Homework

1. 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.

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

3. Tsunamis

4. 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

5. 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

6. A Tsunami is one large wave • True • False

7. Tidal waves and Tsunami waves are the same thing. • True • False

8. Which would NOT cause a Tsunami • Landslide • Earthquake • Gravitational Pull • Meteorite

9. Submarine earthquakes Similar to the 2004 Tsunami

10. Submarine landslides, etc..

11. Tsunami from Arequipa earthquake, June 2001 0.3m 0 Usually takes about 15-16 hours Image from www.pmel.noaa.gov/~koshi/peru/dcrd/maximum.gif

13. 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

14. 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.

15. A Tsunami acts as a • Deep water wave • Shallow water wave • Interactive wave • Tidal wave

16. A rapidly rising tide1 m….1957 &1946

17. 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

18. Trough arriving firstin 1957 This is why many people Die Not understanding what will come next

19. A bore – April 1st 1946

20. A biggish wave – 1946, Hilo

21. BIGGER? – 1998 Papua New Guinea About 15 meters

22. BIGGER? Hawaii - 1946: 17 m

23. 2004 Tsunami

24. Before and After

25. 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….

26. Destruction in another part ofPapua New Guinea 4m

27. Same place – note wooden building in background

28. The crest of a tsunami always arrives first • True • False

29. 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

30. Some may think they are like hurricanes

31. The flippant – not so funny anymore HOTEL SIGN IN NEW ZEALAND

32. Could this Happen?

33. And, the “Must get my front row seat” attitude 60 People Die

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

35. New Zealand & Hawaii’s place in the World

36. REMEMBER THE RING OF FIRE? Warning Buoy Tsunami Warning Buoys

37. Earthquakes in the 20th century

38. 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….

39. 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?

40. 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….

41. New Zealand’s own unique problem 3 possible Sources: Earthquakes Landslides Volcanoes ALL CAN BE FOUND INNEW ZEALAND !!!!!!!!

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

43. Submarine landslides 3200 km3

44. 150-300 million m3 ~0.25 km3

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

46. Submarine volcanoes VOLCANOES NEW ZEALAND

47. In more detail Source from Walters & Goff, 2003

48. Why all this fuss? – Over a “rare” event • They are unpredictable • They can cause extreme damage • Hawaii deaths: • 1877 - 5 • 1946 - 159 • 1960 – 61 • 2004 – 250,000 Okushiri, 1993

49. 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. 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

50. 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