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Sherburne County Multi -Hazard Mitigation Plan, 2020 The movement of a mass of rock, debris, or earth down a slope by the force of gravity is considered a landslide. They occur when the slope or soil stability changes from stable to unstable, which may be caused by earthquakes, storms, volcanic eruptions, erosion, fire, or additional human -induced activities. Slopes greaterthan io degrees are more likely to slide, as are slopes where the height from the top of the slope to its toe is greater than 40 feet. Slopes are also more likely to fail if vegetative cover is low and/or soil water content is high. Potential impacts include environmental disturbance, property and infrastructure damage, and injuries or fatalities (FEMA, 2013). Landslides/Soil Erosion History in Sherburne County The issue of wind and water induced erosion is not listed as a priority concern in Sherburne County's 2o3.8-2o3.8 Local Water Management Plan. While the County is concerned about erosion, especially along lake and river shorelines, there have not been significant landslides or severe soil erosion issues in the county in the past five years. To determine the probability of future landslide events in the Sherburne County, all past -observed landslide events and the period in which they occurred were examined. Because there are no reported landslide events in the County, the relative frequency of these events is o per year. This relative frequency can be used to infer that the probability of landslide events occurring in the future is very low Landslides/Soil Erosion and Climate Change The increased magnitude and frequency of flooding events and storm activity that may result from climate change may in turn increase the risk of soil erosion and landslides. According to University of Washington geologist Dave Montgomery, "If the climate changes in a way that we get a lot more rainfall you would expect to see a lot more landslides" (Phillips, 203.4). In Minnesota, the wettest days are getting wetter. This can contribute to increased erosion in many locations due to flooding and saturation of soils. Reduced ice cover on lakes and shorelines (due to warmer temperatures) could potentially expose shorelines to increased erosion or damage during weather events when they previously may have been covered with ice (National Climate Assessment Development Advisory Committee, 2013). According to the 2014 National Climate Assessment, "Increased precipitation intensity also increases erosion, damaging ecosystems and increasing delivery of sediment and subsequent loss of reservoir storage capacity" (Pryor, et al., 2014). Vulnerability Human life and safety, structures, and infrastructure are all vulnerable to landslides. Identifying the areas more susceptible to landsliding is challenging, especially at a large scale. The USGS has performed an analysis for potential landslide of the conterminous US, and while highly generalized and not intended to be used for local planning, still provides a general overview of landslide potential. The delineation process is based on geologic formations of the US which were classified as having high, medium, or low landslide incidence; and being of high, medium, or low susceptibility to landsliding (Radbruch-Hall, et al., 3.982). Sherburne County is in a low incidence and susceptibility rated area. Page185