Narrating the history of a territory through its geological and geomorphological heritage: an itinerary between Chiavenna and Piuro (Central Alps, Lombardy)

Since prehistoric times, Alpine valleys have witnessed the growth and development of populations that progressively learned to exploit their natural resources and features, while also dealing with the many natural hazards that these territories present. Traces of this interconnection can be found throughout the entire Alpine chain, the study of which helped us to better comprehend the evolution of the populations that inhabited these areas until present-day. Looking at the Central Alps, the area around Chiavenna and Val Bregaglia (Lombardy, Sondrio Province) represents a place where geological, historical and cultural heritage are inextricably intertwined, well predisposing to a geo-cultural narrative of the area. Chiavenna was raised within the homonymous valley that, since Roman ages, served as an important connection with the northern European regions. The oldest traces of human passage through the valley passes date from pre-historic Mesolitic ages, while the earliest evidence of stable human fruition trace back to Late Bronze and Early Iron Ages [1], with proof of soapstone extraction from the lower southern flank of Val Bregaglia and its processing, an activity that reached its maximum development between the XV and XVII centuries A.D., until an almost total abandonment of the quarries in the XX century A.D. [1]. Soapstone is a commonly used term to indicate talc-schists, metamorphic rocks rich in talc, that in this area lie embedded inside the ultramafic rocks of the Chiavenna Unit [2]. The petrographic features of soapstone are responsible for its good workability and predisposition to the production of everyday objects as pots and vessels, as well as construction and decorative material, as witnessed by dozens of monuments and architectural elements that can be found in historical buildings in the valley. Around Chiavenna, recent surveys [1] reported 35 open pit quarries and 46 underground quarries, locally called “Trone”, most of them scattered at the junction between Valchiavenna and Val Bregaglia. When not directly visible, the presence of underground soapstone quarries is indicated by several engraved boulders, which acted as markers to identify and reach the sites, as well as to indicate their owners. Hundreds of rock engravings are documented in the area, covering a time range of almost two millennia. The best-preserved quarrying example is the renowned Càurga (local term that is usually related to a deep gully), the biggest soapstone quarry in Chiavenna that dates back to Roman ages. Here, the soapstone extraction left a dozen meters-high incision in the peridotitic rocks on which archaeo-botanical Paradiso Park stands. Inside the park, various archaeological and historical remains surrounded by a variety of botanical species are preserved, perfectly embodying the coexistence of biodiversity, archaeology and cultural heritage. The park is developed on a peridotitic relief that rises enigmatically in the middle of the valley, bearing witness to a complex and prolonged geological evolution. Furthermore, the slope behind Chiavenna shows evidence of gravitational collapses that have involved large portions of the valley flank and, over millennia, have reached and occupied the valley floor with large landslide bodies. These phenomena are among the most impacting factors in the past and present-day landscape evolution of this territory. The communities that inhabited the valley learned to take advantage of these masswasting phenomena, for example, occupying the raised morphologies created by their deposits that offered shelters from flood events. At the same time, the circulation of air at constant low temperatures through the year (the so-called “Sorél”) within the crevices among the blocks allowed the use of landslide bodies as cellars, leading to the development of “Crotti”, a distinctive - almost unique - feature, representing a natural refrigeration system for storing food and wine. But the cohabitation between humans and natural evolution has not always been peaceful, as in the case of the catastrophic Piuro landslide that in 1618 completely erased the ancient village [3]. Piuro is located a few kilometres east of Chiavenna, and during the XVI and XVII centuries became a rich and renowned trading centre, where soapstone manufacturing played a central role. Today, the remnants of this ancient village are gradually unearthed thanks to active archaeological excavation sites that, together with several other sites of interest – such as the Piuro Archaeological Museum or the splendid Renaissance Vertemate-Franchi Palace – preserve tangible evidence of a place that no longer exists. In order to stimulate the perception of vulnerability to natural hazards and to permit observation of the interactions between natural and anthropic processes transforming the landscape, illustrative and descriptive panels have been installed near the main sites of interest (Figure 1). Another major factor that reshaped the valley landscape was the ice flow of Pleistocene glaciers flowing from the Engadine area, that in thousands of years carved and modelled the valley flanks, leaving behind, after the retreat, lots of glacial landforms and deposits [4]. Hundreds of subglacial forms consisting of potholes and mounded rocks are still very well preserved in the Marmitte dei Giganti Park, a regional natural reserve that extends between Chiavenna and Piuro. All these coexisting elements allow for a 360-degree view of the geological and cultural history of the territory, not treating each aspect as a single entity, but rather as part of a single overall vision. Several projects for the study, conservation and promotion of these sites took place over the years, with the participation of the Earth Sciences Department “A. Desio” of the University of Milan, which has been working in this area for more than twenty years. Among the most recent, the A.M.AL.PI.18 project (Italian acronym for “Moving Alps, and Movements in the Alps”), aims to encourage an innovative strategy for the promotion of natural and cultural heritage in the Alpine area comprised between Maloja and St. Gotthard, connecting sites which have experienced important geomorphological and anthropic changes due to the occurrence of landslides of great social impact. This project significantly contributed to the study and diffusion of knowledge of the main landslides of the Alps, with special attention to the Piuro landslide. Among the main products of the project stands the AMALPI Trek, a geo-cultural hiking trail between Italy and Switzerland that passes through Val Bregaglia, touching several landslide sites and narrating their features and their stories, but also offering interesting connections with the other local geo-cultural themes previously described, thanks to the help of a dedicated hiking guide [5]. Treading the path of the AMALPI Trek, this work wants to present and promote a one-day and easily accessible geo-itinerary between Chiavenna and Piuro, along which the visitor can draw information from the geocultural sites encountered along the way, learning about the territory on several intertwining thematic levels (Figure 2). Our geo-itinerary starts from Chiavenna Railway Station and passes by the Càurga and the archaeobotanical Paradiso Park. From here, it reaches Piuro passing through the Marmitte dei Giganti natural reserve, where some subglacial forms and “Trone” can be visited. In Piuro, the geo-itinerary touches several sites that witness the catastrophic 1618 landslide and then passes by the natural monument of Acqua Fraggia Waterfalls reaching the western fraction of Piuro and the Vertemate-Franchi Palace. Finally, it returns to Chiavenna along the Mera River, passing through the “crotti” area. The itinerary is 12 km long, covers a difference in level of 350 m and can be covered by a normal hiker, without any hurry, in about 8-9 hours. The huge geo-cultural heritage available in the area between Chiavenna and Piuro represents an excellent way to promote the territory and its story, merging geology, history and culture in a fascinating journey that started millions of years ago up to the present day. Visitors will be encouraged to witness the intimate relationship between geology, territory and population, visualizing how the historic and cultural evolution of a society can be controlled, first and foremost, by the geological predisposition of the territory. The proposal of this geoitinerary is intended to be a virtuous example of promotion, dissemination, fruition and conservation of the local geo-cultural heritage, through a series of installations and infrastructures that stimulate local geotourism, proposing itself as a sustainable source of growth of a local reality. The setting up of a geo-itinerary of this kind could also support alternative and effective ways of teaching the local culture to schools and to disseminate this knowledge through the population. This kind of approach could constitute an example for applications in other areas, especially along the Alpine chain, where geology and man had a closely related evolution that deserves to be acknowledged and appreciated.