The holocene paleo-tsunami history of Western Australia

West Australian coastlines experienced several tsunamis in mid-Holocene times. To expand our knowledge about Holocene tsunami events in West Australia, the authors extended the previously studied spatial scale to include the central- and south-western coastlines. Several of the discovered events were mid- and young Holocene (≤ 1000 yr BP) tsunami impacts on the outer coast of the Cape Range Peninsula. Five hundred kilometres to the south between Cape Cuvier and Point Quobba, additional tsunami evidence exists on top of steep cliffs over a coastal stretch of 30 km. The sedimentary signature of two tsunamis is documented in this area by wide ridges comprised of sand, shell, and clasts (including coral fragments) at heights of 12–30 m asl and 300–500 m inland. Enigmatic boulders (20–100 tons) appear as cliff-top megaclasts up to 100 m inland. Here, radiocarbon dating revealed a minimum of two tsunami events: at 5700 yr BP with waves depositing sandy ridges far inland and at approximately 1000 yr BP with waves depositing boulders originating from the marine environment. As the first dates are congruent with previously published results for the Learmonth region 500 km to the north, we assume that the same mid-Holocene tsunami hits this long coastal section as well. The southwestern coast of West Australia from Cape Naturaliste to Albany also shows signs of impacts by extreme waves. Here, huge granite boulders (80–400 tons) were dislocated and transported to heights up to 10 m above sea level. The most prominent dislocated boulders were positioned at Merchant Rock (Cape Naturaliste National Park), at Islet near Nanarup, and in Cave Bay close to Albany.