Processes Of Periglacial Landforms In Changbai Mountains As Well As The Relationship With Environmental Evolution

Periglacial landforms are effective means in the former climate reconstruction.More than 60 periglacial landforms have been sucseesfully researched.Periglacial landforms and activity are well developed, especially in the mid-latitude Alpes in China.Changbai Mountains are two large periglacial zones in northeastern China, which belongs to the mid-latitude vertical periglacial zones.The main formation force of periglacial landforms are frost weathering and nivation.Changbai Mountains developed over 10 kinds of periglacial geomorphology types. Modern periglacil zone is distributed above 1700 m. Modern periglacial zone should be divided into three vertical periglacial zone according to the distribution features: 1700 ~ 2100 m is the frost heaving and frost sorting zone; 2100 ~ 2400 m is weathering and gelifluction zone; 2400 m to the Peak is weathering and nivation zone. Compared with other high Asia periglacial vertical zones, we found that the summit of Changbai Mountains is lower than the altitude of modern snow line. However, abundant precipitation and low temperature induce the extensive nivation action compared with the other mountain regions, so this thesis renamed it as a cold-wet periglacial zone with moderately periglacial process.Both the recent periglacial processes and the late period of late Pleistocene periglacial processes are discussed herein. The lower limit of present periglacial process lies at 1700 m, and the present theoretical equilibrium line altitude (ELAt) in Changbai Mountains is 3380±100m. The difference between the present theoretical equilibrium line altitude and the present periglacial processes line altitude is 1680±100m. Periglacial processes line altitude during the late period of late Pleistocene is 400m according the difference, pollen and 14C dating, which equals to the precent alpine tundra zone. At that time, the climate is drier than precent, so the difference between the lower limit of periglacial process altitude and ancient snow line altitude is 1900 m. Reconstruction of former climate is based on the discussion about the palaeotempreture significance of periglacial features. However, the relationship between ancient periglacial phenomenon and ancient temperature are still under discussion. Based on the research results from home and abroad, together with field observation, analysis of temperature and precipitation data in Changbai Mountains, this paper discusses the characteristics of distribution and the main causes of the various periglacial landforms. Moreover, the author studies the causes of the talus and the movement mechanism, and formative conditions of block stream. We found that two block fields lies in different altitude.They could have been developed during two cold stages of late Pleistocene according to the glacial sequences in Changbai Mountains and evidence of climate change in the late period of late Pleistocene. They were formed during 22～18ka. and 11.3～10 ka.