Anatomy Of A Wave: What Makes Teahupo'o Unique
Anatomy Of A Wave: What Makes Teahupo'o Unique
On Tuesday morning, surfers once again witnessed surfing's own natural wonder - Teahupo'o in full flight. And this time it happened with the eyes of the world also watching.
Among the Olympic viewership, surfers needn't be reminded about how remarkable Teahupo'o is; for over twenty years we've watched and wondered about this incredible wave.
Yet despite many attempts, no-one has explained why it does what it does. Occasionally a commentator might remark about the deep channel abutting the wave, surmising that its depth is what causes Teahupo'o to fall over itself in perfect fashion.
Anyone who's spent much time in the tropics knows that's an inadequate answer. Where coral grows it's not unusual to have a deepwater pass nearby - sometimes formed by freshwater run-off from mountains, other times by water escaping fringing lagoons.
The question is this: Why, if there are a million coral reefs in the tropics, is there only one Teahupo'o?
The proximity of deepwater may be part of the answer yet there's much more to learn.
Like the rest of us, Tom Shand has wondered about Teahupo'o, however Tom's also a coastal engineer and a wave scientist, meaning he has the means to peer a bit deeper into the mystery of Chopes.
As a set approaches the reef at Teahupo'o, the ocean appears to rise up before Jack Robinson who salutes the specatacle (ISA/Jiminez)
To understand why Teahupo'o breaks as it does, we need to start with bathymetry: the shape of the seabed that influences waves as they approach the shore. At Teahupo'o, a combination of factors comes into play.
Waves arriving at Teahupo'o generally originate from intense Roaring Forties storm systems south of New Zealand. By the time the waves reach Tahiti they have become ordered swell, with periods of 14 to 20 seconds.
These types of long-period waves normally start interacting with the seabed at depths of around 200 metres. On most coasts, this depth would occur several hundred metres to a few kilometres offshore. But at Teahupo'o, it is much closer, just a couple of hundred metres off the reef.
This rapid change in depth forces the wave to shoal very quickly – the wave speed slows, the distance between waves compresses, and the wave height increases.
The change is so abrupt that the wave is still very linear – it hasn’t had time to develop the peaked crest and flat trough typical of waves in shallow water.
Waves breaking on a slope this steep would typically collapse - breaking from the middle of the wave and creating a steppy, unsurfable mess. But at Teahupo'o this doesn’t happen.
Crucially for our understanding of Teahupo'o, at around ten metres depth a flatter shelf in the reef allows the wave to stabilise and 'stand up' with a steep front face, before finally breaking as the reef rises yet again.
And break it does. Owing to the linearity, there is far more water in the crest than most waves, and a deeper trough in front.
This makes for the characteristic extra-thick plunging lip into a trough well below sea level, compressing a lot of air that is forced (spat) out of the wave’s barrel after breaking.
Critically, the larger the wave, the closer to the steep offshore ramp it breaks, and the more extreme the plunging.
Location and bathymetry of of Teahupo'o (elevation data from SHOM, satellite imagery from Airbus)
A range of other unique features contribute to the way the wave breaks at Teahupo’o.
A deep channel runs alongside the shallow reef shelf. The wave doesn’t break in this deeper area, allowing it to peel before it finally closes out onto shallow reef.
A part of the shallow reef platform extends offshore, into the reef pass. This shallow area bends and focuses wave energy from the wider, deeper part of the wave back into the breaking wave. This happens particularly on more westerly-orientated swells, increasing the intensity of breaking and forming the west bowl.
As well as this, the orientation of the wave at Teahupo'o is cross-offshore to the prevailing southeast trade winds, keeping the wave face smooth.
A low tidal range also limits the times the reef is too deep or too shallow to surf. And the wave is near the Passa Hava'e reef pass, which helps the wave’s focusing and breaking. But because it isn’t right in the pass, the wave isn’t affected by high tidal or wave-induced currents.
