Mount Everest Region Research Articles

Assessing decadal glacier changes in southern flank of Mount Everest region with high resolution ALOS data

Assessing decadal glacier changes in southern flank of Mount Everest region with high resolution ALOS data

The Miocene elevation of Mount Everest

The Neogene elevation history of the Mount Everest region is key for understanding the tectonic history of the world's highest mountain range, the evolution of the Tibetan Plateau, and climate patterns in East and Central Asia. In the absence of fossil surface deposits such as paleosols, volcanic ashes, or lake sediments, we conducted stable isotope paleoaltimetry based on the hydrogen isotope ratios (dD) of hydrous minerals that were deformed in the South Tibetan detachment shear zone during the late Early Miocene. These minerals exchanged isotopically at high temperature with meteoric water (dDwater = m156p p 5p) that originated as high-elevation precipitation and infiltrated the crustal hydrologic system at the time of detachment activity. When compared to age-equivalent near-sea-level foreland oxygen isotope (d18O) paleosol records (d18Owater = m5.8p p 1.0p), the difference in d18Owater is consistent with mean elevations of g5000 m for the Mount Everest area. Mean elevations similar to modern suggest that an early Himalayan rain shadow may have influenced the late Early Miocene climatic and rainfall history to the north of the Himalayan chain.

Determination of snow cover from MODIS data for the Tibetan Plateau region

This paper addresses a snow-mapping algorithm for the Tibetan Plateau region using Moderate Resolution Imaging Spectroradiometer (MODIS) data. Accounting for the effects of the atmosphere and terrain on the satellite observations at the top of the atmosphere (TOA), particularly in the rugged Tibetan Plateau region, the surface reflectance is retrieved from the TOA reflectance after atmospheric and topographic corrections. To reduce the effect of the misclassification of snow and cloud cover, a normalized difference cloud index (NDCI) model is proposed to discriminate snow/cloud pixels, separate from the MODIS cloud mask product MOD35. The MODIS land surface temperature (LST) product MOD11_L2 is also used to ensure better accuracy of the snow cover classification. Comparisons of the resulting snow cover with those estimated from high spatial-resolution Landsat ETM+ data and obtained from MODIS snow cover product MOD10_L2 for the Mount Everest region for different seasons in 2002, show that the MODIS snow cover product MOD10_L2 overestimates the snow cover with relative error ranging from 20.1% to 55.7%, whereas the proposed algorithm estimates the snow cover more accurately with relative error varying from 0.3% to 9.8%. Comparisons of the snow cover estimated with the proposed algorithm and those obtained from MOD10_L2 product with in situ measurements over the Hindu Kush-Himalayan (HKH) region for December 2003 and January 2004 (the snowy seasons) indicate that the proposed algorithm can map the snow cover more accurately with greater than 90% agreement.

Glacial lake distribution in the Mount Everest region: Uncertainty of measurement and conditions of formation

This study provides a complete mapping (October 2008) of glacial lakes and debris-covered glaciers in the Mount Everest region. These types of analyses are essential in studies of the impact of recent climate change, and therefore the uncertainty of measurements is discussed with the aim of creating a reference study for use when glaciers and lakes are delineated using remote sensing imagery. Moreover, attention is focused on conditions related to the formation of lakes, which is the greatest evidence of the impact of climate change at high altitudes characterized by debris-covered glaciers. Regarding the formation process of supraglacial lakes, our findings confirm that the slope of the glacier where lakes are located is primarily responsible for the low flow velocity of this zone. Otherwise, this study is novel in its identification of a further boundary condition. The slope of the glacier upstream is able to influence both the low flow velocity and the high ablation rates at the glacier terminus. In fact, the imbalance between the two glacier zones generates the down-slope passage of debris, snow and ice. We found the slope of the glacier upstream to be inversely correlated with the relevant total surface of the lakes downstream. The multiple regression model developed in this study, considering the slopes of the two glacier areas distinctly, has been able to predict 90% of the supraglacial lake surfaces. Concerning the surfaces of lakes not directly connected with glaciers (unconnected glacial lakes), we found they are correlated with the dimensions of their drainage basin, whereas no correlation was found with the glacier cover in the basin. Considering that the evaporation/precipitation ratio at these altitudes is approximately 0.34, the evolution of these lakes appears to be a helpful sign for detecting the precipitation trend of these high-altitude regions.

