Submarine landslides along the flanks of Christmas Island, Indian Ocean

Abstract A variety of geological processes shape and modify the morphology of volcanic islands over a range of temporal timeframes. Amongst the most conspicuous are aerial and submarine landslides that are frequently observed in both island arc and intra-plate volcanic settings. Identifying and understanding the triggering mechanisms of these landslides is crucial to geohazard mitigation as they pose major threats to coastal communities as well as critical onshore and submarine infrastructure. Christmas Island, located in the northeast Indian Ocean rises steeply, more than 5000 m, from the surrounding ocean floor. In this study, we compile a seamless bathymetric surface from a number of sources and systematically describe four large-scale submarine landslides for the first time, with a combined areal coverage of 1711 km 2 , and numerous smaller mass-movements covering 339 km 2 . Based on their geomorphic characteristics observed from the high-resolution bathymetry data, two of the identified landslides can be classified as volcanic debris avalanches and the remainder as slumps. The distribution of landslides and planform orientation of the remnant headlands suggest the presence of volcanic rift zones that may have controlled the location of large landslides and the present-day shape of the island. In addition, we postulate that many of the major landslides formed prior to the emergence of the island as evidenced by relatively undisturbed onshore terraces interpreted as paleo-shorelines. Whilst the smaller slumps are likely triggered by subsequent volcanic eruptions and seismic activity associated with subduction at the adjacent Sunda Trench.