Chapter 21 - Post-depositional changes to tsunami deposits and their preservation potential

Abstract

Tsunami and paleotsunami deposits are critical to improving tsunami hazard assessments. However, their preservation potential must be assessed to avoid underestimation of the hazard. The deposits' preservation potential is limited mainly by sediment supply, available accommodation space and post-depositional (early diagenetic, taphonomic) alterations. This paper presents a review of published studies on post-depositional changes and new examples from coastal plains in various climatic zones: Thailand (2004 Indian Ocean Tsunami), Japan (2011 Tōhokui Tsunami), and Greenland (landslide-generated 2000 Paatuut Tsunami). The local conditions play an important role, and usually at least several-cm-thick tsunami deposits are preserved if accommodation space is available. Moreover, the deposits' sedimentary structures and chemical compositions may be significantly altered (e.g., dissolution of microfossils, sediment mixing, leaching of salts, soil formation). Some of the post-depositional processes may produce new features, which may be used as indicatory (e.g., mud cracks). Human activities often lead to loss of sedimentary records of past tsunamis.