The Miraculous Circumstances that Makes Mundaka Pump

Tony Butt

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Updated 44d ago

Almost everybody in the surfing world has heard about Mundaka, Europe’s most famous wave. Mundaka is pretty special; not just because of its perfection, power or length, but because of the miraculous circumstances that made it the way it is.

Sure, there are waves just as big, long and hollow, but the vast majority break on rock or coral platforms. Mundaka, on the other hand, breaks on a sandbar created by a river. There are many factors that go together to make Mundaka the way it is, but the sandbar is the main protagonist in the story; just like the canyon at Nazaré, or the reef at Pipeline.

Live Cam: Mundaka

To start with, where does that sandbar come from and how does it stay there? The sandbar at Mundaka is built up and maintained in place by a combination of gentle wave action that brings sediment in from the sea, and the flow of the river combined with the outgoing tidal flow, that brings sediment down from the land. It works in a similar way to most rivermouth surf spots (see HERE) but with a few of its own variations.

The onshore transport mechanism is much weaker than the offshore one, but still almost as important. During long periods of small waves, it helps to build up the bar from the offshore side. The offshore transport mechanism – the flow of the river boosted by the outgoing tidal flow – is the main one responsible for supplying sediment to the bar. When the tide is dropping, the two flows form a strong seaward-flowing current which scoops up large amounts of sediment from the bed. In the case of Mundaka (but not necessarily the case with all rivermouths), the tidal flow dominates over the riverflow.

The strength of the tidal flow is why you won’t find many people in the line-up until about half an hour after low tide. On the outgoing tide, the current rips through the line-up, constantly pulling you off the peak, and making the waves practically impossible to catch. The extra half-hour is to allow the incoming tide to neutralise the riverflow, which, as I just mentioned, is added to the tidal flow.

During large storm or swell events, there is more energy coming in from the sea. A lot of big storms or swells, one after the other, eventually tend to destroy the shape of the bar. That is why the best waves at Mundaka usually occur some time during the autumn or early winter. More about this in a moment.

First let’s have a look in a bit more detail why Mundaka has a wave like that, while most other estuaries in the world don’t. The underlying reason is that it depends on a delicate combination of factors, all of which happen to coincide at Mundaka. For example:

*The scale of the river and the estuary must be just right compared to the scale of the waves. The coastal geology and the incoming swells at Mundaka perfectly match each other, so that they can happily produce world-class waves between three and 12 feet. At many other spots in the world, the prevailing swells are either too big or too small for the scale of the coastal features.

*The direction and quality of the incoming swells must combine perfectly with the orientation of the bar. This not only depends on the orientation of the coast where the estuary is situated, but also whether the waves have previously been interfered-with before reaching the estuary. At Mundaka, the raw swells first wrap around a headland called Cabo Matxitxako, about four kilometres away. This filters the waves so that they reach Mundaka as long, ruler-edged lines, which hit the bar at exactly the right angle.

*The shape and length of the bar must be just right. At Mundaka, the orientation of the outer edge of the bar with respect to the incoming swells is at exactly the right angle so that the wave is not too fast and not too slow; the outer edge of the bar is straight enough so that the wave continues to break at almost the same speed along its length. And the depth graduation of the outer edge of the bar is at such an angle that, at is best, the wave can be a round, open barrel from beginning to end.

*The prevailing wind conditions must be right. At Mundaka, if the wind is from the west-southwest, southwest or south, the action of the river valley funnels it round so that it ends up coming from the south at Mundaka, which is offshore. This greatly increases the number of surfable days, particularly since Mundaka is still surfable with strong offshore winds.

A northwest swell refracts around Cabo Matixitxado and arrives at Mundaka.

A northwest swell refracts around Cabo Matixitxado and arrives at Mundaka.

The sandbar at Mundaka and the swells that break on it are closely linked in a kind of feedback loop. The shape of the bar controls the shape of the waves, but the force of the waves also changes the shape of the bar. After a certain length of time with constant swell, the bar tends to get broken and battered, just like you might get injured after surfing big waves for two months. The bar then needs a period of calmer weather to ‘rehabilitate’ and get ready for the next season of big swells. This means that the waves at Mundaka are usually best at certain times of the year. Here is a summary:

*Summer: Not many surfing days, with a lot of small swell and local windseas from the northeast. The lack of storms gives the bar a chance to gradually build up to single hump, the right shape and orientation for when the swells come in the autumn.

*Autumn: Best time of year for the most perfect waves, although not the biggest. Medium to large, long-period swells begin to arrive from distant storms, and local wind conditions are usually good. The bar that has been accumulating all summer is in good shape, so that the waves are long and hollow.

*Early winter: The first half of the full winter season can have the best big waves at Mundaka. The offshore winds tend to be stronger than in the autumn, but this actually makes the bigger swells more makeable. However, some swells are just too big for Mundaka to handle, sometimes closing out from end to end.

*Late winter: After being hammered by swells for a couple of months, or even just after a one really huge storm, the bar will inevitably lose its shape. Instead of a single hump, the bar spreads out over a wider area. The waves might have one or two good sections but probably don’t connect all the way through, or could end up closing out or backing off.
Spring: Typically, a poor time of year, but sometimes you can be lucky. After its winter thrashing, the smaller waves of spring might allow the bar to make partial recovery in time for a late-season swell, perhaps around Easter.

Sediment flowing out of the river to form the sandbar with the waves peeling along the depth contours of between 0.5 and 3 metres, depending on the size of the swell.

Sediment flowing out of the river to form the sandbar with the waves peeling along the depth contours of between 0.5 and 3 metres, depending on the size of the swell.

The waves at Mundaka vary throughout the year, but, in general, they more or less stick to the same pattern every year. The system is in dynamic equilibrium, with the sandbar deteriorating throughout the winter, recovering during the summer, and then producing epic waves again during the first part of the following winter. Of course, some winters have more swells than others, but the behaviour of the sandbar is generally predictable throughout the year, because all the natural factors work in harmony with each other.

Now, if somebody came along and interfered with the system, for example, by dumping thousands of tonnes of sand in the middle of the estuary, it might put things out of balance. That’s what happened in 2003 and what nearly happened in 2015. In a future article I’ll talk more about the importance of preserving spots like Mundaka, which are, in my mind, marvels of Nature, just as unique as Victoria Falls, Mount Everest or the Grand Canyon.

Cover shot, Jon Aspuru.