A sea arch is a natural arch or bridge made of stone that has been created when water wears away the underside of a rock, leaving just the top behind. They commonly form where cliffs meet the sea.
Natural arches are created through the process of land, wind, or water erosion, or some combination of these methods. They are often made by the meeting of two types of rock, with the harder substance on the top of the arch, which forms the bridge. When the bottom rock is a softer type of stone, it will erode away more quickly, leaving behind an arch.
A sea arch is created when the natural erosive forces of water break through a slice of rock and leave behind an arch. Water, after all, is one of the most powerful forces on the planet. It has the power to destroy cities, but it also has the power to make stunning sculptures in the earth, such as the Grand Canyon.
Beautiful sea arches exist all around the world. One particularly well known one named "London Bridge" was located near Victoria, Australia, but collapsed into the water in 1990. Others include the Durdle Door and the Stair Hole on the coast of southern England.
These arches are often formed out of former caves. In many instances, a limestone cave full of sinkholes will begin to collapse, leaving behind what was once the mouth of the cave. This former entrance then becomes an arch.
Because each sea arch is the result of erosion, many of them will eventually collapse, like Australia’s London Bridge. Depending on the age and structure of the arch, it may look sturdy and everlasting or frail, about to fall in on itself. As one falls to rubble at the edge of the ocean, however, another will likely take its place when a cave collapses in on itself or a sliver or weak rock finally gives way to allow the passage of wind and water through the stronger arch above.