Cave Origins

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The Courtesan, Agen Allwedd

Nearly all caves are formed from a sedimentary rock called LIMESTONE.

Around 400 million years ago the Earth was almost entirely covered by sea. The limestone beds were formed from the skeletons of countless billions of marine animals. The layers called limy ooze were, in time covered by other sediments. The weights of the sediments pressed the limy ooze into solid rock.

Over the next several million years movements in the plates that make up the Earth's crust caused many of the limestone beds to be lifted up and left high and dry.

The major period of cave development was from about 2 million years ago to 10 thousand years ago.
The first stage of cave formation is caused by the action of acid rain. Rain becomes acidic by dissolving carbon dioxide from the atmosphere. However, this weak acid becomes much stronger and aggressive as it soaks through the soil and peat covering the limestone.

Had the limestone been a solid sheet the water running over it would have had little to get its teeth into, however the enormous forces which moved the rocks caused them to distort into:

DOWNFOLDS

or

SYNCLINES

and

UPFOLDS

or

ANTICLINES

The pressure on the rock layers caused them to crack.  Now the acidic water could percolate into the limestone beds.

Initially cave passages are formed under water.  First by the rock being dissolved along a joint or bedding plane and then by mechanical action as the water flowed under pressure.

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