A landscape built by chemistry
The terraced pools and dams of Jiuzhaigou Valley are a direct result of water chemistry and physics. The landscape is a high-altitude karst system, formed by glacial and tectonic activity on carbonate rocks like dolomite and tufa. Groundwater flows through flowing through these underground limestone deposits. As it travels, it dissolves the rock, becoming super-saturated with calcium bicarbonate (Ca(HCO3)2).
When this water emerges at springs, it encounters lower atmospheric pressure. This pressure drop causes dissolved carbon dioxide (CO2) to rapidly bubble out of the solution, a process called degassing. The loss of CO2 shifts the water's chemical equilibrium, making it less acidic. This chemical change dramatically lowers the water's ability to hold dissolved calcium, forcing the calcium to precipitate out of the solution as solid calcium carbonate (CaCO3), the primary component of limestone and travertine. This newly formed mineral deposits onto the riverbed, slowly building the structures seen today. The purity of the calcium carbonate in the region is often over 95%.
A self-organizing system with a biological boost
The regular, step-like formation of the dams is a self-perpetuating process. As water flows over a small obstruction, the increased turbulence accelerates CO2 degassing. This localized chemical change causes more calcium carbonate to deposit on that very obstruction, making it grow larger. Over thousands of years, this feedback loop builds a full-fledged dam. Downstream from the dam, the water is temporarily less saturated with calcium carbonate. It flows smoothly for a distance, re-absorbing CO2 from the atmosphere, until it becomes super-saturated again and is ready to build the next dam.
This purely physical and chemical process is amplified by biology. The surfaces of the travertine are coated in a biofilm of algae, cyanobacteria, and mosses. Species like Calothrix, Dichothrix, and the moss Cratoneuron are common. These organisms' sticky extracellular secretions act as perfect nucleation sites for calcite crystals to form, speeding up the deposition process. Photosynthesis by these microbes also removes CO2 from the water, further encouraging the precipitation of calcium carbonate. This combination of geology, chemistry, and biology, unfolding over millennia, creates the valley's series of waterfalls and terraced, colored lakes. The elevation of this vegetated travertine system, from 2200 to 2900 meters above sea level, makes it one of the highest of its kind in the world.