holocene environmental changes in bangong co basin western tibet part 4 discussion and conclusions abstract a 12 4 m core taken in lake bangong provides a continuous holocene climatic record we summarize information on changes in stable isotope and radiocarbon balances in the lake hydrobiology and vegetal cover in the catchment deduced from detailed analytical results given in the three preceding papers the bangong record is then compared with the environmental history of the neighbouring lake sumxi also constructed from multidisciplinary analyses the two records show a major environmental change at 10 9 5 ka b p attributed to a rapid strengthening of the summer monsoonal circulation which led to wet warm conditions this event was followed by a long term trend toward aridity which culminated around 4 3 ka b p in western tibet maximum monsoon rainfall seems to have occurred from 9 5 to 8 7 ka b p and from 7 2 to 6 3 ka b p as two wet pulses separated by a reversal event centered on 8 0 7 7 ka b p our results broadly agree with the records from lake seling in central tibet and lake qinghai at the plateau s northeastern margin and with palaeoclimatic studies in western china which document conditions wetter and warmer than those of today during the early middle holocene the environmental fluctuations recorded in western tibet appear in phase with climatic changes recognized in tropical north africa suggesting that the 8 0 7 7 ka b p and the 4 0 3 0 ka b p dry events were caused by abrupt disequilibrium in the climatic system

holocene climatic instability a prominent widespread event 8200 yr ago the most prominent holocene climatic event in greenland ice core proxies with approximately half the amplitude of the younger dryas occurred 8000 to 8400 yr ago this holocene event affected regions well beyond the north atlantic basin as shown by synchronous increases in windblown chemical indicators together with a significant decrease in methane widespread proxy records from the tropics to the north polar regions show a short lived cool dry or windy event of similar age the spatial pattern of terrestrial and marine changes is similar to that of the younger dryas event suggesting a role for north atlantic thermohaline circulation possible forcings identified thus far for this holocene event are small consistent with recent model results indicating high sensitivity and strong linkages in the climatic system

cosmogenic 3he and 21ne production rates calibrated against 10be in minerals from the coso volcanic field this study calibrates the production rate of cosmogenic 3 he in pyroxene olivine garnet zircon and apatite as well as 21 ne in quartz and pyroxene against the known production rate of 10 be in quartz the devil s kitchen rhyolite from the coso volcanic field in southeastern california elev 1300 m was chosen for this study due to its young age 610 ka and diverse mineral assemblage based on 10 be our two rhyolite samples have apparent exposure ages of 49 and 93 ka indicating substantial erosion after eruption combining data from the two samples we estimate sea level high latitude 3 he spallation production rates of 145 11 141 16 and 144 30 at g 1 a 1 2 for pyroxene olivine and spessartine garnet respectively for zircon and apatite we estimate apparent 3he spallation production rates of 114 8 and 149 28 at g 1 a 1 2 respectively the rates for zircon and apatite are reported as apparent production rates because we do not explicitly address the redistribution of spallation produced 3 he from adjacent minerals these estimates quantitatively account for production of 3 he from both cosmogenic and radiogenic neutron reactions on 6 li within the analyzed phases and also implanted from nuclear reactions in neighboring minerals the high u th and li content of this rhyolite provides a particularly rigorous test of this correction we estimate 21 ne production rates of 17 7 1 6 and 34 1 3 2 at g 1 a 1 2 in quartz and pyroxene fe mg 0 7 by mass respectively although high u and th contents create the potential for significant production of nucleogenic 21 ne this component is small due to the young eruption age of the rhyolite

high frequency holocene glacier fluctuations in the himalayan tibetan orogen abstract holocene glacial chronostratigraphies in glaciated valleys spread throughout the himalayan tibetan orogen including the himalaya tibet pamir and tian shan are developed using a landsystems approach detailed geomorphic mapping and new and published 10be surface exposure dating new studies in the kulti valley of lahul and the parkachik valley of the nun kun massif of the himalaya of northern india define three glacier advances at 14 7 12 2 0 5 ka in addition to one historically dated late 19th century advance in the kulti valley and one late holocene advance at 0 2 ka in the parkachik valley three major climatic groups subdivided into five climatic zones are defined across the orogen using cluster analysis ca and principal component analysis pca to identify glaciated regions with comparable climatic characteristics to evaluate the timing and extent of holocene glacier advances across these regions our regional analyses across the himalayan tibetan orogen suggest at least one lateglacial 15 3 11 8 ka and five himalayan tibetan holocene glacial stages hths at 11 5 9 5 8 8 7 7 7 0 3 2 2 3 1 0 and

bayesian estimation of the normal and shear stiffness for rock sockets in weak sedimentary rocks abstract the design of socketed foundations in weak sedimentary rocks is often governed by settlement the shear stiffness of the rock socket sidewalls and the normal stiffness of the rock socket base are the main parameters that affect the settlement of rock sockets at service load conditions and are needed for settlement calculation in load transfer method or using the theory of elasticity in this paper in situ load test data for socketed foundations in weak rocks are collected the shear stiffness of the rock socket sidewalls and the normal stiffness for the rock socket base are respectively estimated based on the measured side shear stress and shear displacement and base contact pressure and normal displacement relationships the parameters affecting shear and normal stiffnesses are discussed a bayesian approach is used to develop probabilistic models for the rock socket shear and normal stiffnesses which are functions of both rock properties and the rock socket size

fossil cosmogenic 3 he record from k ar dated basaltic flows of mount etna volcano sicily 38 n evaluation of a new paleoaltimeter this study investigates the reliability of a paleoaltimeter based on the elevation dependency of the cosmogenic nuclides production rate the proposed method relies on fossil cosmogenic record indeed measuring the cosmogenic nuclide concentration in an exposed and then buried lava flow combined with an independent estimate by k ar or 40ar 39ar dating of the past exposure duration theoretically allows recording fossil cosmogenic production rates which can thus be converted in paleoelevations this approach was tested by measuring cosmogenic 3he 3hec in olivines and clinopyroxenes of quaternary k ar dated basaltic flows of mount etna volcano sicily 38 n the agreement within uncertainties 1 500 m between current and cosmogenic derived elevations demonstrates the paleoaltimeter reliability however dating imprecision earth s paleomagnetic fluctuations and erosion contemporary to the flow exposure are parameters that may affect the accuracy and the precision of the method on older geological scales their respective influences were thus carefully evaluated and discussed to conclude that the paleoaltimeter can potentially reach resolutions better than 1000 m even for cenozoic records

too young or too old evaluating cosmogenic exposure dating based on an analysis of compiled boulder exposure ages cosmogenic exposure dating has greatly enhanced our ability to define glacial chronologies spanning several global cold periods and glacial boulder exposure ages are now routinely used to constrai

evaluation of peak side resistance for rock socketed shafts in weak sedimentary rock from an extensive database of published field load tests a limit state approach this paper presents analyses of the measured peak side resistance of rock sockets constructed in weak claystone shale limestone siltstone and sandstone the peak side resistance is obtained fro

modelling jointed rock mass as a continuum with an embedded cohesive frictional model abstract the mechanical and hydraulic properties of a jointed rock mass are strongly affected by the characteristics of joints within the intact rock mass in this study a constitutive model for jointed rock masses is developed by incorporating the contributions of both the joint and its surrounding rock mass the behaviour of the joint is represented by a new coupled damage plasticity cohesive frictional model taking into account its dilation evolution and the reduction of both strength and stiffness while the surrounding rock behaviour is assumed to behave elastically the interactions between the joint and the surrounding rock are described by a set of kinematic enhancements and internal equilibrium equations across the interface of the joint the formulation of the proposed model is presented along with its implementation algorithms and validation with experimental data the enhanced kinematics facilitates the incorporation of both behaviour and orientation of the joint together with the size and behaviour of the surrounding rock allowing capturing key characteristics of jointed rock mass responses under mixed mode loading conditions at different spatial scales

late local glacial maximum in the central altiplano triggered by cold and locally wet conditions during the paleolake tauca episode 17 15 ka heinrich 1 the timing and causes of the last deglaciation in the southern tropical andes is poorly known in the central altiplano recent studies have focused on whether this tropical highland was deglaciated before synchronously or after the global last glacial maximum 21 ka bp in this study we present a new chronology based on cosmogenic 3he 3he c dating of moraines on cerro tunupa a volcano that is located in the centre of the now vanished lake tauca 19 9 s 67 6 w these new 3he c ages suggest that the tunupa glaciers remained close to their maximum extent until 15 ka bp synchronous with the lake tauca highstand 17 15 ka bp glacial retreat and the demise of lake tauca seem to have occurred rapidly and synchronously within dating uncertainties at 15 ka bp we took advantage of the synchronism of these events to combine a glacier model with a lake model in order to reconstruct precipitation and temperature during the lake tauca highstand this new approach indicates that during the tauca highstand 17 15 ka bp the centre of the altiplano was characterized by temperature 6 5 c cooler and average precipitation higher by a factor ranging between 1 6 and 3 compared to the present cold and wet conditions thus persisted in a significant part of the southern tropical andes during the heinrich 1 event 17 15 ka bp this study also demonstrates the extent to which the snowline of glaciers can be affected by local climatic conditions and emphasizes that efforts to draw global climate inferences from glacial extents must also consider local moisture conditions

topographic control of asynchronous glacial advances a case study from annapurna nepal 1 differences in the timing of glacial advances which are commonly attributed to climatic changes can be due to variations in valley topography cosmogenic 10be dates from 24 glacial moraine boulders in 5 valleys define two age populations late glacial and early holocene moraine ages correlate with paleoglacier valley hypsometries moraines in valleys with lower maximum altitudes date to the late glacial whereas those in valleys with higher maximum altitudes are early holocene two valleys with similar equilibrium line altitudes elas but contrasting ages are 5 km apart and share the same aspect such that spatial differences in climate can be excluded a glacial mass balance cellular automata model of these two neighboring valleys predicts that change from a cooler drier to warmer wetter climate as at the holocene onset would lead to the glacier in the higher altitude catchment advancing while the lower one retreats or disappears even though the ela only shifted by 120 m

mass balance and equilibrium line altitudes of glaciers in high mountain environments abstract the mass balance characteristics of glaciers in high mountain environments complicate the relationship between glacier equilibrium line altitudes elas and climatic variables such as precipitation and air temperature therefore methods of ela reconstruction employed in low relief environments are commonly not applicable in high mountains or require some modification we review the concept of the ela with reference to the mass balance of a range of glacier types found in high mountain regions we examine the applicability of several commonly used methods of ela reconstruction for different glacier types and propose some general principles to guide the choice of appropriate methods

asynchronous glaciation at nanga parbat northwestern himalaya mountains pakistan we present a new glacial chronology demonstrating asynchroneity between advances of himalayan glaciers and northern hemisphere ice sheet volumes glaciers at nanga parbat expanded during the early to middle holocene ca 9 0 5 5 ka no major advances at nanga parbat during the last global glacial stage of marine oxygen isotope stage 2 mis 2 between 24 and 11 ka were identified preliminary evidence also indicates advances between ca 60 and 30 ka these periods of high ice volume coincide with warm wet regional climates dominated by a strong southwest asian summer monsoon the general lack of deposits dating from mis 2 suggests that nanga parbat was too arid to support expanded ice during this period of low monsoon intensity advances during warm wet periods are possible for the high altitude summer accumulation glaciers typical of the himalayas and explain asynchronous behavior however the holocene advances at nanga parbat appear to have been forced by an abrupt drop in temperature ca 8 4 8 0 ka and an increase in winter precipitation ca 7 5 5 ka these results highlight the overall sensitivity of himalayan glaciation to orbital forcing of monsoon intensity and on millennial or shorter time scales to changes in north atlantic circulation

