Abstract. Failures of glacial lake dams can cause outburst floods and represents a serious hazard. The potential danger of outburst floods depends on various factors like the lake's area and volume, glacier change, morphometry of the glacier and its surrounding moraines and valley, and glacier velocity. Remote sensing offers an efficient tool for displacement calculations and risk assessment of the identification of potentially dangerous glacial lakes (PDGLs) and is especially helpful for remote mountainous areas. Not all important parameters can, however, be obtained using spaceborne imagery. Additional interpretation by an expert is required. ASTER data has a suitable accuracy to calculate surface velocity. Ikonos data offers more detail but requires more effort for rectification. All investigated debris-covered glacier tongues show areas with no or very slow movement rates. From 1962 to 2003 the number and area of glacial lakes increased, dominated by the occurrence and almost linear areal expansion of the moraine-dammed lakes, like the Imja Lake. Although the Imja Lake will probably still grow in the near future, the risk of an outburst flood (GLOF) is considered not higher than for other glacial lakes in the area. Potentially dangerous lakes and areas of lake development are identified. There is a high probability of further lake development at Khumbu Glacier, but a low one at Lhotse Glacier.

[1] We performed three field campaigns in 2004, 2007, and 2010 at the southern margin of the Jakobshavn Isbrae, West Greenland, in order to infer flow velocities and their changes from photogrammetric time-lapse imagery with a temporal resolution of 20 min and a spatial spacing of about 30 m on the glacier surface. Area-wide analysis of more than 3000 three-dimensional trajectories at individual glacier positions allow for both the mapping of the grounding line and the detailed observation of flow variations during major calving events. From 2004 to 2010, the grounding line of Jakobshavn Isbrae retreated 3.5 AE 0.2 km. Considering previously published results, the grounding line retreat amounts to 6 km since 1985. The glacier has an ephemeral floating tongue that can establish during the readvance of the glacier front and break apart after large calving events. Observations of a major calving event show that an acceleration of flow velocities coincides with the onset of the break up during which flow velocities of up to 70 m/d can be reached. Moreover, large vertical displacements of the glacier front in the order of 15 m and lowering of 8 m at positions 500 m beyond the calving front were observed 2 days before the calving event.After the break up, the glacier slowly adjusts to the new boundary conditions within the next 4-5 days. Flow velocity variations caused by calving were detected up to 1 km upstream only which indicates that individual calving events have no immediate effect on the large-scale glacier dynamics.

[1] During the summer of 2004, the front area of the Jakobshavn Isbrae was monitored using a geodetic-photogrammetric survey with temporarily coincident precise observations of local ocean tides in the Disko Bay close to Ilulissat. The geodetic and photogrammetric observations were conducted at the southern margin of the glacier front. The largest observed horizontal flow velocities are in the central part of the front with values up to 45 m/d. This is a factor of 2 greater than the average velocities at the front area observed in the last century. Our new observations confirm previous estimates of an acceleration of glacier flow during the last decade. The photogrammetric survey provided flow trajectories for 4000 surface points with a time resolution of 30 min. These flow trajectories were used to compare the vertical motion of the glacier with the observed tides. The existence of a free-floating glacier tongue in 2004 was confirmed by these data. However, it occupied only a small belt, of at most a few 100 m width, in the central part of the glacier front. Horizontal motion did not appear to depend on the tidal phase, unlike some of the fast-moving ice streams of West Antarctica.

Extensive observations on Nivlisen, an ice shelf at Antarctica's Atlantic coast, are analysed and combined to achieve a new-quality description of its complex glaciological regime. We generate models of ice thickness (primarily from ground-penetrating radar), ellipsoidal ice surface height (primarily from ERS-1 satellite altimetry), freeboard height (by utilising precise sea surface information), and ice flow velocity (from ERS-1/2 SAR interferometry and GPS measurements). Accuracy assessments are included. Exploiting the hydrostatic equilibrium relation we infer the 'apparent air layer thickness' as a useful measure for a glacier's density deviation from a pure ice body. This parameter exhibits a distinct spatial variation (ranging from ≈ 2 m to ≈ 16 m) which we attribute to the transition from an ablation area to an accumulation area. We compute mass flux and mass balance parameters on a local and areally integrated scale. The combined effect of bottom mass balance and temporal change averaged over an essential part of Nivlisen is −654±170 kg m −2 a −1 which suggests bottom melting processes to dominate. We discuss our results in view of temporal ice mass changes (including remarks on historical observations), basal processes, near-surface processes, and ice-flow dynamical features. The question for temporal changes remains open from the data at hand, and we recommend further observations and analyses for its solution.