At first glance, it looks as though a tsunami wave is about to crash into a swathe of high-rise tower blocks.
But for beachgoers and surfers alike along Panama City Beach, Florida, there was no need to panic, the giant wave was just a curious illusion caused by harmless sea fog rolling off the Gulf of Mexico.
This ‘tsunami cloud’ effect is believed to be caused by a phenomenon known as the ‘Kelvin–Helmholtz instability’ that can occur in both air and water.
This is when a fast-moving layer of fluid or air washes over a slower, thicker layer – creating the wispy wave effect.
According to helicopter pilot JR Hott, the clouds appear a few times a year but normally further down the coast.
He added: “The event, while it can form quickly, moves gently and slowly. It isn't something that happens with more than a gentle breeze.”