Diversity of recent tsunami impact, sedimentary record, and hazards from local to distal environments.

Abstract:

One of the goals of paleotsunami research is to define the frequency and magnitude of past tsunamis in order to better understand the hazards posed to coastal communities and ecosystems. Field observations and mapping in the aftermath of several recent tsunamis has greatly improved our understanding of the diversity of tsunami impacts in different environments, the variability observed in the sedimentary record of tsunamis, and the change in these characteristics along the tsunami path from the near- to far-field.

Recent tsunamis originating in the Indian Ocean (2004), South Pacific (2009), Chile (2010), and Japan (2011) have affected both local and distant coastlines across a wide range of coastal environments and morphologies. Coral reefs, beaches, dunes, coastal plains with wetlands and/or beach ridge complexes, and rocky embayed coasts have been examined for depositional patterns and evidence of erosion, landscape and vegetation change, and, at a number of sites, impacts to the built environment. We summarize deposit variability, including thickness, stratification, and composition, in an effort to document the wide range of observed deposit features. We observed evidence where vegetation can modify the tsunami flow characteristics. Our field efforts did not focus on impacts to coastal structures, but observations during the course of our work can be applied to improve hazard assessment and recognition of vulnerable areas.

Tsunami magnitude, deposits, and hazards are most pronounced near the source and tend to decline with distance, although local factors can modify this trend significantly. For example, general trends in the decrease of tsunami height, inundation, and run-up with distance from the source often exhibit local anomalies where interactions between the tsunami characteristics and local physiography, such as slope and orientation of the coast, create complex interactions that may greatly modify general trends. Efforts to relate the sedimentary record to complexities in tsunami inundation will improve our understanding of past events, which may ultimately lead to better hazard assessments.