Which mechanism initiates alluvial fan formation when a mountain stream reaches a broad valley?

💡 Explanation

When a mountain stream reaches a broad valley, a decrease in slope reduces stream velocity and thus sediment transport capacity, leading to deposition because the reduced flow force can no longer carry the sediment load picked up in steeper channel Therefore sedimentation creates an alluvial fan, rather than erosion, incision that are functions on increased transport energy.

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