The movement mechanisms of Ürümqi Glacier No. 1, Tien Shan mountains, China

Beneath Ürümqi Glacier Νo. 1, there is an ice-laden till layer which is more than 10 m thick near the terminus. The 0°C isotherm is generally at some depth below the glacier sole and lies within the bedrock below the ice-laden till layer near the terminus. Thus the glacier is entirely cold and impermeable, except for a thin snow-firn layer at its surface and some crevassed areas. Meltwater drains off mainly by surface channels, assisted by subglacial conduits. Four flow mechanisms have been identified in the glacier. They are ice deformation, bed deformation, shear faulting, and sliding over the bed. At the terminus and along the margins, bed deformation can provide a significant contribution to the overall surface motion. Bed deformation consists of creep and discontinuous slip. However, creep experiments on samples taken from the ice-laden till layer provide no positive indication that this layer deforms more easily than clean ice. Discontinuous slip thus may provide the major contribution to bed deformation.