CANHÃO DA NAZARÉ

CANHÃO DA NAZARÉ

Nazaré Canyon is the biggest underwater ravine in Europe with about 200 km long, developing in the direction E-W and going to 5000 meters deep in the abyssal plain where it ends. The canyon headboard is less than 1 km from the coast to SW. This contiguity of the headboard to the shoreline harnesses singular oceanographically conditions that originate hydrodynamic and sedimentary transport processes, directly related to the presence of the canyon and its morphology.

The proximity of the canyon headboard to the coast affects the undulation characteristics in the less deep contiguous areas, as it is certified for the significant blistering of the wave, in the Praia do Norte, before the breaking zone in situations of West incidence. This phenomenon is due to the interaction of the undulation with the north edge of the headboard that results in a focalization or convergence of the wave for refraction and consequent blistering.

The increase of the wave height verified north of the canyon headboard doesn’t happen south because, although the south edge promotes the focalization, the adjacent bay inverts the effect of the canyon, spreading the wave.

The modulation of the maritime disturbance carried through by the Hydrographic Institute, in the scope of “The North Canyon Show by Garret McNamara”, suggests that this effect depends essentially on the course of the undulation incident. Results prove that the blistering in Praia do Norte is only verified in an expressive way in regimes of undulation around the direction of West incidence.

In the image is presented a typical situation that characterizes the phenomenon of blistering in Praia do Norte in a storm situation. The significant height in Praia do Norte is next to the eight meters, while in the south bay the waves have only a significant height of about four meters.