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Shri Ashtapad Maha Tirth - II
glacial lake outburst flood event in 1940 was found in 1974. The dates of known maximumdiameter lichens growing in other moraines can be estimated by linear extrapolation using the average growth rate (0.06 cm/a) of R. geographicum during 1940-1974. The uncalibrat-ed radiocarbon ages of buried wood were converted to calendar years using the OxCal program v3.10 (Bronk Ramsey, 1995, 2001) from IntCal04 data in Reimer et al. (2004). Radiocarbon dates are presented as 28 calibrated range which means a dating certainty of 95% that the real date falls within the given date range. 2.1 Eastern Tanggula Mountains The eastern Tanggula Mountains lie in the transition zone from monsoonal temperate to continental glaciers. Li et al. (1986) noted that the mean annual temperature at the equilibrium line (at 5200 m asl) in the Bujiagangri region is -6 °C to -7 °C. Only LIA glacier fluctuations of Poge Glacier (No. 1, Fig. 1) were studied. According to four lichen dates on moraines this glacier advanced about 1809, 1857-1888, and 1920 AD respectively (Li et al., 1986). The maximum glacier extension during the LIA occurred before 1809. 2.2 Eastern Nyainqentanglha Range The eastern Nyainqentanglha Range is situated on the southeastern part of the Tibetan Plateau. Many large monsoonal temperate glaciers are developed in this region because it is situated just north of the "Great Bend” of the Yarlung Tsangpo River. The humid monsoon air mass, which penetrates through the "Great Bend", brings abundant moisture to the region. Li et al. (1986) noted that the mean annual and summer (June-August) temperatures at the equilibrium line (at 4500 m asl) on the Arza Glacier are -2.6 °C and 5 °C, respectively, with an annual precipitation of 3000 mm. These climatic conditions make the glaciers very active. Trees are often trapped and buried by advancing glaciers, providing opportunities for radiocarbon dating. Glacier expansion in the Eastern Nyainqentanglha Range during the last two millennia has been recognized at Arza, Laigu, Zepu and Ruoguo Glaciers. Li et al. (1986) carried out a detailed study on Ruoguo Glacier (2; Fig. 1), which is a 13.4-kmlong valley glacier. Three 14C ages on buried tree trunks in the western (3960 m and 3820 m, asl) and eastern (3960 m asl) flanks of lateral moraines show that Ruoguo Glacier was 2 km longer than at present and was advancing into a forest at 200 BC-400 AD, 80-540 AD and 340-660 AD, respectively. This evidence suggests that the forest was covered by the advancing ice on both sides of the U-shaped valley, and a 20- to 30-cm-thick paleosoil was buried under till. A lichen date suggested that the maximum advance of Ruoguo Glacier during the LIA occurred in 1822 AD. Zepu Glacier (3) is a valley glacier located at the headwaters of the Yarlung Tsangpo River. The glacier is 19 km long and extends from 6350 m to 3420 m from west to east-southeast in an area of 66 km? (Li et al., 1986). The terminal 7 km is covered with supraglacial till and has penetrated into a forested area. The detailed investigation was carried out in the glacier forefield (Iwata and Jiao, 1993; Jiao and Iwata, 1993; Jiao et al., 2005). A 14C age from detrital wood buried in end moraines at Baitong, 3.5 km beyond the present glacier terminal position shows that the glacier was advancing before 650-1250 AD. A fresh terminal moraine was found in
Late Holocene monsoonal temperate glacier Fluctuations... -
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