CAVES, or caverns, are holes made in the earth's surface by the forces of nature.
Sea caves were formed by the steady beating of the sea against rocks on shore.
Limestone, or dolomite, caves were formed when water trickled through the cracks of solid rock mountains.
This dissolved the soft limestone rock and formed holes and tunnels; over thousands of years the holes and tunnels became larger and larger until they were caves.
Lava caves form when the hot lava from volcanoes hardens on the earth's surface, while the liquid lava flowed out from beneath the hardened layer.
This created small caves with layers of lava forming roofs.
Ice caves are created in a similar way to limestone caves, but the cold interior allowed the water to freeze and coat the walls in a layer of ice. - amazingfactsworld.com