cosmogenic nuclide constraints on late quaternary glacial chronology on the dalijia shan northeastern tibetan plateau abstract cosmogenic nuclide cn apparent exposure dating has become a widely used method for determining the age of glacial landforms on the tibetan plateau with 1200 published ages we present the first 10be exposure ages from the dalijia shan the most northeastern formerly glaciated mountain range on the tibetan plateau the moraine groups identified from field and remote sensing imagery mapping record four glacial events at 37 07 3 70 to 52 96 4 70 ka mis 3 20 17 1 79 to 26 99 2 47 ka mis 2 16 92 1 49 to 18 76 1 88 ka mis 2 and 11 56 1 03 to 11 89 1 06 ka younger dryas these ages indicate that glaciation in the northeastern tibetan plateau is much younger than previously thought in addition this record is consistent with many other regions on the tibetan plateau with a local last glacial maximum during mis 3 asynchronous with northern hemisphere last glacial maximum during mis 2 the dalijia shan might also include an event of younger dryas age but this needs to be tested in future studies

quaternary glacial history of nw garhwal central himalayas a first account of the quaternary glacial history is presented for northwest garhwal central himalaya on the basis of sediments and landforms one glacial stage has been recognised this is called the bhagirathi glacial stage when extensive valley glaciers advanced down the bhagirathi valley to jhala 40 5 km from the snout of gangotri glacier the ela depression during this stage was ca 640 m the bhagirathi glacial stage is constrained by optically stimulated luminescence dates of ca 63 ka and 5 ka bp and this glaciation is considered equivalent to the last glaciation elsewhere in the world the maximum extent of ice occurred ca 63 ka bp this however does not correlate with the last glacial maximum for the northern hemisphere ice sheets 20 18 ka bp a series of sharp crested moraines are present between 1 to 3 km beyond the snouts of most of the present glaciers these moraines formed during the mid holocene 5 ka bp termed here the shivling glacial advance small moraines are inset into these and are dated at about 200 to 300 bp the bhujbas glacial advance ca 300 to 200 bp and considered equivalent to the little ice age in other parts of the world ela depressions of between 40 100 m and 20 60 m occurred during the shivling and bhujbas glacial advances respectively since the bhujbas glacial advance there has been progressive retreat of glaciers initially by downwasting and retreat and then by simple retreat this retreat has accelerated during the last few decades impressive paraglacial fans are associated with deglaciation representing very rapid resedimentation during and soon after ice retreat

scaling factors for production rates of in situ produced cosmogenic nuclides a critical reevaluation abstract new scaling factors are presented describing the altitude and latitudinal dependence of production rates for in situ produced cosmogenic nuclides the new factors incorporate the influence of the non dipole contributions to the geomagnetic field on the cosmic ray flux the currently used scaling factors of lal earth planet sci lett 104 1991 424 439 are based on the assumption of a dipole field the overall strategy used in deriving the new scaling factors is however very similar to that of lal and relies on the same and or similar nuclear data in this reevaluation data are only used if the effective geomagnetic parameters inclination horizontal field strength can be reconstructed for the time of measurement the absorption free pathlengths for cosmic rays selected for this study are based on observational data at altitudes relevant for exposure age dating sea level to 7000 m at sea level and latitudes between 20 and 40 the new factors are up to 18 lower and at high altitudes more than 30 higher than those of lal in addition to accounting for the influence of the effective geomagnetic field and providing more applicable estimates of the new factors also allow for correction for the significant deviations from the standard pressure altitude relationship that exist in the atmosphere 10

timing of multiple late quaternary glaciations in the hunza valley karakoram mountains northern pakistan defined by cosmogenic radionuclide dating of moraines moraines and associated landforms in the upper hunza valley karakoram mountains northern pakistan provide an excellent record of multiple glaciations during the late quaternary glaciers advanced at least eight times by using 10 be and 26 al surface exposure dating on moraine boulders and scoured bedrock we determined the timing of glaciation for four of these glacial advances ca 54 7 43 2 ka borit jheel glacial stage ca 25 7 21 8 ka ghulkin i glacial stage ca 18 4 15 3 ka ghulkin ii glacial stage and ca 10 8 9 0 ka batura glacial stage for two of the older advances the yunz and shanoz glacial stages our data set a limit of 60 ka although at present the uncertainties in dating make it impossible to describe unequivocally the climate processes controlling glaciations in the hunza valley the results suggest that precipitation changes related to oscillations in the southwest asian monsoonal system combine with cooling that is broadly associated with heinrich events to cause glacial advances in this region

equilibrium line altitudes of the present and last glacial maximum in the eastern nepal himalayas and their implications for sw monsoon climate equilibrium line altitude ela of a glacier can be an adequate indicator for glaciation and local climate this study addresses the present ela in eastern nepal in comparison with that of the last glacial maximum lgm the present ela of each glacier was identified by its surface topography using the latest aerial photograph interpretations elas during the lgm were mostly estimated by the maximum elevation of lateral moraines melms the distinguished higher altitudes of the melm were selected to estimate the elas during the lgm latitudinal profiles of the present equilibrium line show southward gradients interpreted as a product of the reduction in precipitation from monsoon humid wind blowing into the high himalayas latitudinal ela profiles of the lgm show the same southward inclination suggesting that monsoon precipitation is likely to be a ruling resource on glacier nourishment the eastern nepal himalayas hence was under summer monsoon environment during the lgm same as present even if the sw monsoons were weaker

paleoglaciation of the tibetan plateau and surrounding mountains based on exposure ages and ela depression estimates the tibetan plateau holds an ample record of past glaciations and there is an extensive set of glacial deposits dated by exposure dating here a compilation is presented of 10be exposure ages from 485 glacial deposits with 1855 individual samples on the tibetan plateau and ela depression estimates for the glacial deposits based on a simple toe to headwall ratio approach to recalculate the tibetan plateau exposure ages 10be production rates from 24 calibration sites across the world are compiled and recalibrated yielding an updated global reference 10be production rate the recalculated exposure ages from the tibetan plateau glacial deposits are then divided into three groups based on exposure age clustering to discriminate good well clustered from poor scattered deglaciation ages a major part of the glacial deposits have exposure ages affected by prior or incomplete exposure complicating exposure age interpretations the well clustered deglaciation ages are primarily from mountain ranges along the margins of the tibetan plateau with a main peak between 10 and 30 ka indicating glacial advances during the global lgm a large number of deglaciation ages older than 30 ka indicates maximum glaciation predating the lgm but the exposure age scatter generally prohibits accurate definition of the glacial chronology the ela depression estimates scatter significantly but the main part is remarkably low average ela depressions of 337 197 m for the lgm and 494 280 m for the pre lgm indicate restricted glacier expansion

stochastic analysis of strength and deformability of fractured rocks using multi fracture system realizations this thesis presents a systematic numerical modeling framework to simulate the stress deformation and coupled stress deformation flow processes by performing uniaxial and biaxial compressive tests on fractured rock models with considering the effects of different loading conditions different loading directions anisotropy and coupled hydro mechanical processes for evaluating strength and deformability behavior of fractured rocks by using code udec of discrete element method dem a series of numerical experiments were conducted on discrete fracture network models dfn at an established representative elementary volume rev based on realistic geometrical and mechanical data of fracture systems from field mapping at sellafield uk the results were used to estimate the equivalent young s modulus and poisson s ratio and to fit the mohr coulomb and hoek brown failure criteria represented by equivalent material properties defining these two criteria the results demonstrate that strength and deformation parameters of fractured rocks are dependent on confining pressures loading directions water pressure and mechanical and hydraulic boundary conditions fractured rocks behave nonlinearly represented by their elasto plastic behavior with a strain hardening trend fluid flow analysis in fractured rocks under hydro mechanical loading conditions show an important impact of water pressure on the strength and deformability parameters of fractured rocks due to the effective stress phenomenon but the values of stress and strength reduction may or may not equal to the magnitude of water pressure due to the influence of fracture system complexity stochastic analysis indicates that the strength and deformation properties of fractured rocks have ranges of values instead of fixed values hence such analyses should be considered especially in cases where there is significant scatter in the rock and fracture parameters these scientific achievements can improve our understanding of fractured rocks hydro mechanical behavior and are useful for the design of large scale in situ experiments with large volumes of fractured rocks considering coupled stress deformation flow processes in engineering practice

cosmogenic 3he in himalayan garnets indicating an altitude dependence of the 3he 10be production ratio to investigate the potential of using cosmogenic helium in garnet as a dating tool 3hec and 10bec have been measured within garnets and coexisting quartz respectively sampled in the himalayan range at various elevations comparison and correlation of 3hec and 10bec concentrations demonstrate that cosmogenic 3he is well retained in himalayan garnets and can thus be used in this mineral to quantify precisely earth s surface processes this in the case of recently cooled orogenic samples which contain limited amounts of non cosmogenic helium for these high elevation samples the exposure ages derived from 3hec using classical scaling factors lead however to an overestimation of 3hec ages compared to 10bec ages 0 1 to 28 ky by up to a factor of 2 additionally over the samples altitude range 3000 4622 m the theoretically invariant polar 3hec 10bec production ratio 22 5 increases with increasing elevation challenging classical models of production rate evolution to explain this observation we propose a new 3hec production mechanism based on the altitudinal dependence of the energy spectrum of cosmic rays and according to which neutrons or protons resulting from a first spallation reaction within the rock tertiary particles may have sufficient energy to induce an additional in situ spallation reaction producing a second 3h or 3he but insufficient energy to produce 10be the probability of such a mechanism increasing with altitude according to these observations we propose for future and ongoing studies to use the empirically determined attenuation length of 121 g cm2 for helium production at high altitude

the younger dryas cold interval as viewed from central greenland abstract greenland ice core records provide an exceptionally clear picture of many aspects of abrupt climate changes and particularly of those associated with the younger dryas event as reviewed here well preserved annual layers can be counted confidently with only 1 errors for the age of the end of the younger dryas 11 500 years before present ice flow corrections allow reconstruction of snow accumulation rates over tens of thousands of years with little additional uncertainty glaciochemical and particulate data record atmospheric loading changes with little uncertainty introduced by changes in snow accumulation confident paleothermometry is provided by site specific calibrations using ice isotopic ratios borehole temperatures and gas isotopic ratios near simultaneous changes in ice core paleoclimatic indicators of local regional and more widespread climate conditions demonstrate that much of the earth experienced abrupt climate changes synchronous with greenland within thirty years or less post younger dryas changes have not duplicated the size extent and rapidity of these paleoclimatic changes

seismites in the kathmandu basin and seismic hazard in central himalaya soft sediment deformation structures have been analyzed at six sites of the kathmandu valley microgranulometric study reveals that silty levels 60 to 80 silt favor the development of soft sediment deformation structures while sandy levels 60 to 80 sand are passively deformed nonetheless well sorted sand levels more than 80 sand generate over fluid pressure during compaction if located beneath a silty cap leading to fluidization and dike development 3 d geometry of seismites indicates a very strong horizontal shearing during their development using a physical approach based on soil liquefaction during horizontal acceleration we show that the fluidization zone progressively grows down section during the shaking but does not exactly begin at the surface the comparison of bed thickness and strength depth evolution indicates three cases i no soft sediment deformation occurs for thin few centimeters silty beds ii the thickness of soft sediment deformation above sandy beds is controlled by the lithological contrast iii the thickness of soft sediment deformation depends on the shaking intensity for very thick silty beds these 3 cases are evidenced in the kathmandu basin we use the 30 cm thick soft sediment deformation level formed during the 1833 earthquake as a reference the 1833 earthquake rupture zone extended very close to kathmandu inducing there mmi ix x damages a 90 cm thick sediment deformation has therefore to be induced by an event greater than mmi x from a compilation of paleo and historic seismology studies it is found that the great m 8 1 historical earthquakes are not characteristic of the greatest earthquakes of himalaya hence earthquakes greater than m 8 6 occurred kathmandu is located above one of the asperities that laterally limits the extent of mega earthquake ruptures and two successive catastrophic events already affected kathmandu in 1255 located to the west of this asperity and in 1100 to the east

