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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 65: Granular Matter / Contact Dynamics (joint session DY/CPP)
CPP 65.6: Vortrag
Donnerstag, 15. März 2018, 11:30–11:45, BH-N 333
Aeolian sand sorting and megaripple formation — Marc Lämmel1, Anne Meiwald1, Hezi Yizhaq2, Haim Tsoar3, Itzhak Katra3, and •Klaus Kroy1 — 1Institut für Theoretische Physik, Universität Leipzig, Leipzig, Germany — 2Dpt. of Solar Energy and Environmental Physics, Blaustein Inst. for Desert Research, Ben-Gurion University of the Negev, Israel — 3Dpt. of Geography and Environmental Development, Ben-Gurion University of the Negev, Israel
Sand is blown across beaches and deserts by turbulent winds. The seemingly chaotic process creates two dominant bedforms: decametre-scale dunes and centimetre-scale ripples, but hardly anything in between. By the very same process, grains are constantly sorted. Smaller grains advance faster, while heavier grains trail behind. Here, we argue that, under erosive conditions, sand sorting and structure formation can conspire to create distinct bedforms in the forbidden wavelength gap between aeolian ripples and dunes. These so-called megaripples are shown to co-evolve with an unusual, predominantly bimodal grain-size distribution. Combining theory and field measurements, we generate a mechanistic understanding of their shape and migration speed, as well as their cyclic aging, renewal, and sedimentary memory, in terms of the intermittent wind statistics. Our results demonstrate that megaripples exhibit close similarities to dunes and can indeed be mechanistically characterised as a special type of (``reptation'') dunes.