Kaikoura Earthquake produced seven-metre tsunami

November's quake also raised up the coastline, leaving shellfish exposed to the sun. Photo / File

A tsunami generated by November's 7.8 Kaikoura Earthquake reached a height of 7 metres in some places, comparable with some of the biggest events in recent history.

Niwa hydrodynamics scientist Dr Emily Lane said the height was confirmed at surveys conducted at Oaro and Goose Bay, south of Kaikoura, three weeks after the midnight quake on November 14.

Scientists were able to determine the wave height from marine debris such as dead fish and paua shells strewn far up the beach.

"There was basically a very clear line of debris, including lots of marine debris that you wouldn't normally get on the beach, and we found it both on the beach and up the local river valleys."

Lane said it was fortunate that no one was in the tsunami's path when it hit.

"When you're coming from Christchurch toward Kaikoura and following the coast, Oaro is the first settlement where the road meets the sea, then Goose Bay is a little bit further north."

In some places, she said, there was evidence the tsunami had breached a beach berm next to the highway, but the berm was still high enough to protect both settlements.

"We met with some of the people in Oaro, including one woman who was the wife of the Civil Defence controller, and as far as we could tell they did the right thing," Lane said.

"Everyone got up the hill after the earthquake, which is exactly what we always call for."

The tsunami was comparable with some of the largest to hit New Zealand in recent decades.

Gauge readings taken at Kaikoura at the time of the quake showed that, in the 25 minutes immediately after, the tidal level dropped by 2.5m.

In the 15 minutes following that, the tide rose 4m from the lowest point, before a series of waves were recorded over several hours.

Notably, the tide level changed by a metre in the event; reflecting the fact that gauge had been hauled up by that much along with a large stretch of the coastline it sat on.

Elsewhere, the tsunami registered on gauges long after, showing up in readings at Wellington's Queens Wharf and Castlepoint an hour after, and at the Chatham Islands four to five hours following the event.

At Little Pigeon Bay in Canterbury, where a historic cottage was wrecked, wave heights reached 3m.

The force of the tsunami was enough to lift the unoccupied cottage from its foundations and flood it with water a metre deep, leaving debris stuck to its walls.