 Upon exiting the steeper mountain canyon, as the stream gradient is reduced, the debris flow spreads laterally and begins to deposit larger particles on the alluvial fan.Where the stream channel is plugged with debris, lateral channel migration occurs, building upon the existing alluvial fan deposits.Deposition also occurs down-stream of the alluvial fan, where stream gradient decreases, on the floodplain, alluvial plain, coastal plain and river delta.