effects of a perovskite post perovskite phase change near core mantle boundary in compressible mantle convection 1 numerical simulations of compressible isochemical mantle convection are used to investigate the effect of the perovskite to post perovskite phase transition at around 2700 km depth which has recently been discovered by high pressure experiments and ab initio calculations on the convective planform temperature and heat transport characteristics of the mantle the usual phase transitions at 410 km olivine spinel and 660 km spinel perovskite are also included the exothermic post perovskite phase change at 2700 km depth destabilizes the lower thermal boundary layer increasing the heat flow increasing interior mantle temperature and increasing the number and time dependence of upwelling plumes the resulting weak highly time dependent upwellings also have a smaller horizontal spacing than the plumes that occur in the absence of the phase transition while the influence of post perovskite phase change may be smaller than that of some other complexities such as compositional stratification it appears to have an important enough effect that it should not be ignored in dynamical studies of mantle convection

the influence of climate on the tectonic evolution of mountain belts simple physical arguments analogue experiments and numerical experiments all suggest that the internal dynamics of actively deforming collisional mountain ranges are influenced by climate however obtaining definitive field evidence of a significant impact of climate on mountain building has proved challenging spatial correlations between intense precipitation or glaciation and zones of rapid rock uplift have indeed been documented in numerous mountain ranges and are consistent with model predictions more compelling evidence such as tectonic changes in response to rather than just coincident with climate change has however rarely been documented triggered by a climate driven increase in erosion rate friction dominated mountain ranges are expected to show a number of simultaneous responses a decrease in the width of the range a temporary increase in sediment yield a persistent increase in the rate of rock uplift and a reduction in the subsidence rate of surrounding basins the most convincing field evidence for such a coordinated response of a mountain range to climate change comes from the european alps and the st elias range of alaska field studies and experimental research during the past two decades have provided considerable evidence for a significant influence of climate on tectonics recent advances suggest that model predictions can guide future fieldwork aimed at substantiating this view

the influence of post perovskite strength on the earth s mantle thermal and chemical evolution abstract we have investigated the influence of post perovskite ppv viscosity on mantle convective dynamics and stirring efficiency using numerical modeling and simple analytical theory our results show that the strength of ppv has a dramatic influence on convective dynamics the presence of a weak ppv enhances heat transfer across the bottom thermal boundary layer resulting in higher temperatures lower mantle viscosities and considerably larger convective velocities this leads to a significant increase in stirring efficiencies with decreasing the ppv strength by at least one order of magnitude in addition using a simple parameterized convection evolution that includes the influence of ppv coupled to a mixing model we show that during the long term history of the earth s mantle the presence of ppv yields systematically hotter thermal evolution and more efficient convective stirring such a strong effect of ppv strength on mantle stirring efficiency suggests that the influence of ppv phase must be considered when interpreting both geochemical and geophysical observations

effect of post perovskite rheology on the thermal evolution of the earth abstract secular cooling of the earth mantle is a complex process affected by many factors here we present the results of a modelling study focused on efficiency of cooling in the presence of rheologically distinct post perovskite we evaluate combined effects of variable thermal expansivity and diffusivity initial thermal condition and heat source model and concentrate on the effects of rheologically weak post perovskite cooling of the core is included in the model core is assumed to be an isothermal heat reservoir with temperature controlled by heat flux through core mantle boundary our 2d axisymmetric convection model has pressure temperature and phase dependent viscosity and includes the effects of an endothermic phase transition at 660 km depth and an exothermic perovskite post perovskite phase transition in the lowermost mantle in agreement with previous studies we conclude that depth dependent material parameters tend to delay secular cooling presence of the weak post perovskite on the other hand significantly enhances core cooling and its effect on core temperature is opposite and comparable in magnitude

300 mw baspa ii india s largest private hydroelectric facility on top of a rock avalanche dammed palaeo lake nw himalaya regional geology tectonic setting and seismicity article i nfo this study aims for the characterization of the geological setting of 300 mw baspa ii india s largest private hydroelectric facility which was built on top of a relict rock avalanche dammed palaeo lake baspa valley nw himalaya geologically the hydroelectric installation is located in the higher himalayan crystalline just above the active karcham normal fault which is reactivating the early miocene main central thrust one of the principal himalayan faults the area is seismically active and mass movements are common at ca 8200 yr bp the baspa river was blocked behind a 142 10

abnormal monsoon years and their control on erosion and sediment flux in the high arid northwest himalaya abstract the interplay between topography and indian summer monsoon circulation profoundly controls precipitation distribution sediment transport and river discharge along the southern himalayan mountain front shf the higher himalayas form a major orographic barrier that separates humid sectors to the south and arid regions to the north during the indian summer monsoon vortices transport moisture from the bay of bengal swirl along the shf to the northwest and cause heavy rainfall when colliding with the mountain front in the eastern and central parts of the himalaya precipitation measurements derived from passive microwave analysis ssm i show a strong gradient with high values at medium elevations and extensive penetration of moisture along major river valleys into the orogen the end of the monsoonal conveyer belt is near the sutlej valley in the nw himalaya where precipitation is lower and rainfall maxima move to lower elevations this region thus comprises a climatic transition zone that is very sensitive to changes in indian summer monsoon strength to constrain magnitude temporal and spatial distribution of precipitation we analyzed high resolution passive microwave data from the last decade and identified an abnormal monsoon year amy in 2002 during the 2002 amy violent rainstorms conquered orographic barriers and penetrated far into otherwise arid regions in the northwest himalaya at elevations in excess of 3 km asl while precipitation in these regions was significantly increased and triggered extensive erosional processes i e debris flows on sparsely vegetated steep hillslopes mean rainfall along the low to medium elevations was not significantly greater in magnitude this shift may thus play an important role in the overall sediment flux toward the himalayan foreland using extended precipitation and sediment flux records for the last century we show that these events have a decadal recurrence interval during the present day monsoon circulation hence episodically occurring amys control geomorphic processes primarily in the high elevation arid sectors of the orogen while annual recurring monsoonal rainfall distribution dominates erosion in the low to medium elevation parts along the shf

influence of kinematics on landslide mobility and failure mode geometry of discontinuities greatly influences the kinematic behavior of slopes and landslides discontinuous deformation analysis dda is used here to analyze two typical examples of slope failure demonstrating that accurate representation of the geometry of the discontinuities is essential for identification of kinematically correct failure modes then static stability analyses of the vaiont italy landslide of october 9 1963 are used to show that the dda results compare favorably with previously published limit equilibrium studies using similar geometries and that the location and number of discontinuities have a significant effect on the predicted stability and failure velocities of the landslide dynamic dda simulations of the vaiont landslide show that the peak velocity increases up to 50 as the number of blocks increases indicating that internal disintegration of the landslide mass results in increasing acceleration and higher peak velocity dda analyses simulating pore pressure rise resulting from frictional heating of the basal slide plane show that the peak velocity similarly increases up to 50 as the number of blocks increases the magnitude of the increase in peak velocity as a result of disintegration i e increasing number of blocks suggests that as much attention should be paid to the geometry of discontinuities as is typically paid to shear strength and pore pressure

phase transition in mgsio 3 perovskite in the earth s lower mantle a new polymorph of mgsio3 more stable than the pbnm perovskite phase has been identified by first principles computations it has the cairo3 structure with cmcm symmetry and consists of sio3 layers intercalated by eightfoldcoordinated mg ions high temperature calculations within the quasiharmonic approximation give a volume change of f1 5 and a clapeyron slope of f7 5f0 3 mpa k at f2750 k and f125 gpa these pressure temperature p t conditions are close to those in which a phase transition in mgsio3 perovskite has been observed by in situ angle dispersive x ray diffraction measurements this transition appears to be associated with the du discontinuity d 2004 elsevier b v all rights reserved

