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They are the easiest mineral formations to be found in caves. Stalactites hang from the ceiling in the form of pointed cones. Stalagmites, on the other hand, look similar, but grow in the opposite direction, from the ground up. Both arise because the limestone rocks of cave regions are usually quite soluble – that is, easily dissolved by water. Infiltrating through cracks in the ground, water from rain or rivers penetrates underground. On the way, it carries with it the dissolved limestone from the rocks. On the ceiling of the caves, this water begins to drip, slowly forming a kind of straw with the fragments of minerals it carries.
When this straw clogs, waste accumulates at the base, which widens, giving the formation the appearance of a cone, typical of stalactites. On the ground, just below them, the stalagmites appear. Water dripping from the ceiling accumulates minerals in the ground, creating another sculpture that grows towards the stalactite. If the dripping continues, the tendency is for the two blocks to join in a single column. This union, of course, does not happen overnight.
“The growth rate is fractions of a millimeter per year. And that’s if there’s a lot of humidity in the cave”, says geologist Ivo Karmann, from the University of São Paulo (USP). In addition to being a scenario of rare beauty, the caves sculpted by the dripping water keep the history of the climate in the region. “By measuring the growth rate of stalactites and stalagmites, we have an idea of the rainfall in the place. They are the only preserved records of wind and erosion that make it possible to study climate variations up to 100,000 years ago. Therefore, it is very important to conserve them”, says Ivo.