Influence of solar heating on spontaneous rock exfoliation at Arabia Mountain, Georgia, USA

The formation of surface-parallel exfoliation fractures, or “sheeting joints,” in rock domes produces some of the most intriguing and celebrated landforms on Earth. In 1904, G.K. Gilbert outlined three mechanisms for exfoliation fracture formation: (1) contraction during original cooling, (2) decompression during exhumation, and (3) post-exhumation surface processes. Recent research, including direct measurements during spontaneous exfoliation, has emphasized the influence of solar heating on progressive (subcritical) fracture propagation. This study investigates the mechanisms driving exfoliation fracturing at Arabia Mountain, a biotite orthogneiss dome near Atlanta, Georgia (USA), which experienced a spontaneous exfoliation event in July 2023. Digital elevation model differencing and field observations revealed the event uplifted a ~250 m² area by ~30 cm, buckling sheets up to 12 cm thick, and leaving traces of rock fragments and dust thrown meters away from fractures. Following this event, we installed instrumentation during the summer of 2024 to monitor surface-parallel stresses, local seismic activity, and subsurface rock temperatures at the site. Multiple subsequent exfoliation events in June 2024 were captured in real-time, including direct observations of progressive fracture propagation and dynamic rupture during a period of high temperatures. Relative surface-parallel stresses measured at variable depths in two boreholes revealed clear daily cycles that appear correlated with diurnal patterns of solar heating. A decrease in stress magnitudes and rock temperatures and increased lag time with depth further supports links between rock stresses and solar heating at the surface.

These observations support the hypothesis that subcritical cracking can be initiated or propagated due to thermal stresses and highlight the critical role of solar heating in progressive rock fracturing. The implications of these findings extend beyond Arabia Mountain. The sensitivity of rock domes to thermally induced stresses elevate concerns for an increased hazard of spontaneous exfoliation and rockfall events with future climate warming. Understanding the interplay between thermal stresses, mechanical fracturing processes, and pre-existing damage is critical for predicting such hazards and improving mitigation strategies. Furthermore, our observations and monitoring results provide valuable insights into the fundamental mechanics of subcritical fracturing, which can aid in determining the influence of surface weathering and erosion—key processes impacting the evolution of rock domes. We highlight the importance of multidisciplinary research in advancing our understanding of exfoliation joint formation, and more broadly towards disentangling the impacts of climate change on rock dome stability and landscape evolution.