![]() The picture above shows the checkered wave pattern between two breakwaters near Lisbon, Portugal.Īs we've seen above, a cross-sea state is the result of several oceanographic phenomena taking place near the coastline, including: ![]() Nevertheless, it has also been spotted in open waters in the South Pacific and the Atlantic Ocean. The island, located off the coast of La Rochelle, is a tourist attraction even though cross seas only occur during certain times of the year. The most famous place in the world for watching square waves is Île de Ré - Isle of Ré - in France, as seen in the top picture. They can reach 10 feet (three meters) in height.Ĭross seas are relatively rare and can appear and disappear within minutes on many beaches worldwide. Square-shaped waves are fascinating, but these criss-cross ripples pose a real threat to everyone and are too strong to get out of. Swimming or surfing in the middle of a cross-sea is not something you should be doing, even if you're an experienced swimmer or wave rider.Ĭross swells can also cause boating accidents and shipwrecks. Why? Because the phenomenon is usually associated with strong and localized rip tides. If you see square waves in the ocean, get out of the water as soon as possible. The look of square waves is impressive, but they're extremely dangerous, even in small swell conditions. When two opposing swells collide, a unique pattern emerges. In other words, square waves result from the intersection of two seas, also known as cross sea or grid waves.Ī weather pattern in the region causes the waves to form at different angles. Instead, they're the result of the way the water is moving. However, square waves do not result from any circumstance that is taking place below the water. You can easily spot the strange pattern by climbing to the top of a lighthouse or cliff or flying a drone over the area. Looking at these waves from above, it seems like there's an underwater grid forming square-shaped ripples. The phenomenon is rare yet extremely dangerous. However, in some regions of the world, you may notice the creation of a chessboard-like pattern on the surface of the water. ![]() Most waves reach the shore and break horizontally and parallel to the coastline. It will be interesting to see whether such images, both from below and above breaking waves, can be used to learn more about wave dynamics, also in a quantitative way.Have you ever spotted a quadrilateral-shaped wave pattern in the ocean? If so, you've witnessed square waves. This provides so-called Lagrangian observations of a wave as it travels onshore and breaks. Or, and I imagine this takes some practice, a pilot may follow a wave with the drone as in the video below. The stability of drones allows pilots to let the their camera hover in a fixed position and make a video of the waves breaking directly below - a Eulerian frame of reference. Similarly, the rise of drones, or unmanned aerial vehicles (UAV's), provides spectacular shots and videos from above, such as those by Reed Plummer. Underwater photography has given some interesting views of what's going on below breaking waves. However, sometimes things come together (a hot summer and a small swell), allowing Dutch underwater photographers to capture the rib vortices below our own North Sea waves. We also don't have the underwater visibility as seen in the Australian and Hawaiian photos. Energetic, hollow plungers are rarely mentioned in his reports of the Dutch surf. Tobias van Tellingen, the Netherlands' only professional surf forecaster, was also consulted by the author of the item. When such flow patterns reach the seabed, sand is moved about and injected upward where the flows collide (red arrows). As adjacent streamwise vortices (the red and blue tubes) rotate in opposite directions, areas of downward and upward flow are created below the wave (the white arrows). (2017) provide a nice illustration that clearly visualises this process. This is what can be seen in Reed Plummer's image, where the vortices have a brownish colour because of all the suspended sand. When the wave breaks violently and the vortices reach the seabed, they may even push sand upward to the surface.
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