pattern of holocene glaciation in the monsoon dominated kosa valley central himalaya uttarakhand india abstract reconstruction based on the geomorphology lateral moraine stratigraphy and limited optical chronology indicate that the monsoon dominated kosa valley experienced four glacial advances during the late glacial to late holocene the oldest and most extensive glaciation which is termed as raj bank stage 1 rbs 1 is represented by the degraded moraine ridge this glaciation remains undated however the chronology of outwash terrace gravel dated to 12 7 1 3 ka indicates that the rbs 1 probably represents the last glacial maximum lgm the second glacial advance rbs 2 is preserved as a curvilinear lateral moraine and is dated to 6 1 0 4 ka the third glacial advance viz rbs 3 is bracketed between 5 0 0 5 and 4 0 0 4 ka following this the glacier receded in pulses that are represented by two distinct recessional moraines rbs 3a and b the forth glacial stage rbs 4 which is dated between 2 2 0 2 and 1 6 0 2 ka shows a pulsating recession and is represented by a prominent recessional moraine rbs 4a whereas presence of unconsolidated poorly defined moraine mounds proximal to the glacier snout are ascribed as neoglacial advance corresponding to the little ice age lia with the limited chronometric data we speculated that the glaciation was driven during the weak to moderate indian summer monsoon ism aided by lowered temperature presence of recessional moraines associated with mid holocene glacial phase indicate that the monsoon dominated glaciers respond sensitively to minor sub millennial scale changes in temperature and precipitation conditions the observations are broadly in accordance with the studies carried out in other monsoon dominated valleys in the central himalaya implying that in ism dominated regions lowered temperature seems to be the major driver of glaciations during the late glacial to late holocene

comprehensive characterization and clustering of orientation data a case study from the songta dam site china abstract the quantitative description of orientation data in rock masses is fundamental for understanding the engineering geological properties of rock masses however the features of joint orientation distributions are still not easy to describe in practical projects orientation data are randomly distributed in a rock mass and its poles are also randomly distributed on a stereonet the delineation of orientation data on the stereonet is difficult but the density of poles on the stereonet indicates some characteristics of joint geometric patterns which will influence the mechanical and hydraulic properties of rock masses considering the nonlinear distribution of poles density fractal geometry is introduced to describe the orientation data in this study accordingly a framework combining the idea of fractal geometry graphic display and the schmidt upper hemisphere equal area projection plot is proposed for comprehensive characterization of orientation data the monofractal and multifractal descriptions have been used to delineate the orientation data and a fractal indicator is proposed for the dispersion of orientation data in addition the identification and delineation of joint sets with similar orientations are discussed and the optimal method is recommended finally the methods proposed in this study were further applied to a real data set collected from a survey at the dam site of the songta hydropower station china

timing and extent of late quaternary glaciation in the western himalaya constrained by 10be moraine dating in garhwal india glacial chronologies from the himalayan region indicate various degrees of asynchronous glacial behavior part of this has been related to different sensitivities of glaciers situated in contrasting climatic compartments of the orogen but so far field data in support for this hypothesis is lacking here we present a new 10 be derived glacial chronology for the upper tons valley in western garhwal india and initial results for the pin and thangi valleys in eastern himachal pradesh these areas cover a steep gradient in orographic precipitation and allow testing for different climatic sensitivities our data provide a record of five glacial episodes at w16 ka w11 12 ka w8 9 ka w5 ka and 1 ka in the thangi valley our results indicate a glacial episode at w19 ka but no data are available for younger glacial deposits in this valley at their largest mapped extent w16 ka the two main glaciers in the upper tons valley joined and descended down to w2500 m asl which represents a drop of w1400 m compared to the present day glacial extent during the holocene the two largest glaciers produced distinct glacial landforms that allowed us to reconstruct changes in the equilibrium line altitude ela over w20 km north south distance that is presently associated with a steep gradient in rainfall we observe that ela changes have been consistently w2 times higher for the glacier located in a presently wetter climate pointing at different climate sensitivities related to the amount of precipitation that they receive at regional scale our data is in reasonable agreement with other published glacial chronologies from the western himalaya and suggest that glacial advances during the holocene have been largely synchronous in this region comparison of glacial chronologies from the western himalaya with other palaeoclimatic proxy data suggests that long term changes in glacial extents are controlled by glacial interglacial temperature oscillations related to the waxing and waning of the large northern hemisphere ice sheets while the timing of millennial scale advance and retreat cycles are more directly related to monsoon strength

estimates of holocene precipitation for rajasthan india based on pollen and lake level data abstract a pollen profile obtained from lake sediments at lunkaransar rajasthan in northwest india was used along with a pollen climate calibration function to estimate past precipitation between 10 500 and 3500 yr b p the estimated precipitation was about 500 mm yr or about 200 mm yr above the modern value a model was used for the energy and hydrologic budget of a lake basin and lake at sambhar located 240 km se of lunkaransar to calculate that a 200 mm yr increase in rainfall above the modern amount would have raised the lake level about 20 m above the modern level topographic charts and satellite imagery provided some evidence in support of an enlarged paleolake of that elevation but field exploration would be required to confirm the size and date of a former lake after about 3500 yr b p the lunkaransar profile indicated a desiccated lake bed because no pollen was preserved the pollen climate calibration function was of no use for estimating the amount of the precipitation decline a reduction of precipitation of about 200 mm yr below the modern amount was estimated from the energy and hydrologic budget for paleolake sambhar by assuming that the lake was one tenth of its present size during the dry interval

examination of surface exposure ages of antarctic moraines using in situ produced 10be and 26al concentrations of 10be t12 1 5 106 y and 26a1 t12 0 72 106 y have been determined by accelerator mass spectrometry ams in a suite of quartz samples taken from sandstone boulders in several moraines in arena valley a dry valley adjacent to the taylor glacier in the quatermain mountains southern victoria land east antarctica these isotopes are produced in surficial quartz by cosmic ray spallation of o and si the concentrations in these samples ranged from 6 1 105 to 3 0 107 at g 1 for 10be and from 9 4 106 to 1 2 108 at g 1 for 26a1 depending upon the extent of exposure at the surface analyses of 10be in several samples from a single moraine at altitudes ranging from 1300 to 1650 m permitted an estimation of the air attenuation pathlength of cosmic ray neutrons the value of 142 96 41 g cm 2 is consistent with other published values production rates of 17 6 4 at g 1 y 1 for 10be and 113 54 16 at g 1 y 1 for 26a1 at 1300 m and 87 s and a 26al 10be production ratio of 6 5 1 3 1 3 were calculated from the data these values correspond to sea level production rates at high geomagnetic latitude of 6 4 at g 1 y 1 and 41 7 at g 1 y 1 for 10be and 26a1 respectively consistent with determinations based on 11 ky glacially polished surfaces in the sierra nevada in california these production rates imply exposure ages for the various moraines ranging from 50 ky to 2 5 my in accordance with other geological evidence the 10be and 26al ages of these rocks compare favorably with those found using a similar dating method based on in situ production of 3he examination of the 3he concentrations in conjunction with the present data set yields an estimate of 3he production of 230 8540 at g 1 y 1 corresponding to 85 31 15 at g 1 y 1 at sea level this is lower than previously reported values of 240 60 at g 1 y 1 and 190 at g 1 y 1 scaled to sea level and high geomagnetic latitude based respectively on volcanic flows less than 2000 years old at low latitude and samples collected from 14 400 year old volcanic flows this discrepancy is likely due to diffusive losses which may become significant up to 50 for surface exposure ages on the order of 2 0 my nevertheless the general correlations among the three isotopes suggest that 3he does not suffer gross losses through diffusion

nature and timing of quaternary glaciation in the himalayan tibetan orogen abstract much effort has been made in recent years to define the timing and extent of quaternary glaciation throughout the himalayan tibetan orogen these studies are challenging because of the logistical and political inaccessibility of the region and the inherent problems associated with the application of numerical dating techniques nevertheless the studies are providing abundant evidence for significant glacial advances throughout the last several glacial cycles and are beginning to accurately define the extent and timing of glaciation in selected regions studies are showing that himalayan tibetan glaciers in arid regions during the last glacial cycle reached their maximum extent early in the cycle and that global last glacial maximum glacier advances were significantly less extensive however along the more monsoonal influenced greater himalaya there is increasing evidence to suggest that glaciation was more extensive later in the last glacial cycle but this has yet to be fully assessed in addition the new studies are showing that throughout most himalayan tibetan regions significant glacier advances occurred during the lateglacial and early holocene with minor advances in some regions during the mid holocene the still relatively poor chronological control in the himalayan tibetan orogen however makes it difficult to construct correlations across the region and with regions elsewhere in the world this in turn makes it hard to assess the relative importance of the different climatic mechanisms that force glaciation across the himalayan tibetan orogen and to quantify paleoclimate change in this high altitude subtropical region the lateglacial and holocene glacial records however are particularly well preserved in several himalayan tibetan regions glacial successions such as these have the greatest potential to be examined in detail using newly developing numerical dating and geomorphic and sedimentologic methods to derive high resolution terrestrial records of glaciation that will help in paleoclimatic reconstruction for high altitude subtropical regions

himalayan glacial sedimentary environments a framework for reconstructing and dating the former extent of glaciers in high mountains abstract reconstructing paleoenvironmental change from glacial geologic evidence in the himalayas has been difficult because of the lack of organic material for radiocarbon dating and the problems of correctly identifying the origin of highly dissected landforms studies of the contemporary glacial depositional environments and ancient landforms and sediments in the hunza valley karakoram mountains the lahul and garhwal himalaya and the khumbu himalaya illustrate the variability in processes landforms and sediment types these studies can be used to interpret ancient landforms and sediments for paleoenvironmental reconstructions and aid in forming strategies for sampling sediments and rocks for the developing techniques of cosmogenic radionuclide crn surface exposure and optically stimulated luminescence osl dating many himalayan glaciers have thick covers of supraglacial debris derived from valley sides and such debris mantled glaciers exhibit important differences from clean glaciers both in terms of debris transport processes and the depositional landforms that they produce analysis of sediment landform associations can be used to reconstruct processes of sediment transport and deposition and the relationship between moraines and other landforms and climatic forcing cycles such analysis is of fundamental importance in guiding sampling and interpretation in crn and osl dating work

production of 3he in crustal rocks by cosmogenic thermal neutrons accurate determination of cosmogenic 3he concentrations in minerals has to account for nucleogenic 3he produced from the reaction of thermalized neutrons with 6li thermal neutrons from the cosmic ray cascade are typically not considered however in exposed basalts and granites the flux of cosmogenic thermal neutrons ctn is generally 10 200 times higher than the thermal neutron flux produced by n reactions in the rock with the absolute values dependent on composition and geographic location the reaction of ctn with li can account for 5 50 of the cosmogenic 3he in minerals in typical granitiod rocks depending on the li content and distribution and petrography of the rock and may be considerably higher in special cases in basalts this contribution is usually lower 1 5 6 but may still warrant consideration the strong depth dependence of ctn produced 3he in rock may be used to assess erosion of landforms similar to ctn produced 36cl however as 3he is stable it has the potential to extend the useful time range to older surfaces

deglaciation and landscape history around annapurna nepal based on 10be surface exposure dating abstract the high himalaya is a key area for tectonic geomorphological and climate studies because of its extreme relief and location at the transition zone between areas with abundant monsoonal precipitation and the arid semiarid tibetan plateau we present 10be surface exposure ages on 22 boulders from the annapurna area in nepal the ages improve understanding of the late quaternary landscape history and the geomorphological processes operating in this part of the himalaya although our study is reconnaissance in nature it highlights the importance of catastrophic events such as landslides and debris flows for denudation of high mountains holocene exposure ages for the dhampu chooya landslide 4 1 0 6 ka and for 600 m of alluviation in kali gandaki valley 2 1 0 6 ka for example indicate the frequent occurrence and extent of catastrophic events and their implications for natural hazards we also offer an explanation for the differences in late quaternary glacial chronologies at closely spaced study sites in the nepal himalaya topographically controlled and spatially variable precipitation in the himalaya determines the sensitivity of glaciers to changes in temperature and precipitation accordingly some glaciers advanced in phase with northern hemisphere ice sheets whereas others reached their maximum extent at times of increased monsoonal precipitation during marine isotope stage 3 and the early holocene

