Using GIS to Assess the Post-Fire Table Mountain Environment for Mass Wasting Susceptibility

The Table Mountain fire of Central Washington started on September 8, 2012 during a significant lightning storm. The burned area totaled 42,312 acres. Wildfires can form hydrophobic soils, remove duff, and remove stabilizing vegetation from slopes resulting in a decrease in slope stability and an increase in mass wasting susceptibility. The recent and inaccessible nature of the Table Mountain fire has resulted in few studies being conducted on the post-fire environment. My goal was to model how the Table Mountain fire could affect slope stability of burned areas, hence mass wasting susceptibility at Table Mountain. Data was formatted and analyzed in ArcMap 10.1, creating a relative hazard map that encompassed all significant factors potentially influencing mass wasting in the area such as soil burn severity, topography, aspect, geology, vegetation cover, and hydrology. Each parameter was assigned a relative hazard ranking representing their importance in assessing mass wasting hazards. Preliminary results show that DEM’s were useful in providing slope and aspect analysis, and that the use of Landsat 7 imagery was sufficient to show percent vegetation cover. Areas with the greatest landslide susceptibility were near streams in areas with high intensity burning, presence of landslide deposits, and have a slope greater than 35 degrees. Most of the burned area was ranked as moderate mass wasting susceptibility followed by areas of low and high mass wasting susceptibility, respectively, the abundance of basalt bedrock and areas of low slope in the study area may account for the large areas of moderate mass wasting susceptibility.