Rockglacier at the base of Rocchette cliffs

With regard of Morphoclimatology, in the Dolomite region a wide and exemplary representation of geomorphological phenomena linked to past and present climatic conditions can be observed. The warm-humid climate of the Eocene-Miocene (60 to 7 million yrs B.P.), the temperate-humid climate of the Pliocene (7 to nearly 2 million yrs B.P.) and, in particular, the alternation of cold and temperate climates of the Pleistocene and Holocene (about the last 1,800,000 yrs) have generated a sequence of different environments, in which reliefs have been modelled according to diverse processes and landforms: this polygenesis is documented by the numerous forms that make up the Dolomite landscape. Some hypotheses have been proposed on the pre-Pleistocene origin of some relict terraced surfaces which can be observed in some Dolomite summits. Nevertheless, the data available are still scarce and unreliable. Abundant reliable evidence is found only on the glacialism of the last phase of the Würm Pleniglacial (25,000 to 17,000 yrs B.P.) and the so called Lateglacial (up to some 11,500 yrs B.P.). Traces of previous interglacial deposits are recorded in the mid-valleys of Fassa and Gardena, where cemented alluvial or slope deposits underlying Pleniglacial moraine heaps have been identified. During the Last Glacial Maximum (LGM) glaciers used to occupy all the Dolomite valleys, with ice thickness often exceeding 1500 m (in the Bolzano area nearly 2000 m). Therefore, only the highest peaks could emerge in the form of nunataks from this “sea” of ice. The glaciers coming from the large Dolomite groups joined together and created a network of glacial branches intersecting between one valley and another. Some flowed over the present Dolomite passes, which at the time acted as transfluence saddles. The particular diversity and distribution of the rocks in the Dolomites have also led to the identification of the direction of glacier movements by means of specific analyses carried out not only on relief morphology, but also on the distribution of debris transported along valleys or from one valley to another. In this way, some cases of transfluence have been recognised: for example, from the Adige to the Piave basins through the Gardena and San Pellegrino passes. The most evident traces linked to glacial morphogenesis can be attributed to subsequent melting phases, which took place intermittently and discontinuously during the Lateglacial phase which started around 17,000 yrs B.P. The most frequent erosion landforms are: steps, hanging valleys, roches moutonnées, sharp rocky crests and cirques. Hanging valleys are particularly evident at the junction of small valleys with principal valleys. Significant examples are found along the slopes of the Fassa valley at the confluences with the Contrin, Ciampac and Duron valleys. Glacial cirques are scattered almost everywhere near the valley heads: at present, many of them contain small cirque glaciers or glacierets. There is also plentiful till deposited by glaciers in stadial phases. Till is found within many valleys and in characteristic shapes, but mainly in sequences of frontal ridges which can be seen one after another as far as the individual valley heads. Their distribution throughout the NE Dolomite territory is summarized in the geomorphological schematic map. Stadial moraines contain some lakes, for example Lake Misurina (Cristallo Group) and Lake Carezza (Latemar Group). Holocene glacial deposits are plentiful and modelled in well developed ridges, very often showing a sharp profile like a knife blade, several dozen metres high, with marked linear development extending even up to several hundred metres. They are found mainly near the present glaciers, prevalently in the form of lateral moraines. Landforms related to recent or present-day glacier activity are not lacking, even if existing glaciers in the Dolomites are small in size because they have a relatively low mean altitude and high relief energy, which are unfavourable elements for glaciation. Some mountain groups still have ice masses today: the main ones are found on the following mounts: Cristallo, Tofane, Sorapis, Marmarole, Antelao, Marmolada (the largest one), Pelmo, Civetta, Pale di San Martino and the Brenta Group. Most of the ice masses are northward oriented and show an almost symmetrical distribution with respect to the north. Also periglacial or fluvioglacial processes, linked to Pleistocene glacialism, have left many typical traces, such as permafrost and frost thrusting, cracking and sorting, or terraced forms or lacustrine and palustrine depressions. In addition, the confluence of several glacial tongues into narrow valleys during the advancement phase has generated considerable stresses due to glaciopressure on the rock
walls, with consequent deformations in correspondence with discontinuity surfaces. These relict morphological features still condition to date geomorphological dynamics: steep waterfalls with high erosional power flow from the hanging valleys; moraine debris is repeatedly subject to degradation and collapse processes; the melting of permafrost can cause mass wasting processes due to water absorption; the rocks broken up by frost-weathering are affected by debris falls which, in turn, generate debris flows; glaciofluvial terraces are the main sites of pedogenetic processes and situations of phyto-morpho-stasis; kettle lakes and ponds show in some places representative morphostratigraphic sequences containing organic finds. The latter can be dated for paleo-geomorphological reconstructions. Glaciopressure phenomena due to ice confluence have created potential detachment surfaces, along which some of the most spectacular landslides of the Dolomites have occurred. Following glacier retreat, intense debris reworking and accumulation processes have occurred. These deposits were subsequently fixed by vegetation and cut into terraces by water courses. Fluvial erosion, the instability of rock walls and present degradational processes have in turn produced deep gorges, various types of landslides (from rock falls to debris flows), slopes washed out or cut by rivulets or notches etc. Above the tree line, a series of forms resulting from the action of ice and snow can be observed. Several temperature fluctuations below and above 0°C, with consequent cyclic transformation of water (percolating through the rock fissures and pores) into ice, cause the phenomenon of frost shattering in rocks. Among the most typical elements of this landscape there are talus cones and scree slopes: these are a very common and sometimes spectacular feature of the region, binding many mountain groups at their base. A landform which often accompanies these debris heaps is the protalus rampart, which consists of elongated ridges parallel to the slopes, due to the sliding of fallen blocks on snowy slopes. Other typical forms are rock glaciers: these are debris heaps arranged in the form of lobe or tongue, with a series of furrows, undulations or arches on their backs car contain ice. Snow avalanches are one of the most violent and spectacular phenomena. These are snow slides sometimes mixed with ice, debris and vegetal matter, which can occur quite suddenly. They frequently originate above 2000 m, i.e. beyond the upper tree line, from slopes with gradients usually exceeding 20° and with a prevalently northern aspect (winter avalanches) or southern aspect (springtime avalanches): also tracks and avalanche cones are typical landforms. Small landforms due to discontinuous frost and/or snow action (patterned ground) can be observed locally at high altitudes on plateau areas. Gelifluction phenomena also give rise to evident morphological features (scars, lobes, small flows etc.) especially on slopes consisting of pyroclastic and clayey rock types.