Celeris wave model simulating typical surfing conditions at Teahupo’o (Elevation data from SHOM, satellite imagery from Airbus, wave model by Celeria Labs)
New-generation wave models that simulate individual waves, rather than just average energy density, provide insight into what creates a surf break such as Teahupo'o (see video above) These models provide insight into what happens as waves shoal and refract (bend and focus) over the seabed as they approach break point.
They also significantly improve our understanding of what makes a particular surf break unique. This can help in assessing the potential impact of human or natural modifications to the environment.
// TOM SHAND
Comments
Awesome !
very good science
It’s remarkable that this can happen on a flat earth?
Excellent work, Tom. Now tell us about the Bar - no wait, don't :-)
Another critical factor - the bottom is perfect.
No ledges or rocks, big holes etc that will create turbulence in the water as it is drawn violently off the shelf.
If there were any of these the wave would step and boil, but it has a perfect drainage setup so the wave is flawless despite the magnitude of the moving water.
Good point, Tane. No weird reverb running through the lineup.
Which also follows on from Tom's point, that I hadn't previously considered, in that the wave isn't at the end of the reef - i.e breaking into the pass - and therefore prone to water movement.
That weird feature of it tucked away in a bend just up from the reef pass also allows it to break as it does.
One thing I have always wondered which this excellent article doesn't address is what formed the deep channel beside the break.
It's clearly not part of the reef pass proper like other South Pac passes.
Is it a vestigial channel from a previous layering down of coral and represents a more ancient outflow?
Or is it some other kind of geological feature?
Any ideas Tom?
Surely freshwater run off, yeah?
Maybe the steepness of the mountains and the valley(behind the village) continue into the ocean then drops off?
From a different, more ancient channel?
It's definitely not part of the current channel/pass.
Or is it a seabed feature of subsidence ?
The whole area is so geologically spectacular there must be significant movements in the plate.
As a stab in the dark, i'd go with your second guess FR, something exclusive in the rock/seabed feature that has created that elongated flat rock ledge that's stood the test of time, regardless of freshwater flow gouging out the main pass surrounding it. Just a guess though. But as mentioned in the article, there's so many prototypical reef passes that aren't like this, that it would seem it would have to be something a little bit extraordinary to allow that flat shelf to be a part of the set up that gives Teahupoo it's classic characteristics.
Seems a feature of alot of classic slabs. They all seem to have a portion of flat rock shelf to allow a bit of space for the waves to do their thing.
Great article.
Yea really good points here and by FR. It's an oddity amongst reef passes - both the 30-50m shelf extending north into the pass to focus the energy in and then the channel running alongside the shelf in 5-10m water to let it peel. Could be a lot of reasons, kind of sits in a weird space between geology and ecology and I doubt those guys talk much. Possibly when sea levels were lower there was less freshwater coming out this pass - others were taking more - so the channel was narrower. Then as sea levels rose something happened to require more freshwater to exit here limiting coral growth over a wider area and making the higher parts of the pass wider. No idea about the shallower channel though, it's a pretty small feature by reef scale. Got some better bathy on the way, will post an update.
When the sea levels were lower, water was locked up in a cold to frigid manner, the environment was much cooler as temperatures were lower, thus less evaporation from the ocean .
When the atmospheric and oceanic temperatures rose, evaporation , leading to precipitation increased , and this lead to more rainfall coming off the nearby mountains and out into the pass therefore limiting the establishment of coral again. Sea levels would have risen after the thawing events. AW
Hi AW, I’m not sure water temperature and rainfall are that relevant to this specific reef. Presumably it would still have been a tropical climate for some time.
20,000 years ago sea levels were about 100m below current levels so it is probably more a case of erosion processes that initially shaped the drainage line(s) on the flanks of the volcano. Then as sea levels rose the coral reef on the adjoining sides of the drainage line grew upwards. As the coral can grow vertically you then get a near horizontal reef overlying the underlying uneven topography.
Distracted. Hi mate. Hope you’re well.
Just an idea, obviously wrong.
I stand totally corrected by your wonderful explanation.
