The way waves behave is a big subject. But here we’ll look at just one simple aspect, the way the wind shapes breaking waves at the shore.
It is easiest to think of wind at the coast as either onshore – blowing in roughly the same direction as the waves are breaking – or offshore – going in the opposite direction.
An onshore wind causes waves to break earlier, in deeper water and is more likely to create a type of wave called a spilling breaker.
An offshore wind causes waves to break later, in shallower water and is more likely to create a type of wave called plunging breaker.
To summarise: an onshore wind collapses the waves early on, making them spill up the beach, but an offshore wind holds them, giving them a steeper face, until they plunge down onto the beach.
In the picture at the top we are looking at a modest plunging breaker. The offshore wind is holding the wave up. If it looks like you might at some point be able to see through a ‘window’ in a breaking wave, then that is a wave with a steep face – a plunging breaker.
As mentioned, the way waves behave is a big subject. I managed to condense it down to a little over a chapter in my book, How to Read Water. But with a different approach it could fill many books.
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