Beschreibung:
Abstract. In the Karakoram, dozens of glacier surges occurred in the past 2 decades,making the region a global hotspot. Detailed analyses of densetime series from optical and radar satellite images revealed a wide range ofsurge behaviour in this region: from slow advances longer than a decade atlow flow velocities to short, pulse-like advances over 1 or 2 years withhigh velocities. In this study, we present an analysis of three currentlysurging glaciers in the central Karakoram: North and South Chongtar Glaciersand an unnamed glacier referred to as NN9. All three glaciers flow towardsthe same small region but differ strongly in surge behaviour. A full suiteof satellites (e.g. Landsat, Sentinel-1 and 2, Planet, TerraSAR-X, ICESat-2)and digital elevation models (DEMs) from different sources (e.g. Shuttle Radar TopographyMission, SRTM; Satellite Pour l’Observation de la Terre, SPOT; High Mountain Asia DEM, HMA DEM) are used to (a) obtain comprehensive information about theevolution of the surges from 2000 to 2021 and (b) to compare and evaluatecapabilities and limitations of the different satellite sensors formonitoring surges of relatively small glaciers in steep terrain. A stronglycontrasting evolution of advance rates and flow velocities is found, thoughthe elevation change pattern is more similar. For example, South ChongtarGlacier had short-lived advance rates above 10 km yr−1, velocities up to30 m d−1, and surface elevations increasing by 170 m. In contrast, theneighbouring and 3-times-smaller North Chongtar Glacier had a slow andnear-linear increase in advance rates (up to 500 m yr−1), flowvelocities below 1 m d−1 and elevation increases up to 100 m. The evensmaller glacier NN9 changed from a slow advance to a full surge within ayear, reaching advance rates higher than 1 km yr−1. It seems that,despite a similar climatic setting, different surge mechanisms are at play,and a transition from one mechanism to another can occur during a singlesurge. The sensor inter-comparison revealed a high agreement across sensorsfor deriving flow velocities, but limitations are found on small and narrowglaciers in steep terrain, in particular for Sentinel-1. All investigatedDEMs have the required accuracy to clearly show the volume changes duringthe surges, and elevations from ICESat-2 ATL03 data fit neatly to the otherDEMs. We conclude that the available satellite data allow for acomprehensive observation of glacier surges from space when combiningdifferent sensors to determine the temporal evolution of length, elevationand velocity changes.