What causes aeolian sand dunes in Northern Fennoscandia to lose their crests? From mapping and dating to process understanding

The postglacial landscape of Northern Fennoscandia is characterised by abundant depositional landforms, including eskers and aeolian sand dunes. Stratigraphic markers in sand dunes, such as buried soils or charcoal bands, record past environmental and climatic changes, preserving a history of landscape instability and sand movement caused by climate, fire, and land use changes. Although the shape and orientation of the dunes reflect the dominant wind direction during their formation, the mapping of aeolian sand dunes in Fennoscandia remains limited to a few studies and is generally not conducted at the polygon level. To systematically analyse the location, shape, and orientation of dunes over large areas, scalable and reproducible semi-automated mapping approaches based on remote sensing data are needed, with results validated in the field.

While analysing and interpreting digital elevation models, derived hillshades, satellite imagery, and aerial photographs, we observed features we referred to as ‘double-dune ridges’; dunes appearing in direct proximity to each other that mimic each other’s shape and orientation. Ground-truthing fieldwork showed that the ridges are unlikely to represent two separate, quasi-parallel dunes but rather the remnants of single dunes where the crests have been eroded and excavated. In their present form, these mostly parabolic dunes can be described by stable, vegetation-covered windward (stoss) and leeward (lee) sides, with open to low pioneer vegetation covering areas where the former crest once existed.

We discuss this example of dune degradation in Northern Fennoscandia and illustrate how an interdisciplinary approach can provide valuable insights into the dynamics involved. We strongly believe that integrating detailed mapping with chronostratigraphic, tree ring, and remote sensing data is essential for understanding the processes leading to the excavation of the former crest of dunes and, more broadly, to landscape evolution and degradation.