Among the many contributors of data, none was more essential to the systematic reconstruction of the events of 1980 at Mount St. Helens than David Johnston, to whose memory this report is dedicated. Dave, who was present through all of the activity up to the climactic eruption and who lost his life in that eruption, provided far more than data. His insights and his thoroughly scientific attitude were crucial to the entire effort; they still serve as a model for us all.