recurrent quaternary magma generation at baekdusan changbaishan volcano new zircon u th ages and hf isotopic constraints from the millennium eruption abstract it is well known that baekdusan changbaishan an active 2744 m high stratovolcano located on the border between north korea and china initiated trachytic commenditic eruption in the pleistocene but the petrogenetic and temporal evolutions of this alkaline magma system remain insufficiently constrained the so called millennium eruption me in the mid 10th century which resulted in the formation of the world s highest caldera lake cheonji or tianchi atop the mountain was one of the largest and most violently explosive volcanic eruptions to have occurred on earth in the past 2000 years here we present u th disequilibrium ages and hf isotopic compositions of zircons from trachydacitic pumices ejected during the me taken together with the previous u th isotope data our laser ablation multicollector icpms analyses of the zircons yielded multiple age components consisting of an earliest holocene cluster 11 3 1 3 ka and middle late pleistocene populations ca 230 and 110 ka which indicates that baekdusan magma has been generated episodically at intervals of ca 120 100 ky if the eruption ages assigned for the samples analyzed in the previous isotopic studies are correct the consistent age pattern of zircon may suggest the persistent existence of the same magmatic plumbing system beneath baekdusan since the me the wide range of zircon ehf values 5 8 to 3 5 reflects an interaction between the em1 type primitive magma and pre existing crustal materials evidenced by the presence of a xenocrystic zircon core showing a significantly negative ehf value 21 a broad negative correlation observed between zircon ehf and the published 18o values can be ascribed to the progressive assimilation of weathered supracrustal rocks likely in the course of magma chamber expansion

climatic impact of the millennium eruption of changbaishan volcano in china new insights from high precision radiocarbon wiggle match dating climatic impact here we report a new high precision 14 c wiggle match age of a d 9463 obtained from a 264year old tree trunk with bark killed during the eruption using the oxcal s bayesian modeling approach with 27 sequentially sampled annual rings of decadal intervals the new chronology conforms well to the calendar date of a d 946 for the eruption inferred from historical documentary evidence we find no stratospherically loaded sulfate spike that might be associated with the a d 946 eruption in the global volcanism record from the gisp2 ice core suggesting the stratospheric sulfate aerosols produced during the eruption were not transported to the arctic region due probably to its relatively low stratospheric sulfur emission and the seasonal effects of the atmospheric circulation at the time of the eruption that likely occurred in the winter of a d 946 947 since the stratospheric volcanic sulfates are the main cause of large scale climate perturbations this finding indicates that the millennium eruption of changbaishan volcano might have limited regional climatic effects rather than global or hemispheric impact as implied by its magnitude citation xu j b pan t liu i hajdas b zhao h yu r liu and p zhao 2013 climatic impact of the millennium eruption of changbaishan volcano in china new insights from high precision radiocarbon wiggle match dating geophys res lett 40 doi 10 1029 2012gl054246

volatile emission during the eruption of baitoushan volcano china north korea ca 969 ad magma volume dre 24 5 km3 the main phase ca 95 vol is represented by comenditic tephra deposited dominantly as widespread fallout blankets and proximal ignimbrites the eruption column is estimated to have reached ca 25 km and thus entered the stratosphere a late phase 5 vol is represented by trachyte emplaced chiefly as moderately welded ignimbrites the comendites contain 3 and the trachytes 10 20 vol phenocrysts mainly anorthoclase hedenbergite and fayalite primary glassy melt inclusions with no signs of leakage were found only in phenocrysts in the comenditic tephra whereas those in phenocrysts in the trachytes are devitrified the comendite magma is interpreted to have been generated by fractional crystallization from a trachyte magma represented by melt inclusions in the phenocrysts in the comendite tephra the mass of volatiles emitted to the atmosphere during the eruption was estimated using the petrologic method the average h2o concentration of the comenditic matrix glass is 1 5 wt probably largely secondary and of the corresponding melt inclusions 5 2 wt melt inclusions in feldspar and quartz present the highest halogen concentrations with a calculated average for chlorine of 4762 ppm and for fluorine of 4294 ppm the comenditic matrix glasses are represented by a fluorine rich 3992 ppm f and fluorine poor group 2431 ppm f averaging 3853 ppm for chlorine only 20 of all sulfur analyses of the comenditic matrix glasses and melt inclusions are above the detection limit of 250 ppm s the difference between pre and post eruptive concentration of h2o is at least 3 7 0 6 wt h2o taking into consideration re hydration of the matrix glass and possible leakage of melt inclusions the difference between pre and post eruptive concentrations of the halogens amounts to 909 90 ppm cl and 1863 280 ppm and 302 40 ppm f the difference for s was estimated based on the average of the maximum s concentrations in the melt inclusions 455 ppm s and the detection limit resulting in 205 40 ppm s the calculated mass of volatiles injected into the atmosphere based on the erupted magma volume and volatile data is 1796 453 megatons for h2o 45 10 megatons for chlorine 42 11 megatons for fluorine and 2 0 6 megatons for sulfur the 969 20 ad eruption of baitoushan volcano one of the largest eruptions of the past 2000 years is thought to have had a substantial but possibly short lived effect on climate

