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Catastrophic partial drainage of Pangong Tso, one of the largest lakes in Tibet, is supported by the geomorphology of the Tangtse Valley, Ladakh, northern India and cosmogenic 10Be nuclide ages of roche moutonnées, strath terraces, and a flood deposit downstream from the former spillway
. The former spillway for Pangong Tso is ~ 20-m-high and likely allowed ~ 18 km3 of water to drain catastrophically down the Tangtse Valley over a period of about 2 days sometime during the latest Pleistocene to early Holocene. The largest flood deposit, composed of imbricated granitic boulders up to 4.5 m in length, is present ~ 33 km downvalley of the spillway. These boulders have a cosmogenic 10Be exposure age of 11.1 ± 1.0 ka, the age of the outburst flood. The minimum calculated discharge was ~ 110,000 m3 s- 1. One set of strath terraces, upvalley of the flood deposit along the flood's drainage path, shows that the rate of fluvial incision 0.3 ± 0.1 mm y- 1 during 122-10.5 ka increased to 1.5 ± 0.5 mm y- 1 during 10.5 ka to the present. The temporal overlap of this increase in the rate of fluvial incision with the main flood deposit suggests that the flood was important in defining the incision along the Tangste valley. A second set of strath terraces shows little change in incision, from ~ 0.6-0.9 to ~ 0.9-1.4 mm y- 1, sometime between 18 and 27 ka. Roche moutonnées, upvalley from strath terraces, yield a cosmogenic 10Be age of 35.8 ± 3.0 ka, defining the time when glaciers last occupied the Tangtse valley. However, the lack of glacial sediment along the Tangste valley suggests that the flood eroded glacial depositional landforms and sediments resulting in high sediment loads in the floodwater, which in turn increased fluvial incision to form strath terraces. Much of the eroded glacial sediment was subsequently redeposited as the main flood deposit. The catastrophic drainage of Pangong Tso may be the result of breaching of the Pangong-Tangste spillway during very high lake levels in a period of intensified monsoon (10.7-9.6 ka) and/or possibly the consequence of seismic activity along the Karakoram Fault that is associated with the initial formation of Pangong Tso
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Muztag Ata and Kongur Shan massifs represent a significant area of anomalously high topography at the northwestern end of the Tibetan Plateau, rising to > 7500 m above sea-level (asl) from the plateau that has an average elevation of ~ 3500 m asl
. These massifs provide an excellent opportunity to test geomorphic concepts, such as the glacial buzz-saw model. Using remote sensing, digital elevation modeling, field mapping and terrestrial cosmogenic nuclide (TCN) methods, the massifs were examined to determine the relative importance of tectonics and geomorphic processes in shaping the regional landscape and to provide a framework for testing geomorphic models. The gneiss domes that underlie the peaks are the result of exhumation along the Kongur detachment fault that has unroofed the massifs at a rate of between 4-6 km/Ma over the last few million years. This has resulted in rapid uplift and active seismicity, which is exemplified by the numerous fresh fault scarps throughout the region and large historic earthquakes. The geomorphic system is dominated by glaciation and the region contains extensive successions of moraines and paraglacial landforms, including fans, terraces and landslides. Glaciers have oscillated considerably throughout the latter part of the Quaternary, and three major glacier stages are recognized (Karasu [oldest], Olimde and Subaxh [youngest] glacial stage) that include at least 10 smaller glacial advance. The style of glaciation has changed over time from expanded ice caps to piedmont glaciers to valley and cirque glaciers. This possibly reflects a change in climate and/or topographic constraints as the massifs grew and became incised. The topography and glaciers in the region vary across the massifs divided by a broadly N-S trending high ridge and watershed. The western portion, situated upwind (the stoss slopes) of the mid-latitude westerlies, that bring moisture to the region, has gentle high topography and small valley glaciers. In contrast, on the eastern leeward slopes, gradients are higher and long debris-covered valley glaciers are present. The hypsometry of the region indicate two peaks in the distribution frequency of elevation (3600-4100 m and 4400-4800 m asl). These two elevation zones are consistent in space with the former equilibrium-line altitudes during the Olimde and Subaxh glacial stages and suggest that glacial erosion (most effective at the ELA) has helped control topography. This observation supports the glacial buzz-saw hypothesis, which argues that glaciers determine hypsometry by means of rapid surface erosion. Based on TCN methods, basin-wide rates of erosion range from ~ 0.1 to 1.4 km/Ma and are five to ten times lower than the unroofing rate of both massifs. The discrepancy over different time scales suggests that initial unroofing was produced by abrupt tectonic uplift and that the unroofing of the massifs has continued at a slower pace during the Late Quaternary
