A sneaker wave, also called a sleeper wave, is an unusually large wave that can appear in a train of smaller ones without warning. The term is popular rather than scientific. NOAA loosely defines sneaker waves as waves near shore that are unexpectedly and significantly larger than other waves reaching the beach.
Researchers at Oregon State suggest that they come from distant storms that send long-period waves, which then arrive during calm weather and travel higher up the beach than expected. Along much of the U.S. West Coast, sneaker waves kill more people than all other weather hazards combined.
At Carmel Beach, as on all this coast, keep an eye on the water, never turn your back on the surf, and stay off wet rocks. There are no lifeguards.