increased late pleistocene erosion rates during fluvial aggradation in the garhwal himalaya northern india the response of surface processes to climatic forcing is fundamental for understanding the impacts of climate change on landscape evolution in the himalaya most large rivers feature prominent fill terraces that record an imbalance between sediment supply and transport capacity presumably due to past fluctuations in monsoon precipitation and or effects of glaciation at high elevation here we present volume estimates chronological constraints and 10 be derived paleo erosion rates from a prominent valley fill in the yamuna catchment garhwal himalaya to elucidate the coupled response of rivers and hillslopes to pleistocene climate change although precise age control is complicated due to methodological problems the new data support formation of the valley fill during the late pleistocene and its incision during the holocene we interpret this timing to indicate that changes in discharge and river transport capacity were major controls compared to the present day late pleistocene hillslope erosion rates were higher by a factor of 2 4 but appear to have decreased during valley aggradation the higher late pleistocene erosion rates are largely unrelated to glacial erosion and could be explained by enhanced sediment production on steep hillslopes due to increased periglacial activity that declined as temperatures increased alternatively erosion rates that decrease during valley aggradation are also consistent with reduced landsliding from threshold hillslopes as a result of rising base levels in that case the similarity of paleo erosion rates near the end of the aggradation period with modern erosion rates might imply that channels and hillslopes are not yet fully coupled everywhere and that present day hillslope erosion rates may underrepresent long term incision rates

palaeo moisture evolution in monsoonal central asia during the last 50 000 years abstract the late quaternary climate history of monsoonal central asia was inferred from 75 palaeoclimatic records which provide information about moisture conditions in the last 50 ka or part of this period wet conditions occurred during middle and late marine isotope stage 3 while the last glacial maximum lgm was characterized by dry climate conditions in the region a stepwise climate amelioration is suggested by the climate records following the lgm several climate signals of this period which were reported from high latitude ice core records are preserved in archives from monsoonal central asia as well during the early holocene high effective moisture was inferred from most records from the area dominated by the indian monsoon e g the tibetan plateau suggesting that holocene optimal climate conditions occurred there during this period in contrast areas which are dominated by the south east asian monsoon se monsoon and the westerlies in north western and north central china mongolia do not uniformly show an early holocene climate optimum for this area optimal conditions prevailed during the mid holocene these apparent contradictions can possibly be explained by the regional uplift and descent of air masses in the holocene during the early holocene strengthened insolation possibly caused an enhanced low level convergence over the tibetan plateau which led to the intensification of the summer monsoon the strong air uplift caused intensified precipitation and air divergence in the upper troposphere over the tibetan plateau the areas adjacent to the north therefore experienced an intensified descent of air masses and consequently increased aridity the majority of the palaeoclimatic records suggest reduced effective moisture since the late holocene in the region

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

palaeoflood estimates of pleistocene coarse grained river terrace landforms rio almanzora se spain abstract a series of palaeoflood estimation techniques are applied to an inset sequence of middle to late pleistocene river terrace landforms associated with the rio almanzora se spain the study area is a 7 km long transverse reach where 4 terrace levels level 1 highest and oldest level 4 lowest and youngest document some 200 m of incision across an uplifted basement block during the pleistocene for the broader region river terrace aggradation is attributed to increased sediment supply during glacial to interglacial transitions level 1 marine oxygen isotope stages mois 12 11 l2 10 9 l3 8 7 and l4 6 5 within the transverse reach terrace levels 2 3 and 4 are characterised by coarse boulder rich gravels d max 2 5 m organised into 3 5 m high cross beds level 4 is characterised by a series of km scale abandoned meander loops with levels 2 and 3 showing evidence for similar degraded high sinuosity forms the fluvial setting is interpreted as a braided river environment with lateral and longitudinal gravel barforms using field derived sedimentary boulder size etc and morphological width slope etc features flow competence and regime based methods were applied palaeoflood estimates varied from 40 to 2859 m 3 s with mean maximum discharges showing an increase through time l2 278 l3 413 l4 1361 m 3 s palaeoflood estimates were compared to flood events associated with the ephemeral modern rio almanzora catchment 2500 km 2 to establish whether palaeoflood values were reasonable estimations a 46 year 1963 2009 modern flood gauge record shows infrequent flood events with discharges typically 3 s a rare flood event in 1973 5680 m 3 s provides an upper value for comparison with the palaeoflood estimates although estimates appear reasonable they should be considered as minimum values due to 1 some disparities between flow depths derived from the palaeoflood equations 0 7 4 m and field based evidence 3 5 m high cross beds 2 issues related to field sampling of boulders from sections and 3 uncertainties as to the relationship between flood hydrology and transportation of boulders formation of 3 5 m high cross beds and the position of the terrace remnants in the river valley the palaeoflood estimates suggest that relatively large discharges occurred during valley floor aggradation in the glacial interglacial transitions periods characterised by low vegetation cover and high sediment yield discharge increases through time can be explained by the long term drainage evolution of the rio almanzora characterised by an expanding catchment area linked to river capture driven by regional uplift patterns the 3 5 times larger discharge estimates recorded in terrace level 4 are coeval with large and rapid changes in precipitation or elevated seasonal discharge linked to the mois 6 5 glacial interglacial climate transition overall within tectonically active regions affected by river capture fluvial systems could be responding to loss or expansion of catchment areas long term palaeoflood records from inset flights of river terraces could store such signals and may mask complicate any climate palaeoflood relationships

