An alluvial fan is a fan-shaped deposit of sediment that forms where a stream or river, carrying significant sediment load and high kinetic energy, rapidly exits a confined channel and enters a flatter plain. Due to the sudden decrease in gradient, the stream loses energy rapidly, causing the abrasive sediment—which can vary from coarse gravel to fine silt—to drop out and accumulate. These deposited materials spread outward radially from the point of exit, forming a gently sloping, wedge-like structure whose boundary is determined by the angle of repose of the accumulated material. Alluvial fans are significant geomorphological features that profoundly influence local hydrology and are common in arid or semi-arid terrains.