There are so many nice beaches alongside the Thai Southern Line. So what makes for a nice, sandy, crescent-shaped beach in Thailand? The answer: a “discordant” + few million years.
When waves and wind attack a coastline such as the one we’re travelling down, the softer rock will erode first, and the harder rock later. When the layers of soft and hard rock run perpendicular to the coast like here, the hard rocks turn into headlands or promontories, which you may see popping out of the eastern horizon every 10 kilometres or so.
These rocky bluffs serve as anchors for littoral systems in between them. The soft rock is ground down into fine sand by the waves and wind, and pushed into the crescent shape by the rip currents and tides.
Over time, these beaches take more and more of a crescent, concave shape as the erosion process continues. The headland, which separate one beach from another, can eventually find itself at the end of a narrow strip or spit of land, which erodes down to a sandbar, and ‘plop’ the headland becomes and island. Then the beach continues eroding behind it until it finds the next hard rock to serve the role as headland.
So if you’re out searching for the perfect beach, look out for some nice big coastal karst mountains, and also keep an eye out for this process and the stage of erosion your crescent beach is at.