sedimentology petrography and tectonic significance of the shelf flysch and molasse clastic deposits across the indus suture zone ladakh nw india abstract in the ladakh area of india a passive triassic to lower cretaceous continental margin is indicated by indian shield derived clastics on the shelf and atlantic type turbidites off the continental margin mid cretaceous initiation of ocean closing is reflected in pacific type flysch and associated island are volcanics which were initially emplaced over the northern indian continental margin in late cretaceous times resulting in the formation of a fore deep in which flysch and minor continental molasse accumulated briefly during the late cretaceous these transient uplifts were however rapidly destroyed for by the latest cretaceous to latest palaeocene uniform carbonate sediments were being laid down over the area with the early eocene the development of a second fore deep this time filled with very thick flysch and molasse sediment indicates a major uplift of the northern indian margin which we attribute to the development of an andean type magmatic arc on the northern edge of the indian plate uplift and molasse sedimentation in this fore deep continued through the oligocene and miocene when the collision of india and asia caused extensive deformation of all the sequences and the shift of molasse sedimentation southwards to the himalaya foothills and indo gangetic plain

climatic variations and geomorphology of the indus river valley between nimo and batalik ladakh nw trans himalayas during late quaternary abstract the indus river valley is tectonically unstable exhibiting complex topography landscape relief and varied sedimentation the major geomorphic landforms are alluvial fans debris cones fluvio lacustrine deposits scree and talus cones in the present work a transect between nimo and batalik along the river was studied to consider the geomorphological landform evolution during the quaternary based on the distribution of the sediments along the valley mass movements catastrophic land sliding and tectonic activity transported material from steep slopes to valley bottoms which were responsible for forming lakes preserved as thick piles of fine sediment while the outburst floods redistributed sediment down valley three phases of lake formation are recorded in the 136 km stretch 35 000 26 000 bp lamayuru palaeolake 17 000 13 000 bp rizong palaeolake occupying 35 km of the valley length and 14 000 5000 bp khalsi saspol palaeolake 55 km in length and having the highest lake levels the lake formation is attributed to deglaciation after the last glacial maximum lgm and holocene warming tectonic activity seismites are concentrated only at 10 and 6 ka

using sediment travel distance to estimate medium term erosion rates a 16 year record fine grained 80 m magnetite was introduced onto a semi arid grassland hillslope in 1992 as part of a set of rainfall simulation experiments using measurements of magnetic susceptibility the median distance travelled by these magnetite grains during subsequent natural runoff events in the 16 year period up to 2008 was estimated coupling this estimate to direct measurements of sediment flux obtained during the rainfall simulation experiments has enabled estimation of the erosion rate over this period the estimated average erosion rate of between 2 61 10 2 and 4 36 10 2 kg m 1 year 1 is equivalent to a rate of ground lowering between 0 020 and 0 033 mm year 1 this estimate is consistent with in the sense of being less than an estimate of total sediment detachment over the same period the rate of erosion measured using this travel distance approach is an order of magnitude less that obtained from a study based on 137cs in a nearby catchment and compatible with the longevity of continents copyright 2010 john wiley sons ltd

reconstruction of a major storm event from its geomorphic signature the ladakh floods 6 august 2010 extreme precipitation events in arid mountain regions determine flood debris flow and landslide hazards and are principal drivers of geomorphic change increased frequency of intense precipitation in many regions of the world over the past few decades increases the importance of documenting and understanding such events when they occur we use the geomorphic record to reconstruct the distribution and magnitude of river discharge from a devastating convective storm event in the interior of the western himalaya we use this record to estimate the rates magnitudes and distribution of precipitation and magnitude of debris flows generated by the same event the storm occurred on 6 august 2010 over the ladakh range in the northwest indian himalaya killing 600 people and devastating more than 60 villages it triggered numerous debris flows and significantly widened the lower reaches of the main tributary valleys we demonstrate that rainfall was concentrated in a 6 km wide range parallel band centered 4 5 km up from the range front and that within this band precipitation intensity was 30 times that above it at least 75 mm of rain fell in 30 min during the heaviest part of the storm which is at least 1 5 times the highest 24 h maximum for the previous 100 yr the results demonstrate that the geomorphic record can be used to constrain the intensity of rainfall without meteorological stations and also record its distribution better than could be achieved with normal densities of instrumentation

tectonic framework of the indus and shyok suture zones in eastern ladakh northwest himalaya abstract three different phases of plutonic volcanic activity viz 1 1 cretaceous volcanics of the dras and luzarmu formations 2 2 early tertiary granitoids of the ladakh plutonic complex 3 3 oligocene acid volcanics and dykes of the khardung formation have been recognised in the ladakh magmatic arc the dras formation of the indus suture zone and the luzarmu formation of the shyok suture zone were one stratigraphic unit into which granitoids of the ladakh plutonic complex intruded the rocks of the shyok suture zone are interpreted to represent the tectonised remainder of a marginal back arc basin the closure of the marginal basin occurred at the eocene oligocene time boundary and crustal shortening was responsible for generation of neogene 2 mica granites of the karakoram plutonic complex and regional metamorphism of the pangong tso group

