Which process primarily causes the formation of alluvial fans at the base of mountain ranges within arid climates?

💡 Explanation

When a stream exits a confined mountain channel onto a plain, a sudden decrease in gradient occurs, because kinetic energy decreases and the stream loses its capacity to carry sediment, leading to rapid deposition and formation of an alluvial fan. Therefore rapid gradient changes cause alluvial deposition, rather than ice age deposition, localized tectonic activity or wave action.

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