This strange pattern at sea is what happens when two wave systems cross each other at nearly perpendicular angles. This can occur when waves generated by one weather system collides with waves generated by another weather system, usually at a place that is far away from both weather systems.
Waves can travel thousands of kilometers over the surface of the water. Even on the calmest days, storms raging elsewhere on the ocean create rolling waves that radiate away from the storm and washes the shore of distant land. These are called swells, which is different from ocean waves raised by the local wind. Another term for wind waves generated and affected by local winds is “wind sea”. All swells start as wind sea, but after a while the wind ceases to blow and the waves have travelled so far out that it’s no longer generated or significantly affected by the local wind at that time. Then it becomes a swell. When two swells coming from two different directions collide, we get “cross sea”, which is what is happening in this picture.
A “cross sea” or “cross swell” observed at Île de Ré off the west coast of France near La Rochelle. Photo creditRead more »
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