Concept and global context of the glacial landforms from deglaciation

The period between 18.9 and 14.6 ka was characterised by a nonstationary climate and centennial-scale variability that represented the start of deglaciation following the Last Glacial Maximum. During this period both the European Ice Sheet Complex (EISC) and the mountain valley glaciers retreated and then stopped and readvanced, although with remarkable asynchronies according to latitude and position against the oceanic influences. Nevertheless, the ultimate cause of deglaciation remains obscure, with a relevant role of the oceanic circulation, and the increase of insolation and atmospheric CO2. At present, the most common name to identify this period is Heinrich Stadial 1, which covered most of the 18.9–14.6 ka period, during which deposition of Ice Rafted Debris transported by a high discharge of icebergs occurred. This resulted in the arrival of large volumes of freshwater that weakened and even interrupted the Atlantic Meridional Overturning Circulation, thereby reinforcing cooling in a scenario of very low temperature and precipitation. The collapse of the EISC was likely due to isostatic dynamics (altitudinal descent of the areas with snow accumulation) and to the influence of the ocean in the melting of the marine-based ice fronts, in a context of negative snow balance. Morphologically relevant moraines were deposited during short readvances or standstills of the EISC in Central Europe and mountain ranges, in part coinciding with the Heinrich Event 1, and many rock glaciers developed as the walls of the valleys and cirques were free of ice in the European mountains.