There are many mechanisms leading to the formation of cavities and voids underground. Some caves are classified as “primary” because they are generated at the same time as the rocks containing them, others instead form subsequently, due to rock weathering that modify their original characteristics.
Lava cave on Etna, Italy
Blue Hole, Belize
Fingal's Cave, Scotland
Frasassi cave, Italy
Caves of Cala Luna, Italy
Cuevas de Mármol, Chile
Sea caves on Lake Superior, Wisconsin, U
Benagil cave, Portugal
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