BEYOND SAND: USING A BLEND OF NON-COHESIVE AND SEMI-COHESIVE ORGANIC MATERIALS TO DEVELOP ADAPTIVE ANALOGUE DEFORMATION MODELS FOR THE CLASSROOM

Analogue “sandbox” models of compressional and extensional deformation have contributed significantly to the collective understanding of tectonic process. Such models typically use a glass-walled pressure box to deform centimeter-scale sections consisting of alternating layers of dry sand, glass microbeads,or viscous polymers, which represent the behavior of kilometer-scale rock masses of varying shear strength. Central to the realistic output of these models is the range of mechanical properties exhibited by input materials, but cost and dust hazard associated with the materials may limit their classroom usability. Models functioning on the basis of similar mechanical contrasts can be developed using safe and readily-available granular materials, paritcularly degerminated cornmeal and wheat flour, permitting a wide variety of structural styles to be replicated in the classroom setting. Centimeter-scale models utilizing alternating cornmeal and flour horizons of several millimeters thickness are suitable for producing a variety of realistic structures, with particularly good representation of the behavior of mechanically-heterogeneous sedimentary sections. Relative strength of model materials can quickly be demonstrated through visual angle-of-repose tests, allowing students to proportionally combine weak and strong material to customize layer properties and test specific hypotheses. The slightly cohesive character of flour-strengthened horizons also permits demonstration of differential erosion, as weaker materials may be blown away to produce an erosional topography defined by strong horizons. The surface of deformed sections can be cleanly cut on a horizontal plane to produce a “model geologic map,” allowing students to associate outcrop pattern with sub-surface structure in the context of the deformation process and pre-erosion architecture. Comparison of model results to topographically-expressed outcrop patterns visible in Google Earth or Google Maps encourages students to connect structure with process and tectonic setting, enhancing their ability to visualize and interpret deformational and erosional history. Students may be further engaged by filming and digitally editing experiments with the goal of presenting results in the format of an annotated video.