 Ocean Waves Nov. 22, 2013 CGF3M

 Along the shores of oceans and lakes, waves break against the land, tearing it down in some places and building it up in others  Surface waves are movement at the water’s surface, due to wind  Wave height and length can be much greater in areas where the wind is able to blow for long distances

 As the wind moves along the surface of the water, it transfers some of the energy to the water itself  This causes the water molecules to move in a circular motion  In shallower water, the circular wave motion is squeezed into an elliptical orbit

Breaking Waves  When a wave approaches shore, the water becomes shallower and begins to influence wave behaviour  At a depth of ½ its wave length, the wave is said to “feel bottom” and the water movement at the wave’s base slows  As the wave continues towards shore, the water at the top moves forward at a faster rate  The wave height builds until the wave collapses (breaks) and moves up the shore  VIDEO: How does a wave break? VIDEO  FLASH DIAGRAM Flash Diagram 2 FLASH DIAGRAMFlash Diagram 2  There are 3 types of breaking waves:

1. Spilling Breakers  Found on gradually sloping coasts  Break slowly over a long distance  Carry deposits such as sand and build up beaches  Safest for swimming

2. Plunging Breakers  Found on steeper coasts  Create a hollow tube when they break  Plunge toward the base- can pick swimmers up and dump them onto shallow sandbanks or reefs with force  Can loosen and transport rocks and sediments, causing erosion  Preferred by more experienced surfers

3. Surging Breakers  Appear on steep coastlines or on rock platforms  Waves break right on the beach  Can knock swimmers out and pull them into deeper water

Wave Refraction  Rarely do waves approach shore straight on  As the water breaks and washes up on the beach, it does so on a diagonal  The backwash returns to the ocean in a straight line  This pattern, called beach drift, affects sediment transport, moving the particles in a zigzag pattern along the beach  Beach drift FLASH animationFLASH

Rip Current  If backwash becomes concentrated in a particular area at a particular time, the result is a rip current  this is a narrow but powerful current running perpendicular to the shore out to the ocean  Happens when the water finds an opening in a sandbar  Can be dangerous for swimmers  Experienced surfers use rip currents as a shortcut to get quickly back out to sea  Can also cause shoreline erosionVIDEOVIDEO

Surf’s Up?  Where is the closest place to Sioux Lookout to catch a wave?  Along the North Shore of Lake Superior- VIDEOVIDEO