Deciphering Alpine hazard frequencies by amphibious investigations of Holocene lake inventories

• Applicants: Professor Dr. Michael Krautblatter; Privatdozent Dr. Christoph Mayr
• Subject Area: Geology ; Mineralogy, Petrology and Geochemistry
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 558963977

The recent increase of Alpine hazard frequencies and magnitudes is postulated in publications and numerical models predict that these events will occur more frequently and more strongly in the future. However, the likely non-linear increase in Alpine hazard frequencies in recent times is poorly substantiated due to missing or ambiguous long-term records. Thus, ALPHA aims at providing a sound basis for anticipating Alpine hazard frequencies in the foreseeable future under various scenarios of climate change. For existing Alpine lake sediment records, event layers were rarely systematically analyzed, relevant sediment-producing terrestrial Alpine hazard processes were not distinguished, and the magnitudes of these hazards were not derived. In this proposal, we therefore aim to (i) systematically distinguish underlying event processes recorded in lake sediment layers, (ii) estimate the corresponding range of terrestrial process magnitudes, and (iii) decipher the frequency and magnitude increase of phases with elevated climatic forcing such as longer and more intense rainstorms. We hypothesize that Alpine hazard fluctuations in the Holocene Climatic Optimum and the Medieval Warm Period provide the closest analogy for future climate change scenarios. Their understanding enables us to anticipate the likely non-linear and non-stationary increases in Alpine hazard frequencies and magnitudes in the immediate future. In ALPHA, we investigate the lakes Plansee and Achensee (supersites; for long-term event chronologies) as well as Walchensee and Eibsee (complementary sites; for understanding extreme events) in the Bavarian-Tyrolian Landslide Cluster, a globally known hotspot of Late Holocene Alpine hazard events. They were selected due to the quantity of important data gained from systematic pre-studies, including geomorphological mapping, terrestrial and lacustrine geophysics, LiDAR (Light Detection and Ranging) and photogrammetric surface change detection, bathymetric mapping, and sedimentological and geochemical analysis of sediment cores. For the first time, we (i) apply a 4D approach on subaquatic sediment transport by repeated geophysic surveys, repeated coring and calibration using sediment traps, (ii) relate erosion processes, transport and subaquatic deposition in mass and momentum balances, and (iii) link sediment volume in the lacustrine sink with measured terrestrial upstream erosion and mass movement rates calibrated on annual, decadal, and millennial time scales. ALPHA aims at advancing process-understanding of (i) the natural drivers, (ii) sediment sources, (iii) transport mechanisms, and (iv) deposition patterns under fluctuating environmental controls. Future projections of intensity, frequency and seasonality of natural hazards will be developed based on regional climate models with rainfall intensities evaluating the nonstationary response of Alpine hazard frequency rates to global warming.

• DFG Programme: Research Grants
• International Connection: Austria, Switzerland
• Partner Organisation: Fonds zur Förderung der wissenschaftlichen Forschung (FWF)
• Cooperation Partners: Professor Dr. Flavio Anselmetti; Privatdozent Dr. Bernhard Gems; Professor Dr. Jasper Moernaut; Professor Dr. Michael Strasser
• Co-Investigator: Professor Shiva P. Pudasaini, Ph.D.