Civil Defence are concerned that people are becoming blase about disaster evacuation warnings. This particularly pertains to tsunami warnings because of the absence of a damaging tsunami event striking New Zealand. Social media critics are claiming that Civil Defence cry wolf over evacuation alerts and some are engaging in the dangerous and irresponsible practice of sowing division that makes people uncertain in times when certainty is necessary.
But one day a damaging tsunami will occur. The ones that have happened in recent decades have fortunately arrived at times in New Zealand when the tide was out far enough that the waves lost all of their energy making up ground in the tidal zone, or more likely were never going to be very large in the first place and – high tide or not – were simply out of energy when they got to New Zealand.
But picture this. A major earthquake has hit the South American west coast on the tectonic plate boundary off the Chilean coast. A Pacific wide tsunami warning has been issued. The waves will start hitting New Zealand about 13-15 hours from now. The largest wave comes ashore in Chile 10 metres high and causes heavy loss of life and damage.
The tide is coming in in Lyttelton when the first warnings are issued about with about 10 hours leeway. The waves will begin to strike on a rising tide. Based on computer modelling the waves are likely to reach 2-3 metres. Over the next several hours the warnings are refined as data comes in. Major damage has been done along the west coast of South America as far north as Colombia and there are waves heading for Hawaii, New Zealand, Fiji.
People are generally complying with the authorities evacuation advice. Despite the confusion about arrival times and wave size, people accept that a warning has been issued and they need to move to safer ground.
But on social media, disgruntled people are accusing Civil Defence of crying wolf. They say past tsunami’s turned out to be nothing and this one will be nothing as well – why should they worry?
There are some basic rules about tsunami’s that everyone needs to know:
- There is MORE than one wave. Some have up to 8
- The first wave is RARELY the biggest. The 1960 Chilean tsunami was triggered by a massive earthquake and the third wave was the biggest
- The topography of the ocean floor means every tsunami behaves differently – is it for example a long narrow bay with a shallow dipping sea bed? In that case you will probably see the waves coming sometime before they get to you. Or is it an open beach with a steep drop off? In that case the waves will not be obvious until it is too late and hit the coast with significant speed that you will not be able to outrun
- Do NOT go back in between waves as you won’t have time to get away. In tsunami events elsewhere this has cost people their lives
- Be prepared to be gone for several hours
- Stay away from coastal water features such as river mouths, estuaries and lagoons lest you get cut off