WAVES

Anatomy of a Wave Two main parts: 1. Crests 2. Troughs CREST: the highest point of a wave TROUGH: the lowest part of a wave

The top of a rise on a roller-caster track is similar to the crest of a wave, and the bottom of a dip in the track resembles the trough of a wave. The distance between the two adjacent wave crests or wave troughs is the wavelength. The vertical distance between the crest and the troughs is called the wave height. Figure 1 shows the parts of the waves.

Wave Formation and Movement Most waves form as wind blows across the water’s surface and transfers energy to the water. As the energy moves through the water, so do the waves. The water itself stays behind, rising and falling in circular movements *read slide Let’s look at figure 2 in your book to see an example of this. The floating bottle remains in the same spot as the waves travel from left to right. This circular motion gets smaller as the water depth increases, because wave energy decreases as the water depth increases. Wave energy only reaches a certain depth. Below that depth, the water is not affected by wave energy.

Specifics of Wave Movement Wavelength = Wave speed Wave period For any given wavelength, an increase in the wave period will decrease the wave speed and decrease in the wave period will increase the wave speed. Waves not only come in different sizes but also travel at different speeds. To calculate wave speed, scientists must know the wavelength and the wave period. The wave period is the time between the passage of two wave crests (or troughs) at a fixed point. Dividing the wavelength by wave period gives you wave speed. *Figure 3

Deep-Water Waves and Shallow-Water Waves Types of Waves Deep-Water Waves and Shallow-Water Waves Deep water waves—waves that move in water deeper than one-half their wavelength Shallow water waves—waves that reach water shallower than one-half their wavelength and begin to interact with the ocean floor *read slide *Figure 4 shows how deep-water waves become shallow-water waves as they move toward the shore As deep-water waves become shallow-water waves, the water particles slow down and build up. This change forces more water between the wave crests and increases wave height. Gravity eventually pulls the high wave crests down, which causes them to crash into the ocean floor as breakers. The area where waves first begin to tumble downward, or break, is called the breaker zone. Waves continue to break as they move from the breaker zone to the shore. The area between the breaker zone to the shore is called the surf.

SHORE CURRENTS AND LONGSHORE CURRENTS Types of Waves SHORE CURRENTS AND LONGSHORE CURRENTS Undertow—a subsurface current that is near shore and that pulls objects out to sea Longshore Current—a water current that travels near and parallel to the shoreline Shore Currents: when waves crash on the beach head-on, the water they moved through flows back to the ocean underneath new incoming waves. This movement of water, which carries sand, rock particles, and plankton away from the shore is called an undertow. Figure 5 illustrates the back-and-forth movement of water at the shore. Longshore Currents: When waves hit the shore at an angle, they cause water to move along the shore in a current called a longshore current. Longshore currents transport most of the sediment in beach environments. This movement of sand and other sediment both tears downs and builds up the coastline. Unfortunately, longshore currents also carry and spread trash and other types of pollution along the shore

Types of Waves Open-Ocean Waves Whitecaps are the bubbles in the crest Swells are rolling waves of a breaking wave. that move steadily across the ocean. Whitecaps are white, foaming waves with very steep crests that break in the open ocean before the waves get close to the shore. These waves usually form during stormy weather, and they are usually short-lived. Winds that are far away from the shore form waves called swells. Swells are rolling waves that move steadily across the ocean. Swells have longer wavelengths than whitecaps and can travel for thousands of kilometers.

Types of Waves TSUNAMIS Tsunami—a giant ocean wave that forms after a volcanic eruption, submarine earthquake, or landslide. Tsunamis are waves that form when a large volume of ocean water is suddenly moved up or down. This movement can be caused by underwater earthquakes, volcanic eruptions, landslides, underwater explosions, or the impact of a meteorite or comet. The majority of tsunamis occur in the Pacific Ocean because of the large number of earthquakes in that region. Figure 8 shows how an earthquake can generate a tsunami.

Tsunami

Types of Waves STORM SURGES Storm Surge—a local rise in sea level near the shore that is caused by strong winds from a storm, such as those from a hurricane. Winds from a storm surge by blowing water into a big pile under the storm. As the storm moves onto shore, so does the giant mass of water beneath it. Storm surges often disappear as quickly as they form, which makes them difficult to study. Storm surges contain a lot of energy and can reach about 8m in height. Their size and power often make them the most destructive part of a hurricane.