Identification of the Physical and Chemical Characteristics of Volcanic Hazards.

EARTHQUAKES; NATURAL disasters; MOUNTAINS; VOLCANIC eruptions; VOLCANISM; VOLCANIC ash, tuff, etc.

On March 19, 1980, a series of earthquakes beneath Mount St.Helens heralded the beginning of a chain of events that eventually climaxed with the May 18, 1980 eruption. During the early period of activity from March 19 to May 14, 1980, all of the eruptions were relatively small, nonmagmatic in nature, and ejected ash to a maximum altitude of 2.5 km above the summit of Mount St. Helens impacting an area within a 50-km radius of the mountain. Within two weeks of the initial activity, a sampling network consisting of 10 sample sites was set up around Mount St. Helens to collect volcanic ash. The site-selection criteria were based primarily on the prevailing wind direction relative to the mountain and the relative ease of access to the site. The majority of sites were located to the northeast of Mount St. Helens. The closest site was located 9 km from Mount St. Helens and was ultimately destroyed in the May 18 eruption. The majority of these sites were set up in locations that were impacted by most of the ash from this early phase of eruptions. This initial sampling strategy was geologically oriented and operated from late March to early June 1980. The main purpose of the program was to obtain pristine sedimented ash samples, which could later be analyzed for leachable trace elements and elemental composition, and to characterize the mineralogy and morphology of the bulk ash.