Presenter: Chloe Geddes
Authors: Chloe Geddes, Tammy Rittenour, April Phinney
Faculty Advisor: Tammy Rittenour
Institution: Utah State University
The June 2020 Mangum fire ignited 71,000 acres of Ponderosa Pine forest on the Kaibab Plateau, near the North Rim of the Grand Canyon. The rock formation affected by the fire was theHarrisburgmember in the Permian Kaibab Formation, which is composed of varying units of marine evaporites, chert and siliciclastics. This research is designed to experimentally determine the degree of thermal rock-colour alterations in response to controlled exposures of heat and duration to stimulate various intensities of wildfire conditions. Results will be used on rock samples collected within the Mangum Fire burn areas to testify that thermally altered rock colouration can be used to determine wildfire intensity as a metric of interest to assess recent amplified fire regimes across the western United States. Rock samples consists of surface rocks exposed to heat during the Mangum Fire and rocks of the same unit with minimal exposure located in nearby road cuts. Burn severity, outcrop description and facies analysis was documented for the unburned samples. Experimentally determined colour change of the unaltered rock colour was first recorded using the Munsell colour scheme prior to being baked in a muffle furnace. Heating increments were done in 50°C intervals up to 700°C. At first the rock samples were held at set temperatures for 1 hour but then additional assessments tested for varying durations of heating to stimulate a diverse set of wildfire conditions. Laboratory-induced thermal colour alteration will be compared to the rocks collected from high and medium-low severity burn areas of the Mangum Fire. The broader goals of this project are to assess the potential of using thermally altered rock colour alterations as a metric for wildfire intensity. Application to other fire regimes and rock types will need to be experimentally tested to determine the suitability of this technique elsewhere.