EXFOLIATION INSIGHTS FROM DRONE-BASED LIDAR OF LOOKING GLASS ROCK, NORTH CAROLINA, USA

The formation of surface-parallel exfoliation fractures, or “sheeting joints,” in rock domes produces some of Earth’s most celebrated landforms. In 1904, G.K. Gilbert proposed three mechanisms for rock exfoliation: (1) original cooling of the rock, (2) decompression during exhumation, or (3) post-exhumation surface processes. Recent research suggests the size and shape of exfoliation fractures is influenced by pre-existing fractures, with vertical fractures potentially limiting subsequent sheet dimensions, yet the extent to which pre-existing fractures influence subsequent exfoliation joint formation is not clear. Additionally, despite over a century of observations, including direct measurements of active exfoliation, the mechanisms driving subcritical fracture propagation and rock exfoliation remain debated. We present new insights from drone-based LiDAR of Looking Glass Rock, a 3,969-foot-tall granite dome in Pisgah National Forest, North Carolina. Our analysis highlights three fracture types at Looking Glass Rock: (a) exfoliation fractures, (b) vertical joints, and (c) horizontal “eyebrow” fractures on prominent vertical faces. In contrast to recent studies of similar rock domes (e.g., Arabia Mountain, GA; Twain Harte, CA; Yosemite National Park), exfoliation fractures at Looking Glass Rock exhibit a complicated relationship with cross-cutting fractures and thus do not have a clear relationship with modern surface processes such as diurnal thermal cycles which have been linked to subcritical fracturing and spontaneous exfoliation. This raises the broader question: Are exfoliation joints primarily driven by surface processes (e.g., solar heating, weathering), confining stresses from topography and erosion, or interactions between regional tectonic stresses and topography? Understanding these fracture mechanisms and their sensitivity to regional stresses and temperature changes is critical for predicting the impacts of climate change on rock dome stability and forecasting rockfall hazards.