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

fashion and phases of late pleistocene aggradation and incision in the alaknanda river valley western himalaya india abstract we study the aggradation and incision of the alaknanda river valley during the late pleistocene and holocene the morphostratigraphy in the river valley at deoprayag shows the active riverbed a cut terrace and a fill terrace the sedimentary fabric of the fill terrace comprises four lithofacies representing 1 riverbed accretion 2 locally derived debris fan 3 the deposits of waning floods and 4 palaeoflood records the sedimentation style coupled with geochemical analysis and optically stimulated luminescence osl dating indicate that this terrace formed in a drier climate and the river valley aggraded in two phases during 21 18 ka and 13 9 ka during these periods sediment supply was relatively higher incision began after 10 ka in response to a strengthened monsoon and aided by increase of the tectonic gradient the cut terrace formed at 5 ka during a phase of stable climate and tectonic quiescence the palaeoflood records suggest wetter climate 200 300 yr ago when the floods originated in the upper catchment of the higher himalaya and in the relatively drier climate 1 2 ka when locally derived sediments from the lesser himalaya dominated flood deposits maximum and minimum limits of bedrock incision rate at deoprayag are 2 3 mm a and 1 4 mm a

formation of paleovalleys in the central himalaya during valley aggradation abstract the formation of paleovalleys in mountainous regions is considered to result from extreme events such as landslides and glacial or landslide lake outburst floods according to ipcc 2012 the extreme events are rarest of the rare weather climatic events when the climate weather variable is significantly above or below the defined threshold value the present study suggests that paleovalleys can also form during years long periods of valley aggradation a series of paleovalleys thus formed runs parallel to the present river course in this study we suggest that paleovalleys in the alaknanda valley of the central himalaya have formed in two ways 1 major valley aggradation and 2 local events of landsliding and lake breaching most of the paleovalleys in the alaknanda valley formed during a major valley aggradation phase between 15 and 8 ka paleovalleys formed due to local landsliding also formed around 8 ka local landslides were triggered due to high rainfall in lower valley reaches during unstable climatic conditions therefore the formation of paleovalleys both by regional and local mode within 15 8 ka indicates that the valley was receiving excess sediment from upper catchment as well as from lower reaches during this period this phase of excess sediment supply and valley aggradation coincides well with post glacial climatic amelioration therefore the study underlines the role of climate in the time scales of 10 3 years in shaping the landscape of an active mountain like the himalaya the role of other landscape changing agencies such as tectonics and erosion is not accounted in the present study

enhanced arabian sea intermediate water flow during glacial north atlantic cold phases abstract during the last glacial period polar ice cores indicate climate asynchrony between the poles at the millennial time scale yet surface ocean circulation in large parts of the globe varied in tune with greenland temperature fluctuations suggesting that any anti phase behavior to a substantial degree must lie in the deeper global ocean circulation which is poorly understood outside the atlantic ocean here we present data from the north western indian ocean which indicate that the timing of maxima in northward extensions of glacial antarctic intermediate water gaaiw coincides with dramatically reduced thermohaline overturn in the north atlantic associated with the heinrich ice surge events he the repeated expansion of the gaaiw during hes recorded far north of the equator in the arabian sea suggests that southern hemisphere driven intermediate water mass variability forms an integral part of the inter hemisphere asynchronous climate change behavior at the millennial time scale

widespread aggradation in the mountainous catchment of the alaknanda ganga river system timescales and implications to hinterland foreland relationships abstract cut and fill type fluvial terraces are ubiquitous in the lesser himalayan zone of the alaknanda ganga ganges rivers system which flows perpendicular to himalayan lithotectonic units and traverses a steep climatic gradient lithofacies analysis of the sedimentary sequences of cut and fill terraces indicated that the valley aggradation took place via 1 channel bar development and excess sediment supply 2 debris flows composed of mixed rounded to sub rounded lithoclasts resulting from episodic high intensity rainfalls in the upper catchment or 3 debris flows or rockfalls generated by local landslides the luminescence chronology indicates that valley aggradation took place in two phases 49 25 ka and 18 11 ka the incision of the fill started soon after 11 ka paleoclimatic records from marine sediments indicate that the aggradation and incision in the alaknanda ganga river has oscillated in phase with global climatic variations glaciation deglaciation processes in the upper catchment produced huge amounts of sediment between 63 and 11 ka which was fluvially transferred to the lower valley via several cycles of erosion and deposition leading to extensive aggradation the climatic amelioration at 11 ka and the completion of deglaciation processes led to increased fluvial discharge and decreased sediment supply conditions conducive for incision of the alluvial fills records from the indo gangetic plain and the ganga delta demonstrate that the phase of aggradation was regional but that incision in the foreland started at least 2 3 ka later after 7 ka bedrock incision rates as calculated from dated alluvial covers of terraces that are separated by bedrock steps are spatially variable and fall within the range of rates reported from across the himalaya these estimated rates however are higher than the basin average erosion rates calculated using isotopic mass balance in riverbed sediments this study suggests that during the last 50 ka river dynamics in the himalayas were dominated by monsoon variability and the role of tectonic activity was limited to bedrock incision in few reaches only

