•UHT metamorphism is reported for the first time in the Himalaya.•The heat source was an over-thickened crust associated with lithospheric thinning.•Cold vs. granulitized eclogites formed during ...infant vs. mature collisional stages.•2.0–1.8 Ga eclogites have formed by a Himalaya-type global collisional network.
Modern-style plate tectonics, often characterised by subduction, is a fundamental dynamic process for planet Earth. Subduction related eclogites are widely used to indicate initiation of plate tectonics or whether different tectonic regimes dominated Earth history. However, such markers are commonly overprinted in ancient metamorphic terranes and rarely preserved even in most Phanerozoic mountain belts. This study tries to reveal the detailed burial and exhumation processes that formed granulitized eclogites in the Everest east region, central Himalaya, so as to explore the tectonic regimes recorded by similar rocks on early Earth. Robust Pressure-Temperature-time paths were achieved by studying the mineral relicts (Omp, Jd ∼29%), high-temperature mineral textures (Sil-Crd-Qz-Spl-Mesoperthite assemblage, rutile exsolution in biotite), and multiple thermobarometry and petrochronology of eclogites and metapelites. Results show that these eclogites underwent eclogitization at conditions of 730–770°C and ∼20 kbar (∼11°C/km) at ∼30 Ma and were overprinted by a heating and decompression path to ultrahigh temperature (UHT) conditions of 6–11 kbar and 900–970°C (∼40°C/km) during 25–15 Ma. The resulting exhumation rate (2–3 mm/yr) is slow and prolonged (10–15 Myr) (U)HT favoured re-equilibration of the eclogitic mineral assemblage and textures. The obtained UHT conditions, the first time ever reported for the Himalaya, were induced by combined effects of over-thickened (∼60 km) radioactive felsic crust and thinning of lithosphere to <90 km. This case study provides a critical example to understand the heat sources and timescale of UHT condition during continental collision. By comparing with the western Himalaya eclogites, we suggest that formation of cold vs. granulitized continental eclogites during the Himalayan orogeny is caused by different crustal thickness (normal ∼30 km vs. over-thickened ∼60 km) due to different collisional stages (infant vs. mature). In a wider perspective, ancient eclogites were commonly granulitized by stacking into the over-thickened orogenic crust during mature continental collision. According to similar granulitized eclogites preserved on early Earth, Himalaya-type continental subduction/collision should have become a global pattern during the Paleoproterozoic (2.0–1.8 Ga).
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 ~0.32myr−1, 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 not others. Additionally, the probability of a flood is not simply a function of lake volume, but depends on the geometry and structure of the dam, and possible trigger mechanisms such as ice- or rockfalls into the lake. Satellite-based measurements of glacier surface gradient and ice velocities allow probable future locations of base-level lakes to be identified. A base-level lake has begun to grow rapidly on Ngozumpa Glacier west of Mount Everest, and could attain a volume of ~108m3 within the next 2 or 3 decades. Unless mitigation efforts are undertaken, this lake could pose considerable GLOF hazard potential.
What are the main morphological factors that control the heterogeneous responses of debris-covered glaciers to climate change in the southern central Himalaya? A debate is open whether thinning rates ...on debris-covered glaciers are comparable to those of debris-free ones. Previous studies have adopted a deterministic approach, which is indispensable, but is also limiting in that only a few glaciers can be monitored. In this context, we propose a statistical analysis based on a wider glacier population as a complement to these deterministic studies. We analysed 28 glaciers situated on the southern slopes of Mt. Everest in the central southern Himalaya during the period 1992–2008. This study combined data compiled by three distinct studies for a common period and population of glaciers for use in a robust statistical analysis. Generally, surface gradient was the main morphological factor controlling the features and responses of the glaciers to climate change. In particular, the key points that emerged are as follows. 1) Reduced downstream surface gradient is responsible for increased glacier thinning. 2) The development of supraglacial ponds is a further controlling factor of glacier thinning: where supraglacial ponds develop, the glaciers register further surface lowering. 3) Debris coverage and thickness index were not found to be significantly responsible for the development of supraglacial ponds, changes in elevation, or shifts in snow line altitude.
•Downstream surface gradient is the main factor controlling changes in mass balance, surface, SLA, pond density.•Reduced downstream surface gradient is responsible for increased glacier thinning.•Where supraglacial ponds develop the glaciers register further glacier thinning.•Debris coverage and thickness were not found significantly responsible for changes in glacier elevation.