climate at the equilibrium line of glaciers the relationships between temperature precipitation and radiation on glacier equilibrium lines are investigated using 70 glaciers for which the mass balance and meteorological observations have been carried out for sufficiently long periods it is found that the characteristic climate at glacier equilibrium lines can be described using the summer 3 months temperature in a free atmosphere annual total precipitation and the sum of global and long wave net radiation all of these are measured at or very near the equilibrium line altitudes then it is shown how the shift of the equilibriumline will occur as a result of a climatic change finally the effect of the shift of the equilibrium line on the annualmean specific mass balance is analytically derived and compared with observations the present results make it possible to identify the altitudes in climate models where glacierization should begin and to evaluate the mass balance changes as a result of possible future changes in the climate

chronology of late quaternary glaciation and landform evolution in the upper dhauliganga valley trans himalaya uttarakhand india abstract detailed field mapping of glacial and paraglacial landforms supported by optical and radiocarbon dating is used to reconstruct the history of late quaternary glaciation and landform evolution in the trans himalayan region of the upper dhauliganga valley the study identifies four events of glaciations with decreasing magnitude which are termed as purvi kamet stage ia pks ia pks ib pks ii pks iii and pks iv respectively the oldest pks ia and ib are assigned the marine isotopic stgae 3 mis 3 the pks ii to the last glacial maximum mis 2 pks iii dated to 7 9 0 7 ka and the pks iv is dated to 3 4 0 3 ka and 1 9 0 2 ka respectively the largest valley glaciations viz the pks ia occurred during the strengthened summer monsoon corresponding to the mis 3 following this the recessional moraines pks ib represent the gradual decline in summer monsoon towards the later part of mis 3 the valley responded to the global last glacial maximum lgm which is represented by the pks ii moraine implying the influence of strengthened mid latitude westerlies during the lgm the post lgm deglaciation was associated with the onset of summer monsoon and is represented by the deposition of four distinct outwash gravel terraces the early holocene pks iii glaciation occurred around 7 9 0 7 ka and broadly coincides with the early holocene cooling event 8 2 ka this was followed by the deposition of stratified scree deposits and the alluvial fan between 5 5 ka and 3 ka during the mid to late holocene aridity this was followed by marginal re advancement of the valley glacier viz pks iv during the late holocene cool and moist climate although glaciers respond to a combination of temperature and precipitation changes however during the holocene it seems that temperature played a major role in driving the glaciation

climate change vegetation history and landscape responses on the tibetan plateau during the holocene a comprehensive review abstract numerous studies of changes in the climate vegetation and landscape responses of the tibetan plateau tp during the holocene have been published in recent decades however several conflicting interpretations are evident within these studies and a comprehensive review of the topic is needed to reconcile them and thus to provide an improved understanding of the history and forcing mechanisms of holocene environmental changes within the region here we review the evidence for changes in climate temperature precipitation moisture vegetation and landscape attributes glacier and eolian activity on the tp during the holocene our main conclusions are as follows 1 the patterns of holocene mean annual temperature change on the tp remain controversial however an early to middle holocene summer temperature maximum is evident which coincided with high summer insolation and a strengthening of the indian summer monsoon ism this suggests that the summer land sea thermal gradient impacted by the temperature of the tp may be an important factor driving orbital scale ism changes 2 lake level records indicate an optimum in moisture conditions on the southwestern sw tp in the early holocene while on the northeastern ne tp the optimum occurred in the middle to late holocene this out of phase or anti phased relationship may be linked to the role of the ism in dominating precipitation on the sw tp while the westerlies and east asian summer monsoon dominated the precipitation on the ne tp 3 most of the lake sediment based stable isotope records 18o and leaf wax d exhibit a pattern similar to that of stalagmite 18o records from monsoonal asia reflecting the dominance of large scale patterns of atmospheric circulation rather than localized moisture changes reflected by lake level records 4 a synthesis of pollen records reveals that the extent of forest was maximal in the mid holocene while from the early holocene onwards alpine steppe shrunk and alpine meadow and desert gradually expanded 5 evidence of glacier advance increased slightly during the early holocene decreased during the mid holocene and then increased substantially after 3 ka bp 6 the integrated ages of eolian sand and loess from the ne tp reveal that eolian activity intensified during the early and late holocene site inter comparisons reveal that regional climate change played a major role in modulating changes in vegetation and other landscape attributes overall producing holocene climate reconstructions for the entire tp remains a major challenge even though much progress has been made further improvements in terms of the spatial coverage of high resolution paleoclimatic records with robust chronological control and a deeper understanding of the specific climatic significance of several climatic proxies will facilitate an improved understanding of how the monsoon and the westerlies interacted and their impacts on vegetation and landscape changes on the tp

fluvial incision and tectonic uplift across the himalayas of central nepal the pattern of fluvial incision across the himalayas of central nepal is estimated from the distribution of holocene and pleistocene terraces and from the geometry of modern channels along major rivers draining across the range the terraces provide good constraints on incision rates across the himalayan frontal folds sub himalaya or siwaliks hills where rivers are forced to cut down into rising anticlines and have abandoned numerous strath terraces farther north and upstream in the lesser himalaya prominent fill terraces were deposited probably during the late pleistocene and were subsequently incised the amount of bedrock incision beneath the fill deposits is generally small suggesting a slow rate of fluvial incision in the lesser himalaya the terrace record is lost in the high range where the rivers are cutting steep gorges to complement the terrace study fluvial incision was also estimated from the modern channel geometries using an estimate of the shear stress exerted by the flowing water at the bottom of the channel as a proxy for river incision rate this approach allows quantification of the effect of variations in channel slope width and discharge on the incision rate of a river the determination of incision rates requires an additional lithological calibration the two approaches are shown to yield consistent results when applied to the same reach or if incision profiles along nearby parallel reaches are compared in the sub himalaya river incision is rapid with values up to 10 15 mm yr it does not exceed a few millimeters per year in the lesser himalaya and rises abruptly at the front of the high range to reach values of 4 8 mm yr within a 50 km wide zone that coincides with the position of the highest himalayan peaks sediment yield derived from the measurement of suspended load in himalayan rivers suggests that fluvial incision drives hillslope denudation of the landscape at the scale of the whole range the observed pattern of erosion is found to closely mimic uplift as predicted by a mechanical model taking into account erosion and slip along the flat ramp flat geometry of the main himalayan thrust fault the morphology of the range reflects a dynamic equilibrium between present day tectonics and surface processes the sharp relief together with the high uplift rates in the higher himalaya reflects thrusting over the midcrustal ramp rather than the isostatic response to reincision of the tibetan plateau driven by late cenozoic climate change or late miocene reactivation of the main central thrust

diatom biostratigraphy of tsunami deposits examples from the 1998 papua new guinea tsunami abstract distinctive diatom assemblages may be associated with tsunami sediments and may often contrast with the assemblages found within sediments underlying the tsunami deposit as well as those associated with the modern coastal environment sediments associated with the 1998 tsunami that destroyed much of the sissano lagoon area in northern papua new guinea have been investigated surface sediments from three transects across the sediment spit near warapu have been examined for diatom content and preservation the preservation is variable and the data show an often chaotic assemblage that can be attributed to the tsunami waves incorporating and depositing diatoms from distinctive habitat zones during their runup and subsequent backwash the diatoms identified within the warapu sediments indicate an origin from within the inter tidal and offshore area rather than from the beach sand spit complex the sand deposits disclose a high percentage in excess of 75 of broken diatom valves and a predominance of centric circular species due to preferential preservation the study demonstrates that the application of diatom biostratigraphy to modern tsunami deposits can be used in conjunction with other stratigraphical lines of evidence to interpret the source and provenance of historical and palaeo tsunami deposits

time dependent behavior of rock joints considering asperity degradation abstract the time dependent behavior of rock joints specifically creep and stress relaxation govern the long term stability of underground structures but have not been fully understood the effect of asperity degradation on the time dependent behavior of rock joints is investigated in this test triangular synthetic rock joints with four asperity angles 0 10 30 and 45 are tested for creep and stress relaxation it is revealed that the failure mode of a rock joint during creep and stress relaxation shifts from surface sliding 0 to a combination of surface sliding and asperity crushing 10 asperity crushing becomes more severe as increases consequently a rougher rock joint with higher exhibits higher creep and stress relaxation rates due to more asperity crushing for each the creep and stress relaxation rates both increase exponentially with increasing shear stress before the stable long term strength is reached suggesting a higher degree of asperity degradation as shear resistance mobilizes semi empirical correlations are proposed to quantify the effects of asperity angles on creep and stress relaxation of rock joints at various shear stresses

timing and climatic drivers for glaciation across monsoon influenced regions of the himalayan tibetan orogen abstract mapping and thirty eight 10 be terrestrial cosmogenic nuclide tcn ages help define the timing of glaciation in the monsoon influenced greater himalaya in central garwhal india glacial landforms in central garwhal are present only within a few kilometers of the present glaciers and all date to less than 12 5 ka this suggests that the lateglacial and or holocene glacial advances were more extensive than their predecessors and hence destroyed or buried evidence for earlier glaciation or that other processes such as intensive fluvial erosion and or hillslope mass movements have destroyed evidence of earlier glaciation prominent laterofrontal moraines date to the lateglacial the early holocene and the neoglaciation moraines next to the active ice and boulders on contemporary glaciers date to 10 1 10 2 years before present this suggests only a minor glacial advance during the little ice age occurred in central garhwal these young ages indicate that inheritance of tcns in areas that were recently glaciated is very small and likely has little effect when considering tcn ages on moraines older than the global last glacial maximum the new 10 be ages are combined with 1081 recalculated 10 be ages from previous studies to develop a regional framework of glaciation across the monsoon influenced and adjacent regions of the himalayan tibetan orogen we separate what appears to be continuous glaciation into 27 regional glacial stages plus 2 tentative glacial stages that are termed monsoonal himalayan tibetan stages mohits the regional glacial stages cover a wide chronologic range that includes five regional glacial stages older than the last glacial cycle mohits 13 at 483 38 ka to mohits 5e at 122 15 ka thirteen regional glacial stages within the last glacial cycle mohits 5b at 91 15 ka to mohits 2a at 12 9 0 9 ka and eleven regional glacial stages during the holocene mohits 1k at 11 4 0 7 ka to mohits 1a at 0 4 0 1 ka there are strong correlations both with periods of strong monsoons and northern hemisphere events throughout the entire chronologic range with 16 stages linked to the monsoon 11 stages linked to the mid latitude westerlies and two unassigned because of large age uncertainties overall we see a complex pattern of glaciation influenced by two climatic systems throughout the mid late quaternary

high resolution holocene environmental changes in the thar desert northwestern india sediments from lunkaransar dry lake in northwestern india reveal regional water table and lake level fluctuations over decades to centuries during the holocene that are attributed to changes in the southwestern indian monsoon rains the lake levels were very shallow and fluctuated often in the early holocene and then rose abruptly around 6300 carbon 14 years before the present 14c yr b p the lake completely desiccated around 4800 14c yr b p the end of this 1500 year wet period coincided with a period of intense dune destabilization the major harrapan indus civilization began and flourished in this region 1000 years after desiccation of the lake during arid climate and was not synchronous with the lacustral phase

