Imprint of a dead-ice environment on lidar imagery—Spatial patterns at the last Scandinavian Ice Sheet margin (N Poland)

There is a unique glacial landscape system in the southern Żarnowiec Moraine Plateau of northern Poland. Here the terrain is characterized by a very high concentration of ridges that are often adjacent to pits, which together constitutes a special type of hummocky topography. The morphological diversity of the study-area ridges and pits was determined from high-resolution lidar imagery that was qualitatively and quantitatively processed, then analysed. Fourteen test fields of spatial dimensions 0.5 km × 0.5 km were selected within the moraine plateau for detailed studies. The results show that the ridges and pits constitute a very dense network of approximately circular, diverse-oriented forms of various sizes, most of which are linked to each other in a step-wise fashion. The pits are surrounded by ridges of various heights and widths that separate one pit from another. A characteristic feature of the studied pits is the orientation of their long axis. Form-based morphological analysis revealed that their genesis was associated with a glacial rather than a periglacial environment. It is believed that ridge orientation reflects a spatial pattern related to ice crevasses. A moraine plateau constituted a terrain obstacle that acted as a counterslope to the advancing ice sheet. The studied landforms and landscape resulted from the ice sheet's breaking up into dead-ice blocks of various sizes. The very dense system of perpendicular, parallel, and diagonal crevasses was related to ice sheet advance from a northerly direction, resulting in a flow around the obstacle and differences in ice-mass speed.