eli5: Waves come in at New York, and waves come in at Europe. What happens in the middle?



eli5: Waves come in at New York, and waves come in at Europe. What happens in the middle?

In: Earth Science

There are waves in the middle.

Waves “come in” because the water is getting shallower as you get close to the beach/coast. In the middle, they just go up and down.

Giant waves in between. They are harder to notice because the whole ocean is moving/they are more underwater.

Imagine the earth is a cup of water, and if you move it around, the water goes from one side to the other, you don’t really notice the peak of the water moving in the middle but you do when it hits the sides.

Now imagine the cup is a ball (Earth) instead and gravity is holding the water in at all angles, give it a spin and that’s what we got.

The waves pass through each other in the middle. When the waves hit a shoreline some of that energy gets reflected and begins moving in the opposite direction, back towards the other shoreline on the opposite continent. Most waves aren’t perfectly reflected though so they end up moving at angles to each other which allows them to move past one another without too much energy loss. And some waves moving towards the same shoreline will meet up and add together. The moon also adds energy by constantly pulling on the water as it gets closer and farther over the night cycle.

You can try the experiment yourself in the bathtub, stay as still as you can and wait for the bathwater to calm to a still state, then just push your hand through the water towards the back of the bathtub and watch the wave bounce off the back. It will then travel towards the front and then bounce towards the back again. Here your hand is adding energy like the moon and you can start to get predictable tides if you add waves at a constant rate.

More waves. Wind blows the water to create most surface level waves. This happens in deep water as well.

Most of all the waves are cause by wind. The friction between the wind and the water causes waves to form. You can verify this by blowing over a pan of water. Especcially in open water, waves can build up energy, becoming very long in wavelength and high in amplitude. Near shores it gets less deep, this forces the waves to become of shorter wavelength and slower. Because of this, the waves always turn towards the shores, and not in the original wind direction.

Also, I am surprised by the amount of bad answers i read in this thread. Many people apparently overestimate their knowledge on this.


Waves are not current. Waves are really just pulses of energy and can pass through each other. They are mostly generated by wind. They can reflect and refract like light.

In the middle of the ocean, most of the waves travel in the direction of the wind. When the wind changes direction, the already generated waves will keep traveling in the same direction (and will eventually dissipate) and it will start generating waves in a different direction. As a result, the open ocean has sets of waves traveling in several directions. Form the perspective of a small boat, there will be a main swell and then “under” it, you can usually notice secondary swells traveling in different directions.

Waves go slower in shallower water. Like light entering a lens, this causes the waves to turn towards shore. As a result, any waves traveling at an angle towards the beach will get steered straight towards it.

Wind and waves. Wind blowing across the ocean creates waves that move in the direction of the wind. These waves can travel across entire oceans. So the ocean is full of waves , often moving in different directions. When waves meet, they just pass through each other and continue on their way. So there can be one group of waves moving toward New York and another group of waves heading towards Portugal.

If you go to [windy.com](https://www.windy.com/?43.197,-44.297,4) you can see all the different wind patterns. You can zoom in and out using the + and – buttons in the top right, click and drag to check out other areas, and hit the play button on the bottom left to see the wind forecast play out. Spain and Portugal are going to have some great surf in a few days from that cyclonic system heading towards their coasts.

Waves tend to go in the direction of the prevailing wind. The waves don’t actually move, the energy spins in a circular motion. The energy goes down in front of the wave and up in the tail of the wave.

The the faster the wind blows over the fetch ( distance and duration the wind blowing the same direction), the more energy builds up.

The amplitude of the waves increase as the depth of the water decrease because the circling energy starts pushing against the bottom.

When the depth of the water reaches 1.4x the height of the swell, the waves breaks.

Swells are measure by period in seconds and amplitude ( ft in USA ). The the larger the period the period the faster the wave energy moves, resulting in a bigger breaking wave.

The more quickly the depth of the water changes the more powerful the wave break. Look up the heavy deep water Reef breaks ( Jaws or Pipeline ) vs mushy beach break in the Gulf of Mexico.

A seismic wave (tsunami ) is very low amplitude but travels almost 2x as fast as a regular wave.


A good way to think about it is if a tsunami was approaching. The tsunami is barely noticeable out in open water below you, but closer to shore you get, depth is lower so the only place the wave has to go is UP.


I dunno, I find all these explanations quite weird for a 5 year old.

The water is moving the same anywhere, put a wall /coast anywhere in the ocean and you’ll get the same thing.

Imagine a pool, water “waves” up on the sides, but it also waves up against you, just because you’re in the way

On a related note, can you go under a wave? Like in a sub or scuba diving? How far down do they go?