Abstract
Knowledge of the processes driving debris-flow fan evolution are critical in the support of efforts to mitigate related hazards, reduce risk to populations and infrastructure, and reconstruct the history of sediment dynamics in mountainous areas. Research on debris-flow fan development has focused on topographic controls, debris-flow volume and rheology, and the sequence of occurrence of debris flows. While these items have explained a great deal about fan formation and specifically avulsion and runout mechanisms, there is a need to further investigate other properties as they relate to debris-flow fan formative process. Here, we examined the role of debris-flow grain-size distribution on fan formation. Flume experiments were employed to examine the morphology of debris-flow fans that resulted from flows with mono- or multi-granular sediment composition with the same average grain size. All other flow characteristics were held constant. The mono-granular flows formed a symmetric-like fan morphology because there was little avulsion during the formation process. The multi-granular flows produced fans with an asymmetric morphology. Avulsions occurred on both lateral extents of the fan during the early stages of fan development and caused the runout direction to shift produce the fan asymmetry. Grain-size distribution was closely related to spatial diversity in fan morphology and stratigraphy.
Highlights
IntroductionDebris-flow fans are substantive sediment sinks persisting greater than 102 years in many locations throughout the world (e.g., Dühnforth et al, 2007; Schürch et al, 2016)
Knowledge of the processes driving debris-flow fan evolution are critical in the support of efforts to mitigate 10 related hazards, reduce risk to populations and infrastructure, and reconstruct the history of sediment dynamics in mountainous areas
Flume 15 experiments were employed to examine the morphology of debris-flow fans that resulted from flows with mono- or multigranular sediment composition with the same average grain size
Summary
Debris-flow fans are substantive sediment sinks persisting greater than 102 years in many locations throughout the world (e.g., Dühnforth et al, 2007; Schürch et al, 2016). Debrisflow fan forms have been determined to result in great part to autogenic behavior whereby the natural progression is one where debris flow runout over time involves backfilling of the existing channel on the fan, a loss in channel capacity, subsequent avulsions, channelization processes, and a repeat of these same process.
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