Crossing Thresholds – Human Responses to Tsunami Forcing in the Pacific

Abstract:

The 11 March 2011 Tohoku-oki tsunami caused widespread devastation to coastal communities in Japan. This event however was merely the latest in a long line of similar occurrences throughout the Pacific over time. All the recent large tsunamis have had their predecessors, and a growing database of palaeotsunamis in the Pacific suggests that several past events have been either similar in magnitude or greater than their historical counterparts. Not only are we gathering data concerning Pacific palaeotsunamis but we are also identifying contemporaneous punctuated histories of changing human settlement patterns across the Pacific. In particular, the almost two millennia ‘long pause’ in eastward Polynesian migration and the abandonment of long distance sea-voyaging in the 15th century. It is suggested that large palaeotsunamis and their generating mechanisms forced major societal responses.

Given the unquestioned impacts of recent tsunamis on human societies, it is reasonable to suggest that past societal responses can be used as proxies for contemporaneous environmental forcing in those parts of the world where independent evidence of the effects of these events is still being gathered. In the Pacific there are a range of responses that extend well beyond the abandonment of long distance sea-voyaging such as the outbreak of region-wide conflict and the associated abandonment of settlements in exposed (coastal) locations. The contemporaneity of these effects across a vast region requires a driver that is external to particular island groups. Given that this must have impacted coastal resources severely and enduringly, the only possibility is that this driver was of oceanic origin. This hypothesis is compelling when considered alongside the growing database of more conventional lines of evidence. The question therefore is how well are similar threshold responses recognised throughout the World? Are there similar region-wide responses that have been pigeonholed under the more prosaic interpretations of archaeological dogma?