The Nazaré North Canyon is a underwater canyon and the main responsible for the generation of the big waves at Praia do Norte - Nazaré - Portugal, in conjunction with other nature elements, sometimes in a favorable way, like the big Atlantic Ocean swells, the collision of two waves directions, the wind, the tides, the sea currents and sea floor.
The Nazaré North Canyon is one of the largest submarine canyons in the World, a giant hole in the bottom of the sea! It is 227km long and 5 Km maximum depth, with several steep slopes.
The origin of the Canyon is still shrouded in mystery, because it belongs to a complex geological area. However, researchers believe that it might be related with the Nazaré fault, a fracture zone with movements that can cause earthquakes.
Since old times, the surrounding area of Nazaré has always been feared by fishermen due to the strong sea. Several shipwrecks occurred and even a German submarine of the World War II that was sunk in the depths of the Nazaré canyon - event reported by elderly people who saw. The cause of this hazard zone is below the water... right in the bottom of the ocean!
Right in front of Nazaré beach, often serene and inviting for a swim, there is a sleeping giant! When he wakes up, he shoots waves of 30 meters (almost a 100ft)!
It has long been known that something is different in North Beach! On special days, with the combination of several elements of nature, as if it were a conspiracy, the magic happens!
In the following video, WSL shows the phenomenon of generating large waves in the Nazaré canyon very well (segment from "2018 Nazare Tow in sessions" video):
Large offshore storms in the Atlantic Ocean can cause strong swells when they have a high period and a Northwest (NW) direction,
the Nazaré Canyon divides the swell into two distinct parts: a swell funneled by the canyon channel and another swell beside the canyon.
The swell that crosses the canyon channel maintains its power and speed thanks to the great depth and changes its direction to be more perpendicular to the coast, due to the geography of the channel itself.
When these two swells meet again closer to shore, they collide, causing a constructive triangle interaction
which considerably amplifies the final size of the waves.
In addition, the current coming from the beach in the opposite direction adds a few more meters to the waves, and the wind interaction can also be constructive with a Northeast (NE) wind.
These factors combined result in much bigger and more powerful waves than in other areas of the Portuguese coast even a few hundred meters from Praia do Norte.
In the following video you can clearly see the shock of the two waves and the creation of the famous triangle wave:
In summary, for the giant wave to be born, it is important to guarantee some conditions:
Nazaré North Canyon can amplify up to 3 times the size of the predicted wave for the Nazaré area.
Check here the waves forecast for the next days at Nazaré.
The most important factor is the occurrence of strong storms in the North Atlantic, in the autumn/winter, which bring considerable swell to the canyon.
For a more detailed technical analysis of how large waves are formed, consult this page from Instituto Hidrográfico (in Portuguese).
Also check the following videos that explain how giant waves form (in Portuguese). The first is from Instituto Hidrográfico and the second from SNIMar:
Check also the Records and Brief history of Nazaré waves.