Waves in the Sea An ocean wave is a rhythmic rise and fall of the water’s surface. Most commonly produced by wind. Also by undersea earthquakes and the effects of the moon in producing tides. The height of a wind formed wave depends on: The length of time that the wind blows. Fetch: the length of open water over which the wind blows Choppy seas form from gusts that change direction. Swells are regular intervals of smooth waves.

Features of Water Waves Wave height is the difference between its high point (crest) and its low point (trough). Wavelength is the distance from one crest to the next. On average the wavelength is 20-30 times its height.

The period of a wave is the time it takes one wavelength to pass a given point. Most ocean waves have a period that ranges from 2s to 10s. Speed=wavelength/period Find the speed of a wave 30m long with a period of 5 sec. 6 m/s

Tsunamis Waves with periods ranging from 5-60 minutes are called long waves. Tsunamis are caused by underwater earthquakes. A tsunami may have a wavelength of 150 km and a period of 12 minutes, giving it a speed of 12.5 km/min, or 748 km/h. Such speed can cause immense damage. http://videos.howstuffworks.com/science-channel/7401-tsunami-video.htm

Water is not carried along with the motion of a wave. Each water particle moves in place in a circular motion. Water particles bump into the next one and passes the energy along, passing the energy through the water. Wave motion also takes place below the surface, moving water molecules in smaller and smaller circles.

Most waves approach a shoreline at an angle. The waves tend to bend as they hit the shoreline, called refraction. The end of the wave closest to shore scrapes the bottom first and slows down, The end in the deep water continues at normal speed and the wave approaches nearly parallel to the shore. This reduces erosion in shallow bay. Headlands erode faster than bays because the wave energy gets concentrated at headlands

Breakers Waves approach the shoreline smoothly until they reach water so shallow that they touch the bottom. Water depth is usually about half the wavelength The lower part of the wave slows down The upper part of the wave moves ahead, until there is not enough water to support the wave The crest falls over and breaks into surf. The line of breakers is where the crests break Surf is a powerful agent of erosion.

Shoreline Currents Waves may come from any direction, most strike the shore at an angle. The motion of water up the beach is swash, it moves sand up the beach at an angle. Most water runs back down the beach in a backwash current, which drags sand straight back to the sea. A very strong backwash is an undertow. A longshore current forms beyond the breakers that runs almost parallel to shore. Rip currents are strong surface currents that flows away from the beach.