identifying environmental controls on the shoreline of a natural river delta river deltas form where sediment laden water debouches into a basin the spatial delineation of a delta is nontrivial and yet is fundamental to systematically evaluating fluxes across its surface here we study shoreline dynamics of the wax lake delta wld a naturally developing delta downstream of the atchafalaya river usa we demonstrate the ability to extract hydrodynamic and morphodynamic shorelines from time series of satellite imagery and topography data respectively the hydrodynamic shoreline corresponds to the traditional dry wet interface whereas we introduce the concept of a morphodynamic shoreline demarcating the topset foreset transition of a delta to quantitatively express the degree of inundation of a delta plain these shorelines enable us to assess environmental controls on inundation of the wld delta plain noting the abundance of satellite imagery whereas time series of bathymetric data from delta plains are scarce from the analysis of noaa and u s geological survey environmental data we identify the effects of river discharge tides wind and vegetation on shoreline position in particular using delft3d simulations and a simplified momentum balance we highlight the nonuniform and nonlinear effect of wind on delta plain inundation our analyses reveal that wind riverine discharge and tides significantly contribute to inundation of the wld and hence incorporating their interaction is essential to the accurate modeling of hydrodynamics and ecodynamics of the wld delta plain as well as to the dynamic shape of delta plains in general

grain size controls on the morphology and internal geometry of river dominated deltas predictions of a delta s morphology facies and stratigraphy are typically derived from its relative wave tide and river energies with sediment type playing a lesser role here we test the hypothesis that all other factors being equal the topset of a relatively noncohesive sandy delta will have more active distributaries a less rugose shoreline morphology less topographic variation in its topset and less variability in foreset dip directions than a highly cohesive muddy delta as a consequence its stratigraphy will have greater clinoform dip magnitudes and clinoform concavity a greater percentage of channel facies and less rugose sand bodies than a highly cohesive muddy delta nine self formed deltas having different sediment grain sizes and critical shear stresses required for re entrainment of mud are simulated using deflt3d a 2d flow and sediment transport model model results indicate that sand dominated deltas are more fan shaped while mud dominated deltas are more birdsfoot in planform because the sand dominated deltas have more active distributaries and a smaller variance of topset elevations and thereby experience a more equitable distribution of sediment to their perimeters this results in a larger proportion of channel facies in sand dominated deltas and more uniformly distributed clinoform dip directions steeper dips and greater clinoform concavity these conclusions are consistent with data collected from the goose river delta a coarse grained fan delta prograding into goose bay labrador canada a reinterpretation of the kf 1 parasequence set of the cretaceous last chance delta a unit of the ferron sandstone near emery utah usa uses ferron grain size data clinoform dip data clinoform concavity and variance of dip directions to hindcast the delta s planform the kf 1 last chance delta is predicted to have been more like a fan delta in planform than a birdsfoot delta

