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Throughout the Blue Ridge, landslides are a common process, threatening life, property, and changing the morphology of mountain slopes. They occur when gravity exceeds the soil’s ability to hold to the mountain slope. Activities or events that destabilize the soil and rocks on a mountain slope like drought, increased rainfall, earthquakes, wildfires, and human driven deforestation, can all increase the likelihood of a landslide. Large storms and hurricanes can act as a trigger for landslide prone areas. From 1916 to 2006, 7 major cyclonic storms impacted Western NC and set off hundreds to thousands of landslides. The steep slope along the Blue Ridge Escarpment makes this area particularly vulnerable to landslides because it creates a high potential energy environment for rocks, dirt, and other debris situated on mountainsides and hillslopes. The mountains of Western North Carolina also have relatively shallow soil deposits and are experiencing increased development which both increase the likelihood of landslides.
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The most common type of landslide along the Blue Ridge Mountains and the Blue Ridge Escarpment are called debris flows or mudslides. They frequently occur after heavy rains, when the hillslope is fully saturated. Hollows, or concave hillsides, are more prone to landslides because the soil is under the weight of the uphill soil, so it takes less pore pressure to destabilize the hillslope. The thickness of the soil plays a role because thinner deposits of soil (<6ft) thoroughly saturate faster. Deforested areas are also more prone to debris flows because roots are no longer there to hold onto soil, but with enough rain, debris flows can happen on unmodified slopes as well.
Debris flows contain rock and soil, and on a steep enough slope, they can move very quickly, reaching speeds of over 50 km/hour (Wooten). They tend to flow downhill in a similar fashion as water and flow through drainages or stream channels to flat land where the debris deposits in the form of a debris fan. The presence of a debris fan marks that area as a landslide prone environment and can indicate where future landslide debris will deposit. Unfortunately, debris fans are gently sloping mounds at the base of mountains and can make desirable real estate for an unsuspecting developer or homeowner.
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In addition to their prevalence, landslides in North Carolina and the rest of the Blue Ridge are dangerous because unaware development puts people in harm’s way. Many people live directly in gullies or along steam channels where debris is likely to flow and others live on top of debris fans (see Figure 3). In either case, the dangers of landslides should not be ignored. Previous risk assessments in North Carolina halted after only 4 counties, Macon, Watuga, Buncombe, and Henderson, were analyzed. Each of these 4 counties had many landslides that occurred in the past and areas that were a potential hazard today.
Click here to see details about landslides in Linville Gorge
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Additional References
https://www.charlotteobserver.com/opinion/op-ed/article9110051.html
Cites Consulted
Wooten, R. M., Witt, A. C., Miniat, C. F., Hales, T. C., & Aldred, J. L. (2016). Frequency and Magnitude of Selected Historical Landslide Events in the Southern Appalachian Highlands of North Carolina and Virginia: Relationships to Rainfall, Geological and Ecohydrological Controls, and Effects. In C. H. Greenberg & B. S. Collins (Eds.), Natural Disturbances and Historic Range of Variation: Type, Frequency, Severity, and Post-disturbance Structure in Central Hardwood Forests USA (pp. 203–262). Springer International Publishing.
https://www.cdc.gov/disasters/landslides.html
https://www.usgs.gov/faqs/what-a-landslide-and-what-causes-one