Last weekend, thousands of beachgoers along the southwest of England enjoying an otherwise normal summer's day were shocked to glimpse what appeared to be a tsunami racing towards them. The towering edifice, however, turned out not be water, but a massive cloud of fog.
The phenomena, more commonly known as a fog bank, occurs around the world and, as shown in one such incident below on Lake Huron, can look like it's straight out of a disaster film.
Depending on the time of day and the conditions outside, they can also take on the appearance of a towering tsunami, indistinguishable from the water below.
The good news is that these fog tsunamis are relatively harmless, with visual impairment the only true danger for those caught within the wave of mist.
According to the National Weather Service, the phenomena forms when warm air condenses over colder ocean water. "Once that happens, the sea fog bank forms and is transported by the prevailing wind," explains meteorologist Morgan Palmer. "If that wind is onshore, then fog will ride slightly inland."
As shown in the video below of Lake Superior during winter, the inverse (cold air, warm water) can trigger a similar phenomenon known as sea smoke or steam fog.
So rest easy, beachgoers. That's likely not a 10-story-tall tsunami bearing down on you but one of the world's more frightening illusions.
Well played, Mother Nature.