IMPORTANT - PLEASE READ: SEROUS TSUNAMI THREAT TO NZ

[DazzaMc]

One-metre waves from quake hit six NZ locations

Sea-level measurements reveal that six locations around the country saw peak wave heights of more than a metre generated by last week's devastating earthquake near Chile.

A tsunami warning was issued for New Zealand after the three-minute, 8.8-magnitude quake struck off the coast of the Maule region of Chile last Saturday. A death toll of at least 550 has been estimated.

Small tsunami waves arrived first at Scott Base in Antarctica, then reached the Chathams about 11 hours after the earthquake. They reached the East Cape nearly an hour later.

Results from 19 sea-level gauges showed Lyttelton, near Christchurch, experienced the largest waves, with a peak one of 1.9m in mid-afternoon six hours after the first wave.

Other peak heights over 1m were measured in the Chathams, Gisborne, Sumner, Timaru and Whitianga.

The tsunami was measured along the west coast of the country as well but peak wave heights were much smaller, between 0.3m and 0.5m.

Mostly the highest waves did not occur for some time, ranging from 1.2 hours to 26 hours after the first one.

A National Institute of Water and Atmospheric Research principal scientist, Rob Bell, said the delay in arrival of the largest waves from a distant tsunami source was due to waves bouncing off continental shelves and coastal headlands.

http://www.nzherald.co.nz/nz/news/article.cfm?c_id=1&objectid=10630247

[nitpicker1]

we had it .5 to .8m up our river

Tsunami surges bounced around the coast
NZPA March 5, 2010, 8:50 pm
Scott Base and the Kermadec Islands were the first New Zealand sites to be hit by the tsunami from the Chile's magnitude 8.8 earthquake last weekend, but the surges of water reverberated around New Zealand like water bouncing around a bathtub.

Results from 19 sea-level gauges around the nation showed six sites had peak wave heights of over 100cm.

But at most locations the highest waves didn't arrive for some time, ranging from 1.2 hours to 26 hours after the first wave arrived.

In all cases in New Zealand, the first wave to arrive was a lift in the water level, rather than the receding tide that people often look for as a warning sign of a tsunami.

Tsunami waves arrived first at Scott Base, although the waves were small, then reached the Chatham Islands (Kaingaroa) about 11.6 hours after the earthquake in Chile.

It touched down on the North Island at East Cape nearly an hour later. The biggest waves hit Lyttelton, with a peak wave of 1.9m (crest-to-trough) arriving in mid-afternoon, six hours after the first wave.

Other peak wave heights over 100cm were measured in Chatham Islands, Gisborne, Sumner, Timaru and Whitianga.

"The tsunami was measured all along the west coast as well, but peak wave heights were much smaller (0.3-0.5 metres)," said National Institute of Water and Atmospheric Research principal scientist Dr Rob Bell.

The delay in arrival of the largest waves from a distant tsunami source was because they were bouncing off continental shelves and coastal headlands. Much slower-travelling waves were "trapped" on the coast and spread along the coastline, diminishing slowly.

He said the findings provided important feedback to civil defence and emergency management agencies so that they can refine tsunami warnings work out when to scale down to a tsunami advisory.

The epicentre of the quake was about 200km northeast of where a magnitude 9.5 earthquake struck Chile in 1960. That was the largest earthquake ever recorded and resulted in a destructive tsunami that killed many thousands of people around the Pacific.

The latest big quake resulted from the Nazca tectonic plate under the floor of the Pacific Ocean being thrust under the South American plate just off the coast of Chile.

http://nz.news.yahoo.com/a/-/latest/6894084/tsunami-surges-bounced-around-the-coast/

[Ferney]

I remember this one in 1960.   I was at work in a 1st floor office at the bottom of Queen St (opposite the CPO) and the warning of a tidal wave came through and the possibility it could come up Queen St.   Everyone kept going to the windows to check. 

Chile tsunami, 1960
The most powerful earthquake of the 20th century was of magnitude 9.5, off the coast of Chile on 22 May 1960. It generated a tsunami that killed several thousand in Chile and across the Pacific, including 61 people in Hawaii and 199 in Japan.

In the late evening and early morning of 23 and 24 May the first of many tsunami waves began arriving at New Zealand’s east coast. The tsunami caused wild fluctuations in the water level along the coast for several days, damaging boats and harbour facilities.

In the North Island, at Napier, waves that reached 4.5 metres above high-tide level damaged a footbridge over the Ahuriri estuary, wrecked many pleasure boats and swept others out to sea. At Scapa Flow the waves inundated beach homes and boat houses. At a seaside campground at Te Awanga, north of Hastings, eight people were washed out of their tents, and waves battered cabins.

Further north at Whitianga, the waterfront road and the airport were flooded, and a number of small craft were washed out to sea. During later fluctuations the sea retreated from the shore, exposing the wreck of HMS Buffalo, which had sunk in 1840. Some people ran out to the wreck to collect relics, but were forced to retreat when the sea returned.

At the port of Lyttelton in the South Island, the tsunami came in at 2.7 metres above the tide level of the time, damaging boats and electrical gear. A hotel and several houses were flooded, and 200 sheep drowned.

Several days later, warnings of another possible tsunami from a major aftershock sparked an evacuation of many areas on the New Zealand coast.


http://www.teara.govt.nz/en/tsunamis/3

[dragontamer]

My boss lives on the Sumner waterfront.  They were all evacuated early and were up on the hill watching the waves until 1pm and then allowed back home.  The residents association had a meeting last Wednesday because they were allowed back before that biggest surge hit.  No damage or anything, but there could have been. 

