This vast Dolomite system shows a particular intrinsic geodiversity, made up of rocky massifs, such as Cima Vezzana, Mt. Agner, Mt. Civetta, Mt. Tamer and Mt. Ramezza; plateaux, such as Pale di San Martino and the Erera – Piani Eterni mountain group. A set of valleys separates or intersects the mountains of this region. Nevertheless, this system presents a typical case of extrinsic geodiversity at a regional level. Indeed, it can be quoted as a typical and representative dolomite landscape with a marked and homogeneous physiognomy, although there are various degrees of articulation. From a morphotectodynamic viewpoint, at Pale di San Martino a NW-SE oriented neotectonic fault, uplifted on the NE side, is morphologically revealed by an aligned series of well exposed saddles and deeply cut tracks. The Plio-Quaternary and Holocene activity is made evident by very fresh geomorphological evidence and by a series of numerous recent landslides occurring all over the area. From a morphotectostatic viewpoint, many NE-SW trending alignments, which developed at a regional scale, have constrained the physical arrangement of this system, especially regarding the valley axes and the trend of the dolomite mountain tops. Among the former the Gares, Canali, Listolade and Moschesin valleys; among the latter are the Cima Vezzana – Cima di Focobon and the Croda Grande - Monte Agner alignments, the crests NW of Mt. Civetta and Mt. Pizzon and the alignment between Mt. Pavione and Mt. Ramezza. Furthermore, a series of escarpments, rock cliffs and crests constrained by a joint network is present. From a morpholithological viewpoint, the various landforms result from the structure of the area which is formed by different rock types. The Pale di San Martino plateau is an original surface of the dolomite reef, uncovered thanks to the erosion of the younger formations. On this plateau a paleo-karst surface caused by the mid-Triassic emergence which interrupted the carbonate production of the platform, is documented. The best paleo-karst evidence is in an area of approximately 2 km2, between Manna Riviera and the moraine complex of Fradusta Glacier. The evident paleo-karst features are formed by small pockets and large cavities with clastic filling, sedimentary dykes and intra formation breccia deposits. On the plateau there are also interesting surface karst forms: crevices and pits, dolines of various shapes and size and large closed hollows which have made the surface of the plateau rugged and undulating. Also on Mt. Civetta the surface karst morphological features are spread throughout the outcropping belt characterised by the Calcari Grigi and the upper limestones of the Cassian platforms. The latter two are formed by a sinkhole which has given its name to the “Pian della Lora” at the foot of the Pelsa area. On the other hand, Van delle Sasse features spectacular examples of karren. From a karst viewpoint, the most interesting areas are the Van delle Sasse and Van della Moiazza. In these two areas there are snow pits with perennial ice up to 45 m deep, which have developed within the Calcari Grigi and the Dachstein Limestones. The Erera – Piani Eterni plateau is a complex physiographic, polygenic system with wide areas consisting of rocks with low relief energy (altitudes between 1700 and 1900 m a.s.l.), where karst morphogenesis often finds the right morpho-structural conditions to develop. In fact, this is the major karst group in the system and one of the most representatives of the Dolomites, in terms of landform variety and density, this means a high specific intrinsic geodiversity at a local scale. In general, karst morphology is combined with glacial and structural landforms and its current evolution is mainly affected by the long presence of snow (nivo-karst). This area can be divided into more morphostructural units. The Piana di Erera is a glacio-karst depression with structural influences and the shape of a small polje; the floor of the depression is flat and covered with thin alluvial or colluvial deposits and torrential fans. The depression is drained by means of sinkholes located at the basis of the alluvial fans. The Piani Eterni highland is a plateau constrained by stratification with wide rocky areas, structural terraces, structural surfaces with crevasses, different types of karren and a couple of glacio-karst depressions (SE and E areas). Circo di Cimia features at the bottom a glacio-karst depression with microforms of corrosion, structural terraces, crevasses and pits. The Pelsa area consists of structural terraces and wide rocky surfaces with karst spurs that look like giant karren or “rock cities”. A network of over 200 underground cavities is also found. Drainage often takes place through subsurface karst network flow lines. Several springs have originated in this way, such as Colmeda (Lamon valley), Stien (San Martino valley) and Val Neva (Val Canzoi) on the mountain tops of the Feltre area.
