slip rate measurements on the karakorum fault may imply secular variations in fault motion beryllium 10 surface exposure dating of offset moraines on one branch of the karakorum fault west of the gar basin yields a long term 140 to 20 thousand year right lateral slip rate of 10 7 0 7 millimeters per year this rate is 10 times larger than that inferred from recent insar analyses 1 3 millimeters per year that span 8 years and sample all branches of the fault the difference in slip rate determinations suggests that large rate fluctuations may exist over centennial or millennial time scales such fluctuations would be consistent with mechanical coupling between the seismogenic brittle creep and ductile shear sections of faults that reach deep into the crust

nature and timing of large landslides in the himalaya and transhimalaya of northern india four large landslides each with a debris volume 10 6 m 3 in the himalaya and transhimalaya of northern india were examined mapped and dated using 10 be terrestrial cosmogenic radionuclide surface exposure dating the landslides date to 7 7 1 0 ka darcha 7 9 0 8 ka patseo 6 6 0 4 ka kelang serai and 8 5 0 5 ka chilam comparison of slip surface dips and physically reasonable angles of internal friction suggests that the landslides may have been triggered by increased pore water pressure seismic shaking or a combination of these two processes however the steepness of discontinuities in the darcha rock slope suggests that it was more likely to have started as a consequence of gravitationally induced buckling of planar slabs deglaciation of the region occurred more than 2000 years before the darcha patseo and kelang serai landslides it is unlikely that glacial debuttressing was responsible for triggering the landslides the four landslides their causes potential triggers and mechanisms and their ages are compared to 12 previously dated large landslides in the region fourteen of the 16 dated landslides occurred during periods of intensified monsoons seismic shaking however cannot be ruled out as a mechanism for landslide initiation because the himalaya has experienced great earthquakes on centennial to millennial timescales the average holocene landscape lowering due to large landslides for the lahul region which contains the darcha patseo and kelang serai landslides is w0 12 mm yr previously published large landslide landscape lowering rates for the himalaya differ significantly furthermore regional glacial and fluvial denudation rates for the himalaya are more than an order of magnitude greater this difference highlights the lack of large landslide data lack of chronology problems associated with single catchment large landslide based calculations and the need for regional landscape lowering determinations over a standardized time period

quaternary glaciation of the himalayan tibetan orogen glacial geological evidence from throughout the himalayan tibetan orogen is examined to determine the timing and extent of late quaternary glaciation in this region and its relation to similar changes on a global scale the evidence summarised here supports the existence of expanded ice caps and extensive valley glacier systems throughout the region during the late quaternary however it cannot yet be determined whether the timing of the extent of maximum glaciation was synchronous throughout the entire region or whether the response was more varied the lack of organic material needed for radiocarbon dating has hindered past progress in glacial reconstruction however application of optically stimulated luminescence and terrestrial cosmogenic radionuclide methods has recently expanded the number of chronologies throughout the region limits to the precision and accuracy available with these methods and more importantly geological uncertainty imposed by processes of moraine formation and alteration both conspire to limit the time resolution on which correlations can be made to milankovitch timescales several ka in order to put all studies on a common scale well dated sites have been re evaluated and all the published terrestrial cosmogenic nuclide ages for moraine boulders and glacially eroded surfaces in the himalayan tibetan orogen have been recalculated locally detailed studies indicate that there are considerable variations in the extent of glaciation from one region to the next during a glaciation glaciers throughout monsoon influenced tibet the himalaya and the transhimalaya are likely synchronous both with climate change resulting from oscillations in the south asian monsoon and with northern hemisphere cooling cycles in contrast glaciers in pamir in the far western regions of the himalayan tibet orogen advanced asynchronously relative to the other regions that are monsoon influenced regions and appear to be mainly in phase with the northern hemisphere cooling cycles broad patterns of local and regional variability based on equilibrium line altitudes have yet to be fully assessed but have the potential to help define changes in climatic gradients over time copyright 2008 john wiley sons ltd

topography relief and trmm derived rainfall variations along the himalaya 1 along the southern himalayan topographic front the indian summer monsoon modulates erosive processes and rates to investigate the influence of topography and relief on rainfall generation and resultant erosion we processed satellite rainfall amounts for the last 8 years 1998 2005 from the tropical rainfall measurement mission trmm based upon a spatial resolution of 5 5 km for the himalaya we identify 1 the spatial distribution of rainfall and 2 the large scale relationships between topography relief and rainfall locations our results show two distinct rainfall maxima along strike in the himalaya the first outer rainfall peak occurs along the southern margin of the lesser himalaya within a narrow band of mean elevation 0 9 0 4 km and mean relief 1 2 0 2 km the second discontinuous inner band typically occurs along the southern flank of the greater himalaya elevation and relief both 2 1 0 3 km

a late quaternary catastrophic flood in the lahul himalayas impressive flood deposits are described resulting from a catastrophic lake outburst in the upper chandra valley in the lahul himalaya northern india reconstructions of the former glacial lake glacial lake batal and the discharges were undertaken using landforms and sediment data the glacial dam burst released 1 496 km3 of water in 0 72 days with peak discharges of between 21 000 and 27000 m3 s at batal dating by osl suggests the flood occurred ca 36 9 if 8 4 to 43 4 2 10 3 ka ago this cataclysmic flood was responsible for major resedimentation and landscape modification within the chandra valley journal of quaternary suence

early holocene climate recorded in geomorphological features in western tibet cosmic ray exposure ages for formation of perched alluvial terraces and for abandonment of an alluvial debrisflow fan on opposite sides of the tangtse valley the outflow at the northwest end of lake panggong which is in the karakorum range of western tibet provide evidence of a humid period at v11 5 to v7 ka this is consistent with other regional records and supports a controversial chronology for the sedimentary record from lake panggong fan abandonment appears to have occurred at v11 5 ka as the climate presumably became more humid in response to initiation of enhanced monsoonal circulation consistent with previously reported onset of humid conditions in a sedimentary record from the easternmost basin of the lake in contrast the terraces did not form until about 7 ka with downcutting of the transverse valley by overflow from lake panggong this lag can be explained in light of the bathymetry of lake panggong the modern lake consists of five basins separated by shallow sills and outflow through the tangtse valley could not occur until the water level was substantially above its present level the easternmost basin receives the inflow of the major rivers feeding the lake making its chemistry highly sensitive to changes in precipitation however sustained wet conditions are required to fill the basins to the west to the sill depth necessary for overflow through the tangtse valley and resultant downcutting and terrace formation 2003 elsevier b v all rights reserved

a 1000 year history of large floods in the upper ganga catchment central himalaya india abstract determining the frequency magnitude and causes of large floods over long periods in the flood prone himalaya is important for estimating the likelihood of future floods a thousand year record with some information from 2600 years ago of the frequency and some estimates of velocities and discharges of large floods has been reconstructed in the upper ganga catchment india using written reports litho stratigraphy and sedimentology and dated by optical and radiocarbon methods in the upper ganga catchment rainfall triggers large landslides that dam rivers and release large amounts of water when they burst thereby amplifying the effects of rainfall the large floods in the catchment may be the result of landslide dam bursts rather than glacial lake bursts and these are likely to continue and possibly worsen as the monsoon intensifies over the next century however preliminary information suggests that the recent devastating flood of june 2013 was the result of heavy rainfall not landslide dam bursts the frequency record is non random and shows a high frequency between ad 1000 and ad 1300 omitting uncertainties then a low frequency until a cluster of floods occurred about 200 years ago then increased frequency this temporal pattern is like but not identical with that in peninsular india and both appear to be the result of variations in the monsoon

