Ocean Waves, Tides and Currents

1. Ocean Waves, Tides and Currents

2. Movement of Water Very important for ocean transportation (trade), sediment transport, climates. Water is set in motion by: Waves Tides Currents

3. Introduction to waves Waves

4. Waves A rhythmic movement that carries energy through matter or space. • in the ocean = the up and down movement of the ocean surface.

5. Waves and the currents they generate are the primary factors in transport and deposition of coastal sediments. • Waves move material along the bottom and suspend itfor weaker currents to transport.

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

7. 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 • Wave Period - The time it takes one wave to pass a given point.

9. Waves Caused by 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 • Fetch: Distance over which the wind blows • Length of time the wind blows

10. Friction from the wind moving over the water causes the water to move along with the wind. If the wind speed is high enough, the water begins to pile up and a wave is formed.

11. Swells • Waves that extend beyond the windy area in which they were generated. Swells may travel thousands of miles until they hit shore and release energy in crashing waves.

12. When a wave passes through the ocean, individual water molecules move in circles but do not move forward or backward. . Traveling Swell As wave propagates, particles move in an orbit and return to roughly the same place (objects bob up and down).

13. BREAKERS= COLLAPSING WAVES

14. BREAKERS • As it approaches shore, the wave hits bottom. • Friction slows down the bottom.

15. Tsunamis They are sometimes incorrectly called tidal waves.

16. Tsunamis Caused by: Under sea EARTHQUAKES LANDSLIDES VOLCANIC ACTIVITY

18. As they move out from their source: • waves formed end up having very small heights (1 - 2 ft.) • very long wave lengths (up to 150 miles) • move at high speed (up to 435 miles per hour).

19. Until they hit • the shallows!

21. 2004 Tsunami • 9.1 earthquake • 225,000 deaths

22. Tsunamis As they move out from their source, the waves formed end up having very small heights (1 - 2 ft.), very long wave lengths (100+ miles long) and they move at high speed (hundreds of miles per hour). Tsunami warning system

24. Tides A view of the tides at Halls Harbour on Nova Scotia's Bay of Fundy. This is a time lapse of the tidal rise and fall over a period of six and a half hours. During the next six hours of ebb the fishermen unload their boats on the dock. That's a high tide every 12 and 1/2 hours! There are two high tides every 25 hours.

25. The highest tides in the world are at the Bay of Fundy, which separates New Brunswick from Nova Scotia. At some times of the year the difference between high and low tide is 16.3 m, taller than a three-story building. http://www.classzone.com/books/earth_science/terc/content/investigations/es2406/es2406page01.cfm

26. Tides The rise and fall in sea levels. http://www.classzone.com/books/earth_science/terc/content/investigations/es2406/es2406page03.cfm

27. Tides • The rise and fall in sea level is called a tide. • Tides are actually shallow water waves and depend heavily upon topography. • 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

28. What Causes Tides The gravitational attractions of the Moon and Sun acting on the rotating Earth.

29. 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.

30. Main tidal forces caused by the Moon. • Earth rotates every 24 hours on its axis. • Moon orbits the Earth every 29.5 days: 360˚/29.5 = 12.2˚/day movement of the Moon. • Therefore, it takes the Earth (12.2/360) X 24 ~ 50 minutes extra to catch up so the “Tidal Day” is 24 hours and 50 minutes.

31. Earth-Moon-Sun positions and the monthly tidal cycle

32. Gravitational Effect of the Sun and Moon • Spring Tides -every 2 weeks • Earth, Moon, and Sun are lined up • High Tides ~20% higher than normal • Low Tides are lower than normal

34. Gravitational Effect of the Sun and Moon • Neap Tides- • Earth, Moon, and Sun form right angles • High Tides are ~20% lower than normal • Low Tides are higher than normal

35. Diurnal One high and one low tide each lunar day Semidiurnal Two high and two low tides of about the same height daily Tidal patterns

36. Mixed Tides Characteristics of both diurnal and semidiurnal with successive high and/or low tides having significantly different heights larger tidal range)

37. http://home.hiwaay.net/~krcool/Astro/moon/moontides/TideAni.gifhttp://home.hiwaay.net/~krcool/Astro/moon/moontides/TideAni.gif

38. Tidal Bores • A high wave caused by an extreme incoming tidal flow. • Shape of estuary must be shallow and uniform. • Only occur in about 100 rivers in the world.

39. Tides and crabs

41. Ocean Currents • Mass movement or flow of ocean water • River within the ocean • Two types • Surface and Deep

42. Surface Current Link • Horizontal, stream-like movements of water that occur at or near the surface of the ocean • Can reach depths of several hundred meters

43. Surface Currents • Controlled by three factors • Global winds • Coriolis Effect • Continental Deflections

44. Surface Currents Global Winds • Cause surface currents to flow in the direction the wind is blowing • Coriolis Effect Link • The apparent curving of moving objects due to the Earth’s rotation

45. Coriolis Effect • Northern Hemisphere = clockwise • Southern Hemisphere = counter clockwise • Continental Deflections • Shape of continents change the direction of current flow

49. Surface Currents and Climate Warm Water currents On the east coasts of continents Bring warm water to colder regions. Example: Gulf Stream

50. A river like current in the Atlantic Ocean. It follows the Eastern Coast of the U.S. and then goes towards Europe. Discovered by Benjamin Franklin. Gulf Stream