I think it must depend on a few factors – the force of the tide hitting the coast at that particular place (rough seas will erode quicker!) and the type of rock that the coast is made of. “Soft” rocks like chalk and limestone will erode quicker and make beautiful caves and things!! I was in a limestone cave last month – it was awesome and so beautiful!! 🙂
Hi Dangermousegirl. At my old university they had a big water tank with a wave generator and a gravel beach trying to investigate this question. Sea water hitting land isn’t as simple as just eroding – the waves can wash up new sand as well, or shift it from one part of the coast to the other. It has to do, as Amy says, with the force and direction of the waves, the tides, and the exact shape of the coast. I’ve seen places where putting up a protective sea wall has accidentally caused a beach to disappear.
Hi dangermousegirl! The sea both deposits and removes materials, so our coastlines are pretty dynamic. Whether a particular shoreline is being built up or eroded away depends on complex current processes throughout the ocean. These depend on global weather patterns so there are a lot of both spatial and time scales involved! Basically there are a lot of factors that come into play! This is on top of the fact that different beaches are made of different materials.
I love the beach! Its so fun to watch the waves, and so amazing to think about what they can do over time!