Solution weathering, County Fermanagh

These caves, were carved by solution weathering when water seeped into cracks in the limestone, gradually enlarging them. Most limestone caves in Britain formed like this.

Rainwater becomes acidic as it dissolves carbon dioxide from the air and soil, and can dissolve away the rock to form cave systems.

Beautiful cave formations can result when water, dripping from cracks in the cave roof, loses some of its dissolved carbon dioxide and deposits some of its dissolved calcium carbonate - forming stalactites (hanging from the roof), stalagmites (growing up from the floor) or forming layers of smooth flowstone.

The caves of Fermanagh are carved into limestones laid down in tropical seas during the Carboniferous Period, around 350 million years ago.