holocene glacier fluctuations a global overview of glacier advances and retreats grouped by regions and by millennia for the holocene is compiled from previous studies the reconstructions of glacier fluctuations are based on 1 mapping and dating moraines defined by 14 c tcn osl lichenometry and tree rings discontinuous records time series and 2 sediments from proglacial lakes and speleothems continuous records time series using 189 continuous and discontinuous time series the long term trends and centennial fluctuations of glaciers were compared to trends in the recession of northern and mountain tree lines and with orbital solar and volcanic studies to examine the likely forcing factors that drove the changes recorded a general trend of increasing glacier size from the earlyemid holocene to the late holocene in the extra tropical areas of the northern hemisphere nh is related to overall summer temperature forced by orbitally controlled insolation the glaciers in new zealand and in the tropical andes also appear to follow the orbital trend i e they were decreasing from the early holocene to the present in contrast glacier fluctuations in some monsoonal areas of asia and southern south america generally did not follow the orbital trends but fluctuated at a higher frequency possibly triggered by distinct teleconnections patterns during the neoglacial advances clustered at 4 4e4 2 ka 3 8e3 4 ka 3 3e2 8 ka 2 6 ka 2 3e2 1 ka 1 5e1 4 ka 1 2e1 0 ka 0 7e0 5 ka corresponding to general cooling periods in the north atlantic some of these episodes coincide with multidecadal periods of low solar activity but it is unclear what mechanism might link small changes in irradiance to widespread glacier fluctuations explosive volcanism may have played a role in some periods of glacier advances such as around 1 7e1 6 ka coinciding with the taupo volcanic eruption at 232 5 ce but the record of explosive volcanism is poorly known through the holocene the compilation of ages suggests that there is no single mechanism driving glacier fluctuations on a global scale multidecadal variations of solar and volcanic activity supported by positive feedbacks in the climate system may have played a critical role in holocene glaciation but further research on such linkages is needed the rate and the global character of glacier retreat in the 20th through early 21st centuries appears unusual in the context of holocene glaciation though the retreating glaciers in most parts of the northern hemisphere are still larger today than they were in the early and or mid holocene the current retreat

accuracy of cosmogenic ages for moraines analyses of all published cosmogenic exposure ages for moraine boulders show an average age range of 38 between the oldest and youngest boulders from each moraine this range conflicts with the common assumption that ages of surface boulders are the same as the age of the landform the wide spread in boulder ages is caused by erosion of the moraine surface and consequent exhumation of fresh boulders a diffusion model of surface degradation explains the age range and shows that a randomly sampled small set of boulders n 3 7 will always yield a lower age limit for the moraine the model indicates that for identical dating accuracy six to seven boulders are needed from old and tall moraines 40 000 100 000 yr 50 100 m initial height but only one to four boulders from small moraines 20 000 100 000 yr 10 20 m by following these guidelines the oldest obtained boulder age will be 90 of the moraine age 95 probability this result is only weakly sensitive to a broad range of soil erosion rates our analysis of published boulder ages indicates that 3 of all moraine boulders have prior exposure and 85 of these boulders predate the dated moraine

scale effect on the shear behaviour of rock joints based on a numerical study abstract a large number of studies have been carried out to investigate the effect of scale on the shear behaviour of rock joints however the nature of scale dependency of rock joints is still unknown and remains an ongoing debate this paper investigates the effect of joint length on the shear behaviour of rough rock joints using pfc2d in this numerical approach the intact material is simulated by a dense packing of bonded particles and the joint is represented by micro scale slip surfaces at contacts between particles the validity of this numerical approach in reproducing the shear behaviour of rock joints has been studied in previous studies of authors against the physical experiments analytical and empirical models in this study numerical direct shear tests on a natural tensile joint and subdivided joints were carried out and the shear behaviour of these joints at different scale was investigated results of this study show that as the joint length increases the peak shear strength peak dilation rate and shear stiffness decrease while the peak shear displacement increases in order to find out the reason of observed scale dependency the mechanism of asperity degradation at different scales was investigated and it was found that the mobilisation of different sized asperities at different scales resulted in the observed scale effect

c4 plants decline in the himalayan basin since the last glacial maximum abstract the bengal fan turbiditic system supplied by the ganga brahmaputra river system provides an integrated record of himalayan system erosion thanks to minor inputs of marine organic matter and almost complete preservation of riverine organic carbon organic matter buried in bengal fan sediments is a proxy of himalayan basin paleo vegetation the active channel levee system of the middle fan documents the last 19 ka and allows the reconstruction of vegetation change in the himalayan basin since the last glacial maximum lgm we measured 13 c of organic carbon c org in order to track changes in the proportions of c3 and c4 plants in the himalayan basin from lgm to mid holocene 13 c of bulk c org shifts of 3 4 towards more negative values relative abundance of individual n alkanes reveals that terrestrial higher plant inputs represent a dominant fraction of c org buried in bengal fan sediments 13 c of higher plants biomarkers mimic that of bulk c org showing that the later can be used as continental paleo vegetation proxy 13 c negative shift from lgm to mid holocene mostly indicates the transition from a dominant input of c4 plants to a dominant input of c3 plants and therefore reveals that c4 plants were more abundant in the basin under glacial conditions vegetation repartition in the basin simulated using the caraib dynamic vegetation model is consistent with c org data the model indicates a dominance of c4 plants in the gangetic plain during the lgm while eastern part of the basin remains dominated by c3 plants the comparison between our data and proxies of regional paleo climate suggests that the large decline of c4 plants after the lgm was due to combined increase of atmospheric co 2 and humidity levels integrated record of himalayan basin paleo vegetation suggests more arid conditions during the lgm than during the mid holocene and agrees with reconstructions of the monsoon indicating stronger sw monsoon during interglacial and stronger ne monsoon during glacial periods

empirical methods to estimate the strength of jointed rock masses abstract the ultimate strength and deformation of jointed rock mass are important parameters that designers look for in selecting sites for foundations of civil and mining engineering structures in rocks in the field it is extremely difficult to stress a rock mass to its ultimate failure stress consequently the field tests are performed up to a certain predefined stress level it is shown in this study that the results of these tests can be used to arrive at the ultimate strength of the rock mass a large number of uniaxial compressive strength ucs tests were conducted on the specimens of jointed block mass having various combinations of orientations and different levels of interlocking of joints four dominating modes of failure were observed the strength and the tangent elastic modulus values of the mass for a specific failure mode when plotted on the deere miller classification chart are found to follow an empirical straight line indicating strong correlation between them using the gradient of this empirical line correlations have thus been suggested to assess the ultimate strength of the jointed rock mass the findings of the study have been verified by applying it to estimate the ultimate rock mass strength of nine rock types from few dam sites in the lower himalayas the ultimate strength obtained by the present methodology is compared with that obtained through the q classification system it is concluded that reasonably good estimates on field strength of jointed rocks are possible by using the correlations suggested in this study

evaluation of existing criteria in estimating shear strength of natural rock discontinuities abstract as evident from the literature there are a number of shear strength criteria proposed by different researchers in spite of that barton s jrc jcs model is probably the most widely used criterion in routine engineering environments ease of determining the input parameters and efficiency in estimating the shear strength are the two key aspects which make this criterion widespread in rock engineering activities when the shear strength criteria existing in the literature had been analyzed by the authors it became apparent that the difficulty levels or eases involved in determining the input parameters of eleven criteria including barton s criterion are broadly comparable however the existing criteria do not seem to have been compared in terms of their practicality applicability while estimating shear strength of real natural rock discontinuities in the present investigation a total of 196 direct shear tests were performed on natural discontinuities of three distinct rock types i e granite quartzite and sandstone from india at normal stresses within a range of 0 22 2 01 mpa the estimated shear strengths were compared to the determined shear strengths the efficacies of the eleven shortlisted criteria in estimating shear strength of real natural rock discontinuities were critically evaluated the criteria emerged to be the most efficient in this regard were highlighted and plausible reasons behind all the findings of this study were also explained

monsoonal forcing of holocene glacier fluctuations in ganesh himal central nepal constrained by cosmogenic 3he exposure ages of garnets abstract in the himalayas the late pleistocene glacier oscillations have produced spectacular glacial landforms detailed reconstructions of the chronology and extent of these oscillations are essential to document the sensitivity of the himalayan glaciers to past and future climatic changes in this paper we present a new cosmogenic helium 3 3hec dating on garnets that were sampled on moraine blocks and ice scoured surfaces in a small glaciated valley of the central nepal the mailun valley and that provided a detailed chronology of himalayan glacier fluctuations during the holocene soon after the younger dryas the glacier of the mailun valley underwent a significant retreat around 10 ka this retreat was followed by relative stability of the extent of the glacier between 8 5 and 7 5 ka a second phase of rapid retreat occurred at 7 ka but rapidly slowed down at 5 6 ka finally a last phase of re advance occurred between 0 and 1 ka the interpretation of the equilibrium line altitude ela variation deduced from this chronology for the holocene period and carbon 14 14c dating for the pleistocene period shows that the early history of the mailun valley deglaciation late pleistocene is in good agreement with the global paleoclimatic records the main extent of the glacier and the major ice volume drop are in phase with the global last glacial maximum 25 17 ka and with the major worldwide temperature increase following the younger dryas respectively indicating that the mailun glacier was primarily driven by temperature oscillations during the late pleistocene in contrast the glacier chronology during the holocene suggests that the mailun glacier was modulated by the variation in annual precipitation and is asynchronous relative to most glaciers of the northern hemisphere the significant sensitivity of the himalayan glaciers to precipitation might explain the striking lack of synchronism of the himalayan glaciers both along and across the himalayan arc

tropical climate instability the last glacial cycle from a qinghai tibetan ice core an ice core record from the guliya ice cap on the qinghai tibetan plateau provides evidence of regional climatic conditions over the last glacial cycle 36 cl data suggest that the deepest 20 meters of the core may be more than 500 000 years old the 18 o change across termination i is 5 4 per mil similar to that in the huascaran peru and polar ice cores three guliya interstadials stages 3 5a and 5c are marked by increases in 18 o values similar to that of the holocene and eemian 124 000 years ago the similarity of this pattern to that of ch 4 records from polar ice cores indicates that global ch 4 levels and the tropical hydrological cycle are linked the late glacial stage record contains numerous 200 year oscillations in 18 o values and in dust nh 4 and no 3 levels

beryllium isotope geochemistry in tropical river basins abstract the distributions of beryllium 9 and beryllium 10 in rivers within the orinoco and amazon basins have been examined to extend our understanding of their geochemical cycles and to develop their use both in geochronometry and in studying erosional processes beryllium 9 the stable isotope is weathered from mineral lattices before entering the riverine dissolved or exchangeable phase the cosmogenic radioisotope 10be t 1 2 1 5 myr is produced primarily in the atmosphere and is brought into riverine systems via rainfall in dissolved or exchangeable form it may be used to examine the processes which affect beryllium partitioning between the dissolved and particulate phases ancillary data such as major ion distributions provide a basis for selecting regions in which riverine chemistry is dominated by a single geochemical process allowing examination of its effects on be distributions in isolation analyses of 9be in dissolved and suspended material from rivers with a wide range of chemical compositions indicate that its geochemistry is primarily controlled by two major factors 1 1 its abundance in the rocks of the watershed and 2 2 the extent of its adsorption onto particle surfaces the relative importance of these parameters in individual rivers is determined by the extent of interaction with flood plain sediments and the riverine ph this understanding of 9be geochemistry forms a basis for examination of the geochemical cycling of 10be in rivers which are dominated by interaction with sediments the riverine concentration of dissolved 10be is far lower than that in the incoming rainwater indicating that a substantial proportion of it is retained within the soils of the basin or is adsorbed onto riverine particles however in acidic rivers in which the stable dissolved be concentration is determined by the be level in the rocks of the drainage basin dissolved 10be has essentially the same concentration as in precipitation these observations imply that the soil column in such regions must be saturated with respect to 10be and that the ratio of the inventory to the flux does not represent an age as may be the case in temperate latitudes but rather a residence time

