The Green Bridge of Wales is a natural arch formed from Carboniferous Limestone within the Pembrokeshire Coast National Park, Pembrokeshire, Wales. It is located in the Castlemartin military training area just beyond the car park at Stack Rocks and beside the Pembrokeshire Coast Path.
The arch formed when the sea wore away the rock underneath. Once the arch was a point of high land that juts out into the sea of rock, jutting into the sea. It was solid, with no hole or arch to be seen. Weaknesses in the rock, known as joints and bedding planes, allowed the sea and the force of the waves to wear away the rock. At first, it is likely that a cave was formed in each side of the spur. As the sea gradually washed more rock away, the two caves joined together to make an arch.
It is thought that one day in the future the centre of the arch will collapse, and the arch will become a stack.
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