Gypsum karst geohazards in China

China has the worlds largest proven gypsum (CaSO4.2H2O) resources in the world. The gypsum ranges from pre-Cambrian to Quaternary in age and occurs in varied geological environments. The rapid dissolution rate of gypsum means that gypsum karst development can be very fast, resulting in progressively worsening geohazards. This paper reviews the characteristics of the gypsum deposits and their associated geohazards in China.Three kinds of gypsum karst are discussed. These include karst in massive thick beds of gypsum, karst in thin-bedded gypsum and compound karst in gypsum and carbonate rocks. Some site-specific problems are also examined. In the Shanxi coalfield, breccia pipes, or collapse columns, caused by the dissolution of Ordovician gypsum, penetrate the overlying Carboniferous and Permian coal-bearing sequences resulting in difficult coal mining conditions. In Guizhou Province re-activated gypsum karst is associated with leakage of water through the gypsum from a reservoir. Remedial engineering works have been carried out, but leakage still occurs. Groundwater abstraction from gypsiferous sequences is also problematical. It can yield sulphate-polluted water and cause subsidence problems both through gypsum dissolution and groundwater drawdown