Expanding the Tephrochronological Record in the Alps: Discovery of the Laacher See Tephra in Lake Plansee (Austria)

Abstract We present the first documented occurrence of the Laacher See tephra (LST) in the Eastern Alps, identified in lake Plansee, Austria. The LST is a key chronostratigraphic marker for correlating and dating Late Glacial sedimentary archives. This discovery was made by progressively narrowing down observational limits from rough estimates of potential cryptotephra presence and position to pinpointing the volcanic ash layer with great precision, using a rapid, non‐destructive scanning workflow that integrates core‐scanning techniques (CT, MS, XRF) with targeted high‐resolution methods (μ‐XRF, EPMA). This core‐scanning workflow bridges the gap between rapid scanning and detailed analysis of discrete sediment samples. Notably, the detection relies not only on glass shards but also on associated tephra mineral phases, demonstrating the method's effectiveness in chemically altered, glass‐poor sediments and more unconventional settings. The presence of LST in alkaline sediments of Plansee indicates a more extensive and spatially variable tephra dispersal than previously mapped, highlighting the need for a re‐evaluation of established fallout models for the 13 cal ka BP eruption. This finding emphasizes the potential of sediment archives in more challenging sedimentary records (e.g., alpine lakes, paleo‐lakes, alkaline lake sediments) to host cryptotephra layers and underscores the value of incorporating mineral‐based detection strategies into tephrochronological workflows. By refining regional chronologies and expanding the spatial scope of eruption impact assessments, this work contributes to a deeper understanding of Late Glacial environmental changes within a precise temporal framework and paves the way for advancements in future volcanic risk assessments.