Local Hazard History
Portland's largest threat is the one it can't see coming. Offshore lies the Cascadia Subduction Zone, a 700-mile fault that the USGS warns can produce a magnitude-9.0+ megaquake and tsunami; the last full rupture was on January 26, 1700, and scientists expect a major Cascadia quake to cut off roads, water, and power across the region for weeks when it strikes. Two other hazards already arrive most summers. In the June 2021 heat dome, Portland reached an all-time record 116°F on June 28 — nine degrees beyond any temperature in the city's recorded history — and the heat killed 72 people in Multnomah County alone, with at least 96 deaths across Oregon. Just months earlier, in September 2020, the Riverside Fire in nearby Clackamas County drove about 40,000 people from their homes and pushed Portland's air quality to roughly 314 on the AQI — briefly the worst of any major city on Earth. Winter brings the metro's fourth hazard: ice storms, like the February 2021 storm that knocked out power to hundreds of thousands across the region.