towards defining the transition in style and timing of quaternary glaciation between the monsoon influenced greater himalaya and the semi arid transhimalaya of northern india abstract to help delineate the transition in pattern and timing of glaciation between two contrasting regions lahul to the south and ladakh to the north moraines in the puga and karzok valleys of sanskrit in the transhimalaya of northern india were mapped and dated using cosmogenic 10 be in lahul late quaternary glaciation was extensive with total valley glacial systems being 100 km in extent whereas glaciation in ladakh has been comparatively restricted with glaciers advancing only 15 km from the contemporary glaciers during the last 200 ka in the puga valley glaciers advanced 15 km at 129 ka and 10 km at 46 ka 4 2 ka and 0 6 ka in the karzok valley glaciers advanced 1 km at 3 6 ka boulder exposure ages from a large moraine complex in karzok indicate a glacial advance at 80 ka of 4 km from the present ice margin the oldest moraine in karzok is 311 ka indicating that glaciers advanced 10 km from the present ice margin during or before marine isotope stage 9 the glacial chronology of the two valleys shows a lack of early holocene glaciation and generally asynchronous glaciation between them moraines in the puga and karzok valleys broadly correlate with previous studies in the zanskar range but the paucity of data for many of the glacial stages across the zanskar region makes the correlations tentative the lack of early holocene glaciation in the puga and karzok valleys is in stark contrast to many regions of the himalaya including lahul and the restricted glacial extent in zanskar is more similar to the style of glaciation in ladakh the similarity between the glacial records in the puga and karzok study areas suggests that the transition to lahul style glaciation is to the south of the karzok valley showing that this geographical transition is abrupt

the formation and failure of natural dams of the numerous kinds of dams that form by natural processes dams formed from landslides glacial ice and late neoglacial moraines present the greatest threat to people and property landslide dams form in a wide range of physiographic settings the most common types of mass movements that form landslide dams are rock and debris avalanches rock and soil slumps and slides and mud debris and earth flows the most common initiation mechanisms for dam forming landslides are excessive rainfall and snowmelt and earthquakes landslide dams can be classified into six categories based on their relation with the valley floor type i dams 11 of 184 landslide dams from around the world that we were able to classify do not reach from one valley side to the other type ii dams 44 span the entire valley floor in some cases depositing material high on opposite valley sides type iii dams 41 move considerable distances both upstream and downstream from the landslide failure type iv dams 1 are rare and involve the contemporaneous failure of material from both sides of a valley type v dams 1 also are rare and are created when a single landslide sends multiple tongues of debris into a valley and forms two or more landslide dams in the same reach of river type vi dams 3 involve one or more failure surfaces that extend under the stream or valley and emerge on the opposite valley side many landslide dams fail shortly after formation in our sample of 73 documented landslide dam failures 27 of the landslide dams failed less than 1 day after formation and about 50 failed within 10 days over topping is by far the most common cause of failure the timing of failure and the magnitude of the resulting floods are controlled by dam size and geometry material characteristics of the blockage rate of inflow to the impoundment size and depth of the impoundment bedrock control of flow and engineering controls such as artificial spill ways diversions tunnels and planned breaching by blasting or conventional excavation glacial ice dams can produce at least nine kinds of ice dammed lakes the most dangerous are lakes formed in main valleys dammed by tributary glaciers failure can occur by erosion of a drainage tunnel under or through the ice dam or by a channel over the ice dam cold polar ice dams generally drain supraglacially or marginally by downmelting of an outlet channel warmer temperate ice dams tend to fail by sudden englacial or subglacial breaching and drainage late neoglacial moraine dammed lakes are located in steep mountain areas affected by the advances and retreats of valley glaciers in the last several centuries these late neoglacial dams pose hazards because 1 they are sufficiently young that vegetation has not stabilized their slopes 2 many dam faces are steeper than the angle of repose 3 these dams and lakes are immediately downslope from steep crevassed glaciers and near vertical rock slopes and 4 downstream from these dams are steep canyons with easily erodible materials that can be incorporated in the flow and increase flood peaks the most common reported failure mechanism is overtopping and breaching by a wave or series of waves in the lake generated by icefalls rockfalls or snow or rock avalanches melting of ice cores or frozen ground and piping and seepage are other possible failure mechanisms natural dams may cause upstream flooding as the lake rises and downstream flooding as a result of failure of the dam although data are few for the same potential energy at the dam site ownstream flood peaks from the failure of glacier ice dams are smaller than those from landslide moraine and structed earth fill and rock fill dam failures moraine dam failures appear to produce some of the largest downstream flood peaks for potential energy at the dam site greater than 1011 1012 joules differences in flood peaks natural dam failures appear to be controlled by dam characteristics and failure mechanisms

periodic black auroral patches at the dawnside dipolarization front during a substorm 1 periodic black auroral patches were observed in the canadian postmidnight sector by ground based all sky cameras during an auroral substorm the aurora consisted of several black patches of 50 km 1 in longitude scales that appeared along the equatorward edges of the proton auroras over a 3 h local time segment from gillam to sanikiluaq ground stations 15 min after the auroral intensification occurred in alaska to the best of our knowledge this type of black auroras has never been reported before although the surrounding luminous auroras evolve into the well known torch structures later in situ observations by the themis satellites three of which were close to being magnetically conjugate in the plasma sheet as well as ground based proton auroral observations show that a dipolarization front and associated dawnward ion flows propagated eastward at poleward of the black patches coinciding with their appearance the flow motions of auroras observed poleward of the black patches are possibly generated by decelerations of dawnward ion flow because of the consistency of both durations and positions we speculate based on manifestations of high pressure regions in dipolarized flux tubes the pressure driven interchange instability formed a beading shape periodic black patches of field aligned currents the black auroral patches developed into torch structures after the flow disappearance indicating the dawnward flows might stabilize and limit the instability within a narrow l shell where the pressure gradient is directed earthward and flows cannot enter we conclude that the periodic black patches arise as a consequence of a relaxation process of enhanced plasma pressure near the inner boundary of the plasma sheet during a substorm

peak discharge of a pleistocene lava dam outburst flood in grand canyon arizona usa abstract the failure of a lava dam 165 000 yr ago produced the largest known flood on the colorado river in grand canyon the hyaloclastite dam was up to 366 m high and geochemical evidence linked this structure to outburst flood deposits that occurred for 32 km downstream using the hyaloclastite outburst flood deposits as paleostage indicators we used dam failure and unsteady flow modeling to estimate a peak discharge and flow hydrograph failure of the hyaloclastite dam released a maximum 11 109 m3 of water in 31 h peak discharges estimated from uncertainty in channel geometry dam height and hydraulic characteristics ranged from 2 3 to 5 3 105 m3 s 1 for the hyaloclastite outburst flood this discharge is an order of magnitude greater than the largest known discharge on the colorado river 1 4 104 m3 s 1 and the largest peak discharge resulting from failure of a constructed dam in the usa 6 5 104 m3 s 1 moreover the hyaloclastite outburst flood is the oldest documented quaternary flood and one of the largest to have occurred in the continental usa the peak discharge for this flood ranks in the top 30 floods 105 m3 s 1 known worldwide and in the top ten largest floods in north america

relationships between right lateral shear along the karakoram fault and metamorphism magmatism exhumation and uplift evidence from the k2 gasherbrum pangong ranges north pakistan and ladakh the karakoram fault is a major nw se aligned dextral strike slip fault that has accommodated minor extrusion of thickened tibetan crust since the mid miocene controversy exists as to whether the fault is lithospheric in scale resulting in synkinematic metamorphism and granite melting or whether it is an upper crustal fault cutting through earlier metamorphic and granitic rocks structural metamorphic and geochronological data from the karakoram fault show that 1 metamorphism and granite genesis occurred prior to strike slip shearing meaning that u pb zircon and monazite ages from deformed granites cannot be used as proxies for dating strike slip shearing only as a maximum age constraint on initiation of ductile shearing 2 sheared miocene leucogranites along the fault are equivalent to the baltoro granite batholith offset 40 150 km along the fault and show a strain gradient from high ductile strain to undeformed away from the fault 3 40 ar 39 ar and fission track ages of k2 orthogneisses and gasherbrum diorite show that rocks adjacent to the fault cooled during cretaceous to mid tertiary time and were not reset during shearing indicating that shear heating was not important 4 the gasherbrum diorite adjacent to the fault has never been at depths greater than 6 km since the early cretaceous and less than 3 km of material has been eroded off since then we conclude that the karakoram fault has had no significant influence on regional metamorphism or melting at least at levels exposed today and is restricted to the upper middle crust

