4.6: Case Study: Risk Perception and Warning of the Mt. St. Helens Eruption

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In late March, 1980, Mt. St. Helens began a series of ash and steam eruptions that culminated six weeks later in a blast that ejected one cubic mile of material from the top of the mountain. Prior to the March eruptions, most residents of nearby communities were aware that Mt. St. Helens was a volcano and could name a specific threat that could affect their safety (Perry & Greene, 1983). The majority of those within about 20 miles of the volcano expressed concern about ashfall, whereas most of those in communities 30-40 miles away were concerned about mudflows and floods. The severity and immediacy of the volcano threat led people to search for information frequently—most of them sought information four times a day or more. The unfamiliarity of the threat led them to rely on the news media more than peers. Reliance on authorities was very high in communities closest to the volcano, but very low farther away. Similarly, residents of areas closest to the volcano thought they were more likely to evacuate and had made more preparations to evacuate.

On the day of the May 18 eruption, most of those living close to the volcano (Toutle/Silverlake) were warned by authorities (48%) but almost as many were warned by peers (41%) and few were warned by the news media (11%). By contrast, most of those living farther away the volcano (Woodland) were warned by peers (59%) and equal proportions of the remainder were warned by authorities (21%) and the news media (20%). The initial response also differed by community. Toutle/Silverlake residents were most likely to prepare to evacuate (40%), but many took family oriented action (18%), sought to confirm the warning (19%), or continued normal routines (18%). Woodland residents were most likely to take family oriented action (41%), while others sought to confirm the warning (21%) or continued normal routines (29%) rather than prepare to evacuate (7%). Most residents of both communities sought warning confirmation, but those in Toutle/Silverlake were less likely to use the mass media (33% vs. 59% in Woodland) and more likely to contact peers and local authorities.