alluvial fan Fan-shaped area of alluvium (water-borne sediment) deposited by a river when the stream reaches a plain on lower ground, and the water velocity is abruptly reduced. Organic matter is also transported, making the soil highly fertile. Valuable minerals such as cassiterite (tin ore, SnO₂), diamonds, gold, and platinum are often found in alluvial fans.

alluvial fan(alluvial cone) A mass of sediment deposited at some point along a stream course at which there is a sharp decrease in gradient (e.g. between a mountain range and a plain). Essentially, a fan is the terrestrial equivalent of a river-delta formation.

alluvial fan (alluvial cone) Mass of sediment deposited at some point along a stream course at which there is a sharp decrease in gradient, e.g. between a mountain range and a plain. Essentially, a fan is the terrestrial equivalent of a river-delta formation.

alluvial fan A mass of sediment deposited at some point at which there is a sharp decrease in gradient, e.g. between a mountain range and a plain. Essentially, a fan is the land-bound equivalent of a river-delta formation.