Ancient tsunami mapped

Ancient tsunami have been mapped in a new interactive project.

The New Zealand Palaeotsunami Database was compiled from old records by the National Institute of Water and Atmospheric Research.

The free, searchable map, shows the range of tsunami recorded around the coastline and offshore islands since prehistoric times, including events in which waves inundated inland to an elevation of 30 or more metres.

A ‘palaeotsunami’ is defined as one occurring before written records and dated using geological and anthropological evidence.

Project leader and Niwa scientist Darren King said the aim of the database was to increase awareness of New Zealand’s tsunami hazard and help in the analysis of palaeotsunami.

There was strong evidence New Zealand’s largest tsunami occurred between 1450 and 1480 at Henderson Bay in Northland, where deposits reached 32 metres above sea level and inundated inland for 1000m.

The team used geological evidence and, in some cases, anthropological evidence from Maori oral traditions, to estimate minimum distances tsunami travelled inland and the elevation - where deposits were recorded at their highest point above sea level.

King said the information used to build the database was hard to access.

‘‘If you are assessing tsunami risk, it is helpful to know the history of past events in your area.

‘‘This is an easy way to look at multiple records to understand risk profiles based on the available evidence.’’

The records show tsunami have occurred along most of the coastline but concentrated along the east and west coasts of the upper North Island.

‘‘There’s a general rule of thumb in that for deposits to be preserved you need a physical environment to preserve and you need waves capable of transporting material, something like five metres [in height].’’

Records were in spreadsheets, or held in previously unpublished reports, logs, and historical documents with research stretching back a couple of decades, King said.