Homework  Read pages  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 1. True 2. False

Tidal waves and Tsunami waves are the same thing. 1. True 2. False

Which would NOT cause a Tsunami 1. Landslide 2. Earthquake 3. Gravitational Pull 4. Meteorite

Submarine earthquakes Similar to the 2004 Tsunami

Submarine landslides, etc..

Tsunami from Arequipa earthquake, June m Usually takes about hours Image from

Facts A 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 1. Deep water wave 2. Shallow water wave 3. Interactive wave 4. Tidal wave

A rapidly rising tide 1 m… & 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 first in 1957 This is why many people Die Not understanding what will come next

A bore – April 1 st 1946

A biggish wave – 1946, Hilo

BIGGER? – 1998 Papua New Guinea About 15 meters

Hawaii : 17 m 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….

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

Same place – note wooden building in background

The crest of a tsunami always arrives first 1. True 2. False

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.. Some will realize that reality is somewhere in the middle of all that. is somewhere in the middle of all that. Let’s have a look

New Zealand & Hawaii’s place in the World

REMEMBER THE RING OF FIRE? Tsunami Warning Buoys Warning Buoy

Earthquakes in the 20 th 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 problem 3 possible Sources:EarthquakesLandslidesVolcanoes ALL CAN BE FOUND IN NEW ZEALAND !!!!!!!!

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

Submarine landslides 3200 km 3

million m 3 ~0.25 km 3

Kaikoura submarine canyon About once every 160 years There is a submarine landslide 1833 and 1728 Next???

Submarine volcanoes VOLCANOES NEW ZEALAND

In more detail from Walters & Goff, 2003 Source

Why all this fuss? – Over a “rare” event They are unpredictable They are unpredictable They can cause extreme damage They can cause extreme damage Hawaii deaths: Hawaii deaths: – – – 250, – 250,000 Okushiri, 1993

Tsunamis They are also confounding – with our knowledge of oceanography we should be able to understand them better. Right? They represent almost the “supreme wave” – every fundamental piece of information on wave dynamics, seafloor structures, coastal topography, and tectonics all fit together to make each one unique. They represent almost the “supreme wave” – every fundamental piece of information on wave dynamics, seafloor structures, coastal topography, and tectonics all fit together to make each one unique. It is that very uniqueness that is the key to really understanding Oceanography It is that very uniqueness that is the key to really understanding Oceanography In Essence if we can understand Tsunamis we will have a better understanding of Oceanography as a whole

Summary A tsunami is a SERIES of fast-moving, LONG WAVELENGTH, waves generated by large disturbances of 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 deep water Damage is highly variable – can extend kms inland and RUNUP (vertical height above sea level) 30 meters or more, it can also do nothing

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