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The lherzolites of Lago dei Gulli

When you reach the site, you will have the chance to interpret the forms of the landscape modelled by the Torrente Erro (meanders, potholes, and fluvial terraces) and see the peridotite rock originated within the mantle of the Earth. Following the Alpine orogenesis, almost all the peridotites of the mantle metamorphosized, transforming themselves into serpentine schist rock of a light green colour which can be seen in the outcrops. Some of these rocks, however, were not altered and partly conserved their minerals when they were several kilometres beneath the oceanic crust. At this site you can clearly see these rocks, called lherzolites, characterised by associations of minerals such as pyroxenes and olivine. They appear in the form of large brown spheres, a few metres in diameter, within the serpentinite rocks. Looking from above at the Lake of the “Gulli” – which is a name in dialect for the fish living in these waters – you can see that it is not a true lake despite the form and size. It is a “meander” inlet of the Torrente Erro, at the confluence with the Rio Cìua.

This area, characterized by outcrops of serpentine schist and peridotite rock, presents a landscape mainly modelled by waterways. The main valley of the Torrente Erro was cut out by the river which sank deeper and deeper with the passing of time. Looking around carefully it is not hard to identify the traces of the old levels of the river. These are “fluvial terraces”, i.e., flat surfaces that testify fy an ancient level, generally covered by deposits of pebbles and sand when the river flowed at that level. To identify these terraces you need to pick out the various flat surfaces just above the current level of the water (for more recent terraces) or rolling-plain ridges at higher levels (for more ancient terraces), using the photograph below as a help.

Location: Sassello Municipality: Sassello (SV) | View on Map
Gulli lake
Gulli lake
(photo by PR Beigua)
 
Rocks of Gulli Lake
Rocks of Gulli Lake
(photo by Cristiano Queirolo)
 
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