HR: 1330h
AN: H52A-1146    [PDF]
TI: Applications of Physical Modeling to the Evolution of Slot Canyon Morphology
AU: * Carter, C L
EM: ccarter@es.ucsc.edu
AF: Department of Earth Sciences, University of California Santa Cruz, 1156 High St., Santa Cruz, CA 95064 United States
AU: Anderson, R S
EM: andersrs@colorado.edu
AF: Department of Geological Sciences and INSTAAR, University of Colorado, Boulder, Campus Box 450, Boulder, CO 80309 United States
AB: Abrasion-dominated fluvial erosion generates slot canyons with intricately undulating wall morphology. Flows in slot canyons are unique in that the walls comprise a significant portion of the wetted perimeter of the flow. Wire Pass, UT incises through massive cross-bedded Navajo Sandstone. The canyon ranges in width from $<$1 m to $\sim$5 m in the slotted sections, and in depth from $\sim$5 m to $\sim$25 m. Incision in Wire Pass and related slots is limited to ephemeral flash floods; paleoflood debris indicates that the depth-to-width ratios of these flows are at least 1:1. Sub-meter resolution field mapping of a 20 m length of Wire Pass shows that the wall morphology is a complicated combination of both in-phase (meander-like), and out-of-phase (pinch and swell) type undulations. In order to understand the evolution of slot canyon wallforms, and the influence of these shapes on flow dynamics, we recorded the evolution of four distinct canyon wall morphologies in a 2.4 m flume box at the St. Anthony Falls Laboratory. In a substrate consisting of approximately 3:2 mixtures of F110 sand and plaster of Paris, we molded in-phase and out-of-phase undulations, and wide (6.5 cm) and narrow (4 cm) straight initial wall profiles. Sediment-laden water flowed through each canyon at discharges ranging from 2.6 L/s to 4.2 L/s. We made velocity measurements in three dimensions in sections of each canyon. At 5 hr intervals we documented wall and bed morphology at 0.5 cm resolution using a Keyance LK-500 laser mounted on a moving cart. Initial results show that wall faces in both undulating canyons evolve at different rates, and their flow fields are strongly asymmetric. Upstream-facing walls in undulating canyons eroded most rapidly. In the straight-walled canyons, small perturbations developed in the walls. Each canyon incised downward and headward from a knickpoint generated by a consistent lower boundary. Incision depths averaged $\sim$6 cm. Incision generally propagated around small cracks in the substrate and in potholes formed around small pebbles. The location and shape of scallops on the bed of each canyon was strongly controlled by wall morphology. Continued analysis of slot canyon dynamics in the field and laboratory should further the understanding of bedrock canyons dominated by abrasion.
DE: 1800 HYDROLOGY
DE: 1815 Erosion and sedimentation
DE: 1824 Geomorphology (1625)
DE: 1894 Instruments and techniques
SC: Hydrology [H]
MN: 2003 Fall Meeting