Sea caves or littoral caves are formed primarily from erosion caused by waves. They can be formed along the ocean coast and lakeshores where water impacts bedrock. Most sea caves are formed along weaknesses in the rock, such as faults, fractures, or bedding/foliation planes and can occur in nearly every type of rock.
Sea Cave Development
1) Bedrock with fractures and large fault.
2) Caves develop as waves erode the faults and fractures near the edge of the water.
3) With continuing erosion, the cave becomes open at both ends forming a natural bridge or arch.
4) Arch roof collapse leaves behind a sea stack and further erosion turns another cave into an arch.
Coastal Erosional Features
As erosion progresses, the cave can become open at both ends to form a natural bridge or arch. When the arch roof collapses, it leaves behind a sea stack, no longer connected to the mainland above mean high tide. Caves and arches will continue to form as waves erode more of the bedrock.
Sea caves can be important habitat to many types of animals. Sea Lions use caves as haulouts that provide shelter and protection from predators. Many marine fish and invertebrates also use the dim, dark, environment for shelter.
The unique environment of sea caves provides home to several invertebrate species including crickets, spiders, and marine invertebrates, including an undescribed troglobitic isopod known to occur in only two caves in the Golden Gate National Recreational Area (Elliot et al. 2017).
Humans, modern and ancient have made use of sea caves for shelters and other purposes. Objects such as rafts, wooden kayaks, and other items have been found cached in caves. Most of these caches have been found in caves now well above sea level due to the retreat of glaciers. Petroglyphs, and pictographs suggest some sea caves may have been used as temporary shelters or hiding places, and possibly ceremonial sites.
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Find Your Park—Sea/Littoral Caves
The following is a partial list of National Park Service units that include sea or littoral caves:
Last updated: April 27, 2022