Great glacial giants: erratic boulders of northern Poland as witnesses of the Pleistocene ice age and beyond

Erratic boulders are among the most spectacular geological phenomena left in the landscape by past ice sheets. In Central Europe, the Fennoscandian Ice Sheet (FIS) advanced and retreated several times during the Pleistocene, depositing thick layers of clastic sediments and fragments of Scandinavian bedrock of various sizes, including large erratics. Northern Poland, in particular, features a landscape rich in erratic boulders deposited by the last FIS around 24–15 ka. These large erratics are fascinating geological objects, providing valuable information about the flow directions of the last FIS (through petrographic properties) and the timing of the ice sheet's retreat (via cosmogenic nuclide inventories). They also hold significant societal importance, serving as natural resources, providing notable landmarks, and serving as a fantastic source for geomythology.

In this study, we present the occurrence and characteristics of erratic boulders within the area covered by the last and penultimate glaciations in northern Poland. Large erratics were identified using books, maps, and catalogues dedicated to environmentally protected sites (e.g., lists of natural monuments). We compiled all available information about large erratics into a GIS database and screened it to identify the largest in situ boulders potentially suitable for surface exposure dating with cosmogenic ¹⁰Be. In subsequent phases of our study, these boulders were used as key dating sites for reconstructing the chronology of the last FIS retreat in northern Poland. Additionally, some of these boulders hold significant cultural importance for local communities, paving the way to legends and myths, serving as esoteric places, or becoming locations commemorating important historical events.

This work was supported by the National Science Centre, Poland (grants No. 2023/49/N/HS3/02181 and 2022/46/E/ST10/00074).