclastic flows had changed over time, as they became less pumaceous, (2) the magmas contained high quantities of volatile water, chlorine, and sulfur, and (3) underground mixing of the felsic (silicic) magmas with less-viscous mafic (basaltic) magmas could have triggered eruptions. Mount Augustine was also the site of an early near-disaster for Johnston, when he became trapped on the mountain during an eruption after high winds grounded the first two evacuation aircraft. During the summers of 1978 and 1979, Johnston led studies of the ash-flow sheet emplaced in the 1912 eruption of Mount Katmai in the Valley of Ten Thousand Smokes.〔 The gas phase is extremely important in propelling volcanic eruptions. Because of this, Johnston mastered the many techniques required to analyze glass-vapor inclusions in phenocrysts embedded in lavas, which provide information about gases present during past eruptions. His work at Mount Katmai and other volcanoes in the Valley of Ten Thousand Smokes paved the way for his career, and his "agility, nerve, patience, and determination around the jet-like summit fumaroles in the crater of Mt. Mageik" impressed his colleagues.〔 Later in 1978, Johnston joined the United States Geological Survey (USGS), where he monitored volcanic emission levels in the Cascades and Aleutian Arc. There he helped to strengthen the theory that eruptions can be predicted, to some degree, by changes in the makeup of volcanic gases. Fellow volcanologist Wes Hildreth said of Johnston, "I think Dave's dearest hope was that systematic monitoring of fumarolic emissions might permit detection of changes characteristically precursory to eruptions ... Dave wanted to formulate a general model for the behavior of magmatic volatiles prior to explosive outbursts and to develop a corollary rationale for the evaluation of hazards."〔 During this time, Johnston continued to visit Mount Augustine every summer and also assessed the geothermal energy potential of the Azores and Portugal. In the last year of his life, Johnston developed an interest in the health, agricultural, and environmental effects of both volcanic and anthropogenic emissions to the atmosphere.〔 Johnston was based at the Menlo Park, California, branch of the USGS, but his work on volcanoes took him all over the Pacific Northwest region. When the first earthquakes shook Mount St. Helens on March 16, 1980, Johnston was nearby at the University of Washington, where he had pursued his doctorate. Intrigued by the possible advent of an eruption, Johnston contacted Stephen Malone, a professor of geology at the university. Malone had been his mentor when Johnston had worked at the San Juan complex in Colorado, and Johnston admired his work.〔 Malone stated that he "put him to work" almost instantly, allowing Johnston to escort interested reporters to a place near the volcano.〔Hill, p. 33.〕 Johnston was the first geologist on the volcano,〔 and soon became a leader within the USGS team, taking charge of monitoring of volcanic gas emissions.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「David A. Johnston」の詳細全文を読む スポンサード リンク
|