What Causes Square Waves and Why Are They Dangerous?

by Sagar Nerala3 months ago
Picture What Causes Square Waves and Why Are They Dangerous?

The vastness of Earth’s oceans is simultaneously captivating and intimidating. It has long fascinated and intrigued humans and is the source of many myths and legends. There’s no doubt that the ocean is alluring, but also very dangerous. Highly unpredictable natural forces shape and move a world beneath the tumultuous surface. These forces often create dangerous conditions on the surface, one of them being the rare “square waves.” Let’s take a deeper dive and explore what square waves are.

A unique confluence of oceanic forces forms square waves

Square waves near the shore
Square waves near the shore.

Square waves, also known as “cross seas,” are a relatively uncommon phenomenon. They form due to a combination of tidal currents, wind patterns, and ocean floor topography. These conditions need to align precisely for square waves to occur.


Cross seas form when two opposing forces, both above and below the water’s surface, interact. These opposing forces can be ocean swells and sea winds or two conflicting ocean swells. Instead of moving parallel to the shore, these forces collide at oblique angles. This leads to the creation of two sets of waves with a distinctive square-grid pattern. These waves differ significantly from the typical graceful curves of regular waves.

These waves often occur close to the coast, the area with the highest chances for these conditions to occur. Cross seas have no warning signs and can appear in a matter of seconds. The randomness of the wind and ocean swells makes it nearly impossible for humans to predict cross seas.

These peculiar waves may look fascinating, but they are a warning sign of danger

Square waves found on the coast of Lisbon, Portugal.
Square waves found on the coast of Lisbon, Portugal. Image Credit: Rehman Abubakr/Wikimedia.org

Square waves are not noticeable while in or on the water. To properly observe the unique square pattern, a vantage point is necessary. The evenly spaced geometric shapes can be mesmerizing as one does not expect such a sight on something as ever-changing as the ocean, but don’t let their allure lull you into a false sense of security. Even if they don’t look like extremely large or fast waves, they can be dangerous!


Cross seas are dangerous due to the unpredictable conditions they create in the water and on its surface. The rapid changes in wave direction and intensity can easily disrupt boats and disorient swimmers.

Cross seas are dangerous due to the unpredictable conditions
Cross seas are dangerous due to the unpredictable conditions. Image Credit: Martin Roell/Wikimedia.org

While regular waves run parallel to the shore, cross waves intersect each other. These waves can be over 10 feet (3 meters) high on the surface and create powerful and dangerous rip currents. Rip currents can drag swimmers out further into the sea, and they are not visible from the surface. The size of the waves puts even large boats at risk and has caused many ship accidents over the years.


One of the biggest worries concerning cross seas is their ability to form suddenly and without much warning. Due to the unpredictability of swells and winds, vigilance is essential to spot square waves. While this wave formation is considered rare, certain coasts witness square waves with surprising regularity. Tourists flock to the west coast of France as the geology of the Isle of Rhé appears to be very conducive to the creation of square waves.

What if you are already in or on the water when square waves start to form?

Waves gently intersecting in the ocean, forming a cross sea
Waves gently intersecting in the ocean, forming a cross sea.

If square waves do form, the best course of action is to avoid going into the water altogether. However, if one is already in the water or on a boat during cross seas, certain measures can help to maximize your safety.


The first is to remain calm, as panicking may lead to rash decisions and expending more energy. Swimmers should try and make it to shore as soon as possible or try and stay afloat until professional help arrives. People on boats should wear their life jackets and secure their cargo to avoid the boat capsizing. Everyone should alert the authorities, such as the coastguard, if people or boats are spotted in cross seas.

Square waves are another reminder of how the ocean is a magnificent yet unforgiving environment. If you do happen to spot these waves, relax on the shore while working on your tan. The waves can only affect you if you are in the water, after all!

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Picture What Causes Square Waves and Why Are They Dangerous?
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