Le cengie nei versanti in calcari e dolomie

Step morphology in limestones and dolostones

Abstract

In the general problem of the slope morphology, the case of carbonatic rocks can be considered a simpler system than others, since in most areas erosion by surface water is negligible. Vertical cliffs are often interrupted by moderate slopes of varying size, with constant dips of about 30-35° (Richter slope). These gently dipping steps (in Italian cengia, from the Latin cingula, belt) are formed in horizontal strata of weaker rocks, and can join a dynamic equilibrium. Analogous steps are often also present in homogeneous rocks, but their evolution is different: the steps, with the interposed cliffs, migrate with time towards the top of the slope. Their origin must be searched in pre-existing undulations in the profile of the slope, which can have various origins, connected with cliff-generating events: glacial erosion (U-shaped valleys), marine abrasion, variations in the relation between talweg deepening and slope recession. Hence the steps can be considered as an heritage of past various morphogenetic events.