A sneaker wave is a disproportionately large coastal wave that can sometimes appear in a wave trainwithout warning. The terminology is popular rather than scientific: there is no scientific coverage of the phenomenon as a distinct sort of wave with respect to height or predictability—as there is on other extreme wave events such as rogue waves. One American oceanographer distinguishes "rogue waves" as occurring on the ocean and sneaker waves as occurring at the shore. Because they are much larger than preceding waves, sneaker waves can catch unwary swimmers and even people on the beaches and ocean jetties and wash them into the sea. Sneaker waves are mainly referred to in warnings and reports of incidents for the coasts of Northern California, Oregon, and Washington in the western United States. These sneaker waves also occur on the coast of British Columbia in western Canada, especially this province's southern coast, because they commonly occur on the west coast of Vancouver Island. Sneaker waves are common on the southern coast of Iceland, and warning signs have been erected at Reynisfjara and Kirkjufjara beaches, following three unrelated tourist deaths in recent years. King waves occur especially in Western Australia and Tasmania.
Seventh wave
In many parts of the world, local folklore predicts that out of a certain number of waves, one will be much larger than the rest. "Every seventh wave" or "every ninth wave" are examples of such common beliefs that have wide circulation and have entered popular culture through music, literature, and art. These ideas have some scientific merit, due to the occurrence of wave groups at sea, but there is no explicit evidence for this specific phenomenon, or that these wave groups are related to sneaker waves. The saying is likely derived more from a cultural fascination with certain numbers, and it may also be designed to educate shore-dwellers about the necessity of remaining vigilant when near the ocean.
