AbstractAlluvial fans form through primary and secondary geomorphic processes. Primary processes comprise major geomorphic events that build the fan by transporting sediment from the watershed to the fan; these events occur at decadal time scales. Secondary processes include the smaller flood events which recruit little sediment from the watershed but can re‐mobilize and rework sediment already delivered to the fan. The experiments described herein study the effects of secondary processes on alluvial fan morphology and channel behavior. We conducted four experiments, in which alluvial fans were built by alternating between primary events, with high flows and high sediment supply, and secondary events, with moderate flows and no sediment supply. In our experiments, primary events are best described as debris floods and secondary events correspond to smaller floods with much lower sediment concentrations. The duration of the secondary events varied between experiments, but the number and duration of the primary events was held constant keeping the total volume of sediment delivered to the fan the same. We monitored fan gradient, area, channel patterns and avulsions. Experiments with longer secondary events generated larger fans with gentler gradients. In addition, longer secondary events led to increased flow channelization and centralization between primary events. These morphologic changes resulted in fewer avulsions during primary events, which occurred later during the event. These results indicate that changes to the relative duration of primary and secondary events caused by climate change can affect fan morphology, wet fraction, and avulsion frequency, with implications for potential flood hazard.