A tombolo (Italian, from Latin tumulus – mound) or sometimes ayre (Old Norse Eyrr – gravel beach)'s a deposition landform in which an island's attached to the mainland by a narrow piece of land such as a spit or bar. Once attached the island's then known as a tied island. They usually form because the island causes wave refraction, depositing sand and shingle moved by longshore drift in each direction around the island where the waves meet. Eustatic sea level rise may also contribut… (More on Tombolo)