DOES “GEOLOGIC SETTING” HAVE A PLACE IN LANDSLIDE INVENTORIES?

Creating a landslide inventory is an opportunity to convey landslide information about particular locations to people who may never see the site. Oftentimes, inventories include information about the type of material and movement, how the data was collected, and sometimes there is information about the slope geometry. But these simple categories do not capture the more variable and harder to define slope setting categories. These categories may include geomorphological setting, landform, vegetation, or geologic setting. Including setting categories allows for inclusion of broader patterns in a database for iterative analysis and potential use in developing future susceptibility models.

When reviewing the results of landslide inventory mapping in Transylvania County, NC, patterns began to emerge relating to landslide locations, historical rainfall, and unique slope settings. Transylvania County is located in the southern part of the North Carolina Blue Ridge Mountains. The Blue Ridge Escarpment defines the southern border of the county (and the NC/SC line), while high ridges define the northern border. The Brevard Fault Zone extends through the center of the county, contributing to the geologic, and therefore topographic, variability in the county. Furthermore, portions of the county are dominated by variably-weathered intrusive rocks, changing the character of the slopes and hydrology as well. The high relief and steep slopes, combined with weather patterns and tropical systems that track over the WNC mountains, create the conditions for abundant heavy rainfall and the resulting landslides. This talk will present some of the geologic setting patterns observed in the county, as well as discuss the potential for additional slope setting categories that could be useful in future landslide inventories.