timing of glaciation during the last glacial cycle evaluating the concept of a global last glacial maximum lgm abstract it has long been known that mountain glaciers and continental ice sheets around the globe reached their respective maximum extent at different times during the last glacial cycle often well before the global last glacial maximum lgm c 23 19 ka which is formally defined by peaks in global sea level and marine oxygen isotope records however there is increasing evidence from around the world that it was not only mountain glaciers which were asynchronous with the global lgm but also some regions of the large continental glaciers the barents kara ice sheet in northern eurasia together with a majority of ice masses throughout asia and australasia reached their maximum early in the last glacial cycle a few thousand years before the global lgm period the east antarctic ice sheet also reached its maximum extent several millennia before the global lgm in numerous mountainous regions at high mid and low latitudes across the world glaciers reached their maximum extent before marine isotope stage mis 2 in mis 5 4 and 3 this is in contrast to most sectors of the laurentide ice sheet the cordilleran ice sheet the se sector of the fennoscandinavian ice sheet and the alpine ice sheet in central europe which appear to have reached their maximum close to the global lgm in mis 2 the diachronous maximum extents of both mountain glaciers and continental ice sheets during the last glacial cycle means that the term and acronym last glacial maximum lgm has limited chronostratigraphical meaning when correlating glacial deposits and landforms

osl dating of past lake levels for a large dammed lake in southern tibet and determination of possible controls on lake evolution fluvio lacustrine terraces along phung chu river on the central southern tibetan plateau indicate that a large palaeo dammed lake formerly existed in this area based on landscape survey optically stimulated luminescence osl dating and sedimentary analyses this research shows that the phung chu was blocked and a dammed lake over 2500 km in size formed before 30 ka ago osl dating analysis suggests the fluvio lacustrine sediments were well bleached and yield accurate age estimates for two lake drainage events the first drainage event took place after 30 ka resulted in river incision and formed a high terrace at 50 m height from the present river level the second drainage happened after 3 7 ka resulted in further river incision and formed the second terrace at 25 m height from the present river level according to the distribution of the fluvio lacustrine sediments active normal faults particularly the kharta fault in this region and the high gradient slopes after phung chu enters the yo ri gorge seismically induced landsliding is regarded as highly likely to have been the cause of river blockage and associated formation of a dammed lake although glacial damming is also a possible cause the volume of drainages from this dammed lake may have led to catastrophic flooding and analogous modern lakes represent significant geo hazard risks to down river human settlements as dammed lakes are special phases in fluvial evolution often involving river blockage breakthrough and drastic catchment change these processes can reveal how tectonic or climatic events modify landforms however such tectonic derived landform changes can also impact palaeo climate of the region thus this study has added new evidence regarding the evolutionary history of a dammed lake including its formation duration extent and final drainage which is crucial for understanding its general landscape process mechanisms and for better assessing geo hazard risks

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

river network evolution as a major control for orogenic exhumation case study from the western tibetan plateau the westernmost tibetan plateau despite being internally drained has a high topographic relief here using apatite u th sm he and 4he 3he thermochronometry we reconstruct the exhumation history of the rutog batholith during the neogene thermal modeling in 1d using the qtqt program indicates that relatively slow cooling occurred from 30 ma to 19 ma which we interpret as an exhumation rate of 10 m ma this was followed by two pulses of moderate cooling from 19 to 17 ma and 11 to 9 ma that correspond to a total exhumation of about 1500 m cooling since 9 ma has been negligible this differs from exhumation patterns in central tibet but reveals timing similarities with externally drained portions of southern tibet we interpret our cooling constraints as recording two different transitions in western tibet from an externally to an internally drained system since the oligocene external drainage allowed this part of the tibetan plateau unlike internally drained portions of central tibet to record regional scale processes the first cooling event at about 20 ma was likely related to a major geodynamic event such as slab breakoff that induced contemporaneous potassic and ultrapotassic magmatism the second rapid cooling pulse from 11 ma to 9 ma and subsequent negligible cooling was most likely controlled by a local factor such as indus and shyok river network reorganization caused by dextral motion of the karakorum fault we discuss these interpretations and their limitations in this contribution

timing and climatic drivers for glaciation across semi arid western himalayan tibetan orogen abstract mapping and forty seven new 10 be ages help define the timing of glaciation in the ladakh and pangong ranges in northwest india five new local glacial stages are defined for the ladakh range from oldest to youngest these include the ladakh 4 glacial stage at 81 20 ka the ladakh 3 glacial stage not dated the ladakh 2 glacial stage at 22 3 ka the ladakh 1 glacial stage not dated and the ladakh cirque glacial stage at 1 8 0 4 ka three local glacial stages are defined for the pangong range which include the pangong 2 glacial stage at 85 15 ka the pangong 1 glacial stage at 40 3 ka and the pangong cirque glacial stage at 0 4 0 3 ka the new 10 be ages are combined with 645 recalculated 10 be ages from previous studies to develop the first regional framework of glaciation across the dryland regions of the greater himalaya transhimalaya pamir and tian shan at the western end of the himalayan tibetan orogen nineteen regional glacial stages are recognized that are termed semi arid western himalayan tibetan stages swhts these include swhts 9 at 311 32 ka swhts 7 at 234 44 ka tentative swhts 6 at 146 18 ka swhts 5e at 121 11 ka swhts 5a at 80 5 ka swhts 5a at 72 8 ka swhts 4 at 61 5 ka swhts 3 at 46 4 ka swhts 2f at 30 3 ka swhts 2e at 20 2 ka swhts 2d at 16 9 0 7 ka swhts 2c at 14 9 0 8 ka swhts 2b at 13 9 0 5 ka swhts 2a at 12 2 0 8 ka swhts 1e at 8 8 0 3 ka tentative swhts 1d at 6 9 0 2 ka tentative swhts 1c at 3 8 0 6 ka swhts 1b at 1 7 0 2 ka and swhts 1a at 0 4 0 1 ka regional glacial stages older than 21 ka are broadly correlated with strong monsoons swhts that are 21 ka or younger have smaller uncertainties and broadly correlate with global ice volume given by marine oxygen isotope stages and northern hemisphere climatic events oldest dryas older dryas younger dryas roman humid period and little ice age

western tibet relief evolution since the oligo miocene western tibet between the karakorum fault and the gozha longmu co fault system is mostly internally drained and has a 1 5 2 km amplitude relief with km large valleys we investigate the origin of this peculiar morphology by combining a topography analysis and a study of the cenozoic sedimentation in this area cenozoic continental strata correspond to a proximal detrital fan deposition and uncomformably rest on a palaeorelief similar to the modern one zircon u pb dating from trachytic flows interbedded within the cenozoic continental sediments indicates that detrital sedimentation occurred at least between ca 24 and 20 ma in the shiquanhe basin while k ar ages suggest it may have started since 37 ma in the zapug basin the distribution of continental deposits shows that present day morphology features including km large 1500 m deep valleys were already formed by early miocene times we suggest that today s internally drained western tibet was externally drained at least during late miocene contemporaneously with early motion along the karakorum fault detailed study of the present day river network is compatible with a dextral offset on the karakorum fault of 250 km at a rate of 10 1 mm yr displacement along the karakorum fault possibly induced the shift from external to an internal drainage system by damming of the bangong co 4 ma ago leading to the isolation and preservation of the western tibet relief