review of eruptive activity at tianchi volcano changbaishan northeast china implications for possible future eruptions one of the largest explosive eruptions in the past several thousand years occurred at tianchi volcano also known as changbaishan on the china north korea border this historically active polygenetic central volcano consists of three parts a lower basaltic shield an upper trachytic composite cone and young comendite ash flows the millennium eruption occurred between 938 and 946 ad and was preceded by two smaller and chemically different rhyolitic pumice deposits there has been at least one additional small eruption in the last three centuries from 2002 to 2005 seismicity deformation and the helium and hydrogen gas contents of spring waters all increased markedly causing regional concern we attribute this event to magma recharge or volatile exhalation or both at depth followed by two episodes of addition of magmatic fluids into the overlying aquifer without a phreatic eruption the estimated present magma accumulation rate is too low by itself to account for the 2002 2005 unrest the most serious volcanic hazards are ash eruption and flows and lahars the available geological information and volcano monitoring data provide a baseline for comprehensive assessment of future episodes of unrest and possible eruptive activity

small scale instabilities below the cooling oceanic lithosphere summary interpretation of satellite altimetry data as well as ship bathymetry data revealed strongly elongated anomalies roughly perpendicular to the mid ocean ridges in the indian and east pacific oceans a spectral analysis of gravity altimetry data along profiles parallel to the east pacific rise indicated wavelengths of about 150 180 km close to the ridge and about 250 km further away a simple model of rayleigh taylor instabilities developing at the base of the cooling lithosphere is discussed and applied to the data by considering thermal divusion and comparing rayleigh taylor growth rates to the velocity of the thermal front in the cooling lithosphere we are able to explain the observed anomalies by instabilities developing below the lithosphere in a layer with a viscosity of about 1019 pa s above an asthenospheric layer with a viscosity reduction of 2 3 orders of magnitude

experimental measurement of the relative importance of controls on shoreline migration abstract shoreline position in sedimentary rocks is a sensitive recorder of the interplay of several controlling factors the most important of these are thought to be the stratigraphic trinity eustatic sea level subsidence and sediment supply in ancient rock sequences it is generally difficult to disentangle the effects of these variables here we analyze the relative influence of sea level subsidence sediment supply and other controlling variables on shoreline migration in an experimental basin equipped with a subsiding floor the experiment used a linear hinge type subsidence profile for which the rate was kept constant in time constant overall sediment supply and base level variation on two time scales that were first applied separately and then superimposed although base level was the only controlling variable that was externally varied in time the base level changes induced changes in other variables indirectly e g by changing the partitioning of sediment between the fluvial and offshore segments of the system we examine the relative importance of measured direct and indirect changes in all the governing variables through the use of a moving boundary equation for shoreline migration when measured values are used for all the variables in the equation shoreline migration rate throughout the run can be predicted with a maximum r2 of 0 92 starting with this optimal prediction of the observed shoreline behavior we successively replace variables in the equation with their run averaged values degrading the prediction the relative loss of prediction accuracy as each variable is replaced is a measure of the importance of that variable in accounting for the observed shoreline migration by this measure base level is the most important variable followed in turn by sediment supply to the foreset geometry of the foreset and the average subsidence rate over the foreset from the shoreline migration equation we also derive a quantitative version of the a s ratio often applied in sequence stratigraphy the new formulation reduces to a form comparable to the traditional descriptive a s ratio if changes in foreset slope gain or loss of sediment to the fluvial system and spatial variation in subsidence rate are all negligible

competition between uplift and transverse sedimentation in an experimental delta mass is commonly injected into alluvial systems either laterally by transport from source regions or vertically from below via local uplift we report results on the competition between these two fundamental processes using an experimental basin with a deformable substrate the lateral supply is via two alluvial fans on orthogonal walls of the basin the uplifting region is downstream of one of the fans axial and opposite to the other transverse we show that the presence of a transverse sediment input increases the erosion rate of the uplifting region by pushing the mixing zone between the two alluvial sources against the uplifting mass however increase in sediment delivery to the transverse fan does not cause a proportional increase in erosion rate of the uplifting region instead the system reaches a steady state balance between uplift and erosion induced by the transverse fan such that there is no change in the total mass above the active alluvial surface a lateral analog of the classical steady state between vertical erosion and uplift we also show that the mixing zone is instrumental in limiting upstream aggradation and funneling sediments to the shore resulting in limited river lateral mobility and increased shoreline progradation hence the interaction between alluvial sources buffers river erosion and leads to consistent deviations from predictions of the area of influence of each fan based on simple mass balance arguments in the ganges brahmaputra meghna delta we suggest that similar dynamics help stabilize the brahmaputra river course in the jamuna valley during holocene time

