Late Weichselian glacier outburst floods in North-Eastern Poland: Landform evidence and palaeohydraulic significance

Geomorphological evidence of catastrophic glacial floods has been discovered in many formerly glaciated areas of North America, in the mountains of Siberia and Central Asia, and in northern Europe. Within the area of the last Scandinavian Ice Sheet in the European Lowland a wide range of landforms related to glacial meltwater flows have been documented but no unequivocal evidence of cataclysmic glacial outburst floods exist. Here we discuss a landform signature of Late Weichselian glacial megafloods in the Suwałki Lakeland, north-eastern Poland. These landforms are oversized ice-marginal spillways, scabland-like features, expansion bars, megadunes, obstacle marks, and clusters of kettle holes. This unique glacial landscape was probably generated by at least two separate glacial megafloods (the older event ca 19 ka ago and the younger event shortly after ca 16 ka ago). Palaeohydraulic calculations based on the morphometric characteristics of the flood landforms suggest that one of those megafloods had water depth of at least 19 m and flow velocity of around 15–17 ms−1. The flood flow regime was from subcritical to supercritical. The calculated maximum flood discharge range was between 0.5 × 106 and 2.2 × 106 m3s−1 with the most likely value of around 2 × 106 m3s−1. These numbers place this megaflood among the largest glacial megafloods worldwide, with a possible impact on global climate through rapid release of large volumes of freshwater into the Atlantic Ocean following a transfer across the European Lowland through prominent ice-marginal meltwater spillways.