late pleistocene holocene morphosedimentary architecture spiti river arid higher himalaya the spiti river drains the rain shadow zone of western himalaya in the present study the fluvial sedimentary record of spiti valley was studied to understand its responses to tectonics and climate geomorphic changes along the river enable to divide the river into two segments i upper valley with a broad braided channel where relict sedimentary sequences rise 15 50 m high from the riverbed and ii lower valley with a narrow meandering channel that incises into bedrock and here the fluvio lacustrine sediments reside on a bedrock bench located above the riverbed the transition between these geomorphic segments lies along the river between seko nasung and lingti villages within tethyan himalaya lithofacies analyses of the sedimentary sequences show six different lithofacies these can be grouped into three facies associations viz a a glacial outwash b sedimentation in a channel and in an accreting bar under braided conditions and c formation of lake due to channel blockage by landslide activities seventeen optically stimulated luminescence ages derived from ten sections bracketed the phases of river valley aggradation between 14 8 and 50 30 ka these aggradation phases witnessed mass wasting channel damming and lake formation events our record when compared with sw monsoon archives suggests that the aggradation occurred during intensified monsoon phase of mis 3 4 and that proceeded the last glacial maxima thus the study reports monsoon modulated valley aggradation in the nw arid himalaya

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

the role of sediment in controlling steady state bedrock channel slope implications of the saltation abrasion incision model abstract the saltation abrasion model is a mechanistic model for river incision into bedrock by saltating bedload which we have previously derived and used experimental data to constrain all parameter values here we develop a method for applying the saltation abrasion model at a landscape scale and use the model as a reference for evaluating the behavior of a wide range of alternative incision models in order to consider the implications of the saltation abrasion model as well as other models for predicting topographic steady state channel slope to determine the single valued discharge that best represents the effects of the full discharge distribution in transporting sediment and wearing bedrock we assume all runoff can be partitioned between a low flow and a high flow discharge in which all bedload sediment transport occurs during high flow we then use the gauged discharge record and measurements of channel characteristics at a reference field site and find that the optimum discharge has a moderate magnitude and frequency due to the constraints of the threshold of grain motion and bed alluviation by high relative sediment supply incision models can be classified according to which of the effects of sediment on bedrock incision are accounted for using the predictions of the saltation abrasion model as a reference we find that the threshold of motion is the most important effect that should be represented explicitly followed in order of decreasing importance by the cover effect the tools effect and the threshold of suspension effect models that lack the threshold of motion over predict incision rate for low shear stresses and under predict the steady state channel slope for low to moderate rock uplift rates and rock strengths models that lack the cover effect over predict incision rate for high sediment supply rates and fail to represent the degree of freedom in slope adjustment provided by partial bed coverage models that lack the tools effect over predict incision rate for low sediment supply rates and do not allow for the possibility that incision rate can decline for increases in shear stress above a peak value overall the saltation abrasion model predicts that steady state channel slope is most sensitive to changes in grain size such that the effect of variations in rock uplift rate and rock strength may affect slope indirectly through their possible but as yet poorly understood influence on the size distribution of sediments delivered to channel networks by hillslopes

late quaternary fluvial aggradation and incision in the monsoon dominated alaknanda valley central himalaya uttrakhand india the present study aims to explain the spatial and temporal variability in phases of aggradation incision in response to changes in climate and seismicity during the late quaternary in the alaknanda river valley a major tributary of the river ganges or ganga geomorphology stratigraphy and optical dating of the fluvial sediment reveal that the oldest fluvial landforms preserved in the south of the main central thrust are debris flow terraces developed during the early part of pluvial marine isotopic stage 3 following this a period of accelerated incision erosion owing to an increase in uplift rate and more intense rainfall occurred in the lesser himalaya three phases of valley fill aggradation around 26 3 ka 18 2 ka and 15 1 ka and 8 1 ka occurred in response to changes in monsoon intensity and sediment flux the last phase was regionally extensive and corresponds to a strengthening of the early holocene indian summer monsoon a gradual decline in the monsoon strength after 8 1 ka resulted in reduced fluvial discharge and lower sediment transport capacity of the alaknanda river leading to valley fill incision and the development of terraces the study suggests that fluvial dynamics in the alaknanda valley were modulated by monsoon variability and the role of tectonics was subordinate limited to providing accommodation space and post deposition modification of the fluvial landforms copyright 2010 john wiley sons ltd

a note on the extent of glaciation throughout the himalaya during the global last glacial maximum abstract quantitative chronologies for the impressive glacial successions that occur throughout the himalaya have until recently been almost totally lacking within the last decade two new techniques have promised to remedy this situation these techniques optically stimulated luminescence and cosmogenic nuclide surface exposure dating enable the age of many glacial features to be determined and have allowed us to study the extent and timing of himalayan glaciation in the late quaternary new data show that the local last glacial maximum lgm occurred during the early part of the last glacial cycle in most areas during marine isotope stage 3 mis 3 mis 3 was a time of increased insolation when the south asian summer monsoon strengthened and penetrated further north into the himalaya the concomitant increased precipitation occurring as snow at high altitudes produced positive glacier mass balances thereby allowing glaciers to advance on the other hand during the global lgm 18 24 ka himalayan glaciation was very restricted in extent generally extending

