Document Type
Thesis
Abstract
High-intensity wildfires have been shown to significantly reduce infiltration in soils and increase erosion on hillslopes by inducing soil hydrophobicity. The Colorado Front Range commonly experiences wildfires in its warm, dry summers, and they are predicted to increase in frequency and magnitude as a consequence of continued climate change. Fourmile Canyon, containing Fourmile Creek, a tributary to Boulder Creek, is representative of the dominant topography in the Front Range, characterized by steep slopes and the presence of an asymmetry between north-facing and south-facing slope aspect, controlling slope and forest density. This study investigates the influence of wildfires and this asymmetry on erosion rates in Fourmile Canyon following the Fourmile Fire of 2010 and Colorado Floods of 2013. I use the fallout radionuclides 7Be, 137Cs and 210Pb as sediment tracers, correlating their relative deficits to sediment loss. Soil samples were taken along four transects in Fourmile Canyon, on north- and south-facing burned and unburned slopes. The north-facing burned slope demonstrated statistically lower 137Cs inventories (AnoVa p < 0.001) than either the north-facing unburned slope or south-facing burned slope, but other slopes were statistically equivalent. Furthermore, a comparison of radionuclide inventory to slope value indicates lower erosion rates on north-facing unburned slopes than for either south-facing slope, but increased erosion on the north-facing burned slope. The slope analysis also suggests the presence of a slope threshold for erosion on north-facing slopes, such that a hillslope with a grade above 0.7 will erode after a burn. Using the unburned north-facing slope as a reference inventory for a 137Cs -based erosion model, the burned north-facing slope experienced a total sediment loss of 4-14 kg/m2 since 1963, though much of this likely occurred within the last 3-10 years. These results demonstrate that wildfires contribute heavily to periodic sediment loss on north-facing slopes, while south-facing slopes are largely unaffected by the effects of fire and experience more consistent erosion.
Date Awarded
2015
Department
Geology
Advisor 1
James M. Kaste
Recommended Citation
Abrahams, Edward R., "Post-fire Hillslope Aspect Controls on Erosional Processes Traced by Fallout Radionuclides in Fourmile Canyon, Colorado" (2015). Geology Senior Theses. William & Mary. Paper 331.
https://scholarworks.wm.edu/geologyseniors/331
