An alluvial fan is a triangular or fan-shaped deposit of gravel, sand, and smaller materials, created where a fast-flowing stream flattens out. Typically found at the base of mountain ranges, alluvial fans form when a stream’s gradient decreases, leading to sediment deposition. They are common in arid and semi-arid regions and are significant in interpreting past climatic and geological conditions, as well as in groundwater studies due to their porous nature.
Source Blair, T. C., & McPherson, J. G. (1994). “Alluvial Fans and Their Natural Distinction from Rivers Based on Morphology, Hydraulic Processes, Sedimentary Processes, and Facies Assemblages.” Journal of Sedimentary Research, 64(3), 450-489.