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Shri Ashtapad Maha Tirth - II
Lhamcoka is a glacial lake situated in the Chola Shan (7), a mountain range running NW-SE rising to 6168 m asl of the Shaluli Shan range. Brauning and Lehmkuhl (1996) and Brauning (2006) studied glacier fluctuations by determining the ages of trees growing on glacier deposits in the forefields of the eastern and western Lhamcoka Glaciers. Ages of trees growing on the terminal moraines yield minimum ages for respective moraine formations during LIA glacier advances. Due to the position of the terminal moraines below the upper tree line and the proximity of seed-providing forests, an ecesis period of 5 years was applied to derive minimum ages (Brauning, 2006). The maximum glacier advance during the LIA occurred at about 17771787 AD, and stages of standstill or short re-advances occurred between 1807 and 1820 AD and the beginning of the 20th century (older than 1907 to 1920 AD). The Gongga Mountains comprise of 5 valley glaciers with a length greater than 10 km, including Hailuogou Glacier (8), Mozigou Glacier, Yanzigou Glacier (9) and Nanmenguangou Glacier (10) on the eastern slope and Gongba Glacier (11) on the western slope. These glaciers are highly active with terminal positions extending into the forest zone at 2940 m asl (Owen et al., 2005). Hailuogou Glacier (8) is the longest monsoonal temperate glacier in the Gongga Shan. It is 13.1 km long and covers an area of 25.7 km. Its lower limit reaches 2980 m. Mean annual temperature and summer mean temperature at ELA (4900 m asl) are -4.4 °C and 3.6 °C, respectively. Zheng and Ma (1994a,b), and Owen et al. (2005) noted that the Neoglacial moraine ridges rise 40-60 m above the present Hailuogou valley while the LIA moraine ridges rise 10-20 m above the present Hailuogou valley. The latter are imbedded into the Neoglacial moraines. The single lateral moraines extend several kilometers up valley from the present ice margins. According to the morphology, three distinct periods of ice margin expansion can be differentiated. From a 50-m stratigraphic section, a 14C age from a tree trunk buried in glacial lake sediment intercalated between the upper and lower layers of moraines suggests that the earliest glacier advance occurred before 1520 BC-1110 BC. Another period can be traced at 340-610 AD based on the dating on buried tree trunks (Zheng Benxing, personal communication, 2006-06-28) within the upper layer of the moraine. A later advance occurred at 710-990 to 1010-1210 AD (Li et al, 1983; Zheng and Ma, 1994a,b; Li and Su, 1996) based on a tree trunk found beneath boulders at 2730 m asl on the distal slope of an end moraine ridge 2 km beyond the present glacier terminal position. This fossil tree was buried by an earlier debris flow or landslide (Zheng and Ma, 1994a,b). A 14C date on the tree trunk gives a maximum date of 1280-1470 AD for the glacier advance. A radiocarbon date from wood between the inner side of the end moraine ridge and the lateral moraine indicates that the glacier was advancing at 1660-1960 AD. At that time the glacier was 1 km longer than at present. Hence the terminal moraine ridges are believed to have formed during the LIA between the 15th and 19th centuries. It is noteworthy that Owen et al. (2005) confirm the Neoglacial at about 1 ka and LIA (a few hundred years) based on CRN ages of the Neoglacial and LIA moraines of Zheng and Ma (1994a,b). Yanzigou Glacier (9) is 10.5 km long and has an area of 32.15 km2, and descends to 3680 m asl (Liu et al., 2000). Smiraglia (1997) reconstructed glacier variations in this region during the past 4000 years by studying a highly eroded inner wall of the east lateral moraine complex at about 3900 m asl. From the base to the top of the moraine complex he identified eight units with organic matter along 500-m length of the moraine. These included six shallow soil
Late Holocene monsoonal temperate glacier Fluctuations... -
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