Treffer: Spalling by Repeated Forest Fires can Mimic Inselberg Flared Slope Profiles.

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. Plain Language Summary: Forest fires can dramatically raise the temperature of a rock surface, leading to flaking or spalling of the surface. But can any particular landform be attributed to forest fires? Isolated outcrops of massive bedrock, particularly in Australia, display peculiar overhangs that ornament the intersection of the outcrop with the desert floor. It has recently been suggested that these "flared slopes" are created by repeated fire‐spalling of the rock. Here we model the temperatures in a rock wall during both forest and brush fires and connect this to damage of the rock. Fires can indeed raise the near‐surface temperatures of the rock to hundreds of degrees C. The thermal effects of the tree fires penetrate much more deeply into the rock. When the rock is allowed to erode due to the fire damage, the profile of the rock wall evolves. The emergent shape mirrors the pattern of radiation from the fires, which reaches a maximum at the mid‐height of the burning trees or brush. The resulting geometry from forest fires closely matches the well‐developed flared slopes documented in Australia and the speed at which it is predicted to form is significant given the otherwise slow nature of other processes. Key Points: Thermal shock from wildfires can both spall flakes and damage rock to depths of several centimetersErosion of rock walls due to repeated fires is rapid at first but slows as the distance to the fires increases, achieving a steady shapeThe emergent shape is scaled by the vegetation height and mimics the geometry of overhangs ornamenting the bases of Australian inselbergs [ABSTRACT FROM AUTHOR]

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