Equilibrium-line altitudes of Late Quaternary glaciers in the Oshtorankuh Mountain, Iran

Valleys in the north flank of Oshtorankuh (central Zagros Mountain Range, IRAN) are presently ice-free except few relict firn basins but they were glaciated during the Late Quaternary. The equilibrium-line altitudes (ELA's) of former glaciers were reconstructed based on the glacio-geomorphological analysis of former glaciations traces. In addition to the field investigations, combined use of 10 m DEM data, satellite image interpretations and 1:25 000 topographic maps were applied to reconstruct the former ELAs. The amount of ELAs during the former glaciations was evaluated based on the position of end moraines. The ELA reconstructions indicated that ELAs were about 3121 m asl during the maximum glacier extension. Based on the calculated value of the modern ELA (4500 m a.s.l.), ELA in the Oshtorankuh area was depressed in the Pleistocene approximately 1380 m to an elevation of 3121 m, and the glaciers extended down at least as low as 2400 m a.s.l. By comparison of the calculated ELA depressions and the amount of the ELA depression around the world, the maximum glacier extension in Oshtorankuh was correlated with the LGM (Last Glacial Maximum). In the study area, perfect recessional moraines are observed at elevations about 2650–3700 m a.s.l which can be formed in the younger glaciation phases. The ELA and ELA depression related to youngest moraines in the study area were about 3848 m a.s.l. and 650 m, respectively. The calculated ELA depression with considering the leeward accumulation of wind-blown snow for Neo-glaciation, is more comparable to the latest phases of Late Glaciations or first phases of Neo-glaciations.The study showed that the depression of the annual temperature during the LGM glaciations was about 9.8 °C and it was about 4.6 °C probably during the youngest glaciation stage.