Melt and thaw of snow, ice, and soil are important processes for the hydrological cycle as well as for energy fluxes. Remote sensing from space allows the monitoring of vast uninhabitated regions like the Siberian Arctic. This study presents results from monitoring of snowmelt events during spring, the thaw of the active layer on different geomorphological units on tundra land surfaces, as well as lake-ice decay from high resolution TerraSAR-X and quad-pol RADARSAT-2 timeseries acquired over the central Lena Delta, Siberia. The main findings are that X-band data do not show a backscatter difference between frozen and thawed soils, whereas the C-band backscatter rises in the order of 3\,dB. Polarimetric decompositions show the spatial extend of snowmelt events and help to distinguish between different geomorphological units. The high spatial resolution of the TerraSAR-X images is extremely helpful to distinguish between land surfaces and the frequent ponds in the investigation area.