Homework Read pages 56-61 Why are tides considered a dominant influence on nearshore beach life? Explain the books statement “the moon does not exactly.

Homework

Read pages 56-61 Why are tides considered a dominant

influence on nearshore beach life? Explain the books statement “the moon

does not exactly rotate around the earth? How long is a full tidal cycle? How large does an earthquake have to be

in order for a tsunami watch to be issued? Define Diurnal, Semidiurnal and Mixed

semidiurnal tides.

“The Great Wave of Kanagawa” by the Japanese artist Hokusai.

Tsunamis

Definition Tsunami:

Japanese word: Tsu = Harbour, Nami = Wave

• It is NOT a Tidal Wave, that is the tide and is caused by the moon, sun etc…• It is a SERIES of fast-moving, LONG WAVELENGTH, waves generated by

large disturbances of the Ocean below or near the seafloor

Events which cause Tsunami’s

Tsunamis are waves generated by displacement of the ocean by impulsive events

Events known to generate tsunamis:

Submarine earthquakes Explosive volcanic eruptions Submarine landslides Terrestrial landslides that enter water bodies Impacts of large extraterrestrial objects (e.g.

asteroids or comets) in the ocean

A Tsunami is one large wave

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1. True2. False

Tidal waves and Tsunami waves are the same thing.

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1. True2. False

Which would NOT cause a Tsunami

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1. Landslide2. Earthquake3. Gravitational Pull4. Meteorite

Submarine earthquakes Submarine earthquakes

Similar to the 2004 Tsunami

Submarine landslides, etc..

Tsunami from Arequipa earthquake, June 2001

0 0.3m

Usually Usually takes takes

about 15-about 15-16 hours16 hours

Image from www.pmel.noaa.gov/~koshi/peru/dcrd/maximum.gif

FactsA tsunami travels at about 800 km per hour (500 mph) or more in deep water, so it

can cross the Pacific easily in a day, from South America to Japan.

Wave height (from crest to sine- which is the water surface) in deep water is usually a meter or less – it is the long wavelength that is important, so ships are OK.

The long wavelength means its speed is controlled by water depth – it acts as a shallow water wave even in deep water

Waves lose energy at an inverse proportion to their wavelength.

Longer wavelength = less energy loss.

So – it is fast and doesn’t lose much energy….

When a tsunami enters shallower water the main control of its speed – water depth – means it slows down. Phew! BUT energy loss is insignificant and the height of the wave grows – it is now easily detectable.

A Tsunami acts as a

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1. Deep water wave2. Shallow water

wave3. Interactive wave4. Tidal wave

A rapidly rising tide

1 m….

1957 &1946

When it reaches the shore it may appear as a rapidly rising and falling tide, or a bore, or one hell of a towering, breaking wave.

In extreme cases, water levels can rise up to 20 meters or more – and it is not always the first that is biggest, oh yes – and sometimes the trough arrives first….. December 2004 Tsunami

Trough arriving firstin 1957

This is why many people Die

Not understanding what will come next

A bore – April 1st 1946

A biggish wave – 1946, Hilo

BIGGER? – 1998 Papua New GuineaBIGGER? – 1998 Papua New Guinea

About 15 meters

Hawaii - 1946: 17 mHawaii - 1946: 17 m

BIGGER?BIGGER?

2004 Tsunami

Destruction……

Damage is highly variable – can extend kms inland and RUNUP (vertical height above sea level) 30 meters or more, it can also do nothing. Can cause complete devastation – or nothing.

The natural topography of the coastline is a major influence on the amount of Damage a Tsunami creates.

Factors include nearshore beach slope, tide level, onshore topography, shape of the coast, etc….

Destruction in another part of Papua New GuineaPapua New Guinea 4m

Same place – note wooden building in backgroundSame place – note wooden building in background

The crest of a tsunami always arrives first

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After all that – when I say TSUNAMI what do you think?

Do you have a pre-conceived idea of what they are – even now is it hard to visualize?

The 2004 Tsunami has changed a lot of people’s ideas about Tsunamis

Some may think they are like hurricanes

The flippant – not so funny anymore

HOTEL SIGN IN NEW ZEALAND

Could this Happen?

And, the “Must get my front row seat” attitude

60 People Die

………….and then...and then..

Some will realize that realitySome will realize that reality is somewhere in the middle of all that.is somewhere in the middle of all that.

