Generalized sorting profile of alluvial fans

• Published in: Geophysical research letters Vol. 41; no. 20; pp. 7191 - 7199
• Main Authors: Miller, Kimberly Litwin, Reitz, Meredith D., Jerolmack, Douglas J.
• Format: Journal Article
• Language: English
• Published: Washington Blackwell Publishing Ltd 28.10.2014; John Wiley & Sons, Inc
• Subjects: Alluvial channels; alluvial fan; Alluvial fans; Alluvial rivers; Boundary conditions; Canyons; Channels; Collapse; Convergence; Deep-sea fans; Distance; Downstream effects; downstream fining; equal mobility; Gravel; gravel-sand transition; Mobility; Movement; Particle size; Particle size distribution; Rivers; Sand; Sedimentation & deposition; selective transport; Self-similarity; Size distribution; sorting
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1002/2014GL060991

Alluvial rivers often exhibit self‐similar gravel size distributions and abrupt gravel‐sand transitions. Experiments suggest that these sorting patterns are established rapidly, but how—and how fast—this convergence occurs in the field is unknown. We examine the establishment of downstream sorting patterns in a kilometer‐scale alluvial fan. The sharp transition from canyon to unconfined, channelized fan provides a well‐defined boundary condition. The channel changes from deep and entrenched at the fan apex to shallow and depositional over a short distance, exhibiting nonequilibrium behavior. The resulting gravel‐fining profile is not self‐similar; the particle size distribution narrows until approximate equal mobility is achieved. Downfan, the gravel‐sand transition appears to exhibit a self‐similar form; field and laboratory data collapse when downstream distance is normalized by the location of the transition. Results suggest a generalized sorting profile for alluvial fans as a consequence of the threshold of motion and nonequilibrium channels. Key Points Gravel sorting is limited by equal mobility of the grain size distributionThe gravel‐sand transition exhibit a self‐similar formTransient dynamics control channel geometry on fan