water transportation from the subducting slab into the mantle transition zone using a recently developed petrogenetic grid for morb h2o we propose a new model for the transportation of water from the subducting slab into the mantle transition zone depending on the geothermal gradient two contrasting water transportation mechanisms operate at depth in a subduction zone if the geothermal gradient is low lawsonite carries h2o into mantle depths of 300 km with further subduction down to the mantle transition depth approximately 400 km lawsonite is no longer stable and thereafter h2o is once migrated upward to the mantle wedge then again carried down to the transition zone due to the induced convection at this depth hydrous phase olivine is stable and plays a role as a huge water reservoir in contrast if the geothermal gradient is high the subducted slab may melt at 700 900 c at depths shallower than 80 km to form felsic melt into which water is dissolved in this case h2o cannot be transported into the mantle below 80 km between these two endmember mechanisms two intermediate types are present in the high pressure intermediate type the hydrous phase a plays an important role to carry water into the mantle transition zone water liberated by the lawsonite consuming continuous reaction moves upward to form hydrous phase a in the hanging wall which transports water into deeper mantle this is due to a unique character of the reaction because phase a can become stable through the hydration reaction of olivine in the case of low pressure intermediate type the presence of a dry mantle wedge below 100 km acts as a barrier to prevent h2o from entering into deeper mantle 2006 published by elsevier b v on behalf of international association for gondwana research

oxygen isotope exchange in a two layer model of oceanic crust abstract a numerical model is presented for the transport and exchange of oxygen isotopes in an idealized two layer oceanic crust basalt carbonate that is saturated with a non advecting pore fluid open to the overlying ocean the model allows for time varying sedimentation rate porosity chemical diffusivity and temperature dependent 18o fractionation factors reaction is modeled as solution precipitation of calcite in the carbonate sediment and as modified solution precipitation basalt dissolves smectite precipitates in the basalt layer generic models using input parameters that are typical of those measured in dsdp odp cores and constant sedimentation rates illustrate the behavior of the system sufficiently well to allow first order effects to be discerned that have important implications for paleotemperature and ocean floor weathering studies the solution precipitation reactions allow oxygen to be exchanged between the low 18o basalt layer and the high 18o carbonate sediment through the medium of the pore fluids this results in 18o increasing upwards in the basalt and decreasing downwards in the sediment pore fluid 18o values decrease with depth from zero to values of 1 to 3 at the basalt sediment interface and to values of 7 to 15 within the basalt because reaction rates are slow relative to diffusion in the pore fluid high frequency 18o variations in the solid are preserved indefinitely but the amplitude of the variations decreases as e rt where r is the reaction rate fraction reacted per unit time the results suggest that the diagenetic shifts of the 18o values of benthic and high latitude planktonic foraminifera samples younger than oligocene age are typically negligible for samples older than 50 ma diagenetic effects are typically significant and generally cause estimates of bottom and high latitude surface ocean temperatures in the cretaceous and early tertiary to be too high on the other hand the model suggests that diagenesis will shift the 18o values of low latitude planktonic foraminifera to higher values and that paleotemperature estimates of low latitude surface waters particularly in the eocene and oligocene may be too low using a synthetic 18o record for dsdp site 167 we demonstrate how numerical models can be used to correct specific measured records for diagenesis this approach could provide a means of extracting paleotemperature information from heavily altered late cretaceous and older samples and for quantifying the subtle effects of diagenesis on the 18o record at all sites

