But for beachgoers and surfers alike along Panama City Beach, Florida, there was no need to panic, the giant wave was just an 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.”