Seven Minutes’ Warning

There has been increased and timely attention to the matter of tsunami since the Boxing Day earthquake and tsunami that struck in Asian waters. The seismically quiet conditions in New Zealand in recent decades have made us more complacent about such things.

On the 26th of March 1947, a fairly heavy earthquake near the North Island’s East Coast at 8:33 a.m. was followed by two seismic waves which affected the coastline between Tokomaru Bay and Mahia.

The first surge swept ashore seven minutes later at 8:40 a.m. with the waters rising 25 feet above normal at Pouawa. “Mr and Mrs A.F. Hall, who had a beach cottage at Turihaua Point, had an alarming experience. They were in the kitchen with a lady visitor when the first outsize wave rolled in. With the water up to his neck, Mr Hall held onto the mantelpiece, and the women clung to him.” They reached a safe spot before the second wave came ashore a few minutes later.

The larger wave reached up to the windows of the hotel at Tatapouri (known as the “Tata” in my day), carried furniture from the bar and swept away some small buildings. The superstructure of the 36-year-old wooden bridge over the Pouawa River was carried half a mile upstream.

A sobering reminder to be aware of the risk of tsunami when earthquakes are felt on the coast. Currently, there is no hard-and-fast rule as to whether an earthquake will or will not produce a tsunami in a specific area. However, much work is now being done to identify areas at risk. The real challenge will be how to alert people to a tsunami that is generated close to shore.

Achieving a balance between our desire to live a normal life in these desirable coastal areas whilst limiting the risk that tsunami impose is a sensible aim.

[Some data from “Historic Poverty Bay and the East Coast, N.I., N.Z.” J.A. MacKay second edition, 1966]

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