What would happen if a tsunami hit Sydney?

Nancy Notzon
Swellnet Analysis

Sitting in the centre of the Indo-Australia plate, Australia is a geologically stable country. The seismic ructions that wreak havoc on neighbours such as New Zealand, Indonesia, and Pacific nations are absent in Australia, and our distance from any plate boundaries mean tsunami are a much reduced threat.

However, tsunami can travel vast distances, so while the danger is reduced it's still a possibility. Recently, researchers at the University of Newcastle have been modelling the effects of a tsunami striking Sydney Harbour.

You might think the tsunami risk to Australia is fairly remote, but you may be surprised to learn they have hit our shores before, and it could happen again.

Whirlpools, flooding, and ocean currents strong enough to sink boats are just some of the possible impacts if a tsunami were to hit Australia's largest city, Sydney, according to research.

The chance of a major tsunami affecting New South Wales is very low, but University of Newcastle researchers say the tsunami risk to Australia is under-researched and needs to be taken seriously.

In 1960 after a quake in Chile, a tsunami hit the east coast and sank boats in Sydney and Newcastle.

Working with the Bureau of Meteorology, the researchers have mapped out several different scenarios of what could happen, including a very unlikely one-in-5,000-year event, to other, more likely, "it could happen in your lifetime" events.

"It's absolutely something we need to plan for, even if this is something we consider to be an infrequent event," lead author Kaya Wilson said. "The costs of being unprepared are so great."

"It's important to remember that a tsunami hitting Sydney Harbour is unlikely to be that kind of Hollywood style wall of water coming towards you. It would be experienced as a sequence of waves that may last for hours or even days."

"The worst-case scenario that we modelled was a one-in-5000-year event. We're lucky in Australia, that it would be caused quite far away, and the Australian Tsunami Warning Centre would issue a warning that hopefully we'd receive at least two hours before the tsunami were to hit."

"It would affect the whole east coast, but within Sydney Harbour we would expect extremely large waves."

"The largest we recorded for this worst-case event was 10 metres from peak to trough — we'd expect land to be inundated across Manly Corso, and we'd expect the waves to come from both the ocean and harbour side, eventually isolating North Head."

Sydney current speeds with largest modelled event. 

In that worst-case scenario, water would move incredibly fast at up to eight knots, and bays along the south side of the harbour such as Double Bay, Rose Bay and Rushcutters Bay would be inundated.

A one-in-20-year event, more likely in our lifetime, might go generally unnoticed.

"In terms of events that are more serious, we're talking a one-in-110-year — on average — event upwards," Mr Wilson said.

"So, with those more serious events, we could expect the sort of currents that would really disrupt the harbour.

"It would be dangerous for anyone in the water or to people on ships and ferries — you wouldn't want to be in the water.

"We know ships will probably be torn from their moorings, we know that currents will be very unpredictable, and the safest thing would be to be out of the water and to stay away from the shore."

While 110 years or more may seem a remote chance, Mr Wilson says it's not that far-fetched.

"For a tsunami of that size, that could occur once on average every 200 years," he said.

"That statistic can be translated into a 30 per cent chance of occurring over an average lifetime."

Warning systems are good

It's not like tsunamis haven't struck Australia before.

The Bureau of Meteorology has a complete list of all the tsunamis that have affected Australia over the years.

Many probably went largely unnoticed.

The worst one, off the mainland on Norfolk Island in 1805, damaged homes and swept one away.

But in 1960, after a quake in Chile, a tsunami hit the east coast and sank boats in Sydney and Newcastle.

Damage at Clontarf after the 1960 Chile tsunami

"We had quite a lot of damage around the Spit Bridge, lots of yachts were torn from their moorings, we had a timber punt down by Anzac Bridge — I think it was capsized," Mr Wilson said.

"There was damage in Newcastle and lots of damage widely reported."

"That is a sort of tsunami that we would expect to happen within our lifetimes again. We could expect a similar size in the harbour once every 50 to 100 years."

Mr Wilson and his team also work closely with the New South Wales State Emergency Service, which oversees tsunami responses and coordinates evacuations.

