Experiments on Reworking by Successive Unconfined Subaqueous and Subaerial Muddy Debris Flows

Debris flows occur under water, e.g., in lakes and the ocean, as well as under air. These two types of debris flow have many similarities, but also differ in striking ways. The focus of the research reported here is on the ability of an unconfined debris flow to remobilize or rework an antecedent deposit over which it runs. Experiments were performed in a tank in order to quantify reworking. The debris slurry was premixed and consisted of a mixture of water, sand, and kaolinite clay. Three experiments were performed, each consisting of four individual runs. In each run the slurry was released impulsively from a head tank. The first run of each experiment formed a deposit over the initial inerodible bed. The second, third, and fourth runs progressed over and reworked to a greater or lesser extent the antecedent deposit(s). Two experiments of four runs each were performed in the subaqueous configuration, and one experiment of four runs was performed in the subaerial configuration. In the subaerial case, reworking was immediate and extensive. In the subaqueous case, reworking of the deposit of the first run by the second run was suppressed. Part of the reason for this appears to be hydroplaning of the head of the debris flow. As the deposit built up, however, considerable reworking was eventually observed in the subaqueous case as well.