drainage basin responses to climate change recent investigations have shown that the extent of the channel network in some drainage basins is controlled by a threshold for overland flow erosion the sensitivity of such basins to climate change is analyzed using a physically based model of drainage basin evolution the golem model simulates basin evolution under the action of weathering processes hillslope transport and fluvial bedrock erosion and sediment transport results from perturbation analyses reveal that the nature and timescale of basin response depends on the direction of change an increase in runoff intensity or a decrease in vegetation cover will lead to a rapid expansion of the channel network with the resulting increase in sediment supply initially generating aggradation along the main network followed by downcutting as the sediment supply tapers off by contrast a decrease in runoff intensity or an increase in the erosion threshold will lead to a retraction of the active channel network and a much more gradual geomorphic response cyclic changes in runoff intensity are shown to produce aggradational degradational cycles that resemble those observed in the field cyclic variations in runoff also lead to highly punctuated denudation rates with denudation concentrated during periods of increasing runoff intensity and or decreasing vegetation cover the sediment yield from threshold dominated basins may therefore exhibit significant variability in response to relatively subtle environmental changes a finding which underscores the need for caution in interpreting modern sediment yield data

the indus clastics forearc basin sedimentation in the ladakh himalaya india abstract the mid cretaceous to early tertiary clastic sediments of the indus group represent the forearc basin succession of the transhimalayan arc trench system in the late albian to early eocene a shallowing upward megasequence tar turbidites to nummulitic limestones and alluvial to deltaic sediments basgo and temesgam formations were deposited respectively on the southern and northern flanks of the basin clastic petrography points to provenance from the largely undissected volcanic cover of the massif with more important plutonic detritus recorded in the northern alluvial units after collision with the indian passive margin in the early eocene sedimentation in the whole basin was characterized by huge alluvial fans nurla formation and then by lacustrine deposits formed in an intermontane depression nimu formation a rapid change in petrographic and geochemical composition is recorded in post early eocene units with sharp increase in plutonic detritus and trace elements typically associated with ophiolites testifying to the uplift of both arc massif and subduction complex sources after collision with the indian passive margin the petrography of the indus basin clastics and the evolution of detrital modes compare well with volcano plutonic suites deposited in modern and ancient forearc basins the composition of sandstone units contained within the accretionary prism instead suggests provenance from an undissected magmatic arc and deposition in abyssal plain and trench settings nindam volcaniclastic turbidites reworking of arc derived sandstones took place in small basins perched on the accretionary trench slope the asian continental margin of the neotethys ocean was thus an active pacific type arc trench system until the eocene when it collided with india underwent polyphase fold thrust deformation and was finally uplifted several kilometers to form the indus suture zone of the himalayas

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

bedrock incision rock uplift and threshold hillslopes in the northwestern himalayas the topography of tectonically active mountain ranges reflects a poorly understood competition between bedrock uplift and erosion dating of abandoned river cut surfaces in the northwestern himalayas reveals that the indus river incises through the bedrock at extremely high rates 2 12 mm yr 1 in the surrounding mountains the average angles of hillslopes are steep and essentially independent of erosion rate suggesting control by a common threshold process in this rapidly deforming region an equilibrium is maintained between bedrock uplift and river incision with landsliding allowing hillslopes to adjust efficiently to rapid river down cutting

climatic influences on profile concavity and river incision 1 longitudinal profiles of alluvial and bedrock rivers are typically concave up and the precise shape of their concavity is known to integrate tectonic climatic and channel grain size distribution factors we isolate climatic hydrologic effects on profile concavity through a spatial analysis of large watersheds with mixed bedrock alluvial trunk channels spanning a steep climatic hydrologic gradient in a tectonically stable landscape forty watersheds on the eastern american high plains were selected to minimize variability in base level relief vegetation rock type and drainage area we calculate stream concavity by two complementary methods an area normalized stream concavity index sci and the slope of a line regressed through log log plot of channel slope and basin area the sci and covary more importantly a positive correlation exists between profile concavity and climatic hydrologic factors such as precipitation intensity and peak annual discharge however modeled profile steepness has no correlation to climate or watershed hydrology we conclude that in tectonically stable settings higher intensity rainfall and greater mean annual precipitation lead to more concave profiles we do not have data to know if the concavity changes reflect primarily bedrock or alluvial grain size processes but generally a doubling of rainfall intensity on the high plains leads to a tripling in concavity manifest as tens of meters of incision such climatically influenced profile concavity could explain some of the often cited late cenozoic incision and increase in local relief for the high plains and rocky mountains traditionally ascribed to tectonics

prediction of flash flood hazard impact from himalayan river profiles to what extent can we treat topographic metrics such as river long profiles as a long term record of multiple extreme geomorphic events and hence use them for hazard prediction we demonstrate that in an area of rapid mountain erosion where the landscape is highly reactive to extreme events channel steepness measured by integrating area over upstream distance chi analysis can be used as an indicator of geomorphic change during flash floods we compare normalised channel steepness to the impact of devastating floods in the upper ganga basin in uttarakhand northern india in june 2013 the pattern of sediment accumulation and erosion is broadly predictable from the distribution of normalised channel steepness in reaches of high steepness channel lowering up to 5 m undercut buildings causing collapse in low steepness reaches channels aggraded up to 30 m and widened causing flooding and burial by sediment normalised channel steepness provides a first order prediction of the signal of geomorphic change during extreme flood events sediment aggradation in lower gradient reaches is a predictable characteristic of floods with a proportion of discharge fed by point sources such as glacial lakes

