Nazaré, a coastal town in Portugal, has gained global recognition for its exceptionally large waves, attracting surfers and spectators from around the world. These towering walls of water are not random occurrences but rather the result of a unique interplay of geological features and oceanic dynamics.
The Deep Nazare Canyon
A primary factor contributing to Nazaré’s enormous waves is the presence of the Nazaré Canyon, an immense underwater gorge situated just off the coast. This submarine canyon is the largest in Europe, extending for over 200 kilometers into the Atlantic Ocean. Its depths plunge significantly, reaching up to 5,000 meters in some areas. The canyon acts as an underwater channel, funnelling incoming ocean swells directly towards the shore. Its unique V-shaped profile in the upper sections gradually transitions to a U-shape further offshore, allowing waves to travel at greater speeds without losing energy to friction with the seafloor.
Wave Amplification Mechanics
The Nazaré Canyon significantly amplifies waves through several physical processes as swells approach the coast. One process is wave refraction, where waves bend as they encounter varying water depths. As swells travel over the deep canyon, they maintain their speed, while waves moving over the shallower continental shelf alongside the canyon slow down. This differential speed causes the wave fronts to bend and effectively funnel towards the canyon’s shallower termination near the shore.
Another process involved is shoaling, which occurs when waves move from deep water into progressively shallower areas. As the seafloor rises, the waves slow down, and their energy becomes compressed into a smaller water column. This compression causes the wave height to increase, transforming broad ocean swells into taller, steeper waves. This effect is particularly pronounced as the fast-moving canyon waves encounter the rapidly shoaling waters near Nazaré’s Praia do Norte.
The most significant amplification comes from constructive interference, where waves that have travelled through the canyon converge with waves that have moved over the continental shelf. These two distinct wave trains, having travelled at different speeds and undergone different transformations, meet at a specific point near Nazaré. Their crests align and combine their energy, resulting in a single, much larger wave peak. This convergence creates the towering waves that characterize Nazaré’s surf.
Distant Ocean Swell Origins
While the Nazaré Canyon and local bathymetry are responsible for amplifying waves, the initial energy for these waves originates far out in the Atlantic. Powerful storms in the North Atlantic Ocean are the primary generators of the large, long-period swells that travel towards the Portuguese coast. These storms, often low-pressure systems, create intense winds that blow consistently over vast expanses of the ocean.
The size and power of the generated swells depend on three factors: wind speed, fetch, and duration. Wind speed refers to the strength of the wind, while fetch is the uninterrupted distance over which the wind blows across the water. Duration specifies how long the wind maintains its speed and direction.
When these three factors are optimal, particularly during the autumn and winter months, they produce significant swells that can travel thousands of kilometers across the open ocean. These powerful swells maintain their energy as they traverse the Atlantic, unaffected by local winds once they leave the storm area. Upon encountering the unique underwater topography of Nazaré, these distant, long-period swells are then dramatically transformed.