a wiggle match age for the millennium eruption of tianchi volcano at changbaishan northeastern china abstract the tianchi volcano located on the border between china and north korea produced a massive plinian eruption of volcanic explosivity index vei 7 around 1000 ad which is referred to as the millennium eruption of tianchi volcano until now this volcanic eruption has not been well dated in this paper we report a series of new calibrated dates using wiggle match dating from carbonized logs collected from fallout deposits on the southern and northern flanks of the tianchi crater fifty ams 14 c ages of tree rings from two logs were obtained for the hengshan site south of the tianchi crater fig 1 these yielded a high precision wiggle match date of 921 941 cal ad 95 4 for the millennium eruption thirty two ams 14 c ages of tree rings of other two logs from the dongfanghong site north of tianchi crater fig 1 produced an age range for the volcanic eruption from 921 to 942 cal ad 95 4 a combined date for the four carbonized logs produced an age of 923 939 cal ad 95 4 for the millennium eruption moreover an exact date of late autumn 938 ad or early spring 939 ad is suggested based on the impact of the tianchi volcano on global climate especially east asian climate and the complete outermost rings of these four trees killed in the eruption

self affinity in braided rivers three braided rivers of different scales and different hydrologic geomorphologic characteristics the aichilik and hulahula in alaska and the brahmaputra in bangladesh are analyzed for spatial scaling using a logarithmic correlation integral method developed earlier by the authors it is shown that the rivers exhibit anisotropic scaling self affinity with fractal exponents vx 0 72 0 74 and vy 0 51 0 52 the x axis being oriented along the river and the y axis in the perpendicular direction the fact that despite large differences in scales 0 5 15 km in braid plain width slopes 7 10 3 to 8 10 5 and types of bed material gravel to sand the analyzed braided rivers show similar spatial scaling deserves special attention it might indicate the presence of universal features in the underlying mechanisms responsible for the formation of the spatial structure of braided rivers also comparison of fractal characteristics of braided rivers with those of single channel rivers and river networks suggests that braided rivers form a class of fractal objects lying between the classes of single channel rivers and river networks

remelting in caldera and rift environments and the genesis of hot recycled rhyolites abstract large and small volume rhyolites are generated in calderas and rift zones inheriting older and isotopically diverse crystal populations from their volcanic predecessors low 18o values in many of these rhyolites suggest that they were derived from the remelting of solid hydrothermally altered by meteoric water protoliths that were once close to the surface but become buried by caldera collapse or rifting these rhyolites persist for millions of years in these environments with little evidence of coeval basalts we present a series of numerical experiments on convective melting of roof rocks by the underplated by near liquidus to superheated silicic melts generated at the base of the chamber by basaltic intrusions in shallow crustal conditions we used a range of temperatures and compositions an appropriate phase diagram with a defined extended eutectic zone appropriate for these environments varied sill thickness viscosity of the boundary layer and considered hydrothermal and lower boundary heat losses the goal was to estimate melting rates and mechanisms define conditions that are required for efficient and rapid remelting in the upper crust quantitatively describe novel details of the dynamics of convecting melting and compare it to the earlier parametric and numerical treatments of roof melting by underplating resolution of numerical experiments allowed us to track mixed thermal and two phase plume like convection in silicic magma with a bulk viscosity of 104 5 105 5 pa s the following results were obtained 1 remarkably fast melting magma generation rates of many meters per year 2 intrinsic inhomogeneities in the roof accelerates convection and melting rates via rapid gravitational settling of refractory blocks and exposing detachment scars to the melting front 3 due to rapid melting hydrothermal heat loss through the roof and conductive heat dissipation through the bottom are less important on melting timescales 4 convective melting is capable of digesting cold roof rocks with high assimilation degrees which are primarily controlled by sill thickness and roof rock temperature thin 10 m sills are able to digest 40 of the initially hot roof rock t 650 c roof rock but 100 m sills achieve the same level of bulk digestion with t 400 c roof rocks the proposed model can explain the origin of hot above 800 850 c crystal poor recycled rhyolites in calderas and rift zones it can also explain the generation of large supervolcanic rhyolite volumes through remelting of their erupted and subvolcanic predecessors on rapid timescales dictated by their zoned and disequilibrium crystalline cargo

