Ground cracks due to underground coal burning

The underground coal in Xinjiang, China, has been burning for thousands of years, which started burning from its seam outcrop on surface or at shallow depth. The burning leads to great ground subsidence and surface fracturing followed by oxygen entrance, which results in furthermore coal burning. Efforts has been devoted to control or restrain the burnings by way of mud filling and/or water flooding since 1970's. However, the burning continues, and the burning sites as well as the total burning area are increasing. This picture shows a huge crack accompanying with meters of ground subsidence in Hoxtolgay, the northwest of Xinjiang. Water flooding is being performed to control this situation.