Lake Marmo–Sella di Scaredi

Lake Marmo, one of the best-known hiking destinations in the Vigezzo Valley, is listed – together with the entire Alpe Scaredi area – in the National Inventory of Geosites maintained by ISPRA (the Higher Institute for Environmental Protection and Research). The lake occupies a glacial over-excavation basin, that is, an area eroded more extensively by the glacier, bounded towards the valley
by a rocky threshold – in this case, white marble – which is clearly visible even from a distance. The lake is perennial as it is fed, during the months when there is no snow cover, by water from springs situated at the base of the Cortechiuso-Laurasca ridge. In the surrounding area there are more mature depressions, which have undergone natural silting up and, over time, have become peat bogs, characterised by high ecological value.

As far as rocks are concerned, the Lago del Marmo area is characterised by marbles and amphibolites from the South Alpine Domain. The marble is composed of calcite and, locally, silicate minerals; it has a granular appearance reminiscent of sugar (which is why it is also known as ‘saccaroid’ marble). Marble is a soluble rock: in the presence of water with a very high carbon dioxide content, karst processes can be triggered, carving out features of varying sizes on the rock outcrops , such as grooves (karren), shower-like furrows and corrosion basins.

The saddle where Alpe Scaredi is situated, along the Cimone di Straolgio–Laurasca ridge, is a depression carved out by the glacier, a process facilitated by the presence of rocks that are more susceptible to erosion due to the activity of the Insubric Line. In this area, one can clearly see hummocky rocks, depressed areas known as over-eroded basins, striations and grooves – all features resulting from the abrasion caused by debris transported at the base of the glacier. These are the effects of the land-shaping action carried out by the glaciers which, during the Pleistocene (a period spanning from 2.58 million to 11.7 thousand years ago), occupied the Loana Valley and the Portaiola Valley.

From a geological point of view, the Insubric Line runs near the Alpe Scaredi saddle, separating the rocks of the Canavese Zone (e.g. phyllonites and phyllites) and the Austroalpine Domain (e.g. gneiss), situated to the north and intensely deformed during the Alpine orogeny, from the rocks of the South Alpine Domain (e.g. amphibolites), situated to the south and having undergone only slight deformation. The phyllites, which outcrop in the glacial saddle, consist of abundant micas and white quartz lenticels, clearly visible in relief on the outcrops, as quartz is more resistant than micas to the erosive action of the glacier