Abstract
In Central Europe, the Late Glacial period (⁓14700-11650 cal. BP) was characterized by dynamic environmental changes. 12,900 years ago, the cataclysmic Laacher See volcanic event (VEI = 6; 6.3 km3 of magma) occurred in western Germany 40 km south of Bonn.
The eruption devastated the surrounding late Allerod landscape and caused substantial lahar-like flood waves in the Lower Rhine and English Channel area. The interaction of magma with groundwater resulted in a highly explosive phreatomagmatic discharge, exceptionally long-distance transport of volcanic shards, and a climate deterioration.
The Laacher See Tephra (LST) is found over much of western Central Europe and forms the most important stratigraphic marker in Late-glacial deposits. We assume that, contrary to many published works, the LST ash cloud traveled also directly east from the volcano.
Therefore, we have studied lake sediment cores from three sites located in the Bohemian Forest Mts., Czech Republic-Germany-Austria border area (distance of 450 - 470 km from the volcanic crater). The characteristic LST particles were documented in all the cores using X-Ray Fluorescence scanning, magnetic susceptibility measurements, and direct observation by scanning electron microscopy.
Subsequently, we used the TESCAN Integrated Mineral Analyzer (TIMA) for automated volcanic shard counting and precise identification of the cryptotephra depth range. Our geochemical results show the closest match with MLST-B phreatomagmatic phase of the eruption.
Moreover, a significant amount of LST related phosphorus, often the limiting nutrient in both terrestrial and freshwater ecosystems, was found in the sediments. In this regard, we also assessed the potential effect of the tephra deposition on the vegetation cover and lake communities using pollen, charcoal, diatom, cladoceran, and chironomid analyses.
Our first results suggest no significant impact on composition of terrestrial vegetation contrasting with a distinct change in diatom, cladoceran, and chironomid assemblages. The discovery of the LST in the Bohemian Forest opens the potential of tephrochronologically supported research of Late-glacial sites in eastern Central Europe.
The study is supported by the Czech Grant Foundation (17-05935S - LAYERS).