I need to do some more reading.
Thanks again for highlighting my error. All the best. AW
Nowhere but SN. So good.
land clearing for crops increases turbidity, freshwater outflows & sediments, smothering & killing coral.
https://pasefika.com/polynesia/timeline maybe 1000 yrs ago;
factor in the effect of mountainous topography, orographic rainfall & prevailing SW swells for creating eddies of mud deposits to the east of the river & channel?
https://www.britannica.com/science/eddy-fluid-mechanics
there would be plenty of similar ledgy waves, just more remote from civilisation & media.
https://www.google.com/maps/place/O%E2%80%98ahu/@21.6754076,-158.0412529,15z/data=!4m6!3m5!1s0x7c006632db726b03:0xd9587d69906fcbc3!8m2!3d21.4389123!4d-158.0000565!16zL20vMGRmY24!5m1!1e4?entry=ttu
Thanks for what makes the wave...very good...can add the mankind factor.
Notice the Teahupoo Lava Plains forged the ocean outfall
Cyclone swell breaches the barrier reef to ramp off Volcanic / sub slope to plunge in/out!
Originally there was a coastal road around whole Tahiti Iti shoreline Island.
Mostly to exploit early resource!
https://i.etsystatic.com/14118280/r/il/5866a2/3066280946/il_1588xN.30662...
Trade wind steeper East sloped shore to barrier reef naturally eroded fastest...washing the road away as it goes.
Hence each adjacent west Town is ever the next "End of the Road" > or Next Town next to go...
Process of 100's of years of evacuated Ghost Towns.
Once each road is washed away the towns cut Water Taxi Channels. (Common thru Pacific Islands!)
Once the Barrier Reef is breached then both road & Water Taxis are rendered useless.
These Towns are then Vacated...
Teahupoo runs Ghost town Water Taxi Tours to rows of neighbouring dead sister 'end of road' towns"
As each Town Road dies the canal network breaches more Lagoons, in so the Volume increases.
Not only increases in volume but speed as the tidal effect is ramped to act like massive billows.
The last destructive Cyclones of late 50's continued to wipe out towns right up to Teahupoo.
See last "End of the Road Town" = Why give it a name it's next to be wiped out as this one!
https://www.reddit.com/media?url=https%3A%2F%2Fpreview.redd.it%2Fa-60s-m...
During the early 60's the local Hodad said No Waves broke into the Teahupoo channel.
He would know as he gazed upon it daily.
Early 70's French installed an Administrative Council..see the retro 70's PK.0 Marker / stonework
The spoils were likely recycled for nearby daggy retro garden beds
Although tbb thinks it was done in 2 goes...Late 60's then early 70's just coz...read 2 renders of such!
Pretty sure it was delayed > Hence the belated Civics & approvals.
They decided to service these Washed out towns by cutting several canals thru to Teahupoo Marina.
Like a broader makeshift servicing / Food & Fuel supplies canal network as opposed to local Mob hack.
Recall a few businesses went broke as new sections impacted on the previous makeshift trader...so on!
Crew can imagine the effect of draining 30kms of East Lagoons thru Teahupoo Pass...
Western Canals were also cut to drain a further 10kms of secondary lagoon thru same Pass.
These cut Water Taxi canals are Shown here in Red. (All are artificial & race currents faster!)
More important to follow all arrows as they all pressure as one to outfall up the Teahupoo wave face
Count All 27 outfall arrows exit as one out the wave face including that little one in bigger swell.
Crew don't even see the mass volume of 40kms barrier reef lagoons banking to drain behind it
http://tuhinternational.com/wp-content/uploads/0101.jpg
They act like bi valves for two massive Lagoons to whoosh mass volumes trapped within the barrier.
As the Ocean Presses against the Volcano it now "Artificially" directs pressure thru nearest cut valves.
But as swell & tide rises it steeps Volcanic slope to repeatedly plunge higher each set wave.
Much like plunging a sink until it rushes water #@%* back up to overflow only it keeps comin' & rising.
