The cave formed when the calcium carbonate was dissolved by groundwater allowing the silica to be washed away.

The cave, which can still be viewed today, formed the settlers' first line of defense.

The caves here formed his summer home from the 1920s until shortly before his death in 1947.

The cave formed in between the branches of this tree.

Liftup caves form on the edges of the pressure ridges or pressure plateaus.

Other caves can form inside pressure ridges when the lava vacates leaving an inflationary cave.

During the summer months snow-melt streams flow beneath the debris piles and cause caves to form in the ice.

The caves themselves formed about 240 million years ago, making them the oldest known caves in the world.

Referred to by local residents as "The Rocks", it has large sandstone deposits in which some caves have formed.

He found nothing, but, finally, a cave formed by two tilting boulders.