Let’s have a lookLet’s have a look

New Zealand & Hawaii’s place in the New Zealand & Hawaii’s place in the WorldWorld

REMEMBER THE RING OF FIRE?

Tsunami Warning Buoys

Warning Buoy

Earthquakes in the 20Earthquakes in the 20thth century century

We need some way of knowing what tsunami will do, because they can obviously be very bad and they are entirely unpredictable – or are they???

OK – so we cannot predict when and where the generating process will occur – and we can’t even predict exactly if a tsunami will be generated from a earthquake.

Examples:

1960 – Large Chilean EQ = Bad tsunami in Hawaii/NZ

2001 – Equally large EQ = 30 cm in NZ, nothing in Hawaii

Hmmmmmmm….

We use geological and historical records, and numerical modeling to try and understand – and predict.

The geology and history show what happened in the past –

Ultimately the aim is to link models with the real time data from the tsunami buoys to have some warning of what will happen.

In the meantime – the models look good, but what do they tell you?

Ultimately the aim is to link models with the real time data from the tsunami buoys to have some warning of what will happen.

In the meantime – the models look good, but what do they tell you?

They make assumptions about the properties of waves and therefore – are they based on reality?

A New Zealand case study or two….

New Zealand’s own unique problemNew Zealand’s own unique problem

3 possible 3 possible

Sources:Sources:

EarthquakesEarthquakes

LandslidesLandslides

VolcanoesVolcanoes

ALL CAN BE FOUND INNEW ZEALAND !!!!!!!!

Earthquakes- Located on the edge Earthquakes- Located on the edge of the “Ring of Fireof the “Ring of Fire

Submarine landslidesSubmarine landslides

3200 km3200 km33

150-300 million m3 ~0.25 km3

Y

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Tsunami generated by aKaikoura Canyon landslide

R. Walters NIWA

WaterLevel (m)

SouthBay

Kaikoura

GooseBay

Oaro

Kaikoura submarine canyonKaikoura submarine canyon

About About once every once every 160 years 160 years

There is a There is a submarine submarine landslidelandslide

1833 and 1833 and 17281728

Next???Next???

Submarine volcanoesSubmarine volcanoes

VOLCANOES

NEW ZEALAND

In more detail

longitude

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165 170 175 180-50

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from Walters & Goff, from Walters & Goff, 20032003

Source

Why all this fuss? – Over a “rare” event

• They are They are unpredictableunpredictable

• They can They can cause extreme cause extreme damagedamage

• Hawaii Hawaii deaths:deaths:• 1877 - 51877 - 5• 1946 - 1591946 - 159• 1960 – 611960 – 61•2004 – 250,0002004 – 250,000

Okushiri, 1993

TsunamisTsunamisThey are also confounding – with our knowledge of They are also confounding – with our knowledge of oceanography we should be able to understand them better. oceanography we should be able to understand them better. Right?Right?

They represent almost the “supreme wave” – every They represent almost the “supreme wave” – every fundamental piece of information on wave dynamics, seafloor fundamental piece of information on wave dynamics, seafloor structures, coastal topography, and tectonics all fit together to structures, coastal topography, and tectonics all fit together to make each one unique.make each one unique.

It is that very uniqueness that is the key to really It is that very uniqueness that is the key to really understanding Oceanographyunderstanding Oceanography

In Essence if we can understand Tsunamis we will have a In Essence if we can understand Tsunamis we will have a better understanding of Oceanography as a wholebetter understanding of Oceanography as a whole

SummarySummary

A tsunami is a SERIES of fast-moving, LONG A tsunami is a SERIES of fast-moving, LONG WAVELENGTH, waves generated by large disturbances WAVELENGTH, waves generated by large disturbances of the Ocean below or near the seafloorof the Ocean below or near the seafloor

•(e.g. submarine earthquakes, submarine landslides, volcanic eruptions, meteor impact)

Can travel at 800 km per hour (500 mph) or more in Can travel at 800 km per hour (500 mph) or more in deep waterdeep water

Damage is highly variable – can extend kms inland and Damage is highly variable – can extend kms inland and RUNUP (vertical height above sea level) 30 meters or RUNUP (vertical height above sea level) 30 meters or more, it can also do nothing more, it can also do nothing

The natural Shape of a coastline is a major influence on The natural Shape of a coastline is a major influence on how the wave comes inland - as is nearshore beach how the wave comes inland - as is nearshore beach slope, tide level, onshore topography, shape of the slope, tide level, onshore topography, shape of the coast, etc….coast, etc….

SummarySummary