Three different things can make waves. The wind, moon, and earthquakes can all make waves.
Wind Waves – Ocean Surface Waves
The waves that bounce your boat or your fishing bobbin up and down are created by the wind. A wave seems to move lots of water along in front of it. But it doesn’t. It only seems to move water. The water is not pushed forward by the wind only the shape of the water is pushed. Remember your fishing bobbin? It always stays where it is at, doesn’t it?
This is hard to understand. To see waves at work, try this experiment. Tie a piece of rope to a pole or some other object that doesn’t move. Take the other end of the rope and walk away so that you pull the rope out. Don’t pull it completely straight – let it fall in a curve.
Wiggle the rope. You will see a wave shape form and move from you to the pole. The shape of the wave moved but the rope stayed where it is, one end stays tied to the tree, the other end stays in your hand.
When a wave reaches the shore, it breaks. When the bottom of the wave touches the ground it stops while the top keeps moving until it falls over onto the beach.
Moon Waves – Tidal Waves
Tidal waves aren’t really waves. They are ocean surface waves (wind waves) that move higher onto the shore because of the moon. The moon changes where and how we see the waves. The moon has gravity just like the earth. Gravity is what helps you stay on the earth and not float up into space. The moon’s gravity pulls on the earth’s water. When the moon is close to one side of the earth, it pulls the water in the ocean towards it.
When the water moves toward the moon, the ocean gets fuller on that side and move higher up on the beach bringing the waves closer to you. This is called high tide. When the water moves towards one part of the ocean, another part gets emptier and the waves don’t come as close to the shore. This is called low tide.
On the side of the earth opposite the moon, it is high tide too. This is because the spinning of the earth causes the water to rush towards the outside of the earth. Because of this there are two high tides every day and two low tides every day.
Earthquake Waves - Tsunamis
There are special waves that are not made by the wind and aren’t affected by the moon. They are called tsunamis. Tsunamis are made when there is an earthquake under the ocean. (Other things can make tsunamis too, such as a volcanic eruption, a sub-marine rockslide, or a large impact in the water from a asteroid, meteor, or a non-marine rockslide). When the earth slides and crashes together under the water, it causes huge waves to be made that rush towards the shore. These waves destroy everything that they touch because they are so big and full of so much water.
Make a tsunami in your bathtub. Sit in the tub. Put your legs straight out in front of you pull them apart and then move them together as quickly as you can. Watch how the water moves and makes big waves. If you make a big enough tsunami it will splash out of the tub onto the floor. Clean the bathroom for your Mom if you make a mess. Maybe put towels on the floor before your tsunami experiment.
