Description of Geomorphology
This system shows a vast and exemplary range of morphostructural and morphoclimatic landforms. With regard to morphotectonics, fault gorges can be observed in the Mt. Pelmo area, east of Forcella Staulanza, and in Becco di Mezzodì, east of Rocchetta: they are deep cuts in correspondence with displacements which were very likely active also during the Pleistocene. With regard to morphotectostatics, there are some examples of hogbacks and cuestas. Among the former is the ridge stretching from Mt. Pelmo to Rocchetta di Prendera, or the top of Mt. Cernera. Among the latter are the slopes SW of Mt. Penna or Mt. Formin. There are numerous crests bounded by tectonic lines. Among the most typical are the Cinque Torri, which can be observed just beyond the northern boundary of the system, which are separated by fractures and trenches, with NW-SE and NNE-SSW preferential directions, or wide troughs located at the top of Mt. Penna. These are found in correspondence with belts of fractures on dolomite or calcareous rocks and are the result of tensional release due to lateral spreading affecting these rock types overlying marly-pelitic formations. An important fault borders to the north the Mt. Pelmo massif. It is E-W oriented and clearly separates Cime di Forca Rossa, to the south, from Cime di Val d’Arcia, to the north. Furthermore, it is marked by a track, a saddle and an alignment of small escarpments and cuts. With regard to morpholithology, there are typical plateaux, as Lastoni di Formin and the northern slope of Mt. Penna, which are located in correspondence with Triassic carbonate shelves. Another typical landform is the ledge (cengia), of which several examples can be observed along the slopes of Mt. Pelmo and Croda da Lago. Finally, some saddles are found where the most erodible rock types crop out, such as Passo Giau and Forcella Staulanza. Moreover, karst landforms set on series of fractures subject to glacio-karst evolution are found on the plateaux. Most of them are concentrated on the top part of Mt. Pelmo. From a morphoclimatic viewpoint, numerous landforms witness the Last Glacial Maximum (LGM). They result from a thick glacial tongue coming from a northerly direction, which flowed to SSE along the present Boite valley, or originated in the highest peaks of this system. Some erosional forms of the Boite glacier are found, such as roches moutonnées and glacial exaration terraces, especially near Mt. Pelmo. Moraine deposits identified in proximity of some Dolomite passes bear witness to transfluences of the Boite glacier towards the Zoldo and Fiorentina valleys. These landforms allowed the altimetric boundary of glaciers to be located between 2150 m to the north and 2050 m to the south. Traces of Pleistocene periglacial processes are also found, such as a cryoplanation surface in proximity of the summit of Mt. Penna. In Mondeval de Sora, at 2150 m a.s.l., there is a glacial cirque where an archaeological site of extraordinary importance was found. In it a well preserved skeleton of a Mesolithic hunter was discovered: it is an example of a properly organised and intentional burial, which makes up the first finding of this kind at such a high altitude. This archaeological site is located in the trough of the glacial cirque and is positioned under a slightly jutting out boulder which was detached from the overlying mountain top and subsequently transported downhill by a Würm Lateglacial glacier. The geomorphological reconstruction also shows that in the Mesolithic period the centre of the trough was occupied by a pond. Recently, the area of this important archaeological find was rightly preserved from the construction of skiing facilities thanks to the efforts of a committed and enthusiastic group of environmentalists. This site can be quoted as an example of historical continuity and integration between geomorphological events, prehistory, present events and sustainability. Lateglacial morphology is represented by numerous, generally well preserved cirques near the highest peaks and by stadial moraine deposits. A kame terrace was also found along the eastern face of Mt. Pelmo. The prevailing morphology is, in any case, glacio-nival and has developed in a fairly continuous way up to the present with rock glaciers (S and W of Forcella Ambrizzola, N of Nuvolau, in the Formin valley and near Passo Giau), protalus ramparts (on the S face of Lastoni di Formin and on the E and NW faces of Mt. Pelmo), and avalanche cones (mainly N of Mt. Pelmo). Some of the most typical cases of landslides are found at Cinque Torri and Lastoni di Formin. An evident topple is observable at the Cinque Torri, an isolated rock outcrop of Dolomia Principale, near