geochemical discrimination of five pleistocene lava dam outburst flood deposits western grand canyon arizona abstract pleistocene basaltic lava dams and outburst flood deposits in the western grand canyon arizona have been correlated by means of cosmogenic 3he 3hec ages and concentrations of sio2 na2o k2o and rare earth elements these data indicate that basalt clasts and vitroclasts in a given outburst flood deposit came from a common source a lava dam with these data it is possible to distinguish individual dam flood events and improve our understanding of the interrelations of volcanism and river processes at least five lava dams on the colorado river failed catastrophically between 100 and 525 ka subsequent outburst floods emplaced basalt rich deposits preserved on benches as high as 200 m above the current river and up to 53 km downstream of dam sites chemical data also distinguishes individual lava flows that were collectively mapped in the past as large long lasting dam complexes these chemical data in combination with age constraints increase our ability to correlate lava dams and outburs

oxygen and carbon isotope patterns archived in shells of the aquatic gastropod radix hydrologic and climatic signals across the tibetan plateau in sub monthly resolution abstract the tibetan plateau tp including its surrounding mountain ranges represents the largest store of ice outside the polar regions it hosts numerous lakes as well as the head waters of major asian rivers on which billions of people depend and it is particularly sensitive to climate change the moisture transport to the tp is controlled by the indian and pacific monsoon and the westerlies understanding the evolution of the interaction of these circulation systems requires studies on climate archives in different spatial and temporal contexts the objective of this study is to learn more about the interannual variability of precipitation patterns across the tp and how different hydrologic systems react to different climatic factors aragonite shells of the aquatic gastropod radix which is widely distributed in the region may represent suitable archives for inferring hydrologic and climatic signals in particularly high resolution therefore sclerochronological studies of 18 o and 13 c ratios in radix shells from seven lakes were conducted each representing a different hydrologic and climatic setting on a transect from the pamirs across the tp the shell patterns exhibit an increasing influence of precipitation and a decreasing influence of evaporation on the isotope compositions from west to east 18 o values of shells from lakes on the eastern and central tp donggi cona yamdrok yumco tarab co mirror monsoon signals indicated by more negative values and higher variabilities compared to the more western lakes karakul bangong nyak manasarovar in yadang co located on the central southern tp the monsoon rains did not reach the lake in the sampling year although it is located in a region which is usually affected by monsoon circulation the 18 o values are used to differentiate the annual hydrological cycle into ice cover period melt water period precipitation period and evaporation period 13 c compositions in the shells particularly depend on specific habitats which vary in biological productivity and in carbon sources 18 o and 13 c patterns show a positive covariance in shells originating from large closed basins the results show that radix shells mirror general climatic differences between the seven lake regions these differences reflect both regional and local climate signals in sub seasonal resolution without noticeable dependence on the particular lake system

landforms and landscape evolution in the skardu shigar and braldu valleys central karakoram abstract the central karakoram which includes k2 in pakistan is one of the most rapidly rising areas on earth and exhibits complex topography and extreme relief impressive valley fills and glacial landforms are present throughout the valleys the dynamics of landscape evolution of the region are currently not well understood consequently the landforms were mapped and assessed in the skardu shigar and braldu valleys to elucidate the spatio temporal scale dependencies of surface processes active in the region these valleys were examined using geomorphic field methods remote sensing geomorphometry and terrestrial cosmogenic nuclides tcns surface exposure dating the glaciers in this region have oscillated considerably throughout the late quaternary and four glacial stages have been recognized including at least six glacial advances surface processes readjusted after glacier retreat and ubiquitous mass movements and catastrophic landsliding transported material from steep slopes to valley bottoms while glaciofluvial meltwater and glacier outburst floods redistributed sediment down valley glacier geochronology and late holocene ages of the outburst flood deposits indicate that landscape evolution has been dominated by glaciation and paraglaciation during the late quaternary

paleohydraulic reconstruction of flash flood peaks from boulder deposits in the colorado front range nine watersheds in the colorado front range with steep bedrock channels were used to test the accuracy of paleohydraulic reconstruction of large flash floods using boulder deposits the nine basins consist of eight small ungauged basins ranging in size from 1 6 to 29 km2 and the big thompson river at the mouth of the big thompson canyon draining 790 km2 between 1923 and 1976 all nine basins had had one catastrophic flash flood the magnitude of which has been estimated by the conventional slope area method in each basin coarse boulder deposits of the large flash floods were identified and three axes of the five largest boulders were measured along with at least two profiles of the valley cross section a simple arithmetic average of two theoretical and two empirical relationships was used to estimate average flood velocity using boulder size and shape average depth was estimated as the arithmetic average of four values computed from the manning equation a regression equation for boulder size and unit stream power a relative smoothness equation and a modified shields relationship the appropriate flood width for the estimated average depth was found by iteration using the valley cross sections the paleohydraulic discharges thus computed generally underestimate conventional slope area discharge estimates on small streams by as much as 75 although the average amount is only 28 too low and the reconstructed discharge in one stream was 31 too large the big thompson river flood of 1976 was overestimated by 76 reasons for discrepancy in reconstructed peaks could include 1 the possibility that floods may have been able to move boulders larger than those available to be moved 2 overestimation of the slope area discharge because high water marks were set prior to erosion of the channel 3 underestimation of original roughness coefficients and 4 macroturbulent effects during fast deep flows the paleohydraulic technique is applied to two other streams in colorado with sedimentological evidence of large flash floods but no conventional indirect discharge estimates a small tributary to the big thompson river draining 1 8 km2 has a paleohydraulic reconstructed flood peak of about 60 m3 s from a flood in 1976 using boulders excavated from a foundation site in holocene alluvium along boulder creek in boulder colorado a paleohydraulic reconstructed flood peak of between 860 and 1 512 m3 s is calculated this is 1 4 to 2 4 times the magnitude of the estimated 500 yr flood

paleodischarge of the late pleistocene bonneville flood snake river idaho computed from new evidence the bonneville flood resulted from catastrophic outflow from pleistocene lake bonneville about 15 000 yr ago when the lake overtopped its rim at red rock pass in southeastern idaho and discharged a vast volume of water down the snake river this paper provides revised estimates of the paleodischarge volume and duration of the bonneville flood based on new evidence of its height and on current understanding of the amount of lowering of lake bonneville evidence for the revised height of the flood is derived from the altitude of erosional features and flood deposits at the head of a constricted reach of the snake river canyon at the mouth of sinker creek and from the altitudes of flood deposits at several places about 53 km upstream using the step backwater method we estimate that peak discharge for the bonneville flood through the constricted reach was from 793 000 to 1 020 000 m 3 s and most likely was 935 000 m 3 s this discharge is 2 2 times the discharge previously reported and is the second largest flood known to have occurred in the world at this rate of discharge the shear stress for the flood would have been 2 500 n m 2 and the unit stream power would have been 75 000 n m s as compared with values of 6 to 10 n m 2 and 12 n m s for recent floods on the mississippi and the amazon other recent studies of the history of lake bonneville show that the volume of water released was 4 700 km 3 or about 3 times greater than the volume previously inferred although this volume indicates a flood duration of 8 weeks at constant peak discharge an accurate estimate of the duration would require dam break modeling at red rock pass from a dam break model flood hydrographs at red rock pass and the hydraulics of the flood wave along the snake river could be computed

