Vall de Núria and the Ribes-Núria cog railway track are situated in a high mountain landscape that presents high sub vertical walls with unevenness of about 300 m and is subject to natural dynamics where geomorphologic destructive processes take place such as rock falls. In this sense Dent d’en Rossell is one of the most active areas of the whole valley. In order to improve the safety of the cog railway track new techniques of study have been incorporated into hazard assessment such as airborne and terrestrial LIDAR. The use of this method allows modelling the topographic surface in a very accurate way, obtaining a DEM. This technique of high precision has allowed us to develop a specific work methodology for Dent d’en Rossell to estimate the geologic risk over the cog railway related with rock fall instabilities, which would be impossible to carry out by using conventional topographic modeler. In this survey are shown two examples of the LIDAR possible applications related with potential instabilities areas detection and rock fall hazard assessment.