Ancient palaeotsunami mapped all the way back to the prehistoric era
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.
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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.
Three tsunami hit the Mataora-Wairau lagoon in Marlborough in the last 2000 years.
Elevation is not the same as wave height. 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].
"They are minimum estimates," he said.
King said a lack of evidence of tsunami did not rule out waves having hit those parts.
"The east coast of the country - that's where the majority of deposits have been found to date."
Records were in spreadsheets, or held in previously unpublished reports, logs, and historical documents.
The research underpinning the work stretched back a couple of decades, King said.
"The information was difficult to look at, there was limited access to it and so few people were using it.
"We think this database has a broad audience including environmental managers, civil defence staff, researchers and the wider public who now have an easy way to look at multiple records, explore the data and look at what has happened in the past."
The interactive features filters for location, timing, and the strength of the historical record. It was based on the work of Professor James Goff, a former Niwa scientist who now works at the University of New South Wales.
The age and type of some of the records means the scientific validity was colour-coded from "excellent" to "moderate" to "poor".
Records include information on the distance of inundation inland, the source of the record, maximum water height, damage, the strength of the evidence, and the date range.
The project team plan to revise the interactive as new research is compiled.
They received funding from the Ministry of Civil Defence and worked with Environment Canterbury, eCoast Marine Consulting and Research and Dumpark data visualisation.