Submarine landslides offshore Yamba, NSW, Australia: an analysis of their timing, downslope motion and possible causes

Radiocarbon isotopic ages and sedimentological data are presented for material recovered from three adjacent translational submarine landslides (YS1, YS2 and YS3) identified on the upper-continental slope offshore Yamba, New South Wales, Australia. The age data indicate that these three co-located upper-slope slides probably occurred independently of each other and not in a single, widespread regional-scale failure event. Numerical estimates of the likely runout distances for slide blocks corresponding to the entire landslide scar volumes range between 10 and 27 km, and represent a ‘runout zone’ in which landslide blocks or debris might reasonably be expected to be located. There is no morphological evidence for large blocks or debris fields derived from two of the Yamba landslide scars within their identified runout zones (YS1 and YS2), suggesting these two failures involved complete disintegration of large slide blocks after failure or the removal of sediment from the landslide sites as grainflows or turbidites. In contrast, the third runout zone (YS3) presents good evidence of at least 12 slide blocks between 100 and 200 m in diameter, suggesting that they were shed as relatively small individual blocks or they were generated due to the dismemberment of a larger slab.