Glaciation in the Rila mountains (Bulgaria) during the Last Glacial Maximum

摘要

Relict glacial landform complexes have been studied in the mountains of the central Balkan Peninsula since the end of the 19th century. Since their existence was proved for the first time by Cvijic, various authors have debated the number of glacial phases, as well as their age. At present, the problem of age determination is being solved by the application of the new methods for numerical dating. This paper is a detailed study of the maximum glaciation in the Rila massif, which is the highest mountain in Bulgaria and in the whole Balkan Peninsula. The application of cosmogenic nuclide dating (~(10)Be) on moraine samples confirmed that the largest extent of former glaciers that left moraine deposits was around the time of the Last Glacial Maximum. Most probably the maximum extent occurred in two phases, the first around the beginning, and the second around the end of the LGM (24-23 ka BP and 18-16 ka BP respectively), separated by a retreat phase during the coldest (but also driest) phase of the glacial stage. The GIS-processed calculations on the basis of field evidence of the former glacier extent, and the preliminary calculations of the Equilibrium line altitude (ELA) through the accumulation-ablation ratio (AAR) method, show that the ELA during the LGM had quite small differences throughout the Rila massif (from about 2150 to 2200 m a. s. 1. in the NW to about 2250-2290 m in the SE), despite the considerable differences in terminal moraine depositional altitudes (from 1150 to 2000 m a. s. 1.). This is due to both the complicated pattern in the directions of moisture supply and to the influences of local topography.