ASPECT-RELATED DIFFERENCES IN SEDIMENT TRANSPORT RATES ON CINDER CONES, SAN FRANCISCO VOLCANIC FIELD REU
A spatial analysis of topography, vegetation and solar radiation of the cones of the San Francisco Volcanic Field (SFVF), a monogenetic cinder cone field in semiarid northern Arizona, reveals significant differences in slopes in areas with varying levels of solar radiation and vegetation. In the SFVF, south-facing slopes receive up to 3x more solar radiation. Two-sample t-tests were conducted on slope magnitudes from cone sections of high and low insolation and high- and low- density vegetation to determine the extent of differences in flank slope. Areas of higher solar radiation and more-dense vegetation within low-insolation areas had average asymmetries of 2.6±2.5 and 1.3±2.3°, respectively. Nonlinear diffusion numerical simulations on transport-limited synthetic cones show a relationship between morphological age and k distributions. On short timescales, the magnitude of the variation of k must be >10 to produce rapidly developing significant flank asymmetries. On 1 Myr timescales, kneed only vary by 2 or 3 to produce similar asymmetry. Given the expected 3x variability of solar radiation in the SFVF, large flank asymmetries on younger cones must be explained by both eruption dynamics and insolation-modulated erosion.
This study demonstrates how flank asymmetry may be used as a morphological dating tool. A quantification of the relationship between solar radiation and diffusion rate can lead to more realistic numerical modeling of hillslope erosion.