Glacial Curvilineations of the Dobrzyń Lakeland—Spectacular Landscape Carved by Subglacial Meltwater Erosion

The Dobrzyń Lakeland (north-central Poland) is characterised by a remarkable subglacialSubglacial landscape generated by the last Scandinavian Ice SheetIce sheet. This landscape exhibits consistently arranged groups of ridges and intervening troughs in a network of anabranching tunnel valleysTunnel valley terminating at the former ice margin. These ridges have been earlier described and interpreted as drumlinsDrumlin, although their geomorphic characteristics are at odds with landforms typically considered as drumlinsDrumlin. Recent studies revealed that these ridges represent a new type of glacial landscape referred to as “glacial curvilineations” (GCLs)Curvilineations, glacial (GCL). GCLs occur in multiple and morphologically diverse swarms occupying tunnel valleys in the broad area referred to as the Zbójno GCL field. These swarms contain numerous elongated, winding and parallel ridges separated by troughs of exceptional regularity and high sinuosity. The GCLs are mostly composed of tills, interbedded with sand and gravel in places. The model of GCL formation invokes erosion by channelised meltwaterMeltwater flows beneath the ice sheetIce sheet. It is proposed that longitudinal vortices within subglacialSubglacial meltwater flows excavated troughs in the bed and left behind ridges as remnants of an older, antecedent landscape. The scale and coeval formation of the entire tunnel valleyTunnel valley network suggests that this unique subglacialSubglacial landscape results from a catastrophic drainage of meltwater stored in supraglacial or possibly subglacialSubglacial lakes.