TSUNAMI AS A MAJOR CONTROL ON COASTAL EVOLUTION, SOUTHEASTERN AUSTRALIA

General concepts of coastal evolution of the southeastern Australian c oastline during the Late Pleistocene involve barrier formation by wind and swell waves during marine transgressions and formation of rock pl atforms by chemical and mechanical weathering at rates of 1-5 mm yr(-1 ). Where evidence indicates rapid change, storms are often invoked as the causative mechanism. These concepts ignore the important role of a repetitive, rapid, catastrophic tsunami in both coastal erosion and a ccretion. The impact of a tsunami can be distinguished by four signatu res: uncemented elastic deposits; boulders that are imbricated, stacke d and uniformly aligned; constructional features; and erosional bedroc k sculpturing. The boulder deposits occur at elevations above both the measured and theorised limits of storm-wave action. Bedrock sculpturi ng has not been attributed previously to marine processes but rather t o catastrophic water flow from icesheets or ice-damned lakes, a phenom enon which has never influenced the mainland coast of Australia during the Pleistocene. Thermoluminescence dating has shown that tsunamis in southeastern Australia, while eroding most Last Interglacial and inte rstadial barriers, have also contributed to the construction of many p resent barriers. They have also shaped the rocky coast by modifying ra ised platforms and in extreme cases ripping enormous slabs of bedrock from promontories and cliff faces up to heights of 40-50 m. A change i n emphasis in the cut-rent thinking regarding the processes responsibl e for coastal evolution is needed in coastal geomorphology to include the impact of repetitive tsunamis which are capable of dramatically an d irrevocably modifying a landscape over very short periods of time.