Italian geographers have reached agreement on defining about ten principal landform types (forme di terreno) in their country, each a characteristic combination of surface features and underlying rocks.
The first principal land-form type consists of mountain areas formed largely of crystalline rocks. In the North these represent the Western Alps and the highest, northern parts of the Central and Monte Viso, the Cervino. The crystalline Alps were for the most part profoundly affected by all the glaciations of the Pleistocene period, the evidence of the latest glaciation being the most conspicuous. Small glaciers survive in places in the highest parts and there are considerable snowfields. Sharp, frost-shattered peaks stand out either individually (Monte Viso, the Cervino) or in impressive clusters (the Monte Bianco and Monte Rosa areas). Valleys are usually steep-sided with narrow flat floors, their cross-sections being U-shaped, while many passes are due to erosion by difluent ice. Minor valleys frequently 'hang'. Other features of the landscape are frequent corries (cirche) and arêtes (creste), especially pronounced in the areas of most resistant rocks, and the numerous alluvial fans along the larger valleys. In Calabria north-east Sicily and Sardinia, crystalline mountain landscapes recur, but they were not affected by glaciation, are lower (below 2,000 metres) and generally more rounded than the Alps.
Limestone is the dominant rock in the southern half of the Alps east of the Ticino, in an extensive area in the central part of the Peninsula, and in smaller mountain areas in the South and Islands. In the Alps it was only affected by glaciation in the higher northern part, where in the Trentino-Alto Adige massive tower-like mountains with precipitous sides and sometimes extensive flat tops in the Dolomites differ notably from the more pointed form of the mountains generally associated with the Alps, but land-form features are broadly comparable.
Features in the area include glaciers and arêtes as well as hanging valleys. Characteristic are the steep but by no means smooth valley sides, the alluvial fan, almost perfectly semicircular in shape, and the flat valley floor, clearly still illdrained in places but with the river course now regularised.
The southern fringe of limestone between the high, glaciated Alps and the Northern Lowland, is lower and less impressive than the areas so far described but is still rugged in many places. Karstic features occur in places. Many of the highest and most rugged areas in the Apennines are also associated largely with limestones. In limited areas they reach 3,000 metres; above about 2,000 metres they have been affected by glaciation, and in the Apuanian Alps of Tuscany and the Gran Sasso in the Abruzzi reproduce in miniature land forms reminiscent of the Alps. They can be spectacular, too, where they approach the coast, as near Naples (the Sorrento Peninsula) and Palermo (Monte Pellegrino). Except in Istria and Apulia, however, karstic features are not widespread in the limestone areas of Italy. This appears to be due both to the widespread occurrence in the predominantly limestone areas of thin beds of other types of rock and to the youthful stage of erosion. Surface drainage is therefore present, but there are also underground streams and caverns (grotte).
The third group of rocks frequently associated with mountain areas in Italy and having certain characteristic surface features are the sandstones, marls and clays of the Peninsula and Islands. These rocks are widely distributed but are most extensive in the Northern Apennines. The general altitude of the sandstone, marl and clay areas is lower than that of the limestone areas and features are generally more rounded. In many places, however, steep-sided cappings (balze) of sandstone or limestone stand above undulating clay outcrops, forming prominent features. Landslides (frane) are common where clays are covered by other more permeable rocks and dip at appropriate angles for these to slip. The clays, in their turn, are afflicted in many areas by gullying and the formation of badlands (calanchi), characteristic particularly of the argille scagliose of Cretaceous times. Although not generally so high as either the limestone or the crystalline mountains of the Apennines, the sandstones, marls and clays can give rise to very broken country, as in parts of the Northern Apennines and in Basilicata. The valley floors are occupied by the gravel-strewn beds of rivers that are full in the winter but dry in the summer. The land rises irregularly but steeply to narrow ridges several hundred metres above the valley floors, only to descend as precipitously to neighbouring valleys. The many small streams are a characteristic feature.
Cones and craters, mostly now extinct, form prominent and characteristic if not very extensive mountain or hill areas (e.g. Monte Amiata, Vesuvius, Etna). In contrast to the volcanic cones are the areas of hill country formed on lava flows. These are widespread in Lazio and occur also in Sardinia. In Lazio they are referred to as the volcanic plateau, the surface of which is dissected by many small rivers in slightly incised valleys, and the edges of which are abrupt in places. Around Vesuvius and the Campi Flegrei the volcanic material forms a plain.