Avalanche Face - Grain flow

Provided by Maarten Kleinhans Utrecht University, The Netherlands

Total Time = 0'09" (987 Kb)

The video shows grain-size sorting in grain flows at the lee-side of a laboratory delta. The experiments were conducted in a narrowed flume at the St. Anthony Falls Hydraulic Laboratory, University of Minnesota with support of Gary Parker and Jeff Marr. The sediment consisted of sand and pea gravel. Sediment deposition and sorting on the lee slope of the delta is the result of 1) grains falling from suspension that is initiated at the top of the delta (to the left), 2) kinematic sieving on the lee slope in the slightly moving sediment layer, 3) failure of the whole slope and the following grain flows, in which protruding large grains are dragged downslope by subsequent grain flows. The result is a fining upward vertical sorting in the delta such as in the picture below for bimodal colored sediment. Systematic variations in the trend depend on the delta height, the migration celerity of the delta front and the flow conditions above the delta top. The dependence on delta height and migration celerity is explained by the sorting processes in the grain flows, and the dependence on flow conditions above the delta top is explained by suspension of fine sediment and settling on the lee side and toe of the delta. Large differences in sorting trends were found between various sediment mixtures. See Kleinhans, M., 2005, Grain-size sorting in grainflows at the lee side of deltas: Sedimentology, v. 52, p. 291-311 and the website of Maarten Kleinhans for more information http://www.geog.uu.nl/fg/mkleinhans/.