A sea cave, also called a littoral cave, begins as a small crack or weak spot in a cliff beside the sea. Ocean waves – salty water full of gravel and sand pound against this spot for centuries, slowly enlarging it and hollowing out a cave in the side of the cliff.
Aside from water, rough forces such as wind and cold temperature also help form sea caves and hollow out delicate details like grand arches and networks of small caves that fit together like a honeycomb. Wind has a strong corrosive power over time, just like water, and it rushes through the caves, especially at low tide. Cold temperature freezes water that creeps into cracks along the surface of the rocks. When it freezes, it expands, hence enlarging those cracks.
Sea cliffs made of soft rock, such as sandstone, present the best conditions for the formation of sea caves. Still, the wind and the waves with their repetitive motion and abrasive content, can form caves even out of hard rock.
Most littoral caves span less than 300 meters from the entrance to the end. The longest sea cave in the world, the Matainaka Cave in New Zealand, is 1,540 meters long. The Sea Lion Caves in Oregon have the largest volume of all the sea caves in the world. They are also the longest caves in the United States.