Glacial Evolution And The Fluence To Entiroment In Changbai Mountains

With the methods that field investigation, sampling and sediment analyzing, dating, contrasting in the laboratory, the characteristics of glacial geomorphology, and the physical features, extent, ages and glacial evolution series were studied in details. Adopting the paleoequilibrium line being reconstructed as the main environmental index, the paper rebuilds the temperature and the precipitation conditions during the different glacial stages. The moraine characteristics mainly based on the moraine section (2000m a.s.l.) close to the Heifengkou。The glacial landforms and deposits such as cirques, trough valley, erratic boulders, polished surfaces and well preserved moraines in Changbai Shan indicate that the area was once glaciated. The typical glacial landforms and remains are distributed inside and outside the volcanic cone. Repeated glaciations of these areas can be divided into two stages: the last glacial maximum (LGM), and Late-glacial stage of the last glacial cycle. Optically stimulated luminescence (OSL) dating results derived from glacial and glacier-sediments and the K/Ar, TIMS, ESR and 14Cages associated with the volcanic rocks suggest that a glaciation about 11Ka, named the Meteorological Station glacier advance, which could be correlated to the Younger Dryas event, and the LGM glaciation, named the Black Wind Mouth glacier advance, took place about 20 Ka. Under the same monsoonal influence, the glacial records in Changbai Shan are the same as those of Taiwanese and Japanese islands during the late stage of the last glacial cycle. Because there are only two absolute OSL age controls in the glacial remains, the glacial advance stages, and the correlation of glacial sequence between Changbai Shan and other glaciated regions in and along the west Pacific Ocean are temporary. Further research is needed in this area, especially the age control and the discussion of climatic change. The temperature and the precipitation were not very clear between the early and the late stage during the last glaciation. Compared with modern temperature and precipitation conditions, the mean annul temperature declined 7°C and the annul precipitation decreased 450mm in the last glaciation.Results show that the cirques have the roughly equidistant features, and the ratios between length and width of cirques distribute about 0.6-1.47. Orientation change of high density cirque took place in Luoji Shan, Diancang Shan, and Gongwang Shan. Compared results indicate that the ratios of lithology type influenced the cirque development are 50% in sedimentary rock, 30% in volcanic rock, and 20% in metamorphic rock, and the cirque extent happened in the volcanic and metamorphic rock regions are relatively larger than that of sedimentary rock region. So many cirques occurred in sedimentary rock regions could be related to the structure. Statistical data suggests that the glacial cirques could develop in any direction. However, the preponderant orientation of cirques on north,northwest and northeast has achieved to 76%, which is similar to other modern glaciated mountains in west China. Different factors such as the tectonic, climatic, landform and the sloping direction control to the development of glacial cirques in the study areas.Based on the Ohmura`s formula in which the relationship between summer (JJA) atmospheric temperature (T) and the annual precipitation (P) at ELA, the present theoretical equilibrium line altitude (ELAt) in Changbsi Shan was 3380±100m. Six methods of AAR,MELM,THAR,TSAM,CF and Hofer were used for calculation of the former ELAs in different stages. These methods provided the ELA for an average value of 2320±20m during the LGM. The ELA was affected by neo-tectonic uplift factor. Adopted 1mm/a as the uplift value, this paper calculated the real snowline position during the LGM and late-glacial. The results show that the real snowline should be 2300±20m during the LGM, and 2454m during late-glacial. The△ELA values were more than 1000m (1080±100m) and about 920m (926±100m) lower than now during the LGM and Late Glacial stage respectively.