|Back to Faculty||
email: Gary Kocurek
Dr. Gary KocurekAeolian Sand Dune Fields As Self-Organizing Phenomena. Fields of aeolian sand dunes represent some of the most widely recognized patterns in nature. Until recently, these patterns were considered the cumulative sum of dynamics beginning with fluid flow and grain transport. Specifically for dune fields, pattern elements such as crest length, spacing and defect density were thought to arise from a template defined by the boundary layer of the wind. Self-organization represents a new paradigm in which the pattern develops spontaneously without any underlying template. Essentially, any stochastic transport of grains yields grain collisions and collections of grains that interact to yield bedform patterns. The parameters that define these patterns evolve as a function of time. This exciting new understanding has the potential to completely alter the way in which we think about bedforms, their patterns, flow regime and fluid dynamics. My students and I are pursuing several avenues of aeolian dune-field pattern self-organization that involves (1) theory development, (2) pattern analysis, and (3) the geomorphic backstripping of dune-field patterns to understand their construction. This work is necessarily global in scope and extends to dune patterns on Mars, and makes use of satellite images and theoretical models, but involves considerable ground-truth in the field and dating of geomorphic features via optically stimulated luminescence (OSL).
Origin of Current Aeolian Sand Dune Field. Although deserts are a climatic phenomena, the occurrence of dune fields is a function of a sediment supply, the availability of this sediment to the wind, and the transport capacity of the wind. Ultimately, it is the coincidence of tectonic, eustatic and climate external forcing factors that gives rises to dune fields. Each dune field is the product of a unique train of events, and we seek to understand the overall dynamics of dune-field evolution by specific case studies. Dune fields that my students and I are studying include fields in the United States, Mexico, the Sahara, Middle East and southern Africa. These studies are a combination of remote sensing, field geomorphology, stratigraphy, and regional/global tectonic, eustatic and climatic analysis.
Ancient Record of Aeolian Systems. The rock record provides the deep-time dimension to the study of aeolian systems. Whereas modern dune fields typically have a greater resolution, these represent thin slices of time. From the stratigraphic record we can understand aeolian system accumulation and preservation in a geologic sense of long-term basin evolution, sea-level change, climate, and aeolian system response to these external forcing factors. Our primary area of research is the Jurassic of the Colorado Plateau that houses probably the finest outcrops of aeolian and related systems globally. The range of study is that from whole systems at the basinal scale to stratification in individual sets of dune cross-strata.
Airflow, Sediment Transport and Dune Dynamics. A great many
fundamental questions remain at the most basic level of aeolian transport.
Sediment transport remains an unsolved problem after a half century of
investigation. Recent technology is, however, now allowing us to measure the
instantaneous stresses that grains experience via turbulence, replacing
time-averaged shear stress as the primary measure of grain transport. The
interaction of bedforms with the flow results in a secondary flow that defines
surface processes and stratification types, which, in turn, can be used in the
ancient record to reconstruct paleoflow conditions. Specifically, in this avenue
of research we "instrument" a series of dunes and quantify the flow conditions
and grain transport under a variety of conditions.