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

the earthquake triggered rock avalanche of cui hua qin ling mountains p r of china the benefits of a lake damming prehistoric natural disaster abstract this paper deals with an investigation of cui hua rock avalanche in the qin ling mountains in the dong cha valley an eastern branch of taiyi river some 30 km south of xi an province of shaanxi p r of china the landslide originated on lithotectonic structures along seismic active fault systems its occurrence could be correlated with an earthquake in 780 bc that must have triggered the landslide due to a stabilizing human input the landslide area in front of the dammed tianchi lake became an area of settlement for native people of this area which used this rapidly geomorphologic changing system for their needs over the past 2780 years nowadays the lake is considered to be a reservoir for drinking water agriculture and a hydropower plant even more the deposit of the cui hua rock avalanche has become a touristic place for sightseeing and vacation

geomorphic evolution of glacier fed baspa valley nw himalaya record of late quaternary climate change monsoon dynamics and glacial fluctuations abstract in glacier fed baspa river valley late quaternary climatic changes are archived in the terraces fan and landslide deposits an initial optically stimulated luminescence osl based stratigraphy of these deposits is developed to deduce geomorphic evolution and palaeoclimatic changes the data show large alluvial fan progradation around sangla till c 45 ka middle of marine isotope stage 3 or mis 3 due to glacial retreat and readjustment of glacigenic sediment under warm and humid conditions followed by incision during the end phase of mis 3 23 ka intensified precipitation blocked the river course near sangla and kharogla by rock avalanches and imposed lacustrine conditions which recorded sedimentation until the beginning of holocene c 11 4 ka reduced sedimentation in these lakes during the last glacial maximum lgm c 23 18 ka suggests a cold and arid climate whereas increased sedimentation during c 18 11 5 ka indicates a warm and humid climate post lgm a palaeolake breach occurred during early holocene and incision continued throughout the holocene with a pulse of fluvial aggradation during c 9 1 6 5 ka over lacustrine remnant in the upper reach of the valley chitkul area coeval aggradation continued from 28 ka until c 19 ka mis 3 to lgm under cold and relatively arid conditions this study emphasizes that late quaternary geomorphic evolution of baspa valley is well synchronous with glacial fluctuations and the rapid response of the glacifluvial system to indian summer monsoon ism dynamics

the indian monsoon and its variability for over 300 years the monsoon has been viewed as a gigantic land sea breeze it is shown in this paper that satellite and conventional observations support an alternative hypothesis which considers the monsoon as a manifestation of seasonal migration of the intertropical convergence zone itcz with the focus on the indian monsoon the mean seasonal pattern is described and why it is difficult to simulate it is discussed some facets of the intraseasonal variation such as active weak cycles break monsoon and a special feature of intraseasonal variation over the region namely poleward propagations of the itcz at intervals of 2 6 weeks are considered vertical moist stability is shown to be a key parameter in the variation of monthly convection over ocean and land as well as poleward propagations special features of the bay of bengal and the monsoon brought out by observations during a national observational experiment in 1999 are briefly described

the role of extension during brittle deformation within the nw indian himalaya 1 synorogenic extension has been recognized as an integral structural constituent of mountain belts and high elevation plateaus during their evolution in the himalaya both orogen parallel and orogen normal extension has been recognized however the underlying driving forces for extension and their timing are still a matter of debate here we present new fault kinematic data based on systematic measurements of hundreds of outcrop scale brittle fault planes in the nw indian himalaya this new data set as well as field observations including crosscutting relationships mineral fibers on fault planes and correlations with deformation structures in lake sediments allows us to distinguish different deformation styles the overall strain pattern derived from our data reflects the large regional contractional deformation pattern very well but also reveals significant extensional deformation in a region which is dominated by shortening in total we were able to identify six deformation styles most of which are temporally and spatially linked representing protracted shortening our observations also furnish the basis for a detailed overview of the younger deformation history in the nw himalaya which has been characterized by extension overprinting previously generated structures related to shortening the four dominant deformation styles are 1 shortening parallel to the regional convergence direction 2 arc normal extension 3 arc parallel extension and finally 4 e w extension this is the first data set where a succession of both arc normal and e w extension has been documented in the himalaya importantly our observations help differentiate e w extension triggered by processes within the tibetan plateau from arc parallel and arc normal extension originating from the curvature of the himalayan orogen

late cenozoic uplift of mountain ranges and global climate change chicken or egg the high altitudes of most mountain ranges have commonly been ascribed to late cenozoic uplift without reference to when crustal thickening and other tectonic processes occurred deep incision and recent denudation of these mountain ranges abundant late cenozoic coarse sediment near them and palaeobotanical evidence for warmer climates where high mountain climates today are relatively cold have traditionally been interpreted as evidence for recent uplift an alternative cause of these phenomena is late cenozoic global climate change towards lower temperatures increased alpine glaciation a stormier climate and perturbations to humidity vegetative cover and precipitation

a doubling of the post perovskite phase boundary and structure of the earth s lowermost mantle a new model of the deep earth allows geophysicists to measure variations in earth s temperature near the boundary between the rocky mantle and core using a recently discovered phase change in the lowest part of the earth s mantle where atoms rearrange themselves in crystals under extreme pressure and temperature the model also explains odd features of this part of the mantle such as patchy regions that reflect seismic waves generated by large earthquakes and inferences of dense partial melting combined with observations the results imply very large variations in temperature providing further evidence for circulation of material throughout the earth s mantle the thermal structure of the earth s lowermost mantle the d layer spanning depths of 2 600 2 900 kilometres1 is key to understanding the dynamical state and history of our planet earth s temperature profile the geotherm is mostly constrained by phase transitions such as freezing at the inner core boundary or changes in crystal structure within the solid mantle that are detected as discontinuities in seismic wave speed and for which the pressure and temperature conditions can be constrained by experiment and theory a recently discovered phase transition at pressures of the d layer2 3 4 is ideally situated to reveal the thermal structure of the lowermost mantle where no phase transitions were previously known to exist here we show that a pair of seismic discontinuities observed in some regions of d can be explained by the same phase transition as the result of a double crossing of the phase boundary by the geotherm at two different depths this simple model can also explain why a seismic discontinuity is not observed in some other regions and provides new constraints for the magnitude of temperature variations within d

inferring the viscosity and the 3 d density structure of the mantle from geoid topography and plate velocities summary in a dynamic earth mantle mass heterogeneities induce gravity anomalies surface velocities and surface topography these lateral density heterogeneities can be estimated on the basis of seismic tomographic models recent papers have described a realistic circulation model that takes into account the observed plate geometry and is able to predict the rotation vectors of the present plates the relationship between the surface observables and the heterogeneities is sensitive to the viscosity stratification of the mantle here we use this model combined with a generalized least squares method in order to infer the viscosity profile of the earth from the surface observations and to get some new insight into the 3 d density structure of the mantle the computed radial viscosity profile presents a continuous increase of more than two orders of magnitude the asthenosphere has a viscosity close to 2 x lo2 pa s no sharp discontinuity is requested at the upper lower mantle interface the largest viscosity 7 x 10 pas is reached in the middle of the lower mantle at greater depth approaching the core mantle boundary the viscosity decreases by one order of magnitude the model suggests that the well known degree 2 and order 2 anomaly in the transition zone of the upper mantle is merely the signature of the slabs it also slightly increases the degree 2 and order 0 in the lower mantle and decreases it in the upper mantle in other words the inversion requests a hotter lower mantle beneath the equator and a colder upper mantle at the same latitudes

landslide dammed paleolake perturbs marine sedimentation and drives genetic change in anadromous fish large bedrock landslides have been shown to modulate rates and processes of river activity by forming dams forcing upstream aggradation of water and sediment and generating catastrophic outburst floods less apparent is the effect of large landslide dams on river ecosystems and marine sedimentation combining analyses of 1 m resolution topographic data acquired via airborne laser mapping and field investigation we present evidence for a large landslide dammed paleolake along the eel river ca the landslide mass initiated from a high relief resistant outcrop which failed catastrophically blocking the eel river with an approximately 130 m tall dam support for the resulting 55 km long 1 3 km3 lake includes subtle shorelines cut into bounding terrain deltas and lacustrine sediments radiocarbon dated to 22 5 ka the landslide provides an explanation for the recent genetic divergence of local anadromous ocean run steelhead trout oncorhynchus mykiss by blocking their migration route and causing gene flow between summer run and winter run reproductive ecotypes further the dam arrested the prodigious flux of sediment down the eel river this cessation is recorded in marine sedimentary deposits as a 10 fold reduction in deposition rates of eel derived sediment and constitutes a rare example of a terrestrial event transmitted through the dispersal system and recorded offshore

