A living stone factory
The Cascades des Tufs at Baume-les-Messieurs are an active geological construction site. These waterfalls are perpetually building themselves out of a porous, limestone rock called tufa. The process begins deep within the Jura Mountains, a region defined by its karst hydrogeology. Rainwater seeps from the plateau above, percolating through Jurassic limestone and becoming heavily saturated with calcium bicarbonate. This mineral-rich water flows through an underground cave network as the river Dard before emerging from the Grottes de Baume.
As the water re-emerges and tumbles over the existing cascades, it experiences a rapid change in pressure and temperature. This causes it to release dissolved carbon dioxide (CO₂) into the air. The loss of CO₂ shifts the water's chemistry, making the calcium bicarbonate far less soluble. As a result, it precipitates out of the solution as solid calcium carbonate (calcite). The chemical reaction is: Ca²⁺(aq) + 2HCO₃⁻(aq) ⇌ CaCO₃(s) + H₂O(l) + CO₂(g). The constant removal of CO₂ by the turbulent water flow drives the reaction to produce more solid calcite. This calcite forms a crust on every surface the water touches, especially the mosses and algae that thrive in the spray.