Saturday's surges caused millions of dollars worth of damage to boats and marina infrastructure at Tutukaka. Photo / Tania Whyte
Saturday's surges caused millions of dollars worth of damage to boats and marina infrastructure at Tutukaka. Photo / Tania Whyte
The government agency in charge of tsunami warnings has defended its call not to issue emergency alerts after the Tongan eruption on Saturday night, saying it has to reserve them for when lives are at significant risk.
It comes after a chorus of criticism from boaties and coastal dwellers caught by surprise by tsunami damage at Tutukaka Harbour.
Dive Tutukaka owner Jeroen Jongejans — whose fleet was lucky to escape damage — was among those querying the point of a tsunami warning system if it wasn't used.
When a tsunami is detected in the Pacific, national science agency GNS Science assesses the threat to New Zealand — from, among other sources, a Pacific-wide network of buoys measuring wave activity — and advises the National Emergency Management Agency (Nema).
If Nema decides there's a threat to land, it will issue a tsunami warning, which will trigger cellphone alerts and evacuations.
Local Civil Defence groups can then activate sirens and order evacuations from specific areas.
If Nema decides tsunami activity is likely to be limited to beach areas, it will issue an advisory urging people to stay off beaches and out of the water.
Nema spokesman Anthony Frith said emergency mobile alerts were not issued for tsunami advisories.
''Emergency alerts are reserved for significant risk to life and safety, when inundation of land is expected and evacuation is required. That was not the case on Saturday night,'' he said.
''The advice from GNS was for beach and marine tsunami activity so we made the decision to issue a tsunami advisory. Obviously there were acute impacts in very particular areas.''
Alerts were issued and evacuations ordered after the March 5, 2021, earthquake in the Kermadec Islands north of New Zealand.
Frith said complicating factors on Saturday night were the effects of Cyclone Cody and the fact the tsunami was triggered by a volcano, rather than an earthquake as was usually the case.
Aerial view of Tutukaka Marina, clearly showing the damage caused by Saturday night's tsunami surges. Photo / Rusty Russell
Jose Borrero, a tsunami hazard specialist from eCoast Marine Consultancy, said the advisory was appropriate given the information at the time.
Tsunami generated by earthquakes were fairly well understood but that wasn't the case with volcanoes.
''We have hundreds of earthquakes to draw on but in recent human history we haven't seen anything like this. In hindsight, what we know now is that is tsunami from volcanoes activate harbours differently.''
That was likely because of the shorter wavelength of tsunami generated by eruptions, Borrero said.
The last comparable example was the eruption of Krakatau, in the Indian Ocean in what is now Indonesia, in 1883.
That wiped the island off the map and generated a tsunami that killed tens of thousands of people.
The Insurance Council says it will be weeks before an estimate for the cost of damage at Tutukaka is known, and at least three months to arrive at a final figure.
Spokesman Christian Judge said, however, it was certain to add up to many millions of dollars.
The council had appointed a coordinator in Tutukaka to coordinate the bigger claims and assist with salvaging the remaining vessels, hiring specialist equipment such as cranes, and surveying the marina to check for unseen damage and debris.
If ongoing work was needed to replace piles and piers it could take longer than three months to come up with a final figure.
''We're also mindful that this is minor damage compared to what has happened to our Pacific neighbours,'' Judge said.
