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Waves

Waves. Neptune's Horses by Walter Crane of 1892.

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Waves

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  1. Waves Neptune's Horses by Walter Crane of 1892 One of the major deities in Greek mythology, Poseidon was the supreme ruler of the seas. The Romans called him Neptune. An awesome, unruly, and powerful god, Poseidon was associated with storms, earthquakes, and some other violent forces of nature. When angry, he could stir the sea to a fury. But he could also calm the raging waters with just a glance. One of his titles, Enosichthon (Earth-shaker), reflected his ability to cause earthquakes by striking the earth and mountains with his trident. Another name for Poseidon was Hippios (lord of horses), and the god presented horses as gifts to various individuals. Poseidon rode the waves in a swift chariot drawn by golden sea horses. He used his mighty trident not only to provoke earthquakes and stir ocean waves but also to raise new land from beneath the sea or cause existing land to sink below the waters. Although often helpful to humans—protecting sailors at sea, guiding ships to safety, and filling nets with fish—Neptune could be a terrifying figure as well. Quick to anger, he directed his fury at anyone who acted against him or failed to show proper respect. Read more: http://www.mythencyclopedia.com/Pa-Pr/Poseidon.html#ixzz1dKdjjyn0

  2. Waves • Transport energy over a body of water • Can cause coastal erosion

  3. WavesOrigin and Type • Wind waves – “wind-generated” • Seiche – “pressure-generated” • Tsunami – “seismic-generated” • Tide – “gravity-generated”

  4. Height Still water line Wave Terminology • Still water line – level of ocean if it were flat w/o waves • Crest – highest part of wave • Trough – lowest part of wave • Wave height (H) – vertical distance between crest and trough • Amplitude – distance between crest and still water line • ½ the wave height • Wavelength (L) – horizontal distance from each crest or each trough • Or any point with the same successive point • Steepness = Height (H)/length (L)

  5. Wave Parameters • Period (T) – the time it takes for two successive waves to pass a particular point • Frequency (f) – the # of waves that pass a particular point in any given time period

  6. Deep Water WaveMotion • Water particles move in orbits • Waves transmit energy, not water mass • Diameter of orbits decrease with depth • Particle motion ceases at ½ wavelength

  7. Waves Types • Deep Water • H2O depth is >1/2 wavelength • Shallow Water • Depth is <1/20 wavelength

  8. Orbital Motion • When under a wave crest • Water moves up and forward • When under a trough • Water moves down and back • Thus, water particles do not move forward • They move in circles

  9. WavesVelocity • The longer the wavelength, the faster the wave travels • Velocity (V) = wavelength (L)/Period (T) • For example: • If T= 10 sec; L = 100 m • Then 100 m/10 sec. = 10 m/sec

  10. WavesGeneration • Generated by Force • wind or air • Generated at storm centers • Separation of waves by differing rates of travel - dispersion • Sea Wrinkles  ripples  wind waves  swells

  11. WavesSize • Factors determining size: • Fetch • Distance wind blows over open ocean • Speed of wind • Wind velocity • Duration • Length of time wind blows

  12. WavesDispersion • Wave train – a set of waves with the same wavelength • Individual waves move faster than wave train • wave dies out at front of train while new waves form at rear • Wave train travels half the speed of individual wave

  13. Wave Interference • Combination of waves • Build from one another = Constructive • Cancel each other = Destructive

  14. Shallow Water Waves 3. Orbits progressively flatten at depth 1. Swell feels bottom at depth < ½ wavelength 2. Wave crest peaks and wave slows 4. Wave height (H) increases and wavelength (L) decreases 5. Wave breaks when H/L ratio > 1/7 6. Just above seafloor particles move in back-and-forth motion

  15. Breaking Waves

  16. Breaking wavesTypes • Type of Breakers: • Depends on steepness (a) Spilling • Gentle slopes • Surf gently rolls over the front (b) Plunging • Moderately steep slope • Wave curls forming a tunnel (c) Surging • Steep slope • Rolls onto beach

  17. WavesCharacteristics • Refraction • Bending of waves • Waves approach shore at angle and drags • Feels bottom first and slows • Diffraction • As waves pass through small opening, waves spread

  18. Seiches • Standing wave oscillates • Rise and fall of water level • Occurs in enclosed basins and/or lakes • Stationary point (node)

  19. Tsunamis • Giant sea waves generated by earthquakes

  20. TsunamiCauses • Earthquake • Volcanoes • Landslides • Meteor impact

  21. TsunamiCharacteristics • Energy passes through entire water column • Shallow water wave • Long periods (T) • T = 10-20 min. • Small Height (H) • H = 1-2 m • long wavelengths (L) • L = 100-200 km • Deep wave base • Travel at great speeds • c = 200 m/s

  22. Earthquake-Generated Tsunami • Usually associated with subduction zones • Water is displaced suddenly

  23. TsunamiCrest and Trough

  24. Today Historical Tsunamis1883 Krakatau • Explosive volcano • Large landmasses fell into the ocean • 36,000 people killed by tsunami

  25. Earthquake-Generated Tsunami • Chile, South America (1960) • 9.5M, largest EQ ever recorded • 3rd wave 11 m (30’) high; 1 hour period • 909 died; 834 missing • Tsunami Warning System in place

  26. Lessons from Chile • Hawaii • 61 died

  27. Chile, 1960 • Japan • 181 deaths

  28. Landslide-Generated Tsunami • As large mass of land falls into ocean, a huge volume of water is displaced

  29. Landslide-Generated Tsubnami • Lituya Bay, Alaska (1958) • 150-m high wave • Stripped vegetation • Ancient tree trim shows previous occurrence

  30. Historical Tsunamis1946 Pacific Tsunami • Aleutian Island Earthquake • Killed 165 people in Hawaii • Resulted in the creation of the 1st “tsunami warning system”

  31. Historical Tsunamis2004 Indonesian Tsunami • 9.0 M earthquake • Deadliest tsunami ever recorded • >260,000 people killed

  32. Japan Tsunami • Tsunami – The Great Wave • Aerial View of Japan Tsunami

  33. Tsunami Dangers Drowning Severe abrasion by dragging Thrown against solid objects Carried out to sea in outgoing wave Hit by debris House, cars, trees, rocks

  34. Tsunami Hazard Mitigation • Land Use Zoning • Build to elevations above flood potential • Structures engineered to resist erosion and scour • Streets and buildings built perpendicular to shore • vegetation

  35. The Pacific Tsunami Warning System Two Steps • Tsunami Watch • Issued when an earthquake > 7.0M is detected in the Pacific Ocean • Tsunami Warning • Significant Tsunami is identified

  36. Tsunami Prediction • Pressure sensor on ocean floor detects changes in wave height • Transmit signal via satellite

  37. Surviving a Tsunami • If you feel an EQ when near the coast, get to high ground • Do not return to shore after initial wave • Never go to the shore to watch a tsunami • An unexpected rise or fall of sea level may indicate an impending tsunami

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