David Johnston, 30-year-old volcanologist with the U.S. Geological Survey, was swept away by the catastrophic eruption of Mount St. Helens on the morning of May 18, 1980. As one of the first members of the U.S.Geological Survey monitoring team to arrive at Mount St. Helens and the scientist in charge of volcanic-gas studies, Dave spent long hours working on and close to the mountain. Ironically, he was caught at an observation post that was considered relatively safe. From his experience with active Alaskan volcanoes, Dave understood better than most the hazards of explosive volcanism. At the same time, he repeatedly voiced the conviction that adequate hazard assessments require accepting the dangers of on-site monitoring of active volcanic processes. The volcano-monitoring effort of which Dave was part helped persuade the authorities first to limit access to the area around the volcano, and then to resist heavy pressure to reopen it, thereby holding the May 18 death toll to a few tens instead of thousands.

Born and raised in Illinois, Dave Johnston was graduated in 1971 from the University of Illinois, Urbana, with "Highest Honors and Distinction" in geology. His strong interest in volcanism began with his first geologic project studying Precambrian volcanic rocks in the Upper Peninsula of Michigan. This interest in volcanic phenomena intensified with subsequent work in the San Juan volcanic field of southwestern Colorado and on Augustine Volcano in lower Cook Inlet, Alaska. The Augustine study was the basis for his doctoral dissertation, completed in 1978 at the University of Washington, Seattle.

Following his Ph.D., Dave increasingly focused on the fundamental role of volatiles in volcanic processes, as he continued his studies on Augustine and began work on Katmai Volcano, Alaska. His work on volcanic gases brought him in 1978 to the U.S.Geological Survey, where he was assigned to expand the program for monitoring volcanic emissions in Alaska and the Cascade Range. A specific objective of such monitoring is to test whether or not changes in gas geochemistry might provide precursory clues of impending eruptive activity. Thus, it was natural that, when Mount St. Helens reawakened in march 1980, Dave Johnston was one of the first geologists on the volcano.

Dave Johnston was an exemplary scientist, and his approach to his work was a model for all: dedicated and hardworking, with meticulous organization and observation followed by careful evaluation and interpretation. At the same time, Dave was unaffectedly genuine, with an infectious curiosity and enthusiasm. But perhaps his most essential quality was the ability to dissipate cynicism; he looked for, saw, and thereby encouraged the best in all of us. Dave would have expected us to carry on without him, learning all we could from the Mount St. Helens catastrophe.