Wildfires as a Weathering Agent of Carbonate Rocks

Abstract

While most of the scientific effort regarding wildfires has predominantly focused on fire effects on vegetation and soils, the role of fire as an essential weathering agent has been largely overlooked. This study aims to evaluate rock decay processes during wildfires, in relation to ground temperatures and rock morphologies of limestone, dolomite, and chalk. In 2010, a major forest fire in Israel caused massive destruction of the exposed rocks and accelerated rock weathering over the burned slopes. While a detailed description of the bedrock exfoliation phenomenon was previously reported, here, we conducted an experimental open fire to determine the temperature and gradients responsible for boulder shattering. The results show ground temperatures of 700 °C after 5 min from ignition, while the peak temperature (880 °C) was reached after 9 min. Temperature gradients show a rapid increase during the first 5 min (136 °C/min), moderate increase during the next 4 min (43 °C/min), and slow decrease for the next 9 min (25 °C/min). After 12 min, all boulders of all formations were cracked or completely shattered. The behaviour of carbonate rocks upon heating was studied to identify the erosive effects of fire, namely the formation of new cracks and matrix deterioration.

Surface Mechanical Effects of Wildfires on Rocks in Climbing Areas

“…This includes mechanical weathering, such as cracking, spalling, and granular disaggregation, and thermochemical weathering with different temperature thresholds. Observed thermochemical reactions include reddening (from 300 • C [1,5-7]), CaCO 3 calcination (partial from 400 • C and total from 600 • C [48][49][50]) resulting in rock decomposition, and intense quartz cracking (from 573 • C [5][6][7]48]). The variety of observed thermochemical reactions coupled with measured SH and UPV allow an approximation of the maximum temperatures attained during the fire [5,51] in a temperature range of 400 to 700 • C, coherent with observed temperature distributions in comparable fires [52].…”