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[[Image:seacaving.jpg|thumb|300px|Exploring a sea cave]]
A '''sea cave''', also known as a '''littoral cave''', is a type of [[cave]] formed primarily by the [[wave]] action of the [[sea]].  The primary process involved is erosion.  Sea caves are found throughout the world, actively forming along present coastlines and as relict sea caves on former coastlines. ISome of the largest wave-cut caves in the world are found on the coast of Norway, but are now 100 feet or more above present sea level. These would still be classified as littoral caves. By contrast, in places like Thailand's [[Phang Nga Bay]], solutional caves have been flooded by the rising sea and are now subject to littoral erosion.

Some of the best-known sea caves are European. [[Fingal's Cave]], on the Scottish island of [[Staffa]], is a spacious cave some 70 m long, formed in columnar basalt. The [[Blue Grotto (Capri)|Blue Grotto]] of [[Capri]], although smaller, is famous for the apparent luminescent quality of its water, imparted by light passing through openings underwater. The Romans built a stairway in its rear and a now-collapsed tunnel to the surface. The Greek islands are also noted for the variety and beauty of their sea caves. Numerous sea caves have been [[Speleology#Cave cartography|surveyed]] in England, Scotland, and in France, particularly on the Normandy coast. The largest sea caves are found along the west coast of the United States and in, the Hawaiian islands, and the Shetland Islands. 

== Formation ==
[[Image:seacave fault.jpg|thumb|left|250px|Sea cave formation along a fault]]
[[Image:seacave dike.jpg|thumb|right|250px|Sea cave formation along a dike]]
[[Image:littoral sinkhole.jpg|thumb|left|250px|Sea cave collapse]]
[[Image:Belvedere della Grotta di Nereo.jpg|thumb|left|250px| The "belvedere" watching place in the north [[Sardinia]] [[Nereo Cave]]]]
[[File:Akun Island basalt sea cave.jpg|thumb|right|[[Akun Island]] [[basalt]] sea cave]]
(contracted; show full) throughout geological time by an interplay between sea-level change and regional uplift. Recurrent [[ice ages]] during the [[Pleistocene]] have changed sea levels within a vertical range of some 200 meters. Significant sea caves have formed in the [[California Channel Islands]] that are now totally submerged by the rise in sea levels over the last 12 000 years. In regions of steady uplift, continual littoral erosion may produce sea caves of great height — Painted Cave is almost 40 m high at its entrance. 
On the Norwegian coast there are huge sea caves now uplifted 30 or more meters above sea level. Sediment dating in the largest of these (Halvikshulen in Osen, 340 m long)shows that it was formed over a period of at least a million years. It may well be the largest wave-cut cave known by both length and volume.

Finally, caves that are larger tend to be more complex. By far the majority of sea caves consist of a single passage or chamber. Those formed on faults tend to have canyon-like or angled passages that are very straight. In Seal Canyon Cave on Santa Cruz Island, entrance light is still visible from the back of the cave 189 m from the entrance. By contrast, caves formed along horizontal bedding planes tend to be wider with lower ceiling heights. In some areas, sea caves may have dry upper levels, lifted above the active littoral zone by regional uplift.
 
Sea caves can prove surprisingly complex where numerous zones of weakness—often faults—converge. In Catacombs Cave on [[Anacapa Island]] (California), at least six faults intersect. In several caves of the Californian Channel Islands, long fissure passages open up into large chambers beyond. This is invariably associated with intersection of a second fault oriented almost perpendicularly to that along the entrance passage. When caves have multiple entrances, they are exposed to more wave action and hence may grow relatively faster. There is an exceptionally large cave underlying the Fogla Skerry, an islet off the coast of Papa Stour, in the Shetland Islands. Though unsurveyed, estimates place it at almost 500 m of passage--meaning it could actually be the world's longest sea cave.

== References ==

* Bunnell, D. 1988. ''Sea Caves of Santa Cruz Island'', Santa Barbara, California: McNally and Loftin Bunnell, D. 1988b.
* Bunnell, D. 1993. ''Sea Caves of Anacapa Island'', Santa Barbara, California: McNally and Loftin 
* Bunnell, D. 2004. Littoral Caves. Chapter in Gunn, J. (Ed.)''Encyclopedia of Caves and Karst'', Fitzroy Dearborn, New York, NY.
* Moore, D.G. 1954. Origin and development of sea caves. ''National Speleological Society Bulletin'', 16: 71–76

== External links ==
* [http://www.goodearthgraphics.com/virtcave/seacaves/seacaves.html Photos and information] on sea caves in the Virtual Cave
* [http://www.andymcinroy.com/5port.htm Great Sea Caverns] of County Antrim, Ireland - Photographic Project

{{Caves}}
{{coastal geography}}

[[Category:Sea caves| ]]
[[Category:Coastal and oceanic landforms]]

[[ja:海蝕洞]]
[[simple:Sea caves]]