If you're confused about what ground swells are, how they're formed, and what all the technical surf forecasting surf jargon is all about, then you're not alone.
It's a little confusing to say the least.
This article however solves all that.
An idiots guide to ground swell (and swell in general for that matter), leaving no stone unturned - with minimal scientific jargon to make things easy for people like you.
Are you ready?
WHAT IS A SWELL?
A swell is an open ocean wave that hasn’t broken yet.
Swell is created by the transfer of energy from wind into water, and the longer and stronger the wind blows, the bigger and more powerful a swell will be.
More on all of that in a minute.
WHAT IS THE DIFFERENCE BETWEEN A WAVE AND A SWELL?
Swell is a wave traveling through deep water.
Think of it like a sound wave generated by the wind that travels through the ocean.
A wave on the other hand is the moment when a swell begins to interact the ocean floor causing it to break.
A wave is the moment where all the power and energy of a swell - created by strong winds often thousands of miles away - is finally realised as the wave breaks, ending the journey.
DOES A SWELL BREAK?
No, swells don’t break.
The moment where a swell begins to break is when it gets recategorised as a wave instead.
So technically a swell doesn't break, but there's a bit of a grey area in there for sure.
WHAT IS A GROUND SWELL?
Ground swells are created by large storms out at sea with strong, powerful winds, blowing over a sustained period of time - that have traveled in excess of two thousand miles before they reach the shore.
These ground swells will be powerful, uniform and well organised, and have a swell period in excess of twelve seconds.
The distance a swell has had to travel is called the 'fetch'.
All of these factors combined make groundswells perfect for surfers.
HOW GROUND SWELLS ARE FORMED
Ok, so I gave you a birds eye view of what a groundswell is above, but I want to go a little deeper and really help you to understand how they’re formed.
Here we go:
STAGE 1: STRONG WINDS BLOW OUT AT SEA
A groundswell's conception is when a storm system begins to blow out at sea.
These strong winds interact with the ocean’s surface creating ripples that turn into swell.
STAGE 2: CHAOS INTO ORDER
As a swell is young its wavelength will be scattered, erratic, and disorganised.
Occasionally these non-uniform wave frequencies will merge with another and synchronise together.
Where there were two small, disorganised waves, there now becomes one.
This process of organisation continues to happen, and the further a swell travels, the more opportunity there will be for waves to merge in this way.
STEP 3: DISTANCE MAKES THE SWELL GROW STRONGER
As these swells travel further they merge together more consistently, becoming more groomed in the process.
So where there were once ten small waves, there is now one.
A single wave with the power of ten smaller ones combined.
WHICH CREATES SWELL PERIOD...
Since ten small waves have been replaced by a single, more powerful one, this increases the swell period.
Swell period is calculated by measuring the interval between waves traveling at sea (measured in seconds)
WHY IS SWELL PERIOD IMPORTANT FOR SURFERS?
Swell period is important for surfers as it gives us some interesting insights into what that swell might be like when it hits the shore.
If the swell period is high we know that the waves will have traveled a long distance, we can also conclude that the swell will be uniform, well organised, and powerful.
All of these things make for great surfing conditions.
That’s why when reading a surf forecast the swell period is an important metric to consider.
LET'S TALK ABOUT WIND SWELL…
Ok, so what is a wind swell?
In short, a wind swell is formed by storm systems closer to shore (usually around a couple of hundred miles out to sea).
Now because these waves haven’t had to travel very far to reach the shore, they haven’t had the opportunity to join together all that much, so the wave period will be reduced.
And as such, the waves will lack uniformity, and lack power too.
Oftentimes (but not always) wind swells will create weak, disorganised waves - not ideal for surfing.
GROUND SWELLs VS WIND SWELLS: WHICH IS BETTER FOR SURFERS?
Groundswells produce powerful, uniform, well organised waves, whereas wind swells produce weak, unorganised waves.
Hence why surfers prefer to surf groundswell over wind swell.
WHAT IS A GOOD SWELL FOR SURFING?
Alright so there’s no hard and fast rule here, as every spot is different, but here’s a rough outline of what to look for:
A QUICK WORD ON SWELL DIRECTION…
I’ll be quick here I promise.
But swell direction is a big deal, and plays a HUGE role in how waves will actually break when they hit the shore.
The swell direction refers to the angle in which the swell is traveling, and this impacts the way waves break considerably.
Think about it, if a swell has to wrap around a headland it’ll lose power. If a swell is running across a beach it’ll create currents moving down the beach, and force the waves to break in that direction too.
So, when checking a swell forecast be sure to take into account the angle of the beach you’re surfing alongside the swell direction too.
*ONE BAD THING ABOUT GROUND SWELL*
Ground swells are great and all, but occasionally, you can get too much of a good thing.
Let me explain.
On a standard beach without very defined sandbanks a deep groundswell will cause the whole beach to become one big closeout.
So yes they’re uniformed, yes they’re powerful - but at the wrong beach they can be straight as hell.
So, depending on your location a smaller swell period may actually create better waves.
SECONDARY & TERTIARY SWELLS
If there are multiple storm systems out at sea, they will each create their own swells traveling at different angles, with different swell periods to boot.
This is why it can be super important to check the secondary, and often tertiary swell forecasts too.
These additional swells can impact the waves at your local considerably.
Get to know how these additional swells work, and you’ll become a master surf forecaster in the process.
WRAPPING IT UP
Damn, we covered a whole lot of ground there.
Ground swells, wind swells, swell period, swell direction…
There’s a lot to take in, and a lot of different factors at play.
All of which combine to create the waves you’re addicted to riding day in day out.
Rowan is the nerd behind the scenes. But when he's not knee-deep in code, you'll find him immersed in the crypto-world or sending it at his local beachie.