Maejima Island Tombolo
Wave-formed link between two islands
Naru Island is only reachable by using one of the ferries that pass by the small island of Maejima on their way to the island’s main port. Connecting Maejima Island to the even smaller Suetsushima Island is a 300-meter-long tombolo, a neck of gravel that is only completely visible at low tide. Tombolos are formed by the natural accumulation of material, normally sand, on the lee side of an island. This builds up over time until it grows long enough to attach to an offshore island (in this case, Suetsushima Island), which becomes what is known as a tied island. The formation of a tombolo is related to wave refraction and diffraction, as waves are bent around the outside island, slowing the wave motion and leading sediment to pile up.
Tombolos are uncommon, and can be destroyed by erosion. The Maejima Island tombolo is made up mostly of gravel, not sand, so eroded rock must be continuously carried from the surrounding islands for the tombolo to exist—a natural phenomenon that occurs without human intervention. This tombolo is especially graceful, and Nagasaki Prefecture has designated it an environmental conservation area.