Progression from South-Directed Extrusion to Orogen-Parallel Extension in the Southern Margin of the Tibetan Plateau, Mount Everest Region, Tibet

In the South Tibetan Himalaya, major detachment systems exhumed midcrustal rocks from different structural levels that are exposed in the Ama Drime and Mount Everest massifs. The South Tibetan detachment system (STDS) accommodated exhumation of the Greater Himalayan Series (GHS) until the Middle Miocene. Field- and laboratory-based structural data presented here indicate that early melt-present deformation in the footwall of the STDS accommodated large-scale flow of a low-viscosity middle crust. Decompression-related anatexis and emplacement of leucogranites in the structurally highest positions of the GHS (∼16–18 Ma) mark the final stages of south-directed extrusion within a relatively narrow solid-state mylonite zone that progressed into a brittle detachment. Estimates of mean kinematic vorticity and deformation temperatures record a progression in deformation conditions, from ultra-mylonitic leucogranite (∼400°–500°C; 51%–67% pure shear) to mylonitic marble (>300°C; 41%–55% pure shear) to moderately foliated marble ∼200°–300°C (46%–59% pure shear). Previous investigations demonstrated that the cessation of movement on the STDS at ∼16–13 Ma was followed by anatexis in the lower portion of the middle crust (∼12–13 Ma; Ama Drime Massif). The Ama Drime and Nyönno Ri detachments (∼8–12 Ma; Dinggyê graben) exhumed rocks from the deepest structural position in the central Himalaya during orogen-parallel extension. Brittle faulting dissected the upper crust (<4 Ma; Tingri–Kung Co graben) in a setting that was kinematically linked to extension in the interior of the Tibetan plateau.

Field Assessment of Tam Pokhari Glacial Lake Outburst Flood in Khumbu Region, Nepal

The Tam Pokhari glacial lake outburst flood (GLOF) in the Mount Everest region of Nepal is described primarily based on field observations by a survey team studying GLOF transmission areas and flood impact along the Inkhu River. An estimated accumulation of 18 billion cubic meters of water was suddenly released down the Inkhu River when a Tam Pokhari glacial lake moraine dam was breached. Field data suggests that the downstream flow consisted of massive sediment erosion and deposition resulting from bed slope changes and flow width and that river channel morphology was dramatically changed by this GLOF. As a consequence, the characteristics of GLOF changed drastically in downstream areas, resulting in infrastructures damage. In addition, the GLOF created numerous debris fans now occupied by settlements, especially tourism-based industries.

Remote Sensing of Suspended Particulate Matter in Himalayan Lakes

Abstract This study presents satellite data and in situ measurements to estimate the concentration of suspended solids in high-altitude and remote lakes of the Himalayas. Suspended particulate matter (SPM) concentrations measured in 13 lakes to the south of Mount Everest (Nepal) in October 2008 and reflectance values of the Advanced Visible and Near Infrared Radiometer type 2 (AVNIR-2) onboard ALOS, acquired a few days after the fieldwork activities concluded, were combined to build a relationship (R2 = 0.921) for mapping SPM concentrations in lakes of the Mount Everest region. The satellite-derived SPM concentrations were compared with in situ data (R2 = 0.924) collected in the same period in 4 additional lakes, located to the north of Mount Everest (Tibet, China). The 13 water samples collected in lakes in Nepal were also used to investigate the absorption coefficients of particles ap(λ) and colored, dissolved organic matter aCDOM(λ), with the aim of parameterizing a bio-optical model. An accurate m...

