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Eugene -Springfield Area Natural Hazards Mitigation Plan <br />2. Hazard Descriptions <br />landslides (within the past 150 years) in Eugene -Springfield tend to be smaller <br />slides or slumps near waterways or slides related to development activity. The <br />potential for larger slides exists primarily in the south hills of Eugene and <br />Springfield. <br />Rockfall incidents are primarily limited to quarry sites where rock has been exposed <br />(e.g., the west face of Skinner's Butte). <br />The primary factors affecting or increasing the likelihood of landslides in Eugene - <br />Springfield are: <br />• Natural conditions and processes including the geology of the site, rainfall, <br />water action, seismic activity, and volcanic activity. <br />• Excavation and grading on slopes for homes, roads, and other structures. <br />• Natural or human -caused drainage and groundwater alterations can trigger <br />landslides. Human activities such as broken or leaking water or sewer lines, <br />water retention facilities, irrigation, stream alterations, ineffective <br />stormwater management, and excess runoff due to increased impervious <br />surfaces. <br />• Change or removal of vegetation on very steep slopes due to timber <br />harvesting, land clearing, and wildfire. <br />• The water content of soils/rock is a major factor in determining the <br />likelihood of sliding for any given slide -prone location. Thus, most <br />landslides happen during rainy months, when soils are saturated with water. <br />Winter storms with intense rainfalls are a common trigger for landslides in <br />the Eugene -Springfield area. <br />2-45 January 2020 <br />