modified mohr coulomb criterion for non linear triaxial and polyaxial strength of jointed rocks abstract rocks encountered in civil and mining engineering fields are invariably jointed and act under triaxial or polyaxial stress conditions the mohr coulomb shear strength criterion is the most widely used criterion for jointed rocks in its present form there are two major limitations of this criterion firstly it considers the strength response to be linear and secondly the effect of the intermediate principal stress on the strength behaviour is ignored a modified non linear form of mohr coulomb strength criterion has been suggested in this study to overcome these limitations barton s concept of critical state for rocks has been imbibed in the linear mohr coulomb criterion to deduce a semi empirical expression for non linear criterion however the shear strength parameters of the conventional mohr coulomb criterion are used in the proposed criterion the proposed criterion is a simple and rational nonlinear polyaxial strength criterion for anisotropic jointed rocks in an earlier publication 1 the applicability of the criterion was evaluated for intact rocks in present paper the criterion is extended to jointed rocks which are anisotropic in nature the applicability of the proposed criterion has been verified by applying it to extensive experimental data on triaxial and polyaxial test results on jointed rocks available from literature applicability of the criterion to explain rock burst conditions for some indian rocks is also demonstrated

a study on the uplift mechanism of tongjiezi dam using a coupled hydro mechanical model during filling in 1992 of the tongjiezi reservoir in southwest china it was noticed that the dam body and the rock masses on the right side of the valley were uplifted up to 22 2 mm and 24 3 mm respectively after reservoir filling in 1993 the uplift continued but the rate decreased and the measured maximum uplift increased from 22 2 mm to 27 5 mm in the dam body and from 24 3 mm to 28 9 mm in the rock masses from 1993 to 2004 based on the geological features of the dam site and observed geomechanics data a numerical method is used to evaluate the representative elementary volume rev and to identify the parameters related to the mechanical and hydraulic properties of the rock mass furthermore a coupled hydro mechanical model is presented to describe the uplift process the simulated results agree well with those measured in addition the time dependent deformation is studied in the laboratory and numerically it is concluded that with the specific hydrogeological conditions at the tongjiezi dam site hydro mechanical coupling during and after the reservoir impoundment is the main factor contributing to the uplift and the time dependent deformation is due to the rheological behavior of rock masses under seepage pressure

empirical estimation of strength of jointed rocks traversed by rock bolts based on experimental observation abstract engineering behaviour of jointed rocks is substantially incompetent as compared to intact rocks due to the presence of joints rock bolts are routinely used to reinforce jointed rocks at project sites the assessment of the strength behaviour of bolt reinforced jointed rock is a challenging task due to the complex interaction between the joints and the bolts the present paper attempts to resolve this issue through an experimental study natural rock cores with a natural joint and synthetic rock cores with smooth joint have been tested under uniaxial compression the tests have been performed on specimens without and with bolt grouted steel bolt was used to reinforce the rock results from the tests indicate that the provision of the bolt alters the failure mode of jointed rock and enhances the strength and modulus values strength and modulus of the reinforced rock were found to be correlated with each other it is proposed that the strength of reinforced rock can be obtained from strength and modulus of the intact rock and the modulus of the reinforced rock the intact rock strength and modulus may be obtained from laboratory tests and the modulus of the reinforced rock may be obtained by back analysing the deformations observed in the field sakurai s critical strain concept has been analysed and it is observed that the correlations suggested through proposed empirical approach closely commensurate with critical strain approach and hence give scale free results

holocene glacier fluctuations and migration of neolithic yak pastoralists into the high valleys of northwest bhutan abstract here we present geomorphologic palaeoenvironmental and archaeo botanical data which elucidate the late pleistocene and holocene glacial history of the high mountain locked himalayan valleys in northwest bhutan and provide one of the earliest proofs of human activity yet known for the high himalaya range in this area difficult to access close linkage between climatic change glacier fluctuations and human migration patterns has been discovered glacier systems in the studied area are characterized by avalanching and debris mantled glacier snouts with the significant local influence of the indian summer monsoon causing decoupling of glacier responses from temperature changes but supporting the idea of monsoonal forcing geomorphologic mapping together with optically stimulated luminescence osl and radiocarbon dating of ice proximal sediments has been used to construct a local glacial chronology local ice stream networks developed during the early holocene ca 10 000 9000 a ago and during the early part of the mid holocene 6710 90 4680 155 cal a bp at which times there were ice advances of about 5 km from the modern glacier termini at such times the intensity of pro and periglacial processes would have intensified and ice dammed lakes were probably common as well rendering human colonization of the high valleys in northwest bhutan impossible an abrupt shift to dry climatic conditions on the tibetan plateau between 5000 and 4500 a bp coincided with glacial decay and the onset of morphodynamically stable conditions on the broad valley floors of the high valleys in this part of the himalaya palynological data suggest that the sudden disappearance of juniper and rhododendron pollen the immediate onset of pollen input from cereals confirmed by detailed sem analysis and a clear pattern of over grazing trampling and peat deterioration can be linked to human arrival in the valleys at ca 4280 130 cal a bp extensive charcoal horizons dating to 4745 250 and 4680 155 cal a bp are interpreted as evidence for human use of fire and forest clearances and agree spatially and temporally with the pollen based picture charcoal occurrences as old as 6710 90 cal a bp might be linked to yet earlier exploration of these himalayan valleys during phases of low glacial activity we provide an account of the colonization of these high valleys in response to glacial and monsoonal change and argue that the most likely founder societies come from the tibetan plateau where yak and barley based pastoralism and neolithic settlements are known to have existed since the mid holocene

sr nd os evidence for a stable erosion regime in the himalaya during the past 12 myr modern erosion of the himalaya the world s largest mountain range transfers huge dissolved and particulate loads to the ocean it plays an important role in the long term global carbon cycle mostly through enhanced organic carbon burial in the bengal fan to understand the role of past himalayan erosion the influence of changing climate and tectonic on erosion must be determined here we use a 12 myr sedimentary record from the distal bengal fan deep sea drilling project site 218 to reconstruct the mio pliocene history of himalayan erosion we use carbon stable isotopes 13c of bulk organic matter as paleo environmental proxy and stratigraphic tool multi isotopic sr nd and os data are used as proxies for the source of the sediments deposited in the bengal fan over time 13c values of bulk organic matter shift dramatically towards less depleted values revealing the widespread late miocene ca 7 4 ma expansion of c4 plants in the basin sr nd and os isotopic compositions indicate a rather stable erosion pattern in the himalaya range during the past 12 myr this supports the existence of a strong connection between the southern tibetan plateau and the bengal fan the tectonic evolution of the himalaya range and southern tibet seems to have been unable to produce large re organisation of the drainage system moreover our data do not suggest a rapid change of the altitude of the southern tibetan plateau during the past 12 myr variations in sr and nd isotopic compositions around the late miocene expansion of c4 plants are suggestive of a relative increase in the erosion of high himalaya crystalline rock i e a simultaneous reduction of both transhimalayan batholiths and lesser himalaya relative contributions this could be related to an increase in aridity as suggested by the ecological and sedimentological changes at that time a reversed trend in sr and nd isotopic compositions is observed at the plio pleistocene transition that is likely related to higher precipitation and the development of glaciers in the himalaya these almost synchronous moderate changes in erosion pattern and climate changes during the late miocene and at the plio pleistocene transition support the notion of a dominant control of climate on himalayan erosion during this time period however stable erosion regime during the pleistocene is suggestive of a limited influence of the glacier development on himalayan erosion

constraints on the late quaternary glaciations in tibet from cosmogenic exposure ages of moraine surfaces abstract this contribution provides new constraints on the timing of tibetan glacial recessions recorded by the abandonment of moraines we present cosmogenic radionuclide 10 be inventories at 17 sites in southern and western tibet 32 crests 249 samples and infer the range of permissible emplacement ages based on these analyses individual large embedded rock and boulder samples were collected from the crests of moraine surfaces and analyzed for 10 be abundance we consider two scenarios to interpret the age of glacial recession leading to the moraine surface formation from these sample exposure ages 1 erosion of the moraine surface is insignificant and so the emplacement age of the moraines is reflected by the mean sample age and 2 erosion progressively exposes large boulders with little prior exposure and so the oldest sample age records the minimum moraine emplacement age we found that depending on the scenario chosen the moraine emplacement age can vary by 50 for 100 ka old samples we consider two scaling models for estimating the production rates of 10 be in tibet which has an important although lesser effect on inferred moraine ages while the data presented herein effectively increase the database of sample exposure ages from tibet by 20 we find that uncertainties related to the interpretation of the 10 be abundance within individual samples in terms of moraine emplacement ages are sufficient to accommodate either a view in which glacial advances are associated with temperature minima or precipitation maxima that are recorded by independent paleoclimate proxies a reanalysis of published data from moraines throughout tibet shows that the variation we observe is not unique to our dataset but rather is a robust feature of the tibetan moraine age database thus when viewed in a similar way with other samples collected from this area uncertainties within moraine exposure ages obscure attribution of tibetan glacial advances to temperature minima or precipitation maxima our work suggests that more reliable chronologies of tibetan glaciations will come from improvements in production rate models for this portion of the world as well as a better understanding of the processes that form and modify these geomorphic surfaces

high lateral strain ratio in jointed rock masses rock masses encountered in the field are jointed and highly anisotropic an important manifestation of this characteristic of rock masses is that the blocks when slipping separate and create voids in the mass resulting in high lateral strain even under low axial stress it has been shown in this study that the ratio of lateral to axial strain may be very high especially if the joints are critically oriented the assumption of isotropic linearly elastic material is not applicable in such situations this observation is based on the outcome of an extensive laboratory testing programme in which a large number of specimens of a jointed rock mass with various joint configurations were tested under uniaxial loading conditions the trends of experimental results for both lateral strain ratio and rock mass strength have also been verified through distinct element modelling the reason for high lateral strains has been attributed to the creation of voids and also to the fact that permanent deformations due to slip commence along rock joints right from the start of loading process a simple mechanistic model has also been suggested to explain the high values of lateral strain for rough and dilatant rock joints the lateral strains in such situations are important in the design of rock bolts an example from a recently completed hydroelectric project has also been discussed where high lateral strain was found to be responsible for excessive wall closure and failure of rock bolts

the limited influence of glaciations in tibet on global climate over the past 170 000 yr extensive ice cover on the tibetan plateau would significantly influence earth s climate in general and the asian monsoon system in particular but extent and timing of quaternary glaciations in tibet remain highly controversial we dated erratics on top of moraines in the climatic key areas of central and east tibet using cosmogenic 10be 26al and 21ne consistent exposure ages obtained by various nuclides indicate a continuous period of exposure since the deposition of the samples our data imply that glacial advances were restricted to a few 10 km during the last 170 kyr in central tibet and during the peak of the last glaciation 24 13 kyr ago in eastern tibet advances of tibetan glaciers were much less prominent than elsewhere in the northern hemisphere most likely due to very arid conditions and high sublimation rates a proposed ice dome covering the entire plateau can be excluded thus albedo increase of tibet most likely did trigger neither northern hemisphere ice ages nor paleomonsoon changes during the last two glacial cycles the glacial advance during marine isotope stage 2 in east tibet and the absence of significant glacial events during the holocene suggest a relation of snowline lowering in east tibet to north atlantic cooling events rather than to periods of high precipitation by an intensified monsoon

review of holocene glacial chronologies based on radiocarbon dating in tibet and its surrounding mountains a compilation of 53 14c ages on moraines constrains the holocene glacial history of tibet and the surrounding mountains several holocene glacial stages are identified the little ice age had three substages at 1 0 0 13 cal ka bp however the glacial advances may have occurred 200 600 a earlier in southern and eastern bordering mountains than in the northern bordering mountains the earlier glacial advance might have been driven by humid conditions in bordering areas of tibet most glacial advances in the neoglaciation occurred at 3 5 1 4 cal ka bp they can be identified in almost every mountain range an early holocene glacial advance occurred 9 4 8 8 cal ka bp in both central tibet and bordering mountains the timings of holocene glacial advances are synchronous with the cooling periods in the 18o record from ice cores and with the results of optically stimulated luminescence dating and cosmogenic exposure dating in tibet copyright 2008 john wiley sons ltd

