Beware of unexpected waves – they are known as “surge waves” or “sneaker waves” because they surprise people by appearing without warning. Waves occur in sets. Small wave sets are often followed by larger wave sets. But waves are unpredictable – they can sneak up on beachgoers by appearing suddenly after a relatively long period of calm (anywhere from 5 – 30 minutes of calm water). By that time, many people have let down their guard and stopped watching the ocean, leading to greater risk as these unexpected waves can surge high up on the beach or rocks with deadly force.