When you think of dangerous ocean phenomena, rip currents, changing tides, and rough waves probably come to mind. However, one of the most hazardous and lesser-known oceanic threats is square waves, also referred to as cross seas. While they might look captivating and unusual, seasoned surfers and experienced ocean-goers know that these waves can be incredibly dangerous. If you spot square waves while at the beach, it’s time to get out of the water — immediately.

 

What Are Square Waves?

Photo: Adrian Hij/Getty Images

Square waves, or cross seas, are a rare but captivating phenomenon that occur when two different wave systems, coming from opposite directions, intersect. These systems usually travel at different speeds, determined by wind direction and force. The resulting effect is a grid-like pattern of waves that resemble a checkerboard or grid layout, often creating large squares or rectangles on the surface of the water. Despite how beautiful the phenomenon may seem from a distance, it’s important to remember that square waves pose significant risks to swimmers, boaters, and anyone in the water.

This phenomenon is also called a cross sea because it forms when two swells, moving at different speeds, cross each other’s paths. While the patterns may appear mesmerizing, they are dangerous, and this wave pattern has historically been linked to shipwrecks. The unpredictability of the waves, combined with their size and strength, creates a perilous situation for anyone unlucky enough to encounter them in the water.

 

What Happens if You Get Caught in a Square Wave?

If you happen to find yourself in the water when square waves are present, the first thing you might notice is the feeling of being pulled in different directions by two opposing currents. The waves themselves can range from relatively mild to extremely dangerous, with some reaching heights of up to 10 feet. This situation can quickly turn dangerous, especially if you’re swimming in deeper waters, as the strength of the waves can make swimming incredibly difficult.

The waves are not just large, but they also create confusing currents that seem to come from multiple directions. This makes it nearly impossible to swim with the current or navigate your way back to shore. What may look like a peaceful stretch of water from the beach can quickly become a chaotic and disorienting environment for swimmers. The best advice is simple: if you notice the water becoming choppier or the waves increasing in strength, it’s time to exit the water and head to the shore. For those further out at sea, cross seas can present a particular danger, making navigation incredibly difficult for boats and ships.

Even for experienced boaters, square waves pose a significant challenge. The waves can create unpredictable shifts in wind and water, which can make controlling vessels increasingly difficult. This makes them a serious risk for not only swimmers but also for recreational boaters, fishermen, and commercial ships. In some of the worst cases, these waves have been responsible for capsizing smaller vessels, leading to accidents and even fatalities.

 

Why Are Square Waves Dangerous?

The primary danger of square waves lies in their unpredictable nature. While most waves follow a relatively predictable pattern of direction and height, square waves come from different angles, creating waves that can hit you from multiple sides. This can cause disorientation and exhaustion, as the swimmer or boater is constantly fighting against unpredictable forces.

Moreover, the wind patterns associated with cross seas can also contribute to the danger. When two wave systems meet, they can create unique wind conditions that interfere with the typical behavior of the water, making it hard to predict the strength or direction of waves. In addition to the physical challenge posed by these waves, these sudden shifts in wind and water movement can make it extremely difficult for any on-water rescue operations to take place, further increasing the risk.

When square waves occur near shorelines or shallow areas, the effect is less severe. However, the risk remains high when they occur farther out in open waters where help is not easily accessible. These swells are not only larger and harder to navigate, but they can also make it difficult for boats to see other vessels or hazards in the water, increasing the likelihood of collisions or accidents.

 

Where Do Square Waves Typically Occur?

Square waves can occur in various parts of the world, but they are most commonly observed in areas where multiple wave systems meet at right angles. Scientists can predict the formation of cross seas using complex mathematical equations, such as the Kadomtsev–Petviashvili equation, which models nonlinear wave dynamics.

One of the most well-known places where square waves are frequently observed is the Île de Ré, a picturesque island off the west coast of France. Located in a region where weather systems from different directions meet, the island is in an ideal position for the formation of quadrangular waves. The phenomenon is best viewed from the Phare des Baleines, the "Whale Lighthouse," which stands 187 feet tall and offers visitors a stunning view of the surrounding ocean.

However, square waves aren’t confined to this area alone. They can also occur in other parts of the world, particularly in regions where wind and ocean currents converge at sharp angles. Cross seas have been reported in various coastal locations, particularly where two distinct wave systems — such as those from different wind patterns — collide. So, while the Île de Ré is a particularly famous spot, square waves can potentially form anywhere that the right conditions exist.

 

 

How to Stay Safe When Square Waves Are Present

1. Stay Alert: Whether you’re a swimmer, surfer, or boater, the most important step is to always stay alert to the water conditions. If you notice changes in wave patterns or see waves forming in unusual patterns, it’s best to exit the water immediately. Cross seas can appear suddenly and can be difficult to predict.

2. Stick to Shallow Waters: If you’re swimming or enjoying water sports, always stay in shallow areas, particularly when you’re unfamiliar with the water conditions. Shallow waters allow for quicker exit in case of sudden changes, while deeper areas pose more risks, especially when square waves form.

3. Pay Attention to Weather Reports: Often, square waves are the result of specific weather conditions, such as changes in wind patterns or large storms. Before heading out to the beach, check the local weather forecast for any unusual wind or wave patterns that could indicate the presence of a cross sea.

4. Avoid Boating in Rough Conditions: For boaters, it’s crucial to avoid venturing out when conditions are rough, especially if you know square waves could form. These waves can make navigation difficult and can pose a serious risk to small boats. Ensure your vessel is equipped with necessary safety equipment and consider delaying or rerouting your trip if conditions seem dangerous.

5. Educate Others: If you’re with a group of friends or family at the beach, make sure everyone is aware of the dangers of square waves. Educating others about the potential risks and how to stay safe can help prevent accidents and ensure everyone enjoys a safer, more pleasant time at the beach.

 

Conclusion: Always Respect the Ocean

While square waves may look visually captivating, they are a serious threat to anyone in the water. These unusual and dangerous ocean phenomena can cause massive swells and unpredictable currents that make swimming, boating, and even basic navigation dangerous. If you encounter a cross sea, the best advice is simple: get out of the water immediately. By staying alert, sticking to shallow areas, and respecting the power of the ocean, you can ensure your safety when enjoying the beauty of the sea. Always remember, no matter how inviting the ocean may seem, it’s essential to never turn your back on the water.