Tombolo
A depositional isthmus linking an island to the mainland.
A tombolo is a depositional landform consisting of a sandy or shingle isthmus that connects an island to the mainland. Once attached, the island becomes known as a tied island. The term originates from the Italian word for 'pillow' or 'cushion'.
Quick Facts
- Etymology
- Italian tombolo, meaning 'pillow' or 'cushion'
- Cluster term
- tombolo cluster
- Possible lagoon formation
- enclosure that can eventually fill with sediment
Facts from the source article.
Formation
True tombolos form through wave refraction and diffraction. As waves approach an island, they slow in the surrounding shallow water and bend around to the opposite side. This wave pattern causes a convergence of longshore drift on the lee side of the island, where beach sediments moving by lateral transport accumulate and conform to the wave shape. The waves sweep sediment together from both sides, and when enough sediment builds up, a spit connects with the island to create a tombolo. In cases where longshore drift results from an oblique wave direction, such as at Chesil Beach or Spurn Head, the flow of material is along the coast and not determined by wave diffraction around the tied island. In these instances, the strip of beach material may technically be called a tombolo but is better understood as a spit, because the ridge is parallel rather than at right angles to the coast.
Morphology and sediment distribution
A tombolo’s shape and size shift more easily than a typical beach due to tides and storms. A small island or even a wrecked ship can redirect waves, changing where sand and gravel pile up. Rising seas can also push sediment higher, adding to the land. The sand and pebbles inside are coarser near the bottom and finer on top. When rough waves strip away the fine surface, the heavier cobbles underneath become visible. To make tombolos more stable, people sometimes build roads or parking lots on them.
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