Large‐Scale Submarine Sediment Waves at Macauley Caldera Volcano: In Situ Evidence of High‐Flux, Syn‐Eruptive Submarine Transport

Two sediment cores were collected from a submarine sediment wave field on the flank of Macauley volcano. Combined with seismic reflection surveys and numerical modeling, we present an integrated model of the formation of large‐scale, eruption‐fed, submarine sediment waves. The sediment waves are large (>100 m high, 1.5 km wide, tens of km long) and composed of juvenile ash and pumice lapilli of rhyolitic to dacitic composition. The sediment waves are interpreted to be related to the 6.3 ka caldera‐forming eruption and Sandy Bay Tephra deposit on nearby Macauley Island. The sediment waves were deposited as cyclic steps and antidunes under supercritical, syn‐eruptive density currents. Facies analysis indicates that the bedforms developed as amalgamated sets of m‐sized bedforms. Numerical modeling and seismic reflection data show that early‐stage density currents were rapid and erosive, whereas later currents persisted over days to weeks. Our data from Macauley volcano is compared to the submarine sediment waves from the 2022 eruption of Hunga volcano, and other known eruption‐fed sediment waves. We discuss implications for the modeling of volcanic eruptions from their submarine deposits, as bedforms associated with supercritical density flows may be confused with volcanic turbidites that have critically different deposition and distribution patterns. Further, the self‐erosive nature of supercritical density currents produces deposits composed of volcanic, syn‐eruptive material that has been continuously mixed through deposition and may obscure any stratigraphic trends associated with eruption dynamics. We discuss the implications for tsunami prediction and modeling associated with the unpredictable nature of these events.