The Himalayan leucogranite belt is evaluated as a prospect for rare-metal mineralization. The Pusila pluton is located 44 km northwest of Mount Everest, and consists of two-mica granite, muscovite ...granite, albite granite, and pegmatites. Numerous pegmatite dikes have intruded the Higher Himalayan crystalline sequence and the granites. Oligocene pegmatites in the Chomogu and Cuore areas, which we constrain to have formed at ca. 25–23 Ma, were investigated in this study, because they are strongly enriched in Li (up to 8460 ppm) and contain abundant spodumene±petalite. Lithium was progressively enriched from the two-mica granite to the muscovite granite, and finally Li mineralization occurred in the highly fractionated pegmatites. The Chomogu No. 1 pegmatite is a well-zoned dike that hosts beryl, columbite, cassiterite, and Li minerals, which are concentrated in the inner parts of the dike. Scanning electron microscopy and cathodoluminescence images reveal two stages of Li mineralization. Primary spodumene (Spd-1) crystallized in the magmatic stage, whereas secondary spodumene (Spd-2) and petalite formed later in the hydrothermal stage. The Pusila pluton is thus an important site of Li mineralization in the Himalayan leucogranite belt.
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•Pusila spodumene pegmatites formed in the Oligocene at ca. 25–23 Ma.•The pegmatites formed by multi-stage fractional crystallization.•Pusila pluton is an important site of Li mineralization in the Himalaya.•Tourmaline is a proxy of Li enrichment in the Pusila pegmatites.•Li mineralization in the Pusila pegmatites occurred in two stages.
The impact of glacial lake development on the evolution of glaciers in the Himalaya is poorly quantified, despite the increasing prevalence of supraglacial and proglacial water bodies throughout the ...region. In this study we examine changes in the geometry, velocity and surface elevation of nine lake-terminating and nine land-terminating glaciers in the Everest region of the central Himalaya over the time period 2000 to 2015. The land-terminating glaciers we examined all decelerated (mean velocity change of −0.16 to −5.60 m a−1 for different glaciers), thinned most in their middle reaches, and developed a more gently sloping surface (−0.02 to −0.37° change) down-glacier over the period 2000–2015. The lake-terminating glaciers we examined all retreated (0.46 to 1.42 km), became steeper (0.04 to 8.68° change), and showed maximum thinning towards their termini, but differed in terms of their dynamics, with one group of glaciers accelerating (mean speed-up of 0.18 to 8.04 m a−1) and the other decelerating (mean slow-down of −0.36 m a−1 to −8.68 m a−1). We suggest that these two scenarios of glacier evolution each represent a different phase of glacial lake expansion; one that is accompanied by increasingly dynamic glacier behaviour and retreat, and a phase where glacial lakes have little impact on glacier behaviour that may precede or follow the phase of active retreat. Our observations are important because they quantify the interaction of glacial lake expansion with glacier ice mass loss, and show that increased glacier recession should be expected where a glacial lake has begun to develop.
•Himalayan glaciers hosting glacial lakes show divergent velocity evolution.•Land-terminating glacier velocity & geometry change consistent within sample.•Glaciers hosting lakes may experience a phase of dynamic retreat and ice loss.
Black soot and the survival of Tibetan glaciers Xu, Baiqing; Cao, Junji; Hansen, James ...
Proceedings of the National Academy of Sciences - PNAS,
12/2009, Letnik:
106, Številka:
52
Journal Article
Recenzirano
Odprti dostop
We find evidence that black soot aerosols deposited on Tibetan glaciers have been a significant contributing factor to observed rapid glacier retreat. Reduced black soot emissions, in addition to ...reduced greenhouse gases, may be required to avoid demise of Himalayan glaciers and retain the benefits of glaciers for seasonal fresh water supplies.
The glacier surface ice velocity (SIV) is important in understanding the glacier state. This study presents results on the SIV of the 18 glaciers spread over the Indian central Himalaya (ICH). The ...SIV was computed by applying Co-registration of Optically Sensed Images and Correlation (COSI-Corr) technique on the Landsat time series data (1993–2017). Results show that the average SIV of all glaciers was 22.63 ± 5.8 m a−1 in 1993/94, which decreased (by ~23%) to 17.32 ± 3.1 m a−1 in 2000/01 and further declined (by ~33%) to 11.50 ± 1.7 m a−1 in 2015/16. Though a secular decline in average SIV is observed, rates of slowdown are considerably heterogeneous for the studied glaciers being largely determined by glaciers size, orientation, altitude and debris cover. Slope was found to have comparatively low influence on the glacier movement. Inter-regional comparison reveals that average SIVs of the ICH glaciers were slightly but consistently lower than that of the western and eastern Himalayan glaciers. Nonetheless, though moving slowly, ICH glaciers are more active than nearby Everest region glaciers with sufficient proportion of active glaciers (referred as Type-I; 39%). However, the point of concern is that owing to declining health, ICH-glaciers are progressively converting from Type-I to partially active (referred as Type-II), and Type-II to entirely stagnant (referred as Type-III). This observed slowdown coupled with negative mass balance and continuous debris growth (as reported in previous studies) may form favorable conditions for supraglacial lake development. We thereby recommend regular monitoring of glacier dynamics in this region for tenable assessment of climatic change impacts.
