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{{short description|Deposition landform in which an island is connected to the mainland by a sandy isthmus}}
{{for|the Italian town|Tombolo, Veneto}}
[[File:Tombolo Paximadhi Eboea.jpg|thumb|right|300px|Tombolo near [[Karystos]], [[Euboea]], Greece]]
[[File:Accreting coast Image6.svg|thumb|300px|right|Tombolo contrasted with other coastal landforms]]
A '''tombolo''' is a sandy or shingle [[isthmus]]. It is a [[deposition (sediment)|deposition]] [[landform]] by which an island becomes attached to the mainland by a narrow piece of land such as a [[spit (landform)|spit]] or [[bar (landform)|bar]].<ref>{{Cite book |chapter-url= https://link.springer.com/referenceworkentry/10.1007%2F978-94-017-8801-4_349 |doi=10.1007/978-94-017-8801-4_349 |chapter=Tombolo |title=Encyclopedia of Estuaries |series=Encyclopedia of Earth Sciences Series|year=2016|last1=De Mahiques|first1=Michel Michaelovitch |pages=713–714|isbn=978-94-017-8800-7|access-date=2021-04-05|archive-date=2021-06-14 |archive-url= https://web.archive.org/web/20210614210520/http://link.springer.com/referenceworkentry/10.1007/978-94-017-8801-4_349 |url-status=live}}</ref> Once attached, the island is then known as a [[tied island]]. The word ''tombolo'' is from the [[Italian language|Italian]] ''{{lang|it|tombolo}}'', meaning 'pillow' or 'cushion', and sometimes translated incorrectly as ''[[Ayre (landform)|ayre]]'' (an ayre is a [[shingle beach]] of any kind).

Several islands tied together by bars which rise above the water level are called a '''tombolo cluster'''.<ref>Glossary of Geology and Related Sciences. The American Geological Institute, 1957</ref> Two or more tombolos may form an enclosure (called a [[lagoon]]) that can eventually fill with sediment.

==Formation==
[[File:Ap Lei Pai viewed from the Tombolo.jpg|thumb|Tombolo connecting [[Ap Lei Pai]] to [[Ap Lei Chau]], Hong Kong]]
The shoreline moves toward the island (or detached [[breakwater (structure)|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 [[Water wave refraction|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.<ref>{{cite book|last=Easterbrook|first=Don T.|title=Surface Processes and Landforms|edition=Second|year=1999|publisher=Prentice Hall|isbn=0-13-860958-6}}</ref>

