Three Sisters is a potentially active volcanic center that lies close to rapidly growing communities and resort areas in Central Oregon.
Volcanic hazards in the Three Sisters region include eruption-triggered events such as tephra fall, pyroclastic flows, lava flows, lahars and flooding, as well as landslides from steep flanks, which need not be triggered by eruptions. Hazard zones that follow river valleys for tens of kilometers downstream from Three Sisters could be inundated by lahars generated either by melting of snow and ice during eruptions or by large landslides. Slow-moving lava flows could issue from new volcanic vents in the region surrounding the Three Sisters cluster. Fallout of tephra from eruption clouds can affect areas hundreds of kilometers downwind, so eruptions at volcanoes elsewhere in the Cascade Range also contribute to volcano hazards in Central Oregon. Rapidly developing communities in Deschutes County to the east, plus several small communities to the west, are at the greatest risk for impact from volcanic hazards.