delta allometry growth laws for river deltas 1 under projected scenarios of sea level rise subsidence and sediment starvation many deltas around the world are expected to drown delta growth dynamics which determine the ability of a delta to adapt to these changes are poorly understood due to the difficulty of measuring change in slowly evolving landscapes we use time series imagery of experimental numerical and field scale deltas to derive four laws that govern the growth of river dominated deltas land area grows at a constant rate in the absence of relative sea level change while wetted area keeps pace maintaining a constant wetted fraction over the delta surface scaling of edge lengths versus areas suggests delta shorelines are nonfractal even though the channel network is fractal consequently channel edge length which provides critical habitat grows more rapidly than delta area these laws provide a blueprint for delta growth that will aid in delta restoration and help predict how existing deltas will evolve

deep electromagnetic sounding in turkmenia summary this paper presents the results of interpretation of magnetotelluric and magnetovariational observations in a vast region including the southern part of the turanian plate and the south caspian megadepression both l d and 2 d interpretations fail to explain the main peculiarities of the natural magnetotelluric and magnetovariational fields observed in the region the 3 d interpretation used in the paper is based on thin sheet modelling and inversion algorithms developed by the authors the final model consists of an inhomogeneous surface layer and a conductive layer embedded in the otherwise laterally uniform medium in the crust under the kopet dagh mountains the surface layer conductance varies between 100 s and 13 ooo s and the crustal anomaly has a conductance of about 2500 s the layered regional structure includes a conductive layer at a depth of 80 100 km whose conductance is about 1800 s the model explains all of the main features of the observed magnetotelluric and magnetovariational fields in the region

quantitative metrics that describe river deltas and their channel networks 1 densely populated river deltas are losing land at an alarming rate and to successfully restore these environments we must understand the details of their morphology toward this end we present a set of five metrics that describe delta morphology 1 the fractal dimension 2 the distribution of island sizes 3 the nearest edge distance 4 a synthetic distribution of sediment fluxes at the shoreline and 5 the nourishment area the nearest edge distance is the shortest distance to channelized or unchannelized water from a given location on the delta and is analogous to the inverse of drainage density in tributary networks the nourishment area is the downstream delta area supplied by the sediment coming through a given channel cross section and is analogous to catchment area in tributary networks as a first step we apply these metrics to four relatively simple fluvially dominated delta networks for all these deltas the average nearest edge distances are remarkably constant moving down delta suggesting that the network organizes itself to maintain a consistent distance to the nearest channel nourishment area distributions can be predicted from a river mouth bar model of delta growth and also scale with the width of the channel and with the length of the longest channel analogous to hack s law for drainage basins the four delta channel networks are fractal but power laws and scale invariance appear to be less pervasive than in tributary networks thus deltas may occupy an advantageous middle ground between complete similarity and complete dissimilarity where morphologic differences indicate different behavior

modelling of electromagnetic fields in thin heterogeneous layers with application to field generation by volcanoes theory and example when interpreting electromagnetic fields observed at the earth s surface in a realistic geophysical environment it is often necessary to pay special attention to the effects caused by inhomogeneities of the subsurface sedimentary and or water layer and by inhomogeneities of the earth s crust the inhomogeneities of the earth s crust are expected to be especially important when the electromagnetic field is generated by a source located in a magma chamber of a volcano the simulation of such effects can be carried out using generalized thin sheet models which were independently introduced by dmitriev 1969 and ranganayaki madden 1980 in the first part of the paper a system of integral equations is derived for the horizontal current that flows in the subsurface inhomogeneous conductive layer and for the vertical current crossing the inhomogeneous resistive layer representing the earth s mantle the terms relating to the finite thickness of the laterally inhomogeneous part of the model are retained in the equations this only marginally complicates the equations whilst allowing for a significant expansion of the approximation limits the system of integral equations is solved using the iterative dissipative method developed by the authors in the period from 1978 to 1988 the method can be applied to the simulation of the electromagnetic field in an arbitrary inhomogeneous medium that dissipates the electromagnetic energy when considered on a finite numerical grid the integral equations are reduced to a system of linear equations that possess the same contraction properties as the original equations as a result the rate at which the iterative perturbation sequence converges to the solution remains independent of the numerical grid used for the calculations in contrast to previous publications on the method aspects of the algorithm implementation that guarantee its effectiveness and robustness are discussed here