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

lateral variations in cmb heat flux and deep mantle seismic velocity caused by a thermal chemical phase boundary layer in 3d spherical convection article i nfo numerical simulations of thermo chemical multi phase compressible mantle convection in a three dimensional spherical shell are used to investigate the relationship between lateral variations in seismic shear wave velocity vs above the core mantle boundary cmb and lateral variations in heat flux across the cmb qcmb when compositional variations and the post perovskite phase transition are included for simple thermal convection the vs qcmb relationship is reasonably but not perfectly linear the post perovskite transition introduces a non linearity that amplifies fast vs anomalies in cold regions but there is still a unique mapping between vs and qcmb lateral variations in composition such as piles of dense material introduce another non linearity that affects hot upwelling regions and introduces a non uniqueness in vs qcmb if the dense material e g morb is seismically fast compared to the surrounding material in this case dense piles are ringed by sharp low vs anomalies if the cmb is covered by a global dense layer than variations in vs and qcmb are reduced but so is the mean value of qcmb in all cases the peak to peak lateral variation in qcmb is similar to or larger than twice the mean value which might create problems for generating a dynamo according to existing numerical dynamo simulations analytical scalings are developed to explain the observed trends

lower mantle seismic discontinuities and the thermal morphology of subducted slabs abstract the nature of the lowermost few 100 km of the mantle holds insights into the scale of convection of the earth s mantle here we investigate the fine structure of this region using seismic migration of shear waves reflecting from velocity discontinuities near the core mantle boundary cmb recorded by a dense network of european seismic stations two main features are found one structure exhibits large scale topography and can be explained by a sharp increase in seismic velocity 206 316 km above the cmb the second structure lies 55 85 km above the cmb and marks a sharp reduction in velocity to explain the origin of these discontinuities we appeal to numerical simulations of three dimensional 3d mantle convection incorporating rigidly moving plates the plates organize the convective flow to allow for the development of large convection cells and cool sheet like downwellings at a convergent plate boundary the results suggest that in places observed seismic complexity in d discontinuity structure may be due to the thermal gradients resulting from the accumulation of cool subducted plate material at the cmb

spherical shell models of mantle convection with tectonic plates abstract a simple three dimensional spherical model of mantle convection where plates are taken into account in the top boundary condition allows to investigate the plate tectonics mantle convection coupling in a self consistent way avoiding the strong difficulties inherent in the numerical treatment of rheology the plate condition appears efficient in reproducing the earth like features as subduction mid oceanic ridges and hotspots whereas the free slip condition leads to a classical polygonal cell pattern with cylindrical hot plumes surrounded by downwellings the plate condition favors the development of strong linear downwellings associated to passive diverging zones along plate boundaries these cold currents very similar to subductions act the main role in mantle convection they drive the whole circulation in that context hot plumes remain almost independent except if on the long term cold material spreading at the core surface induces a slight migration below a few mm yr of their surface impingement the main result is that plate tectonics appear to be more than a simple mode of organization of the surface movements it is the essence of the earth mantle dynamics

variability of dry sediment bulk density between and within retention ponds and its impact on the calculation of sediment yields monitoring sediment yields from catchments is important for assessing overall denudation rates and the impact of environmental change one of the methods used to assess sediment yield is by quantifying sedimentation rates in reservoirs lakes or small ponds before reliable sediment yield values t ha 1 a 1 can be computed from such sedimentation records the measured sediment volumes need to be converted to sediment masses using representative values of the dry sediment bulk density in textbooks simple relations predicting dry sediment bulk density from sediment texture time since deposition and hydrologic condition are presented in this study 13 small flood retention ponds in central belgium were sampled to reveal the variability in dry sediment bulk density and to test the commonly used relations to predict dry sediment bulk density dry sediment bulk density varies not only between the selected ponds 0 78 1 35 t m 3 but also within individual ponds coefficient of variation at 95 per cent ranges from 7 to 80 per cent the observed variability can be attributed primarily to the hydrologic condition of the retention pond and also to sediment texture the existing relations are not a reliable predictor for the observed dry bulk densities because they are primarily based on sediment texture thus when using volumetric sedimentation data from small ponds with varying hydrologic condition to predict sediment yield existing relations predicting dry sediment bulk density cannot be applied instead frequent and dense sampling of sediments is necessary to calculate a representative value of the dry sediment bulk density copyright 2001 john wiley sons ltd

evidence for a ubiquitous seismic discontinuity at the base of the mantle a sharp discontinuity at the base of earth s mantle has been suggested from seismic waveform studies the observed travel time and amplitude variations have been interpreted as changes in the depth of a spatially intermittent discontinuity most of the observed variations in travel times and the spatial intermittance of the seismic triplication can be reproduced by a ubiquitous first order discontinuity superimposed on global seismic velocity structure derived from tomography the observations can be modeled by a solid solid phase transition that has a 200 kilometer elevation above the core mantle boundary under adiabatic temperatures and a clapeyron slope of about 6 megapascal per kelvin

on the structure of the lowermost mantle beneath the southwest pacific southeast asia and australasia abstract the region of the lowermost mantle beneath the southwest pacific australasia and southeast asia 50 s 50 n and 80 190 e has been studied using a wide variety of seismic techniques we complement these studies with results obtained from long period global digital seismograph network gdsn data using a recently developed phase stripping technique that permits the isolation of d reflections from the stronger neighbouring s and scs signals we identify patches with d reflections and areas where we cannot confidently determine the presence or absence of a d reflection a synthesis of our results with other studies suggests that d varies dramatically through the region generally thickening from 100 150 km in a central zone to about 300 km at the eastern and western margins however there are irregularities in this overall pattern including areas where there seems to be little evidence for a d discontinuity inspection of waveform amplitudes shows considerable scatter in not only the d reflected phases but also core mantle boundary reflected phases experiments with synthetic seismograms for a variety of d models and the observed lateral variability through the region suggest that this is to be expected furthermore ray theory calculations for large scale 3d earth models predict significant variations 30 in s wave amplitudes of lowermost mantle turning rays finally we investigate possible correlations between lower mantle velocity flow and d thickness we find some correlation between d thickness and lower mantle velocities obtained from tomographic inversions with a thin d layer in high velocity regions and a thickening of the layer toward slower regions the relationship between predicted lower mantle flow and d thickness is less clear these results are qualitatively consistent with thermal boundary layer predictions for d but do not preclude the possibility of compositionally distinct material in the layer

modeling the evolution of natural cliffs subject to weathering 2 discrete element approach the evolution of slopes subjected to weathering has been modeled by assuming mohr coulomb behavior and by using a numerical approach based on the discrete element method dem according to this method soil and or rock are represented by an assembly of bonded particles particle bonds are subject to progressive weakening and so the material weathering and removal processes are modeled slope instability and material movement follow the decrease of material strength in space and time with the only assumption concerning the weathering distribution within the slope first the case of cliffs subject to strong erosion weathering limited conditions and uniform weathering was studied to compare the results of the dem approach with the limit analysis approach second transport limited slopes subject to nonuniform slope weathering were studied results have been compared with experimental data and other geomorphologic models from the literature fisher lehmann and bakker le heux the flux of material from the slope is modeled assuming degradation both in space and time

seasonal precipitation gradients and their impact on fluvial sediment flux in the northwest himalaya abstract precipitation in the form of rain and snowfall throughout the himalaya controls river discharge and erosional processes and thus has a first order control on the fluvial sediment flux here we analyze daily precipitation data 1998 2007 of 80 weather stations from the northwestern himalaya in order to decipher temporal and spatial moisture gradients in addition suspended sediment data allow assessment of the impact of precipitation on the fluvial sediment flux for a 103 km2 catchment baspa we find that weather stations located at the mountain front receive 80 of annual precipitation during summer may oct whereas stations in the orogenic interior i e leeward of the orographic barrier receive 60 of annual precipitation during winter nov apr in both regions 4 6 rainstorm days account for 40 of the summer budgets while rainstorm magnitude frequency relations derived from 40 year precipitation time series indicate a higher storm variability in the interior than in the frontal region this high variability in maximum annual rainstorm days in the orogenic interior is reflected by a high variability in extreme suspended sediment events in the baspa valley which strongly affect annual erosion yields the two most prominent 5 day long erosional events account for 50 of the total 5 year suspended sediment flux and coincide with synoptic scale monsoonal rainstorms this emphasizes the erosional impact of the indian summer monsoon as the main driving force for erosion processes in the orogenic interior despite more precipitation falling during the winter season

seismic discontinuity at the top of d a world wide feature considering the growing number of observations of a seismic discontinuity at the top of d some 300 km above the core mantle boundary we investigate the scenario of whether this feature could be global we show that the mean first arrivals of p waves as used to build global models can be fit by the two branches of a discontinuous model we argue that the intermittence of the detection of the reflector is due to lateral variations of a global discontinuity these observations put strong constraints on the type of chemical layering that could explain the discontinuity we speculate that the properties of the d discontinuity are better explained in terms of a new phase transition

