Experimental study on the evolution of canyon fire spread behavior under different terrains and the critical conditions for eruptive fire

Background The spread of canyon fire often involves sudden acceleration, which is related to eruptive fire. Aims The purpose of the study is to explore the pattern of fire line evolution and rate of spread (ROS) with topographic conditions in canyon fire, and to clarify the critical conditions for and mechanism of eruptive fire. Methods A systematic experimental study on canyon fire was conducted by igniting dead pine needles with a point ignition. Key results Four different types of fire line contours were identified under different topographic conditions. When the central slope angle α ≥ 15°, the direction of the fire head gradually deviates from the line of maximum slope and moves to the center line, and this deviation increases with α. Accordingly, ROS along the center line also exhibits dynamic characteristics, and ROS increases with α and the lateral slope angle δ. The critical conditions for eruptive fire are α = 27.5° and δ = 20°. Conclusions When eruptive fire occurs, there is significant convective heating ahead of the fire front. This strong convective heating is the basic mechanism for eruptive fire in canyons. Implications Our results may provide a theoretical basis to assist fire commanders to make decisions.