Glacier fluctuations in the Nimaling Mountains, North India

Key words: Late Quaternary, glacier fluctuations, tentative stratigraphic sequences, Indus River basin

The extent of the glaciation of High Asia during the Last Glacial Maximum (LGM) and the elevation of the equilibrium line altitude (ELA) is a source of considerable debate. On the basis of different interpretations the views range from the idea of mountain glaciations, which were restricted to the highest ridges and mountain ranges to the presence of an extensive inland ice sheet. One reason for these different interpretations is the present lack of general agreement on terminology and stratigraphic division of different terminal moraine sequences and till deposits in the various mountain areas. Some relative chronologies exist for mountain glacier oscillations, but the timing is poorly understood due to the lack of numeric ages for the most of the glacial stages. A common and validated stratigraphy based on geomorphological criteria, ELA-depressions and numerical dating as in the European Alps is not yet available.

In the mountain ranges of Ladakh and the surrounding areas (Fig. 1), only a few studies provide information of ELA's for the LGM, which differ significantly from each other within delineated regions. In general, the knowledge on the Late Quaternary glacier fluctuations is poor from the Nimaling Mountains and the Markha Valley. The area is situated in the semiarid central part of Ladakh beyond the monsoon-dominated ranges of the Karakoram and High Himalayas. Terrain altitudes are between 3000 and 4200m a.s.l. on valley floors and 6200 to 6400 m a.s.l. at the Nimaling Plain. The present-day glaciation is restricted to summit areas, flanks, and high valleys (Fig. 2), where glaciers end at lower altitudes of 5100 – 5400 m a.s.l.

Geomorphological studies in the Markha Valley and the northern Nimaling Mountain has revealed eight prominent glacial stages. The two oldest glaciations are marked by glacial abrasion forms as ice-scour limits and glacial ledges above the lower and middle Markha valley. These glaciations probably occurred prior to the last glacial cycle. Furthermore, terminal and lateral moraines and tills provide evidence for three glacial stages in the Markha and Nimaling valleys (Fig. 3), when the equilibrium-line altitude (ELA) was depressed at 670–350 m. The glaciations probably occurred during the LGM, the Late Glacial and the Lower Holocene as indicated by the topographic sequence, the ELA depressions and the tentative glacial stratigraphic divisions for the North Indian areas. Large moraine complexes in the vicinity of the present-day glaciers probably represent three glacial stages of Neoglacial and historical glacial advances. The ELA depressions are 10-70 m. The present glaciation of the Nimaling Mountains (Fig. 4), largely restricted to north flanks and the glacier basins below, covers an area of 45–55 km². The modern ELA is calculated at 5650–5750m a.s.l. on north faces, rising to about 5900–6000m a.s.l. on south faces.

Concerning the LGM in Ladakh and Zanskar there is a widely consensus that both, the Ladakh and the Zanskar Ranges were quite extensively glaciated. The volume and extent of the glaciers were a function of slope, area extent above 6000 m a.s.l., degree of valley dissection and presence of topographic obstacles. As consequence of the dry conditions and the absence of datable organic material from peat, soils etc. in this area radio carbon dates are lacking and only a few OSL dates have been published. However, there is agreement on relative chronology based on the spatial succession of comparable glacier stages as well as on morphological criteria. The observed sequence of moraine deposits is considered to represent the Little Ice Age, the Neoglacial, the Late Glacial and the LGM, respectively (Fig. 5). The Indus valley around Leh was probably not glaciated. In contrast, the extent of ice advances along the upper Indus valley still remains unclear, as well as the question as to where in the valley section below Leh the glacially induced refilling of the Indus valley restarted.

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