connecting source and transport suspended sediments in the nepal himalayas understanding the dynamics of sediment fluxes is a key issue to constrain modern erosion rates in mountain belts and determine the still debated level of control exerted by precipitation topography and tectonics the well defined monsoon seasonality in the himalayas together with active tectonics and strong relief provide an ideal environment to assess these possible interactions for this purpose we present a new compilation of daily suspended sediment data for 12 stations of the major rivers of the nepal himalayas we analyze the relationships of sediment transport with daily river discharge and precipitation data as well as with morphometric parameters we show that suspended sediment concentrations vary systematically through the seasons and asynchronously to river discharge displaying a hysteresis effect this clockwise hysteresis effect disappears when suspended sediment fluxes are directly compared with direct storm discharge therefore we attribute the hysteresis effect to groundwater dilution rather than a sediment supply limitation we infer a rating model to calculate erosion rates directly from long river discharge chronicles we show that when normalized by drainage area and mean sediment flux all rivers exhibit the same trend this similarity implies that all river basins have the same erosion behavior independent of location size and catchment characteristics erosion rates calculated from suspended sediment fluxes range between 0 1 and 2 8 mm yr the erosion rates of the three main basins of nepal are in the range 0 9 1 5 mm yr erosion rates in the higher himalayas are relatively low 0 5 mm yr except for kali gandaki while in the lesser himalayas they range from 0 2 to 2 mm yr we propose that material transport in the rivers depends on hillslope sediment supply which is in turn controlled by those rainfalls producing direct runoff in other words the rivers in the nepal himalayas are supply limited and the hillsopes as a contributing source are transport limited we also show that erosion processes are not as much controlled by infrequently occurring extreme precipitation events than by moderate ones with a high recurrence interval

laterally varying reflector at the top of d beneath northern siberia summary we analyse p wave data from the french laboratoire de dctection et gcophysique l d g network of digital short period seismic stations whereas our previous paper houard nataf 1992 showed a few promising kurd events and depicted the methods we proposed to apply an extensive analysis of 32 earthquakes from the kurivkamchatka region has now been carried out by using the deconvolution technique previously described houard nataf 1992 clear and quantitative evidence of intermediate arrivals between the p and pcp waves is shown in the 75 82 distance range our approach is complementary to previous studies in the same region which used broad band data recorded at a dense narrow aperture array weber davis 1990 weber 1993 or long period data recorded at the wwssn stations gaherty lay 1992 for each station record sections of deconvolved signals from different earthquakes are built and lead us to eliminate crustal reverberations beneath l d g stations as a major explanation for these secondary arrivals a compilation of the most conclusive signals has been made it is perhaps one of the most complete pdp wave record sections since the move out with distance can be followed clearly with a good sampling over more than 5 the move out with distance of this extra pdp arrival its residual slowness value eliminates source complexities diffraction or multipathing through the kuril subduction slab as possible explanations the extra arrivals indicate the existence of a lower mantle reflector the structure of the lay discontinuity is investigated using tpdp tp residual traveltimes two different residual time versus distance tendencies are found which correlate to different geographical bounce point regions indicating the existence of lateral variations of the structure the d region is also sampled further south at distances well beyond the theoretical triplication cross over by analysing events from the honshu ryukyu islands region but only one p wave branch is observed the hodochrones and p a curves of the first p arrival are used as a complementary analysis the global prem model dziewonski anderson 1981 predicts correct p wave slownesses though its smooth lower mantle structure does not account for pdp observations this may be an indication that the lay discontinuity is a global feature however the hodochrones of the first p arrival do not allow us to test the existence of the discontinuity in the 82 85 cross over distance range

late pleistocene holocene vegetation and climate from the palaeolake sediments rukti valley kinnaur himachal himalaya abstract vegetation and climate during later part of pleistocene to major part of holocene 16 6 3 5 ka has been reconstructed based on the palynological and magnetic susceptibility proxies from an exposed section of lacustrine deposit at rukti sangla valley kinnaur western himalaya study shows that along with the general tree line succession to higher altitudes since early holocene the area has also captured the major climatic events of late pleistocene to early mid holocene time the area exhibits a continuation of mixed conifer broadleaved forest at least since 16 6 ka with intermittent phases of expansions of broadleaved tree taxa especially oaks quercus or invasion of conifers especially pine pinus with an increase moist or decrease dry of indian summer monsoon ism respectively this is also supported by the variations in the magnetic susceptibility values the climate was warm and moist during 16 6 ka and changed to cool 13 3 ka followed by increasing ism since 11 5 ka distinct spike in the magnetic susceptibility values between 8 7 and 7 8 ka could correspond to global 8 2 ka cool event thus indicating strengthening of westerly influence and low evaporation subsequent warm conditions could be generalized by the advancement of birch betula line to higher altitude following the resultant retreat of the glacial body study has put forth the potential of such himalayan sites to uncover the major climatic events of global correlation captured by various proxies within a region

seismic imaging of the d and constraints on the core heat flux abstract recent seismic imaging of the deep mantle has revealed lens shaped layers near the bottom of the mantle the morphology of this layering has been attributed to the crossing of the post perovskite phase boundary by the local geotherm we have developed a technique for quantifying the relationships between the depths of the double crossings of the post perovskite transition developed in 3d spherical mantle convection as a means for testing the viability for using the clapeyron slope of the phase transition to put bounds on the heat flux from the core we have argued from the probability distribution of the local heat flow at the core mantle boundary that there are intrinsic problems in using error function from half space cooling curves for constraining the core heat flux because of the non gaussian shape of the probability distribution of the core heat flow in realistic 3d convection models in order to constrain better the core heat flux with the above arguments we need to know much better the mantle viscosity stratification and the pressure dependence of thermal conductivity in the deep mantle only then can we put together enough constraints to discuss with greater certainty about the core heat flux

modification of fabric in pre himalayan granitic rocks by post emplacement ductile deformation insights from microstructures ams and u pb geochronology of the paleozoic kinnaur kailash granite and associated cenozoic leucogranites of the south tibetan detachment zone himachal high himalaya the present day south tibetan detachment std of higher himalaya is a system of low angle normal faults in the himachal high himalaya the std hanging wall is characterized by the presence of s type per aluminous paleozoic 475 ma granite called the kinnaur kailash granite kkg this granite is later intruded by cenozoic leucogranites 18 ma in vicinity of the std zone in this work microstructures anisotropy of magnetic susceptibility ams and u pb geochronology were carried out on the kkg and the leucogranites with an aim to a understand the conditions of fabric development and b decipher the tectonic relationship between deformation along the std and the evolution of these granites microstructural features and magnetic anisotropy indicate that the granites are intensely deformed in vicinity of the std and preserve their emplacement related fabric in the interior parts it is inferred that close to the std zone fabrics of both the kkg and the leucogranite are tectonic and are modified by the cenozoic 20 ma right lateral slip and extensional tectonics magnetic fabric in the interior parts of the kkg is related to its emplacement indicating that original fabric was preserved u pb geochronology of zircons from two samples of the kkg yields crystallization age of 477 6 3 4 and 472 4 ma the leucogranite gives a crystallization age of 18 5 0 6 ma zircons from the kkg also reveal signatures of a deformation event 20 6 2 3 ma at its rim it is inferred that deformation of the external rim of the kkg and crystallization of the leucogranites are synchronous and triggered by ductile deformation along the std

early human impact in the forest ecotone of southern high asia hindu kush himalaya abstract the vegetation of the treeline ecotone of the southern declivity of arid high asia hindu kush northern areas of pakistan himalaya northern central nepal is dominated by hedgehog like open dwarf shrublands of thorny cushions since climatically sensitive ecotones are always also sensitive to human impact the question arises whether the current lack of forests is a result of the subboreal climate decline or of human impact due to inadequate knowledge of the pollen flora and of ecological indicator values of the plants pollen analyses in high asia have mainly been limited to the regional verification of globally known climatic impulses however the role of human impact on regional vegetation patterns has been widely neglected we postulate that today s open dwarf shrublands replace woodlands and forests isolated vigorous juniper trees and successful reforestation appear to confirm our hypothesis an abrupt decline of pinus forests before 5700 and 5400 ka cal yr bp can be demonstrated as the first indicator pollen of human impact appeared at both sites synchronous with the forest pollen decline we infer human impact to be a more decisive cause for this environment change superimposing the effects of a climatic deterioration the forests were displaced by open dwarf shrublands

