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.

• Which risk increases when deforestation significantly reduces levees' vegetation cover?
• Which risk increases when surface salt accumulation blankets desert soils?
• Which process dominates sediment sorting in a proglacial lake experiencing increased meltwater discharge?
• Which mechanism explains localized crustal uplift preceding major earthquakes near subduction zones?
• Which continental effect drives increased aridity downwind of mountain ranges?
• Which shifts in marine trophic structure emerge following the onset of an El Niño event?