Resolution No. 5303 - Laserfiche WebLink

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Eugene -Springfield Area Natural Hazards Mitigation Plan 2. Hazard Descriptions identify areas subject to volcanic hazards. For more information on volcano hazard identification in Oregon, refer to the Oregon Natural Hazards Mitigation Plan. Several of the 20 active volcanoes in Oregon are located along the crest of the Cascades near the eastern boundary of Lane County. These volcanoes include the Three Sisters and Mount Jefferson. The active volcanoes posing the greatest threat to the Eugene -Springfield area are the Three Sisters, which are approximately 50 miles to the east. Lava flow, pyroclastic flows, debris flows, and avalanches from an eruption in the Three Sisters will be limited to the immediate area of the eruption and will not impact Eugene and Springfield. However, hazard zone maps for the Three Sisters show landslides, debris flows, and lahars from an eruption could enter the McKenzie River and its tributaries. This could cause flooding on the McKenzie possibly extending to the Thurston area on the east side of the Eugene -Springfield metro area (Figure 2-10). Lahars can occur both during an eruption and when a volcano is quiet. The water creating a lahar can come from melting snow and ice (especially water from a glacier melted by a pyroclastic flow or surge), intense rainfall, or the breakout of a summit crater lake. Some lahars contain so much rock debris (60 to 90% by weight) they look like fast-moving rivers of wet concrete. Historically, lahars are one of the deadliest volcano hazards. Close to their source, these flows are powerful enough to rip up and carry trees, houses, and huge boulders miles downstream. Farther downstream, they can entomb everything in their path in mud. In Eugene - Springfield, lahar impact areas are expected to be similar to the FEMA- mapped floodplains of the McKenzie River. Lahars running through the McKenzie River could also lead to temporary damming of the River or high turbidity in the water. These impacts could cause degradation of water quality and operational problems at water treatment plants. For the City of Eugene, which currently relies on the McKenzie River as its sole source of drinking water, the Eugene Water and Electric Board (EWEB) has developed procedures to manage high -turbidity incidents and is actively seeking to diversify its sources of drinking water, as described in Annex A. Minimal lahar impact is expected to the groundwater sources used by Springfield Utility Board (SUB) and Rainbow Water District along the McKenzie and Willamette Rivers. Ash fall could extend to the Eugene -Springfield area from an eruption in the Three Sisters, as well as from other eruptions including Mount St. Helens. In all but the most extreme incidents, ash falls in the Eugene -Springfield Metro Area are likely to be very minor, with an inch or less of ash accumulation likely. There is the possibility heavy ash fall into streams and rivers upstream from public water supply intakes from a major eruption in the Cascades could affect public water supplies. In Oregon, awareness of the potential for volcanic eruptions was greatly increased by the 1980 eruption of Mount St. Helens in Washington, which killed 57 people. During this eruption, a debris avalanche moved 3.3 billion cubic yards of material 2-53 January 2020