In rugged topographies, numerical elevation model allows to detect
the most dangerous areas. The simplest method consists in the detection
of steep cliffs. In addition, numerical elevation model coupled with
a characterisation of the main discontinuity sets leads to the identification
of the zones where discontinuities can induce instability, rockfalls
or rock slides. Probability of occurrence of dangerous events can
be assigned to these zones. Then the zones of highest probability
may be subject to more detailed studies such as field work and slope
stability calculations. After such a detection stage, impact areas
and their hazards can be estimated for example by field work or by
trajectography studies that can be used to established danger and
hazard maps.