New Zealands Tsunami Hazard
Most tsunami are generated by geological processes, and most of those are earthquakes with the fault line moving and moving a large ammount of water above it, but can also be a submarine landslide, or volcanic eruption, or even a landslide going into the ocean, and on very rare occasions, even an asteroid hitting the ocean. Faults on the other side of the pacific eg. in Chile, Peru or even North America, Alaska, Japan etc. right around the Ring of Fire can also send tsunami our way.
In those cases, we’re not gonna feel the earthquake but we have sensors, and we’re part of the Pacific Tsunami Warning System so we will get warning, probably 10 or more hours warning ahead of time, that there’s been an earthquake and probably that a tsunami has been generated and our official Emergency management systems will warn you that that’s tsunami is coming, and what you should do. We think about tsunami sources in terms of local, regional and distant sources. Local sources are those ones where the tsunami has got less than an hour to get here.
In those cases, the earthquake will be your only warning. Because if you’re really close to the fault, the tsunami could arrive within minutes, it’s important not wait for anything. Leave immediately, head to higher ground or inland and stay away for many hours. Stay away until you get the official all clear. Waves can keep coming for hours, or even tens of hours from a distance source, and you won’t know when they’re over. All of New Zealand’s coastline is at risk from tsunami,.
But some areas are at risk from bigger or more frequent events than others, especially the East Coast of the North Island between Wellington and East Cape. It faces one of these big subduction zone faults. Tsunami from these largest faults are similar to what we saw in Japan in 2011 and the Indian Ocean in 2004. In these largest subduction zone earthquake and tsunami, how far would we need to go inland to get to safety? I’m gonna show you.
You need to go up hill, or inland. There is a road behind me that I can walk up and show you about how high you need to get in those worst cases. So up here I’m about 30 or a bit more than 30 meters above sea level. It gives you some idea of how high you need to get if you’re right at the coast. The Wellington South Coast communities have decided to paint a blue line across their roads at about the level the largest tsunamis can get to. It’s worth noting that these are just a Wellington initiative at the moment,.
So you not gonna see these around the rest of the country. elsewhere you need to be looking for evacuation maps. This information board at the park in Island Bay shows what those evacuation maps look like. You can see a series of red, orange and yellow zones that can be used especially in official warnings to tell us what areas need evacuating. It may be just the red foreshore, or the orange, and yellow zones that need to be evacuated during official warning. That might be a warning coming from Peru or Samoa. Somewhere far enough away that we can give an official warning.
The key message is, if there is time for an official warning they’ll tell you which zone to evacuate. But if you feel a large earthquake longer than a minute or too strong to stand up easily, you need to evacuate all zones immediately. You don’t know how big it’s gonna be, and those earthquake felt sources are potentially close by, so you need to evacuate without waiting for anything.