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Eugene -Springfield Area Natural Hazards Mitigation Plan 2. Hazard Descriptions History of Impact in Eugene -Springfield There have been no volcano induced epidemics in the Eugene -Springfield area. Risk of Impact Though worldwide risk of an epidemics arising after a volcanic eruption is moderate, the healthcare system and demographics of an area must be considered. Due to these facts the Eugene -Springfield area's risk is low. Hazardous Materials Volcano induced hazardous material spills or releases are not a significant impact for the Eugene or Springfield area. 2.8.6 Probability of Future Occurrence The 2015 Oregon Natural Hazards Mitigation Plan indicates the annual probability of the South and Middle Sister entering a new period of eruptive activity is estimated from 1 in several thousand to 1 in 10,000. However, the ability to calculate the probability of a volcanic eruption is limited due to the fragmented nature of the geologic history for these volcanoes. Uplift was discovered on South Sister in 2001 when geologists and volcanologists observed an area roughly 10 miles in diameter rise by roughly 4 inches at the center. The center of this area was approximately 3 miles from the summit of the South Sister volcano. Uplift continued at roughly 1 inch per year until 2004, when it decreased to one half inch per year. As of 2017, the rate of inflation decreased to 0.2 inches per year.65 While this uplift is significant, it does not indicate an eruption is imminent. Although the presence of active volcanoes in the Cascades threatens the area, Eugene and Springfield estimate the probability of a new volcanic occurrence as low. A low rating means one incident is likely within a 75 to 100-year period. 2.8.6 Vulnerability and Capacity Assessment The Steering Committee rated the vulnerability to a volcanic incident as moderate, meaning 10% to 69% of the population and/or regional assets could be impacted by a volcanic incident. This moderate rating is due to the fact the repercussions of an eruption for Eugene would be limited to ash fall, and a decrease in water quality from the McKenzie River. Due to the expected slow onset, advanced warning, and 65 USGS, Cascades Volcano Observatory. Long -Term Monitoring Tracks Subtle Surface Changes at some Cascade Range Volcanoes — Uplift at South Sister, December 05, 2017. httos://volcanoes.usgs.gov/observatories/cvo/cvo news archive.html 2-56 January 2020