Why do barreling waves spit?

For those watching from the beach, a spitting wave may not catch their attention. But for surfers, the moment a wave spits is both anticipated and celebrated.

It's a peculiar sixth sense developed over time, honed by analyzing countless breaking waves.

The spitting of a wave is more than just an oceanic spectacle; it's an intricate dance of physics and nature, a testament to the power and dynamism of the ocean.

It reminds us that there's more to waves than meets the eye, a complex undercurrent of forces at play beneath the surf's mesmerizing appeal.

Understanding the mechanics behind the spitting waves allows us to appreciate the thrill and joy they provide surfers and the complex, beautiful, and wonderfully chaotic nature of our oceans.

Let's explore the mystery of the cannon waves that fire bullets of mist and air.

What's in a Spit?

"Spit" is the term adopted by surfers to describe the explosive gust of air and spray that fires from the mouth of a breaking barrel wave.

Like a bottled-up volcano that releases its pent-up energy in an explosive eruption, spitting waves also release an air-and-spray mix out the open end of the tube.

But what causes this striking phenomenon?

Understanding the Mechanics

Like many natural phenomena, spitting waves are a result of physics at play. Here's a breakdown:

1. The wave breaks and barrels: As a wave breaks, the falling lip creates a mixture of foam and spray, which gets trapped in the wave's hollow, barrel-like interior;
2. The pressure builds up: This mixture accumulates as the wave barrels down its path, creating a high-pressure environment. The air and spray mixture is seeking an escape route, just like the carbon dioxide in a vigorously shaken champagne bottle;
3. The path of least resistance: As pressure mounts, the air and spray mixture are expelled through the open end of the wave, which is the path of least resistance, causing the roller to "spit."

In other words, spitting waves are like compressed chambers that release pressure through one of their open ends.

The phenomenon is more common at surf breaks with predominantly hollow and plunging waves, like Pipeline, Teahupoo, Jaws, Puerto Escondido, or Supertubos.

Selective Spitting: Not All Waves Are Alike

Interestingly, not all waves spit. Only those waves that break swiftly and maintain an open barrel have the right conditions for spitting.

The swiftness of the break and the wave's open barrel work together to build up the pressure inside the barrel abruptly.

It's this pressure that forces the air and spray out, resulting in a spit.

Contrary to popular belief, wave size is not a critical factor for spitting.

Even small waves, around a foot high, can spit as long as the pressure within the barrel gets high enough.

The abruptness and speed of the breaking event also increase the spit factor.

The Foam Ball Phenomenon

In other types of waves that break consistently but not as swiftly, a different phenomenon can occur - the creation of a "foam ball."

Here, the mixture of air and saltwater isn't expelled violently but instead gets pushed along with the peeling wave, creating a rolling foam ball effect, also referred to as "gargling."

While some of the whitewater produced by the breaking wave rolls toward the beach, part stays at the tube's entrance, tumbling like a wheel.

It's a mix of water and air and often a tricky place for surfers to be in.