Ocean waves fill a unique space in human experience.
“Modern quantum physics and ancient mysticism alike tell us that all life is made up of waves — light waves, sound waves, radio waves. Even physical matter, that which appears solid, is little more than a field of energy, vibrating at a certain frequency. Waves. The ocean surf we ride is the only form in which wave energy can be experienced on a human scale,” writes Tim Baker in “High Surf: The World’s Most Inspiring Surfers.”
But just because we can see a wave or ride it doesn’t mean we can easily understand how it works.
Surfers, unsurprisingly, know well the importance of watching and understanding waves before trying to ride them. Often seen standing around the edge of the beach looking like they’re being social, they may in fact be studying the waves — a task that can take some time — to know where the set is and where the wave breaks.
Wave height, direction, frequency and rhythm are important in understanding not only waves to ride but waves to avoid. For the beachcomber, potentially deadly sneaker waves (described in the last Vista Point column, “Science of sneaker waves: Seeing isn’t always believing,” March 5) fall in the latter category, and wave science is making headway in discovering the secrets of how and when they form, and why, counterintuitively, they’re more likely to occur when seas appear calm.
A basic primer on what is well-understood: Ocean swells and waves are mostly caused by wind, typically from storms many thousands of miles away. Sometimes more than one set of swells will move through an area, products of different storms in different places and swells of different size, frequency and direction.
Tides, currents, storm surges and the occasional tsunami may interact with swells, and some or all of these influences can be present on any given day in your stretch of the sea, primary swells interacting with secondary swells to potentially create larger waves.
The difference between a wave and a swell, it should be explained, is that swells are the smooth, gradually sloped lumps that move across the ocean’s face, while waves are the sharper peaks that form at the tops of steep swells in high winds and where water grows shallow, such as coasts. The swell-vs.-wave difference to the mariner, says National Weather Service Meteorologist Troy Nicolini, is trivial.
The more meaningful distinction that says more about waves’ safety and ease to navigate is whether the wave face will be steep or gradual, and that is a matter of the interval, measured in seconds, between waves.
“A 10-foot-high wave with an interval of 20 seconds you almost barely notice. Inversely, if it has a 7- or 8-second interval, now the waves are much steeper and make a boat go up and down more dramatically, and this is usually when people get sick and boats can be more likely to capsize,” Nicolini explains.
But there is an exception to the rule about wave intervals and the hazard they pose — sneaker waves.
“With sneaker waves, we’re finding that there can be 15–30 minutes of not very big waves, which is why people will go out on the jetties when there aren’t big waves and then get caught by a big wave, and we’re starting to identify what happens when there is a very big wave without warning,” Nicolini says.
“It’s the interval that makes the difference. Waves that don’t seem that big and have a really long interval are the ones that can seem flat for a long time and then suddenly get much bigger,” Nicolini says.
Got it? Short intervals: bad. Long intervals: also bad … possibly.
To illustrate this, Nicolini uses another dynamic force that moves on a human scale: a walkathon.
“A thousand people start off walking 5 miles, and they’re all going more or less the same speed, but when they reach the finish line, they don’t all cross the finish line at the same time; they come in at the end in clumps. We’re not sure why it happens, but it’s good imagery,” Nicolini says.
Although scientists aren’t sure why waves moving in the same direction will separate over long distances, they have a better handle on how they can converge, far across the ocean from whatever storm produced them, and form sneaker waves.
At some point, after as much as half an hour of gentle seas, waves moving at different intervals will come into sync with each other — like a clump of walkathoners catching up to another clump and making an even larger clump — creating a much larger wave that can surge far higher up the beach than anyone would expect.
Fortunately this kind of wave pattern doesn’t happen all the time, and for more on when these conditions are likely to be present, stop by the next Vista Point for more on sneaker wave science and safety: how to know when it’s safe to be close to the water, how to enjoy the beach worry-free and why jetties just aren’t as safe as wall-walkers would like to think they are.