Drumlins are landforms essential to understanding of ice sheet movement over soft beds, sediment transport along the ice/bed interface, and the formation of a wide range of glacial deposits. Although investigated more than any other glacial landform, the origin of drumlins remains contentious. Using high‐resolution LiDAR imagery and field data, we investigate the geomorphology and internal composition of one of the biggest drumlin fields in the North European Lowland. The Stargard drumlin field consists of over 1300 drumlins and related streamlined subglacial bedforms in a terminal part of a major Weichselian palaeo‐ice stream of the southern Scandinavian Ice Sheet. The drumlins are typically 600‐800 m long, 200‐250 m wide, 3‐6 m high and have axial elongation ratios ~2 but in some cases exceeding 15. Several subzones inferred from drumlin morphometry exist reflecting different ice flow dynamics. The most elongated drumlins occur in areas where ice moved down‐slope and where thick fine‐grained deposits of low hydraulic conductivity occur in the substratum. The largest portion of land occupied by drumlins and the greatest frequency density of drumlins occur where the ice moved up‐slope. Stargard drumlins are composed of a wide variety of glacial deposits including various types of tills and meltwater sediments, which range from undisturbed to heavily deformed. There is no correlation between the deposits in the drumlins and the drumlin forms indicating that the deposits pre‐date the drumlinizing process. It is suggested that the drumlin field was generated by a combination of direct glacial erosion and subglacial meltwater erosion by removing antecedent material from the inter‐drumlin areas and streamlining the resultant bumps. Our data support the search for a unifying theory of drumlin formation and suggest erosion as the most plausible single mechanism generating drumlin landscapes. © 2019 John Wiley & Sons, Ltd.

Numerical experiments suggest that the last glaciation severely affected the upper lithosphere groundwater system in NW Poland: primarily its flow pattern, velocities and fluxes. We have simulated subglacial groundwater flow in two and three spatial dimensions using finite difference codes for steady-state and transient conditions. The results show how profoundly the ice sheet modifies groundwater pressure heads beneath and some distance beyond the ice margin. All model runs show water discharge at the ice forefield driven by ice-sheet-thickness-modulated, down-ice-decreasing hydraulic heads. In relation to nonglacial times, the transient 3D model shows significant changes in the groundwater flow directions in a regionally extensive aquifer ca. 90 m below the ice-bed interface and up to 40 km in front of the glacier. Comparison with empirical data suggests that, depending on the model run, only between 5 and 24% of the meltwater formed at the ice sole drained through the bed as groundwater. This is consistent with field observations documenting abundant occurrence of tunnel valleys, indicating that the remaining portion of basal meltwater was evacuated through a channelized subglacial drainage system. Groundwater flow simulation suggests that in areas of very low hydraulic conductivity and adverse subglacial slopes water ponding at the ice sole was likely. In these areas the relief shows distinct palaeo-ice lobes, indicating fast ice flow, possibly triggered by the undrained water at the ice-bed interface. Owing to the abundance of low-permeability strata in the bed, the simulated groundwater flow depth is less than ca. 200 m.

Subglacial groundwater flow was an integral part of glaciological systems of past ice sheets, but its impact on the origin of active-ice landforms remains unexplored. Using numerical experiments, we attempt to constrain groundwater flow dynamics under a major paleo-ice stream of the southern Scandinavian Ice Sheet and its impact on the formation of the Stargard drumlin field. Flow models show a total reorganization of groundwater dynamics under the advancing ice stream to a depth of up to~200 m. A mosaic of intervening groundwater recharge and discharge areas originates, whereby the same areas may experience multiple shifts in flow directions. A prominent time-and space-transgressive pressure pump recharges groundwater in a subglacial zone up to about 20 km within the ice margin and discharges it in front of the ice sheet. The simulated groundwater flow pattern suggests that drumlins occupying a portion of the ice stream area occur preferentially where groundwater upwells and discharges at the ice/bed interface. Consistent with the geological composition, a possible drumlin-forming mechanism involves an excess of pressurized water under the ice reducing the strength of the subglacial deposits and facilitating glacial erosion, erosion by turbulent meltwater flows or both, streamlining antecedent deposits into drumlin shapes. This study emphasizes the importance of causal feedback between subglacial groundwater flow and the ice sheet dynamics and suggests an impact of the former on the formation of streamlined subglacial landforms in general.

Ground wa ter vul ner a bil ity based on four dif fer ent as sess ment meth ods and their quan ti ta tive com par i son in a typ i cal North Eu ro pean Low land river catch ment (the Pliszka River catch ment, west ern Po land) The as sess ment of ground wa ter vul ner a bil ity is a cru cial part of plan ning and wa ter man age ment be cause it can iden tify areas where aqui fers are more sus cep ti ble to con tam i na tion. De pend ing on the vul ner a bil ity as sess ment method, the re sults can dif fer sig nif i cantly. Con se quently, dif fer ent meth ods can pro vide am big u ous in for ma tion that could fur ther in flu ence de cision-mak ing pro cesses in plan ning or wa ter man age ment. For the Pliszka River catch ment, the in trin sic ground wa ter vul nera bil ity of the up per most aqui fer was es ti mated us ing four dif fer ent meth ods: DRASTIC, GOD, and two meth ods that are based on em pir i cal for mu las of wa ter res i dence time in an un sat u rated zone. The in put data in clude a se ries of the matic maps sup ple mented by 1,322 shal low bore hole pro files and lab o ra tory tests of sam ples col lected in the course of field work. The col lected data were pro cessed in GIS soft ware, and the re sults of each method were mapped in high res o lu tion. The result ing maps of ground wa ter vul ner a bil ity were then quan ti ta tively com pared to val i date their ap pli ca bil ity for the as sess ment of ground wa ter vul ner a bil ity in a typ i cal North Eu ro pean Low land river catch ment. The maps gen er ated by the DRASTIC and GOD meth ods are dom i nated by ar eas with mod er ately high (54.6 and 48.4%, re spec tively) and mod er ate ground wa ter vulner a bil ity (32.7 and 32.3%, re spec tively). No ar eas of high ground wa ter vul ner a bil ity are pres ent. One of the wa ter res i dence time meth ods pro vides re sults sim i lar to the pre vi ous meth ods at the catch ment scale, and one method yields high groundwa ter vul ner a bil ity val ues for the ma jor ity of area.