morpho sedimentary records at the brahmaputra river exit ne himalaya climate tectonic interplay during the late pleistocene holocene morphological and sedimentary records at the exit of brahmaputra river at pasighat in the ne himalaya inform about the climate tectonic interplay during the past ca 15 ka the geomorphology of the area comprises 1 fan terrace t3 2 a high angle fan 3 terrace t2 4 terrace t1 and 5 a low angle fan geomorphic consideration suggests that the fan terrace t3 and high angle fans are the oldest units and were coeval the low angle fan is the youngest geomorphic unit sedimentological studies and optically stimulated luminescence chronology suggest that i fan terrace t3 formed between 13 and 10 5 ka and comprised multiple events of debris flows separated by the aggradation as channel bars in a braided river environment ii the high angle fan formed during 15 10 ka and comprises channel bar aggradation in braided river conditions iii terrace t2 formed during 10 8 ka due to aggradation in a braided channel environment with lesser events of debris flows iv terrace t1 formed during 7 and 3 ka took place as bars of the braided river sudden coarsening of the sediment indicated a tectonic rejuvenation in the provenance region between 7 and 3 ka and v the low angle fans dated to 3 ka formed due to aggradation in a small tributary joining the brahmaputra river this implies a phase when the main channel of the brahmaputra did not flood regularly and the tributaries were actively aggrading the sedimentation style and incision of these geomorphic units responded to contemporary climatic changes and uplift in the siwalik range along the himalayan frontal fault copyright 2008 john wiley sons ltd

hydrological evolution during the last 15 kyr in the tso kar lake basin ladakh india derived from geomorphological sedimentological and palynological records abstract the tso kar lake basin in ladakh northwestern himalayas 33 18 n 78 e 4527 m a s l is located close to the modern boundary of effective moisture transport from the indian summer monsoon in order to reconstruct the possible monsoonal impact on the hydrology of the lake basin during the last 15 kyr we studied the geomorphology of the basin and combined the results with multi proxy records from tso kar lake sediments major analyses comprise geochemical data high resolution x ray fluorescence xrf mineral composition xrd aquatic pollen and non pollen palynomorphs npp although the chronological framework based on 41 14c ams dates remains speculative for the lateglacial and late holocene periods our results indicate major hydrological phases linked to regional climate variations and tectonic activity the maximum glacier advance falls within the period between the global lgm and ca 15 kyr bp while the basin remained open and may have drained along the paleo tso kar river tectonic pulses may have triggered terrace development and the closure of the lake the estimated mean vertical displacement rate accounts for 7 9 mm yr considerable summer monsoon moisture supply occurred for the periods around 12 5 kyr bp and between ca 11 5 and 8 6 kyr bp indicated by deposition of more profundal lake facies and the development of aquatic fauna and flora the lake level rise about 11 8 kyr bp was due to intensified glacier melt and summer monsoon effective moisture supply the lake reached its maximum level and extent between 8 5 and 7 kyr bp under warm moist climate conditions permafrost was absent from the basin summer monsoon influence weakened after 8 kyr bp with a short reverse trend at ca 5 6 kyr bp the lake shrank gradually after 7 kyr bp towards its lowest stand at about 4 2 kyr bp with return of permafrost activity subsequent terrace formation was probably amplified by tectonic movement the lake remained at a low level with minor fluctuations the results indicate that the orbitally driven regional climate variability is well reflected in the tso kar basin by hydrological variations considerable summer monsoon moisture seems to have influenced the area only during the early holocene the late quaternary evolution of the tso kar was controlled by the interplay of climate forces local morphodynamics and tectonic impact

magmatism and metamorphism in the ladakh himalayas the indus tsangpo suture zone abstract ladakh india provides a complete geological section through the northwestern part of the himalayas from kashmir to tibet within this section the magmatic metamorphic and geotectonic evolution of the northern himalayan orogeny has been studied using petrographic geochemical and isotope analytical techniques the beginning of the himalayan cycle was marked by large basaltic extrusions panjal trap of permian to lower triassic age at the northern margin of the gondwana continent indian shield these continental type tholeiitic basalts were followed by a more alkaline volcanism within the triassic to jurassic lamayuru unit of the gondwana continental margin lower jurassic to cretaceous oceanic crust and sediments ophiolitic melange s s accompany the triassic to cretaceous flysch deposits within the indus tsangpo suture zone the major structural divide between the indian shield high himalaya and the tibetan platform so far no relic of paleozoic oceanic crust has been found subduction of the tethyan oceanic crust during upper jurassic and cretaceous time produced an island arc represented by tholeiitic and calc alkaline volcanic rock series dras volcanics and related intrusives accompanied by volcaniclastic flysch deposits towards the tibetan continental margin subsequent to the subduction of oceanic crust large volumes of calc alkaline plutons trans himalayan or kangdese plutons intruded the tibetan continental margin over a distance of 2000 km and partly the dras island arc in the ladakh region the collision of the indian shield and tibetan platform started during the middle to upper eocene and caused large scale still active intracrustal thrusting as well as the piling up of the himalayan nappes the tectonically highest of these nappes is built up of oceanic crust and huge slices of peridotitic oceanic mantle spongtang klippe in the high himalayas the tectonic activity was accompanied and outlasted by a barrovian type metamorphism that affected triassic sediments of the kashmir nun kun synclinorium up to kyanite staurolite grade and the deeper seated units up to sillimanite grade cooling ages of micas are around 20 m y muscovite and 13 m y biotite towards the indus tsangpo suture zone metamorphism decreases with no obvious discontinuity through greenschist prehnite pumpellyite to zeolite grade remnants of possibly an eo himalayan blueschist metamorphism have been found within thrust zones accompanying ophiolitic melange in the suture zone

