Ocean Movement - Waves and Tides
Waves
A wave is the rhythmic rising and falling of ocean water due to wind or some other disturbing force. This illustration shows the anatomy of an ocean wave. No matter their size, all waves share similar characteristics. In this interactivity, click on each of the icons to learn more about the parts of a wave. Click the player button to begin.
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How do surfers find big waves to ride, and how do scientists study those big waves? Learn more about larger than average waves by viewing the video Science of Big Waves from eMediaVA℠. As you view the video, consider how these waves get to be so big and what other systems are involved. Would you be daring enough to ride one of these big waves?
A wave’s height, length, and period are determined by three major influences: wind speed, the length of time the wind has blown, and the fetch. The fetch is the distance the wind has blown over open water. The time and intensity of the wind over the water creates larger, faster moving waves of energy. Sometimes waves reach a critical point where they are so large compared to the depth of water below them that they collapse or break. You have seen this if you have even seen a wave crashing on a beach or a whitecap out in open water.
Tsunamis
One example of a disturbing force is an underwater earthquake or volcano that displaces a large amount of ocean water resulting in an enormous and treacherous wave called a tsunami. Tsunamis are interesting, intense, and rare wave events. The vast majority of waves are created by the wind. All types of waves transmit energy, rather than water, across the oceans. The stronger and longer the wind blows, or the larger the disturbing force, the larger the wave becomes.
Since a large amount of water is displaced in a tsunami, the wave has an increasingly long wavelength when compared to wind generated waves. These waves can go undetected until they reach shore and the front of the wave is slowed. This pushes the water into a tremendous height that washes onshore as a flood. While you might think that a tsunami is one large wave, these events are almost always a series of waves.
Tsunami warning systems only exist in the Pacific Ocean. Since the majority of tectonic activity occurs around the Pacific Ocean, in the Ring of Fire, a warning system is needed for the countries bordering this body of water. In this interactivity, click on each of the dots to learn key warning signs of an approaching tsunami. Click the player button to begin.
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Tides
A tide is a wave that is caused by gravity. A tide is the periodic rise and fall of the ocean water levels. Click the player button to begin. In this interactivity, use the NEXT and PREV buttons to learn more about tides, and how they are created by forces out in space. Click the player button to begin.
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Both the Sun and the Moon play a vital role in the tides. There are also different types of tides based on the positions of the Earth, Moon, and Sun. View Watching the Tides from eMediaVA℠ to learn how tides occur. In this video segment, you will also learn how a tidal station operates by remote sensing.
Tidal Patterns
Tidal Patterns of the World
Did you know there are different tidal patterns? Some areas receive only one high tide and one low tide per day. These areas are called diurnal tides. Some places, like Hampton Roads in Virginia, receive two high tides and two low tides per day. These are called semidiurnal tides. Some places receive two high tides and two low tides per day, but the water levels are all mixed up; thus they are called mixed tides. Mostly, the shape and depth of the ocean basins cause these tidal patterns. Look at the tidal patterns around the world as depicted in the image above.
Ocean Movement - Waves and Tides Review
Now that you have learned about waves and tides, practice what you have learned. In this non-graded activity, follow the directions on each question slide. Click the player button to get started.