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

holocene environmental changes in lake bangong basin western tibet part 1 chronology and stable isotopes of carbonates of a holocene lacustrine core abstract a 12 4 m core collected from the eastern part of lake bangong is analyzed for mineralogy radiometric chronology and stable isotope contents of authigenic inorganic carbonate isotopic compositions of the modern lake waters and of its major tributaries are first presented radiocarbon activity of these waters show that equilibrium with the atmospheric co2 is not reached because of admixture of dead carbon in solution in the system a model is thus developed to correct the radiocarbon ages of fossil material of aquatic origin for this ageing the core provides a continuous holocene record changes in mineralogy of bulk sediments and in 13c and 18o contents of authigenic carbonates reveal extremely large changes in environmental conditions induced by climate changes and or local hydrological factors e g closure opening of the lake system controlled by the altitude of the outflow sill the eastern basin of lake bangong was closed before 9 6 and after 1 2 ka b p in response to aridity on the catchment wet warm conditions attributed to the monsoon influence were established suddenly at 9 6 ka b p and maintained until 6 2 ka b p although minor reversal events occurred between 8 6 and 7 7 ka b p the return towards aridity is non linear dry spells at 6 2 3 9 3 2 and 1 3 ka b p are alternated with short term periods with positive precipitation evaporation balance

climate driven bedrock incision in an active mountain belt measurements of fluvial bedrock incision were made with submillimeter precision in the east central range of taiwan where long term exhumation rates and precipitation driven river discharge are independently known they indicate that valley lowering is driven by relatively frequent flows of moderate intensity abrasion by suspended sediment is an important fluvial wear process and channel bed geometry and the presence of widely spaced planes of weakness in the rock mass influence erosion rate and style

transient quaternary erosion and tectonic inversion of the northern range trinidad abstract cosmogenic 10be measured in sediments from northern range catchments on the island of trinidad reveals low millennial scale rates of erosion average 40 mm ka that increase roughly eightfold from 11 to 92 mm ka eastward across the mountain range these results in conjunction with an analysis of mountain morphometrics are consistent with quaternary east side up tilting of the northern range which has occurred recently 100 ka the highest millennial scale erosion rates coincide spatially with quaternary east side surface uplift albeit not in magnitude high modern rainfall rates low topographic relief and convex longitudinal stream profiles indicating transient quaternary erosion we interpret that hillslope adjustment and erosion of the northern range is buffered from climatic and tectonic forcings by dense tropical vegetation cover thick saprolite and porous regolith compared with longer term thermochronology exhumation rates we document that an order of magnitude deceleration of and reversal in the locus of erosion and exhumation has occurred during the pliocene to the holocene we suggest that these combined data sets highlight distinct syn and post collisional phases of northern range development that are related to a major change in relative caribbean south american plate motion from oblique convergence to transform motion oblique collision during the mid miocene likely caused relatively higher rates of and asymmetric exhumation of the northern range post collisional mountain scale tilting is likely caused by a combination of crustal extension in the gulf of paria and by deep subsurface lithospheric detachment processes that drives dynamic topography

using clast geometries to establish paleoriver discharges testing records for aggradation and incision from the upper indus river ladakh himalaya abstract river systems in the himalaya have been studied extensively to understand the processes driving periodic river valley aggradation and incision resulting due to rainfall high relief and ongoing deformation when climatic forces are considered the debate continues on whether wetter climatic intervals with localized glacier melting promote river aggradation through increased discharge and enhanced sediment load or instead it is during drier conditions that aggradation occurs through increased sediment to water ratio this study for the first time attempts to constrain discharge during periods of established river aggradation and incision over late quaternary here geometric data from imbricated gravels of channel fills are used to calculate paleodischarges during net river aggradation at 47 23 ka and preserved slack water deposits swds at 14 10 ka are used to constrain paleodischarges that occurred during net river incision catchment area normalized discharge derived from these valley fill sequences ranges from 0 78 to 3 26 10 7 m s 1 syn incision discharge estimates yielded normalized discharge values of 6 17 10 7 m s 1 are considerably higher than discharges estimated from periods of aggradation morphometric analysis chi slope and ksn along the indus river observed no relation with the paleodischarge this case study implies that net river incision in the upper indus river occurs predominantly during relatively wetter climatic conditions than the climate during aggradation

karakoram fault zone rocks cool in two phases the karakoram fault zone of ladakh india is a major strike slip boundary along which the tectonic evolution of tibet has been accommodated in this paper 40 ar 39 ar isotopic age data are integrated with structural and metamorphic data to infer an exhumation history for granites and low to intermediate grade metamorphic rocks exposed adjacent to two strands of the fault zone near tangtse leucogranites which crystallized c 17 ma ago are cut by the karakoram fault zone indicating that fault movement was initiated subsequent to 17 ma the 40 ar 39 ar data give temperature time histories which indicate that the two phases of rapid cooling of karakoram fault zone rocks are evident one at c 17 ma to c 13 ma and another following an intervening period of relatively slow cooling starting at c 8 ma and continuing until at least 7 ma uplift since c 17 ma via dextral oblique thrusting has resulted in exhumation from amphibolite facies metamorphic conditions possibly with a larger thrust component from 17 to 13 ma followed by a change to dominant strike slip motion at about 13 ma rapid cooling starting at c 8 ma at greenschist facies temperatures is probably the result of renewed oblique thrusting it is notable that the two episodes of rapid cooling recorded in karakoram fault zone rocks coincide with episodes of exhumation in the pakistani karakoram and also in southern tibet

reconstruction of the 30 40 ka bp enhanced indian monsoon climate based on geological records from the tibetan plateau abstract multi proxy records from ice caps lakes and pollen records from the tibetan plateau are used to reconstruct the palaeoclimate during the period 30 40 ka bp lake geomorphological and lacustrine sedimentological studies show that numerous high lake level stands and or freshwater lakes occurred in large areas of western china at this time including over the tibetan plateau where the area contains mostly shallow water and saline hypersaline water lakes under extremely dry conditions of today pollen based reconstruction of tibetan vegetation shows systematic differences from the present alpine steppe forests were shifted ca 400 km further north and the alpine conifer forest extended ca 400 800 km beyond their present western limits variations in 18 o curves from ice cores from the plateau suggest that the temperature was 2 4 c higher and precipitation was 40 to over 100 higher than today all of the evidence consistently suggests the existence of an exceedingly strong summer monsoon climate over the plateau the vigorous evaporation of the tropical ocean surface would also play an important role in promoting the penetration of moisture rich southwest monsoon over the tibetan plateau these climate patterns with strong summer monsoon circulation during the period 30 40 ka bp reflect the 20 ka earth orbital precessional cycle when the tibetan plateau region received greater solar radiation which thus enlarged the thermodynamical contrast between the plateau and the mid south portion of the indian ocean

a catastrophic flood caused by drainage of a caldera lake at aniakchak volcano alaska and implications for volcanic hazards assessment aniakchak caldera located on the alaska peninsula of southwest alaska formerly contained a large lake estimated volume 3 7 10 9 m 3 that rapidly drained as a result of failure of the caldera rim sometime after ca 3400 yr b p the peak discharge of the resulting flood was estimated using three methods 1 flow competence equations 2 step backwater modeling and 3 a dam break model the results of the dam break model indicate that the peak discharge at the breach in the caldera rim was at least 7 7 10 4 m 3 s 1 and the maximum possible discharge was 1 1 10 6 m 3 s 1 flow competence estimates of discharge based on the largest boulders transported by the flood indicate that the peak discharge values which were a few kilometers downstream of the breach ranged from 6 4 10 5 to 4 8 10 6 m 3 s 1 similar but less variable results were obtained by step backwater modeling finally discharge estimates based on regression equations relating peak discharge to the volume and depth of the impounded water although limited by constraining assumptions provide results within the range of values determined by the other methods the discovery and documentation of a flood caused by the failure of the caldera rim at aniakchak caldera underscore the significance and associated hydrologic hazards of potential large floods at other lake filled calderas

