Thufur morphology within the Ponor depression (Stara Planina, Serbia)

Thufur (earth hummocks) are small periglacial landforms typical for subpolar latitudes, as well as for the high alpine areas at lower latitudes. Their presence in the mountains of the Balkan Peninsula was spotted during the mid-20th century. In this paper we analyze morphometry and morphology of thufur in the context of physio-geographical conditions for their formation. The main aims are to inventorize the thufur in the study area and to determine the physio-geographical factors which enabled their formation at non-zonal elevations. Statistical analysis was performed on the sample of 305 thufur mapped in the field, measuring their circumference, height, and delineating their areas. Classification of the results revealed morphological varieties in terms of horizontal and vertical development. The elevation of the sampling location Ponor is 1,410 m a.s.l., which is considerably lower than the zonal periglaciation in Serbia, at approx. 1,900 m. Therefore, the role of relief as a climate modifier is analyzed in the context of conditions for the azonal development of periglaciation process. Topographical conditions for thufur formation were analyzed through slope inclinations and vertical dissection, determined using the Digital Elevation Model over Europe with 25 m resolution.