They are flipping out because all the tsunami warnings they thought they had don't exist.  No sirens, no nothing.  They had the police and CD going house to house, but they thought there was more self-management and warnings in place.  People were saying things like "Well, the siren hasn't gone, so it can't be that bad".  But there isn't a siren - somewhere along the way it had been decommissioned and nobody realised.

[guest49]

The earth is revolting over the parasites that infest its skin!  [If I cant shake the bastards off, I'll wash them off!]

[DazzaMc]

One thing most people don't seem to realize is the uncertainty around arrival these times - it all depends on just where the energy was focused and what the waves run into on their travels. Even the media was calling it a non-event just 10 odd minutes after the first predicted times had passed, and even worse - CD starting lowering warnings just hours after the first waves. BIG Mistake.

This event has helped in a lot of areas and one of those is the raising of awareness that this is not a precise science (yet) - there are no 'data-points' in-between Chile and here and as such we had NO IDEA what was coming our way until it hit the Chatham's, and even then we only had a ballpark figure. It was with great relief that I watched those Gauges at the Chatham's bob up and down the 1-2 meters they did instead of the 40 meters last seen on the other side of the Pacific. For a while there I was actually starting to get VERY concerned.

Here's why:



At Isla Robinsón Crusoe (620 odd km off the coast of Chile) they had 40 meter waves. 600km from the epicenter a fair distance from the rupture to have 40 meter waves washing ashore. To top that off - Station 32ST0 (a buoy which sits in 4524 meters of water) recorded a 60cm wave height - which is also MASSIVE in the deep ocean.

New Zealand would do well to place 1-2 buoys out in the middle of the Pacific in-between here and Chile...



Anyway...  here's hoping many lessons have been learn't.
The New Zealand public should by now be very well educated about these events - and as such respect should be building.
We hope.


Our turn will come one day...


 
 

[nitpicker1]

The earth is revolting over the parasites that infest its skin!  [If I cant shake the bastards off, I'll wash them off!]

or freeze 'em?  http://www.abc.net.au/news/video/2010/03/05/2837523.htm   http://xtranewscommunity2.smfforfree.com/index.php/topic,6332.0.html

[Magoo]

New Zealand would do well to place 1-2 buoys out in the middle of the Pacific in-between here and Chile...

NZ does have a very cavalier attitude toward such things.    The sheer number of people who headed to the coast shows us that there is a lot to be learned about natural disaster in this country.   Obviously the devastation in Samoa wasn't enough to make everyone stop and think.   You did good Dazza.   Thank you.

[guest49]

Look apon it as evolution in action [Niven]
Those that rush down to watch a tidal-wave roll in, are no great loss to the gene-pool.

The major problem is that it seems as if "Wolf" has been called so many times, that people just have a "ho-hum - yet another tsunami warning.  I think I'll just go surfing" attitude. 

[DazzaMc]

Those that rush down to watch a tidal-wave roll in, are no great loss to the gene-pool.

I agree.

 

[nitpicker1]

New Zealand would do well to place 1-2 buoys out in the middle of the Pacific in-between here and Chile...

NZ does have a very cavalier attitude toward such things.    The sheer number of people who headed to the coast shows us that there is a lot to be learned about natural disaster in this country.   Obviously the devastation in Samoa wasn't enough to make everyone stop and think.   You did good Dazza.   Thank you.

In the absence of official info from our council, or from our local CD contacts, (until AFTER this latest goddam thing was supposed to arrive,)  I took the conservative action and told our punters what was going on at 6am, advised them to up and off before and in case the roads out were affected.

funny, isn't it that several of them are back again this weekend; I was apologetic but they are saying they feel much safer knowing there is a finger on the pulse.

[DazzaMc]

Yep - you did the right thing Nit's.

With so much warning there really isn't any excuse for leaving things until the last hour... especially when lives are at stake.

 

[Magoo]

I was apologetic but they are saying they feel much safer knowing there is a finger on the pulse.

Well done Nitz.  It does instil confidence.

[ssweetpea]

I found out what happened to the GB camp over on Rangitoto last weekend.

They didn't hear the police loud hailer warning clearing out Islington Bay (5-8 year old girls are noisy). There are only 4 baches in Gardener's Gap now and only 2 of those are regularly occupied. One is right at the bridge (causeway) and the other (GB) is the last, most northerly, one.

Anyway, fortunately one of the bach holders between the Islington Bay wharf and the bridge knew that there was a camp at the GB bach and ran around with the warning. So after breakfast the girls were walked up to the nursery on Motutapu (much closer than similarly high ground on Rangitoto) and spent the morning there.

However the people on the mainland that were keeping them up dated where doing so from an internet site that wasn't being kept properly up to date so they thought that the warning had been canceled and had taken the girls back down to swim in one of the waterholes in the Gap at low tide after lunch. Just as well the wave that did hit Auckland was small.

The proceedures are going to be updated so that future camps get the info directly from Civil Defence instead.

One little bit of historical info did emerge however.

The bach holder who warned them could recall the 1966 tsunami. As I said before her bach is near the head of Islington Bay between the wharf and the bridge.

Tsunamis do not go up into Islinton Bay as it faces south towards the Auckland coastline.

However Islington Bay is still connected to Gardener's Gap by a channel about 4.5 m wide. It was wider before the causeway and bridge were built in WWII linking the two islands.

In 1966 the tsunami travelled up the channel from the Gap and under (but not over) the bridge with enough force to shift a sand bar in front of this bach holder's bach.