quaternary glaciation in the nubra and shyok valley confluence northernmost ladakh india abstract three glacial stages deshkit 1 deshkit 2 and dishkit 3 glacial stages are identified in the nubra and shyok valleys in northernmost ladakh northwest india on the basis of geomorphic field mapping remote sensing and 10be terrestrial cosmogenic nuclide surface exposure dating the glacial stages date to 45 ka deshkit 1 glacial stage 81 ka deshkit 2 glacial stage and 144 ka deshkit 3 glacial stage a mean equilibrium line altitude depression of 290 m for the deshkit 1 glacial stage was calculated using the area accumulation ratio toe to headwall ratio area altitude and area altitude balance ratio methods comparison of glaciation in the nubra and shyok valleys with glaciations in the adjacent central karakoram of northern pakistan and northern side of the ladakh range of northern india indicates that glaciation was synchronous on milankovitch timescales across the region during mis 6 but differed greatly in extent with more extensive glaciation in the karakoram than the morphostratigraphically equivalent glaciation on the northern slopes of the ladakh range this highlights the strong contrast in the extent of glaciation across ranges in the himalaya tibetan orogen necessitating caution when correlating glacial successions within and between mountain ranges

how large is the upper indus basin the pitfalls of auto delineation using dems summary extraction of watershed areas from digital elevation models dems is increasingly required in a variety of environmental analyses it is facilitated by the availability of dems based on remotely sensed data and by geographical information system gis software however accurate delineation depends on the quality of the dem and the methodology adopted this paper considers automated and supervised delineation in a case study of the upper indus basin uib pakistan for which published estimates of the basin area show significant disagreement ranging from 166 000 to 266 000 km 2 automated delineation used arcgis archydro and hydrology tools applied to three good quality dems two from srtm data with 90m resolution and one from 30m resolution aster data automatic delineation defined a basin area of c 440 000 km 2 for the uib but included a large area of internal drainage in the western tibetan plateau it is shown that discrepancies between different estimates reflect differences in the initial extent of the dem used for watershed delineation and the unchecked effect of iterative pit filling of the dem going beyond the filling of erroneous pixels to filling entire closed basins for the uib we have identified critical points where spurious addition of catchment area has arisen and use google earth to examine the geomorphology adjacent to these points and also examine the basin boundary data provided by the hydrosheds database we show that the pangong tso watershed and some other areas in the western tibetan plateau are not part of the uib but are areas of internal drainage our best estimate of the area of the upper indus basin at besham qila is 164 867 km 2 based on the srtm dem and 164 853 km 2 using the aster dem this matches the catchment area measured by wapda swhp an important lesson from this investigation is that one should not rely on automated delineation as iterative pit filling can produce spurious drainage networks and basins when there are areas of internal drainage nearby

terrestrial cosmogenic nuclide surface exposure dating of the oldest glacial successions in the himalayan orogen ladakh range northern india terrestrial cosmogenic nuclide surface exposure dating of moraine boulders and alluvial fan sediments define the timing of five glacial advances over at least the last five glacial cycles in the ladakh range of the transhimalaya the glacial stages that have been identified are the indus valley glacial stage dated at older than 430 ka the leh glacial stage occurring in the penultimate glacial cycle or older the kar glacial stage occurring during the early part of the last glacial cycle the bazgo glacial stage at its maximum during the middle of the last glacial cycle and the early holocene khalling glacial stage the exposure ages of the indus valley moraines are the oldest observed to date throughout the himalayan orogen we observe a pattern of progressively more restricted glaciation during the last five glacial cycles likely indicating a progressive reduction in the moisture supply necessary to sustain glaciation a possible explanation is that uplift of himalayan ranges to the south and or of the karakoram mountains to the west of the region may have effectively blocked moisture supply by the south asian summer monsoon and mid latitude westerlies respectively alternatively this pattern of glaciation may reflect a trend of progressively less extensive glaciation in mountain regions that has been observed globally throughout the pleistocene

quaternary glacial history of the central karakoram abstract the quaternary glacial history of the world s highest mountains the central karakoram is examined for the first time using geomorphic mapping of landforms and sediments and 10 be terrestrial cosmogenic nuclide surface exposure dating of boulders on the moraines and glacially eroded surfaces four glacial stages are defined the bunthang glacial stage 0 7 ma the skardu glacial stage marine oxygen isotope stage mis 6 or older the mungo glacial stage mis 2 and the askole glacial stage holocene glaciers advanced several times during each glacial stage these advances are not well defined for the oldest glacial stages but during the mungo and askole glacial stages glacial advances likely occurred at 16 11 13 5 and 0 8 ka the extent of glaciation in this region became increasingly more restricted over time in the braldu and shigar valleys glaciers advanced 150 km during the bunthang and skardu glacial stages while glaciers advanced 80 km beyond their present positions during the mungo glacial stage in contrast glaciers advanced a few kilometers from present ice margins during the askole glacial stage glacier in this region likely respond in a complex fashion to the same forcing that causes changes in northern hemisphere oceans and ice sheets teleconnected via the mid latitude westerlies and also to changes in monsoonal intensity

impulsive alluviation during early holocene strengthened monsoons central nepal himalaya the steep walled bedrock gorges of the greater himalayan rivers currently lack significant stored sediment suggesting that fluvial erosion and transport capacity outpace the supply of sediment from adjacent hillsides despite this appearance of sustained downcutting such rivers can become choked with sediments and aggrade during intervals of higher precipitation cosmogenic dating 10 be and 26 al of fluvially carved bedrock surfaces indicates that sediment at least 80 m thick filled the marsyandi river valley in central nepal during a time of strengthened early holocene monsoons despite threefold differences in height 43 124 m above the modern river these fluvial surfaces display strikingly similar cosmogenic exposure ages clustering around 7 6 1 ka we speculate that enhanced monsoonal precipitation increased pore pressure and the frequency of landsliding thereby generating a pulse of hillslope derived sediment that temporarily overwhelmed this alpine fluvial system s transport capacity after the easily liberated material was exhausted ca 7 ka the hillslope flux dropped and the river incised through the aggraded alluvium it concurrently eroded adjacent rock walls thereby removing previously accumulated 10 be and 26 al and resetting the cosmogenic clock in the bedrock unlike previous studies these exposure ages cannot be used to derive river incision rates instead they record a coupled fluvial hillslope response to climate change

intra seasonal hydrological processes on the western tibetan plateau monsoonal and convective rainfall events at 7 5 ka abstract the tibetan plateau and the himalayas influence monsoonal circulation patterns and represent the water towers of humanity modern coupling of atmospheric circulation and the hydrological cycle over and on the plateau can be observed and delineated and the factors that control lake levels can be identified recent monitoring of lakes has shown that many have grown for decades due to higher meltwater inflow or stronger rainfall from different sources depending on the location the long term dynamics of lakes however can be best described by using high resolution climate archives we focus here on the often controversial discussion of holocene lake development and use the bangong co drainage basin on the western tibetan plateau as a case study we aim to identify the factors that influence lake level such as monsoonal or convective precipitation and meltwater to accomplish this shells of the aquatic gastropod genus radix were collected from an early middle holocene sediment sequence in the nama chu subcatchment of the eastern bangong co and sclerochronlogical isotope patterns for five shells were obtained at a weekly to submonthly resolution our data suggest that at ca 7 5 ka monsoonal rainfall was higher than it is today however summer precipitation was not continuous but occurred as extended moisture pulses this result implies that the northern boundary of the sw asian monsoon was similar to that today we identify convective rainfall events significantly stronger than today and relate these events to higher soil moisture and larger lake surface areas under higher insolation conditions the regional amount of meltwater corresponds with the westerly derived winter snowfall exceptionally heavy 13c values archived in the shells were likely at least partly triggered by biogenic methane production we suggest that our approach is suitable for studying other lake systems on the tibetan plateau from which fossil radix shells can be obtained

