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2024 Hennepin County All -Jurisdiction Hazard Mitigation Plan <br />Volume 2 — Hazard Inventory <br />I St fO'N COMPREHENSIVE NATURAL HAZARD ASSESSMENTS <br />NATURAL HAZARD PROFILES <br />411;111 Hazard Assessment: LANDSLIDES <br />4.1.1.1. Definition. A landslide is the downward <br />movement of rock, soil, or other debris along a slope. <br />Other terms used for landslides are debris flow, earth <br />flow, mudslide, slump, slope failure, mass wasting, and <br />rock fall. The rate of landslide movement ranges from <br />sudden to very slow and may involve small amounts of <br />material up to very large amounts. The kinds of <br />movement include falling, sliding, and flowing. Material <br />can move as an intact mass or become significantly <br />deformed and unconsolidated. The slopes that have <br />landslides can range from near vertical to gently rolling <br />with slopes above 30% having the highest susceptibility. <br />4.1.1.2. Range of magnitude <br />Further work is needed among the Hennepin County landslide assessment team to develop range of <br />magnitude. <br />4.1.1.3. Spectrum of Consequences B211b <br />4.1.1.3.1. PRIMARY CONSEQUENCES: <br />4.1.1.3.1.1. Transportation: Mobility is frequently stopped or slowed by landslides. <br />When at the foot of slopes, roads and highways can be impacted by fallen rock, soil flows <br />and landslide debris. When routes are at the crest of slopes, surfaces may be undercut by <br />slides and fall away leaving voids and gaps in the road. Railroads are similarly impacted <br />by landslides. The practice of cut and fill in road and rail grade construction can increase <br />susceptibility to this problem. Besides direct damage to surface transportation routes, <br />secondary impacts can occur if vehicles carrying hazardous materials rupture if struck by <br />slides. <br />4.1.1.3.1.2. Electric utilities: Electric service lines often follow alongside roads, including <br />their routes through valleys and ravines or along the crests of slopes. This makes them <br />vulnerable to disruption from landslides. Cut power lines are a frequent feature of <br />landslide activity. Landsides impact both lines suspended from utility poles and buried <br />power lines. <br />4.1.1.3.1.3. Water, sanitary and storm sewer services: Cracked, broken or leaking water <br />or sewer lines often have a significant role in triggering landslides in susceptible areas. <br />13 <br />