influence of secular variation of the geomagnetic field on production rates of in situ produced cosmogenic nuclides abstract scaling factors are presented that allow a full description of the cosmic ray flux modulation during secular variation of the geomagnetic field these scaling factors are analogous to those determined in a similar work dunai t j earth planet sci lett 2000 176 157 169 that were accurate for field strengths equivalent to present day field strength but cannot accommodate field strength variations strategies to derive the relevant geomagnetic field parameters are discussed and are tested with existing production rate calibrations for 3 he a production rate of 103 4 2 atoms g olivine yr sea level and for zero cutoff rigidity was derived from calibration sites from hawaii western usa and canary islands covering the time range of 2 281 kyr

reconstruction of the late quaternary glaciation of the macha khola valley gorkha himal nepal using relative and absolute 14c 10be dendrochronology dating techniques abstract late quaternary glacier fluctuations in the macha khola valley gorkha himal nepal were reconstructed using relative and absolute dating techniques our results indicate that younger moraine complexes were left by late holocene

characteristics of late quaternary monsoonal glaciation on the tibetan plateau and in east asia abstract glaciers fed by monsoonal precipitation are mainly located on the tibetan plateau and easternmost asia these are characterized by simultaneous accumulation and ablation in summer season the southeast part of the tibetan plateau experiences monsoonal precipitation in excess of 1000 mm yr resulting in maritime temperate glaciers in contrast precipitation in the middle and northwest part of the tibet plateau decreases from 1000 to 200 mm yr resulting in the formation of continental cold glaciers during the last glacial the regions of heavy monsoonal precipitation were restricted to the southeast corner of the plateau the westerly weak precipitation zone shifted southward and occupied the major northwest part of the plateau where the extreme continental type glaciers greatly expanded in the eastern margin of asia including taiwan central japan hokkaido and probably mount changbai maritime type glaciers were more extensive because of higher monsoonal precipitation especially heavy snowfall in northwest japan owing to the rich moisture content of the winter monsoon over the japan sea the millennial scale monsoon intensity and glacial cycle in the tibetan plateau are strongly affected by the precession cycle and the orbit inclination cycle which dominate the solar irradiance variation in low latitudes as the high radiation and strong monsoon caused the warmer and wetter climate during 40 30 ka the low radiation produced a weak monsoon and large depression of temperature and precipitation around 21 ka this climatic pattern differs from that in the high latitudes where the eccentricity cycle is prominent the temperature during the last glacial maximum lgm was 6 9 c lower than today on the tibetan plateau and the equilibrium line altitude was depressed by about 1000 m in the southeast part and in the east south and west margins of the plateau where precipitation was high the equilibrium line depression was 500 300 m in the inner and especially the west part of the plateau this variation in equilibrium lines might be caused by the combined effect of the decrease in precipitation the expansion of extreme continental glaciers and the active uplift of glaciated mountains the estimation of a glaciated area of about 350 000 km2 in the tibetan plateau and roughly 500 000 km2 in high asia based on observations of prominent features of lgm glacier extension may be the direct evidence that shows there was no quaternary unified ice sheet developed in the tibetan plateau

cosmogenic radionuclide dating of glacial landforms in the lahul himalaya northern india defining the timing of late quaternary glaciation the timing of glaciation in the lahul himalaya of northern india was ascertained using the concentrations of cosmogenic 10be and 26al from boulders on moraines and drumlins and from glacially polished bedrock surfaces five glacial stages were identified sonapani i and ii kulti batal and chandra of these cosmogenic exposure ages were obtained on samples representative of the batal and kulti glacial cycles stratigraphical relationships indicate that the sonapani i and ii are younger no age was obtained for the chandra glacial advance batal glacial stage deposits are found throughout the valley indicating the presence of an extensive valley glacial system during the kulti stage glaciers advanced ca 10 km beyond their current positions moraines produced during the batal stage ca 12 15 5 ka are coeval with the northern hemisphere late glacial interstadial bolling allerod deglaciation of the batal glacial stage was completed by ca 12 ka and was followed by the kulti glacial stage during the early holocene at ca 10 11 4 ka on millennial time scales glacier oscillations in the lahul himalaya apparently reflect periods of positive mass balance coincident with times of increased insolation during these periods the south asian summer monsoon strengthened and or extended its influence further north and west thereby enhancing high altitude summer snowfall copyright 2001 john wiley sons ltd

beryllium 10 dating of mount everest moraines indicates a strong monsoon influence and glacial synchroneity throughout the himalaya moraine successions in glaciated valleys south of mount everest provide evidence for at least eight glacial advances during the late quaternary cosmogenic radionuclide crn surface exposure dating of moraine boulders defines the timing of each glacial advance and refines the previous glacial chronologies the crn data show that glaciation was most extensive during the early part of the last glacial marine oxygen isotype stage mis 3 and earlier but limited during mis 2 the global last glacial maximum and the holocene a previously assumed neoglacial advance is dated to 3 6 6 0 3 ka and the crn dates confirm a glacial advance ca 1 ka these results show that glaciations on the south side of everest were not synchronous with the advance of northern hemisphere ice sheets yet glaciations within the himalaya the world s highest mountain belt were synchronous during the late quaternary the existence of glacial advances during times of increased insolation suggests that enhanced moisture delivered by an active south asian summer monsoon is largely responsible for glacial advances in this part of the himalaya these data allow us to quantify the importance of global climate change and monsoon influence on glaciation in the himalaya

shear behaviors of real natural un matching joints of granite with equivalent joint roughness coefficients abstract contact planes of a natural unfilled rock joint often portray dissimilar roughness characteristics particularly at shallow depth some researchers investigated shear strength behaviors of un matching joints i e joints with dissimilar surface morphologies through laboratory experiments using mimicked discontinuities this study aimed to explore shear behaviors of real natural un matching joints with similar averaged joint roughness coefficients jrcs in the singhbhum granite india based on laboratory investigations direct shear tests were performed on a total of 18 encapsulated jointed samples split into three groups under a three different low normal stresses 0 70 mpa with increasing values b three different high normal stresses within a range of 0 98 1 99 mpa with increasing values and c one particular intermediate normal stress 0 99 mpa for five times where direction of shearing was kept same as the dip direction of the joints in situ shear behaviors of the investigated joints portray diverse patterns moreover most of the obtained behavioral patterns look different from the typical shear stress shear displacement graph in the literature that are based on direct shear test results in case of matching rock discontinuities influence of surface morphology on shear behavior shear stress fluctuations with displacement variation of jrc values with the increase in normal stresses and observations on peak friction angle were critically analyzed effect of cycles of shearing on shear strength was also examined plausible reasons behind the uniqueness of the results were explained

anomalous cosmogenic 3he production and elevation scaling in the high himalaya the production rate of cosmogenic 3he in apatite zircon kyanite and garnet was obtained by cross calibration against 10 be in co existing quartz in glacial moraine boulders from the nepalese himalaya the boulders have 10 be ages between 6 and 16 kyr and span elevations from 3200 to 4800 m in all of these minerals 3he correlates with 10 be and is dominantly cosmogenic in origin after modest correction for non cosmogenic components 3he 10 be systematics imply apparent sea level high latitude slhl apparent production rates for 3he of 226 atoms g 1 yr 1 in zircon 254 atoms g 1 yr 1 in apatite 177 atoms g 1 yr 1 in kyanite and 153 atoms g 1 yr 1 in gamet these production rates are unexpectedly high compared with rates measured elsewhere in the world and also compared with proposed element specific production rates for apatite and zircon the data are sufficient to conclude that the 3he 10 be ratio increases with elevation if this reflects different altitudinal scaling between production rates for the two isotopes then the slhl production rates estimated by our approach are overestimates we consider several hypotheses to explain these observations including production of 3he via thermal neutron capture on 6li altitudinal variations in the energy spectrum of cosmic ray neutrons and the effects of snow cover because all of these effects are small we conclude that the altitudinal variations in production rates of cosmogenic 3he and 10 be are distinct from each other at least at this location over the last last 10 kyr kyr this conclusion calls into question commonly adopted geographic scaling laws for at least some cosmogenic nuclides if confirmed this distinction may provide a mechanism by which to obtain paleoelevation estimates

geomagnetic dipole moment and 10be production rate intercalibration from authigenic 10be 9be for the last 1 3 ma 1 a synthesis of authigenic 10be 9be ratio records constructed from sedimentary sequences deposited over the last 300 ka in the north east atlantic and over the 500 1300 ka bp interval in the west equatorial pacific ocean is compared with proxies of the geomagnetic moment variations over the same time intervals these proxies consist in 1 relative paleointensity records obtained from the same sediments 2 a seafloor magnetization record derived from magnetic anomalies and 3 an absolute virtual dipole moment vdm record constructed from an updated database of absolute paleointensities the authigenic 10be 9be ratio records document the occurrence of the paleomagnetic events excursions and reversals reported for these time intervals by paleomagnetic studies reconstructions of 10be 9be derived magnetic moment records based on theoretical and empirical relationships between 10be 9be ratio and absolute vdm allow establishing 10be derived vdm records that exhibit the same overall structures as the geomagnetic proxy records

glacial activity reflected in a continuous lacustrine record since the early holocene from the proglacial laigu lake on the southeastern tibetan plateau abstract the southeastern tibetan plateau is an important area of monsoonal maritime glaciation and it serves as a watershed for several major asian rivers including the brahmaputra river and the lantsang river glacial activity is sensitive to climate change in this area however due to high annual ablation and accumulation in this region ice cores over long time scales are difficult to retrieve in addition reconstructed glacial activity from moraine dates is usually discontinuous here we use a sediment core retrieved from laigu lake which is a proglacial lake located in the headwaters of the parlung zangbo river the largest tributary of the brahmaputra river to reflect glacial activities over the last 8000 years in this area samples of the sediment core were analyzed for magnetic susceptibility xrf x ray florescence scanned elemental concentration and grain size the results indicated that the magnetic susceptibility and cps peak area counts per second of strontium sr could be used as proxies for glacial activity the cps of sr and the magnetic susceptibility were lower and the glacial activity was weak before 4 3 cal ka bp expansion of the glaciers in this area began from 4 3 cal ka bp and continued to develop after 3 3 cal ka bp from 2 2 cal ka bp to 1 6 cal ka bp the glaciers retreated substantially followed by another development period until the onset of modern global warming based on our findings and other climate records we concluded that glacial activity in the southeastern tibetan plateau areas was mainly influenced by northern hemisphere temperatures and summer insolation over a sub orbital time scale but did not respond to the indian monsoon

timing of late quaternary glaciations south of mount everest in the khumbu himal nepal moraines south of mount everest in the khumbu himal were dated using optically stimulated luminescence clustering of ages and morphostratigraphy allowed three advances to be dated 1 the periche glacial stage ca 18 25 ka 2 the chhukung glacial stage ca 10 ka and 3 the lobuche stage ca 1 2 ka the periche stage is coincident with oxygen isotope stage 2 the chhukung stage represents a late glacial or early holocene glacial advance and the lobuche stage is a late holocene glacial advance that predates the little ice age

