Tsunami versus storms: Diagnostic sedimentary criteria in coastal lakes, lagoons and sinkhole deposits

Sedimentary deposits of coastal flooding by tsunamis and storms extend archives of these events across millennia. However, the utility of these records remains clouded by an inability to unequivocally differentiate between a deposit of storm or tsunami origin. This review takes a novel approach by compiling a large integrated dataset of modern and palaeo tsunami and storm deposits in coastal lakes and lagoons to infer the processes that occur during these events. We find that storm and tsunami deposits each comprise three differing groups. Using these groups, we infer the processes involved in tsunamis, including the formation of a sediment gravity flow as the tsunami flows into the lake; the progression of a dense, cohesionless flow head, or the displacement of the shallow lake water by the tsunami wave. In contrast, storm deposits are inferred to be formed by bedload under an overwash regime or in a dilute flow under full inundation of the coastal lake or lagoon. From these processes, we show that the composition of tsunami deposits is dependent on the environmental setting of the lake or lagoon whereas, for storms, the event size is a greater factor. Our findings show that in most cases, storm events are inherently unable to generate the tsunami deposits found in coastal lakes and lagoons. This insight enables the establishment of recognition criteria and a framework that can be applied to candidate deposits to differentiate unequivocally between the two event types. Nonetheless, for some deposits, a differentiation on sedimentology alone is impossible.