Morphometric differences between megafans and alluvial fans

Authors: M. Anwar Sounny-Slitine*, University of Florida, Edgardo M Latrubesse, The University of Texas at Austin
Topics: Geomorphology, Physical Geography, Geographic Information Science and Systems
Keywords: Megafans, Megageomorphology, Morphometrics
Session Type: Paper
Day: 4/11/2018
Start / End Time: 1:20 PM / 3:00 PM
Room: Balcony N, Marriott, River Tower Elevators, 4th Floor

Size matters in geomorphology and this is very apparent with the morphometric differences between megafans and alluvial fans. Megafans are often defined as being very large alluvial fans of radial lengths greater than 100-km, but we demonstrate through morphometrics that size is just one of many differences between the fans. Megafans are not just alluvial fans at a larger scale. While the smaller alluvial fan has received much attention in the literature, the much larger megafan still have many unanswered geomorphic questions. Our understanding of alluvial fans does not scale up, since megafans exhibit different behaviors from alluvial fans. In this study, we highlight these differences through morphometrics. We have cataloged a large global sample of megafans and alluvial fans into a geodatabase. From this sampling, we have delineated the sizes and extent of basins both upstream and downstream from the apex of the fans. Finally, through remote sensing and elevation modeling, we populated the geodatabase with morphometric measurements, qualitative descriptions, and basin parameters. Metrics include planform area, catchment area, gradient, relief indices, drainage density, and others. From this database, we have tested the relationships between morphometrics at various scales. For example, the ratio between catchment and fan size area. Morphometric approaches have given much insight into the processes driving alluvial fan formation, but many of these approaches have not included large megafans. We explore alternative morphometrics in order to provide an intrinsic approach to differentiating megafans from alluvial fans.

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