Landscape evolution in the context of the Quaternary uplift of the Apennines: the changes of the hydrographic network of the Corno River (central Italy)

Geologic and geomorphic data suggest that the topographic growth of the Apennines has been very slow during the crustal shortening phase (Miocene-Pliocene) and greatly accelerated in the Quaternary. Such different uplift rates should have generated peculiar landforms that preserve information regarding the long-term evolution of the landscape. In this framework, we studied the geomorphology of the Corno River drainage basin, focusing on low local relief surfaces and on the river network features. The drainage basin of the Corno River is underlain by overthrusted Tertiary carbonates and marls, that have been offset by normal faults since the end of Pliocene. The topography of the study area is characterized, at elevation between 1000 and 1150 m, by low local relief surfaces, bordered by fluvial or structural steep scarps and locally offset by faults. In the study area extension generated three intermontane basins (Leonessa, Cascia and Norcia), drained by the Corno River and its tributaries. The Cascia and Norcia basins show a higher residual relief with respect to Leonessa basin, reflecting the progressive action of the headward river erosion and its interaction with the activity of the bordering faults. The Corno network appears to be more strongly influenced by faults that generate abrupt changes of the main trunk direction and knickpoints in its long profile. Except in the Leonessa depression and close to Cascia, the river flows in a very narrow and deep valley, showing locally entrenched meanders. Four orders of fluvial terraces have been found, although only the youngest one is widely preserved. On the valley slopes, at elevation between 50 and 170 m above the present valley bottom, we found out several subhorizontal surfaces that could be straths. We interpret the low relief surfaces as relics of an old landscape with relief lower than present, graded to or near base level. This landscape was drained by a river network characterized by wide valleys and internally-drained basins (the intermontane depressions). As a consequence of the strong increase of the uplift rate at the end of lower Pleistocene, the lowering of the base level induced a general deepening and a new organization of Corno basin network, commonly influenced by faults. Alluvial terrace and strath formation follows the general model of hillslope and watershed response to Quaternary climatic changes.