Rapid subglacial streamlined bedform formation at a calving bay margin

Using the LiDAR-derived Swedish national height model we have identified previously undescribed shallow streamlined glacial bedforms, small-scale drumlins, on the Närke plain in south-central Sweden. These drumlins could only be detected with high-resolution LiDAR, due to both their subtle size and forest cover. In this area the ice margin receded in a subaqueous environment with a proglacial water depth in the order of 100 m during the last deglaciation. As indicated by the configuration of marginally formed De Geer moraine ridges draping the drumlinoids, the receding ice margin formed deeply indented calving bays. These were located around subaqueous outlets of the subglacial melt-water drainage, with their apex position marked geomorphologically by beaded esker ridges. The mapped small-scale drumlins are aligned perpendicular to the reconstructed ice sheet margin and suggest formation along flow lines adjusted to the configuration of these calving embayments as they propagated up-flow with ice margin retreat. Based on these geometric relationships we argue that the emplacement of the drumlins was near-marginal, ∼7.7–1 km from the margin, on a short timescale (∼5–35 years).