Origin of spectacular fields of submarine sediment waves around volcanic islands
Understanding how large eruptions and landslides are recorded by seafloor morphology and deposits on volcanic island flanks is important for reconstruction of volcanic island history and geohazard assessment. Spectacular fields of bedforms have been recognised recently on submerged flanks of volcanic islands at multiple locations worldwide. These fields of bedforms can extend over 50 km, and individual bedforms can be 3 km in length and 150 m in height. The origin of these bedform fields, however, is poorly understood. Here, we show that bedforms result from eruption-fed supercritical density flows (turbidity currents) in some locations, but most likely rotational landslides at other locations. General criteria are provided for distinguishing between submarine bedforms formed by eruptions and landslides, and emphasise a need for high resolution seismic datasets to prevent ambiguity. Bedforms associated with rotational landslides have a narrower source, with a distinct headscarp, they are more laterally confined, and internal bedform structure does not suggest upslope migration of each bedform. Eruption-fed density currents produce wide fields of bedforms, which extend radially from the caldera. Internal layers imaged by detailed seismic data show that these bedforms migrated up-slope, indicating that the flows that produced them were Froude supercritical. Due to the low density contrast between interstitial fluid and sediment, the extent and dimensions of submarine eruption-fed bedforms is much greater than those produced by pyroclastic density currents on land.