•Velocities for 18 central Himalayan glaciers have been estimated between 1990 and 2015.•All the studied glaciers have significantly slowed-down during ~1990–2015.•Central Himalayan glaciers moved slowly than western and central Himalaya.•Entirely active glaciers have progressively been converted into entirely stagnant glaciers.•Glacier’ size, orientation, altitude and debris cover determine movement heterogeneity.
The dynamics of supraglacial pond development in the Everest region are not well constrained at a glacier scale, despite their known importance for meltwater storage, promoting ablation, and ...transmitting thermal energy englacially during drainage events. Here, we use fine-resolution (~0.5–2m) satellite imagery to reveal the spatiotemporal dynamics of 9340 supraglacial ponds across nine glaciers in the Everest region, ~2000–2015. Six of our nine study glaciers displayed a net increase in ponded area over their observation periods. However, large inter- and intra-annual changes in ponded area were observed of up to 17% (Khumbu Glacier), and 52% (Ama Dablam) respectively. Additionally, two of the fastest expanding lakes (Spillway and Rongbuk) partially drained over our study period. The Khumbu Glacier is developing a chain of connected ponds in the lower ablation area, which is indicative of a trajectory towards large lake development. We show that use of medium-resolution imagery (e.g. 30m Landsat) is likely to lead to large classification omissions of supraglacial ponds, on the order of 15–88% of ponded area, and 77–99% of the total number of ponds. Fine-resolution imagery is therefore required if the full spectrum of ponds that exist on the surface of debris-covered glaciers are to be analysed.
•Inter- and intra-annual pond area changes were up to 17% and 52% respectively.•Spillway and Rongbuk lakes declined in area, attributed to drainage reorganisation.•Khumbu Glacier is developing a series of connected ponds on the lower ablation area.•9340 ponds were classified using fine-resolution satellite imagery.•Coarser-resolution imagery cannot capture the pond size distributions encountered.
A bacterial strain, designated S9-5
, was isolated from moraine samples collected from the north slope of Mount Everest at an altitude of 5 500 m above sea level. A polyphasic study confirmed the ...affiliation of the strain with the genus
. Strain S9-5
was an aerobic, Gram-stain-negative, non-spore-forming, non-motile and rod-shaped bacterium that could grow at 10-40 °C, pH 5-8 and with 0-9 % (w/v) NaCl. Q-10 was its predominant respiratory menaquinone. Diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, an unidentified phospholipid, an unidentified aminophospholipid and eight unidentified lipids comprised the polar lipids of strain S9-5
. Its major fatty acids were summed feature 8 (C
7
and/or C
6
) and C
. The G+C content was 65.75mol%. Phylogenetic analysis based on 16S rRNA sequences showed that strain S9-5
was phylogenetically closely related to
DCY91
(98.17 %),
K-1-16
(98.11 %) and
DSM 17494
(97.39 %). The average nucleotide identity values among strain S9-5
and
DCY91
,
K-1-16
and
DSM 17494
were 78.82, 78.87 and 78.29 %, respectively. Based on the morphological, physiological and chemotaxonomic data, strain S9-5
(=JCM 34750
=GDMCC 1.2714
) should represent a novel species of the genus
, for which we propose the name
sp. nov.
Bacteria in the genus
have been found in extreme environments, e.g. glaciers, brine and mural paintings. Here, we report the discovery of a novel pink-coloured bacterium, strain QL17
, capable of ...producing an extracellular water-soluble blue pigment. The bacterium was isolated from the soil of the East Rongbuk Glacier of Mt. Everest, China. 16S rRNA gene sequence analysis showed that strain QL17
was most closely related to the species
KR32
. However, compared to
KR32
and the next closest relatives, the new species demonstrates considerable phylogenetic distance at the whole-genome level, with an average nucleotide identity of <85 % and inferred DNA-DNA hybridization of <30 %. Polyphasic taxonomy results support our conclusion that strain QL17
represents a novel species of the genus
. Strain QL17
had the highest tolerance to hydrogen peroxide at 400 mM. Whole-genome sequencing of strain QL17
revealed the presence of numerous cold-adaptation, antioxidation and UV resistance-associated genes, which are related to adaptation to the extreme environment of Mt. Everest. Results of this study characterized a novel psychrotolerant
species, for which the name
sp. nov. is proposed. The type strain is QL17
(GDMCC 1.2948
=JCM 35246
).
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