the margin N of the system. The Cinque Torri consist of some monoliths affected by lateral spreading phenomena, at an advanced stage of evolution, and by collateral movements, such a falls, topples, slides and flows. The gravitational phenomena are mainly conditioned by the superposition of the Dolomia Principale of the Cinque Torri on an incompetent substratum, consisting in reddish marls and sandstones belonging to the Travenanzes Formation. This is the typical case of a superposition of hard and rigid rocks on soft and plastic materials, a situation which is well known to be very favourable to the development of deep-seated gravitational deformations. The monoliths are highly interested by degradational phenomena (mainly frost shattering), favouring the occurrence of rock falls and topples, which contribute to the nourishment of the scree slopes present at the base of the rock walls. The direction of the fractures and trenches separating the blocks follows the tectonic style of the area, which shows a system of discontinuities with NW-SE and NNE-SSW preferential directions. The strata of the Travenanzes Formation dip downstream with the same angle of the slope; this fact surely contributed to the splitting up of the plateau and to the tilting of the blocks. The Torre Grande, the highest monolith (2361 m upon sea level), characterized by almost vertical walls reaching the height of 150 m, is affected by open fractures which extend as far as the substratum; this leads to the subdivision of Torre Grande in some rock blocks and has favoured the rock topple here considered. One of the most peculiar cases of deep-seated gravitational deformation is that of the Lastoni di Formin which are located on the right side of the Rio Falzarego. It is part of the mountain group which includes Mt. Nuvolau and La Rocchetta. The Lastoni di Formin can be described as a thick plate of Santa Croce/Heiligkreuz Formation and Cassian Dolomite overlying the marls, arenites and clays of the S. Cassiano Formation. From a structural point of view, the strata show a NW-SE strike and dip gently to NE. Moreover, the area is characterized by a system of discontinuities which controls the dismemberment of the plate and many other gravitational deformations and slope movements within almost the entire basin at the Boite torrent. The wide structural surface of the Lastoni di Formin is affected by deep-reaching fractures, whose direction runs parallel to the strike of the strata and consequently to the direction of the slope. The dimension of the fractures varies depending on the different evolutive stages of the phenomenon, which are quite clearly observable in the field. In fact, in the upper part of the Lastoni di Formin there are trenches reaching a maximum width of about 1 m, while in the lower part the trenches reach widths of decametric scale, with vertical displacements of similar entity. The peculiarity of this phenomenon consists in the presence of various stages of evolution at the same time. Lateral spread phenomena are prevalent in the upper part accompanied by progressive displacements of the blocks downslope, which gives the slope a step-like morphology. In the lower parts of the slope, lateral spread evolves in block slide, while at the base of the slope “simple” slope movements, such as falls, topples and slides take places. This is demonstrated by the presence of several dolomitic monoliths and boulders (some of them reaching some hundreds of cubic meters) isolated from the rocky plate and toppled inside the wood at the foot of the slope. In the latter two cases a series of collateral movements, such falls, topples, slides and flows are also found which show exemplary scientific and educational evidence. with a very wide range of the types quoted in literature. There are many mass movements of various age and dimensions, some of which are here quoted. Rock falls: concentrated around the dolomite faces of Mt. Pelmo and Nuvolau, the western face of Lastoni di Formin and the southern face of La Rocchetta. Rock slides: found in Val d’ Arcia and north of Forcella Ambrizzola. Sackung: found in particular on the eastern face of Mt. Pelmo. Mud and earth flows: affecting the terrigenous formations (Santa Croce/Heiligkreuz, Travenanzes etc.), as on the southern slope of Mt. Pelmo. Debris flows frequently originate from the numerous talus cones and scree slopes, like the one occurring on 14th September 1994 on the northern slope of Mt. Pelmo. A series of landforms shows high extrinsic and intrinsic geodiversity from morphostructural and morphoclimatic point of view. Furthermore, typical talus cones and scree slopes are found: they show an accentuated morphological uniformity on a regional scale.