Watch Wonders online: Episode 3 The Carlsbad Caverns

The Carlsbad Caverns, beneath the unrelenting deserts of New Mexico, are among the most spectacular underground cave systems in the world. So extraordinary are they that the caves were used as the set for Journey to the Centre of the Earth. This film will tell the story of how the caverns were formed and how they came to be discovered. The National Park in which the Caverns are set contains more than a hundred limestone caves. Two hundred and fifty million years ago a 400 mile reef in an inland sea covered this part of New Mexico. Later this reef of sponges, algae, seashells and calcite were uplifted. Then rainwater seeped into the cracks in the reef, slowly dissolving the limestone to create large underground chambers. The exposed reef became the Guadalupe Mountains and the underground chambers became the wonder of the Carlsbad Cavers.

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