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

chronology of late quaternary glaciation in the pindar valley alaknanda basin central himalaya india abstract palaeoglacial reconstruction based on geomorphological mapping in the pindari glacier valley alaknanda basin central himalaya has revealed five glacial stages with decreasing magnitude the oldest and most extensive stage i glaciation deposited sediments at 2200 masl khati village the stage ii glaciation was around 7 km long and luminescence dated to 25 2 ka and has deposits at 3200 masl phurkia village stage iii glaciation is represented by degraded linear moraine ridges and is dated to 6 1 ka and its remnants can be found around 3850 masl a sharp crested crescentic moraine extending from around 3650 masl to 3900 masl is attributed to stage iv glaciation and is dated to 3 1 ka following this there appears to have been a gradual recession in pindari glacier as indicated by four sharp crested unconsolidated moraines stage v on the valley floor which abuts the stage iv moraine we suggest that the stage i glaciation occurred during the cool and wet marine isotopic stage 3 4 mis 3 4 stage ii glaciations began with the onset of mis 2 whereas the stage iii and iv glaciations occurred during the mid to late holocene mis 1 we speculate that the first sharp crested unconsolidated moraines around 3600 masl correspond to the later phase of the little ice age lia historical data suggests that the remaining three ridges represent pindari glacier snout positions at 1906 1958 and 1965 we argue that the late quaternary glaciations in the pindar valley were modulated by changing insolation and summer monsoon intensity including the lia whereas the 20th century recessional trends can be attributed to post lia warming

thick and anisotropic d layer beneath antarctic ocean 1 waveform modeling and travel times analyses of s scs and sks phases recorded at the broad band permanent station syo in the antarctic are used to determine the shear wave velocity structure and transverse isotropy in the d layer beneath the antarctic ocean the sh wave structure has a discontinuity with the velocity increase of 2 0 at 2550 km the sv structure is similar to prem model the magnitude of the anisotropy is highest at the top of d layer and lowest at the core mantle boundary the d layer beneath the antarctic ocean is significantly thicker than those beneath alaska and the caribbean sea we attribute this anisotropic d layer to paleo slab materials the subduction in and around the antarctic ocean has started 180 ma and is the one of the oldest in the world it has provided a large amount of the slab materials in the lowermost mantle citation usui y y hiramatsu m furumoto and m kanao 2005 thick and anisotropic d layer beneath antarctic ocean

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

a new inference of mantle viscosity based upon joint inversion of convection and glacial isostatic adjustment data we present new profiles of mantle viscosity derived on the basis of non linear occam style joint inversions of an extensive set of data associated with mantle convection and glacial isostatic adjustment gia the convection related observables include satellite derived free air gravity harmonics the geodetically inferred excess ellipticity of the cmb and tectonic plate motions the gia constraints involve two classes of observables previously shown to be relatively insensitive to errors in the late pleistocene ice history the so called fennoscandian relaxation spectrum frs and a set of site specific decay times determined from the postglacial sea level history in hudson bay and sweden the inverted viscosity profiles show a significant three orders of magnitude increase from the upper mantle mean value of f4 10 20 pa s to a high viscosity 10 23 pa s peak at

three dimensional structures and dynamics in the deep mantle effects of post perovskite phase change and deep mantle layering 1 three dimensional numerical simulations of thermo chemical mantle convection with multiple phase transitions olivine spinel perovskite post perovskite are used to investigate the morphology of compositional and post perovskite ppv boundary structures above the core mantle boundary cmb compositionally dense subducted morb partially segregates above the cmb forming ridge like dense piles morphologically similar to structures in previous spherical or cartesian studies in which a dense layer was inserted a priori an anti correlation is observed between regions where a thick post perovskite layer occurs and regions containing piles of dense material as in our previous two dimensional study lateral variations in the thickness or occurrence of a ppv layer cause very strong seismic shear wave velocity anomalies which may dominate thermal or composition related seismic heterogeneity in the depth range where the variable ppv boundary occurs and also generate sharp sided structures as observed seismologically both compositional and ppv effects may be necessary to simultaneously explain large scale heterogeneity and the global distribution of the discontinuity atop d

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

modern erosion rates in the high himalayas of nepal abstract current theories regarding the connections and feedbacks between surface and tectonic processes are predicated on the assumption that higher rainfall causes more rapid erosion to test this assumption in a tectonically active landscape a network of 10 river monitoring stations was established in the high himalayas of central nepal across a steep rainfall gradient suspended sediment flux was calculated from sampled suspended sediment concentrations and discharge rating curves accounting for solute and bedload contributions the suspended sediment fluxes were used to calculate watershed scale erosion rates that were then compared to monsoon precipitation and specific discharge we find that in individual watersheds annual erosion rates increase with runoff in addition our data suggest average erosion rate increases with discharge and precipitation across the entire field site such that the wetter southern watersheds are eroding faster than the drier northern watersheds the spatially non uniform contemporary erosion rates documented here are at odds with other studies that have found spatially uniform long term rates 10 5 10 6 yr across the pronounced rainfall gradient observed in the region the discrepancy between the modern rates measured here and the long term rates may be reconciled by considering the high erosional efficiency of glaciers the northern catchments were much more extensively glacierized during the pleistocene and therefore they likely experienced erosion rates that were significantly higher than the modern rates we propose that in the northern watersheds the high rates of erosion during periods of glaciation compensate for the low rates during interglacials to produce a time averaged rate comparable to the landslide dominated southern catchments

is io s mantle really molten abstract the tremendous heating dissipated by jovian tides in io s interior is essentially evacuated by an intense volcanic activity so that the heat is removed from the interior to the surface much more by advection than by conduction through the lithosphere the efficiency of this heat pipe cooling process is investigated through numerical models of convection performed in spherical geometry with a permeable top boundary this new heat transfer model provides a cooling twice as efficient as that obtained with an impermeable condition traditionally used in mantle convection modeling the globally averaged temperature varies as ra 1 2 where ra is the rayleigh number whereas the power law exponent is classically 1 4 so that the expected ra would not be in excess of 10 7 if the whole mantle of io is involved in the convection process the major portion could remain solid while a possible molten zone could be confined to a 100 km thick layer between the solid part and the core this model predicts the existence of a strong lithosphere which is required to support the observed topographic amplitude of the io s relief

the mechanism of high speed motion and damming of the tangjiashan landslide abstract understanding the mechanisms of landslide failure and resulting damming processes is crucial for constraining the hazard chain associated with landslide damming events on may 12 2008 the wenchuan earthquake caused a large number of secondary hazardous events such as landslides and collapses most of which occurred in high mountain gorges in these areas the sliding distance of landsides is often very short and the landslides are often characterized by high speed short distance and damming using the tangjiashan landslide damming events induced by the wenchuan earthquake as a model this paper reconstructs the three dimensional failure and associated damming caused by the landslide based on a detailed geological investigation of the landslide area and using the dynamic finite element technique the study proposes a four stage model for the failure and damming process of the tangjiashan landslide earthquake induction and progressive destruction of the slide body destruction and high speed sliding of the slide body slide body impact disintegration and river blockage for the formation of a damming body and vibration compression the average speed of the tangjiashan landslide reached a maximum value of 22 m s about 30 s after the earthquake and the landslide reached stability about 60 s later

3d numerical modeling using smoothed particle hydrodynamics of flow like landslide propagation triggered by the 2008 wenchuan earthquake abstract the extremely strong wenchuan earthquake triggered thousands of landslides in sichuan province china flow like landslides such as the tangjiashan wangjiayan and donghekou landslides were among the most destructive causing many casualties and serious economic damage it is therefore important to identify the flow mechanisms and investigate the specific characteristics of these flow like landslides this paper presents a three dimensional model based on smoothed particle hydrodynamics sph to simulate rapid landslide motion across 3d terrain the navier stokes equations in a cfd framework are used as governing equations and artificial viscosity is incorporated into the pressure terms in the momentum equation to dissipate energy to avoid numerical oscillation and particle penetration thus improving the stability of the numerical results a non newtonian fluid model the bingham model has proven suitable for describing the relationship between the shear strain rate and the shear stress in highly deformed soil materials in the proposed model it is used as the constitutive model to describe the fluidization characteristics of flow like landslides combined with the mohr coulomb yield criterion the model incorporates a no slip boundary condition to consider the effect of a solid boundary on slope movement ghost particles are created and assigned an artificial velocity the viscous force caused by the solid boundary is calculated using the relative velocities between the fluid and the boundary particles open multiprocessing openmp an api for multi platform shared memory parallel programming is used to improve the efficiency of the sph code running to show the validity of the proposed approach a benchmark problem of 3d dam break was simulated the calculated distances of the surge front at different times agree well with the test results numerical modeling of the propagation of the tangjiashan wangjiayan and donghekou landslides was performed by the application of sph models to real flow like landslides the whole flow processes of these flow like landslides across the 3d terrain are represented the landslides change direction split or join in and spread or contract in their flow path in response to the local topography time history curves of the velocity and displacement were obtained to analyze the movement characteristics of the landslide mass the shapes of the deposition zones after slide occurrence were investigated comparisons of the sph simulated geometry and the surveyed landslide configurations for the tangjiashan wangjiayan and donghekou landslides were conducted and show a high degree of similarity this indicates that the proposed 3d sph model can accurately represent the evolution of the final slide shape the prediction of the fluidization characteristics of earthquake induced flow like landslides can notably reduce sudden loss of life as it provides a means for mapping hazardous areas for estimating the hazard intensity and for identification and design of appropriate protective measures

