Claimed Mount Rainier eruption over Seattle

Background. Mount Rainier is an active stratovolcano in the Cascade Range, located 59 miles south-southeast of Seattle. It is the highest mountain in Washington and the most topographically prominent in the contiguous United States. The mountain is considered one of the most dangerous volcanoes globally due to its high probability of eruption and proximity to major urban areas.

Geologic Evidence. The United States Geological Survey reports that the most recent recorded volcanic activity occurred between 1820 and 1854. This broad timeframe contradicts the legacy claim of a specific eruption in January 1820. While eyewitnesses reported activity in later years such as 1858 and 1870, no source confirms a specific event in 1820 visible from Seattle.

Risk Context. Mount Rainier is on the Decade Volcano list due to its danger to nearby populations. Approximately 80,000 people are at risk in lahar-hazard zones, and 150,000 live on old lahar deposits. The likelihood of a major eruption in the Cascade Range is estimated at 2–3 per century.