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

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

geology of the cenozoic indus basin sedimentary rocks paleoenvironmental interpretation of sedimentation from the western himalaya during the early phases of india eurasia collision this study reassesses the stratigraphy sedimentology and provenance of the indus basin sedimentary rocks deposited within the indus tsangpo suture zone itsz during the early phases of india eurasia collision using field observations biostratigraphy and petrographic and isotopic analyses we create a paleodepositional reconstruction within the paleotectonic setting of the early phases of india eurasia collision we then re examine existing constraints to the timing of india eurasia collision previously interpreted from the earliest occurrence of mixed indian and eurasian derived detritus in the succession from mid cretaceous to early paleocene times the jurutze and sumda formations were deposited within an arc bounded marine basin between the dras and kohistan ladakh island arcs the 51 ma aged deltaic chogdo formation then filled the basin until deposition of the 50 8 49 4 ma aged nummulitic limestone during a marine incursion before continental facies developed in an evolving intermountain basin with the deposition of the paleogene indus group within these systems sediment was sourced from the eurasian margin to the north and was transported southward into the suture zone in this section we see no unequivocal evidence of indian plate input to the sedimentary succession and thus no evidence of mixed indian eurasian derived detritus indicative of india asia collision until the upper stratigraphic horizons of the indus group when facies are representative of an axial northwesterly flowing river system we suggest that the paleo indus river was initiated within the itsz during late oligocene early miocene times sedimentation of the indus group continued until the late miocene

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

lacustrine sedimentation in a semiarid alpine setting an example from ladakh northwestern himalaya abstract the lamayuru lacustrine strata in ladakh typify many of the carbonate rich pleistocene alpine lakes found in the semiarid environment of the northern himalaya created by a 200 m thick landslide the lake was in existence by at least 35 000 yr ago and may have persisted until 500 1000 yr ago represented in the center by thin turbidites and laminated muds the lacustrine sedimentation along the lake margins and low relief deltas characteristically displays a marked contrast between 1 clastic lenses representing rapid sporadic matrix poor debris flows and periglacial inputs from the alpine slopes and 2 abundant diverse shallow water biologically dominated carbonate strata among which organism rich chalky beds and oncolithic and encrusted stem rich strata predominate resemblances of the lamayuru lacustrine strata and their setting to those of former lakes throughout areas north of the greater himalayan crest suggest that the alpine semi arid environment would favor diversified spacially restricted carbonate sedimentation punctuated by occasional clastic influxes such a depositional regime contrasts strongly with that found immediately south of the himalayan crest where more humid conditions promote a more continuous clastic influx into intramontane lakes

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

early holocene fluvial activity from the sedimentology and palaeohydrology of gravel terrace in the semi arid mahi river basin india abstract palaeocompetence analysis and palaeodischarge estimation techniques are applied to a late pleistocene early holocene gravel terrace in the mahi river basin western india terrace sedimentology comprising gravels overlain by sand lithofacies suggests a gradual change in palaeohydrological conditions marking a switch from braided to meandering fluvial styles the discharge values for the gravel bedforms based on the clast size and the cross bed set thickness are estimated between 150 180 m 3 s 1 comparable with the present day observed values albeit with a much higher competence results indicate that fluvial aggradation occurred under low discharge conditions with intermittent high discharge events depositing longitudinal gravel bars the incision of these gravel bars and the formation of terraces can be attributed to the higher discharge regime post 9 2 ka the study further indicates that whereas the aggradation of the gravel terrace during the early holocene was controlled by the large sediment influx the incision that followed was in response to the increase in the discharge and competence of the river flow

solutions of the stream power equation and application to the evolution of river longitudinal profiles 1 erosion by bedrock river channels is commonly modeled with the stream power equation we present a two part approach to solving this nonlinear equation analytically and explore the implications for evolving river profiles first a method for non dimensionalizing the stream power equation transforms river profiles in steady state with respect to uniform uplift into a straight line in dimensionless distance elevation space second a method that tracks the upstream migration of slope patches which are mathematical entities that carry information about downstream river states provides a basis for constructing analytical solutions slope patch analysis explains why the transient morphology of dimensionless river profiles differs fundamentally if the exponent on channel slope n is less than or greater than one and why only concave up migrating knickpoints persist when n 1 at migrating knickpoints slope patches and the information they carry are lost a phenomenon that fundamentally limits the potential for reconstructing tectonic histories from bedrock river profiles stationary knickpoints which can arise from spatially varying uplift rates differ from migrating knickpoints in that slope patches and the information they carry are not lost counterparts to migrating knickpoints called stretch zones are created when closely spaced slope patches spread to form smooth curves in distance elevation space these theoretical results are illustrated with examples from the california king range and the central apennines

