Surge-type Glaciers in the West Kunlun Shan, NW Tibet

Surge-type glaciers oscillate between long-quiescent phase and short-active phase (i.e. decades of slow flow and shorter periods of rapid flow). Surge-type glaciers are distributed around the world and cluster around specific region and it's believed that at least 1 % of world glacier caused surge. Direct observations are difficult due to decades surge cycle and remote situation. To identify surge-type glacier, surface structures, such as looped-moraine and maze-crevasse, are used alternatively. The mechanisms of glacier surges are still not understood completely but recent studies suggest that glacier surge is likely a result of changing hydrological and/or thermal conditions. Many mountain glaciers are developed in West Kunlun Shan (WKS) located in NW Tibetan plateau. Scherler et al. (2011) mentioned that unusual low velocities at frontal part were associated with past surges in WKS but there are no reports of spatio-temporal data of glacier surge, to our knowledge. We detected glacier surge and its velocity change in WKS. We used offset tracking method based on Synthetic Aperture Radar (SAR) data, assumed that glaciers flow parallel to surface topography derived from SRTM4 digital elevation model and converted offset-results to surface velocity field. Also, we detected glacier front change using SAR intensity images and Landsat optical images. We paid attention to 36 glaciers in WKS. Among 5 glaciers were obviously classified as surge-type glacier. Surface velocity of these glaciers gradually accelerated and decelerated, accompanied by advance of glacier terminus. For example, Chongce glacier on the south slope of WKS was active phase in 1990's. Surface velocity increased up to ~700m/year in 1996. No surge signal detected from 2003. Velocity profile of Chongce glacier dramatically changed. The upper part was ~20-30m/year but the lower part was ~0-5m/year. We detected same behavior at Zhongfeng glacier (branch 1) on the south slope. Except for Chongce glacier and Zhongfeng glacier (branch 1), many glaciers in WKS had stagnant flow and probably classified as surge-type glaciers. However, dead ice caused stagnant flow. Continuous monitoring is necessarily to elucidate entire surge cycle in WKS.