57 People lost their lives in the Mt. St. Helens 1980 eruption. Most of these deaths were as a result of asphyxiation or trauma from pyroclastic flows. However, some of these deaths were attributed to indirect causes, road accident and cropduster collision with power lines due to poor visibility during ashfall and two heart attacks from ash shoveling (Carson, 2000).
The death toll would have significantly higher had the eruption occurred on a weekday instead of the Sunday that it did. Much of the land impacted by the landslide and pyroclastic flow was used for forestry.
Within a few years of the eruption, much of the ash was eroded from slopes of gradient 50% or steeper, with redeposition nearly always local and immediate. It was during severe rainstorms that the ash was readily eroded from the steep slopes and swept into streams and rivers. Such erosion is similar to the behavior of soils on non-vegetated land during severe rainstorms.
Within a few years of the eruption, much of the ash was eroded from slopes of 50 percent or steeper, with redeposition nearly always local and immediate. It was during severe rainstorms that the ash was readily eroded from the steep slopes and swept into streams and rivers. Such erosion is similar to the behavior of soils on non-vegetated land during severe rainstorms.
Volcanic ash from the 9-hour explosive eruption on 18 May 1980 that fell across eastern Washington consisted of 3 to 7 percent free silica (cristobalite and quartz) in the sub-10 micron size fraction.
At this proportion of free silica, the NIOSH-recommended standard would be exceeded if exposure to respirable ash was regularly greater than 0.8 to 1.0 milligram/m3 of air (Baxter and others., 1981).
Exposures to the ash and free silica by the general population in the affected communities of eastern Washington were of limited duration, and silicosis was not considered a potential threat to the general population. People who worked in areas of high concentrations of respirable ash, for example loggers removing timber near the volcano or agricultural workers in central Washington, were advised to take protective action.
Media caution: Within days of the 1980 eruption, there were reports in the media that the volcanic ash from Mount St. Helens contained 60 percent or more free crystalline silica—far greater than the actual 3 to 7 percent of the respirable size fraction. This misinformation may have occurred because chemical analysis of ash and lava is commonly reported in terms of the percentage of total silica content, ranging from about 45 to 77 percent; the analysis includes that which is chemically combined with other elements, not free silica.