A contribution to the geomorphology of the coastal range of the state of São Paulo

Abstract

Current definitions of scarps do not usually take into account topomorphological features of length, slope and local reliei, which are basic to an understanding of their evolution. The northern sector of the coast of the state of São Paulo presents a set of scarps in Precambrian rocks, bounding the Atlantic Plateau to the interior. Two compartments can be discerned. The upper one has scarps with extensive straight and sloping segments, cut by valleys and amphitheaters of strong relief. The retreat of such scarps may proceed parallel to the front, under the control of lito-tectonic features, or transversely forrning "alveoli" (small basins). Processes of weathering and pedogenesis yield materiais that are moved downslope by mass movements and colluviation, mainly during intense pluvial episodes. On the lower compartment, on the middle and low slopes, scarps are degraded or worn down, resulting in topographic leveis ove r secondary spurs, erosive and colluvial ramps, residual hills and "alveoli", under structural control. They are modelled into convex forms by weathering and pedogenesis, by overland and subsurface flows and also by mass movements, more frequently slump slides; colluvial ramps and debris talus occur among the spurs and residual hills . Maps of slope, landslide scars and isopleths show close relationship among themselves. ln the vicinity of Caraguatatuba, two areas with a high incidence of scars present isopleths above 30 coinciding with long and steep slopes in the area of strongest relief.