But the lagoons can't drain over neighbouring higher shallow bars in heavy swell.
Nowhere to go but out the Teahupoo running Cut Canals > 40kms of Barrier Lagoons stoke the Teahupoo wave face.
In reality the whole Iti Island current drains at Teahupoo by default, including sub land neck currents.
Due to Sub Island Lava Tube effect...like a constant circulating sub sea current.
Once it starts it aint stoppin' with nowhere to go but to follow the only escape up the Teahupoo Tsunami.
The inward swell equally stokes the outbound swell at this exact point.
Because lava flow coral seabed is Solid it can't push down, scour or erode any deeper > Can only rise upward!
Basically the more Canals ya cut will keep ramping the wave higher each time...to a point...
So yes...one could widen or cut even more canals to energize an even faster higher wave!
With exact science you could cut custom canals to achieve greatest effect...but! Big But...
The Cutting of the East Canal puts immense pressure at that exact spot and led to the full fault-line crack!
The crew can now feel the reverberation because it's now unstable...so no more cutting of canals.
The only way of Stabilizing the Reef is to rejoin it fully to the land as before to block the Lagoon Exit!
Then the wave would partly die down & communities are again isolated.
No water Taxis + Would need to fill over the open cable...may not be that easy!
Not without massive delays and such!
But it's unlikely these towns will survive long enough to run larger vessels that need upgrades.
However the recent Olympics required deeper Fuel Tanks & some inshore cutting near marina & tower.
Locals also called out the Footbridge weir that fuelled extra flooding + Raised Fields.
All saw the effect of Mass Lagoons swamp Teahupoo to spit out cars like toys! (That's New they say!)
All locals agree & joined to blame recent 'Water' works that ramped the ocean system...
So it's not that wot tbb shares here would shock them...as similar effect is fast acknowledged right now!
60's Hodad said he began seeing Teahupoo shape up & was first to surf it with his mate in early '70's
No large waves, surfers or Ship Wrecks seen before until canals were breached to billow both Lagoons.
It is the hand of man that stokes and feeds their ramped Mutant Wave...as The Wedge & 1,000's more!
If all these canals were blocked & reefs re-connected whole to Volcanic Plains the whole show backs down.
Towns would die without the water Taxi / cable Network...so they gotta chance their own bastardized fate!
Once ya fill in the canals yer left with standard River Only outfall or about 10% of current Volume.
Back to being a placid deep water pass with standard wave swell crashing on front reef.
Just as it was pre 1960's > As the Hodad says > No waves will rise enough to run into the channel.
As the standard default river flow just cruises out as all them 100's-1,000's years prior.
If crew looks closer to Tahitian Islands here / afar ...the more ya look the more cut canals ya see.
Very few Passes would break as years gone by...All their Surf history has been bastardized as ours!
No point claiming this wave resembles some Surf God's local hang...it can't possibly be similar!
Vastly different and changing faster each year with more canal networks being cut!
There is a history of these earlier canals > For Timber > Livestock etc...long well altered in time.
tbb explained how Brisbane & Tweed dredge estuaries beneath sea level to invite the angry sea.
Once the angry sea enters it Flushes a tidal wave 40km up whole river...(tbb timetabled this with record dredging!)
Same effect as a Kid'z Sand Castle Moat...soon as yer canal reaches the Ocean...Stand Back...
Tiny Grom's hand scoops then a A Gigantic Rush of Ocean floods & wipes out Castle & levels all in seconds.
Everywhere else is as is...untouched & natural > All but where the hand of man Stoked the angry sea!
The sea does what it does and falls path of least resistance as a river down to the sea.
This is exactly the same Childlike devastation at play...as beachgoers we all see & know how.
Just a larger Volcano and Moat with restricted outfall to weaponize the wave like The Wedge.
Same deal...revert coastline outfalls to natural & all dies down in a heartbeat...nothin' to see!
Further onto this...the recent Olympic / Island cabling rests in these same canals but left uncovered.
