## 4 Results
### Variations in Elevation Since 2001  
Using data from the topographic surveys from 2001, from LiDAR (2008, 2010 and 2015) and from field visits during the last 20 years, an overall shoreward progradation of the dune could be observed, as already mentioned for the front dune. In this sense, a decrease in maximum elevation could be observed, with emerging evidence that the sediments are spreading northward, resulting in a decrease both in dune slope and in crest area. This advance leads to the fossilization of older plant-covered dune levels in some sectors (especially on the north side). Another effect was the progressive extension of the interdune corridor following an NNE-SSW direction, parallel to the dune crest, between it and the first level of plant-covered dunes located close to the beach (Figures 7 and 8).  
Figure 8: Topographic profiles in the crest of dune mobile sector between 2001 and 2015. The position of these profiles appears in Figure 1c in red color.  
Figure 7: Topographic profiles in dune mobile sector between 2008 and 2015. The position of these profiles appears in Figure 1c in black color.  
As shown in Figure 7, a decrease in dune elevation occurred during the 2008-2015 period, especially in the crest. While in 2001 the maximum elevation was 21 m, this elevation decreased to 20.31 m in 2008, 19.59 m in 2010 and 18.51 in 2015. These modifications were more relevant in the central zone of the mobile dune (Corrubedo P2 and P3 in Figure 7), which corresponds to the highest sector and the one with the greatest amount of sediments.  
To analyze variations since 2001, the analysis focused on the peak sector of the dune system, about which abundant information is available. As shown in Figure 8, elevation decreased across all profiles. This fact is related to the erosion of the seaward flank and shoreward dune progradation.  
The analysis of LiDAR data from 2008 onwards showed a general decrease in elevation in the whole analyzed sector. The overall results showed that erosion was the dominant process in the seaward dune flank. In the inner flank, large accumulations of sand transported to the crest by deflation channels were formed, leading to movements caused by gravity that helped slow the progression of the dune towards the shore (Figure 9). In Figure 9, a clear increase in elevation related to the advance of the mobile dune is shown in green. This dynamic appeared in the system in the 1980s.  
Between 2008 and 2015, a \(-0.55\) m decrease in average elevation could be observed. A 74.8% proportion of the area experienced variations above the LoD (0.5 m for this period) and 83% of this area experienced a decrease in elevation, resulting in a volume loss of 269,481 m\({}^{3}\). In the partial analysis for the period between 2008 and 2010, the area that experienced variations was 32% and elevation decreased in 80% of this area, resulting in a net volume loss of 99,124 m\({}^{3}\). The net variation in elevation was \(-0.2\) m. Finally, in the 2010-2015 period, a similar decrease in elevation took place, with an average decrease of \(-0.23\) m, although the area that experienced changes above the LoD increased up to 70.9%, with 75% of the area experiencing loss. The net balance of volumetric change in this case was \(-110  
Figure 9: Evolution of surface elevation in large shifting dune sector. (**a**) Difference of Digital Elevation Models (DoD) between 2008 and 2010; (**b**) DoD between 2010 and 2015; and (**c**) DoD between 2008 and 2015.