The underlying rock is predominantly limestone, which dissolves to form sinkholes and underground caves.

A lava tube runs from the volcano to the sea, billowing out to form caves along the way.

Over time, this process can form caves.

This type of limestone easily dissolves when exposed to water, forming caves and natural voids.

The sea attacks weak points, forming caves, then arches until eventually a whole section of cliff falls.

Between those ribs, at floor level, sub-chambers formed deep caves.

His bushy eyebrows formed caves in which pale-blue eyes fixed on her.

To some degree moisture is always available in actively forming Karst caves.

Most of these lava tunnels have collapsed but sections of them form caves and can be accessed from private properties in the area.

These flank vents formed the arches and caves seen today.