Sea cave
Caves formed by wave erosion along coastlines worldwide.
A sea cave, also known as a littoral cave, is a type of cave formed primarily by wave action through erosion. Found worldwide, sea caves actively form along present coastlines and exist as relict caves on former coastlines, with notable examples in Europe, the United States, Hawaii, and New Zealand.
- type
- Geological formation
- primary_process
- Erosion by wave action
- host_rock_types
- Sedimentary, metamorphic, igneous
- largest_known_by_length
- Matainaka Cave, New Zealand, 1.5 km
- notable_locations
- Norway, Scotland, Italy, Greece, California, Hawaii, New Zealand
Lore & Background
Sea caves form when wave action exploits weak zones in host rock, such as faults, dikes, or bedding planes. The process involves hydraulic pressure, air compression, and abrasion by sand and rock. Blowholes attest to the force of compressed air. Most sea-cave walls are irregular, but some are smoothed by swirling cobbles. Rainwater and organic acids may assist weakening, and small speleothems can develop. Life such as sea urchins can also enlarge caves by drilling into rock.
Reader's Guide
Sea caves are significant as dynamic coastal features that illustrate the power of marine erosion. Factors influencing size include the nature of the weak zone, exposure to prevailing seas, host rock strength, and time. The world's largest sea cave by length, Matainaka Cave in New Zealand, formed in heavily fractured sandstone, challenging prior assumptions. Relict sea caves in Norway, uplifted over 100 feet above sea level, demonstrate long-term geological change. Hybrid caves, such as those in Thailand's Phang Nga Bay, combine dissolutional and littoral processes. Sea caves can collapse into littoral sinkholes or form sea stacks when tunnels cut through headlands.
Did You Know?
- Matainaka Cave on New Zealand's Otago coast is the world's most extensive sea cave at 1.5 km in length.
- Some relict sea caves in Norway are now 100 feet or more above present sea level.
- The Blue Grotto of Capri has a Roman-built stairway and a now-collapsed tunnel to the surface.
More in Coastal & Marine Geology 1-21
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