Huanglong

Carbon and oxygen isotopic data to show that the springs are not fed by shallow groundwater in the glacial material that fills the valley. Instead, the water originates in the surrounding mountains and percolates through fractured Pennsylvanian carbonates, where it reacts with the bedrock to become charged with calcium ions (Ca⁺⁺), bicarbonate (HCO₃^-) and carbon dioxide (CO₂), before emerging at springs in the valley floors. Travertine deposition occurs when agitation, pressure release, increased temperature, or organic activity lowers the CO₂ content of the water. Decreasing the CO₂ content reduces the solubility of the dissolved solids and causes travertine, which is principally calcite (CaCO₃), to precipitate. A positive feedback loop forms at sites of agitation, such as waterfalls, and causes them to increase in height. It is likely that the location of these waterfalls has been controlled by the initial topography of the valley, perhaps forming over now-buried glacial moraines. The same mechanism on a smaller scale has produced the remarkably high thin walls of the pools, producing bathtub-like features (above). One pool has a rim 6.8 m (22') high! Placid waters fill most of the pools to their brims, and they glisten in the still air like a field of mirrors. Other pools stand dry, emptied by evaporation. Their water supply has been deflected by the growth of features above them.

The mists festoon the mountains as I start up a long progression of planked walkways constructed over the rounded travertine formations. Although the pools are the most beautiful features at Huanglong, it is the calc-sinter plains that particularly strike me. These consist of wide expanses of golden travertine up to 30 m (100') thick deposited on the valley floor. The largest calc-sinter plain is Jinshatan (Golden Sand Beach) which 40-125 m wide and 1.3 km long. Huanglong means "golden dragon" and it is easy to imagine that the long series of yellow-orange travertine deposits filling the valley would look like a serpent from above.

I am chilled, and my little thermometer reads 47^o F when I reach the uppermost Flower-Turning springs, which form a delicate series of low travertine steps. Trails of bubbles rise through the crystalline water as the CO₂ escapes. The Chinese have long recognized the beauty of Huanglong’s pools and there are several temples and pagodas around the uppermost springs. The temples with their peaked roofs and swooping eaves are barely visible in the cloud bank that has swallowed the valley. The pagodas date from the Ming dynasty (1368-1644 AD) and are said to mark the burial place of Cheng Shichang, grandson of the founder of the Tang Dynasty, Cheng Yaoji. The depth to which they have been buried in travertine indicates that the carbonate builds up at about 5 mm/yr. Travertine at the bottom of the deposits elsewhere in the valley has been dated using ¹⁴C yielding an age of 10,560 years. This date implies an average accumulation rate of about 2 mm/yr and reveals that deposition has proceeded since the Late Pleistocene, commencing at the end of the last ice age.