ASPECT-RELATED DIFFERENCES IN SEDIMENT TRANSPORT RATES ON CINDER CONES, SAN FRANCISCO VOLCANIC FIELD REU

Cinder cones are excellent landforms for the examination of aspect-related differences in sediment flux. The conical forms have a complete range of aspect, and it is possible to control for age, lithology, and original form. Sediment flux is assumed to be controlled by local slope and a rate constant (diffusion coefficient, k). k lumps properties of the soil, lithology, and climate, which can vary across space, depending on microclimate feedback influenced by sun, soil and vegetation. Many examinations of cinder cone topographic development have held kspatially constant. However, higher levels of insolation should result in differences in soil moisture, evapotranspiration, and weathering affecting the vegetation patterns and relative transport rates. As a result, differential exposure to solar radiation should produce a morphological asymmetry.

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.