The May 18, 1980 eruption of Mount St. Helens was the most expensive in US history, costing about $1 billion in damages. The eruption killed 57 people, approximately 7,000 big game animals, and about 12 million fingerlings in hatcheries. Lahars destroyed 27 bridges and nearly 200 homes, and volcanic ash caused the first known in-flight aircraft engine failure plus disrupted thousands of households for many months. Volcanic eruptions in the Cascade Range have occurred at an average rate of 2-3 times per century during recent millennia.
Communities and individuals can minimize loss of life and property by making basic preparations now, such as learning the locations of hazard zones, inquiring about local emergency planning efforts, and preparing households and businesses for emergencies as they would for most other hazards.
There will be some warning before eruption begins, but the time between the first signs and eruptive activity might be short. During the days, weeks, or months prior to volcanism, the movement of rising magma gives detectable signals—heightened gas emissions, deforming of the volcano, and unique earthquake signatures. To keep communities safe, the USGS and its partners at the University of Washington monitor hazardous Cascade volcanoes so that they can detect the onset of volcanic unrest. This is the only way to forewarn communities at risk in enough time to activate emergency response plans, which will ultimately help save lives and property.