"Our research is ultimately about providing more data for our national institutions to make better decisions and keep people safe," he said.

New South Wales SES planning coordinator Nicholas Kuster said they were implementing data from the new study into their own tsunami plans.

"To get this kind of information, it's gold for us emergency services," Mr Kuster said.

Earthquake science explained

The seeds of an earthquake lie in the tectonic plates that make up the Earth's surface and on which the continents sit.

"It helps us refine our evacuation areas in time and helps us prioritise vulnerable areas in the event of a real-life, land-threat tsunami — but also marine-threat tsunamis as well.

"[The research] is expensive, time-consuming, and tsunami planning hasn't really been a large priority for Australia before the 2004 tsunami."

The researchers say a tsunami originating from one of the nearest source zones, the Puysegur Trench, south of New Zealand, could reach Sydney in about two hours.

But Australia has good systems in place, so a warning would go out well before then.

Mr Kuster said it was crucial to always heed the warnings.

"We have a saying up here, 'Up, up and away': Up 10 metres, up the estuary 10 kilometres, and away from the coast one kilometre."

The work is published in the journal Scientific Reports, with the researchers next planning to model potential tsunami impacts in their home city, Newcastle.

//NANCY NOTZON
© Australian Broadcasting Corporation. All rights reserved.

Comments

Westofthelake's picture
Westofthelake's picture
Westofthelake commented Tuesday, 16 Oct 2018 at 9:57am

I grew up in Newcastle with the understanding that "earthquakes don't happen here". That teaching was well and truly proven incorrect .
Even a 2m tsunami in Newcastle would be disastrous considering the extent of the harbour and the quantity of immediate areas at sea level.
Fingers crossed we are never faced with a tsunami event.

uncle_leroy's picture
uncle_leroy's picture
uncle_leroy commented Tuesday, 16 Oct 2018 at 11:39am

There has been a series or earthquakes in the past 6 weeks in the area Walpole to Lake Muir, most recent on Sunday just gone.
The threat for the NW WA is real for a tsunami. Lots of northward facing bays that will magnify any wave coming down from Indonesia. Documented tidal surge was recorded at shark bay following the 2004 tsunami, wave surge that flooded campsites at steep point and Tamala station.

Hadyn Vones's picture
Hadyn Vones's picture
Hadyn Vones commented Wednesday, 17 Oct 2018 at 12:32am
uncle_leroy's picture
uncle_leroy's picture
uncle_leroy commented Wednesday, 17 Oct 2018 at 9:25am

I wonder if the recommended tsunami warning system for the NW WA has been installed. Threat is very real.
Interesting on the Flinders Bay, Augusta being drained. That faces south, it’s as if the wave has passed down the coast and then continued to draw the water away with it, 1.5-2m worth. Very interesting and I bet left many people scratching their head on the day it occurred.
I wonder if any new extra low tide reefs were surfed along the margs coast that day

channel-bottom's picture
channel-bottom's picture
channel-bottom commented Tuesday, 16 Oct 2018 at 4:29pm

Narra might struggle as well particular houses on Ocean St and Lagoon St, plus Flight Deck etc..

velocityjohnno's picture
velocityjohnno's picture
velocityjohnno commented Tuesday, 16 Oct 2018 at 6:00pm

Traffic congestion would improve if half of the cars floated out to sea.

truebluebasher's picture
truebluebasher's picture
truebluebasher commented Wednesday, 17 Oct 2018 at 12:44am

Professor Ted Bryant noted( 6 Sydney Mega Meteorological Tsunamis in 10,000 yrs).
1491 (Most recent) A 60m wave washed over Sydney Heads
1500 Was a 130m wave that swamped over Jervis Bay Heads
4-5000 y/ago Tsunami swamped 10 kms up Shoalhaven to Nowra

Ted's Stories of Ghost Comet that fires 5,000 pellets into Ocean to arc km's Jet Stream.
This Geyser of 5000 degrees sheers then plummets ocean to fire up monster tsunami.
Similar to boiling hot Micro burst Tsunami...Both invisible power punches- deadly to Planes.

