Find in Library

The Flemish Ardennes (W Belgium) are known to be affected by deep-seated landslides. The assessment of the landslide reactivation hazard requires understanding the driving processes and delimiting precisely not only the landslide boundaries but especially that of their most active parts. <P style='line-height: 20px;'> Precise 3D models of 13 landslides were produced by digital stereophotogrammetry using aerial photographs of different dates. Dealing with photographs at the scale 1:25000 or larger, we obtained for each model an accuracy better than 0.5m. <P style='line-height: 20px;'> As a first result, the main size parameters of the landslides (width, length, depth, volume, ...) are easily computed. <P style='line-height: 20px;'> Moreover, the obtained DTMs may be subtracted from each other in order to determine the apparent vertical displacement of each pixel during the interval of time considered. Provided that more than 2 epochs are documented, such DTMs not only supply precise information about distribution and style of the landslide activity but may also point to temporal variations in this activity. <P style='line-height: 20px;'> The subtraction of DTMs allows us to give an estimation of the volume of the 'uplifted' and 'collapsed' terrains between two epochs.