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Eolian Sand Dunes: Models of Emergent Features in Self-Organizing Systems

Maslyn, R. Mark
Consultant, Littleton, CO

"Self-organizing" is a term applied to dynamic systems of independently acting agents that together produce coherent behavior or features. Sand dunes, built one sand grain at a time, are self-organizing features that emerge from simple rules for sand transport and deposition applied to a set of initial conditions. Resulting dune types depend on surprisingly few variables: initial sand concentration (availability) and wind regime (velocity, variability, and complexity).

The author has written a simulation program that incorporates these variables and graphically displays sand dunes as they are built on a grain by grain basis. Major dune types such as barchanoid, star, and longitudinal can be created from specific sand concentration and wind regime values identified by the author. Published wind regime values for each dune type along with experimentally determined sand availability values were used as starting points to find the values that best produced each dune type. Intermediate model values resulted in dunes transitional in form between these types.

Since these are real-time simulations, changes in wind regime values while running the simulation resulted in concurrent changes in dune morphology and orientation. With the new values, the sand dune areas re-organized into different patterns. There is also evidence that with simulation values held constant, sand dune patterns can continue to evolve with time. For example, in several longitudinal dune simulations multiple individual sand ridges formed early in the simulation over time began to merge into fewer but larger longitudinal ridges with the same orientation.