Nature’s beauty often conceals hidden dangers, and square waves, also known as cross seas, are a prime example. These mesmerizing checkerboard patterns on the ocean’s surface captivate observers but can be perilous for those in the water.
Square waves occur when two wave systems intersect at angles greater than 45 degrees, or when wind-driven waves collide with swells moving in a different direction. This interaction creates a grid-like appearance on the water’s surface. While visually stunning, these conditions generate powerful currents that are treacherous for swimmers and challenging for vessels to navigate.
The European Space Agency noted in 2010 that such conditions are common in the ocean, occurring when multiple swell systems coexist. A 2004 study highlighted that a significant percentage of ship accidents happened in crossing sea states, underscoring the hazards square waves present.
One notable location where square waves are observed is the Île de Ré along France’s western coast. Tourists can safely view this phenomenon from a lighthouse on the island, as entering the water during such conditions is extremely dangerous.
For a visual explanation of this natural phenomenon, you can watch the following video:
