THE NOT-SO-STRAIGHT BUT DEFINITELY NARROW OF BEDROCK RIVERS: UNDERSTANDING CONTROLS ON SEDIMENT DISTRIBUTION AND MORPHOLOGY IN CANYONS

Slot canyons, especially steep headwater canyons, are among the least studied forms of bedrock rivers. However, because of the strong connectivity they exhibit among the hydrologic regime, channel boundary conditions, erosion rate and style, and sediment dynamics, slot canyons have the potential to act as natural laboratories that exemplify hypothesized relationships between knickpoint migration, sediment dynamics, fracture geometry, and morphology. The impacts of heterogeneity in fracture geometry, rock strength, and sediment supply likely exert strong controls on channel morphology, erosion rate and style, and long-term landscape evolution. However, we lack field data to broadly explore the variability in these relationships in bedrock rivers. We hypothesize that: 1) anisotropy in fracture geometry, which sets the dimensions and orientation of pluckable blocks, will strongly influence channel morphology and erosion style, and 2) channel boundary (e.g., lithology, fracture geometry) controls on morphology and sediment dynamics will vary strongly across hydrologic regimes and geologic structures. We present extensive field data from 20 canyons in the Spanish Pyrenees to test these hypotheses. We examine how fracture geometry influences channel form and inferred rates and styles of erosion, how channel morphology in turn influences alluvial cover distribution, and how broad-scale forcings such as climate and geologic structure modulate more local-scale controls on channel morphology. We present statistical modeling that will lay the foundation for more detailed modeling and experimental examination of bedrock river evolution.