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TsunamiInformation Sheet

Tsunami waves are different fromnormal wavesTsunami are dierent rom normal waves you see atthe beach. With a normal wind swell wave, it is only thewater on top o the ocean that is moving. In contrast, the

passage o tsunami involves the movement o water allthe way to the sea oor.

BEWARE: you cannot surf a tsunami!ImagecourtesyofUSGS

A tsunami can really move!In the deep ocean a tsunami can travel up to 950km/hr,the speed o an aeroplane and may be less than one metrehigh. This is why the Japanese fshermen did not noticethe tsunami in the deep ocean. Tsunami wavelengths areextremely long with hundreds o kilometres between wavecrests in the deep ocean.

As tsunami approach the coastline they slow down but

do not lose energy. The back o the wave catches upwith the ront, causing the wave to grow in height up toseveral metres. It is not so much this movement o waterbut the energy moving through it that makes tsunami so

dangerous.

Prior to an undersea earthquake

At the time of an undersea earthquake

After an undersea earthquake

Above is a picture of the lower tectonic plate

dragging against the upper plate, causing stress.

Stress on the tectonic plates causes the upper

plate to rebound to its initial position, causing

tsunami.

There is a temporary drop in water level above the

fault, as the tsunami spreads outwards across the

ocean.

Illu

strationcourtesyofGeoscienceAustralia

What is a tsunami?A tsunami is a series o ast, low and long ocean waves,

that move out rom a central area, due to a sudden

disturbance o a large body o water. In the past, tsunami

have been known as tidal waves but this is not correct as

tsunami are not caused by t ides.

Tsunami (pronounced soo-nah-mee) is a Japanese word

meaning harbour wave. It came rom an old story about

some Japanese fshermen who, when out in the deep

ocean, did not notice a tsunami travelling underneath them.When they arrived back at port they ound the harbour

destroyed.

What causes a tsunami?The most common cause o tsunami is large, undersea

earthquakes that occur along the boundaries o the

Earths tectonic plates. As the plates move, stress slowly

builds up over hundreds, or even thousands, o years

along geological structures known as aults. During an

earthquake the stress along these aults can be released

within a matter o seconds. This causes a sudden

movement o the sea oor which disturbs the ocean above.

The aected ocean then spreads out rom the location o

the earthquake as a tsunami.

Although undersea earthquakes are the most common

cause o tsunami, they can also be caused by volcanic

eruptions, landslides and even asteroid impact in or near

the ocean.

Earthquake-generated tsunami

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The natural warning signs of tsunamiIn Australia you will most likely receive an ofcial tsunamiwarning. However, beore a tsunami arrives you may, butnot always, experience some natural warning signs.

You may:

FEELtheearthshake. I you are near the ocean andyou eel the ground shake, a strong earthquake may haveoccurred and possibly caused a tsunami. However, youmay not eel the earth shake i the earthquake occurred along way away.

SEEtheoceandrop. Beore a tsunami arrives, theocean level may (but not always) drop dramatically beorereturning as a wall o water. I you notice that the water isdisappearing, tell your amily and riends and prepare tomove to higher ground.

HEARanunusualroaringsound. I you hear a loudroaring sound rom the ocean (a bit like an aeroplane ora train), tell your amily and riends. This sound may beheard beore a tsunami arrives.

Will we get an ofcial warning?

The Joint Australian Tsunami Warning Centre runs 24hours a day to identiy any tsunami threat to Australia.

They use sea surace buoys and undersea sensors to

measure earthquake activity and the likelihood o a tsunami

aecting Australia.

In Australia, warnings will be issued through the media, but

you should also listen to emergency workers, lieguards

and Sur Liesavers.

Remember:

Ifatsunamiwarningisissuedyoushouldfollowinstructions and move inland or to higher ground.

Alwayslistentolifeguards,SurfLifesaversand

emergency workers.

IfatsunamiwarningisissuedDONOTgobacktothe

water until you are told it is sae.

IFYOUHEARATSUNAMIWARNINGMOVEINLANDORTOHIGHERGROUND.DONOT

STAYTOWATCH.DONOTGOBACKTOTHEBEACHUNTILYOUARETOLDITISSAFE.

ImagecourtesyofAndersGrawin

Drawdown of the ocean on this Thailand beach warned of the

arrival of the 2004 Indian Ocean tsunami.

5746

www.symagy.com

Moreinformationontsunamiisavailableatwww.ema.gov.au

Will tsunami occur in Australia?While the risk rom tsunami is lower in Australia than

other parts o the world, tsunami do have an eect on our

coastline. Even with relatively small tsunami, there could be

strong waves, rips and currents and unusual sea levels that

can be dangerous.

On17July2006,campersatSteepPointontheWestern

Australian coast were lucky to escape when a tsunami hit

their campsite. It was strong enough to pick up their 4WD

vehicleandmoveit10metresupthebeach.Theywere

alerted to the tsunami by a loud roar rom the ocean, which

is one o the natural warning signs o tsunami. Above is a

picture o the damage to their campsite.

ImagecourtesyofPaulDickenson

English schoolgirl saves 100 livesIn December 2004, 10-year-old English schoolgirl, Tilly Smith,

was enjoying a family holiday on the coast of Thailand. On the

morning of 26 December, her family were enjoying a walk on

the beach when Tilly noticed the ocean drop dramatically.

It then returned rapidly covered in froth, which she described

as looking like the top of a beer. As the ocean moved quickly

towards the beach, Tilly knew a tsunami was approaching

having learned about tsunami in a geography lesson a couple

of weeks earlier. She raised the alarm and the beach was

cleared, saving 100 lives.

Commonwealth o Australia 2009. This work is copyright. Apart rom any use as permitted under the Copyright Act 1968, no part may be reproduced by any process without prior written permission rom the Commonwealth.RequestsandinquiriesconcerningreproductionandrightsshouldbeaddressedtotheCommonwealthCopyrightAdministration,Attorney-GeneralsDepartment,3-5NationalCircuit,Barton,ACT,2600orpostedatwww.ag.gov.au/cca.Disclaimer. The purpose o this Inormation Sheet is to provide general inormation and ad vice. Following the procedures in this Inormation Sheet will not guarantee protection against the consequences o tsunami or their atermath. Incase o tsunami, you should ollow instructions and advice rom competent authorities. The Australian Government does not accept any legal liability or responsibility or loss, damage, injury or death arising rom, o r despite, the use o theinormation in this Inormation Sheet. Although all due care has been taken, this Inormation Sheet may contain technical inaccuracies or typographical errors.