Geological Survey Circular 838 Guides to Some Volcanic Terrances in Washington, Idaho, Oregon, and Northern California

Dave Johnston, 30-year-;old volcanologist with the U.S. Geological Survey, was swept away by the great directed blast of Mount St. Helens on May 18, 1980. Because Dave had been an organizer of the AGU meeting at Bend, am editor of its abstracts and field-trip guidebooks, and a champion of the Pacific Northwest, it is particularly appropriate to dedicate this volume to him, in grateful remembrance of the effect that Dave's enthusiasm, diligence, and vitality had upon so many of us. As a working colleague and daily running companion, I was asked to try to summarize Dave's career and my impressions of him.

Dave Johnston was born and raised in Illinois, and it remained his custom to return there every Christmas season to visit his parents and sister, who survive him. At school and college, Dave became an outstanding scholar, rumner, and photographer and, in 1971, he graduated from the University of Illinois with "Highest Honors and Distinction" in Geology. His first geologic project was on the Upper Peninsula of Michigan where, ten years ago, he studied the progressive metamorphism of a pile of Precambrian basaltic lavas and a differentiated gabbroic sill. Here was the inception of Dave's petrographic acuity and, here too, in an associated intrusion of gabbro and diorite, were the roots of Dave's first volcano.

Dave Johnston, relaxed and happy in the land he loved, Valley of Ten Thousand Smokes, Alaska, June 1978. Posing here at the base of Novarupta, the rhyolite dome extruded at the close of the great eruption of 1912, Dave had sampled the fumaroles atop several nearby volcanoes and had undertaken a study of the emplacement, compaction, and welding of the 1912 ash-flow sheet. The initials are those of petrologist C. N. Fenner and his assistant Charles Yori, who worked in the valley in 1919 and 1923. (Photo by Dan Kosco.)

In 1971 and 1972, Dave assisted Pete Lipman in mapping the Platoro and Lake City calderas in the San Juan Mountains volcanic field of southwestern Colorado. This fortunate apprenticeship so confirmed his enthusiasm for field petrology that, as a graduate student at the University of Washington, Dave undertook a detailed mapping, dating, and geochemical study of the Cimarron Volcano, an andesitic complex of Oligocene age in the western San Juans. His intricate reconstruction of the eruptive style and structural history of this center from evidence provided by its intertonguing pyroclastic and alluvial deposits prepared Dave very well for his big jump to the study of active volcanism.

The jump came in the summer of 1975 when, with Jürgen Kienle's group from Fairbanks, Dave took part in a geophysical survey of Augustine Volcano, an island in lower Cook Inlet. When Augustine erupted explosively in early 1976, Dave rushed back to study the sequence and mechanisms of its eruptions and the petrology of their ejecta. His careful field and microprobe work demonstrated convincingly (1) that the pyroclastic flows had become less pumiceous with time (correlating with a change in emplacement mechanism); (2) that H₂O, Cl, and S contents of the magmas were notably high; and (3) that basaltic magma, although at no time actually erupted, had mixed with the more silicic melts and had possibly triggered their outburst. Only 25 months later, Dave turned in his Ph.D. thesis, not on his nearly completed Cimarron project, but on Augustine. This was a remarkable achievement, since both studies were labor-intensive and of high quality.

Every summer Dave returned to Augustine and, in 1978 and 1979, he went to Katmai as well. In the Valley of Ten Thousand Smokes, Dave was taking the lead in studying physical aspects of the emplacement, compaction, welding, and degassing of the ash-flow sheet as part of our comprehensive restudy of the 1912 eruption. The fundamental role of the gas phase in volcanic processes had, by 1978, led Dave increasingly to focus his work upon magmatic volatile components, the main evidence for which is preserved in glass-vapor inclusions within phenocrysts, in quenched crystal-liquid equilibria, and in the fumarolic emissions of active volcanoes. Characteristically, Dave pursued all three lines of evidence vigorously. He became an exceptionally rigorous analyst, whether with the microprobe, gas chromatograph, extraction line, or mass spectrometer, but Dave knew better than most not to waste his time on a lousy sample. Thus, he put enormous energy into improving the equipment and techniques necessary to collect meaningful and representative samples, especially the least fractionated and least contaminated gas samples possible. Dave's agility, nerve, patience, and determination around the jet-like summit fumaroles in the crater of Mt. Mageik were to me a spectacle of unforgettable beauty.