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http://www
.sciencedirect.com/science/article/B6V93-4SFG4HC-4/2/dc8ebe655b19d344c1e73cc4a027c0f7
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Mountain glaciers are sensitive probes of the local climate, and, thus, they present an opportunity and a challenge to interpret climates of the past and to predict future changes
. Furthermore, glaciers can constitute hazards, including: glacier outburst floods; changes in the magnitude and timing of runoff in the mountains and adjacent regions; and, through worldwide loss of glacier ice, a global rise in sea level. To understand and ultimately to predict the dynamics and nature of climate and associated glacial and hydrological changes requires an integrated approach with communication and collaboration among glaciologists, glacial geologists, atmospheric scientists, geomorphologists, geochronologists, and tectonists. Current strategies of research are evolving towards integrating research on mountain glaciers to address key scientific, socio-economic and political issues. Given the rapid birth and growth of new technologies and tools with which to study glaciers and glacial landscapes, this community stands poised to address many of these challenges in the near future. The key challenges that must be met soon include: 1) determining the spatial-temporal pattern of fluctuations of mountain glaciers from the last glacial cycle through the present; 2) relating historical and past fluctuations in glaciers to variability in the primary features of ocean-atmospheric circulation; 3) identifying important but poorly understood processes controlling the motion and erosion of glaciers; 4) developing and expanding the application of numerical models of glaciers; 5) modeling the evolution of mountain landscapes in the face of repeated glaciation; 6) examining the climate and the balance of energy and mass at the surface of glaciers; 7) characterizing the role of intrinsic climate variability on glacier variations; and 8) predicting the distribution, sizes, and nature of glaciers in the future. While these ambitious goals are achievable and the research tools exist, success will require significant bridging between the existing research communities involved and ambitious integration of research on mountain glaciers
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Glacial geological evidence from throughout the Himalayan–Tibetan orogen is examined to determine the timing and extent of late Quaternary glaciation in this region and its relation to similar changes on a global scale
. The evidence summarised here supports the existence of expanded ice caps and extensive valley glacier systems throughout the region during the late Quaternary. However, it cannot yet be determined whether the timing of the extent of maximum glaciation was synchronous throughout the entire region or whether the response was more varied. The lack of organic material needed for radiocarbon dating has hindered past progress in glacial reconstruction; however, application of optically stimulated luminescence and terrestrial cosmogenic radionuclide methods has recently expanded the number of chronologies throughout the region. Limits to the precision and accuracy available with these methods and, more importantly, geological uncertainty imposed by processes of moraine formation and alteration both conspire to limit the time resolution on which correlations can be made to Milankovitch timescales (several ka). In order to put all studies on a common scale, well-dated sites have been re-evaluated and all the published terrestrial cosmogenic nuclide ages for moraine boulders and glacially eroded surfaces in the Himalayan–Tibetan orogen have been recalculated. Locally detailed studies indicate that there are considerable variations in the extent of glaciation from one region to the next during a glaciation. Glaciers throughout monsoon-influenced Tibet, the Himalaya and the Transhimalaya are likely synchronous both with climate change resulting from oscillations in the South Asian monsoon and with Northern Hemisphere cooling cycles. In contrast, glaciers in Pamir in the far western regions of the Himalayan–Tibet orogen advanced asynchronously relative to the other regions that are monsoon-influenced regions and appear to be mainly in phase with the Northern Hemisphere cooling cycles. Broad patterns of local and regional variability based on equilibrium-line altitudes have yet to be fully assessed, but have the potential to help define changes in climatic gradients over time
