Interactions between trunk and local glaciers in distal Alpine valleys (southeastern Alps, Italy)

During the Last Glacial Maximum (LGM), the European Alps were occupied by an extensive glacial network in which major trunk glaciers interacted with smaller tributary glaciers. In several areas, local glaciers flowed in directions opposite to those of trunk glaciers, particularly in distal sectors characterized by complex topography and high precipitation. Despite their likely widespread occurrence, the dynamics, the peculiar morphologies and specific related depositional facies of these glacier–glacier interactions remain poorly constrained.

In the southeastern Alps (Italy), the glacial system was dominated by the Adige trunk glacier. Regional-scale reconstructions have defined glacier geometry, flow paths, and Equilibrium-Line Altitudes across the Adige and Astico valleys, including an ELA of ~1580 m for the Fiorentini glacier (Monegato et al., 2024). However, these reconstructions primarily address trunk glacier behavior, leaving the interactions with local valley glaciers largely unexplored.

This study focuses on valleys where the Adige trunk glacier interacted with local glaciers descending from adjacent massifs, with the two ice bodies flowing in opposite directionsunder conditions of high orographic precipitation. The Terragnolo Valley represents a key example, where the presence of the distal Adige glacier, is documented by moraines at elevations of ~1400 m a.s.l., and were it interacted with local glaciers descending from the Monte Pasubio massif (~2200 m a.s.l.). Similar geomorphological configurations are found also in the Vallarsa and Ossaria valleys, enabling a comparative, valley-scale analysis within the same glacial system.

In the Terragnolo Valley, the interaction zone is marked by a thick glacigenic succession extending for ~10 km upstream, dominated by locally derived carbonate clasts, with only minor contributions from lithologies typical of the trunk glacier. This sedimentary pattern indicates a complex interaction between the two ice bodies and raises key questions regarding ice-flow coupling, relative timing of glacier advances, and the degree of dynamic independence of local glaciers during the maximum extent of the trunk glacier.

Overall, the studied valleys highlight how interactions between trunk and local glaciers in distal sectors can generate complex dynamics and sedimentary architectures, providing new constraints for reconstructing Alpine glacier dynamics and the distribution of glacigenic deposits in the tributary valleys.