His work on volcanic gases brought Dave in 1978 to the U.S. Geological Survey, where he was assigned to expand our program for monitoring volcanic emissions in Alaska and in the Cascades. He knew that such studies could improve our understanding of the nature and evolution of magma bodies, eruptive mechanisms, and contributions of magmatic volatiles to hydrothermal systems, but I think Dave's dearest hope was that systematic monitoring of fumarolic emissions might permit detection of changes characteristically precursory to eruptions. Behind the image conveyed by his exceedingly solitary work was, in fact, a great concern for making a contribution to society. 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. But Dave also held the conviction that, as a scientist, he should devote time, energy, and imagination sufficient to communicate effectively to the non-scientific public the true range of potential volcanic hazards, the geologic (or sometimes instrumental) reasons for our poor predictive capability, and some notion of the characteristic time scales upon which volcanic behavior proceeds. Dave's concern for the societal importance of his work was nowhere more evident than in the thoroughness and dedication with which he recently undertook an assessment of the geothermal-energy resources of the Azores and mainland Portugal. Also during his last year, Dave developed growing interests in volcanic contributions of halogens, sulfur, and CO₂ to the atmosphere and in the long-range effects on climate, health, and agriculture of both volcanic and anthropogenic emissions.

Thus, it was only in part by accident that when Mount St. Helens resumed its activity in March 1980, Dave Johnston was the first geologist on the mountain. From the earliest outbreak until the catastrophic event, Dave spent virtually the entire seven weeks at Mount St. Helens, monitoring SO₂ emissions with a correlation spectrometer and coordinating the airborne sampling of gases and particulates. It deserves emphasis that Dave's work was an important contribution to a well-coordinated, scientifically multi-faceted, group effort that persuaded the authorities to resist public pressures to re-open the area around the volcano, thereby holding the May 18th death toll to a few dozen instead of thousands. Ironically, Dave was caught at an observation post thought to be relatively safe, by an unusual eruptive event that was largely unanticipated, in magnitude or style, except perhaps by Dave himself. Three years ago, Dave had published this warning about Augustine: "High-temperature and high-velocity shock waves extended far beyond the limits of discernable deposits [of the 1976 eruption]. Hazard zones defined on the basis of deposits [alone do not] reflect this more extensive shockwave hazard, which at Augustine extends many kilometers offshore." No one was more aware of the danger of directed blasts, pyroclastic surges, and the shock waves that sometimes accompany explosive eruptions than was Dave Johnston. Dave repeatedly voiced his convictions that studies of deposits left by old eruptions provide only part of the story and that informed hazards assessment requires accepting the dangers of on-site monitoring of active volcanic processes. Dave was unaffectedly genuine in everything he ever said or did, so he gave his energy and vitality to advance our understanding and thus our predictive capability.

Dave Johnston is gone now, and many of us who were close to him can still scarcely believe it. Dave was a natural scientist in the finest sense, and to the extent that natural science is a collaborative effort, he was our shining example, and we are all diminished. His infectious curiosity and enthusiasm, his unaffected concern for the opinions and feelings of other people, and his joyful spontaneity uplifted his friends and touched people who barely knew him. His generosity was unsurpassed, and I am recurrently astonished whenever I recall that Dave voluntarily carried 40 kg of rocks out of Katmai for me. Dave Johnston was as self-aware and capable a person as I have ever known, a man who would learn to do and dared to do whatever might be necessary to get the job done. In his final year, he began taking a night course to improve his mathematics. And, fed up with the stage fright that plagued his speaking career (though he gave excellent talks), Dave took the bull by the horns and (though he otherwise rarely drank) solved the problem by taking a jug to the podium with him.

But perhaps his most essential quality was the ability to dissipate cynicism spontaneously and to uplift the mood all around him. Dave looked for, saw, and thereby encouraged the best in all of us. Dave Johnston would expect us to carry on the game without him, with all his wonderful enthusiasm.

Wes Hildreth
July 1980