Glacial cirque morphometry of Rila and Pirin Mountains (Bulgaria)

Cirque valleys are typical landforms of formerly glaciated high mountains, which also play an important role in paleoclimate reconstruction. In Bulgaria, the Rila (highest peak, Musala 2925 m) and Pirin (highest peak, Vihren 2915 m) mountains were the only terrains, where significant glacial cover developed during the Pleistocene glaciations, although some minor glacial landforms also exist elsewhere in Bulgaria. During the glacial periods, valleys of the Rila and Pirin Mts were re-shaped by glacial erosion and currently are characterized by glacial cirques and U-shaped valleys reaching lengths of 22 km (in Rila) and 13.5 km (in Pirin).

In these two mountain ranges, a comprehensive, quantitative geomorphometric analysis of glacial cirques valleys has not yet been carried out, thus we try to fill this gap with the present work. Primarily, digital terrain models and GIS tools were used to delineate the cirques. Based on the delineations, the main morphometric parameters of the cirques (elevation, relative depth, width, length, area, aspect, slope conditions, etc.) were calculated and a careful statistical analysis of these parameters was performed. Both the topographic orientation and the lithological structure of the two neighbouring mountains are different, that gives us an opportunity for a comparison of topo-climatic and lithological factors of cirque development. For instance, based on elevation, size and orientation of the cirques, the possible correlations with the paleoclimate factors, like exposure or moisture transport directions can be examined. Finally, our results were compared with available cirque valley morphometric data of other high mountains rising on the Balkan Peninsula.