## 4 Results
### Pre-Landslide Topography and Geology Reconstruction  
The retrospective analysis of a landslide through mathematical modeling requires knowledge of the topography and geology prior to it. This is a characteristic difficulty in landslides as old as this one. However, and despite having a certain degree of subjectivism, we believe that in this case there are geomorphological-geological criteria of the environment and information on the geometry of the landslide sufficient to address this aspect with guarantee. Thus, a methodology is proposed to reconstruct the pre-landslide topography in 3D that approximates with sufficient detail to the proposed purposes. The reasoned steps that have been followed for the reconstruction of the topographic and geological profile are the following (see Figure 4):  
1. First, it is necessary to start from two certainties: one, that the failure of the landslide exclusively affected the formation of clays and lutites (unit 22), and is limited towards the base, by the presence of the hard layers of limestone (contact 22-23) north and in depth, and to the roof by unit 21 that outcrops to the south. The second certainty is that the slide occurred at some point in the retreat of the glacier during deglaciation. This is evident since the lateral moraine that remains with the slide has been cut by it (Figure 3D). It is seen that the moraine continued on the slope where the movement occurred. In other words, the slope was stable before the glaciation and also during the maximum advance of the glacier (supporting the slope by the ice tongue). Figure 4: Process followed in the reconstruction of the relief before the landslide (see explanation in text): (**A**) Current topography in the area of the slope; (**B**). Reconstruction of the topographic and geology of the slope during the maximum advance of the glacier and under the ice of the glacier tongue and without moraines. (21) Sandstones and lutites (22) Lutites and clays (23) limestone; (**C**). Topographic map in the situation of the maximum advance of the glacier and with a thickness of the glacial tongue of 140 m; (**D**). Topographic map in the situation of regression of the glacier and with a thickness of the glacier tongue of about 40 m.  
The fact that the slope remained stable with its natural slope before the glaciation is very interesting from the geotechnical point of view, since it informs us of the minimum angle of stability. This angle is 14\({}^{\circ}\) and is the one that has the slopes of the valley above the lateral moraines not affected by the glacial excavation and which are very well preserved. The height of the slope before the glaciation was about 300 m (1900-1600 m). 2. Reconstruction of the topography of the pre-glacial valley is not difficult as it is fairly well preserved in the upper part of the slopes unaffected by glacier erosion. It is a regularized and constant slope of about 14\({}^{\circ}\) that, prolonged for both slopes downwards, emerges a height from the bottom of the pre-glacial valley in this sector where the landslide is located (towards 1600 m) (Figures 2 and 3). It is thus deduced that on the left bank, where the outcrop of clays and lutites gave rise to the landslide, was stable with a natural slope of 14\({}^{\circ}\) and a drop of 300 m (1900 from the head minus 1600 m from the bottom of the valley). In the area affected by the landslide, the lateral moraines on the left bank, which were dragged by this mass movement, are not preserved. In the area on the right bank, the lateral moraine perched over three valleys, as has been said, is very well preserved. 3. However, we are interested in knowing the topography and geology just before the landslide, as a result of the excavation of the pre-existing valley by the glacier.