Monster tsunami artwork stuff of Hollywood movies

A109 Light Utility Helicopter flight with mayor Gisborne City from the air in November 2023.

Opinion

May I point out that the last Weekender insert featured an imagined mega-thrust tsunami that is the stuff of Hollywood disaster movies.

Comparing the wave pictured with Tuamotu Island (36 metres high), Young Nick’s Head (177 metres) and the distant shore hills, this monster would have to be an absurd several kilometres high!

Recent scientific studies have estimated the height of a magnitude 9 mega-thrust tsunami to be anywhere between 12m and 30m.

The problem with tsunamis — as has been shown in the past 20-odd years — is that they do NOT appear as towering waves.

Film of recent tragic tsunami events shows the rise in sea level is imperceptible until it is almost on top of people caught on beaches.

Then it is too late.

The only warning sign, if the triggering earthquake is not nearby, is a withdrawal of water from a beach, as if the tide has suddenly gone out.

Even this may not give people enough time to get to safety.

As for the illustration showing a giant wave breaking, tsunami waves do not break until they hit shallowing water close to land — and then the wave front is not like a surf wave, just a rolling, irresistible churn of white water moving faster than a person can run.

The article itself seem liked another handout from council, patting itself on the back for its new civil defence building and its exercise.

I personally gained nothing helpful from it whatsoever.

Information on what the public could do in such an event would have been relevant — but if a 30-metre tsunami wave rolls in, even the new Civil Defence building at Lytton will not be safe.

Roger Handford

Footnote from Ed: Gisborne District Council has responded that modelling undertaken by independent experts, then peer-reviewed, does not support a worst-case scenario of a 30m wave as stated in this letter. Rather, waves of 12m to 15m could be expected if the Hikurangi margin fault ruptured off Gisborne City. 
“The new Emergency Coordination Centre is located where it is (15 Potae Ave) for the very reason that the worst-case scenario tsunami inundation would not come near the facility, or the hospital, or Lytton School or houses in that area.”
Council has maps showing the potential worst-case tsunami extent for Gisborne City and many other areas, available for viewing here:
www.gdc.govt.nz/services/civil-defence/tsunami-inundation-and-evacuation-maps