## 4 Results II: Glaciological Interpretation
### Surface Elevation Changes in the Khumbu Himal  
Since the large Khumbu and Ngozumpa glaciers are located in two parts of the Pleiades acquisitions (see Figures 3-5), it was necessary to create mosaics based on the individual Pleiades scenes of the Khumbu Himal study area. While this is a straightforward process, the fit between the individual parts within the final mosaic was impacted by the DEM being calculated without the use of GCPs. The difference in z-values for the overlapping areas ranged from 0.3 m for the southwestern and northwestern DEM for the spring 2016 acquisition to 1.2 m for the southwestern and northwestern DEM for the spring 2015 acquisition. Due to fringe effects, which make the fringes of the calculated DEM not usable, the overlapping areas of the different images were too small to properly co-register the parts of the different DEM of a single acquisition. Therefore, we did not use data based on mosaicked DEM, but mosaicked the calculated dDEM. This has the advantage that, by solely using the differences, which are calculated based on already well-co-registered DEM, the non-perfect fit of the different DEM of one acquisition to each other is less of an issue. For the overlapping areas of the respective acquisition, the mean value of the two dDEM covering the area was used in the final dDEM for the respective glacier. Despite the efforts regarding the correction of distortion and misalignments of the DEM and dDEM, data from different images of one acquisition does not always fit perfectly in some areas of the Khumbu Himal study area. This is visible in the dDEM with surface differences of more than 0.5 m in stable areas, or steps in the surface elevation changes, e.g., on the tongue of Ngozumpa glacier for the winter surface elevation difference (see Figure 13). Figure 12: One-year surface elevation change of the investigated part of Hochjochferner autumn 2014–autumn 2015. UTM 32 N.  
Some noteworthy glaciological features are revealed by the DEM differencing in the Khumbu Himal study area. Since the glaciers in the Khumbu Himal are of the summer accumulation type [46; 47], surface elevation change rates are very low in winter. Very little change on the glaciers seems to occur between October and April (see Figures 13-16), although there seems to be some winter accumulation in the highest parts of the Lhotse Nup glacier, which fits to the findings of [48]. As surface elevation change mainly occurs in summer, the altitudinal distribution of the surface elevation change over the whole year is similar to the one just for the summer period (see Figures 13-16). The lower areas of all of the glaciers show very little average surface elevation change, although there seems to be a slight positive change for the Lhotse Nup and Khumbu glaciers, and a slight decrease in the average surface elevation for the Lhotse and Ngozumpa glaciers. Decreases in surface elevation are mainly located in the lower elevation bands, which also have larger areas, while surface increase occurs in the higher elevation bands with rather small areas. The total volume change of the four glaciers is shown in Table 5.  
Secondly, surface elevation change rates on the heavily debris-covered glacier tongues are relatively low, with the highest changes at exposed ice cliffs. Nearly no winter season surface displacement is visible on the glacier tongues (see Figures 13 and 16). The results for the highest parts of the Ngozumpa glacier, which are located above 7000 m a.s.l., show high changes in surface elevation, especially between the two spring acquisitions and the spring 2015 and autumn 2015 acquisitions (see Figures 17 and 18). The values, which show surface elevation