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Abundant glacial geologic evidence present throughout Tibet and the bordering mountains shows that glaciers have oscillated many times throughout the late Quaternary
. Yet the timing and extent of glacial advances is still highly debated. Recent studies, however, suggest that glaciation was most extensive prior to the last glacial cycle. Furthermore, these studies show that in many regions of Tibet and the Himalaya glaciation was generally more extensive during the earlier part of the last glacial cycle and was limited in extent during the global Last Glacial Maximum (marine oxygen isotope stage 2). Holocene glacial advances were also limited in extent, with glaciers advancing just a few kilometers from their present ice margins. In the monsoon-influenced regions, glaciation appears to be strongly controlled by changes in insolation that govern the geographical extent of the monsoon and consequently precipitation distribution. Monsoonal precipitation distribution strongly influences glacier mass balances, allowing glaciers in high altitude regions to advance during times of increased precipitation, which are associated with insolation maxima during glacial times. Furthermore, there are strong topographic controls on glaciation, particular in regions where there are rainshadow effects. It is likely that glaciers, influenced by the different climatic systems, behaved differently at different times. However, more detailed geomorphic and geochronological studies are needed to fully explore regional variations. Changes in glacial ice volume in Tibet and the bordering mountains were relatively small after the global LGM as compared to the Northern Hemisphere ice sheets. It is therefore unlikely that meltwater draining from Tibet and the bordering mountains during the Lateglacial and early Holocene would have been sufficient to affect oceanic circulation. However, changes in surface albedo may have influenced the dynamics of monsoonal systems and this may have important implications for global climate change. Drainage development, including lake level changes on the Tibetan plateau and adjacent regions has been strongly controlled by climatic oscillations on centennial, decadal and especially millennial timescales. Since the Little Ice Age, and particularly during this century, glaciers have been progressively retreating. This pattern is likely to continue throughout the 21st century, exacerbated by human-induced global warming
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New dares for late Quaternary glaciations in the Himalayas show that,\nduring the last glacial cycle, glaciations were not synchronous throughout\nthe region
. Rather, in some areas glaciers reached their maxima at\nthe global glacial maximum of e. 18-20 ka sp, whereas in others glaciers\nwere most extensive at c. 60-30 ka sp. Comparison of these data with\npalaeoclimatic records from adjacent regions suggest that, on millennial\ntimescales, Himalayan glacier fluctuations are controlled by variations\nin both the South Asian monsoon and the mid-latitude westerlies
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This paper presents the first glacial chronology for the Lahul Himalaya, Northern India
. The oldest glaciation, the Chandra Glacial Stage, is represented by glacially eroded benches at altitudes greater than 4300 m above sea-level. This glaciation was probably of a broad valley type. The second glaciation, the Batal Glacial Stage, is represented by highly weathered and dissected lateral moraines, which are present along the Chandra valley and some of its tributaries. This was an extensive valley glaciation. The third major glaciation, the Kulti Glacial Stage, is represented by well-preserved moraines in the main tributary valleys of the Chandra valley. This represents a less extensive valley glaciation. Two minor glacial advances, the Sonapani I and II, are represented by small sharp-crested moraines, which are within a few hundred metres or few kilometres of the present-day glaciers. The change in style and extent of glaciation is attributed to an increase in aridity throughout the Quaternary, due either to global climatic change or uplift of the Pir Panjal mountains to the south of Lahul, which restricted the northward penetration of the south Asian summer monsoon
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