PHYSICAL WEATHERING OF CHLORITE AND SMECTITE AS A RESULT OF POST-FIRE SOIL CONDITIONS

Chlorite and Smectite (montmorillonite) are clay minerals common to soil. These minerals have been shown to physically alter upon exposure to forest fire. This study aims to determine a timeframe in which physical weathering occurs following the application of fire. To do this, a laboratory experiment was created in which several weathering solutions were generated by means of vacuum filtration. These solutions included rainwater filtered through soil, through ash, and through ash over soil. Rainwater filtered through ash and soil was meant to replicate the post-fire environment. The individual minerals were then exposed to these treatments, at surface conditions, for three-week intervals for 24 weeks. The minerals were then extracted from the weathering solutions and analyzed for particle size distribution. The pH of the weathering solutions + mineral were also determined before each extraction.

The preliminary results of this study indicate an overall decrease in pH for all weathering treatments + chlorite with the lowest recorded pH at 15 weeks. Smectite shows an initial pH decrease in ash treated samples followed by an increase as 12 weeks is approached. Both chlorite and smectite show apparent physical weathering for samples replicating the post-fire environment based on particle size distribution analysis. Chlorite shows an increase in fine particles beginning at three weeks while smectite shows an increase in fine particles beginning at 9 weeks. We anticipate the most significant physical weathering will occur at 15 weeks for chlorite and 12 weeks for smectite as it should correlate with the pH data. These minerals will be analyzed for structural alteration and changes in bulk chemistry at a future time. This chemical weathering data will be compared with the current physical weathering results to determine a complete analysis of mineral weathering in the post-fire environment.