UNCOVERING CENTURY OLD SECRETS FROM A CLUSTER OF LARGE LANDSLIDES TRIGGERED DURING NORTH CAROLINA’S GREAT FLOOD OF 1916

Severe storms and associated landslides pose significant hazards and risks to communities in western North Carolina (WNC). This study aims to enhance our understanding of predisposing geologic conditions, modes and mechanisms of slope failure, and debris runout for four landslides triggered by the North Carolina’s storm of record for 24-hour rainfall, The Great Flood of 1916. This event caused catastrophic floods and landslides resulting in over 80 deaths across WNC. The study area, Andy Cove in Pisgah National Forest, experienced severe impacts from this event, including 7 debris flow related fatalities. We selected four of the larger landslides and debris flows in the study area for detailed study.

We use a variety of methods to assess the relationship between the local geologic/terrain conditions in the study area compared to the region of WNC. We compare the areal magnitude and volumes of these four 1916 landslides with those in the NCGS landslide database to gain insights into their importance and relevance to hazard and risk assessment as it pertains to landslide volume and runout distance. Our analysis reveals that the areas of these landslides exceeds more than 90% of the other slide/flow landslides in the database (n = 4,006). These four landslides are within an area class between 10,000 and 25,000 m2 that represents about 5% of the landslide database covering about one-third of the land area of WNC.

We combine field observations, lidar interpretation, terrain classification, and structural analysis to understand the relationships between slope failure and debris runout. Similar structural and lithologic conditions persist in the landslide source areas, and yet the four landslides we analyzed have various modes of failure and distinct runout mechanisms, including: incipient rockslide, wedge failure, debris avalanche, debris slide, and channelized/unchannelized debris flow.

Using terrain classification techniques, we assess regional landform assemblages associated with the distinct landslide modes and mechanisms which may improve our understanding of landslide susceptibility for larger landslides across the region. Our findings contribute to the development of effective mitigation strategies, land-use planning, and disaster management approaches for areas prone to similar events in the future.