What is "megafan"

n. 1 (context geology English) (rfdef: English) 2 (context informal English) An obsessively enthusiastic fan.

An alluvial megafan is a large cone or fan-shaped deposit built up by complex deposition patterns of stream flows originating from a single source point known as an apex. Megafans differ from Alluvial fans in their sheer size. Due to their larger size, they may be formed by different geomorphic processes. The criterion of what differentiates megafans from typical alluvial fans is an artificial one of scale. The scale divide varies in the literature, with the most common being a 100-km apex-to-toe length. Alternative values as little of 30-km apex-to-toe length have been proposed, as well as alternative metrics like coverage areas of greater than 10,000 square-km.