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18/07/2012 4:05 pm
The Park mainly has outcrops of the Piedmont calc-schist complex with greenstone (ophiolite of the ultrabasic rock complex of Mont Avic prevail in Val Chalamy; calc-schist prevail in Champorcher Valley). The ophiolites are a fragment of the Piedmont oceanic basin, involved in the alpine orogenesis following the continental collision between Africa and Europe.
From the morphological point of view, the territory of the Park is still in a youthful evolutionary phase with high reliefs, deep valley incisions and steep slopes.
The morphology is the result of numerous factors, such as the combined erosive and deposit action of watercourses and glaciers, with the formation of glacial cirques and corresponding alpine cirque lakes, moraine deposits of considerable extension and depth, significant differences in height between the valley floor and the reliefs.
The morphology of the Val Chalamy is characterised by high reliefs and deep valley incisions. The direction of schistosity of the metamorphic rocks is relatively homogeneous with immersion prevalent towards the north determining a sharp asymmetry of the two main slopes: on the left bank the slopes are steeper, while the right bank has a gentler morphology alternating hillocks, shelves and depressions (these last partly a consequence of swarms of faults).
The action of the Quaternary glaciers (erosion, ablation and deposit) is particularly evident in the southern sector of the valley, rich in smooth, striated rocks and roche moutonnée, as well as numerous glacial cirques currently filled by bodies of water. In the eastern portion can be seen significant moraine deposits and numerous erratic boulders.
The water courses have dug deeply into the valley, contributing to the transport of solid materials towards its outlet: the imposing fluvio-glacial deposits immediately downstream of Chevrère are made evident by the processes of instability that have led to conspicuous erosion furrows, rather unusual in the alpine environment.
The Champdepraz area is part of the Piedmontese Calc-schist complex with greenstone. The calc-schist are made up of rocks low or even free of calcite, and include sericite phyllite, mica schists and, more rarely, quartzite and albite gneiss. Greenstones are metamorphic derivatives of basic intrusive rocks; these are mainly gneissic prasinites, or prasinitic gneisses gradually passing to prasinites by a decrease in quartz and muscovite.
Unlike some neighbouring sectors of Champorcher Valley where there are mostly calc-schists with poor intercalations of prasinites and some lenses of serpentinite, within the Champdepraz territory powerful successions of greenstone emerge, with a prevalence of peridotites (tectonic peridotites of Mont Avic), eclogite metagabbro, eclogite-glaucophanite metabasalt, alternating with volcanic sedimentary sequences. In this area, within the Park and in its immediate surroundings, there are some particularly interesting mineralizations, since at least some of them were worked for a very long period and up to the first half of the last century. The magnetite mineralizations of Lake Gelato located at 2,600m were already being mined in 1693 and their exploitation continued intermittently until 1893. The iron-copper mineralizations of Hérin, located outside the Park above the chief town of Champdepraz at 1700m, were intensively exploited in the 18th century and intermittently until 1951.
Also noteworthy are the numerous minerals found in several parts of the Park within rodingite veins (apatite, epidote, garnet, smaragdite, vesuvianite, etc.).
The quaternary surface deposits of the Champdepraz area constitute frequent and relatively continuous outcrops. These are mainly glacial deposits, bottom and lateral moraines from the last phases of the post-Wurm retreat or from recent glacial phases (little ice age), debris deposits, cones or aquifers, originating from the decay and subsequent gravitational deposition at the foot of the rock walls, and peat sediments resulting from the filling of the numerous lake beds and paleo-lake beds. The moraine deposits appear extended throughout the valley floor, mainly from 1,300 to 800m, testifying to the presence, during the glacial periods, of large glaciers. Moraines are chaotic clusters of rocks of different lithology and particle size, consisting of a sandy or silty matrix which includes even large rock fragments. Alluvial deposits are small size deposits on the valley floor, mainly comprising gravel and sand, but also blocks of considerable size, which can be seen in the river bed of Torrente Chalamy.
The overall features of the recently enlarged area of the Park, which is the top portion of the Torrente Ayasse water catchment area, differ distinctly from those found in the Champdepraz valley: specifically, the extensive outcrops of calc-schist and the presence of deeper and more fertile soil ensures a higher percentage of vegetation cover than in Val Chalamy, with a considerable variety of flowers in the alpine plain. On the north side of the Rosa dei Bianchi mountain, a glacier can be seen that is clearly larger than the residual glacial system located on the northern slopes of Mont Glacier.
In the absence of substantial glacial systems, the sources in the summer for the main waterways are the late melting of the snow on the high slopes exposed to the north and the water contained in the debris-moraine coulters. The hydrological regime, characterised by significant changes in flow rate also due to the predominantly superficial soils, is very low in the winter and very high in late spring. The circulation of groundwater is abundant and widespread, with the consequent presence of numerous springs; the resurgences located on the lower left bank of Val Chalamy determine specific environmental contrasts, since they are inserted in what tend to be xeric environments.
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