The rocks of the Brenta Dolomites tell a story...
- 2 days
- April, May, June, July, August
- Natura & Benessere
An excursion in the heart of the Brenta Dolomites, Natural World Heritage Site, reading the pages written in the limestone rocks of these mountains that formed in the tropical seas 230 million years ago.
From Passo del Grostè to Vallesinella, passing near the Coste di Vallesinella and alongside numerous springs that are typical of the geological structure of this valley. Along the journey, enjoy the broad views of the great glaciers of the Adamello Group.
• Departure from Rifugio Stoppani at Passo del Grostè, which can be reached with the lifts of Madonna di Campiglio from Passo Campo Carlo Magno.
• We follow trail 301 downhill to Rifugio G. Graffer.
• We then take trail 382 and passing by Rifugio Vallesinella di Sopra, we arrive at Rifugio Vallesinella.
• By shuttle bus, we head back to Madonna di Campiglio and from there we take the bus to Passo Campo Carlo Magno.
Waters that flow on the surface and disappear, swallowed underground. We are witnessing Karst erosion, that gives rise to the formation of an underground fairy-tale environment, with rivers, tunnels, huge caves, and that strikingly shapes the earth's crust, like the area we observe at Passo del Grostè.
The phenomenon occurs when slightly acidic water, like rainwater enriched by small amounts of carbon dioxide (CO2), encounters rocks composed of calcium carbonate (CaCO3). The acid water dissolves the calcium carbonate, transforming it into soluble bicarbonate (Ca(HCO3)2). This reaction is reversible; in other words, calcium carbonate can form again from bicarbonate and give rise to stalactites and stalagmites.
The erosive surface forms of Karst most common here, those formed by the dissolution of calcium carbonate, are the furrowed fields, showing ruts a few meters deep at the most, almost parallel and sometimes separated by ridges that can be sharp and pointy.
A glance over the Adamello
Along the trail, the gaze turns inevitably to the West, towards the Adamello range, with its extensive glaciers. These are the largest in the province of Trento. The slender, isolated pyramid is that of Carè Alto (3,462 m). At the base of its northern side is the Lares Glacier. With an area of 500 hectares, it is the third vastest glacier of the Adamello range. In the loamy soil of this stretch of trail we can observe small silvery minerals, similar to minuscule specks. These are the micas, minerals found in the rocks of the Adamello range and carried here by the wind during past interglacial periods.
Castelletto di Mezzo, a natural freezer
Looking to the left you can see the pinnacle of Castelletto di Mezzo. On its wall, at about 2,450 m above sea level, lies the entrance to a cave discovered in 1964. At the end of the cave, a little over 1000 metres in length and dropping by 50 metres, lies a wide hall, known as "il Duomo" or "the Cathedral", which hosts a spectacular wall of layered ice almost 25 metres high. Recent studies have helped explain this singular presence. The ice began to form in the first half of the 1500s, at the beginning of the Little Ice Age, the cold period that affected the Alps until about the mid-19th century. Due to the low temperatures inside the cave, the circulating water freezed, resulting in the gradual growth of the ice wall, which continued to grow until the end of the 1980s.
Since then there has been a progressive and inexorable decline of its volume that, given the current climate trend, will lead to its complete disappearance within a few decades.
The Upper Vallesinella is the water catchment basin, or hydro-geological basin, which channels water into the springs of Vallesinella located a few hundred metres further down. It is a Karst area of approximately 12 km2 bordered to the East by Passo del Grostè and Cima Brenta, to the North by Altopiano dello Spinale and to the South by Cima Freddolin. The rainwater or the water from the melted snow flows only for short distances on the surface. It rapidly infiltrates the subsoil, captured by the dense network of cracks that pervades for hundreds of metres the deep layers of the Main Dolomite, a carbonate sedimentary rock that formed about 220 million years ago. This underground reticle originated from numerous rock fractures. The gradual dissolution of the rock caused by the flowing water continuously expands the network of cracks, forming a veritable natural reservoir where huge volumes of water accumulate and transit.
The water, after it has seeped into the rock at higher elevations and has flowed underground, can escape from a crack in the rock, forming a Karst spring.
This is the case of the Cascate Alte (high falls) of Vallesinella, nourished by a group of Karst springs between 1550-1615 m high, which form the Sarca di Vallesinella. The water, which runs in the heart of the Altipiano dello Spinale, flows down from the horizontal fissures separating the layers of the Main Dolomite.
Throughout the year, the waterfalls morph their appearance, as the Karst springs are typically seasonal. When the temperature cools in spring or during heavy rainfall, all the springs are active and full of water; in winter or drought, they can even disappear. Only the lower springs are perennial, while the ones higher up flow progressively, acting much as relief valves when there is particular abundance of water. Daily changes in the water flow, instead, are linked to the melting of snow and ice that is minimal at sunrise and at its highest in the late afternoon.