Chapter 21 Section 2

Ocean Waves Objectives Describe the formation of waves and the factors that affect the wave size Explain how waves interact with the coastline Identify the cause of destructive ocean waves

Ocean Waves A wave is a periodic disturbance in a solid, liquid, or gas as energy is transmitted through the medium A wave has two basic parts- a crest and a trough Wave height Wave length(2 trough's) Wave period(2 crests)

Ocean Waves Pressure differences from uneven heating on Earth causes air to move Friction between moving air and water causes ripples in ocean water The longer the wind blows from a given direction the more energy is transferred and the bigger a wave can become

Ocean Waves As the energy of a wave moves from water molecule to water molecule in the direction of the wave, the water itself moves very little The water moves in a circular motion and as depth increases the circular energy of the wave decreases Below a depth of about one-half the wave length there is almost no circular motion of water

Ocean Waves Three factors determine the size of a wave The speed of the wind The length of time the wind blows The fetch (the distance that the wind can blow across open water)

Ocean Waves Strong gusty winds produce choppy water that has waves of various heights, lengths, and from different directions

Ocean Waves When wind blows the crest of a wave off, whitecaps form Whitecaps reflect incoming solar radiation and may affect climate

Ocean Waves In shallow water the bottom of the wave touches the ocean floor This happens when the depth is about half the wave length The friction slows the bottom of the wave and causes the wave to break These are called breakers

Ocean Waves The size and force of breakers are determined by the size of the original wave, the wavelength, and the steepness of the ocean floor close to the coastline If the coastline is steep, the wave height increases rapidly and the wave breaks with great force If gentle the wave has a gentle rolling break

Ocean Waves Most waves approach the coastline at an angle, as the wave reaches shallow water it bends Refraction is the process by which ocean waves bend towards the coastline as they approach shallow water Shallow water slows, deeper water maintains the energy

Ocean Waves Water carried unto a beach by breaking waves is pulled back into deeper water by gravity This motion is called an undertow (these are usually not strong)

Ocean Waves Rip currents form when water from large breakers return to the ocean through channels that cut through underwater sandbars that are parallel to the beach These can quickly carry a swimmer out to sea

Ocean Waves The most destructive waves in the ocean are not powered by wind Tsunamis are giant seismic waves which are usually caused by earthquakes on the ocean floor, but may be caused by underwater landslides, or volcanic eruptions

Ocean Waves Tsunamis have a great amount of energy and can cause massive destruction because of the wave length which can be as long as 500 km As the tsunamis reaches the shore the height greatly increases and the wave lows, these can reach 30- 40 m in height Maybe signaled by a sudden pull back of the shoreline