scaling time integrated in situ cosmogenic nuclide production rates using a continuous geomagnetic model abstract spatial and temporal variations in earth s magnetic field affect the corresponding time integrated distribution of in situ cosmogenic nuclide cn production rates these effects can be quantified by the effective vertical cutoff rigidity r c a measure of the energy required for primary cosmic rays to penetrate the geomagnetic field and interact with the atmosphere at a given location recent cn production rate scaling models are based on atmospheric cosmic ray measurements parameterized using r c estimates derived from detailed modern geomagnetic field representations which include both dipole and non dipole field contributions however published methods for quantifying time integrated geomagnetic effects on cn production rate scaling rely on various geocentric dipolar approximations to r c driven by separate records of paleomagnetic pole position and paleointensity therefore applying dipolar paleomagnetic records spanning millennial time scales which explicitly ignore past non dipole effects to scaling models derived using modern geomagnetic field representations may lead to systematic errors in any calculated results a recently published continuous geomagnetic model covering the last 7 kyr cals7k 2 m korte and c g constable continuous geomagnetic field models for the past 7 millennia 2 cals7k 2005 geochem geophys geosyst 6 q02h16 doi 10 1029 2004gc000801 may allow reduction of such errors by bridging the gap between detailed modern geomagnetic and simplified paleomagnetic models we have developed a new model framework describing temporal and spatial variation in r c for 0 7 ka and earlier based on cals7k 2 which explicitly accounts for non dipole field effects while attempting to mitigate systematic scaling biases scaling factors derived using the new r c framework predict significant longitudinal variability in time integrated cn production while predictions using dipolar geomagnetic approximations do not one can test these predictions using in situ cosmogenic 14 c in situ 14 c in quartz due to its short half life 5 73 kyr 14 c attains secular equilibrium between production and decay after approximately 25 kyr of exposure at which point its measured concentration is only a function of its integrated average production rate initial in situ 14 c results from samples at secular equilibrium from 38 n and 3 5 km in tibet and eastern california are consistent with the longitudinal variability predicted by the new framework

cosmic ray production rates of 10be and 26al in quartz from glacially polished rocks we have studied the concentrations of 10be and 26al in quartz crystals extracted from glacially polished granitic surfaces from the sierra nevada range these surfaces were identified with the glacial advance during the tioga period 11 000 years ago our measurements yield the most accurate estimates to date for the absolute production rates of these nuclides in sio2 due to cosmic ray nucleons and muons for geomagnetic latitudes 43 8 44 6 n and altitudes 2 1 3 6 km the estimates are relatively free from uncertainties in snow cover since we studied a suite of rock surfaces inclined 0 75 with respect to the horizontal the principal uncertainty arises due to the lack of a precise date for the glacial retreat event about 10 the 26al 10be ratio at production 6 0 is determined more accurately since the exposure age of the samples is 2 orders of magnitude smaller than the mean lives of the two nuclides production rates of 10be and 26al in quartz at other latitudes and altitudes in the troposphere can be determined from the present measurements by scaling using the known altitude and latitude dependence of cosmic ray fluxes of nucleons and negative muons knowledge of the production rates of these nuclides is a prerequisite for their application in erosion and geomorphological studies

tibetan plateau river incision inhibited by glacial stabilization of the tsangpo gorge much attention has focused on how and when the tibetan plateau formed but far less research has been done on the controls on river incision into the plateau itself oliver korup and david montgomery address this issue which also relates to the question of why the tibetan plateau is still there at all despite hosting one of the deepest gorges on earth the plateau edge is extremely well defined and according to widely accepted stream power theory should be heavily dissected by one of asia s most powerful rivers the yarlung tsangp or yarlung zangbo korup and montgomery propose that the southeastern edge of the plateau was preserved in part by the presence of glaciers that were large enough during the holocene to stall aggressive river downcutting along the plateau margin a considerable amount of research has focused on how and when the tibetan plateau formed in the wake of tectonic convergence between india and asia1 although far less enquiry has addressed the controls on river incision into the plateau itself2 widely accepted theory3 predicts that steep fluvial knick points river reaches with very steep gradients in the eastern himalayan syntaxis at the southeastern plateau margin should erode rapidly4 driving a wave of incision back into the plateau preservation of the plateau edge thus presents something of a conundrum that may be resolved by invoking either differential rock uplift matching erosional decay5 6 7 or other mechanisms for retarding bedrock river incision8 9 in this region where high stream power excludes the potential for aridity as a simple limit to dissection of the plateau10 here we report morphologic evidence showing that quaternary depression of the regional equilibrium line altitude where long term glacier mass gain equals mass loss was sufficient to repeatedly form moraine dams on major rivers such damming substantially impeded river incision into the southeastern edge of the tibetan plateau through the coupled effects of upstream impoundment and interglacial aggradation such glacial stabilization of the resulting highly focused river incision centred on the tsangpo gorge could further contribute to initiating and accentuating a locus of rapid exhumation known as tectonic anaeurysm6

late quaternary geomorphic scenario due to changing depositional regimes in the tangtse valley trans himalaya nw india abstract records from the tangtse valley in the trans himalaya reveal depositional history since 48 ka with fluvial aggradation followed by incision lacustrine sediment fill and later incision varied sedimentary architecture with fluvial episodes intervened by lacustrine pulses flood events colluvial and glacial activity are preserved the valley is located west of the pangong tso bangong co one of the largest lakes in tibet which has served as a spillway flooding and damming the entire tangtse valley resulting in the formation of a lake today pangong tso consists of five basins separated by shallow sills and is fed by snow melt documentation based on 14 c and osl chronologies of the sediment sections throughout the valley reveals evidence of a sixth basin of pangong tso toward west occupying the present day tangtse valley between 9 6 5 1 ka this event coincides with periods of high lake levels in tibet china as well as intensified monsoon periods over the indian subcontinent a fluvial regime around 48 ka and 30 21 ka with comparatively arid conditions and dry phases interspersed by flooding is documented the valley has been incised to depths of 40 50 m in the upper part and to 130 m in the lower part the incision rate ranges from 0 3 to 1 2 mm yr 1 in the upper part and reaches as high as 10 8 mm yr 1 in the lower valley much of the incision took place between 22 and 9 6 ka although repeated sediment fill incision cycles in the valley from 30 22 ka 22 9 6 ka 9 6 5 1 ka 5 1 ka and even to present time were observed

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

paleofloods records in himalaya we use paleoflood deposits to reconstruct a record of past floods for the alaknanda mandakini rivers garhwal himalaya the indus river ladakh nw himalaya and the brahmaputra river ne himalaya the deposits are characterized by sand silt couplets massive sand beds and from debris flow sediment the chronology of paleoflood deposits established by optically stimulated luminescence osl and c 14 ams dating techniques indicates the following i the alaknanda mandakini rivers experienced large floods during the wet and warm medieval climate anomaly mca ii the indus river experienced at least 14 large floods during the holocene climatic optimum when flood discharges were likely an order of magnitude higher than those of modern floods and iii the brahmaputra river experienced a megaflood between 8 and 6 ka magnetic susceptibility of flood sediments indicates that 10 out of 14 floods on the indus river originated in the catchments draining the ladakh batholith indicating the potential role of glacial lake outbursts glofs and or landslide lake outbursts llofs in compounding flood magnitudes pollen recovered from debris flow deposits located in the headwaters of the mandakini river showed the presence of warmth loving trees and marshy taxa thereby corroborating the finding that floods occurred during relatively warm periods collectively our new data indicate that floods in the himalaya largely occur during warm and wet climatic phases further the evidence supports the notion that the indian summer monsoon front may have penetrated into the ladakh area during the holocene climatic optimum c 2016 elsevier b v all rights reserved