Pause this vid [1:34] for Google / Chinese Olympic media Cable Map
Map also lends direction & flows of Currents as it follows the deepest line...Got It!
Again...this sub-lagoonal cable replaces Late 1950's washed away roadside poles'n'wires...Check!
It all tells & shares the same recent eroding timeline of infrastructure switch to canal network...ya see!
These Barrier Reefs & cut canals are their lifelines for transit / tech...more vital than roads.
None evaluate or review canals as none can revert to any Roads...some talk of new estate hookup?
https://la1ere.francetvinfo.fr/polynesie/tahiti/polynesie-francaise/4g-a...
Uncovered, high risk in shore cables...Tahiti just leased these cable stations to Google. (Soon-Private!)
Science tests show this AC/DC current in unprotected state will affect pooled habitat life force.
Not sure how or if these cables needed attaching due to massive water flow like a whipping waterfall!
Current will likely ramp & be trapped within the lineup to energize all around it more than any other!
Young bucks be wise to consider lead lined boardies if ya plan on 3 hrs in volatile live Googly current
Be motioning locals to runnin' tests or get a reading on these 'stronger' uncovered currents!
Just like the Wave > Everything is a bastardized upgrade without care of actions on last hot mess!
Oz / tbb's Goldie are no different...Rainbow dredges offshore Quarries only to faster erode beaches!
Then build an inshore reef to divert & trap cross cutting current to watch beach disappear > on & on!
Now the dredges run full loads for 20 years to try & fill these long distant Rainbow Quarries!
Does anyone know if there has been any higher resolution 3d Bathymetry scanning done? These maps are great but they seem a bit low-res and may not pick up a nuances of this wave and why it's so special, It would be awesome to see some more details on the curves and shapes of the bottom profile such as a 1mx1m grid resolution. The amount of boats that are out there everyday, you could have a 1cmx1cm grid by now, if they had some scanning equipment .
Further up the comment thread Tom (article author) mentioned he had better bathy readings coming shortly.
Thanks for the info Stunet. I'm looking forward to seeing those, as I'm sure they would explain a lot.
If you want to study nuances, imagine watching this slow motion footage on a giant Imax screen.
Mesmerizing.
S.R, you'd think so wouldn't you with the tens of thousands of photos taken but nope there's not a scrap of bathy out there for this particular reef. Until SHOM (French Hydrographic institute) generated some satellite-derived bathy. Agree it's pretty poor quality but does show the major features well enough for this type of model. You can see the macro-scale features though in this shot from Ben Thouard - the usual spurs and grooves of coral reefs (useful to wedge yourself into before taking one on the head) and the deep channel running alongside the reef platform.
https://i.pinimg.com/736x/b2/40/15/b240151f1ca31de63429bd89ca39970f.jpg
I have got some better satellite-derived bathy but it still doesn't show this resolution of features. For that you'd need multibeam sonar or bathy LiDAR - they actually collected some a couple of years ago but stopped just down the coast :(
The bottom must have a lot of water bouncing up off it and also back into the wave; otherwise there would be lots of deaths there (unlike Pipe, which seems to drive surfers into the reef).
?si=R8miD5TKs8I6WncHwipeout at 35 seconds
?si=KthdZj0B7hAipNC1 ?si=AoK8iTSwwCYiQ-UaIs the right hander on the opposite side of the channel surfable?
Or am I venturing into "Hush, it's a secret!" territory?
No secrets there mate. Not even the XL ultra perfect& totally epic right also on the same island
Be interesting to compare it to Sapinus. I've never been there but lots of boog footage looks exactly like Teahupoo.
Hey Tom. What’s your going rate? Love for you to come check on the beaches along the Mornington Peninsula and try and give us some scientific analysis as to why Portsea is so shit compared to the other beaches.
Thanks in advance,
Concerned resident.
Better with why breaks are good than why they're average Nick - too many potential reasons ;) Feel for you though, beach I grew up on only got good every 5 or so years when we got the right bar configurations. Keeps the crowd down at least...