Physical, chemical and hydrological properties of Ponderosa pine ash

In this study, ash is analysed as a geological material; in particular, we focus on ash produced by the burning of Ponderosa pine, a conifer that is widespread throughout mountainous landscapes of western North America. One set of ash samples used in the analyses was collected from a wildfire site and another set was created in the laboratory. We found that the median particle size of the ash was in the fine sand to silt range with at least 25–50% of the particle size distribution in the appropriate range for maintaining debris flow behaviour. Measurements of the infiltration capacity of ash found values similar to fine sands, indicating that a layer of ash can reduce the infiltration capacity of coarse soils. The elemental composition of ashes analysed through inductively coupled plasma emission spectrometry was dominated by Ca, K, Mg, P, Mn, Fe and Al. X-ray diffraction analysis revealed the presence of calcite, quartz and feldspars in ashes created from a variety of fuels; fuel type and combustion temperature were found to have a dominant control on ash mineralogy. The results suggest that the elemental and mineral composition of ash could be used to identify dominant fuel sources and combustion temperatures.