Three-Dimensional Modeling of Polygonal Ridges in Salt Playas

In this work, we investigate the formation of the curious
polygonal
salt ridges that tessellate salt playas worldwide using suitable three-dimensional
modeling and simulation of the dynamical processes that are responsible
for their formation. We employ the principles of fracture mechanics
under cyclic wetting and drying, fluid and mass transport in fracture
channels, and processes of crystallization and self-organization to
finally replicate the almost Voronoidal pattern of salt ridge mosaics
observed in playas. The model is generic and applicable to playas
having different salt compositions, as the effect of the salt diffusion
coefficient and critical salinity for crystallization are factored
in. The final pattern of polygonal salt ridges obtained by simulation
visually resembles the geometry of the salt ridges reported in the
literature. A single equation describing the time of first crystallization
of salt in terms of evaporation suction pressure P, diffusion coefficient D of salt, and relative
salinity Δc with respect to critical salinity
at saturation, has been proposed. The saturation of crystal growth
rate is shown to be a dynamic equilibrium between advection and diffusion
processes. We show that the stable polygonal geometry of the salt
playas is an effort toward the total minimization of system energy.