Catastrophic wave (tsunami?) transport of boulders in southern New South Wales, Australia

Abstract

Deposits of large boulders above modern limits of storm waves along the coast of southern New South Wales record catastrophic wave action. The largest boulders that were moved weigh 80-90 tonnes, and the maximum height of wave action was 32 m. Hydraulic reconstruction indicates flow depths of 3.4 and perhaps > 4 m and velocities of 5.5 m/s to 10.3 m/s. Cavitation features on some rock surfaces support the estimates of maximum velocities. A remarkably limited range in the orientation of imbricated boulders along 150 km indicates that the deposits record a single event that approached from the SE. to SSE. The fabric and size of the deposits point to a tsunami wave train rather than to exceptional storm waves. The most probable source of the wave train is the Macquarie Ridge in the south Tasman Sea. An earliest Holocene age for the event is indicated by a thermoluminescence determination of 9.5ka from sand associated with one boulder deposit, and by the transport of some boulders from below present sea level.