Crescent Moon Spring: a disappearing natural wonder in the Gobi Desert, China.

Introduction Yueya Spring, or Crescent Moon Spring, is a geological wonder located about 6 km south of Dunhuang city, Gansu Province, northwest China. It owes its name to the shape of the spring, or more precisely, the pond fed by the spring water, which resembles a Crescent Moon (Figure 1). Currently, the pond is about 200 m long in an east-west direction and about 50 m wide. The water surface in the pond is about 1134 m above sea level. Surrounding the spring is the equally famous Mingsha Mountain, also known as Singing Sand or Echoing Sand Mountain, which is simply a giant sand dune. The dune takes its name from the sounds made by the sand as the wind sweeps across the desert. The dune stands more than 100 m above the spring (Figure 1). This part of Gansu Province has a typical continental arid climate with extremely cold winters and scorching summers. The average yearly rainfall is less than 40 mm, whereas the potential evaporation is over 2400 mm.