Warn­ing signs talks planned but a tsunami un­likely on Lake Tekapo

The Timaru Herald - - FRONT PAGE - MARK QUINLIVAN AND MATTHEW LITTLEWOOD

Sci­en­tists have con­cluded that there is a small chance an earth­quake could cre­ate a tsunami on lakes in the Macken­zie Basin.

Fur­ther tsunami re­search mod­el­ling has been car­ried out by Na­tional In­sti­tute of Wa­ter and At­mo­spheric Re­search (Niwa) sci­en­tists on the Tekapo lake bed.

The re­search was dis­cussed at a re­cent Tekapo Com­mu­nity Board (TCB) meet­ing.

En­vi­ron­ment Can­ter­bury (ECan) has a role in as­sess­ing nat­u­ral haz­ards in the re­gion, which as­sists coun­cils with civil de­fence and land use plan­ning func­tions.

The TCB said ECan had pre­vi­ously com­mis­sioned back­ground work from GNS Science in 2015 to look at whether there was any po­ten­tial for tsunami on the Macken­zie Basin lakes.

Fol­low­ing on from that, fur­ther work has been un­der­taken by Niwa study­ing the bed of Lake Tekapo, the TCB agenda states.

Sci­en­tists mapped the Tekapo lake bed and stud­ied its sed­i­ments, to de­ter­mine whether un­der­wa­ter land­slides have hap­pened in the past, and are us­ing this in­for­ma­tion to de­ter­mine whether tsunamis could be cre­ated

Ac­cord­ing to Niwa’s re­port, the like­li­hood of a tsunami at Lake Tekapo was still rare.

ECan sci­en­tist He­len Jack said the Niwa re­port was more com­pre­hen­sive than the 2015 re­port, which was more of a ‘‘desk­top’’ assess­ment.

‘‘There have been no recorded tsunamis in the last 200 years or so.

‘‘It’s a pretty un­likely event. How­ever, Niwa’s re­search shows it could reach as high as 5m on the lakeshore,’’ Jack said.

‘‘So it’s ob­vi­ously a po­ten­tial dan­ger.’’

Lake Tekapo was cho­sen over other lakes, such as Wakatipu, Wanaka, and Taupo, the re­port says.

Tekapo was cho­sen be­cause it is a good size and depth to eas­ily sur­vey, and be­cause there is pop­u­la­tion and in­fra­struc­ture at risk, the re­port says.

‘‘The good thing about this lat­est re­search is that it’s given us a much bet­ter idea of the po­ten­tial size of a tsunami at some point on the lake. It’s given us a rea­son­able scope.

‘‘The data is a lot more ro­bust, so it gives us more op­por­tu­ni­ties to plan.’’

Jack said ECan would talk to the Macken­zie District Coun­cil about putting signs up on pop­u­lar spots on the lakeshore, re­mind­ing peo­ple to move to higher ground in the event of an earth­quake or tsunami.

‘‘The im­por­tant mes­sage is that th­ese events are rare, but in the off chance that a tsunami does oc­cur in the lake, you don’t want to be on the lake beach.

‘‘The most likely trig­ger for a lake tsunami is an earth­quake, so, like any coastal or lake area in New Zealand, if you feel a long or strong earth­quake, move off the lake beach and to higher ground as soon as the shak­ing stops.’’

Niwa used an echo-sounder to map the Tekapo lake bed, as well as seis­mic re­flec­tion sur­veys.

‘‘They could use the in­for­ma­tion gath­ered to de­ter­mine what sort of land­slides there have been in the past,’’ Jack said.

The re­port says any tsunami in Lake Tekapo would be highly de­pen­dent on the lake level at the time, which has an op­er­at­ing range of al­most nine me­tres.

Even if a tsunami in the lake does not flood land, it may still cause slosh­ing in the lake, and surges on the lake beach, so it is im­por­tant peo­ple know they should stay away from the lake shore af­ter a strong earth­quake, the re­port says.

The re­port con­cluded that there is a small chance that a tsunami could be cre­ated on the Macken­zie Basin lakes, in­clud­ing Tekapo, Pukaki, Ohau, Alexan­d­rina, and Ru­atani­wha.

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