late quaternary valley infill and dissection in the indus river western tibetan plateau margin abstract the indus one of earth s major rivers drains large parts of the nw himalaya and the transhimalayan ranges that form part of the western tibetan plateau margin in the western himalayan syntaxis where local topographic relief exceeds 7 km the indus has incised a steep bedrock gorge at rates of several mm yr 1 upstream however the upper indus and its tributaries alternate between bedrock gorges and broad alluvial flats flanked by the ladakh and zanskar ranges we review the late quaternary valley history in this region with a focus on the confluence of the indus and zanskar rivers where vast alluvial terrace staircases and lake sediments record major episodes of aggradation and incision new absolute dating of high level fluvial terrace remnants using cosmogenic 10 be optically and infrared stimulated luminescence osl irsl indicates at least two phases of late quaternary valley infilling these phases commenced before 200 ka and 50 20 ka judging from terrace treads stranded 150 m and 30 40 m above modern river levels respectively numerous stacks of lacustrine sediments that straddle the indus river 200 km between the city of leh and the confluence with the shyok river share a distinct horizontal alignment constraints from irsl samples of lacustrine sequences from the leh spituk area reveal a protracted lake phase from 177 ka to 72 ka locally accumulating 50 m thick deposits in the absence of tectonic faulting major lithological differences and stream capture we attribute the formation of this and other large lakes in the region to natural damming by large landslides glaciers and alluvial fans the overall patchy landform age constraints from earlier studies can be reconciled by postulating a major deglacial control on sediment flux valley infilling and subsequent incision that has been modulated locally by backwater effects of natural damming while comparison with pleistocene monsoon proxies reveals no obvious correlation a late or post glacial sediment pulse seems a more likely source of this widespread sedimentation that has partly buried the dissected bedrock topography overall the long residence times of fluvial alluvial and lacustrine deposits in the region 500 ka support previous studies but remain striking given the dominantly steep slopes and deeply carved valleys that characterise this high altitude mountain desert recalculated late quaternary rates of fluvial bedrock incision in the indus and zanskar of 1 5 0 2 mm yr 1 are at odds with the longevity of juxtaposed valley fill deposits unless a lack of decisive lateral fluvial erosion helps to preserve these late pleistocene sedimentary archives we conclude that alternating 10 4 yr long phases of massive infilling and incision have dominated the late quaternary history of the indus valley below the western tibetan plateau margin

late quaternary intensified monsoon phases control landscape evolution in the northwest himalaya the intensity of the asian summer monsoon circulation varies over decadal to millennial time scales and is reflected in changes in surface processes terrestrial environments and marine sedi ment records however the mechanisms of long lived 2 5 k y intensified monsoon phases the related changes in precipitation distribution and their effect on landscape evolution and sedimen tation rates are not yet well understood the arid high elevation sectors of the orogen correspond to a climatically sensitive zone that currently receives rain only during abnormal i e strength ened monsoon seasons analogous to present day rainfall anom alies enhanced precipitation during an intensified monsoon phase is expected to have penetrated far into these geomorphic threshold regions where hillslopes are close to the angle of failure we as sociate landslide triggering during intensified monsoon phases with enhanced precipitation discharge and sediment flux leading to an increase in pore water pressure lateral scouring of rivers and ov ersteepening of hillslopes eventually resulting in failure of slopes and exceptionally large mass movements here we use lacustrine deposits related to spatially and temporally clustered large land slides 0 5 km 3 in the sutlej valley region of the northwest him alaya to calculate sedimentation rates and to infer rainfall patterns during late pleistocene 29 24 ka and holocene 10 4 ka inten sified monsoon phases compared to present day sediment flux measurements a fivefold increase in sediment transport rates re corded by sediments in landslide dammed lakes characterized these episodes of high climatic variability these changes thus em phasize the pronounced imprint of millennial scale climate change on surface processes and landscape evolution

slip rates of the karakorum fault ladakh india determined using cosmic ray exposure dating of debris flows and moraines most recent major glacial advance occurred at 90 15 ka this is consistent with the inference of others that alpine glaciers in this region have not necessarily expanded in concert with northern hemisphere continental ice sheets if features including lateral moraines that liu inferred to have been offset 300 350 m by the karakorum fault date from the same period they too imply a slip rate of 3 4 mm yr 1 this slip rate is comparable to rates of extension across grabens within tibet with recent evidence that slip along the altyn tagh fault occurs at 10 mm yr 1 our rate suggests that slip along the boundaries of tibet is not significantly more rapid than extension within the plateau hence plate tectonics in the strictest sense ought not be applied to tibet because tibet does not behave as a rigid plate index terms 1824 hydrology geomorphology 1625 1035 geochemistry geochronology 9320 information related to geographic region asia 8107 tectonophysics continental neotectonics keywords karakorum fault slip rate cosmic ray exposure age beryllium 10

catastrophic partial drainage of pangong tso northern india and tibet abstract catastrophic partial drainage of pangong tso one of the largest lakes in tibet is supported by the geomorphology of the tangtse valley ladakh northern india and cosmogenic 10be nuclide ages of roche moutonnees strath terraces and a flood deposit downstream from the former spillway the former spillway for pangong tso is 20 m high and likely allowed 18 km3 of water to drain catastrophically down the tangtse valley over a period of about 2 days sometime during the latest pleistocene to early holocene the largest flood deposit composed of imbricated granitic boulders up to 4 5 m in length is present 33 km downvalley of the spillway these boulders have a cosmogenic 10be exposure age of 11 1 1 0 ka the age of the outburst flood the minimum calculated discharge was 110 000 m3 s 1 one set of strath terraces upvalley of the flood deposit along the flood s drainage path shows that the rate of fluvial incision 0 3 0 1 mm y 1 during 122 10 5 ka increased to 1 5 0 5 mm y 1 during 10 5 ka to the present the temporal overlap of this increase in the rate of fluvial incision with the main flood deposit suggests that the flood was important in defining the incision along the tangste valley a second set of strath terraces shows little change in incision from 0 6 0 9 to 0 9 1 4 mm y 1 sometime between 18 and 27 ka roche moutonnees upvalley from strath terraces yield a cosmogenic 10be age of 35 8 3 0 ka defining the time when glaciers last occupied the tangtse valley however the lack of glacial sediment along the tangste valley suggests that the flood eroded glacial depositional landforms and sediments resulting in high sediment loads in the floodwater which in turn increased fluvial incision to form strath terraces much of the eroded glacial sediment was subsequently redeposited as the main flood deposit the catastrophic drainage of pangong tso may be the result of breaching of the pangong tangste spillway during very high lake levels in a period of intensified monsoon 10 7 9 6 ka and or possibly the consequence of seismic activity along the karakoram fault that is associated with the initial formation of pangong tso

asymmetrical erosion and morphological development of the central ladakh range northern india abstract variations in erosion were quantified across the topographically and morphometrically asymmetrical central ladakh range in nw india to elucidate erosion and sediment transfer processes across space and time and to gain insight into how mountains erode and evolve morphometric analysis and 10 be cosmogenic nuclide analysis of 14 fluvial sediment samples from active channels in six catchments conducted across the mountain range constrains 100 ka timescale erosion rates for catchments on the northern side of the mountain range and are between 56 12 and 74 11 m ma while catchments on the southern side of the mountain range to between 20 3 and 39 8 m ma for the last 300 ka maximum elevation from swath analysis across the range shows a strong correlation with the elas of 382 contemporary glaciers the higher erosion rate to the north likely relates to tectonic tilting of the central ladakh range and to active rock uplift on the northern side of the range along the karakoram fault morphometric analysis shows that the maximum and average elevations increase at nearly the same rate on a catchment scale across the central ladakh range with higher elevation on the northern side this suggests that greater erosion on the northern side of the range is not keeping pace with rock uplift moreover long term denudational unloading does not play a significant role in the tectonic tilting of the central ladakh range