But, like Larderello, today's geothermal electricity comes from unique geologies, where hot rocks and underground water sit together, close to the surface of the earth.

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That seemed to support the notion that underground liquid water may reside close enough to the surface in some places that it can seep out periodically.

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Detailed studies of the surface indicate that these were formed by a lake caused by the flow of underground water that periodically made its way to the bottom of the crater.

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Cold ocean water leaks through the rock, hits the red-hot underground lava and bubbles up to the surface.

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Because most of the peninsula sits on a limestone shelf, there are no surface rivers, and rainwater quickly seeps underground where it gathers and forms subterranean bodies of water known as cenotes.

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