A massive 17.6-meter wall of water that appeared in the waters off British Columbia, Canada, in November 2020 has now been confirmed as the largest “rogue” wave ever recorded in terms of its proportion to surrounding waves, according to a new study. The wave reached a height equivalent to a four-story building, the scientists said.

Rogue waves, also called killer or freak waves, have only been accepted as real by scientists over the past few decades – after being part of marine folklore for decades. These are the waves that are greater than twice the size of surrounding waves and seemingly come out of nowhere. They are very unpredictable and usually come unexpectedly from directions other than the wind.

Scientists are still trying to understand how and why these waves form, and only a few potential causes have so far been identified. They seem to form because swells travel across the ocean at different speeds and directions. As they pass through one another, their crests and lengths and troughs can sometimes coincide and reinforce each other – forming very large waves.

Rogue waves are suspected to have been implicated in the disappearance of many ships across the years, such as the SS Waratah, which vanished in 1909 while going to Cape Town, and the SS Edmund Fitzgerald, which sank in 1975 in Lake Superior. As the waves follow each other closely, ships can’t recover and shed the water from the first before the others strike.

The first rogue wave ever measured by scientists happened near the coast of Norway in 1995. It reached 25.6 meters in sea state, with wave heights of about 12 meters – twice the size of those happening around it. The wave now recorded near in Canada was 17.6 meters in sea state, with wave heights of six meters – three times the size of the waves around it.

“Proportionally, the wave is likely the most extreme rogue wave ever recorded,” Johannes Gemmrich, who studies large waves as a researcher at the University of Victoria, said in a statement. “Only a few rogue waves in high sea states have been observed directly, and nothing of this magnitude. The probability of such an event occurring is once in 1,300 years.”

A really massive wave

The newly identified rogue wave, dubbed Ucluelet due to the region of Canada where it was identified, was recorded by a sensor buoy close to Amphitrite Bank – about seven kilometers offshore of Ucluelet. The buoy is part of a network of 26 buoys strategically placed on coastlines and in oceans across North America by the company MarineLabs.

Scott Beatty, CEO of MarineLabs, said in a statement that studying rogue waves could help scientists to better understand the forces behind them as well as their potential impacts. “They can be incredibly dangerous to marine operations and the public,” he said, while acknowledging that that potential to predict rogue waves is still an open question.

The study behind the newly identified rogue wave was published in the journal Nature.