Generally, the caves that extend into the cliff beyond the level of highest high tides are called sea caves. The sea caves can be classified as overhanging and underhanging caves, the former being those whose roofs overlie than their openings and the latter being those whose roof and opening line up.
Sea caves are formed in much the same way as sea stacks. The only difference is that they are entirely under water.
Their formation begins when churning waves undercut a rock or a piece of rock, resulting in the formation of small cavities, which are initially inhabited by marine creatures.
These creatures leave behind deposits of carbonate minerals which solidify over time, thus combining with the rock to form limestone.
The roofs of caves collapse and the sea cliffs recede further inland. Retreat of the cliff may leave some remnants of rock standing isolated as small islands just off the shore. Such resistant masses of rock, originally parts of a cliff or hill are called sea stacks.
