Quaternary glaciations of the Rongbuk Valley, Tibet

Mann, Daniel H.; Sletten, R. S.; Reanier, Richard E.

doi:10.1002/(sici)1099-1417(199607/08)11:4<267::aid-jqs242>3.0.co;2-v

Cited by 10 publications

(9 citation statements)

References 68 publications

(37 reference statements)

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“…Best estimates of glacier ELAs on the north side of Mount Everest are in the range~5900 to 6300 m (Mann et al, 1996;Owen et al, 2009). The general northward rise of ELAs in the region is attributed to the precipitation gradient, reflecting the diminishing influence of the South Asian monsoon (Asahi, 2010).…”

Section: Glaciers Of the Everest Regionmentioning

confidence: 96%

Response of debris-covered glaciers in the Mount Everest region to recent warming, and implications for outburst flood hazards

Benn

Bolch

Hands³

et al. 2012

Earth-Science Reviews

498

585

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In areas of high relief, many glaciers have extensive covers of supraglacial debris in their ablation zones, which alters both rates and spatial patterns of melting, with important consequences for glacier response to climate change. Wastage of debris-covered glaciers can be associated with the formation of large moraine-dammed lakes, posing risk of glacier lake outburst floods (GLOFs). In this paper, we use observations of glaciers in the Mount Everest region to present an integrated view of debris-covered glacier response to climate change, which helps provide a long-term perspective on evolving GLOF risks. In recent decades, debris-covered glaciers in the Everest region have been losing mass at a mean rate of 0.32 m yr¹, although in most cases there has been little or no change in terminus position. Mass loss occurs by 4 main processes: (1) melting of clean ice close to glacier ELAs; (2) melting beneath surface debris; (3) melting of ice cliffs and calving around the margins of supraglacial ponds; and (4) calving into deep proglacial lakes. Modelling of processes (1) and (2) shows that Everest-region glaciers typically have an inverted ablation gradient in their lower reaches, due to the effects of a down-glacier increase in debris thickness. Mass loss is therefore focused in the mid parts of glacier ablation zones, causing localised surface lowering and a reduction in downglacier surface gradient, which in turn reduce driving stress and glacier velocity, so the lower ablation zones of many glaciers are now stagnant. Model results also indicate that increased summer temperatures have raised the altitude of the rain-snow transition during the summer monsoon period, reducing snow accumulation and ice flux to lower elevations. As downwasting proceeds, formerly efficient supraglacial and englacial drainage networks are broken up, and supraglacial lakes form in hollows on the glacier surface. Ablation rates around supraglacial lakes are typically one or two orders of magnitude greater than sub-debris melt rates, so extensive lake formation accelerates overall rates of ice loss. Most supraglacial lakes are 'perched' above hydrological base level, and are susceptible to drainage if they become connected to the englacial drainage system. Speleological surveys of conduits show that large englacial voids can be created by drainage of warm lake waters along pre-existing weaknesses in the ice. Roof collapses can open these voids up to the surface, and commonly provide the nuclei of new lakes. Thus, by influencing both lake drainage and formation, englacial conduits exert a strong control on surface ablation rates. An important threshold is crossed when downwasting glacier surfaces intersect the hydrological base level of the glacier. Base-level lakes formed behind intact moraine dams can grow monotonically, and in some cases can pose serious GLOF hazards. Glacier termini can evolve in different ways in response to the same climatic forcing, so that potentially hazardous lakes will form in some situations but no...

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Section: Glaciers Of the Everest Regionmentioning

confidence: 96%

Response of debris-covered glaciers in the Mount Everest region to recent warming, and implications for outburst flood hazards

Benn

Bolch

Hands³

et al. 2012

Earth-Science Reviews

498

585

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“…Subsequent studies present only a few radiocarbon ages (e.g. Derbyshire et al, 1991;Pachur et al, 1994;Mann et al, 1996).…”

Section: Timing Of Glaciationmentioning

confidence: 99%

Quaternary glaciation of the Himalayan–Tibetan orogen

Owen

Caffee

Finkel

et al. 2008

J Quaternary Science

206

143

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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 monsooninfluenced 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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“…Reconstructed multiple glacial sequences have been reported from parts of the Himalaya where LOM ice-sheet outlet glaciers have been proposed (ej Zheng, 1988;Burbank and Kang, 1991;Mann et al, 1996;Owen et al. 1998).…”

mentioning

confidence: 99%

The Quaternary glacial history of the Zanskar Range, north-west Indian Himalaya

Taylor

2000

Quaternary International

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Quaternary glaciations of the Rongbuk Valley, Tibet

Cited by 10 publications

References 68 publications

Response of debris-covered glaciers in the Mount Everest region to recent warming, and implications for outburst flood hazards

Response of debris-covered glaciers in the Mount Everest region to recent warming, and implications for outburst flood hazards

Quaternary glaciation of the Himalayan–Tibetan orogen

The Quaternary glacial history of the Zanskar Range, north-west Indian Himalaya

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