INVESTIGATING THE RELATIONS AMONG EOLIAN DUST ACCUMULATION, RILL FORMATION, AND MORPHOLOGIC AGE FOR CINDER CONES, SAN FRANCISCO VOLCANIC FIELD REU

The San Francisco Volcanic Field (SFVF) in northern Arizona includes over 600 Plio-Quaternary basaltic cinder cones. Some cones such as Sunset Crater (~900 ya) and SP Crater (59 ka) are dated, but most are not. Cinder cones in the SFVF formed from loose explosive volcanic products into which water can infiltrate quickly. As the cones age, soil develops from the deposition of eolian dust, filling the voids in the volcanic edifice and enabling overland flow. Over time, the processes that control hillslope evolution change from dominantly diffusive to increasing flow concentrated in rills. This study investigates how the formation of rills on the flanks of cinder cones may indicate relative morphologic ages through the analysis of fine material in soil pits, the construction of analog models in a controlled laboratory environment, and the calculation of drainage densities on cones of variable or unknown ages. The percent material <2mm in soil pits dug into SP Crater, Crater 173 and Vent 100, combined with previously gathered information on soil development on Sunset Crater cinders, indicate that the amount of fine material mixed with scoria increases as the cones age. Analog models consisted of a terrarium with a scoria cone model of varying percent fine material in the center and simulated rain for erosion. The models consisting of scoria alone did not appreciably change. The model with 20% fine material in the upper layer of scoria experienced diffusive-like erosion and formation of a scoria apron around the cone. The model with a <1mm scoria core and a fine grain mixture on top developed rills. Drainage densities mapped on the SFVF cones mentioned above and the undated Francis Cone indicate that the amount of rilling on the sides of cinder cones increases with age until the cone begins to lose relief due to erosion and drainage density decreases. Sunset Crater, the youngest cone, has no rills visible in aerial photographs. SP Crater has the greatest drainage density, 8.7 x 10^-3 m/m², while the geomorphically older Francis Crater has a lower drainage density of 6.9 x 10^-3 m/m². This research suggests the inclusion of non-diffusive processes in computer modeling of hillslope evolution. Studying the relationship between rill development and geomorphic age can help estimate the recurrence interval of volcanic activity in the SFVF.