The May 18, 1980, Eruption of Mount St. Helens, Washington State: A synopsis of events and review of Phase 1 from an eyewitness perspective

The May 18, 1980, eruption of Mount St. Helens comprised a complex series of events that started with a magnitude 5.1 earthquake. Studies of eyewitness photographs and observations provided important information in determining the chronology of events. The eruption has been subdivided into six phases, based on evidence provided by this chronology and detailed stratigraphic work. The first phase, which included the lateral blast, has come under the closest scrutiny, but even here observations of the eye witnesses have provided useful information that must be accounted for in any model of the phenomena.