HU3720 : Sands of the tombolo, St Ninian's Isle
taken 13 years ago, near to Bigton, Mainland, Shetland Islands, Scotland
A tombolo is a beach or bar (sometimes called an "ayre") which connects an island either to another island or to the mainland. It therefore effectively results in the smaller island becoming a peninsula, though this depends on definitions.
Tombolos are formed by the refraction and diffraction of waves around the island causing sand, gravel and pebbles to be swept in both directions around the island until they meet on the mainland-ward side of the island. The sand/pebbles then pile up to create a bar or spit of land above normal sea level, creating a causeway to the island.
The finest (and largest) tombolo in the British Isles is considered to be that which links St Ninian's Isle to the island of Mainland, Shetland. See HU3720 : St Ninian's Isle tombolo to view this example.
Lying off the west coast of Mainland Shetland adjacent to the village of Bigton, St Ninian's Isle is connected to the main island by a shell-sand tombolo, reckoned to be the finest (and largest active) example in the British Isles.
St Ninian's occasionally becomes a true island when tides and weather combine to inundate the tombolo, but usually it is, strictly speaking, a peninsula.
The little island has an area of approximately 178 acres (72ha) and rises to a maximum elevation of 174' (53m). According to the information board on the Bigton side of the tombolo, the coastal walk around the island is approximately 3½ miles (5.3km) long and will take about 1½ - 2 hours to complete. This board also tells us that the island was inhabited until 1775, though Wikipedia gives a date of 1796.
On 4th July 1958, a schoolboy, Douglas Coutts, who was helping visiting archaeologists, uncovered the fantastic Pictish silver "St Ninian's Isle Treasure" dating from c.800 AD see Link and Link for more details.