The Science Behind Surfing: How Waves Form at Black’s Beach

For San Diego surfers, there are plenty of surf spots that don’t require a long hike down steep cliffs that may or may not involve accidentally bumping into nudists.

Yet scores of surfers every day are drawn to , smitten by the long, powerful waves that are typically two or three feet bigger than other San Diego breaks (needless to say, advanced surfers only).

Owen Davis, a 38-year-old surfer who was at his car gearing up for a session near the , offered a sentiment that seems to be shared by many San Diego surfers.

“I try and surf as much as I can,” Davis said. “The waves are really consistent. It might be the best spot in San Diego.”

With so many beach breaks in San Diego, why are the waves typically bigger, heavier and better shaped at Black’s Beach?

First, it’s important to understand how waves form in general.

Strong winds in storms, often as far away as the Gulf of Alaska during fall and winter, create long-period waves (swell). These swells eventually reach the coast of San Diego. 

Waves change as swells move from deeper water to shallower water. As is the case with spots like or Teahupoo, waves can become significantly larger when swells move rapidly from really deep water to really shallow water.

Conventional wisdom says that a deepwater submarine canyon off Black's Beach, a rare geographical feature in San Diego, is a magnet for approaching waves. Many websites state that swells move from the deepwater submarine canyon and quickly approach the beach, increasing wave heights. 

But according to Kai Hally-Rosendahl, a graduate student of physical oceanography at , that’s not necessarily what’s occurring at Black’s.

“There’s a pretty common misconception about how the submarine canyon influences the surf,” Hally-Rosendahl said.

If the submarine canyon’s role is misunderstood, what’s happening then?

Those “peaky” waves that surfers rave about at Black’s are actually the result of waves traveling through the submarine canyon and being redirected.

Keep in mind that the submarine canyon system is made up of two branches: the Scripps Canyon and the La Jolla Canyon (see map).

“The Scripps Canyon runs roughly perpendicular to the shore just south of Black’s Beach, and it’s responsible for the small waves shoreward of the canyon head, and the larger waves north of the canyon at Black’s,” Hally-Rosendahl said. “Waves travel faster in deeper water and slower in shallower water. So if you look at a wave that’s traveling over the edge of the Scripps Canyon, the part of the wave in the deeper water travels faster, and the part in the shallower water travels slower. The end result is that the waves actually bend northward away from the canyon; this process is called refraction.”

Think of it this way: Winter waves approach Black’s Beach traveling southeastward. Part of the waves hit the Scripps Canyon. These waves travel along the canyon, and instead of continuing southeastward, they bend to the north and travel northeastward towards Black’s Beach. When the two different parts of the waves crisscross and combine energies, “peaky” waves are created (see second picture for a visualization of the phenomenon).

“It’s not that the canyon directly amplifies waves,” Hally-Rosendahl said. “What the canyon does is change the direction of some of the waves. And then it’s the constructive interaction between the waves whose direction has been changed and the waves whose direction hasn’t been changed that creates the larger, well-peaked waves at Black’s.”

Another key to Black’s year-round consistency is the direction of the beach. Due to the angle it faces on the coastline, Black’s favors a west or northwest swell, but it’s also able to receive a southwest swell.

While the Scripps Canyon and slope of the beach are the constants that make Black’s a great spot, variables to consider, like any surfing spot, include tide, wind, the state of the sand bars and swell period.

If conditions fall into place? Enjoy competing for barrels with hordes of other San Diego surfers. And take solace in the fact that La Jolla is blessed with not only great waves, but scientists who can explain them.