Distribution, characteristics and formation of esker enlargements

Eskers are primarily ridges of glaciofluvial sediment deposited in subglacial, englacial and supraglacial conduits. They are typically straight to sinuous features, however, their planform morphology can be highly diverse. Esker enlargements are spatially confined ridge sections that are significantly wider than the trunk ridge (typically 250–400 m) and that reconverge downflow. The enlargements include complex ridge networks or coherent sediment bodies. We mapped >1400 esker enlargements across Fennoscandia and Keewatin, Canada, to investigate their distribution and morphological characteristics. Esker enlargements are less abundant below the marine limit, and tend to become more abundant in areas of faster ice retreat. They form local clusters along particular ridges, and can occasionally be traced laterally between adjacent esker systems. Based on morphological observations, we link their formation to roof collapses in subglacial conduits. The distribution of esker enlargements indicates that subglacial conduit collapse became an increasingly significant process during the final stages of deglaciation of both the Scandinavian and Laurentide ice sheets, and may have exerted a positive feedback on ice sheet retreat at land-terminating ice margins.