Abstract
Recent research has revealed much geomorphological evidence for major tsunamis on the southeastern coast of Australia prior to British settlement in 1788. This discovery is important because this tectonically very stable coast was believed to be safe from the hazard of tsunamis because no major tsunami has occurred here in the last 200 years. But high level marine deposits of Holocene age along the coast south of Sydney show that tsunamis ran up to heights of >30 m, and at one site to heights probably >100 m. Developing a chronology for these catastrophic events is of great importance to the study of coastal geomorphology and to coastal hazard planning. Here we outline a chronology based on 22 C14 ages and 23 TL (thermo¬luminescence) ages from sites along 400 km of coast. The grouping of these dates indicates that at least 5, and probably 6 major tsunamis struck this coast during the Holocene. These events occurred at about 250, 500-800, 1,600-1,900, 3,000, 6,500 and 8,700-9,000 years ago. The frequency of these events was about 1 in 1,300 years over the whole Holocene, but increased to about 1 in 600 years during the last 3,000 years. This is the same frequency as the tectonically active Ryukyu Islands. Fre¬quent tsunamis can be a major hazard on coasts far from tectonically mobile areas. C14 ages on shells associated with the deposits, and TL ages of sand exposed to solar radiation, provide the most reliable guides to the timing of tsunami impact. We also demonstrate that sand transported rapidly onshore by tsunamis during the Holocene can retain a Pleistocene TL signal. TL analysis thus provides an important new tool for the identification of ancient tsunami deposits.
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Publication Details
This article was originally published as Young, RW et al, Chronology of Holocene Tsunamis on the Southeastern Coast of Australia, Transactions of the Japanese Geomorphological Union, 18, 1997, 1-19.