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DY: Fachverband Dynamik und Statistische Physik

DY 41: Poster - Pattern/ Nonlinear Dyn./ Fluids/ Granular/ Critical Phen.

DY 41.1: Poster

Donnerstag, 3. April 2014, 17:00–19:00, P3

Formation of salt polygons on salt playas — •Antoine Fourrière and Lucas Goehring — Max Planck Institut for Dynamics and Self-organization, Göttingen, Germany

On the grounds of natural salt deserts or in evaporation pools for industrial salt extraction, one can see some self-organized polygonal network of 1-2m diameter. The edges of these periodic structures are formed by salt crystal ridges, that is the reason why we call them 'salt polygons'. In this work, we analyze three different potential mechanisms to explain the formation and the scaling of salt polygons: (i) dessication cracks, (ii) non-linear wrinkling of an elastic layer and (iii) porous medium convection cells in the soil. We built a 2D experiment to test these ideas and most particularly the third one. A Hele-Shaw cell is filled with a porous medium saturated with a salty solution and heated from the side. Surface evaporation causes a steady upward flow of salty water, which leads to precipitation near the surface. Hence, a vertical salt gradient builds up in the porous medium and causes a overturning of denser saltier water. An appropriate Rayleigh number (cf. Lapwood 1948) controls the onset of convection in the porous medium. We change the Rayleigh number by varying the evaporation rates or the permeability of the model soil and measure the wavelength of the salt features that form at the surface. We also visualize the water movements into the Hele-Shaw cell during the experiment. Finally, by using our experimental observations, we revisit the natural formation of these patterns with a pinch of salt.