Morphometry as a tool to investigate the tectonic influence on landscape evolution: the example of northern Calabria (southern Italy).

In active tectonic landscapes, topography is shaped by the interactions of tectonic activity that uplift and deform rocks and geomorphic processes that erode and unroof rocks. So in active orogens, the production of topography, that reports an uplift rate equal or higher than erosion rate, is an expression of plate convergence and of its interaction with erosional and depositional processes(Hovius, 2000; Willett and others, 2001). The study of uplift is a way to add important information to the comprehension of the mechanisms that build up mountain chains. In the Italian Apennines, the topographic growth of the range was slow during the phase of major crustal shortening (Miocene-Pliocene), but accelerated significantly in the Quaternary, when it was already dominated by extension Such disparate rates of rock uplift above sea level should influence the development of peculiar landforms. We have investigated the geomorphic expression of active tectonics in northern Calabria (southern Italy). Here the Apennines are a narrow, rugged peninsula, comprises pre-Alpine plutonic and metamorphic rocks, continental and oceanic metamorphic rocks overlying tectonically Mesozoic carbonates and flysch .Low-standing extensional basins surrounding the relief (Catena Costiera and Sila Massif) are filled by several upper Tortonian–Holocene depositional sequences made up of poorly consolidated marine and fluvial conglomerate, sand, and clay.We examined the tectonic geomorphology of a transect across northern Calabria, focusing on the general morphometry, drainage patterns, and river longitudinal profiles. Using several methods of map and DEM-based topographic analyses, the strong tectonic influence on the geomorphology and landscape evolution has been characterized.The collected data are consistent with a landscape dominated by extensional tectonics, following regional relative base level fall (rock and surface uplift). The overall drainage pattern for the study area argues for streams that must adjust to local extensional structures (evidenced by several knickpoints on stream long profiles, high SL index values) and to a recent strong uplift (convex general shape of stream long profiles, high residual relief). In particular, they compete with each other to integrate into the Sila Massif interior, where a high-standing plateau is characterized by gentle upland surface. A similar rolling landscape is located also on top of Catena Costiera, although its dimension is much less. Six cross sections provide a common frame of reference for comparing data extracted from the topographic analysis. Moreover two swath profiles, including maximum, minimun, mean and residual elevations underline again the influence of local extension and regional uplift on the present topographic setting.The comparison of the morphometry data with the field observation of a gentle upland surface of low local relief and of five terrace orders on the Ionian coast (0.6 mm/yr rates of coastline emergence in the last 330.000 years; Gliozzi, 1988; Molin et al., 2002), confirms the broad uplift of the area. These results speak to a paleo-landscape less rugged than the modern relief indicating a previous slow uplift that allowed the emergence of at least part of the study area before Quaternary. At the end of lower Pleistocene, a strong acceleration of the uplift rate generated the present relief isolating the relics of the old landscape on the Catena Costiera top and on the Sila Massif plat