=== Unidirectional longshore drift ===
In the case of longshore drift due to an oblique wave direction, like at [[Chesil Beach]] or [[Spurn Head]], the flow of material is along the coast in a movement which is not determined by wave diffraction around the now [[tied island]], such as the [[Isle of Portland]], which it has reached. In this and similar cases like [[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 (landform)|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 [[shore]]lines. 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#Change|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==
{{div col}}
* [[Aupōuri Peninsula]], New Zealand
* [[Barrenjoey, New South Wales|Barrenjoey Headland]], [[Pittwater]], [[New South Wales]], Australia
* [[Beavertail State Park|Beavertail Point]], [[Conanicut Island]], [[Rhode Island]], United States
* [[Biddeford Pool]], [[Maine]], United States<ref>{{cite book|last=Neal|first=William|title=Atlantic Coast Beaches: A Guide to Ripples, Dunes, and Other Natural Features of the Seashore|year=2007|publisher=Mountain Press Publishing Company|location=Missoula, MT|isbn=978-0-87842-534-1|pages=272|author2=Orrin H. Pilkey|author3=Joseph T. Kelley}}</ref>
* [[Bijia Mountain]], China
* [[Broulee Island Nature Reserve|Broulee Island]], New South Wales, Australia
* [[Bruny Island]], [[Tasmania]], Australia
* [[Burgh Island]], [[Devon]], England
* [[Los Morrillos (Cabo Rojo)|Cabo Rojo]], Puerto Rico
* [[Cádiz]], [[Andalucía]], Spain
* [[Cana Island]], [[Wisconsin]], United States
* [[Chappaquiddick Island]], [[Martha's Vineyard]], [[Massachusetts]], United States
* [[Charles Island, Connecticut|Charles Island]], [[Connecticut]], United States
* [[Chausey]], [[Manche]] département, France (two features connecting the main island and two smaller outcrops)
* [[Chesil Beach]], [[Isle of Portland|Portland]], [[Dorset]], England
* [[Cheung Chau]], [[Hong Kong]]
* [[Crimea]], [[Ukraine]]
* [[Eaglehawk Neck]], [[Tasmania]], Australia
* [[S'Espalmador]], [[Formentera]], Spain
* [[Fingal Bay]], New South Wales, Australia
* The [[Rock of Gibraltar]]
* [[Grand Island National Recreation Area]], [[Michigan]], United States
* [[Grótta]], [[Seltjarnarnes]], Iceland
* [[Las Palmas de Gran Canaria|Guanarteme, Las Palmas de Gran Canaria]], [[Canary Islands]], Spain
* [[Gugh]], [[St Agnes, Isles of Scilly|St Agnes]], [[Isles of Scilly]], England
* [[Gwadar]], [[Pakistan]]
* [[Hakodate]], [[Hokkaido]], Japan
* [[Howth Head]], [[Dublin]], Republic of Ireland
* [[Inishkeel Island]], [[Narin, County Donegal|Narin]], Republic of Ireland
* [[Isola Bella (Sicily)]], [[Italy]]
* [[Kapıdağ Peninsula]], [[Balıkesir]], Turkey
* [[Konet Island]], [[Kuala Sungai Baru]], [[Malacca]], Malaysia
* [[Kurnell]], [[Sydney]], New South Wales, Australia
* [[Lake Pomorie]], [[Bulgaria]]
* [[Langness]], [[Derbyhaven]], Isle of Man
* [[Little Heart's Ease, Newfoundland and Labrador]] beach, [[Newfoundland]], Canada
* [[Llandudno]], North [[Wales]]
* [[Louds Island]] at [[Muscongus Bay]], [[Maine]], United States
* [[Maharees]], [[Dingle Peninsula]], Republic of Ireland
* [[Mare Island]], [[Vallejo, California|Vallejo]], [[California]], United States
* [[Maria Island]], Tasmania, Australia
* [[Maury Island]], [[Washington (state)|Washington]], United States
* [[McMicken Island State Park]], Washington, United States
* [[Miquelon]], [[Saint-Pierre and Miquelon]], France
* [[Monemvasia]], [[Laconia]], [[Peloponnese]], Greece
* [[Monte Argentario]], [[Tuscany]], Italy
* [[Mont-Saint-Michel]], [[Normandy]], France
* [[Mount Maunganui]], New Zealand
* [[Mount Taipingot]], [[Rota (island)|Rota]], Northern Marianas
* [[Nahant, Massachusetts|Nahant]], Massachusetts, United States (a natural tombolo, but connected to the mainland by a [[causeway]])
* [[Nissi beach]], [[Ayia Napa]], Cyprus
* [[Nusa Dua]], [[Bali]], Indonesia
* [[Ormara]], [[Pakistan]]
* [[Palisadoes]], [[Kingston, Jamaica|Kingston]], Jamaica
* [[Pangandaran]], [[West Java]], Indonesia
* [[Peniche, Portugal|Peniche]], Portugal
* [[Peniscola]], [[Province of Castellón|Castellon]], Spain
* [[Presque Isle Township, Michigan|Presque Isle]], Michigan, United States
* [[Giens Peninsula|Presqu'ile de Giens]], [[Hyères]], France
* [[Presqu'ile Provincial Park]], [[Ontario]], Canada
* [[Quiberon]], France
* [[Ras Hafun]], [[Somalia]]
* [[Sainte-Marie, Martinique|Sainte-Marie]], [[Martinique]], France
* [[Scotts Head, Dominica|Scotts Head]], [[Dominica]]
* [[Seongsan Ilchulbong]] in [[Jeju Province]], South Korea
* [[Sharp Island]], [[Sai Kung District]], Hong Kong
* [[Silver Strand (San Diego)]], [[Coronado, California]], United States
* [[St Michael's Mount]], [[Cornwall]], England
* [[St Ninian's Isle]], [[Shetland]], Scotland
* [[Sveti Stefan]], near [[Budva]], Montenegro
* [[Tombolo (Dogashima)|Tombolo]] at [[Dogashima]] in Japan
* [[Vatersay]], [[Scotland]] – the island comprises two sections connected by a broad tombolo
* [[Zhifu Island]], [[Yantai]], China 
<!--<ref>{{:D.D. Williams, CBI TAMUCC //CBI cbi.tamucc.edu/CHRGIS/University-Beach/}}</ref>-->
{{div col end}}

