By central Apennines we usually mean the set of mountain ranges of Umbria and the Marche and of Abruzzo. We said earlier that the Apennines form an arc with its convex side towards the east. The curvature is particularly marked precisely between Romagna and the Marche, where the mountains come remarkably close to the Adriatic coast (Monti Sibillini and the Gran Sasso massif).
The Apennine arc is characterised by an uneven variety of geographical and geomorphological features. Compared with the northern area, the central Apennines have long ridges, each with its own distinctive features.
The Umbria-Marche Apennines are characterised by evident folds; these folds become particularly deep where the rock turns out to be made of limestone materials easily subject to erosion. The main morphological element of this area of the Apennines is represented by the great carbonate ridges culminating in the Monti Sibillini, whose highest peak is Monte Vettore (2476 metres), and in Monte Terminillo in the Monti del Reatino.
Moving down along the ridge towards the south-east, the other morphological feature of interest is the so-called karst basins (Colfiorito, Castelluccio), surrounded by bare walls with little vegetation. In the more inland areas, on the other hand, we find the intermontane basins (Norcia, Gualdo Tadino, Gubbio, Rieti, Foligno), made up of more or less impermeable sandstone formations which keep rainwater on the surface, feeding rivers and streams along which lush nature thrives.
The limestone mountains of the most central area, the Velino and Sirente group, the Majella, the Marsicano and the Monti Simbruini, are cut by long rivers above which the mountains rise dizzyingly and sheer. Together with the Gran Sasso, they are mountains characterised by rocks of limestone composition, extremely permeable to the infiltration of water, which the ground cannot hold. On the whole these mountains are very dry, in spite of the abundant precipitation, both snow and rain.
These bare mountains, touched by Quaternary glaciation, are morphologically rather soft, almost never marked by sharp peaks.
The last sign of the past ice age is the presence on the Corno Grande of the by now shrunken Calderone glacier; glaciation which, in the area of the central Apennines, never reached below 1300 metres.
Finally, still on the subject of karst phenomena, so predominant in the central Apennines, the marshy karst plain of Avezzano is emblematic. A karst plain, known today as the Piana del Fucino, which held what was once the Lago del Fucino.
As early as Roman times a first drainage of the lake had been carried out. Further drainage works came from the 1800s onwards and later in the Fascist era. These reclamations certainly wrested excellent farmland from the marshes, but they are probably at the root of a certain drying out of the foothill area, with the resulting thinning of the woods along the mountain slopes of the Velino and the Sirente.