In fractured media, the factors that make evolve a stable fractured media towards a landslide highlight the watereffect as an aggravating and a triggering factor of slope instabilities. Long term water effect on stability isstudied from spring water chemistry, which gives data about the weathering state in the slope (aggravating factorof the instability) and about infiltration event in the massif (triggering factor).Thus, hydrochemistry enables to propose a conceptual model of flow in unstable slope. A multi scale approach,in two alpine valleys, of relations between the flows and the instability structures highlights the draining role ofthese structures. Slopes comparison enables to discuss the long term evolution of the effect between waterseepages and slope destabilization. Slow movements (toppling, sagging and creep) decompress the upper part ofthe slope, increase the infiltrated water volumes and create perched aquifers in the decompressed areas. With thedestabilization, the water / deformation coupling evolves, from high water pressure effect in low storativefractures to a water high charging effect in the high storative zone, in the upper part of the slope, and can initiatea rupture.Hydrogeochemical equilibrium, observed in stable slope, is modified by large landslide crisis. Thus, sulfatedissolution evolves with active deformation of the slope. This observation enables to demonstrate the possibilityto use hydrochemistry to monitor unstable slopes that can record slow deformation in the slope.
