Waves travel in and out of your life every day, even if you live nowhere near the ocean. Light travels in waves, as do other forms of energy that you can't see, like radio waves and sound waves.

But the waves you are probably most familiar with are water waves. As different as they are, all these waves have similar properties.

One interesting property of waves is that they transmit energy, but move matter very little distance during this process. For example, sound waves travel through the air without making wind, and water waves move through water without necessarily moving it forward.

If you look at a swimmer floating on the water out past where the waves break at the shore, you can see that even though waves move underneath him, the swimmer bobs up and down but stays pretty much in the same place.

If we could see the individual water particles beneath the wave, we would observe the same thing. The particles move in small circles as the wave passes, but don't travel very far from their starting points. They are affected by the passing energy, but they aren't pushed very far along with it.

Until the waves reach the shore, that is. In this lesson, you will explore the characteristics of water waves and also learn why tsunamis are unusual, but still follow the same basic rules as regular ocean waves. Let's look at some of these rules.

Here is a diagram of a simple wave. In it you can see that waves have high points, called crests, and low points, called troughs. The horizontal distance between two adjacent crests or troughs is called the wavelength. The vertical distance between the top of a crest and the bottom of the trough immediately in front of or behind it is called the wave height . Wavelength and height are just two of the ways that waves can differ from one another.

Now imagine you start a stopwatch when a trough passes and stop it when the next trough arrives, signaling that a complete wave has passed. The time it takes a complete wave to pass a point is the wave period.

Because waves can have different wavelengths, period alone doesn't tell us the speed or velocity of a wave. But we can use the wavelength and period to calculate wave speed using the equation:

Wavelength (L) / Wave Period (T) = Wave Speed

The two waves shown here have equal wave periods of 10 seconds, but they are traveling at different speeds because their wavelengths are so different. They also differ greatly in their wave heights.

The bottom wave has a wavelength three times larger than the top wave. Because the waves have the same wave period, we know that the bottom wave must be traveling three times faster.

Most waves in water are created by wind blowing across the surface. The stronger the wind and the longer it lasts, the higher the waves will be.

Storms at sea can make mighty waves this way, sometimes 15 meters, or 50 feet, high or even greater. Wind waves at sea often have wavelengths from 10 to several hundred meters, and average periods of 10 to 30 seconds.

But waves can also be created from below the ocean instead of from winds above. For example, the largest tsunami waves are created by earthquakes that can make many square kilometers of sea floor rise up. These waves are quite different from wind waves. They can have wavelengths of more than one hundred kilometers and periods of 10 to 60 minutes or even longer—off the chart by wind wave standards.

Now, let's further compare the wavelengths of wind waves and tsunami waves.

Tsunami wavelengths are commonly 100 to 500 kilometers. By contrast, the biggest wind waves might have wavelengths of around 100 to 200 meters. Now answer the following question, remembering that there are 1000 meters in a kilometer.

When most waves travel through the deep sea, they don't change very much along the way. Even if they travel thousands of kilometers from a distant storm, they may still have the same wave height and wavelength as they did when they were formed.

But when waves approach coastlines and begin to rush up onto the shore, they change dramatically. The rest of this lesson explores the difference between deep water and shallow water waves.

When wind creates waves at sea, these waves are called "deep water waves." Within a short distance from the surface, a deep water wave no longer affects the water underneath at all. The depth in which the wave is felt is equal to only one-half its wavelength. For this reason, even during a fierce storm the water is typically calm below about 150 meters. The bottom of the ocean is completely unaffected by deep-water waves.

When these same waves approach shore, however, they eventually become "shallow water waves." Once waves reach areas where the sea bottom is less than their wave depth, they begin a transformation. Shallow water waves are those in which the water depth is less than one-twentieth of their wavelength. Another way to say this is that the depth to wavelength ratio is less than 1/20. In the shallower water, the waves "feel" the bottom. That is, the water particles that orbit within them begin to interact with the bottom, which causes the wave properties to change. How might these changes affect the wave?

As waves enter shallower water, they do three things. First, they slow down as the water depth decreases; second, their wavelength decreases; and third, their wave height increases. Eventually, the wave height becomes so unstable that they often "break," sometimes causing the classic curl sought after by surfers.

You can think of this change as squeezing the wave, and because the wave loses only a little of its energy to friction, the wave has to grow higher when its wavelength decreases.

In addition to squeezing, as waves enter shallower water the circular paths of the water particles beneath them become flattened until the water is moving completely horizontally, rushing forward like a current. The bigger the wave, the stronger the current.

The ocean averages 4.3 kilometers deep, and reaches depths of around 10 kilometers only in the deepest trenches. Tsunami wavelengths are commonly 100 to 500 kilometers. So what type of wave is a tsunami in the deep sea?

Now, imagine what happens when a tsunami reaches the coast of a continent, and the depth of the sea goes from five kilometers to one meter, and even less. As you can imagine, a tsunami wave that is one meter high at sea can quickly become 30 meters high at the shore as the wave is "squeezed" and its height increases.

But because the wavelength remains relatively large, a tsunami almost never becomes steep enough to curl and break like suicidal surfers might wish. In fact, a tsunami wave may appear more like a fast rising tide as it approaches the shore.

As the water begins to move horizontally like a current at the shore, the tsunami wave slows down from over 800 km/h (500 mph) to something closer to 48 km/h (30 mph)—still fast enough to easily outrun people and push far inland over low-lying areas and up streams and rivers.