2. The Story Of Waves

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

4. Wavelength Wave Height Crest Trough Still Water Wave Parts

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

6. Period The time it takes for one full wavelength to pass a given point. Most waves have periods ranging from 2 to 10 seconds. speed = wavelength period

7. Wind or Storm Waves The most familiar waves are wind generated. The most familiar waves are wind generated.

8. Wind or Storm Waves Three things determine how large these waves can become. Three things determine how large these waves can become.

10. Waves Caused by Wind When wind blows across a body of water, friction causes the water to move along with the wind. When wind blows across a body of water, friction causes the water to move along with the wind. Wave Height depends on : Wave Height depends on : 1. Wind speed 2. Length of time the wind blows 3. Distance over which the wind blows

11. 1. Wind Speed This is the speed that the wind is blowing. This is the speed that the wind is blowing. This is usually measured in knots or nautical miles per hour. This is usually measured in knots or nautical miles per hour.

12. 2. Duration Duration refers to the time over which the wind blows. Duration refers to the time over which the wind blows. Winds in some areas may blow strong for long periods of time which can produce large waves. Winds in some areas may blow strong for long periods of time which can produce large waves.

13. 3. Fetch Fetch refers to the distance over which the wind blows. Fetch refers to the distance over which the wind blows. If a wind blows over thousands of miles the waves can get much larger than blowing across a small pond. If a wind blows over thousands of miles the waves can get much larger than blowing across a small pond.

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

17. Winds at the ocean’s surface cause waves

21. Waves On The Beach Most of the waves we see are at the beach. Most of the waves we see are at the beach.

22. Waves On The Beach As the wave travels in shallower water it slows and eventually falls forward as a breaker. As the wave travels in shallower water it slows and eventually falls forward as a breaker.

23. Wave Movement When a wave breaks against the shore, the crest outruns the trough and the crest collapses. When a wave breaks against the shore, the crest outruns the trough and the crest collapses. This is called a breaker. This is called a breaker. The wave breaks into what is called surf. The wave breaks into what is called surf.

24. Wave refraction Close to coast, water gets more shallow Close to coast, water gets more shallow Waves are slowed down Waves are slowed down If waves arrive at an angle, one part is slower than the rest If waves arrive at an angle, one part is slower than the rest Causes waves to bend = wave refraction Causes waves to bend = wave refraction

29. Waves arriving at bays are slow (deposition) Waves arriving at bays are slow (deposition) At headlands, faster (erosion) At headlands, faster (erosion)

30. Wave cut cliffs

31. Sea Stack

32. Sea Arch

33. Sea Arches

34. Sea Cave

35. Sandy Beach

36. Rocky Beach

37. How is sediment transported along a coastline ? Most waves move toward the shore at a slight angle. Consequently, the uprush of water (swash) from each breaking wave is on an angle.

38. The direction of swash is oblique. However, the backwash runs back to the water at a right angle. Sediment particles are therefore transported in a zig-zag pattern along the beach. This “beach drift” can carry sand and pebbles hundred to thousands of metres per day. Beach drift

39. Longshore drift In a similar manner, water in the shoreface zone flows toward the shore at an angle, and flows back at a right angle to the shore. The net result is a current that flows parallel to the shore. This is called a longshore current. The movement of shoreface sediment by a longshore current is called longshore drift. Longshore drift

41. Coastal deposition Result of longshore drift and a lot of sediment Result of longshore drift and a lot of sediment = produces extensions of deposit from the shoreline = produces extensions of deposit from the shoreline

42. May grow across a bay (baymouth bar) May grow across a bay (baymouth bar) May link an island to the main land (tombolo) May link an island to the main land (tombolo) spit = curved extension

45. Spit

47. Baymouth Bar

48. Lagoon

49. Tombolo

50. Barrier Islands Barrier Islands Wave Action creates sand bars Wave Action creates sand bars Waves and Longshore current - can form barrier islands Ex. Fire Island Waves and Longshore current - can form barrier islands Ex. Fire Island

51. Jetty

52. The sand trapping effect of the jetties to the north at Charleston, South Carolina has deprived Morris Island of needed sand. As a result, the island has eroded to the point that this previously land based lighthouse is now 400 meters out to sea.

53. Port Washington Breakwater

54. Rip Currents Breaking waves approaching the beach carry water toward the beach. The water can't just pile up there: it has to escape back out to sea somehow. Various “paths of least resistence” (e.g low areas along sandbars) provide areas for water to flow back to the sea. If caught in a rip current, swim parallel to shore !

55. How to spot a rip channel Rip channels (as seen from the air) Head of Rip channel (as seen from beach) Note: a rip current is different from undertow

56. Undertow results when water cannot escape as a rip current. Remember that water that is pushed toward the beach must return to the sea somehow ! If the water can’t escape as a rip current, it returns to the sea by flowing underneath the waves. Undertow Swimmers are less likely to drown from undertow than in a rip current (most so-called “undertow drownings” result from swimmers losing their balance in backwash and getting pulled out in a rip current).

57. Tsunamis Tsunamis were once called Tidal waves, but they have nothing to do with the tides.

58. Tsunamis They are produced by earthquakes and other seismic disturbances. That’s why they’re also called seismic sea waves.

59. Tsunamis are very long, fast moving waves! They can have wavelengths of 150 miles.

60. They can travel at over 450 miles per hour! As fast as a jet!

61. The Danger of Tsunamis In the open ocean, a tsunami may only have a wave height of a few feet.

62. As the wave approaches shallow water, it builds to heights that can reach greater than 100 feet.

63. Tides Tides are caused mainly by the gravitational pull of the moon.

64. Other Things That Influence Tides The gravitational pull of the sun. The distance of the sun and the moon from earth. Winds and other factors.

65. Tides tend to be high where the gravitational force between the earth and the moon are the strongest, along with the opposite side of the earth where the centrifugal force is strongest. Tides tend to be high where the gravitational force between the earth and the moon are the strongest, along with the opposite side of the earth where the centrifugal force is strongest.

66. Tidal Range Spring Tides Spring Tides Tides have the greatest range during spring tides. Tides have the greatest range during spring tides. This occurs during the new and full moons. This occurs during the new and full moons.

67. Tidal Range Neap Tides Tides have the least amount of range during neap tides. Tides have the least amount of range during neap tides. This occurs during the first and third quarters. This occurs during the first and third quarters.