Tsunami warning

Written By: - Date published: 12:24 pm, September 17th, 2015 - 21 comments
Categories: disaster - Tags: ,

21 comments on “Tsunami warning”

  1. vto 1

    Lucky tides are small otherwise a few big slops over a few seawalls would surprise

  2. vto 2

    The first pulse is now 1,600 km away and closing at 800 km per hour…..

  3. millsy 4

    Save the Tsunami warnings for something of substance — ie one that stands to cause *a lot* of damage (ie Japan, 2011) and not something that provides an extra swell for the surfers.

    • vto 4.1

      This tsunami warning is entirely appropriate. The last one to hit Canterbury in 2010 caused significantly increased tidal flows and surges which gouged at coastal edges and pushed all the way up Lyttelton Harbour flooding the low-lying end of it. If it had been a big high tide when it arrived it would have slopped over and into Chch seaside suburb streets.

      That is the risk and it is real – threat to property in low-lying coastal zones whereby large volumes of water slop around the streets and drains and creeks and seawalls with considerable force and the ability to do damage.

      • dukeofurl 4.1.1

        Trouble is low level warnings repeatedly given will be forgotten over time.
        30 cm of water level change when NZ tides are often 3m or more in harbours is of little concern.
        That reaction in Whitianga where they left the school 12 hours before waves could reach NZ was just alarmism

        • weka

          Are all warnings of the same level though?

          “30 cm of water level change when NZ tides are often 3m or more in harbours is of little concern.”

          It’s a different kind of water movement I think. I seem to remember the last time this happened, maybe a 1M tsunami surge was expected and they were concerned for people on the water, or right on the edge, on the coast where sudden changes of water in tricky places can cause problems. Those people deserve to be warned.

          I agree there is a cry wolf possibility, but I’m more concerned that we don’t acutally know what is supposed to happen. When I was growing up we had the CD sirens, but I gather those are being phased out. What are they being replaced with and how are people being educated on what to do? We’re still pretty crap at this considering how much warning we’ve now had about big disasters.

          • dukeofurl

            Well we do know what has happened, I have family photos of tsunami waves in Lyttleton harbour back in 1960s, small rise even then ( it was high tide) and a small amount sloshed over in dry dock.

            Computer modelling shows what the rise will be around NZ places, due to the shallow offshore continental shelf ( in most places- an area off Kaikoura isnt) there is minimal risk. The wall of water they talk about- which did occur after boxing day tsunami- cant seem to happen here.

            local earthquakes and kermadec trench quakes could be a different story

            • weka

              I’m not really a sea person, but what I understood from one a few years ago was that the ‘rise’ is not like a normal tide, and it affects places that have odd water movements or just changes how the water moves in places that people are used to. It’s not a big wall of water like we normally think of tsunamis, it’s about currents and land masses and what happens there. This would affect people in boats and other craft, people fishing on the shore, people simming etc. I’m not sure if those are the things you are talking about, and you may be right that it’s not an issue here, but I’d like to see a range of expert opinion on this before writing off the CD response.

              Having said that, the way the whole siren thing is being handled my confidence in CD has diminished.

          • Bill

            My understanding is that’s all down to wavelength.

            A regular 30cm high wave slaps harmlessly on the sand or whatever, but a 30cm wave that stretches back however far, suddenly becomes a shit-load of water being pushed forwards and on-shore.

            Wanna take the school kids down to the beach for a look? I believe a NZ teacher did that a few years ago. I guess they were only going to watch a bigger (higher) than normal wave break on the beach…

  4. dukeofurl 5

    My analysis from Summer, near Lyttleton is that you get a over about 5 -6min a peak rise of of 0.4m and then a quick fall over 4 min or so.

    Thats not a wall of water either, a very flat wave form


    • dukeofurl 6.1

      Heres the Raoul island SL measurements at 1 min intervals as tsunami arrives

      2015-09-17 16:05:00 2.243m
      2015-09-17 16:06:00 2.27
      2015-09-17 16:07:00 2.238
      2015-09-17 16:08:00 2.159
      2015-09-17 16:09:00 2.167
      2015-09-17 16:10:00 2.313
      2015-09-17 16:11:00 2.438
      2015-09-17 16:12:00 2.343
      2015-09-17 16:13:00 2.217
      2015-09-17 16:14:00 2.174
      2015-09-17 16:15:00 2.242
      2015-09-17 16:16:00 2.259
      2015-09-17 16:17:00 2.289
      2015-09-17 16:18:00 2.258
      2015-09-17 16:19:00 2.235
      2015-09-17 16:20:00 2.26

      Seems to be a lot of small changes quickly say 5cm in in 1 minute and likely to go up and then down

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