Sodium azide induced mutation of Actinomycetes I

Sodium azide was employed to generate mutants of actinomycetes from Mount Everest region, viz. Sagarmatha National Park, Jorsale, Kalapatthar and Namche. Individual isolates of actinomycetes were inoculated on Starch Casein Agar plates containing 10, 50 and 100 ppm of sodium azide. Depending on complete inhibition of their growth , actinomycete isolates were categorized as highly sensitive , moderately sensitive and tolerant, respectively. Out of a total of 38 actinomycetes isolates, two (5.3%) were highly sensitive, 23 (60.5%) moderately sensitive and 13 (34.2%) tolerant. A total of 21 mutants were generated by treating 8 of the 23 moderately sensitive actinomycetes with 20, 30 and 40 ppm (sublethal concentrations ) of sodium azide and analyzed morphologically and biochemically. All mutants like wild strains were able to hydrolyse starch, Tween 20 and casein and utilize fructose and lactose. All were urease and catalase positive , but were different from wild strains in colony color or texture or both. Altogether nine (43 % ) mutants having negative mutation in loci of utilization of galactose or mannose (loss-of-function LOF, single mutants ) , two LOF double mutants in utilization of both galactose and arabinose , one gain-of-function (GOF) single mutant having positive mutation in the loci of utilization of galactose, one GOF double mutant in utilization of mannose and galactose and five double mutants (25%) having GOF ( arabinose or sucrose ) as well as LOF (mannose or galactose or arabinose) were obtained. Key words : Mt. Everest, Sagarmatha, actinomycetes, sodium azide, mutation, LOF, GOF DOI: 10.3126/ijls.v3i0.2385

Timing of Midcrustal Metamorphism, Melting, and Deformation in the Mount Everest Region of Southern Tibet Revealed by U(‐Th)‐Pb Geochronology

U(‐Th)‐Pb dating of zircon, monazite, and xenotime from metamorphic and igneous rocks at two outcrops along a north‐south transect in the Mount Everest region of southern Tibet provide new constraints on the timing and duration of thermal events associated with channel flow and the ductile extrusion of the Greater Himalayan Series (GHS). At the southernmost outcrop in the Kangshung Valley, Th‐Pb ages from monazite indicate that prograde metamorphism associated with crustal thickening following the India‐Asia collision occurred at least as early as $$38.9\pm 0.9$$ Ma. A subsequent sillimanite‐grade metamorphic event at $$28.0\pm 1.2$$ Ma was followed by two phases of leucogranite emplacement at $$20.8\pm 0.8$$ and $$16.7\pm 0.4$$ Ma. At Thongmön, ∼40 km to the northeast of the Kangshung Valley, prograde metamorphism was occurring at ∼25.4 Ma and lasted until $$16.1\pm 0.1$$ Ma, reaching ∼740°C and 5 kbar at $$22.4\pm 0.2$$ Ma. Immediately following metamorphism, two phases of leucogranite were emplaced at $$15.2\pm 0.2$$ and $$12.6\pm 0.2$$ Ma, with an intervening phase of ductile deformation. These data combined with ages from the Rongbuk glacier and Ama Drime range, north and east of Everest and the North Himalayan Mabja dome 100–140 km to the northeast, suggest that GHS metamorphism lasted ∼20 m.yr. and that migmatization and south‐directed channel flow peaked around ∼23–20 Ma and ended by ∼16 Ma. The youngest leucogranites crosscut all ductile fabrics related to the Miocene channel flow.

High concentration of surface ozone observed along the Khumbu Valley Nepal April 2007

Increasing air pollution in Southeast Asia has the potential for dramatic impacts on the population and climate in relatively pristine regions such as the Himalaya. Recent measurements near Mount Everest indicate the presence of elevated levels of ozone at elevations from 5000m to 9000m that are the result of both the long‐range transport of tropospheric pollutants from Southeast Asia as well as the descent of ozone‐rich stratospheric air. Here we report on the first surface ozone concentration transect in the Mount Everest region. The data collected at elevations from 2900m to 5200m indicate an increase in concentration with height as well as 8‐hour average exposures in excess of 140ppb. Satellite data and meteorological diagnostics suggest a stratospheric source for the high levels observed. The majority of values observed exceed guidelines for human exposure and therefore are of a magnitude to suggest that they are of physiological relevance.

