Ocean Waves and Tides

1. Ocean Waves and Tides

2. Waves • A Wave is a rhythmicmovement that carries energy through matter or space. • In oceans, waves move through seawater

4. Waves Caused by: • Wind • Earthquakes • Gravitational force of the Moon and Sun.

5. Parts of a Wave • Crest – highest point of a wave • Trough – lowest point of a wave • Wave Height – vertical distance between the crest and the trough • Wavelength – horizontal distance between two crests or two troughs

6. Wavelength Crest Wave Height Still Water Trough Wave Parts

7. Wave Movement • When a wave passes through the ocean, individual water molecules move up and down but they do not move forward or backward.

9. Wave Movement • When a wave breaks against the shore, the crest outruns the trough and the crest collapses. • Called a breaker. • In this case, water does move forward and backward.

11. Cause of Waves • Wind • When wind blows across a body of water, friction causes the water to move along with the wind. • Wave Height depends on – • Wind speed • Distance over which the wind blows • Length of time the wind blows

14. Tides • The rise and fall in sea level is called a tide. • Caused by a giant wave. • One low-tide/high-tide cycle takes about 12 hrs and 25 min. • Tidal range is the difference in ocean level between high-tide and low-tide

15. What is the Tidal Range? • HT = 30 ft, LT = 20 ft • HT = 20 ft, LT = 12 ft • HT = 50 ft, LT = 20 ft

16. Gravitational Effect of the Moon • Two big bulges of water form on the Earth: • one directly under the moon • another on the exact opposite side • As the Earth spins, the bulges follow the moon.

18. The Cause of Tides • The primary body that influences the tides is the moon • The gravitational pull is greatest on the side of Earth closest to the moon, causing Earth to be stretched slightly • On the side of Earth closest to the moon, the pull of the moon’s gravity on the oceans is greater than it is on solid Earth • Water will flow towards this tidal “bulge”, creating a high tide • As Earth rotates, it will go “through” the tidal bulges, resulting in alternating high and low tides

19. Cause of Tides

20. Tidal Cycle • The sun also produces tidal bulges, slightly smaller than those produced by the moon • The influence is most noticeable during new and full moon phases (Earth-moon-sun are aligned), causing larger tidal bulges • Tidal Range – the difference in height between successive high and low tides • Spring Tides – have the greatest tidal range due to the alignment of the Earth-moon-sun system (new and full moons) • Neap Tides – daily tidal range is less due to the sun and moon acting against each other

21. Gravitational Effect of the Sun • Spring Tides • Earth, Moon, and Sun are lined up • High Tides are higher and Low Tides are lower than normal

22. Spring Tides

23. Gravitational Effect of the Sun • Neap Tides • Earth, Moon, and Sun form right angles • High Tides are lower and Low Tides are higher than normal

24. Neap Tides

25. Tidal Patterns • Tides at various locations respond differently to the tide-producing forces • Three main tidal patterns exist worldwide: diurnal tides, semidiurnal tides, and mixed tides • Diurnal Tidal Pattern – characterized by a single high tide and a single low tide each tidal day • Semidiurnal Tidal Pattern – characterized by two high tides and two low tides each tidal day • Mixed Tidal Pattern – characterized by a large inequality in high water heights, low water heights, or both

26. Tidal Patterns

27. Hopewell Rocks near Bay of Fundy https://www.youtube.com/watch?v=hbU0c9798sY https://www.youtube.com/watch?v=EnDJ6_XpGfo

28. b. Earthquakes- Waves caused by earthquakes are called Tsunamis • Tsunamis were once called Tidal waves, but they have nothing to do with the tides. • They are produced by earthquakes and other seismic disturbances. That’s why they’re also called seismic sea waves. • Sudden outflow of water then it returns much higher

29. iii. Tsunamis are very long, fast moving waves! • They can have wavelengths of 150miles, wave heights of 100 ft and move as fast as 450 mph (jet speed!).

30. The End