Small surges detected after Northland tsunami alert advisory issued

Jeroen Jongejans at Tutukaka Marina where the waters were as flat as a pancake despite a national tsunami advisory. Photo / Supplied

Predictions of unpredictable surges along Northland's coastline following an overnight earthquake in the Pacific failed to eventuate.

Civil Defence early yesterday

issued a national advisory for strong and unusual currents and unpredictable surges at the shore following a magnitude 7.7 earthquake southeast of Loyalty Islands, near New Caledonia.

Northland was likely to have been one of the first regions affected.

People in or near the sea were advised to move out of the water, off beaches and shore areas and away from harbours, rivers and estuaries.

The first tsunami activity causing these strong currents and surges was predicted to reach waters around North Cape from about 4.20am yesterday

and Civil Defence said the threat must be regarded as real until the advisory was cancelled.

It was cancelled just after 9am yesterday.

"Based on the most recent modelling and decreasing tsunami amplitudes at North Cape, Great Barrier Island and the East Cape, the tsunami threat has passed for New Zealand," the National Emergency Management Agency said.

However, it said there could still be large unexpected currents and the public were advised to continue to take precautions in coastal zones for the rest of yesterday.

There were no reports of any major surges or incidents around Northland.

Dive Tutukaka sent three boats out and co-owner Jeroen Jongejans said he had noticed very little change in sea conditions, even during high tide at 8am yesterday.

"We have received similar tsunami advisory in the past and it mostly relates to areas down in the estuary but out in the sea, you hardly notice anything.

"The swells are coming from the north rather than the east so they have little effect here. We made the assessment that it's perfectly safe for our boats to go out," he said.

Northland harbourmaster Jim Lyle was notified about 4am that coastal areas could be affected.

He alerted the marina at Tutukaka, the harbour usually most affected by surges, and NorthPort, where three ships tied up to the wharf were advised to check their mooring lines were secure.

Regional council tide gauges had recorded slight changes at Whangaroa, Marsden Pt and Opua, but measured in millimetres rather than centimetres.

A few small surges had been seen at Tutukaka.

Given the size of the earthquake it was fortunate Northland hadn't been affected, he said.

Russell Booking Centre owner Collette Kershaw is perfectly placed to observe any surges or unusual marine phenomena — her office is at the end of Russell wharf — but she noticed nothing unusual.

The first she knew was when she got a phone early in the morning to let her know the Happy Ferry would not be sailing as a precaution until the tsunami advisory was lifted.

The other ferries started their morning sailings and by 10am all ferries between Russell and Paihia were operating as usual.