Fluctuation of Glaciers During Neoglaciation in Bogda and the Urumqi River Head, Tian Shan
Zheng Benxing and Zhang Zhenshuan (Lanzhou Institute of Glaciology and Cryopedology, Academia Sinica)
It was found from our field work of 1981 in Bogda area that the moraines of Neoglaciation in Holocene are of small scale, 1-5 km away from the existing glacial termini. These moraines occupy only a little more than a half of the lower U-shaped valley and their tills have been weakly weath- ered with no caliche on their surfaces, obviously different from the tills with caliche formed under the dry and hot climate during the climatic optimum in Holocene. The C14 age of the caliche at the head of Urumqi river is 5500±220 B.P. and 3949±141 B.P.. Therefore, the earliest glacial advance of Neoglaciation may be considered as 3000 years ago corresponding to the age 2980 ±150 ago of the first glacial advance in the Neoglaciation of Qinhai-Xizang Pltaeau.The end moraines of the three stages of glacial advance in Neoglaciation are very distinct in this region, for example, the end moraine at the altitudes of 3200 m, 3500 m and 3600 m in front of the Glacier No.5 in the Sigong river head on the northern slope of Mt. Bogda; the series of end moraine at the altitutes of 3320 m, 3420 m and 3540 m in front of the Glacier No. 10 at the Cuban Bogda river head on the southern slope of Mt. Bogda; and the end moraine at the altitudes of 3560 m, 3600 m and 3640 m in front of Glacier No.l, as well as at the altitudes of 3580 m,3640 m and 3720 m in front of Glacier No.6 at the Urumqi river head.The three stages of Neoglaciation reflect the strong climatic fluctuation in a period of every 1000 years, that is, at about 3000 years ago, 2000 years ago and 300 years ago. The end moraine of the Little Ice Age from 300 years ago up to now can be divided into 4 rows reflecting a period of variation at every 100 years, formed in 17th, the middle of 19th century, the beginning of 20th century to the 1930s, and the 1960s respectively. The eight rows of end moraine in front of glacial tongue moraine lakes at No.10 Glacier of the Guban Bogda river, probably reflect a periodic climatic variation of about every 30 years.