Big slow movers: a look at weathered-rock slides in Western North Carolina
The North Carolina Geological Survey (NCGS) is currently implementing a landslide hazard-mapping program in western North Carolina authorized by the North Carolina Hurricane Recovery Act of 2005. To date, over 2700 landslides and landslide deposits have been documented. A small number of these landslides are relatively large, slow-moving, weathered-rock slides, termed "big, slow movers" (BSMs). Three examples of BSMs are described in this paper.
The Toxaway River Slide is a composite BSM located in Transylvania County. This Cacre slope movement likely began moving in 1916, and tree ring studies indicate subsequent movement relates to multi-year wet cycles. Recent reactivation of a 0.5-acre BSM at the Lake Logan Center, located southeast of Waynesville, was triggered by heavy rainfall in September 2004. High, antecedent soil moisture conditions and undercutting of the toe were the likely triggers for observed, recent movement. A 1.5-acre BSM is impacting homes in the Hunters Crossing subdivision, located just outside of the Waynesville city limits. Residents first noted movement in September 2005, and to date, four homes have been severely damaged and four others are endangered.
BSMs appear to have geomorphic and geologic settings similar to each other, and are often difficult to recognize without detailed field investigations.