Some of these may be simple isthmuses, and not have the deposition creation that defines a true tombolo.<ref>{{Cite book|url=https://link.springer.com/referenceworkentry/10.1007%2F0-387-30843-1_474|doi=10.1007/0-387-30843-1_474|title=Beaches and Coastal Geology|series=Encyclopedia of Earth Sciences Series|year=1982|last1=Owens|first1=Edward H.|pages=838–839|isbn=978-0-87933-213-6|access-date=2021-04-05|archive-date=2022-03-22|archive-url=https://web.archive.org/web/20220322032423/https://link.springer.com/referenceworkentry/10.1007%2F0-387-30843-1_474|url-status=live}}</ref>

===Image gallery===
<gallery widths="200px" heights="200px">
File:Tombolo St Ninians 5940.JPG|The tombolo connecting [[St Ninian's Isle]] with the [[Mainland, Shetland|Shetland Mainland]]
File:Laguna di Orbetello.JPG|[[Monte Argentario]], [[Tuscany]], Italy
File:ChesilBeach.JPG|[[Chesil Beach]], seen from the [[Isle of Portland]] looking towards mainland [[Dorset]]
File:Angel Road Shodo Island Japan01s3.jpg|The Angel Road of [[Shōdoshima]], Japan
File:Evening view from the Mount over Mount Maunganui.jpg|Looking south from the summit of [[Mount Maunganui (mountain)|Mount Maunganui]], New Zealand, to the city of [[Tauranga]]
File:2010-10-01 02-27-36 DSC 0354 Boris.jpg|The eastern end of [[Bennett Island]] with its [[glaciated]] tombolo in the background
File:Gwadar satellite view.jpg|Satellite view of [[Gwadar]], Pakistan
File:Aerial view of Dublin 2.JPG|An aerial photo of the isthmus of [[Sutton, Dublin|Sutton]] which connects [[Howth Head]] and [[County Dublin]]
</gallery>

==See also==
{{portal|Geography|Islands}}
* {{anl|Ayre (landform)}}
* {{anl|Bar (landform)|Bar}}
* {{anl|Causeway}}
* {{anl|Cuspate foreland}}
* {{anl|Isthmus}}
* {{anl|Peninsula}}
* {{anl|Tied island}}
* {{anl|Shoal}}

== References ==
{{reflist}}

== External links ==
{{Commons category|Tombolos}}
* [http://geology.about.com/library/bl/images/bltombolo.htm Geology.About.com's page on tombolos] (useful for its descriptive photograph)
* [http://alyssawrites.com/tombolo-sainte-marie/ Tombolo in Sainte-Marie, Martinique] (useful for its photos and description)
* [https://web.archive.org/web/20151112071446/http://www.vliz.be/wiki/Detached_breakwaters further reading on Detached breakwaters from Vlaams Instituut voor de Zee in Belgium]
* [https://web.archive.org/web/20150723225935/http://www.leovanrijn-sediment.com/papers/Coastalstructures2013.pdf further reading on coastal structures from Prof. Leo van Rijn in Holland]

{{coastal geography}}

[[Category:Coastal and oceanic landforms]]
[[Category:Coastal geography]]
[[Category:Tombolos| Tombolo]]
[[Category:Oceanographical terminology]]