Sedimentological, geomorphological and dynamic context of debris-mantled glaciers, Mount Everest (Sagarmatha) region, Nepal

This paper presents the sediment, landform and dynamic context of four avalanche-fed valley glaciers (Khumbu, Imja, Lhotse and Chukhung) in the Mount Everest (Sagarmatha) region of Nepal. All four glaciers have a mantle of debris dominated by sandy boulder-gravel that suppresses melting to an increasing degree towards the snout, leading to a progressive reduction in the overall slope of their longitudinal profile. Prominent lateral–terminal moraine complexes, also comprising sandy bouldergravel, enclose the glaciers. These terminal moraines originally grew by accretion of multiple sedimentary facies of basal glacial and supraglacial origin, probably by folding and thrusting when the glaciers were more dynamic during the Little Ice Age. The four glaciers are in various stages of recession, and demonstrate a range of scenarios from down-wasting of the glacier tongue, through morainedammed lake development, to post-moraine-dam breaching. Khumbu Glacier is at the earliest stage of supraglacial pond formation and shows no sign yet of developing a major lake, although one is likely to develop behind its >250 m high composite terminal moraine. Imja Glacier terminates in a substantial body of water behind a partially ice-cored moraine dam (as determined from geophysical surveys), but morphologically appears unlikely to be an immediate threat. Chukhung Glacier already has a breached moraine and a connected debris fan, and therefore no longer poses a threat. Lhotse Glacier has an inclined, free-draining tongue that precludes hazardous lake development. From the data assembled, a conceptual model, applicable to other Himalayan glaciers, is proposed to explain the development of large, lateral-terminal moraine complexes and associated potentially hazardous moraine dams. – 2008 Elsevier Ltd. All rights reserved .

Bacterial ‘cosmopolitanism’ and importance of local environmental factors for community composition in remote high‐altitude lakes

In October 2004, plankton samples were collected from six permanent lakes located between 4960 and 5440 m a.s.l. in the Mount Everest region (Nepal) to assess how spatial and local environmental factors affect natural bacterial community composition. Fingerprinting analysis of the bacterial 16S rRNA gene fragment was done by denaturing gradient gel electrophoresis (DGGE).The number of DGGE bands (range: 12-23) was not correlated with lake area or remoteness, but there was a strong negative correlation with the ratio of catchment to lake area (r = -0.826, P < 0.05), suggesting that hydraulic retention time affects the establishment of the bacterial community in these seepage lakes.Most dominant sequences belonged to Betaproteobacteria except in two lakes where members of Bacteroidetes made the largest relative contribution. Up to 81% of the phylotypes had high similarity (>98 to 100%) in partial 16S rRNA gene sequence to those reported from other alpine lakes and glaciers around the world, suggesting the presence of 'cosmopolitan' bacteria.An analysis based on dissimilarity matrices and the Mantel test revealed the existence of dissimilarities in bacterial community composition related to geographical distance over a small spatial scale (<6 km), but determined by local environmental constraints.Our results suggest that several bacterial phylotypes are ubiquitous in the freshwater aquatic realm, but taxon sorting by local environmental constraints is important.

Stratigraphic correlation of Cambrian–Ordovician deposits along the Himalaya: Implications for the age and nature of rocks in the Mount Everest region

