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Marble columns

As groundwater flows through the limestone substrate, it dissolves the rock in underground systems called karsts. This process, studied by geologist William Sallun Filho, creates caves with a diverse range of features. Vale do Ribeira, south of São Paulo, is home to many such caves. In Gruta Fria (Cold Grotto – photograph), pillars hanging from the ceiling—known to experts as pendants—show how the water flowed through a labyrinth of conduits, creating these structures that avoided erosion at the crossing points. The marble that this cave is made of does not dissolve easily.

Image submitted by William Sallun Filho, a researcher at the São Paulo State Institute for Environmental Research