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The Sesia Val Grande UNESCO Geopark, in Piedmont, combines spectacular geology of international significance with biodiversity and human culture.
Geodiversity
The value of diversity
The geodiversity of a territory is understood as the natural variety of rocks, minerals, fossils, and geological, geomorphological and pedological processes – in other words, all those abiotic processes that create the conditions necessary for the development of life on Earth.
In Piedmont, RegionalLawNo. 23/2023 ‘Provisions for the conservation, management and enhancement of the geological heritage’recognises the public interest in geodiversity and the geological heritage, and identifies geosites and geoparks as elements of particular scientific, cultural and landscape value, promoting their conservation, the improvement of knowledge and management, and their scientific, educational, cultural and tourist enhancement, including through the establishment of a regional register of geosites.
A window onto the Earth’s crust
The Sesia Val Grande Geopark encompasses an extraordinary variety of rocks and landscape features resulting from various geological processes: the entire area still bears the marks of the numerous events that have shaped it over hundreds of millions of years.
The geological significance of the Sesia Val Grande Geopark lies in the opportunity it offers to observe various orogenic processes: those that first formed ancient mountain ranges that have since disappeared, and subsequently, those responsible for the formation of the Alps, resulting from the collision between the African and European continents. These phenomena have brought to the surface rocks from deep within the Earth’s crust and mantle, now visible in one of the world’s most spectacular geological cross-sections. In sequence, various types of rock can be observed, ranging from the deepest (plutonic and metamorphic rocks) to the most superficial (volcanic and sedimentary rocks). Although involved in the collision between the continents, these rocks have retained distinctive characteristics attributable to earlier geological events. They therefore serve as a benchmark for interpreting scientific data on the continental crust.
What makes the Geopark’s geological section even more extraordinary is the presence, in its southern part, of the so-called ‘Sesia Supervolcano’. Here, one can identify the rocks belonging to its deep magma chamber and its caldera, formed by an explosive eruption.
To the north-west of the Supervolcano, the collision of the continents has, in contrast, profoundly transformed the rocks, creating a highly complex geological structure. The enormous forces at play fractured the Earth’s crust, stacking the fragments on top of one another as in a game of cards and folding the rocks, which had been rendered ductile by extremely high temperatures and pressures. Taken together, these processes transformed the very minerals that make up the rocks, forming new ones: metamorphic rocks.
The ‘boundary’ between the two continents – one exceptionally well-preserved and the other profoundly transformed – is the Insubric Line: this is a series of aligned fractures (faults), along which the tectonic movements of the Earth’s crust were concentrated during the final stages of Alpine orogenesis.
Geomorphology shaped by time
The mountains of the Geopark do not merely preserve evidence of our planet’s internal processes: they also feature splendid examples of how the surface has been shaped by glaciers – through their advances and retreats – and by rivers: these are processes that are still active today, and it is possible to observe both their action and their effects.
In short, the various rocks and landscape features of the Geopark reveal numerous chapters in a very long geological history: a ‘geodiversity’ that tells us of ancient oceans, shifting continents, volcanoes and ice ages. This constitutes a genuine geological heritage: not only evidence of our planet’s dynamics, but also phenomena that have profoundly influenced the development of local culture.
High-altitude routes and climate change
High-altitude trails offer the chance to observe the effects of climate change at close quarters, particularly in glacial and periglacial environments. The retreat of glaciers, the emergence of new lakes and the transformation of mountain slopes are all signs of processes that are still underway, clearly visible along these routes. These environments also represent a vital resource for humankind: veritable ‘water towers’ that feed rivers, aqueducts and mountain communities. The geotrails thus help us to understand the value of abiotic ecosystem services and the delicate balance between nature and human presence at high altitudes.
Passo dei Salati in the Monte Rosa massif
Ossola Valley
Valsesia side of Monte Rosa
Glaciers on the Valsesia side of Monte Rosa, seen from the Regina Margherita Hut
Lake Baranca in Val Mastallone
Candoglia marble and Milan Cathedral
In the quarries of Candoglia, in the upper Val d’Ossola, aprized pink marble, formed from ancient metamorphic rocks, has been quarried for centuries.
Since 1387, it has been the official stone of Milan Cathedral, and to this day the blocks destined for the cathedral are marked with the initials ‘A.U.F.’ (Ad Usum Fabricae) and transported along the River Toce and the River Ticino.
This link between geology and culture makes Candoglia a symbol of the deep connection between stone, art and tradition.
Soapstone
A soft, ash-green schist , composed of talc and magnesite, which is easy to work with and resistant to high temperatures, has been used since prehistoric times to make pots and artefacts, and is a key historical resource in the Sesia Val Grande Geopark area.
Candoglia’s Cava Madre, the quarry from which the pink marble for Milan Cathedral is extracted
Il Castello, an outcrop of soapstone in the Basso Valley
Pink marble bas-relief depicting the Candoglia area
Boulder in the Municipality of Malesco from which soapstone was extracted
Milan Cathedral in Candoglia marble
