Expanding the proxy toolkit to help identify past events — Lessons from the 2004 Indian Ocean Tsunami and the 2009 South Pacific Tsunami

Some of the proxies used to identify palaeotsunamis are reviewed in light of new findings following the 2004 Indian Ocean Tsunami and the 2009 South Pacific Tsunami, and a revised toolkit provided. The new application of anisotropy of magnetic susceptibility (AMS) to the study of tsunami deposits and its usefulness to determine the hydrodynamic conditions during the emplacement of tsunami sequences, together with data from grain size analysis, are presented. The value of chemical proxies as indicators of saltwater inundation, associated marine shell and/or coral, high-energy depositional environment, and possible contamination, is demonstrated and issues of preservation addressed. We also provide new findings from detailed studies of heavy minerals. New information gathered during the UNESCO — International Oceanographic Commission (IOC) International Tsunami Survey of fine onshore sediments following the 2009 South Pacific Tsunami is presented, and includes grain size, chemical, diatom and foraminifera data. The tsunami deposit varied, ranging from fining-upward sand layers to thin sand layers overlain by a thick layer of organic debris and/or a mud cap. Grain size characteristics, chemical data and microfossil assemblages provide evidence for marine inundation from near shore, and changes in flow dynamics during the tsunami.