Spalling by Repeated Forest Fires can Mimic Inselberg Flared Slope Profiles

Abstract Wildfires can play an important role in shaping bedrock‐dominated landscapes. Fire can break down rock by spalling exposed surfaces. In massive rock, spalled flakes tend to be of the order of 1 cm thick and several to tens of centimeters in diameter. In central Australia, erosion rates from fire‐induced rock spalling have been proposed by Buckman et al. (2021, https://doi.org/10.1038/s41467‐021‐22451‐2 ) to result in unique overhangs called flared slopes that ornament the base of bedrock outcroppings (inselbergs) that dot the otherwise flat landscape. The long‐term evolution of rock surfaces exposed to repeated fires inspires our numerical modeling of the fire spall process. We honor the radiative balance on the rock wall and address two fire geometries. We incorporate a thermally modulated damage criterion to mimic the cracking of the rock. The penetration depth of the thermal perturbation is scaled by the square root of the duration of the fire, reaching many cm for a tree fire, and several mm for a brush fire. Modeled erosion of rock walls due to repeated fires is rapid at first but slows as the distance to the fires increases. The emergent steady shape is scaled by the height of the vegetation. The pattern of radiation from a tree fire, and the predicted damage caused by it, mimic the geometry of flared slopes that ring Australian inselbergs, supporting the hypothesis of long‐term wildfire driven lateral erosion of these features. The timescale predicted is an order of magnitude larger than the erosion rates measured across the inselberg tops in previous work.