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.

In Orkney, most beach sand is rich in shell and even when sea salts are removed by rain the sand retains a high pH. Active dune systems are present at Dingieshowe, Aikerness, Scapa, Stronsay and Sanday among others. Dune sands have begun to accumulate on the Churchill Barriers. Along the western seaboard, the Birsay Links, Skaill Bay and Warebeth Beach, the dune ridge systems are less obvious. These subdued dunes and links may relate to sand movement and dune formation from a beach front that lay much further west than today. The links at Skaill show dune sands that overlie fresh water loch peat deposits dated at 6580 ± 80 yrs. A site at Tofts Ness, Sanday was settled from the Neolithic period but was then abandoned in the late Neolithic/early Bronze Age for approximately 1000 years before being resettled in the late Bronze Age and then permanently abandoned in the Iron Age. Sand layers lying above the late Neolithic soils have been dated by OSL to about 4000 BP. The increase in dune-building activity in Orkney may correlate with the Hekla 4 and 3 eruptions in Iceland (Sommerville, et al., 2001).

Tres Ness, Sanday. Image from Alan Moar

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.

Churchill Barriers, Orkney. Image by Alan Moar.

  • The outer coast of Orkney is an outstanding location to study the erosion of hard rock coasts. Evidence of major erosion is not hard to find. The great bowl of Enegars corrie is losing its edge to the sea. The egg-shaped headland of Marwick Head is a dome half lost.

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  • Amongst the many beauties of Orkney are the beaches which fringe the bays and ayres of the inner coast. These are dynamic forms, changing shape with the seasons and gradually retreating landward as sea level rises.

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  • Orkney is a dissected landmass drowned by postglacial sea level rise. A drop in sea level of just 35 m would unite the archipelago into a single island. The individual islands may represent hills that formed the watershed areas of preglacial drainage basins but it is linear glacial erosion which has separated one island from another and severed Orkney from the rest of Scotland.

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  • World coasts have seen sea-level variation of approximately 100 metres within the past 11,500 years through melting of the ice caps. When the ice caps melt the sea level rises globally (eustatically). The relative sea-level at any location is measured proportionate to the nearby land, which is itself subject to tectonic movement both up and down.

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