High alpine preglacial caves modified by glacial processes and late condensation-corrosion in the Scerscen Valley (Valmalenco, Western Alps, Italy)

The Scerscen Valley (western Italian Alps) is home to caves at an altitude of around 2600 m, opening close to the edge of a glacier. The aim of the research as part of a multi-disciplinary project was to reconstruct the evolution of the caves related to the geological and paleo-environmental evolution of the area and to evaluate the role of some of the most recent processes, such as condensation-corrosion and sediment deposition. We performed cosmonucleide burial dating, recorded morphology and micrometeorology, carried out mineralogical identification by XRD, and hydrogeology using dye tracing and physical and chemical analyses. The cosmonucleide dating of quartz pebbles showed that the Veronica Cave is the oldest, with deposits dated at 1.3 ± 0.4 Ma, and possibly even older. It certainly formed at a much lower altitude (approx. 1300 m a.s.l. or lower) during the Alpine uplift. The Morgana and Marsooi caves, given the smaller volume of their phreatic conduits (1/3 of Veronica), are possibly more recent, formed during interglacials and evolved close to a glacial body. The caves initiated in dolomitic marble under the influence of sulfuric acid speleogenesis (SAS) due to pyrite oxidation. The conduits were then enlarged dramatically under phreatic conditions. The caves have evolved since their preglacial formation, with phases of filling by fluvio-glacial sediments and unclogging. Water tracing and physico-chemical analysis attest to a well-karstified aquifer, with rapid water circulation (>20 m/h) and low temperatures (~2 °C), draining towards the main spring, “La Prediletta”, located at the foot of the dolomitic marbles. Microclimatic records (cave temperature and humidity) show seasonal cycles of condensation and evaporation, influenced by air exchanges with the outside atmosphere. These processes contributed to the formation of secondary minerals by evaporation (gypsum, hydromagnesite…) and, above all, to the significant enlargement of passages by the retreat of walls with characteristic morphologies (facets and grooved walls). The Scerscen caves bear witness to a long geological and climatic history, from their formation before the Mid-Pleistocene ice ages to their present-day evolution. They offer valuable insights into karst processes in the high mountains, and interactions between glaciers and aquifers. • Well-developed caves were discovered close to the retreating Scerscen glacier • These caves formed at the glacier edge and interacted with meltwaters • The largest cave (Veronica) contains fluvial pebbles washed in at least 1.3 ± 0.4 Ma ago • All caves show clear signs of late stage condensation-corrosion • The caves are part of a small stripe karst mountain aquifer