Geological itinerary in Vallter

On Saturday August 31, a geological itinerary in Vallter took place, organized by the Ter-Freser Natural Park, with the cooperation of the CST. The guide was Miquel Casas, a geologist and shepherd, who is currently working on the inventory of the park's geological heritage.

The outing began at 9:45 a.m. from the upper parking lot of Vallter 2000. The route consisted of ascending the Morens valley until reaching the Old Refuge and descending on the other side of Puig dels Lladres, passing by the Ulldeter refuge.

Along the route, there were various stops at strategic locations to observe the landscape and rocks. These stops were accompanied by explanations, mostly focused on the glacial geological activity in the area. Participants were able to familiarize themselves with some typical terms of glacial geology, as well as the names of some of the most characteristic rocks in this area, such as schists and banded gneiss.

Undoubtedly, the main protagonists of the route were the ice and glaciers. The Ulldeter and Morens valleys, separated by Puig dels Lladres, were sculpted by the passage of a glacier present during the glacial maximum, about 60,000 years ago (BP, Before Present). In some areas, this glacier reached a height of 250 meters. Today, although there is no longer glacial activity in the area, remnants of the ice’s passage remain in the landscape, and some were identified during the route, such as:

• Rock deposits typical of rock glaciers that formed about 11,000 years BP and traveled shorter distances than the dominant glaciers during the glacial maximum.

• Obstruction deposits, represented by rock deposits that formed after falling from mountain slopes and were halted by the passage of the glacier in the main valley.

• Till deposits, consisting of a mixture of particles of different sizes dragged and deposited directly by the action of the glacier. The ice, thanks to its slow but continuous movement, also transports large blocks.

• The U-shaped valley typical of a glacial valley, as opposed to V-shaped river valleys.

• Moraine deposits, rock deposits at the glacier's front, lateral, or bottom areas, characterized by their lobe or crest-like arrangement. These deposits also indicate the glacier's maximum extent before it receded.

• Roche moutonnée (or sheepback), rocks scraped on the surface and showing cracks due to the passage of ice over them.

During the route, typical features of periglacial (or quasi-glacial) conditions were also observed. These conditions occur when frozen water is present in the ground for most of the year, leaving characteristic surface morphologies, such as crescent shapes in vegetation and terraced structures. Currently, these conditions still exist at the peaks in the area.

However, today, the water shaping the Ter valley landscape is mostly in liquid form, flowing through small streams that eventually form the Ter River. These streams are fed by precipitation falling on the mountain peaks, which then percolates and moves between rocks, through fractures and lithological differences.

During the route, scree slopes and alluvial cones (sets of rocks descending the mountain slopes and forming a fan shape) were also observed. Other curiosities were also shared, such as how rocks heat or cool only at a very superficial level due to the static nature of their atoms; that the “spine” of one of the peaks in the area is formed by a quartz vein; that there is a fault line passing through the Coll de la Marrana; that the old Ulldeter refuge was once a modernist building, but due to the harsh weather, now only ruins and an information panel remain.

Today, ascending through the Morens valley means being unable to avoid the ski slopes, an anthropogenic element that, during their construction and due to a lack of awareness of the geological heritage, damaged some of the most characteristic features of the glaciers' passage through this area.

During the route, guide Miquel Casas skillfully wove together geological history, which often seems so distant, with a current reality that urgently calls for changes and the recognition of the substrate that supports us and makes life possible. It is important to continue inventorying geological points of interest to know what to preserve, how to manage it, and how to reinterpret it for future generations."