Chapter 20 - Introduction to a Tsunami‐Deposits Database

Abstract

Abstract The nature, distribution and recurrence rate of tsunamis remain rather poorly documented. To better understand the impact of tsunamis on coastal zones around the world, studies are needed to identify geological records of sedimentary event horizons generated by tsunamis and to radiometrically date the events to establish recurrence rates on a regional or even on a local level. To achieve a better understanding of the nature of tsunami deposits, we have initiated a Tsunami-Deposits Database, which currently consists of lithological characteristics of 278 tsunami-deposit publications (of roughly 1000 identified sources). The data compilation shows an uneven distribution of publications with only 13% describing historic tsunamis and the remainder describing palaeotsunami events. The most common type of tsunami deposit is a sand sheet. Common observations include the following: • beach sediments are transported inland leaving a sand sheet in wetlands and other coastal settings; • sands have been carried inland, and buried grasses and other vegetation: the bent vegetation can be used to document the current direction; • drain-back deposits frequently contain sand and mud (particularly mud rip-up clasts) transported from land to the sea and carrying charcoal and organic debris; • tsunami waves can overtop or ‘blow-out’ coastal sand dunes and leave a catastrophic inundation record within marshes; • a ‘tsunami stratigraphy’ (of lithological couplets) remains and is associated with inundation and drain-back; • tsunami run-ups leave one or more sand sheets, reflecting multiple waves; • the deposits left onshore often contain marine shells/fossils transported into a non-marine setting; • tsunami deposits are ephemeral in nature and are easily removed by the subsequent erosion by normal coastal processes and modification of the environment by humans.