Take a second to quietly clear your mind.  

Now, picture yourself on a shimmering, sunny beach. Smell the salty wind, feel the sand between your toes, and listen to the gentle and repetitive crashing of blue waves. 

Maybe you imagine yourself running into the sea and swimming. Or just sitting and admiring the great blue sea. Whatever you picture yourself doing, observe the waves of the ocean and their swelling beauty. 

Now, return to the present moment, still listening to the quiet crashing of the waves.

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The beautiful and powerful oceans, which cover two-thirds of the Earth, seem to have a life of their own. 

We can see this especially in their waves, which can range anywhere from tiny beach crashers to massive tsunamis. But where do they come from? What is the force that mysteriously powers them?

Whether the ocean is your favorite destination or you’ve never been, I invite you to keep reading this second part of the Science Behind the Everyday series, where we’ll be learning about what causes the oceans’ magnificent, strange, and sometimes terrifying waves. 

Windy origins

To understand how waves form, you can perform a little experiment. First, get a bowl and fill it with water. Then, gently blow over the bowl, diagonal into the water. Now, blow harder. What do you notice? 

You actually just created waves - and this is also how waves are made in the ocean! Well, not by someone blowing air, but by the wind, which travels all around the Earth and blows on the ocean. 

From ripples to swells

In that mini-experiment you did, you might have noticed that the waves all looked the same size. However, in the open ocean, waves form a bit differently. This is because the ocean is extremely large. 

First, the wind blows against the ocean’s surface. This creates capillary ripples, tiny waves only a few centimeters high. 

Next, as the wind continues to blow, these capillary ripples eventually grow past 10 centimeters, becoming what are called gravity waves. 

Then, these gravity waves grow larger, separating into swells, or groups that are similar in size and direction. These swells travel over the open ocean towards beaches all over the world!

So, in short, the wind causes most of the waves on this planet (except for some like tidal waves and tsunamis). 

Energy

It’s really easy to think that the waves you see are made up of the same water from thousands of miles away. However, when waves travel across the ocean, it isn’t the water that moves - it's an invisible thing called energy that does. This energy starts in the wind and then travels through the water, making it move up and down in a wavelike motion. 

Different waves

If you’ve been to the beach or seen waves on the internet, you probably have noticed that waves come in different sizes. Why does this happen? Well, how big a wave is depends on:

1. The speed of the wind → faster wind means bigger waves

2. How long the wind blows for → more wind means bigger waves

3. How big the patch of water the wind blows over is (this patch is called the fetch) → a larger fetch equals larger waves

4. How deep the water is → deeper water means bigger waves

This is why bigger waves happen in storms, where the wind is really powerful. Sometimes, the wind can create humongous waves called rogue waves. These are a fisherman’s worst nightmare!

Breaking 

But, what about when waves crash on the beach? How does this happen, and why do waves do this in different ways? 

Well, put simply, when a wave approaches a beach, the bottom part rubs against the ocean floor. Friction causes the bottom part to slow down. But not the top part - the top part of the wave moves forward faster than the bottom part and crashes over onto the beach. 

In fact, the type of beach causes different types of waves. Beaches that slope gradually create spilling waves, which are pretty peaceful. Steep beaches create plunging waves, which are what surfers love to ride. And really steep beaches cause surging waves, which don’t spill over the top. 

Spilling waves             Plunging waves                  Surging waves

Tidal waves 

Despite what a lot of people think, tidal waves aren’t ginormous or terrifying at all. In fact, they are quite the opposite - they are small and peaceful. These tiny waves are actually caused by the sun and the moon instead of the wind. This is because of the sun’s and moon’s gravitational forces. This invisible force pulls on the Earth, keeping it moving around the sun and also keeping the moon moving around the Earth. These gravitational forces also tug on the Earth’s oceans, causing the water to move and thus causing tidal waves. But, because these oceans are so huge, and these forces aren’t extremely strong, tidal waves aren’t that big.

Tsunamis

Tsunamis, on the other hand, are massive, terrifying, and extremely dangerous waves. Like tidal waves, they aren’t created by the wind. What causes tsunamis are underwater earthquakes. When these happen, a big chunk of the ocean floor shifts upwards, pushing up a lot of water. This wave doesn’t look like anything when out far away in the open ocean. But, as it approaches a beach it grows and grows until it is a towering wall of water! 

And not just earthquakes can cause tsunamis. So can meteorites and volcanic explosions. In fact, the meteorite that wiped out the dinosaurs 65 million years ago might have created a 1000 foot high tsunami! But, the biggest recorded tsunami occurred in Lituya Bay in Alaska in 1958. Triggered by a magnitude 7.8 earthquake, a massive rockslide released 90 million tons of Earth into Lituya Bay, causing tsunami waves up to 1720 feet high!