crustal structure of the himalayan orogen at 90 east longitude from project indepth deep reflection profiles international deep profiling of tibet and the himalaya indepth deep seismic reflection profiles show that the indian lithosphere is underthrusting the central himalaya along a gently north dipping decollement that is traceable northward beneath the tethyan belt to 28 6 n and to a depth of about 45 km the decollement carries in its hanging wall a near crustal thickness slice of internally deformed indian continental basement and cover represented in outcrop by the greater himalayan belt and structurally overlying tethyan belt geometric relationships suggest that the decollement probably ramps downward beneath the northern tethyan belt to near the base of the crust and that the hanging wall crustal slice was detached from indian mantle lithosphere that presently underlies southern tibet to the north the north himalayan anticlinorium kangmar dome appears to be a large duplex ramp anticline in the hanging wall of the decollement the south tibetan detachment appears to have been imaged in two areas in the wagye la area it appears to follow the tethyan belt greater himalayan belt contact northward in the subsurface and to have been folded over the kangmar dome in the zherger la area it appears to have been active relatively recently as a 30 north dipping normal fault that cuts deeply into the greater himalayan belt allochthon palinspastic reconstruction indicates a minimum of about 326 km of shortening of the indian basement across the himalaya since the initiation of the main central thrust hence indian continental lithosphere largely stripped of its overlying crust can extend northward beneath the tibetan plateau to at least 32 n where earthquake seismological observations show that the properties of the upper mantle change markedly e g mcnamara et al 1995 taken together the seismic reflection and earthquake seismological observations lend support for the view that the indian mantle lid mechanically underplates roughly the southern half of the tibetan plateau the indepth reflection data do not show that indian crust attached to this lithosphere extends north of southernmost tibet kangmar dome nor do they negate this possibility similarly the reflection data do not yield direct evidence for or against lower crustal subduction beneath the himalaya

miocene to holocene exhumation of metamorphic crustal wedges in the nw himalaya evidence for tectonic extrusion coupled to fluvial erosion the himalayan crystalline core zone exposed along the sutlej valley india is composed of two high grade metamorphic gneiss sheets that were successively underthrusted and tectonically extruded as a consequence of the foreland directed propagation of crustal deformation in the indian plate margin the high himalayan crystalline sequence hhcs is composed of amphibolite facies to migmatitic paragneisses metamorphosed at temperatures up to 750 c at 30 km depth between eocene and early miocene during early miocene combined thrusting along the main central thrust mct and extension along the sangla detachment induced the rapid exhumation and cooling of the hhcs whereas exhumation was mainly controlled by erosion since middle miocene the lesser himalayan crystalline sequence lhcs is composed of amphibolite facies para and orthogneisses metamorphosed at temperatures up to 700 c during underthrusting down to 30 km depth beneath the mct the lhcs cooled very rapidly since late miocene as a consequence of exhumation controlled by thrusting along the munsiari thrust and extension in the mct hanging wall this renewed phase of tectonic extrusion at the himalayan front is still active as indicated by the present day regional seismicity and by hydrothermal circulation linked to elevated near surface geothermal gradients in the lhcs as recently evidenced in the himalayan syntaxes active exhumation of deep crustal rocks along the sutlej valley is spatially correlated with the high erosional potential of this major trans himalayan river this correlation supports the emerging view of a positive feedback during continental collision between crustal scale tectono thermal reworking and efficient erosion along major river systems

viscous heating a potential mechanism for the formation of the ultralow velocity zone abstract the detection of several ultralow velocity zones ulvz on the core mantle boundary cmb together with the recent estimates of the lower mantle solidus would suggest that some sort of melting may occur inside the upwellings in the deep mantle we have studied the possibilities of viscous heating as a mechanism for producing favorable conditions leading to melting inside deep mantle upwellings a two dimensional model in an aspect ratio 3 box with temperature and pressure dependent rheology and two major phase transitions has been employed both viscous and adiabatic heating have been included and various amounts of internal heating have been applied viscous heating can heat up the interior of the deep mantle plumes to around 100 degrees above the cmb temperature this amount of temperature rise is sufficient to cause melting inside upwellings in the deep lower mantle we propose here that viscous heating plays an important role in producing conditions leading to the formation of the ulvz massive melting within rising plumes might have been more prevalent in the past

high resolution imaging of lowermost mantle structure under the cocos plate 1 broadband seismic shear waves are analyzed to investigate the fine velocity structure in the lowermost mantle beneath the cocos plate a region where previous studies have indicated the presence of a shear velocity increase about 200 300 km above the core mantle boundary data from 14 south american earthquakes recorded at california broadband networks provide dense ray path sampling of the lowermost mantle in an approximately 700 km long north south corridor roughly 150 km wide application of a simplified seismic migration method that uses a homogeneous background velocity model suggests topography of the previously imaged positive impedance jump varying in depth from north to south by as much as 150 km with a weakly reflecting transition zone in between the migration approach enables examination of small scale spatial variations and out of plane scattering effects topography of the discontinuity may account for observed variations in the amplitude of reflected arrivals or there may be lateral variations in the velocity contrast across the boundary lateral variations of the shear velocity structure within the d layer may produce some apparent topography in the discontinuity image but any such volumetric structure is not yet well enough determined to incorporate in the migration a localized negative impedance contrast reflector or scatterer is imaged at depths about 100 km below the positive reflector in the northern portion of the study area several scenarios can explain these results including 1 a slab that reaches the lowermost mantle 2 the birth of an upwelling beneath a recumbent slab or 3 chemical layering in this region

postperovskite phase transition and its geophysical implications 1 the stability of mg fe sio3 perovskite in the deep lower mantle has long been uncertain recently a phase transition from perovskite to postperovskite was discovered through a significant change in the x ray diffraction pattern at high pressure and high temperature conditions corresponding to the core mantle boundary region this phase transition was also confirmed by first principles calculations these suggest that mg fe sio3 postperovskite is the predominant mineral in the lowermost mantle called the d layer and phase transition from perovskite to postperovskite has significant geophysical implications for its nature and dynamics the postperovskite phase may account for the large seismic anomalies observed in the d region such as the d discontinuity s wave anisotropy and anticorrelation between the anomalies in s wave and bulk sound velocities in addition this phase transition is a strongly exothermic reaction it destabilizes the thermal boundary layer at the base of the mantle and should promote the formation of high temperature upwelling plumes

mantle control of the geodynamo consequences of top down regulation the mantle global circulation including deep subduction and lower mantle superplumes exerts first order controls on the evolution of the core the history of the geodynamo and the structure of the geomagnetic field mantle global circulation models that include realistic plate motions deep subduction and compositional heterogeneity similar to the observed large low seismic velocity provinces in the lower mantle predict that the present day global average heat flux at the core mantle boundary cmb exceeds 85 mw m 2 this is sufficient to drive the present day geodynamo by thermochemical convection and implies a very young inner core with inner core nucleation between 400 and 1100 ma the mantle global circulation also generates spatially heterogeneous heat flux at the cmb with peak to peak lateral variations exceeding 100 mw m 2 such extreme lateral variability in cmb heat flux in conjunction with the high thermal conductivity of the core implies that the liquid outer core is thermally unstable beneath the high seismic velocity regions in the lower mantle but thermally stable beneath the large low seismic velocity provinces numerical dynamo simulations show how this pattern of heterogeneous boundary heat flux affects flow in the outer core producing localized circulation patterns beneath the cmb tied to the mantle heterogeneity and long lived deviations from axial symmetry in the geomagnetic field

sedimentation pattern in a trans himalayan quaternary lake at lamayuru ladakh india abstract located on the indo tsangpo suture zone lamayuru lake in western ladakh was created by neotectonic instability around 35 40 ka the valley fill sequence about 110 m thick reveals an interplay of lacustrine to fluvio deltaic to colluvial processes operating in response to changing climate and tectonic conditions based on integrated approach of sedimentology and palaeontological analysis we propose a sedimentation model for lamayuru lake with reference to changing climatic conditions and neotectonics the coarsening upward succession was divided into five lithofacies associations associations a e each association comprising one or more lithofacies represents a specific depositional environment and marks an independent episode of sedimentation a dominantly muddy sequence of facies association a a product of a lacustrine environment is followed by coarsening upward cycles association b composed of silt to sand that implies laterally shifting deltas thereafter thick sand and gravel deposits constituting fining upward fu unit cycles associations c and d represent deposition in a fluvial domain the upper part of association d composed of matrix supported gravel horizons was deposited as debris flows and marks the termination of sedimentation in the valley the clastic lithofacies facies associations a to d with plant fragments and charcoal presumably indicate warm humid climatic conditions in contrast association e comprising marl lithofacies occurring at four different levels is biogenic and indicates arid to semi arid climatic phases five main types of trace fossils including rhizoliths seem to be representatives of scoyenia ichnofacies and animal burrows indicating a thin population of soft bodied annelid and arthropod communities living under low energy condition nine fossiliferous horizons have yielded characteristic ostracods charophytes and gastropods indicating shallow low energy and cold water ecological conditions coarsening up lake succession extensive synsedimentary deformation tilting of lake beds and the entrenchment of the lamayuru drainage indicate basin evolution under an effective role of neotectonics in the area

