Preliminary Research on Physical and Mechanical Properties and Avalanche of Seasonal Snow Cover at the Avalanche Station In T'ien-shan, China

Abstract The mountains of western and central T’ien-shan have extensive snow cover and consequent avalanches, however conditions in this area of central Asia are different from those in many other regions with avalanches. Snow cover is not very thick but it experiences very large temperature gradients which dominate its metamorphism, thus depth hoar forms extensively and becomes the principal snow type, so the density therefore remains low as does mechanical hardness. Avalanching activity and total volume vary enormously from year to year; 1968-69, with 211 avalanches of 147 000 m 3 , accounts for 53% of the avalanches and 75% of the volume of all the avalanches in the seven years 1967-74 in the area of the Gunes avalanche station. Although they can occur from November to April, the main months are January and March with a minimum in February. A snow depth of 50-60 cm is needed for avalanching. Below —10°C dry-snow avalanches occur, while above about —5°C wet-snow avalanches happen. These are often caused by melt water penetrating rapidly through the extensive depth hoar and initiating full-depth avalanches.