climatic and topographic controls on the style and timing of late quaternary glaciation throughout tibet and the himalaya defined by 10be cosmogenic radionuclide surface exposure dating abstract temporal and spatial changes in glacier cover throughout the late quaternary in tibet and the bordering mountains are poorly defined because of the inaccessibility and vastness of the region and the lack of numerical dating to help reconstruct the timing and extent of glaciation throughout tibet and the bordering mountains we use geomorphic mapping and 10 be cosmogenic radionuclide crn surface dating in study areas in southeastern gonga shan southern karola pass and central western nyainqentanggulha shan and tanggula shan tibet and we compare these with recently determined numerical chronologies in other parts of the plateau and its borderlands each of the study regions receives its precipitation mainly during the south asian summer monsoon when it falls as snow at high altitudes gonga shan receives the most precipitation 2000 mm a 1 while near the margins of monsoon influence the karola pass receives moderate amounts of precipitation 500 600 mm a 1 and in the interior of the plateau little precipitation falls on the western nyainqentanggulha shan 300 mm a 1 and the tanggula shan 400 700 mm a 1 the higher precipitation values for the tanggula shan are due to strong orographic effects in each region at least three sets of moraines and associated landforms are preserved providing evidence for multiple glaciations the 10 be crn surface exposure dating shows that the formation of moraines in gonga shan occurred during the early mid holocene neoglacial and little ice age on the karola pass during the lateglacial early holocene and neoglacial in the nyainqentanggulha shan date during the early part of the last glacial cycle global last glacial maximum and lateglacial and on the tanggula shan during the penultimate glacial cycle and the early part of the last glacial cycle the oldest moraine succession in each of these regions varies from the early holocene gonga shan lateglacial karola pass early last glacial western nyainqentanggulha shan and penultimate glacial cycle tanggula shan we believe that the regional patterns and timing of glaciation reflect temporal and spatial variability in the south asian monsoon and in particular in regional precipitation gradients in zones of greater aridity the extent of glaciation has become increasingly restricted throughout the late quaternary leading to the preservation of old 100 ka glacial landforms in contrast in regions that are very strongly influenced by the monsoon 1600 mm a 1 the preservation potential of pre lateglacial moraine successions is generally extremely poor this is possibly because lateglacial and holocene glacial advances may have been more extensive than early glaciations and hence may have destroyed any landform or sedimentary evidence of earlier glaciations furthermore the intense denudation mainly by fluvial and mass movement processes which characterize these wetter environments results in rapid erosion and re sedimentation of glacial and associated landforms which also contributes to their poor preservation potential

decoupling of erosion and precipitation in the himalayas the hypothesis that abrupt spatial gradients in erosion can cause high strain rates in active orogens has been supported by numerical models that couple erosional processes with lithospheric deformation via gravitational feedbacks1 2 3 most such models invoke a stream power rule in which either increased discharge or steeper channel slopes cause higher erosion rates spatial variations in precipitation and slopes are therefore predicted to correlate with gradients in both erosion rates and crustal strain here we combine observations from a meteorological network across the greater himalaya nepal along with estimates of erosion rates at geologic timescales greater than 100 000 yr from low temperature thermochronometry across a zone of about 20 km length spanning the himalayan crest and encompassing a more than fivefold difference in monsoon precipitation significant spatial variations in geologic erosion rates are not detectable decreased rainfall is not balanced by steeper channels instead additional factors that influence river incision rates such as channel width and sediment concentrations must compensate for decreasing precipitation overall spatially constant erosion is a response to uniform upward tectonic transport of greater himalayan rock above a crustal ramp

chronology and climatic implications of late quaternary glaciations in the goriganga valley central himalaya india abstract goriganga valley which is located in the transition zone between the dry steppe of the tibetan plateau in the north and the sub humid himalayan climate in the south has preserved four events of glaciation with decreasing magnitude the oldest stage i glaciation is represented by a 12 5 km long discontinuous diamictite ridge which terminates north of rilkot 3100 m asl the stage ii glaciation is represented by sub rounded and partially eroded lateral moraines and terminates around martoli village 3240 m asl the stage iii and iv glacial moraines are sharp crested unstable and terminate proximal to the present day glacier at 3640 m asl and 3740 m asl respectively the stage ii moraines have been optically dated between 25 2 ka and 22 1 ka implying that glacier expanded during the global last glacial maximum lgm this is contrary to the suggestion that during last glacial maximum lgm glaciation was limited in extent due to weak indian summer monsoon ism in the monsoon dominated regions of the himalaya we ascribe the lgm glaciations to a combination of the lowered temperature and enhanced mid latitude westerlies following the lgm glaciation goriganga valley experienced two major pulses of deglaciation the older event is dated between 16 and 12 ka and is coeval with the initiation of the ism whereas the younger events 10 8 ka represent the early to mid holocene strengthened ism the stage iii and iv glaciations which terminated proximal to the modern glacier are speculated to occur during the mid holocene and little ice age lia respectively

timing of past glaciations in kanchenjunga himal nepal by optically stimulated luminescence dating of tills abstract optically stimulated luminescence osl was used to date glacial sediments to elucidate the ages of past glacial advances in kanchenjunga himal eastern nepal seven glacial sediments samples were collected from four different moraines and quartz grains were extracted from samples however the luminescence from feldspars existing as minor contamination and or microinclusion in the quartz grains was so bright it masked the quartz signal after etching the fraction 20 min extra with hf the natural infrared stimulated luminescence irsl signal which indicates the existence of feldspar almost disappeared equivalent dose de values were estimated by the single aliquot regenerative dose protocol using two different quartz fractions fraction a which was etched 20 min extra and fraction b which was prepared by the standard procedure still had a strong feldspar signal although the natural irsl intensity for fraction a was so weak the regenerated irsl was relatively strong and not negligible for most of the aliquots such aliquots were omitted because the sensitivity of the feldspar is much higher than quartz and the difference in the sensitivity can cause de underestimation out of 42 aliquots from four samples for fraction a only six aliquots from two samples were remained the de values for single aliquots were uniformly distributed for fraction b moreover the calculated osl ages for fractions a and b from the two samples agreed with each other it is suggested that both quartz and feldspars grains or microinclusions in quartz grains were likely to have been bleached while glacial debris has been transported on the glacier the resulting osl ages suggest that the glaciers expanded at 5 6 8 10 and 20 21 ka in the kanchenjunga himal

experimental and numerical study of asperity degradation in the direct shear test abstract in this paper the shear behaviour and mechanisms of asperity degradation of rock joints under direct shear tests were studied using numerical and experimental approaches pfc2d was used for numerical simulations in which the intact material is simulated by a dense packing of circular particles bonded together at their contact points and by breakage of these bonds under loading regimes the damage process is simulated the joint interfaces were simulated by a newly developed modified smooth joint model in which micro scale slip surfaces are applied at contacts between particles of upper and lower blocks of the shear box in order to study the ability of this numerical approach in reproducing the shearing mechanisms and asperity degradation of rock joints in direct shear tests a comparative study was carried out against the physical experiments experimental and numerical direct shear tests were carried out on saw tooth triangular joints with the base angles of 20 and 30 under different normal stresses three shearing mechanisms of sliding surface wear and asperity shearing off were observed in these experiments the comparison of the shear behaviour and mechanisms of asperity degradation of physical and numerical experiments showed that the results of numerical models are in good agreement with physical experiments and this numerical approach can reproduce the shear behaviour of rock joints under different loading conditions

holocene variations of monsoon rainfall in rajasthan two reconstructed histories of the monsoon rainfall in rajasthan show that the monsoon was weak or absent in latest glacial time with the advent of holocene climatic patterns fresh water lakes formed in dune fields and the pollen rain preserved in these reservoirs provides a basis for the reconstruction of the monsoon history the two reconstructions separated by only 150 km have some features in common and some striking differences both show maximum monsoon amounts in the early holocene with a roughly two thirds decrease to the present both show salinization in sub boreal time both show long intervals of near complete desiccation in the last four millennia the shorter term variations however are not closely parallel these shorter term variations may be explained in terms of the behavior of the present day interannual variability

mid pleistocene cosmogenic minimum age limits for pre wisconsinan glacial surfaces in southwestern minnesota and southern baffin island a multiple nuclide approach abstract paired 10 be and 26 al analyses n 14 indicate that pre wisconsinan glaciated bedrock surfaces near the northern baffin island and southern minnesota paleo margins of the laurentide ice sheet have long and complex histories of cosmic ray exposure including significant periods of partial or complete shielding from cosmic rays using the ratio 26 al 10 be we calculate that striated outcrops of sioux quartzite in southwestern minnesota southern margin were last overrun by ice at least 500 000 years ago weathered bedrock tors on the once glaciated uplands of baffin island northern margin are eroding no faster than 1 1 m myr 1 the equivalent of at least 450 000 years of surface and near surface exposure our data demonstrate that exposure ages and erosion rates calculated from single nuclides can underestimate surface stability dramatically because any intermittent burial and the resultant lowering of nuclide production rates and nuclide abundances will remain undetected

timing and extent of holocene glaciations in the monsoon dominated dunagiri valley bangni glacier central himalaya india abstract field stratigraphy and optical and radiocarbon dating of lateral moraines in the monsoon dominated dunagiri valley of the central himalaya provide evidence for three major glaciations during the last 12 ka the oldest and most extensive glaciation the bangni glacial stage i bgs i is dated between 12 and 9 ka followed by the bgs ii glaciation 7 5 and 4 5 ka and the bgs iii glaciation 1 ka in addition discrete moraine mounds proximal to the present day glacier snout are attributed to the little ice age lia bgs i started around the younger dryas yd cooling event and persisted till the early holocene when the indian summer monsoon ism strengthened the less extensive bgs ii glaciation which occurred during the early to mid holocene is ascribed to lower temperature and decreased precipitation further reduction in ice volume during bgs iii is attributed to a late holocene warm and moist climate although the glaciers respond to a combination of temperature and precipitation changes in the dunagiri valley decreased temperature seems to be the major driver of glaciations during the holocene

mechanical analysis of controls on strain partitioning in the himalayas of central nepal we present a mechanical analysis of the problem of slip partitioning between the major thrust systems in a collisional range we focus on two structures in the himalayas of central nepal the main himalayan thrust mht and the main central thrust mct we use finite element modeling to test the influence of various parameters such as friction coefficients and surface processes and we investigate how they affect the distribution of deformation between these two faults we observe that reproduction of the late quaternary kinematic pattern across the range with our model requires strict conditions on the friction coefficients such that the mht is very weak whereas the mct is significantly stronger the most important parameter that controls slip partitioning appears to be the dip angle of the mct with a gentler or steeper mct promoting or inhibiting slip respectively we also show that transient loading and unloading through focused glacial erosion in the higher part of the range can unclamp the mct and allow a significant increase in slip rates the results of this mechanical sensitivity investigation have important implications for the dynamics of the himalayan wedge and point toward along strike structural variations as a first order control on slip partitioning

the little ice age in the himalaya a review of glacier advance driven by northern hemisphere temperature change northern hemisphere cooling between 1400 and 1900 in the common era ce resulted in the expansion of glaciers during a period known as the little ice age lia early investigation of recent advances of himalayan glaciers assumed that these events were synchronous with lia advances identified in europe based on the appearance and position of moraines and without numerical age control however applications of quaternary dating techniques such as terrestrial cosmogenic nuclide dating have allowed researchers to determine numerical ages for these young moraines and clarify when glacial maxima occurred this paper reviews geochronological evidence for the last advance of glaciers in the himalaya the 66 ages younger than 2000 years 0 2000 ce calculated from 138 samples collected from glacial landforms demonstrate that peak moraine building occurred between 1300 and 1600 ce slightly earlier than the coldest period of northern hemisphere air temperatures the timing of lia advances varied spatially lik

an empirical method for determining the mechanical properties of jointed rock mass using drilling energy abstract characterization of jointed rock masses and evaluation of their mechanical properties are challenging tasks in rock engineering this paper presents an experimental investigation of the response characteristics of drilling energy to the discontinuity of rock mass using a drilling method the linear relationship between the drilling energy and discontinuity frequency is revealed which only depends on the rock type and is independent of calculation units a new empirical method for determining the rock quality designation rqd versus the variation of drilling energy is proposed based on the discontinuity frequency comparison between the prediction and in situ investigation results demonstrates that the rqd can be estimated from this empirical method the em er modulus ratio and cm c strength ratio versus rqd relations are modified for the determination of rock mass strength and deformation modulus in order to consider the continuous variation of em er and cm c with the model parameter which is related to the drilling energy and modulus of elasticity of intact rock and the variation of drilling energy for rock mass the results show that the modified em er cm c versus rqd relations can give proper values compared with the field test results as well as compared with the various proposed relations from rmr q and gsi the modified relations can provide a practical fast and easy to use method for the estimated rock mass strength and deformation modulus but they are only a first approximation