The SW escarpment of the Montagna del Morrone (Abruzzi, Central Italy): geomorphology of a faulted-generated mountain front.

The relief features of the Central Apennines are formed by carbonate ridges, separated one from the other by narrow valleys, parallel to the ridges, cut in terrigenous sediments, or by wide intermontane depressions. The ridges have N-S, NW-SE or E-W orientations and steep slopes and they are broken by deep cuts and gorges. The landscape of the ridges is related to the morphostructural and morphosculptural evolution of fault scarps and fault line scarps. The purpose of this study is the analysis of the geomorphological characteristics of the SW escarpment of Montagna del Morrone (2061 m a.s.l.), one of the main Central Apennine ridges. The study investigated the geomorphology of the escarpment, focusing on the interaction between extensional tectonics, drainage evolution and the distribution of morphogenetic processes. Particular attention was devoted to the morphometry of the slope, of the drainage pattern, of the drainage basins and of the alluvial fan/catchment systems. Working from geomorphological and morphometric data we defined the processes that have generated and shaped the escarpment, and established the timing of its morphogenetic evolution. Various types of analysis were combined: basic geological analysis, geomorphological survey, morphometric and slope analysis, morphometric analysis of drainage basins and drainage network, and morphometric analysis of alluvial fan/catchment systems. Topographic data, surface hydrology, and geomorphological data were geo-referenced and processed in a GIS. The results indicate that the SW escarpment of the Montagna del Morrone ridge has the geomorphological features of high activity fault generated mountain fronts. This fault generated mountain front, however, shows a peculiar morphostructural setting variable both longitudinally and transversally. This led us to define a partition into three distinct sectors made up of adjoining relatively downfaulted and uplifted blocks: northern sector, central sector and southern sector. In order to summarize the features characterising the three sectors, six morphostructural sections were drawn (three on straight transversal profiles and three on stream channel and interfluve profiles). The geomorphological analysis highlighted a complex growth evolution, rapid in the earlier stages and continuing in succeeding stages with the dominance either of morphostructural factors, linked to the conflicting fault activity and regional uplift, or of morphosculptural processes, controlled by the litho-structural setting and by climatic change, particularly during the cold stages. In a general balance, due to the local subsidence of the Sulmona basin relative to the Montagna del Morrone blocks along two major normal fault systems in a general uplift of the chain, the growth of the escarpment has strongly exceeded the effect of denudation. The morphogenetic processes are mostly due to drainage network linear down-cutting in the mid and lower parts of the northern and central sectors, while slope gravity areal denudation is prevailing in the upper part of the northern and central sectors and in the southern sector. Finally, an attempt was made to summarise the main stages of the morphostructural evolution from Early Pleistocene to Holocene.