Pacific Subduction zone palaeotsunamis – joining up the dots?

Abstract

In 2011 we pointed out that the study of palaeotsunamis in the Pacific was in its infancy. This is still the case, but it is hardly surprising given that there are 1,000 kms of circum-Pacific coastline that are largely unstudied and even several countries where palaeotsunami research is yet to be carried out. Within the Pacific Basin there are some 20,000 Pacific Islands, all of which have the potential to add to our understanding of the magnitude, frequency and source of past tsunamis. This is a huge jigsaw puzzle and in reality we have only got a few of the pieces, but even so a combination of Pacific Island and circum-Pacific country data is starting to provide clues about past events. We discuss some of our findings from the SW Pacific region with respect to palaeotsunamis generated by subduction zone events and look at not only the geological evidence, but also a wider multi-proxy toolkit that includes both archaeology and anthropology. In other words, we may argue about the dating or geological validity of a specific event on a specific island, but the bigger story being told of widespread, contemporaneous societal change provides an additional line of evidence that we ignore at our peril. This is all well and good, but what about the rest of the Pacific? Where to from here?

It has long been recognised that the Hawaiian Islands are exposed to tsunamis from almost every large subduction zone in the Pacific - Alaska (1946), Kamchatka (1952), Chile (1960) and Japan (2011) to name but a few. Furthermore, it has also been shown that the geological evidence for such events can be found in the islands. Recently, some researchers have suggested that the well-known Makauwahi Cave deposit on Kauai is the “missing link” of evidence for a giant Aleutian subduction zone event in the 16th/17th century. In the absence of more physical evidence this may be drawing something of a long bow, BUT the key take home message here is that different events from different sources affect different coasts of different Hawaiian Islands differently. Historical events alone indicate that the islands can act like a giant tsunami “rose diagram“, so why are we not looking harder at these islands and others within the Pacific to vastly improve our understanding of palaeotsunamis in the Pacific? For example, what about the now famous 1700 AD Cascadia and 869 AD Jogan events? © 2014 The Geological Society of America (GSA).