Investigating historic tsunami is currently engaging geologists and geographers trying to bridge the gap between older geological events and more recent tsunami recorded instrumentally. This research is essential if a proper understanding of the magnitude and frequency of tsunami impact on the global coastline is to be gained. Therefore, all attempts to unravel tsunami activity worldwide throughout the historic period, however locally defined, should be welcomed.
Problems arise, however, in the location, recognition and interpretation of often-scattered references to such events within historic documents, oral history, myths and legends, many of which fall outside of conventionally accepted data sources usually employed by earth scientists. However, this serious task is slowly being acknowledged with, for example, the recent Geological Society of London Special Publication Myths and Geology, and a Journal of Geology article citing 17th century books as evidence, alongside physical signatures, for a possible tsunami in southwest Britain in AD 1607.
Atwater et al. present an important addition to this emerging field, linking written accounts from an historic civilisation on one side of the Pacific with physical evidence from a prehistoric contemporary event over 7500 km away! The book is lively and informative, clearly aiming to attract a wide audience with numerous colour figures, photographs, and boxed panels, busily crammed into the available pages (even the index includes photographs). It is organised in three parts, with each double-page spread addressing a different heading making it easy to dip in and out of the book, which wouldn't be out of place on a coffee table.
In Part 1, physical evidence from the Cascadia region of northwest America is compiled, suggesting that an earthquake, probably around magnitude 9, struck sometime (based on dendrochronology) between August 1699 and May 1700. Co-seismic subsidence, tsunami signatures, and native American stories, are cited to support a convincing, and now relatively well-known, hypothesis for the region. In Part 2, however, various Japanese documents are examined that describe a tsunami occurring on 28th January 1700. It is termed an ‘orphan’ tsunami because it came ashore without a familiar precursor earthquake being felt by the inhabitants, so taking them by surprise and, as a consequence, many lives were lost.
These Parts are examples of thorough geological and historical research with the only question arising because the coastal flooding in Japan was not accompanied by an earthquake (a relationship that some use to discount tsunami interpretations of local coastal floods elsewhere – there are no dated flooding accounts elsewhere in the Pacific at this time) and that a storm arrived in Japan 12 hours later, making it difficult to exclude the possibility of a meteorological cause. Part 3, however, attempts to knit these together, presenting a convincing argument that the American and Japanese evidence represent the same event: a high magnitude Cascadia subduction zone earthquake that spawned a pan-oceanic tsunami. Accepting this relationship, the authors then consider the likelihood and impact of a similar event in the future.
This book is another example demonstrating that however unusual sources may first appear, and the inevitable speculative interpretation that derives from them, we should not be deterred from interrogating them and considering the questions that they raise. Ignoring them may be costly in the long term.
