About the Cover

The mountainous landscape of SW Gansu Province in China is prone to a wide variety of geohazards. The landscape was created through the uplift of the Tibetan plateau and the associated incision by the Yellow River, amongst other processes; most importantly there is a widespread and often thick cover of loess (aeolian silts). River terraces and undulating bedrock surfaces are masked by a drape of this light-brown, fine-grained material. Level surfaces of this fertile soil are intensively farmed. However, interaction with water can result in the structural collapse of these deposits. River terrace edges such as here at Heifangtai along the Yellow River, some 60 km west of Lanzhou, have been significantly affected by large, fast moving flow slides. The collapsing ground surface shown in the photo provides a good indication of the scale of deformation occurring within these deposits that starts with small scale particle rearrangement and gradually progresses to form internal cavities and the kind of surface features caused by the collapse of the cavities. The fissures shown in this image range in width at the surface from a few centimetres to a few tens of centimetres. The surface cavity visible in the centre is approximately three metres across.