Research Article| March 01, 2009 Stratigraphic correlation of Cambrian–Ordovician deposits along the Himalaya: Implications for the age and nature of rocks in the Mount Everest region Paul M. Myrow; Paul M. Myrow † 1Department of Geology, Colorado College, Colorado Springs, Colorado 80903, USA †E-mail: pmyrow@coloradocollege.edu. Search for other works by this author on: GSW Google Scholar Nigel C. Hughes; Nigel C. Hughes 2Department of Earth Sciences, University of California, Riverside, California 92521, USA Search for other works by this author on: GSW Google Scholar Michael P. Searle; Michael P. Searle 3Department of Earth Sciences, Oxford University, Parks Road, Oxford, OX1 3PR, UK Search for other works by this author on: GSW Google Scholar C.M. Fanning; C.M. Fanning 4Research School of Earth Sciences, The Australian National University, Canberra, ACT 0200, Australia Search for other works by this author on: GSW Google Scholar S.-C. Peng; S.-C. Peng 5State Key Laboratory on Paleobiology and Stratigraphy, Nanjing Institute of Geology and Paleontology, Nanjing, 210008, China Search for other works by this author on: GSW Google Scholar S.K. Parcha S.K. Parcha 6Wadia Institute of Himalayan Geology, Dehra Dun, Uttranchal, 248001, India Search for other works by this author on: GSW Google Scholar GSA Bulletin (2009) 121 (3-4): 323–332. https://doi.org/10.1130/B26384.1 Article history received: 04 Dec 2007 rev-recd: 06 Jul 2008 accepted: 09 Jul 2008 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Paul M. Myrow, Nigel C. Hughes, Michael P. Searle, C.M. Fanning, S.-C. Peng, S.K. Parcha; Stratigraphic correlation of Cambrian–Ordovician deposits along the Himalaya: Implications for the age and nature of rocks in the Mount Everest region. GSA Bulletin 2009;; 121 (3-4): 323–332. doi: https://doi.org/10.1130/B26384.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The depositional age and stratigraphic correlations of metamorphosed and variably deformed rocks of Mount Everest are poorly known because of limited recovery of diagnostic fossils. Detailed study of Cambrian and Ordovician strata from along the length of the Himalaya has produced a coherent stratigraphy that stretches from northern India to Tibet. Our work also demonstrates that the North Col Formation rocks (= Everest series), between the Qomolangma and Lhotse detachments of the South Tibetan detachment system, still locally preserve sedimentary textures and primary stratigraphy that match those within Cambrian strata ~1100 km to the west in northern India. This demonstrates a coherency of depositional systems and stratigraphic architecture for Cambrian deposits along much of the Himalaya Tethyan margin. It also allows, for the first time, identification of precise depositional ages of several units in the Everest region, in particular, the Yellow Band carbonate and directly underlying siliciclastic strata, which are both shown to be late Middle Cambrian in age. Detrital zircon data presented herein for a sample from these siliciclastic strata contain a similar age spectrum to those from Middle Cambrian strata in northern India, as well as grains as young as ca. 526 Ma, both of which support the depositional age and continuity of depositional systems along the length of the Himalaya. Highly fractured rocks of the Ordovician lower Chiatsun Group in the hanging wall of the South Tibetan detachment system in Nyalam, 75 km to the west of Everest, correlate with Ordovician strata of the Mount Qomolangma Formation on Mount Everest. Our correlations indicate that the base of the summit pyramid of Everest, the foot of the “Third Step,” is composed of a 60-m-thick, white-weathering thrombolite bed. The top of this ancient microbial deposit crops out only 70 m below the summit of Mount Everest. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Glaciers, glacial lakes and glacial lake outburst floods in the Mount Everest region, Nepal

AbstractRecent climate changes have had a significant impact on the high-mountain glacial environment. Rapid melting of glaciers has resulted in the formation and expansion of moraine-dammed lakes, creating a potential danger from glacial lake outburst floods (GLOFs). Most lakes have formed during the second half of the 20th century. Glaciers in the Mount Everest (Sagamartha) region, Nepal, are retreating at an average rate of 10–59 ma–1. From 1976 to 2000, Lumding and Imja Glaciers retreated 42 and 34 ma–1, respectively, a rate that increased to 74 ma–1 for both glaciers from 2000 to 2007. During the past decade, Himalayan glaciers have generally been shrinking and retreating faster while moraine-dammed lakes have been proliferating. Although the number of lakes above 3500 m a.s.l. has decreased, the overall area of moraine-dammed lakes is increasing. Understanding the behaviour of glaciers and glacial lakes is a vital aspect of GLOF disaster management.

Sedimentological, geomorphological and dynamic context of debris-mantled glaciers, Mount Everest (Sagarmatha) region, Nepal

