Thermal imaging of sedimentary features on alluvial fans

Aerial thermal imaging is used to study grain-size distributions and induration on a wide variety of alluvial fans in the desert southwest of the United States. High-resolution aerial thermal images reveal evidence of sedimentary processes that rework and build alluvial fans, as preserved in the grain-size distributions and surface induration those processes leave behind. A catalog of constituent sedimentary features that can be identified using aerial thermal and visible imaging is provided. These features include clast-rich and clast-poor debris flows, incised channel deposits, headward-eroding gullies, sheetflood, lag surfaces, active/inactive lobes, distal sand-skirts and basin-related salt pans. Ground-based field observations of surface grain-size distributions, as well as morphologic, cross-cutting and topographic relationships were used to confirm the identifications of these feature types in remotely acquired thermal and visible images. Thermal images can also reveal trends in grain sizes between neighboring alluvial fans on a regional scale. Although inferences can be made using thermal images alone, the results from this study demonstrate that a more thorough geological interpretation of sedimentary features on an alluvial fan can be made using a combination of thermal and visible images. The results of this study have potential applications for Mars, where orbital thermal imaging might be used as a tool for evaluating constituent sedimentary processes on proposed alluvial fans.