With summertime quickly coming upon us in the Northeast, thoughts will soon turn toward the beach. There are many beach and ocean activities we will be starting to prepare for—boating, swimming and surfing among them—and all have an important factor to think about: the mighty (or maybe not so mighty ) ocean wave.
Let’s take a few moments and see what an ocean wave is made of, and how it comes about.
First, what do mean by “wave”? Well, an ocean wave is actually caused by the wind. High winds, like in storms, cause big waves; little winds cause small waves. No wind, no wave—mostly, there are a few other causes. Basically, however, it is simply the force of the wind dragging the surface of the ocean’s water forward. Other causes are boats and tsunamis. A wave caused by the movement of a boat is called a wake. Tsunamis are powerful waves caused by underwater earthquakes.
Like all physical waves, light for instance, ocean waves have a few basic parts. The peak, or highest point in the wave, is called the crest. The lowest point in the wave is the trough. The distance between two waves (crest to crest or trough to trough) is called the wavelength. Finally, there is frequency and period, which are not the same thing. Frequency is a measure of how often something happens. In our case let’s say we want to know how often a wave hits the beach in one minute. If there are 10 waves hitting the beach every 60 seconds, then the frequency would be 10 waves/minute. Period is the length of time it takes for the wave to complete a cycle—say, the time from when the wave first forms till it arrives on the beach. If this is 1hour, then the wave’s period would be 1 hour. Of course, frequency and period don’t normally come into play when talking about ocean waves.
It is interesting to note that waves actually travel in groups called wave trains. This is simply a series of waves traveling in the same direction and spaced at regular intervals, i.e. they all have the same wavelength.
These are the basic characteristics of all waves, whether it is light or ocean waves, which we shall now take a closer look at.
Ocean waves come in many forms, such as breakers, wakes, tsunamis, and swells.
Breakers are formed as the wave reaches shore and the height of the wave surpasses the depth of the water; the wave just topples over as it becomes top heavy. There are three types of breakers: spilling, plunging, and surging. The type of breaker which forms depends on the slope of the shore.
Spilling breakers form when shallow waves come up on a gentle slope. In periods of high wave activity, these waves tend to pull water towards the beach. However in low wave activity, water is pulled away from the beach, causing a rip tide.
Next, plunging breakers. These are steep waves over moderate slopes. This could be a dangerous wave for swimmers due to backwash from the previous wave.
The last type of breaker is the surging breaker. This wave forms when the slope has a steeper angle than the wave. Upon breaking, the wave forms a lot of foam.
Wakes are generally not caused by wind, but by boats. The bigger the boat, the bigger the wake. The wave train left behind as the boat moves through the water is the wake. On the TV show “Mythbusters” Tory Bellucci actually water-skied in the wake of a cruise ship.
A tsunami, from the Japanese term meaning “harbor wave” is probably the most feared kind of wave. These are powerful waves caused by underwater earthquakes or landslides, generally in the Pacific Ocean, namely in the Ring of Fire, where many of the earth’s continental plates and active volcanoes are. Tsunamis are very fast moving waves which could hit the shore at 50 mph, causing much damage in life and property. They are very common in Japan, with nearly 200 events on record.
Not all tsunamis are caused this way. There is something called a meteotsunami, which are caused by tropical depressions in a storm. These waves can cause the tide to go much higher than normal. Both types of tsunamis look exactly the same from the shore, the only difference is the cause.
Finally, there are swells. Swells form in the open ocean after a lot of the energy from the wave generating area has dissipated. These are smooth, rounded waves which can be small ripples or large, flat crested waves.
Ocean waves are very fascinating, complex things. They are the cause of great destruction, like with tsunamis, but are also the agent of great fun and they deserve respect. As we spend time on the beach this summer, running and jumping in the waves, let’s recognize the power that surrounds us.