Last Century Oz Wide Tsunami Guides set 20 metres as low point.
Get your "Flood fire tree" Map (To Measure incremental Sea Level by Metres)

Flood.firetree.net

Now If you set it to 20m (Good!) Now just above Flood Line look for local Church-Schools.
These are likely Tsunami Shelters built for end of world Millennial Bug. (Gods Chosen few!)
My house gets wiped out but 20m Baptist Evacuation centre is in heaven just over the road.

This Century Oz wide adopted a much lower 10 metre low point.
Possibly climate change reverses Tsunami height to Micronamis ?

GeoScience > (Federal Government Site)
Identifies the Tsunami within 15 minutes (Apart from Meteorological ones)
Over next 30 minutes clocking speed/time. (Tsunami Times are approx)
10 hrs = South America to Sydney
2 hrs = New Zealand to Sydney (3hrs NZ to Gold Coast)
2-3hrs= Indonesia to Perth
2 Hrs = Papua New Guinea to Gold Coast
4 hrs= Antarctica to Melbourne/Adelaide

Life saving Tip tune to JATWC
Joint Australian Tsunami Warning Centre has direct feed to Data/Emergency & Whole of Oz.

Tsunami Colour Code
[Green] No Threat (and/or) Threat is over
[Amber] Listen for info/ watch others
[Code Blue] Warning for sea/Beaches Evacuation
[Code Red] Warning for Land Evacuation

Evacuation Zones (Which Century?) Set your handy incremental Sea-rise Map to...
10m Tsunami (Sydney) Not too bad really... Mostly keep clear of Botany Bay
20m Tsunami (Sydney)
North head to Chatswood >Hornsby
South head for Sutherland >Merrylands
East head for Randwick
West head for Merrilands

10-20m Tsunami Gold Coast.
Head on up to Hinze Dam from here all help from Ipswich/National Route is fine
10-20m Tsunami Tweed
Head up to Carrie Hall Dam as help from west routes also prevail.

In real Tsunami Alerts the reverse happens as all from Safe Mountains head to the coast.
Black Stump fire brigade kick over sandcastles & CWA marks'women take out toe dippers .
Sunbakerz/Bodybasherz/Beachcomberz are rounded up and mounded into breakwalls.
Up to 10 million Boardriders get blown kisses to tame the beast! Cowabunga!

Mort's picture
Mort's picture
Mort commented Wednesday, 17 Oct 2018 at 12:54am

Shit, would happen.

truebluebasher's picture
truebluebasher's picture
truebluebasher commented Wednesday, 17 Oct 2018 at 1:59am

I did mean to thank Nancy & ABC also Swellnet for going the extra yards. Excellent job guys!

Mort's picture
Mort's picture
Mort commented Wednesday, 17 Oct 2018 at 3:22am

what you talking about Willis?

Mort's picture
Mort's picture
Mort commented Wednesday, 17 Oct 2018 at 2:18am

There would be good surf and a decent loss of life.

uncle_leroy's picture
uncle_leroy's picture
uncle_leroy commented Friday, 9 Nov 2018 at 8:32am
truebluebasher's picture
truebluebasher's picture
truebluebasher commented Friday, 9 Nov 2018 at 10:17am

uncle_leroy saves the day! You know who your mates are! Swellnetonians are 1st to kit out!
Tsunami is rising up Joondalup Surfhouse drain hole- likely to wet the bar'n'all...Surfs Up!

factotum's picture
factotum's picture
factotum commented Friday, 9 Nov 2018 at 7:22pm

That earthquake this morning was pretty wild. Woke me up. My first thought was that someone was in the house stomping up and down the wooden floorboards!

truebluebasher's picture
truebluebasher's picture
truebluebasher commented Friday, 9 Nov 2018 at 10:58pm

Lake Muir area 600 quakes in a few months
Sep 16th = 5.7
Oct 12th = 4.6
Nov 9th = 5.4 (Same as Newcastle 1989)

ABC have complied a quality vid of deep cracks/rises in earth + surrounds + damage.
https://www.abc.net.au/news/2018-11-09/earthquake-hits-lake-muir-western...

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