a sph depth integrated model for popocatepetl 2001 lahar mexico sensitivity analysis and runout simulation abstract lahars are debris flows of volcanic origin which can endanger or even destroy communities located near the flanks of volcanoes lahars are not always triggered by eruptions they can form during heavy rainfall or after hydrothermal alteration and volcanic edifice collapse decision makers need lahar hazard maps to devise hazard prevention measures that will prevent casualties so lahar modelling is an important tool for assessing flow behavior and determining inundation areas the depth integrated numerical model used in this study is derived from the velocity pressure of the biot zienkiewicz model and was discretized using the smoothed particle hydrodynamics sph method to simulate a lahar that occurred at popocatepetl volcano in 2001 in order to investigate the convergence of the model we used a range of different sph mesh resolutions once the optimum mesh resolution was bounded we analyzed the model s sensitivity to the initial lahar volume the density of the geomaterial and the rheological parameter of the bingham fluid the results show that the sph depth integrated model produced a highly accurate simulation of the distribution and velocity of the 2001 lahar the study also shows the effects of sph mesh resolution and the relevant influence of rheological parameters

degree one mantle convection dependence on internal heating and temperature dependent rheology 1 geophysical and geological observations suggest that a degree one mantle flow pattern consisting of one upwelling and one downwelling may have existed at some time in the mantles of mars the moon and perhaps even for the earth during times of supercontinent formation simple fluid experiments utilizing isoviscous rheologies predict shorter wavelength flow patterns and it is therefore important to determine fluid dynamical parameter sets which lead to larger wavelength flow patterns consistent with observations we perform a series of numerical fluid dynamics calculations in a spherical 3 d geometry in which we vary rayleigh number rheological activation parameter and the degree of internal heating in order to define which parameter choices can lead to degree one mantle convection we find that increasing the degree of internal heating increases the interior temperature of the mantle which leads to a larger viscosity contrast across the top thermal boundary layer and that degree one mantle flow occurs only in cases which exhibit internal heating utilize activation coefficients which lead to 103 or higher viscosity contrasts across the mantle and have viscosity contrasts across the top thermal boundary layer within the range of 200 3000

analysis of the chiufengershan landslide triggered by the 1999 chi chi earthquake in taiwan abstract a disastrous earthquake rocked taiwan on september 21 1999 with magnitude m l 7 3 and an epicenter near the small town of chi chi in central taiwan the chi chi earthquake triggered landslide on the dip slope at the chiufengershan in this study a review of the topography and geology of this area was followed by field investigations laboratory testing was applied to understand the geomaterial composing the slope then based on a series of limit equilibrium analyses the failure mechanism of this landslide and the risk of the residual slope were studied according to the stability analyses the pre quake slope is quite stable with factor of safety of 1 77 dry to 1 35 full groundwater level explaining why there is no written record of a landslide here for the past 100 years in contrast a back analysis shows that the chi chi earthquake induced dynamic loading is far more than the dip slope can sustain due in part to the short distance to the epicenter a monte carlo type probability analysis suggests that the residual slope is more dangerous than the pre quake slope and needs more attention

fluvial response to large rock slope failures examples from the himalayas the tien shan and the southern alps in new zealand we describe remnants of large 10 7 10 10 m 3 late pleistocene to holocene rockslides and rock avalanches that block ed rivers and are preserved in the himalayas the tien shan and the new zealand southern alps despite rates of uplift and erosion of up to 10 mm year 1 these natural dams control fluvial response on 10 1 10 4 year timescales by a storing and releasing sediment during forced alluviation and fluvial re incision b relocating river channels through diversion or seepage c inhibiting river erosion into bedrock d formingpersistentlong profileknickpointsandknickslopesassociatedwithsteephigh energy n10 3 wm 2 breachand epigenetic bypass gorges and fluvial hanging valleys and e shaping valley floor morphology sediments indicate that rockslidedammed lakes may persist up to 10 4 years before being drained or infilled several short lived 10 0 10 2 year historical rockslide dams in the indian and nepal himalayas and the southern alps have had marked volumetric impacts on catchment sediment budgets shortly following failure therefore we caution against the linear extrapolation of sediment delivery from prehistoric rockslide dams through time as a response variable we find reach scale changes to channel gradient to be prominent and persistent indicators of fluvial response to large rock slope failures 2006 elsevier b v all rights reserved

seismites an attempt at critical analysis and classification abstract the main types of seismites are reviewed following the proposed classification and are illustrated by our own case studies the large variety of seismites depends on the sedimentologic hydrodynamic and diagenetic characters of the deposits subject to seismic shocks on a given site generally different types of seismites cane be related to the same seismic event these peculiar but widespread sedimentary structures are not always univocal and may often be related to different causes therefore the structures discussed must necessarily be placed in a detailed geological context

effects of a realistic mantle thermal conductivity on the patterns of 3 d convection abstract a physical model describing the temperature and pressure dependences of mantle thermal conductivity has recently been provided by a m hofmeister science 283 1999 1699 1706 we have studied numerically the influences of such a temperature and pressure dependent thermal conductivity on 3 d constant viscosity convection a large aspect ratio box of 4 4 1 has been taken for rayleigh numbers greater than 104 to 106 the power law index governing the phonon contribution to the thermal conductivity controls the style of convection for silicates the pattern of convection is quite different from that of constant conductivity whereas the pattern of convection associated with conductivity of oxides is close to the case for constant conductivity both boussinesq and extended boussinesq models with viscous and adiabatic heatings have been examined major effects of variable thermal conductivity on mantle convection are 1 heating up of the lower mantle 2 longer wavelength boussinesq convection 3 shorter wavelength for extended boussinesq convection 4 thick stable plumes with large plumeheads 5 thicker thermal boundary layer of around 500 km at the base of the mantle the contributions from the new terms due to the variable conductivity in the energy equation have magnitudes several times that of chondritic heating at the boundary layers a large region of superadiabatic lower mantle with about a 400 to 600 k excess is caused by variable thermal conductivity this finding has an interesting implication on the recent seismic finding of a lighter density in the deep portion of the lower mantle

mantle convection and the dynamic geoid of mars this study compares different 3d spherical models of thermal convection in the martian mantle the best fit to the tharsis bulge is obtained if the endothermic phase transition to perovskite occurs closely above the core mantle boundary in this case a large scale flow develops and the associated geoid anomaly explains approximately half of the observed long wavelength geoid the shallower exothermic phase transitions have little influence on the planform of the flow and on the shape of the geoid previous studies that included exothermic transitions were biased by effects of a soft lithosphere which introduces a large scale mantle flow even without a deep endothermic phase transition however such models predict a continous resurfacing and a dominant geoid low which is in conflict with observations

dynamical consequences in the lower mantle with the post perovskite phase change and strongly depth dependent thermodynamic and transport properties article i nfo we have carried out numerical simulations of large aspect ratio 2 d mantle convection with the deep phase change from perovskite pv to post perovskite ppv using the extended boussinesq approximation for a fluid with temperature and pressure dependent viscosity we have investigated the effects of various ppv phase parameters on the convective planform heat transport and mean temperature and viscosity profiles since ppv is expected to have a relatively weak rheology with respect to pv and a large thermal conductivity we have assumed that the transition from pv to ppv is accompanied by both a reduction in viscosity by 1 to 2 orders of magnitude and by an increase in thermal conductivity by a factor of 2 furthermore we have analyzed the combined effects of a strongly decreasing thermal expansivity in pv and steeply increasing thermal conductivity according to recent evidence from high pressure experiments and first principle calculations as long as the thermal expansivity and conductivity are constant ppv exerts a small but noticeable effect on mantle convection it destabilizes the d layer causes focusing of the heat flux peaks and an increase of the average mantle temperature and of the temporal and spatial frequency of upwellings when the latest depth dependent thermal expansivity and conductivity models are introduced the effects of ppv are dramatic on the one hand without ppv we obtain a very sluggish convective regime characterized by a relatively cool mantle dominated by large downwellings that tend to stagnate beneath the transition zone with ppv on the other hand we observe an extremely significant increase of the average mantle temperature due to the formation of large sized and vigorous upwellings that in some cases tend to cluster thus forming superplumes if a very large thermal conductivity at the core mantle boundary is assumed k 20 wk 1 m 1 we obtain a quasi steady state regime characterized by large and stable plumes with long lifetimes the combination of strongly depth dependent expansivity and conductivity is a viable mechanism for the formation of long wavelength long lived thermal anomalies in the deep mantle even if a low viscosity ppv atop the core mantle boundary is included

