Tombolos

A tombolo is a depositional coastal landform consisting of a narrow strip of sand or gravel that connects an island to the mainland or to another island. The feature forms when sediment carried by longshore drift and waves accumulates in the space between the island and the adjacent landmass, creating a spit or bar that grows toward the island and eventually links the landmasses.

Formation and dynamics occur as sediment transport along the coast builds up material in the lee of an island or reef. As the spit extends, it reduces water depth in the intervening channel, allowing more sediment to accumulate and the connection to solidify. The resulting land bridge may be exposed at low tide but can be submerged at high tide, and its width and extent are influenced by storm events, sea level change, and sediment supply. Tombolos are dynamic features that can shift or reconfigure over time.

Characteristics commonly include a sandy or gravelly composition and variable width. Some tombolos are simple links between two larger landmasses, while others form compound systems that connect multiple islands via a shared spit. Their presence alters local hydrodynamics and ecology, creating new habitats and affecting sediment budgets and coastal erosion patterns.

Examples include Chesil Beach in Dorset, England, which is often cited as a classic tombolo connecting the Isle of Portland to the mainland. Tombolos remain important in coastal geology for understanding sediment transport and land formation along shorelines.