Abstract: The Karakoram glaciers are attracting more and more attentions for ‘Karakoram Anomaly’ due to glacier surge or positive mass balance. To understand the mechanism of the glacier surge or positive mass balance, a huge debris-covered glacier-Yengisogat glacier was selected to be investigated in detail. Yengisogat glacier, the glacier of the largest area in China, developed on the northern slope of K2 located in the Karakoram Mountains, is a dendritic glacier covered area of 493 km2 with four main tributaries and more than ten small glacier flows. TanDEM-X/TerraSAR-X data (acquired in Feb.2014) and SRTM-X dem (acquired in Feb.2000) were employed to calculate the glacier elevation change using differential interferometry method. Similar penetration depth was assumed for the same acquired season. The glacier surface elevation change and surface velocities from published articles were integrated to discuss the mass change characteristics. The results indicated that the glacier average surface elevation was decreased by 1.68±0.94 m between 2000 and 2014,which means that the glacier has lost mass by -0.12±0.07 m·a^-1.The glacier surface elevation changes showed no uniformity. The southern main tributary was decreased drastically. This was caused by rapid surface flow velocities which transfer the glacier mass from high altitude to low altitude ablation area. The southern main tributary occupied the original glacier trunk impeded the glacier mass transfer to low elevations which made the section elevation increased. The increased surface elevation in the tongue of glacier main trunk may be explained by glacier surge. Glacier surface elevation started to decrease along with the elevation increasing and then stayed stable, yet showing volatility at the same time. Surface elevation of thin debris-covered glacier in low altitude zones was prone to decrease than that of the exposed glacier ice. Glacier surface elevation was decreased more dramatically with the decreasing of glacier surface slope in the area where slope are less than 30 degrees. Surface elevation of glaciers with southern orientation was increased slightly while that with south-west orientation was decreased slightly, and the others were decreased drastically. The debris-covered Yengisogat Glacier experienced an overall surface elevation decline which indicated it had the mass loss although it had some local surface elevation increase due to the glacier surge.

Key words: Yengisogat Glacier, TDX/TSX, D-InSAR, surface elevation change, glacier surge