An­cient tsunami mapped

Central Leader - - YOUR PAPER, YOUR PLACE - JOHN EDENS

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.

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