beach 

dune

spits and bars

 

 

Tres Ness, Sanday. Image from Alan Moar

 

Tombolos or ayres

Definition: a spit that connects the mainland with an island

Although tombolos are by no means rare in archipelagos, they are numerically few relative to other classic forms of marine deposition. In the Northern Isles, tombolos are known locally as ayres (Old Norse Eyrr - gravel beach). The majority are formed of materials coarser than sand, including gravel, cobbles or, occasionally, boulders.

Where the coastline changes direction abruptly, as at the opening of bay, longshore drift often continues in the same direction. The load of sand and gravel will be dropped in the deeper water, leading to the growth of a spit down drift. The spit may grow until it joins the other side of the bay and form a tombolo or ayre.

At Tres Ness, the tombolo joins a low shore platform to the island. The tombolo forms a beach 1.5 km long, backed by dunes. Other good examples of tombolos occur at Copinsay and Corn Holm.