Articles | Volume 5, issue 2
Research article
08 May 2017
Research article |  | 08 May 2017

Self-similar growth of a bimodal laboratory fan

Pauline Delorme, Vaughan Voller, Chris Paola, Olivier Devauchelle, Éric Lajeunesse, Laurie Barrier, and François Métivier

Abstract. Using laboratory experiments, we investigate the growth of an alluvial fan fed with two distinct granular materials. Throughout the growth of the fan, its surface maintains a radial segregation, with the less mobile sediment concentrated near the apex. Scanning the fan surface with a laser, we find that the transition between the proximal and distal deposits coincides with a distinct slope break. A radial cross section reveals that the stratigraphy records the signal of this segregation. To interpret these observations, we conceptualize the fan as a radially symmetric structure that maintains its geometry as it grows. When combined with slope measurements, this model proves consistent with the sediment mass balance and successfully predicts the slope of the proximal–distal transition as preserved in the fan stratigraphy. While the threshold-channel theory provides an order-of-magnitude estimate of the fan slopes, driven by the relatively high sediment discharge in our experimental system, the actual observed slopes are 3–5 times higher than those predicted by this theory.

Short summary
Alluvial fans are sedimentary deposits that take place at the outlet of mountain range. This location makes them the first sedimentary archive where sediments, eroded from mountains, are deposed. Their morphology is controlled by the water and sediment discharges and sediment characteristics. By using controlled laboratory experiments, we show that an alluvial fan composed of two distinct sediments has a characteristic shape; it can be decomposed into two fans made up of one sediment.