A massive wave submerged a California beach. Was it a rogue wave?
Jenna Benchetrit | CBC News | Posted: December 30, 2023 12:24 AM | Last Updated: December 30, 2023
Sailors have long documented the monster waves. Here's what scientists know about them today
Rogue waves were once a spooky bit of marine storytelling, written in ship logs while scientists searched for a way to measure them.
Sailors recounted sightings of freakishly large waves that seemingly came out of nowhere, crashing into their ships — or completely submerging others, never to be seen again.
"It's something that seagoing peoples have documented for a long time," said Warren Currie, a Burlington, Ont.-based research scientist with the department of Fisheries and Oceans.
"One example that's often used is The Great Wave Off Kanagawa," he added, referring to a famous Japanese print by the artist Hokusai that depicts a monstrous wave engulfing several boats.
Rogue waves are a real — yet rare — scientific phenomenon. One of the most famous instances of a scientifically measured rogue wave came in 1995, when the Draupner wave was recorded in the North Sea off the coast of Norway.
And when a massive wave hit a Ventura, Calif., beach on Thursday, many were quick to call it a rogue.
But was it? And what are rogue waves, anyway?
WATCH | Massive freak wave inundates a California beach:
What are rogue waves?
Rogue waves are a relatively rare phenomenon, but they can be dangerous. The largest one ever recorded, measuring 17.6 metres, was detected off the coast of B.C. by researchers at the University of Victoria in November 2020.
Those who study the ocean use a measure called significant wave height — which is the average of the largest 33 per cent of waves observed in the ocean — to determine if a wave is large enough to be considered a rogue.
"A rogue wave is a rogue if an individual wave is at least two times that significant wave height," said Scott Beatty, the CEO of coastal intelligence firm MarineLabs in Victoria, B.C.
LISTEN | A Canadian oceanographer on the record-setting wave recorded in 2020:
In other words, rogue waves are usually more than twice the size of the waves around them, according to the U.S. National Ocean Service.
The agency's website also says that the waves are "very unpredictable," often coming from unexpected directions that are inconsistent with the typical direction of winds and waters.
Rogues might be called "freak" or "killer" waves, but scientists refer to them as "extreme storm waves."
They're often described as resembling walls of water, with steep sides and deep troughs.
Was the wave that hit a California beach a rogue?
"Rogue waves are often called rogue waves by accident, because people think just, 'I saw a big wave, therefore it must be a rogue,'" said Beatty.
However, rogue waves have a technical definition — and Beatty says it's hard to say whether the wave that crashed into a Ventura, Calif., beach on Thursday met that criteria.
A large individual wave, or set of waves, combined with a high tide might form something that looks like a rogue wave, Beatty explained, "but it is just indeed very large waves that end up running up along the beach and up and over barriers."
WATCH | More views of the surge in Ventura County:
Lisa Phillips, a meteorologist at the National Weather Service in Oxnard, Calif., says that the incident in Ventura was what's called a "wave run-up."
"When you have really large surf, some of the waves are bigger than others and the water will wash up much further on shore than some of the other waves. So it can catch people by surprise," she said.
What causes a rogue wave?
Rogue waves are difficult to predict because scientists don't fully understand how they're formed, but they happen more often than we think.
Like an avalanche, there are certain conditions that make a rogue wave more likely to occur, "but we couldn't say there will be a rogue wave at 11:01 a.m. at this location," says Beatty, who studied ocean wave energy during a PhD in mechanical engineering at the University of Victoria.
What are those conditions? Extreme waves form because sea swells collide to create larger, taller waves, especially when travelling in the same direction. When the crests (highest points) of two waves meet, they can merge to form a huge rogue wave, according to research published by National Geographic.
There's another way that rogue waves can emerge, according to the National Ocean Service. When waves that were formed during a storm move against the typical direction of the current, they can interact in a way that leads to more waves passing through a fixed point during a shorter period of time. That can cause waves to join together and form large, long-lasting rogue waves.
Are El Niño or climate change contributing factors?
El Niño is a naturally occurring climate pattern associated with warming of the ocean surface temperatures in the central and eastern tropical Pacific Ocean. That pattern is causing larger waves than usual, according to Beatty.
"We are definitely expecting to see some of this kind of activity for this winter," said Phillips, the meteorologist. "It could have a correlation to our strong El Niño that we're in, because strong El Niños mean that low-pressure systems can be more intense."
WATCH | Crews work to protect beachfront homes after massive wave:
What about climate change? It would be challenging to say whether that's a factor in giant waves, Beatty said. However, observers have noticed that "the wave energy in the ocean is gradually increasing as climate change has more effect," he added.
"As the ocean is warming, storms are getting more intense, which means winds are more intense. And winds are what create waves, and so that means waves are getting more intense."
Currie, the research scientist, added that it's also much easier now to measure this type of phenomena.
"It's a combination of both having the observational power to see these things, and also recognizing that there's increased energy in the whole system," he said. "So we have an expectation of there being more of these events happening as well."