The tropical mountainous regions, as in the coastal massifs of Rio de Janeiro city, has been suffering, in last decades, intense mass movements and erosive process promoted by summer rains, generating serious social-environmental consequences. The Pedra Branca massif, the most important geomorphological form in the county, presents its hillsides with strong erosive potential, identified by present investigation, through morphological and morphometric analysis of its hydrographic basin associated to the dominant study of its litho-structural picture.

From the analysed micro-basin (71 in total), the ones located in the east and south watersheds (30 sub-basins) situated toward the lowland of Jacarepaguá, are distinguished as the ones with greater potential, from which the river Grande and Camorim basins are more important, with their valley structurally controlled, by means of faults systems with predominant directions N50-60E and N50-60W. The occurrence of intense erosion processes during the rains of february/1996 ratify such statement.

On the other hand, the north watershed of the massif looking toward hinterland lowland, presents draining deficiencies, resultant from identified low draining density values and low hydrographic density, and the west watershed presents its hydrographic basin with morphological and morphometric appearance similar to the first one, but with lower structural control.

The integrated analysis from such informations as compared with the dominant soil use and occupation characteristics will allow the identification of the most critical areas, as concerned to vulnerability to slides inside each basin, reinforcing the actions of the ambiental control organizations (ex. of GEORIO Foundation), as a preventive work against natural disasters.