Nazaré's 80-foot Waves Intimidate Even Pro Big-Wave Surfers

Ocean waves occur when something disturbs the water. In a swimming pool, it might be when the neighborhood bully does a massive cannonball off the high dive. On the open water, waves might appear as wake from a speedboat driven by a guy having a midlife crisis.

In a not-so-funny scenario, cascading waves called tsunamis come from underwater earthquakes that literally shake the ocean. However, most of the time, ocean waves come from good old wind. That's right, the waves crashing on the beach were started by gusts of wind somewhere offshore.

But it takes more than just wind to craft the truly massive waves surfed by the likes of Maya Gabeira, Sebastian Steudtner and Garrett McNamara at Nazaré. One of the other factors behind those monster waves is the layout of the ocean floor.

Your standard, everyday wave breaks on the beach because water has run out of real estate. As the moving water approaches shore, emerging land pushes that water upward, and it rises into a curl before breaking under the downward force of gravity. The same thing happens at Nazaré, only on a much more dramatic scale. That's because this stretch of coastline is no ordinary beach.

The big wave events at Nazaré's Praia do Norte owe to four main factors:

At first glance, Nazaré looks like your typical European beach with a sandy shore and (for much of the year) relatively placid waters. When conditions are calm offshore, you can actually have a very normal beach day at Nazaré.

Nazaré Canyon

But just off the coast, the ocean floor is anything but normal. It's home to the Nazaré Canyon, an underwater trench that is 140 miles (230 kilometers) long and up to 16,000 feet (4,877 meters) deep. And it's this underwater canyon that turns normal waves into monsters.

When inbound waves speed toward the Portuguese coast, Nazaré Canyon splits them in two. Some of the water dives into the canyon while still propelling forward. The rest of the water pushes forward, creating the same kind of wave that happens anywhere a continent meets the sea.

Nazaré Canyon ends right by Nazaré's Praia do Norte (North Beach). At this point, the canyon's inbound water gets pushed upward as it hurtles toward the Portuguese shore. This wall of water combines with the surface-level wave. The two stack on top of each other, creating a double wave that is especially large.

Constructive Interference

As Edward Santilli, a physics professor at Thomas Jefferson University, explains it: "Most of the time, waves interact randomly and produce nothing special. But if they meet in just the right way, they can either annihilate each other (destructive interference) or join forces to make a new larger wave (constructive interference)."

Nazaré is a great example of constructive interference. It's the offshore canyon that makes constructive interference such a potent force at Nazaré's Praia do Norte.

"Shallow water waves travel slower than deep water waves," explains Santilli. "Waves tend to slow down as they approach the shore. But this means that the wave's front may be in shallower water than its middle or back, causing the trailing parts of the wave to catch up to the front. As this happens, the wave becomes narrower, but all of that water needs to go somewhere, so it goes up — the wave becomes taller."

There's one more factor that amplifies Nazaré's waves, and that is a current that runs along the local coastline. Due to the nature of the offshore canyon, the giant waves in Nazaré come from the southwest and are effectively headed north and east when they break at the Praia do Norte.

But in ideal big-wave conditions, Nazaré experiences mild winds from the northwest that push water southward along the shore, and this water creates a bit of a barrier. As mega-waves roll in from the southwest, they hit this current running from north to south.

The bigger, stronger waves from the southwest vault above the shoreline current (think about how your car pops up when you go over a speed bump at high velocity). This final vaulting element gives Nazaré's waves their legendary height.

If you go back and look at the list of world record-setting waves, you'll notice another trend: They all were surfed during the late fall and early winter. This owes to the fact that fall and winter are the prime seasons for big storms in the North Atlantic Ocean.

Remember that wind is the genesis for nearly all ocean waves. However, for large waves to form, these wind events have to happen well offshore.

The Atlantic Ocean's biggest winter storms take place hundreds of miles from the coast of Portugal, yet over time they produce swells that push eastward toward the Portuguese coast at ever-increasing speeds. When water passes over Nazaré Canyon, it speeds up even more because there's nothing in the canyon to dissipate the wave's energy.

While that's going on out at sea, the primo surfing days also feature a mild wind out of the northwest that pushes a stream of water southward along the Nazaré coastline. That creates the final barrier of water that produces a significant shoaling effect, lifting the inbound waves even higher than they'd normally be.

And this leads us to one final point about the ideal wave conditions at Nazaré. For the waves to reach maximum height, the winter storms should not be occurring right at the beach. They should be far, far out at sea, while Praia do Norte experiences a mild northwest wind.

If you look at photos and videos from record-breaking surf days, you'll notice that there isn't a raging storm overhead. In fact, if the storm were directly above Nazaré, it would mess up the ideal surf conditions.