Articles | Volume 5, issue 2
Earth Surf. Dynam., 5, 239–252, 2017
Earth Surf. Dynam., 5, 239–252, 2017

Research article 08 May 2017

Research article | 08 May 2017

Self-similar growth of a bimodal laboratory fan

Pauline Delorme1, Vaughan Voller2, Chris Paola2, Olivier Devauchelle1, Éric Lajeunesse1, Laurie Barrier1, and François Métivier1 Pauline Delorme et al.
  • 1Institut de Physique du Globe de Paris, Paris – Sorbonne Paris Cité, Université Paris Diderot, Paris, France
  • 2Saint Anthony Falls Laboratory, University of Minnesota, Minneapolis, Minnesota, USA

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.