NEW EVIDENCE FOR PALEOTSUNAMIS ALONG HECATE STRAIT, BRITISH COLUMBIA, CANADA

Virtually all of the geological evidence for historic and prehistoric tsunamis in British Columbia has been recovered from the west side of Vancouver Island during a field campaign that ended some two decades ago. In 2014, a new multi-national paleotsunami initiative was launched in British Columbia to extend the temporal and geographical record as well as enhance the resolution of the geological evidence on Vancouver Island and many smaller islands stretching through Hecate Strait as far north as Prince Rupert. Ship support by the Canadian Coast Guard provided the opportunity to access a number of remote inlets and bays in this unique region of the province. The field effort to the north focussed mainly on the seaward facing coast line of several islands and the mainland that could have been subjected to local, regional and trans-Pacific tsunamis (earthquake or landslide generated). This region is characteristically rocky in nature, provides few situations for sediment accretion and preservation, and is regularly subjected to extreme weather and sea conditions. Peat deposits and soils are generally rare, and if present, are normally thin and lack sufficient materials to reflect appreciable time. Fortunately, shovel excavations at over two dozen widely spaced localities yielded strong evidence for past tsunami inundation. Sites with evidence of past tsunamis ranged from those with a single past event to those preserving several events. Field descriptions and organic samples for C14 and Pb dating were supplemented with multiple core samples at each site. Cores up to 1 m in length were collected for laboratory studies: imagery, gamma ray absorption, magnetic susceptibility, P-Wave velocity, X-Ray fluorescence, colour photospectrometry, as well as foram and diatom analysis. The results of this work are important in managing risk associated with future tsunamis as new critical infrastructure facilities are developed and old facilities are replaced along Canada’s west coast.