Tsunamis - we can't get them in NZ
WEDNESDAY DECEMBER 06, 2017
When I was a child I did not ever hear the word 'tsunami'. But it was probably not that they did not occur then. It is a Japanese word, and was only applied to events in Japanese waters. We can't get tsunamis here. The water is not deep enough and the earthquakes here are generally not powerful enough. But suddenly we are hearing about them more and more. Why? The only thing that has changed has been the level of media scaremongering. Now it is just one more thing we can add to the list of things that can 'get' us.
, in the 84 years between 1929-2013 there have been only 25 registered tsunamis in the world. In the first 40 years, to 1960, 9 or 10 had occurred. In the next 40 years to 2000, another 9 or 10. During the 13 year gaps between 1933-1946 and between 1964-1976 no tsunamis were recorded. But in the last decade
there have been a whopping six
. What has happened?
It is because every time there is a large earthquake the media are now poised, salivating, hoping for a tsunami so they can gleefully report a certain number of deaths. This hoping makes it a media reality.
Now even no tsunami is called one. Let me explain. The 20cm wave that arrived on NZ shores from Chile in 2013 was called a "small tsunami". But there is no such thing as a small tsunami. By definition a tsunami is a huge destructive tidal wave.
Lucky for NZ, only 7% of it sits above the waves. That means it is relatively shallow water around it. You need deep water, to supply the destructive wave in enough quantity, and to keep 'loading' it. For a tsunami to occur, an earthquake must
exceed a certain threshold. The 8.9-magnitude (on the Richter Scale) of Japan's
earthquake was enough to trigger a tsunami, and the magnitude-7.7 earthquake
that struck Indonesia in October 2010 only just surpassed the threshold.
Earthquakes below 7.5 or 7.0 usually do not trigger
them. A 7.1 or a 7.4 will not do it. Two earthquakes have exceeded 7.7mag, in 1855, in Lake Wairarapa, a 8.2mag and 2016, in Kaikoura.
Neither saw any sign of a destructive tsunami and certainly no loss of life. (In 1855 a hotel was carried away when a higher tide entered an inlet, but no population was endangered).
There is a website about tsunamis put up by the earthquake commission. It bears the title of Tsunami but is well-written and mentions the 1855 event, the 1868, the 1947, and the 1960 as extra-high tidal systems that can cause tsunamis.
Of deaths it says Only one tsunami death has been officially recorded – on the Chatham Islands in 1868.
If you read on it says this poor chap went into the water to try to retrieve a boat. That's asking trouble in a storm. Then we read
the 1960 event was
a major disaster in New Zealand. No lives were lost or even threatened.
So when we invited stories about natural disasters, the 1960 tsunami accounts tended to be
more amusing than terrifying.
But the Richter Scale
was only developed in 1935. So magnitude of seismic events prior to that is
only estimation. The fact remains that in our nearly 200 year history of
settlement, over 2 million earthquakes
have been recorded, and from them less
than a single handful of tsunami scares.
Compare that to the annual tragic road toll of several hundred lives
lost. We have extensive
tsunami alarm systems in place
costing ratepayers thousands of dollars e.g along the Kaikoura coastline, all for something that won't happen, but
few road risk alarm systems in place for something that kills people every day. It is disproportionate.
NZ is unlike Japan, which drops deeply into the
Pacific. Resting on a plate that extends 200 miles east of the Wairarapa, NZ gets relatively shallow waves from the east. (See the picture at the top of this article)
In the Pacific Islands the currents go east, so
higher waves from a Samoa tsunami could not
threaten NZ. They just dissipate further east. Earthquakes that occur around our coast are not able to threaten
to travel inland with any destructive force. To get some perspective on this, consider that the
2004 Indian Ocean Asian earthquake was only 10kms down, the Samoan tsunami (magnitude 8.0) was
at a depth of 18 km, and the 11 March 2011 Japanese tsunami was an 9-mag at the
depth of 32kms. And directly beneath each of those was a deep sea.
Tsunami scares are part of the alarmist funding industry often called 'the fake news'. They are
alongside other dubious and unproven beat-ups intended for sensationalist value, so the media can stay relevant. There is now the incorrect belief that every earthquake is a potential tsunami.
have now been whipped into a state of permanent fear. You can see it in the schools as regular 'tsunami drill'. If a large earthquake hits us, making for higher ground which may open up, is a rather silly thing to recommend. I believe the beach is much safer.
To find out more about tsunamis, read the book (that this article is extracted from)