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August 20, 2018 | by  | in Features | [ssba]

Tsunamis: Riding the Wave of Disaster

When I was little, I had a big fear of natural disasters. I wouldn’t go to the school bathroom alone, in case an earthquake struck. Visiting my Auckland aunt meant stepping into volcano territory. And in the scene outside a window, my mind would conjure a giant ship, riding a giant wave, coming nearer and nearer to little me, set to run me down and drown me on dry land.
But as it turns out, earthquakes became a part of my daily life in Christchurch in 2011. Volcanoes are still horrifying, but not as prominent in my mind as the fear of leaving university and not finding a job. And I learned, just yesterday, that tsunamis are not actually one big wave, but a succession of waves, like the ripples that form when you drop a pebble in a pond. Which is worse actually, if you think about it.
The word tsunami comes from Japanese tsu, meaning “harbour” and nami, meaning “wave”. Although the word can operate as both singular and plural, because of English language trends, tsunamis is also commonly used and accepted. Tsunamis are often caused by an earthquake out at sea. The waves are a result of the seabed moving violently upwards, pushing water out in all directions. A tsunami wave seen from the air is a circle. Events such as landslides, even meteors, can cause tsunamis too, as the water is displaced by something huge and heavy falling into it. Most waves are around 3m high, but the biggest tsunami ever recorded was the 1958 Lituya Bay megatsunami, caused by a landslide, which reached 524m in height.
It’s easy to underestimate the force of a tsunami. If the wave is only 3m tall, what’s the big deal? YouTube is overflowing with videos of people standing in the path of a tsunami with their phones out, waiting to record the disaster as it happens around them. But a car is barely 2m high, and you wouldn’t stand in the way of a car, would you? A car, presumably travelling at even 50km/h, could kill you. A tsunami, despite being made up of a non-rigid material, can reach speeds of 800km/h. Ouch.
The size of a tsunami wave grows in proportion to water depth. In deeper water, you might not even notice it, but in shallow water, such as the Wellington harbour, the wave maintains the power it had in deep water, but instead grows in visible height. Out on the sea, these waves can be hundreds of miles long, but no taller than a few feet above water. They can travel at the speed of a jet plane. When the waves approach land, they will slow, and begin to grow in height as the wave enters the harbour.

As if this wasn’t bad enough, a harbour can then exacerbate the effects of a tsunami, creating a phenomenon known as harbour resonance, or a seiche (“saysh”) wave. Basically, if two waves are travelling past each other in opposite directions at the same rate, the place where the two peaks overlap will become one big peak, and where the two troughs overlap will become one big trough, resulting in one huge wave made up of two smaller ones. This occurs in places where waves bounce off the sides of something resembling a container, such as a lake, or the Wellington harbour.

So What Do I Do??
This is all sounding Pretty Horrific. Researching this did nothing to ease my fear of tsunamis, and the inner five-year-old in me was very close to asking my flatmate to accompany me to the bathroom, just in case. But then, I looked up the WREMO evacuation map. To my relief, more than half of the city is in the safe zone. Wellington, despite being in the unlucky location of a harbour, is also nicely surrounded by natural tsunami safe zones; hills.
The best way to survive a tsunami is to get out of its way. To do this, you first need to know the warning signs. There are tsunami sirens in all coastal areas and the central city, which sound a little like WWIII is starting. You won’t miss it. The Wellington Region Emergency Management Office (WREMO) advises that, “if you feel an earthquake that is either longer than a minute OR strong enough that it’s hard to stand up, as soon as the shaking stops, get to high ground, out of all zones (past the blue line)!” Some suburbs, like Houghton and Owhiro Bays, have blue lines painted on footpaths showing the maximum water run-up height in a tsunami. In Wellington, the safe zone line follows roughly along Lambton Quay, Manners, Courtney, and along Oriental Parade. Officially, the danger zone is 1 mile or 1.6km within the coast, and 15m above sea level.
If a tsunami is forming out at sea, anyone on the beach or waterfront may notice the water drawing back from the shore, sometimes leaving the seabed exposed much further out than it is at the lowest tide. This water is being sucked back to fuel the giant approaching wave, and this, accompanied in some cases by a rushing, roaring sound as the water gathers power, is the sign of an impending wave of watery doom. At this point, you should probably get gone. A local earthquake means a tsunami could be minutes away. If you can see the wave, you should assume you’re too close to outrun it. In this case, try to get as high off the ground as possible. This could be a building, or even a tree. If you happen to be on a boat in the open ocean, you are bloody lucky, and should stay there. The wave will likely pass under your boat and you won’t even notice. If you’re in the harbour you should get further out to sea, as the wave in the harbour will likely push your boat inland and smash it against the shore.
The number one thing WREMO say is; don’t wait for a tsunami alarm. I know it can feel like an overreaction to run for the hills (literally) after every little shake — after all, we’ve been fine so far. But you’re better up the hill than dead, and a small earthquake here could have been a large one out at sea, resulting in a giant wave with time to build before it reaches us.

But What Do I Take??
You may need to stay in the evacuation zone for up to 4 hours. In the worst case scenario, you won’t have a home to return to, but let’s think positive. Take your pets, unless you’re a heartless monster, and a leash or cage, your phone, phone charger, and keys — remember to lock up! Take your wallet, and any medication you need regularly. If you’re within easy reach of important documents such as passport or birth certificate, these might be useful and, more to the point, are expensive to replace. If you can, put other expensive or sentimental items up high in case of flooding. Take a water bottle, and if you’re feeling hungry (when aren’t you?) perhaps some snacks. Ideally, the bag you take to work or uni will be semi-permanently contain most of these things, allowing you to just grab it and go. Plus, you’ll save those expensive textbooks! Chuck on a warm jacket and good walking shoes, and head up the nearest hill.

If there’s been an earthquake, watch out for downed power lines, and be careful of debris falling from buildings or bridges in an aftershock. Stay away from rivers or streams, as these provide easy routes for tsunami water to hurtle down. Go on foot to ease traffic congestion, and if you can’t get to a hill in time, a building will suffice. A reputable (and only slightly sleep-deprived) fourth year architecture student has informed me that the best buildings to withstand pressure from an oncoming wave are those with concrete foundations and steel framing — for example, the Wellington Central Police Station. The bigger the building, the better, as it’s more likely to have deep foundations.
Most importantly, wait for the all clear from authorities before returning home, as the worst may be yet to come. If you’ve taken a phone or something capable of receiving internet, perhaps even a radio, listen in for the all clear. Before disaster even strikes, WREMO recommend you regularly take pictures of rooms for insurance purposes, and this could be helpful in any disaster. Keep these up to date, as it could save you time and hassle later. Personally, I recommend you always take a friend to the bathroom. Just in case.


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