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

style and timing of glacial and paraglacial sedimentation in a monsoon influenced high himalayan environment the upper bhagirathi valley garhwal himalaya abstract the gangotri glacier at the source of the ganges river has fluctuated greatly throughout the late quaternary in response to climatic oscillations this has resulted in impressive moraines paraglacial debris flow fans and terraces along the upper stretches of the bhagirathi valley cosmogenic radionuclide crn dating of glacial and paraglacial landforms shows that fans terraces and associated moraines formed approximately synchronously as the landscape readjusted to changing environmental conditions this synchronicity suggests that fan and terrace formation is intimately related to glaciation and that fluctuations in glacial and associated environments during times of climatic instability cause rapid sediment transfer and resedimentation of glacial landforms the crn dates show that all existing glacial and paraglacial landforms in the upper bhagirathi valley formed during the late pleistocene and holocene this demonstrates that in this high mountain environment paraglacial and glacial landforms are eroded and resedimented within about 20 000 years furthermore this testifies to the dynamic nature of glacial environments in monsoon influenced high mountain regions

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

himalayan tectonics explained by extrusion of a low viscosity crustal channel coupled to focused surface denudation recent interpretations of himalayan tibetan tectonics have proposed that channel flow in the middle to lower crust can explain outward growth of the tibetan plateau1 2 3 and that ductile extrusion of high grade metamorphic rocks between coeval normal and thrust sense shear zones can explain exhumation of the greater himalayan sequence4 5 6 7 here we use coupled thermal mechanical numerical models to show that these two processes channel flow and ductile extrusion may be dynamically linked through the effects of surface denudation focused at the edge of a plateau that is underlain by low viscosity material our models provide an internally self consistent explanation for many observed features of the himalayan tibetan system8 9 10

seismostratigraphy and thermal structure of earth s core mantle boundary region we used three dimensional inverse scattering of core reflected shear waves for large scale high resolution exploration of earth9s deep interior d and detected multiple piecewise continuous interfaces in the lowermost layer d beneath central and north america with thermodynamic properties of phase transitions in mantle silicates we interpret the images and estimate in situ temperatures a widespread wave speed increase at 150 to 300 kilometers above the coremantle boundary is consistent with a transition from perovskite to postperovskite internal d stratification may be due to multiple phase boundary crossings and a deep wave speed reduction may mark the base of a postperovskite lens about 2300 kilometers wide and 250 kilometers thick the core mantle boundary temperature is estimated at 3950 200 kelvin beneath central america a site of deep subduction the d is relatively cold t 700 100 kelvin accounting for a factor of two uncertainty in thermal conductivity core heat flux is 80 to 160 milliwatts per square meter mw m 2 into the coldest d region and 35 to 70 mw m 2 away from it combined with estimates from the central pacific this suggests a global average of 50 to 100 mw m 2 and a total heat loss of 7 5 to 15 terawatts

core evolution driven by mantle global circulation abstract reconstructions of the phanerozoic history of mantle global circulation that include past plate motions are used to constrain the thermochemical evolution of the core according to our mantle global circulation models the present day global average heat flux at the core mantle boundary lies in the range 80 90 mw m 2 with peak to peak long wavelength lateral variations up to 100 mw m 2 associated with compositional and thermal heterogeneity in the d layer for core thermal conductivity in the range k 100 130 w m 1 k 1 we infer that the present day outer core is thermally unstable beneath the high seismic velocity regions in the lower mantle but thermally stable beneath the large low seismic velocity provinces a numerical dynamo shows how this boundary heat flux heterogeneity generates departures from axial symmetry in the time average geomagnetic field and the pattern of flow in the outer core standard thermochemical evolution models of the core driven by mantle global circulation heat flow predict inner core nucleation between 400 and 1100 ma with thermal conductivity k 100 w m 1 k 1 the core heat flow derived from our mantle global circulation models is adequate for maintaining the geodynamo since inner core nucleation supercritical for dynamo action by thermal convection just prior to inner core nucleation and marginal for inner core convection

bedload to suspended load ratio and rapid bedrock incision from himalayan landslide dam lake record about 5400 cal yr bp a large landslide formed a n400 m tall dam in the upper marsyandi river central nepal the resulting lacustrine and deltaic deposits stretched n7 km upstream reaching a thickness of 120 m 14 c dating of 7 wood fragments reveals that the aggradation and subsequent incision occurred remarkably quickly 500 yr reconstructed volumes of lacustrine 0 16 km 3 and deltaic 0 09 km 3 deposits indicate a bedload to suspended load ratio of 1 2 considerably higher than the 1 10 that is commonly assumed at the downstream end of the landslide dam the river incised a new channel through 70 m of greater himalayan gneiss requiring a minimum bedrock incision rate of 13 mm yr over last 5400 yr the majority of incision presumably occurred over a fraction of this time suggesting much higher rates the high bedload ratio from such an energetic mountain river is a particularly significant addition to our knowledge of sediment flux in orogenic environments 2007 university of washington all rights reserved

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

the influence of tectonic plates on mantle convection patterns temperature and heat flow summary the dynamic coupling between plate motion and mantle convection is investigated in a suite of cartesian models by systematically varying aspect ratios and plate geometries the aim of the study presented here is to determine to what extent plates affect mantle flow patterns temperature and surface heat flux to this end we compare numerical convection models with free slip boundary conditions to models that incorporate between one and six plates where the geometries of the plates remain fixed while the plate velocities evolve dynamically with the flow we also vary the widths of the plates and the computational domain in order to determine what constraint these parameters place on the mean temperature heat flux and plate velocity of mantle convection models we have investigated the influence of plates for three whole mantle convection cases that differ in their heating modes internally heated and basally heated and rheologies isoviscous and depth dependent viscosity we present a systematic investigation of over 30 models that exhibit increasingly complex behaviour in order to understand highly time dependent systems using the insight gained from simpler models in models with aspect ratios from 0 5 to 12 we find that for the same heating mode variations in temperature can be as much as 40 per cent when comparing calculations with unit width plates to models incorporating plates with widths equal to five times the model depth mean surface heat flux may decrease by 60 per cent over the same range of plate widths we also find that internally heated mantle convection models incorporating plates exhibit novel behaviour that we believe has not been described previously in mantle convection studies specifically in internally heated models plate motion is characterized by episodic reversals in direction driven by changes in the mantle circulation from clockwise to counterclockwise and vice versa these flow reversals occur in internally heated convection and are caused by a build up of heat in the interiors of wide convection cells close to mantle downwellings we find that flow reversals occur rapidly and are present in both single plate and multiple plate models that include internal heating this behaviour offers a possible explanation for why the pacific plate suddenly changed its direction some 43 ma

holocene versus modern catchment erosion rates at 300 mw baspa ii hydroelectric power plant india nw himalaya abstract 300 mw baspa ii is india s largest private hydroelectric facility located at the baspa river which is an important left hand tributary to the sutlej river in the nw himalaya india in this valley the sangla palaeo lake has been dammed around 8200 yr bp behind a rock avalanche dam and baspa ii is located exactly on top of this palaeo lake this special location represents a very rare possibility to evaluate the short term river load and hydrological parameters measured during the planning and operational stages of baspa ii with the long term parameters gained from the palaeo lake sediments from the catchment sedimentological and geomorphological investigations of the lacustrine sediments have been used to reconstruct environmental changes during 2500 years of its existence the mid holocene erosion rates of the baspa catchment estimated from the volume and duration of deposition of the exposed lake sediments are at 0 7 1 0 mm yr 1 almost identical with the modern erosion rates calculated from river gauge data from baspa ii several charcoal layers and charcoal pieces from the uppermost palaeo lake levels around 5000 cal yr bp might be related to woodland clearance and they possibly represent one of the oldest evidences for human presence in the baspa valley during neolithic time

the nature of the earth s core the properties of the earth s core are overviewed with emphasis on seismologically determined regions and pressures and seismologically measured density elastic wave velocities and gravitational acceleration attention is given to solid state convection of the inner core and it is noted that though seismological results do not conclusively prove that the inner core is convective the occurrence and magnitude of seismic anisotropy are explained by the effects of solid state convection igneous petrology and geochemistry of the inner core a layer at the base of the mantle and contact metasomatism at the core mantle boundary and evolution of the core mantle system are discussed it is pointed out that high pressure melting experiments indicate that the temperature of the core is ranging from 4500 to 6500 k and a major implication of such high temperature is that the tectonics and convection of the mantle as well as the resulting geological processes observed at the surface are powered by heat from the core as a result of the high temperatures along with the compositional contrast between silicates and iron alloy the core mantle boundary is considered to be most chemically active region of the earth