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DY: Fachverband Dynamik und Statistische Physik

DY 12: Granular Matter / Contact Dynamics Part II

DY 12.6: Talk

Monday, March 16, 2015, 16:45–17:00, BH-N 128

Aeolian sand sorting and megaripple formation — •Marc Lämmel, Anne Meiwald, and Klaus Kroy — Institut für Theoretische Physik, Universität Leipzig, Germany

Turbulent flows drive sand along riverbeds or blow it across beaches and deserts. This seemingly chaotic process creates a whole hierarchy of structures ranging from ripple patterns over dunes to vast wavy sand seas. Moreover, by the very same process, grains are constantly being sorted, because smaller grains advance faster while their heavier companions trail behind. Starting from the grain-scale physics, we model the sorting dynamics by erosion and show how it creates the characteristic bimodal grain size distribution that is a prerequisite for the formation of so-called megaripples [1]. Due to the separation into small and big grains, these structures have a lot in common with their bigger relatives, aeolian sand dunes, whose physics is much better understood. This enables us to adapt a well established dune model [2] to predict formation, morphology, and dynamics of the megarippels. Preliminary tests against field data strongly support our approach, which, moreover, provides a roadmap for future systematic field and laboratory measurements.

[1] Qian, G. et al., Sedimentology 59, 1888 (2012)

[2] Kroy, K. et al., Phys. Rev. Lett. 88, 054301 (2002)