Tombolo

Source: Wikipedia, the free encyclopedia.
For the Italian town, see Tombolo, Veneto.
Tombolo near Karystos, Euboea, Greece
Tombolo contrasted with other coastal landforms.

A tombolo is a sandy or shingle

bar.[1] Once attached, the island is then known as a tied island
.

Several islands tied together by bars which rise above the water level are called a tombolo cluster.[2] Two or more tombolos may form an enclosure (called a lagoon) that can eventually fill with sediment.

Formation

The shoreline moves toward the island (or detached breakwater) owing to the accretion of sand in the lee of the island, where wave energy and longshore drift are reduced and therefore deposition of sand occurs.

Wave diffraction and refraction

True tombolos are formed by

wave refraction and diffraction. As waves near an island, they are slowed by the shallow water surrounding it. These waves then bend around the island to the opposite side as they approach. The wave pattern created by this water movement causes a convergence of longshore drift on the opposite side of the island. The beach sediments that are moving by lateral transport on the lee side of the island will accumulate there, conforming to the shape of the wave pattern. In other words, the waves sweep sediment together from both sides. Eventually, when enough sediment has built up, the beach shoreline, known as a spit, will connect with an island and form a tombolo.[3]

Unidirectional longshore drift

In the case of longshore drift due to an oblique wave direction, like at

Cádiz, while the strip of beach material connected to the island may be technically called a tombolo because it links the island to the land, it is better thought of in terms of its formation as a spit
, because the sand or shingle ridge is parallel rather than at right angles to the coast.

Morphology and sediment distribution

Tombolos demonstrate the sensitivity of

shorelines. A small piece of land, such as an island, or a beached shipwreck can change the way that waves move, leading to different deposition of sediments. Sea level rise
may also contribute to accretion, as material is pushed up with rising sea levels. Tombolos are more prone to natural fluctuations of profile and area as a result of tidal and weather events than a normal beach is. Because of this susceptibility to weathering, tombolos are sometimes made more sturdy through the construction of roads or parking lots. The sediments that make up a tombolo are coarser towards the bottom and finer towards the surface. It is easy to see this pattern when the waves are destructive and wash away finer grained material at the top, revealing coarser sands and cobbles as the base.

Examples

Some of these may be simple isthmuses, and not have the deposition creation that defines a true tombolo.[7]

Image gallery

See also

References

  1. ISBN 978-94-017-8800-7. Archived
    from the original on 2021-06-14. Retrieved 2021-04-05.
  2. ^ Glossary of Geology and Related Sciences. The American Geological Institute, 1957
  3. ISBN 0-13-860958-6
    .
  4. ISBN 978-0-87842-534-1
    .
  5. S2CID 225314966 – via ResearchGate
    .
  6. S2CID 133158096
    .
  7. ISBN 978-0-87933-213-6. Archived
    from the original on 2022-03-22. Retrieved 2021-04-05.

External links

Wikimedia Commons has media related to Tombolos.
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