morpho sedimentary records of active tectonics at the kameng river exit ne himalaya abstract the kameng river in the ne india cuts through the rising siwaliks the frontal ranges of the himalaya and forms four levels of alluvial terraces the geomorphic configuration and overlying alluvial cover of each terrace has been studied to decipher the uplift history of the himalayan front and varying sedimentation pattern of the river the ratio sa ratio of the thicknesses of alluvial cover and bedrock strath is used as a measure of geomorphic instability gi and a gi index has been calculated for each incision and aggradation phase it is suggested that the area was geomorphologically most unstable when the kameng river was incising from terrace t2 to t1 the luminescence chronology constrained this phase to be at 7 ka b p the older incision phases namely t4 t3 and t3 t2 occurred 14 and 10 ka b p respectively the alluvial cover of the terraces is composed of four major lithofacies viz 1 matrix supported pebble 2 clast supported pebble 3 parallel laminated medium sand and 4 bioturbated fine sand the vertical variation of the lithofacies indicates that the river was flowing under a braided pattern the study suggested that kameng river incised 95 m from terrace t4 to t2 in the span of 8 ka between 14 6 ka bp suggested the uplift rate of 11 9 mm year however the total uplift in the siwaliks as indicated by the height difference of terraces t4 t0 in the area is 105 m which occurred during the last 14 ka at the rate of 7 5 mm year indicating a varying rate of siwalik uplift in the holocene the studies corroborate with published incision rates from the central himalaya in nepal

giant landslides topography and erosion abstract distributions of slope angles in tectonically active mountain belts point to the development of threshold conditions where hillslopes attain a critical inclination or height at which they fail readily because of limitations in material strength it has been proposed that hillslopes adjust to rapid uplift and bedrock incision through an increase in the rate of relief limiting landsliding rather than gradual slope steepening here we test this concept by investigating the relationship between mean local relief h which we take to be a proxy of long term erosion rates e and the occurrence of over 300 of the largest v 10 8 m 3 terrestrial landslides on earth we find that nearly two thirds of these giant landslides have occurred in the steepest 5 of the earth s land surface where relief is close to its proposed upper strength limit they are primarily located in deeply incised valleys along fault bounded fringes of active mountain belts and in volcanic arcs this distribution coincides with areas of high long term erosion rates 4 mm yr 1 confirming that giant landslides contribute to rapid denudation of mountains most of the eroded volume is concentrated in the smallest but steepest parts of mountain belts and volcanic arcs first order estimates of minimum erosion rates accomplished by the largest landslides are 0 01 mm yr 1 these rates are between 1 and 10 of the late pleistocene to holocene mean erosion rates in a given area importantly the landslide erosion rates show a nonlinear increase with mean local relief suggesting that the contribution of giant landslides in total and per event increases significantly with increasing overall erosion rates however giant landslides also occur in areas of lower than average relief h 300 700 m irrespective of whether threshold hillslopes have developed or not factors contributing to these failures include soft rocks extensive low angle discontinuities high rates of fluvial bedrock incision and tectonically driven deformation and slope loading

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

the role of heating winds and topography on sea level changes in the north atlantic seasonal and interannual to decadal variations of large scale altimetric sea surface height ssh owing to surface heating and wind forcing in the presence of topography are investigated using simplified models the dominant forcing mechanisms are time scale dependent on the seasonal time scale locally forced thermosteric height explains most of the ssh variance north of 18 n first mode linear long baroclinic rossby waves forced by changes in the winds and eastern boundary conditions explain most of the variance between 10 n and 15 n and are also important east of greenland on interannual to decadal time scales local thermosteric height remains important at several locations in the middle and high latitudes a topographic sverdrup response explains interannual to decadal ssh between 53 n and 63 n east of greenland farther south the linear rossby wave model explains ssh variations on interannual to decadal time scales between 30 n and 50 n from mid basin to the eastern boundary propagation of the eastern boundary condition into the interior dominates the interannual to decadal ssh signals south of 30 n the effect from nao related heat flux on ssh is small but forcing the topographic sverdrup models with nao regressed winds gives slightly better agreement with the observed ssh in the subpolar gyre on interannual to decadal time scales than using the full winds

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

quaternary geology tectonics and distribution of palaeo and present fluvio glacio lacustrine deposits in ladakh nw indian himalaya a study based on field observations abstract the ladakh region of the northwestern indian himalaya is rich in quaternary deposits but it has not received much attention previous quaternary research in the region has focused on the glacial sequences and only some scattered data of the lacustrine deposits are available this article addresses the reconstruction of the palaeo lacustrine deposits and the present day lakes and their distribution in the ladakh region the region was under the influence of tectonic activity and cold climate during the late quaternary times tectonic activity at 50 000 years bp 35 000 years bp and 25 000 years bp has been recorded we report the presence of three major lakes in the region in the late quaternary these formed due to the damming of the indus river and its tributaries by debris avalanches initiated mainly by tectonic activity along the indus suture shyok suture and the karakoram fault these are the spituk leh palaeolake formed 50 000 years bp the lamayuru palaeolake dated to 35 000 years bp in the indus valley and the khalsar palaeolake 60 km in length in the shyok valley vast exposures of the palaeolake deposits ranging from 25 to 150 m in thickness are reported spituk section 25 m lamayuru section 110 m and khalsar 150 m and hundri 100 m and which have a wide lateral extent a glacial lake basin at bhaktpur city north of baralacha la is now completely filled the tsokar lake has been subdivided into smaller units now and the water level is lowering other lakes in the region e g pangong tso tso morari the twin kyun tso lakes are confined to the western side of the study area limited chemical weathering rapid erosion and cold climatic conditions in late quaternary times are suggested by the stable illite values in the lamayuru section four levels of palaeoseismic structures convolute structures sand dykes intraformational folds micro faulting are present in the khalsar section and at three levels in the tirit section at shyok nubra confluence palaeoseismic activity was also prevalent after 25 000 years bp as is evident from the three levels of palaeoseismic structures in the younger sediments