DEM identification of macroscale stepped relief in arctic northern Sweden

Stepped relief is a characteristic feature of many upland areas on Earth. In this study, we examine if stepped relief can be identified objectively by GIS-analysis of digital elevation models (DEMs). We specifically study the stepped relief landscapes of northern Sweden, comprising areas of contrasting topography in the mountainous northern Scandes and on the inselberg plains of the Precambrian basement east of the Caledonides. We mainly use hypsographic curves to examine the elevation distribution of the study areas and to identify palaeosurfaces. Peaks in the hypsographic curves are interpreted as palaeosurfaces, while hypsographic minima are interpreted as breaks in slope, separating these surfaces. In the northern Scandes, where only patchy remnants of palaeosurfaces remain, we use empirical cutoff values of slope angles to restrict palaeosurface areas to those identified in the field and in air photos. In addition, air photo and field mapping of glacially eroded areas is necessary to exclude glacially formed low relief surfaces, such as valley floors. These latter procedures introduce an unavoidable degree of subjectivity to the study. Our results indicate that in the northern Scandes, surfaces with an inclination of < 11°, after glacially formed features are abstracted, correspond well with palaeosurface remnants. Breaks in slope separating the surface generations in the mountains are centred around 860, 1320, and 1520 masl (above sea level), respectively. On the plains east of the northern Scandes, hypsographic data were filtered to remove inselbergs in order to analyse only the plains. Hypsographic curves of both the filtered and the unfiltered data of the inselberg plains show minima at elevations that correspond to steps separating multiple palaeosurfaces at elevations of 190, 250, and 400 masl. The steps separating the different palaeosurfaces are, in places, aligned with known geological discontinuities, but extensive remnants also transect structure. The presence of stepped relief is consistent with existing models of phased Cenozoic uplift and incision in northern Fennoscandia.

Research highlights
► We develop an objective system to identify stepped relief in digital elevation models.
► Glacially eroded areas have to be abstracted to achieve correct results.
► Comparison with geological structures is of immense importance.
► The mountains and the lowlands of northern Sweden include a stepped preglacial relief with multiple palaeosurfaces, confirming earlier studies.
► Palaeosurfaces in both the mountains and the lowlands are often developed across units of diverse bedrock geology and appear to be true erosion surfaces.