Post-fire Debris Flow Mechanisms in Different Lithological Zones
Post-fire debris flows are common in areas after wildfires under rainfall conditions.Wildfires destroy vegetation,alter soil structure,and change soil physical properties,leading to significant changes in soil bulk density,porosity,and permeability in the burned areas.These changes result in a distinct mechanism of debris flow formation compared to ordinary debris flows.Moreover,burned areas in different rock formation regions(represented by gray phyllite,light-colored granite,and red mudstone)exhibit considerable differences in the initiation mode,disaster evolution process,dynamic characteristics,and scale of post-fire debris flows.In this study,it conducted field investigations and sampling analyses at debris flow channels in different rock formation areas to explore the physical and mechanical properties,as well as the permeability of the parent rock in the burned areas,weathered colluvial soil on slope surface,plant roots,and at different depths of influence.This study revealed the mechanism and the reasons for the scale differences of post-fire debris flows in different rock formation areas.(1)Post-fire debris flows exhibited characteristics of high density and large viscosity fluids.(2)There were differences in the initiation modes,disaster processes,dynamic characteristics,and runout scales of post-fire debris flows in different lithological regions.The primary source of material replenishment for the first surge of post-fire debris flow in different lithological regions mainly comed from ash and sediment on slope surfaces;during subsequent replenishment processes,metamorphic rock regions were characterized by channel undercutting and lateral erosion-induced landslides;igneous rock regions were primarily supplied by channel undercutting and bedrock erosion;and sedimentary rock regions were characterized by scraping and gradual entrainment of channel-derived materials.This research provides a scientific basis for prevention and control of post-fire debris flows in mountainous areas of China.
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