This paper presents the sediment, landform and dynamic context of four avalanche-fed valley glaciers (Khumbu, Imja, Lhotse and Chukhung) in the Mount Everest (Sagarmatha) region of Nepal. All four glaciers have a mantle of debris dominated by sandy boulder-gravel that suppresses melting to an increasing degree towards the snout, leading to a progressive reduction in the overall slope of their longitudinal profile. Prominent lateral–terminal moraine complexes, also comprising sandy boulder-gravel, enclose the glaciers. These terminal moraines originally grew by accretion of multiple sedimentary facies of basal glacial and supraglacial origin, probably by folding and thrusting when the glaciers were more dynamic during the Little Ice Age. The four glaciers are in various stages of recession, and demonstrate a range of scenarios from down-wasting of the glacier tongue, through moraine-dammed lake development, to post-moraine-dam breaching. Khumbu Glacier is at the earliest stage of supraglacial pond formation and shows no sign yet of developing a major lake, although one is likely to develop behind its >250 m high composite terminal moraine. Imja Glacier terminates in a substantial body of water behind a partially ice-cored moraine dam (as determined from geophysical surveys), but morphologically appears unlikely to be an immediate threat. Chukhung Glacier already has a breached moraine and a connected debris fan, and therefore no longer poses a threat. Lhotse Glacier has an inclined, free-draining tongue that precludes hazardous lake development. From the data assembled, a conceptual model, applicable to other Himalayan glaciers, is proposed to explain the development of large, lateral-terminal moraine complexes and associated potentially hazardous moraine dams.

P–T–t–D paths of Everest Series schist, Nepal

AbstractU(–Th)–Pb geochronology, geothermobarometric estimates and macro‐ and micro‐structural analysis, quantify the pressure–temperature–time–deformation (P–T–t–D) history of Everest Series schist and calcsilicate preserved in the highest structural levels of the Everest region. Pristine staurolite schist from the Everest Series contains garnet with prograde compositional zoning and yields a P–T estimate of 649 ± 21 °C, 6.2 ± 0.7 kbar. Other samples of the Everest Series contain garnet with prograde zoning and staurolite with cordierite overgrowths that yield a P–T estimate of 607 ± 25 °C, 2.9 ± 0.6 kbar. The Lhotse detachment (LD) marks the base of the Everest Series. Structurally beneath the LD, within the Greater Himalayan Sequence (GHS), garnet zoning is homogenized, contains resorption rinds and yields peak temperature estimates of ∼650 ± 50 °C. P–T estimates record a decrease in pressure from ∼6 to 3 kbar and equivalent temperatures from structurally higher positions in the overlying Everest Series, through the LD and into GHS. This transition is interpreted to result from the juxtaposition of the Everest Series in the hangingwall with the GHS footwall rocks during southward extrusion and decompression along the LD system. An age constraint for movement on the LD is provided by the crystallization age of the Nuptse granite (23.6 ± 0.7 Ma), a body that was emplaced syn‐ to post‐solid‐state fabric development. Microstructural evidence suggests that deformation in the LD progressed from a distributed ductile shear zone into the structurally higher Qomolangma detachment during the final stages of exhumation. When combined with existing geochronological, thermobarometric and structural data from the GHS and Main Central thrust zone, these results form the basis for a more complete model for the P–T–t–D evolution of rocks exposed in the Mount Everest region.

Orogen-parallel extension and exhumation enhanced by denudation in the trans-Himalayan Arun River gorge, Ama Drime Massif, Tibet-Nepal

Focused denudation and mid-crustal flow are coupled in many active tectonic settings, including the Himalaya, where exhumation of mid-crustal rocks accommodated by thrust faults and low-angle detachment systems during crustal shortening is well documented. New structural and (U-Th)/He apatite data from the Mount Everest region demonstrate that the trans-Himalayan Ama Drime Massif has been exhumed at a minimum rate of ~1 mm/yr between 1.5 and 3.0 Ma during orogen-parallel extension. The Ama Drime Massif offsets the South Tibetan detachment system, and therefore the South Tibetan detachment system is no longer capable of accommodating south-directed mid-crustal flow or coupling it with focused denudation. Previous investigations interpreted the NNE-SSW–striking shear zone on the west side of the Ama Drime Massif as the Main Central thrust zone; however, our data show that the Ama Drime Massif is bounded on either side by 100–300-m-thick normal-sense shear zone and detachment systems that are kinematically linked to young brittle faults that offset Quaternary deposits and record active orogen-parallel extension. When combined with existing data, these results suggest that the Ama Drime Massif was exhumed during orogen-parallel extension that was enhanced by, or potentially coupled with, denudation in the trans-Himalayan Arun River gorge. This model provides important insights into the mechanisms that exhumed trans-Himalayan antiformal structures during orogen-parallel extension along the southern margin of the Tibetan Plateau.

