The gullies ("voçorocas") are concentrated on area of arquean basement rocks (gneisses, migmatites and granites), which are covered by tens of meters (up to 50 m) of saprolite and by some meters (up to 6 m) of elluvium (residual soil) or colluvium.

Two main phases of gullying were identified: the first is characterized by reshaped gullies (amphitheater-like hollows), with smoothed scarps, partially filled with alluvial-colluvial sediments (ramps) of upper quaternary age. These sediments are connected to deposits of fluvial terrace (T1, about 6 meters above the current floodplain). The second erosion phase is connected to the current drainage system and is characterized by gullies with well-marked scarps, hummocky bottoms, which developed as a consequence of deleterious land practices in the last 300 years. The gullies of the second phase frequently follow the hollows of the first one (eroding their sedimentary filling) and widen to huge digitated forms when they reach the rock saprolites. Coalescent gullies due to the interfluve erosion are common features.

A geomorphological and a detailed stratigraphic analysis have been conducted as well as a structural analysis in order to explain these types of gullying and to understand how erosion begins, succeeds and stops. Preliminary data show that the gullies are structurally controlled.

The residual soil/colluvium are more resistant to erosion than the saprolite, thus the erosion only grows when the subsurface mechanisms are activated. Superficial washing over scarp (plunge-pool) or collapsed materials and retreat of scarps by collapsing or slumps are other mechanisms. The choice among different erosion management options should be based on these data.
*This work was done under the joint auspices of the FAPEMIG, UFRJ e UFOP.