From a morphoclimatic viewpoint, the most relevant feature is given by the evidence of the Lateglacial and Holocene LGM glacialism. In the Group of Pale di San Martino there are various moraine deposits, especially around the Primiero hollow, in the Valle del Cismon and Valle dei Canali that merge here, and in the high basins of Mis, in Val Sarzana, Val Imperina and Val Biois. The moraine deposits are made up of ridges and terraces and are often characterised by large erratic blocks, belonging to the LGM or, mainly, to subsequent periods. Moreover, there are numerous more recent moraines in the higher talwegs and cirques, or in the more protected mountain areas, up to the historic moraines in front of the small present-day glaciers. Also Mt. Civetta is rich in traces of moraine deposits, which are particularly widespread over the NW and E slopes, extending also outside the core area, towards the Cordevole and Maè valleys, respectively. Less common, although still present, are the small moraine arcs at Mt. Tamer, Mt. Talvena, and Mt. Pizzon, found as far as Mt. Ramezza and Mt. Pavione. This depositional morphology is accompanied by a whole series of glacial cirques, also set in a step-like arrangement, as at Pale di San Martino. Other forms of glacial erosion are represented by roches moutonnées and quarrying processes. Typical examples of hanging valleys can also be found, especially on the left-hand slopes of the main valleys of the torrents Cordevole and Cismon. Some valley cuts show evidence of rock bars and basins resulting from differentiated glacial exaration. The highest peaks, that used to emerge from the ice covers, show evident forms of periglacial morphogenesis, whereas the already quoted glacio-karst phenomena are present on the plateaux.
The processes that modelled them have continued their action in subsequent times and to date still characterise glacionival morphogenesis. The products of frost thrusting, cracking and sorting form an interlacing of talus cones and scree slopes, which characterise the geouniformity of the whole system, i.e. they represent a low degree of intrinsic geodiversity, with reference to this type of deposit. In some places cryoclastic debris is arranged in the form of protalus ramparts, as at the foot of the scree of Vette Grandi and Pavionet, in the Vette Feltrine. A typical example of rock glacier is found uphill of the moraine circles of Busa delle Vette, in the Feltre Dolomites. During the glaciers’ retreat phase there were rock falls from the dolomite walls which had been subject to glaciopressure during the progression stages of the LGM glaciers, in correspondence with the confluence of two or more glaciated valleys. A typical example is found at San Martino di Castrozza, at the confluence of the Tognolo, Cigolera, Bonetta, Cismon and Malga Pala streams, where Pleniglacial apparatuses were once present. The collapse of the Cima Rosetta dolomite wall caused the damming of the Cismon valley. Another example is found NE of Fiera di Primiero at the confluence of various tributary and sub-tributary streams of the Cismon valley itself. Another one is found at the head of the Mis valley. Other landslides, fallen from dolomite rocks at the NE boundary of the system, can be observed downstream of Forno di Zoldo, in the area across which the streams Maè, Duran, Malisia, Pramper, Cerveana and Torto flow. This zone shows evidence of the confluence of ancient glacial valleys. Failures affect dolomite rocks: they obstructed the Zoldo valley causing the subsequent formation of a vast impoundment, the sediments of which now appear as terraces in the village of Forno. The largest one can be observed just outside the system boundary, near Sospirolo, at the confluence of the Cordevole and Mis valleys, which were previously occupied by glaciers. The accumulation of a large-block landslide (marocche) occurred as translational slide from the slope of Mt. Peron, damming the Mis valley, where an artificial lake is now present. This impoundment corresponds largely to the natural lake caused by landslide damming, which was subsequently filled in by alluvial deposits. A rock fall occurred on 3 December 1908 on the southern slope of the Pale di San Lucano. The villages of Prà and Lagunaz, located in the San Lucano valley, were almost destroyed and 28 peoples were killed. The volume of material detached from the vertical slopes of the mountain massif, consisting of Cassian Dolomite, has been estimated in 250,000 m3. The most frequent present-day gravitational processes, apart from the already described talus cones and scree slopes, are debris flows, which originate mainly from Pale di San Martino and Mt. Civetta. This system includes two small glaciers: Cristallo, on the NW wall of Mt. Civetta, and Giazzer, in Val dei Cantoni.
As previously pointed out, this system shows many elements of geodiversity, of various grade and type and at different scales.
- High extrinsic geodiversity at global scale: typical dolomitic lanscape;
- High extrinsic geodiversity at regional scale: rocky cliffs, plateaux, valleys, a series of steeples ecc.;
- High intrinsic geodiversity at regional scale: glacial and periglacial landforms;
- High intrinsic geodiversity at local scale: karst landforms;
- High geo-uniformity (low intrinsic geodiversity) at regional scale: talus cones and scree slopes.