Impact of Atmospheric Conditions on the Erosion Potential of Burned Soil

One of the principal side effects of wildland fire extreme events is a subsequent mass soil erosion event of the scorched earth denuded by the fire. Erosion of ash and ash-soil mixes above the fire produced hydrophobic layer, and soil below the hydrophobic layer has different erosion potentials but combine to produce mudslides. These soil erosion events may be devastating and extreme in their own rights, damaging critical infrastructure downslope or downstream of the burn area itself with potential to release toxins into waterways. Researchers in the wildland fire space have long known that in very intense fire regimes that the atmosphere at the ground surface and in the pore space of the soil just below the surface is oxygen deprived due to the consumption of oxygen in the fire. This produces a nitrogen rich atmosphere at the micro-scale. It is unknown if this locally nitrogen rich atmosphere affects the changes to soil structure that impact soil erodibility below the hydrophobic layer. It is known that oxygen is a major chemical component of many geochemical processes in soil at high temperature. It is thus hypothesized that soils heated to the same temperature and for the same duration in a fire will have different resultant soil structures with different erosion potentials due to the variation in oxygen levels associated with each heating method. An experimental program was thus designed and implemented to measure differences in soil structure and erosion potential with kiln heating in a normal atmosphere versus simulated wildfire in a container burn. These data show that there are surprising differences to soil structure and erosion potential, highlighting the need to better understand soil geochemical processes in wildland fire.