A landscape built by water
In the Val d'Orcia region of Tuscany, the ground is actively building itself. The area's famous travertine terraces, particularly visible at Bagno Vignoni, are geological formations created by hot, mineral-rich thermal waters. The process begins with rainwater seeping deep underground, where it is heated by geothermal energy from the magma chamber of Monte Amiata, a dormant volcano whose last known activity was about 200,000 to 300,000 years ago.
As this hot water moves through subterranean limestone, it dissolves calcium carbonate (CaCO3). When the water, heated to temperatures around 52°C (125°F), emerges at a spring, it experiences a rapid drop in pressure and temperature. This change causes carbon dioxide to release from the water, which in turn causes the dissolved calcium carbonate to precipitate out of the solution. This precipitated calcite, a form of limestone, builds up layer by layer, forming the terraced structures. Cyanobacteria and algae living in the warm water provide surfaces that encourage the calcite crystals to form, contributing to the lacy, porous texture of the rock. The entire village of Bagno Vignoni is on a travertine mound more than 40 meters high, built by this process over thousands of years.