The September 18, 2018, Debris Slide in Warrensville, NC: A Landslide Response Case Study.

A debris slide and subsequent fire on September 18, 2018, destroyed a bank building and damaged property in Warrensville, North Carolina. The slide pushed a propane tank and an electrical generator against the bank. In that collision, an electrical arc caused the propane to explode, which produced a fireball. Employees in the bank narrowly escaped with minor injuries, and slide debris buried part of an unoccupied drive-through lane. North Carolina Geological Survey geologists responded to a request from the Ashe County Emergency Manager and investigated the slide area to assess slope stability for public safety. Aided by uncrewed aerial system imagery, we documented slope and debris slide features and geologic materials and constructed a geologic cross section through the 1,400 m2 debris slide. We concluded that record above-normal precipitation followed by rainfall from the remnants of Hurricane Florence during September 15-18, 2018, induced the slide, and that geologic conditions and hillside modifications over prior decades had predisposed the slope to failure. Colluvial deposits derived from sheared amphibolite bedrock, and curved trees within and adjacent to the 2018 slide indicated preexisting marginally stable hillslope conditions. The 2018 slide included the area of a 2000 slide that involved a cut slope constructed during earlier site development. Stability analyses showed that the described conditions led to an unstable slope at the time of the 2018 slide. A septic leach field involved in the 2018 slide was damaged; however, it is uncertain if it was a causal factor in the slide. [ABSTRACT FROM AUTHOR]