Sneaker wave is a term used to describe disproportionately large coastal waves that can often appear in a wave train without warning. Sneaker waves form when the energy of a number of smaller waves becomes "focused," meaning that several smaller waves have run into each other and created what is known as constructive interference. Constructive interference means that the individual wave peaks coincided and created a new wave that is the sum of those that were superimposed. This is similar to the way deep ocean freak waves are thought to form, albeit on a much smaller scale. Because they are much larger than preceding waves, sneaker waves can catch unwary swimmers or even people on the shore unawares, washing them out to sea. Sneaker waves are a universal coastal phenomenon, although they are known to be more common in some areas than others; in the United States, Northern California, Oregon and Washington are particularly affected.