Microbial community structure in moraine lakes and glacial meltwaters, Mount Everest

The bacterial diversity and abundance in two moraine lakes and two glacial meltwaters (5140, 5152, 5800 and 6350 m above sea level, respectively) in the remote Mount Everest region were examined through 16S rRNA gene clone library and flow cytometry approaches. In total, 247 clones were screened by RFLP and 60 16S rRNA gene sequences were obtained, belonging to the following groups: Proteobacteria (8% alpha subdivision, 21% beta subdivision, and 1% gamma subdivision), Cytophaga-Flavobacteria-Bacteroides (CFB) (54%), Actinobacteria (4%), Planctomycetes (2%), Verrucomicrobia (2%), Fibrobacteres (1%) and Eukaryotic chroloplast (3%), respectively. The high dominance of CFB distinguished the Mount Everest waters from other mountain lakes. The highest bacterial abundance and diversity occurred in the open moraine lake at 5152 m, and the lowest in the glacial meltwater at 6350 m. Low temperature at high altitude is considered to be critical for component dominancy. At the same altitude, nutrient availability plays a role in regulating population structure. Our results also show that the bacteria in Mount Everest may be derived from different sources.

An eastern Tethyan (Tibetan) record of the Early Jurassic (Toarcian) mass extinction event

ABSTRACTA record of the Early Jurassic mass extinction event is reported from eastern Tethyan (Tibetan) locations for the first time. In the Mount Everest region a thick Lower Jurassic carbonate formation, here named the Yungjia Formation, is developed within the predominantly clastic Triassic–Jurassic succession. Within the formation a sharp transition from peloidal packstones/grainstones to thin‐bedded, pyritic micrite‐shales interbeds records a sharp pulse of deepening and development of dysoxic bottom waters. Both the lithiotid bivalves and the lituolid foraminifera are important constituents of the lower Yungjia Formation but they disappear at this flooding surface or a short distance below it. This extinction event is comparable to that seen at the base of the Pliensbachian/Toarcian boundary in western Tethyan platform carbonates but the Tibetan events occurred late in the Toarcian Stage as indicated by nannofossil biostratigraphy and C isotope chemostratigraphy. The Early Jurassic extinction event (and the associated spread of oxygen‐poor waters) was therefore not synchronous throughout the Tethyan region.

Prevention of Acute Mountain Sickness by Acetazolamide in Nepali Porters: A Double-Blind Controlled Trial

This study aimed to determine the efficacy, tolerability, and practicality of acetazolamide for the prevention of acute mountain sickness (AMS) in Nepali trekking porters early in the trekking season. This study was a randomized, double-blind controlled trial with 400 male Nepali porters in the Mount Everest region of Nepal, trekking from Namche Bazaar (3440 m) to Lobuche (4930 m), the study endpoint. Participants were randomized to receive 250 mg acetazolamide daily or placebo, and AMS symptom scores (Lake Louise) were compared in highlanders vs lowlanders. Only 109 (27.2%) of the 400 porters completed the trial (28 highlanders, 81 lowlanders). The rest either dropped out (275/400 porters, 68.8%) or were excluded (16/400 porters, 4%). Acute mountain sickness occurred in 13 (11.9%) of 109 porters; all were lowlanders; 7 were taking acetazolamide, 6 taking placebo. Birthplace, acclimatization in the week before the trial, ascent rate, and rest days were the most important variables affecting the incidence of AMS. No highlanders, but 13 (16.1%) of 81 lowlanders had AMS (P = .016). Acclimatization in the pretrial week reduced AMS incidence (P = .013), as did a slower ascent rate (P = .0126), but rest days were the most potent prophylactic variable (P = .0001). Side effects were more frequent in porters taking acetazolamide than in the placebo group (P = .0001), but there were no serious side effects. Acetazolamide was tolerable, but impractical for the routine prevention of AMS in Nepali porters. A good trekking schedule and adequate acclimatization remain the most effective preventive measures. This study identified lowland porters as a high-risk group for developing AMS.