simple models for late holocene and present day patagonian glacier fluctuations and predictions of a geodetically detectable isostatic response summary the late holocene glacial moraine chronology in the southernmost south american andes includes four 14c dated neoglacial advances and retreats these are used as proxy information to characterize mass fluctuation of the patagonian icefields during the last 5000 years modelled ice loads force a phase lagged viscoelastic gravitational deformation of the solid earth the ancient glacier fluctuations may therefore drive present day crustal motion even in the absence of present day ice mass imbalance numerical models show that such rates of present day uplift and subsidence are larger than those driven by the viscous memory of late pleistocene deglaciation both spherical and flat earth models are employed the latter being used to study exhaustively the evects of glacial load history on the predicted vertical crustal velocity recent assessment of net mass balance from 1944 to 1985 indicates that the southern patagonian icefield has significantly deteriorated due to snout retreat and thinning volume loss rates are estimated at about 3 4 9 3 km3 yr 1 the predicted vertical isostatic response to this recession and to the modelled holocene neoglaciations is at a marginally detectable level 1m m yr 1 if the mantle asthenosphere beneath patagonia has a viscosity of about 1021 pa s however for reduced mantle viscosities the younger holocene glacial load histories predict larger signatures in fact if the viscosity is about 2 1020 pa s or lower then geodetically detectable vertical motion may be driven by a regional little ice age lia 1400 1750 ad glacier advance and subsequent 20th century retreat although this value for mantle viscosity is lower than thought typical of continental shield mantle 1021 pa s it is consistent with inversions for post seismic relaxation time constants in island arc environments and in regions with significant neogene continental tectonism in the viscosity regime of 5 1018 2 1019 pa s the predicted rates of vertical crustal motion are similar to those presently occurring in fennoscandia and hudson bay 5 10 mm yr 1 geodetic data may be sensitive to the time integrated growth and subsequent retreat of patagonian glacier ice mass over the last 600 years

origin of a cretaceous low 18o granitoid complex in the active continental margin of se china abstract low 18o felsic igneous rocks with 18o values of 1 low sr y 7 23 49 5 and la yb ratios 6 87 46 0 and relatively low zr saturation temperatures 730 c in addition the diorites and granodiorites contain a variety of inherited high ca plagioclase an 60 87 we demonstrate that the xiaocuo granitoid rocks were derived from preexisting subduction related metabasic source rocks their low 18ozrc values 3 8 5 2 are reflective of their source compositions the formation of the low 18o source rocks is most likely formed in a subduction induced lithospheric extension regime during early jurassic to early cretaceous time when a basin and range like province developed in se china intensive lithospheric extension could have increased the fracture permeability and facilitated deep circulated surface waters for exchanging with the source rocks at high temperature at depth making the metabasic source rocks depleted in 18o remelting of the 18o depleted metabasic intrusive source rocks produced the xiaocuo low 18o granitoid complex at 116 ma our work indicates that in addition to the caldera and rift settings extensional active continental margin could also be a favorable setting for the formation of low 18o granitoid rocks

experimental evidence of dynamic scaling and indications of self organized criticality in braided rivers the evolution of an experimental braided river produced in our laboratory has been monitored and analyzed it has been shown that in addition to the spatial scaling revealed by sapozhnikov and foufoula georgiou 1996a braided rivers also exhibit dynamic scaling this implies that a smaller part of a braided river evolves identically in the statistical sense to a larger one provided the time is renormalized by a factor depending only on the ratio of the spatial scales of those parts the small value of the estimated dynamic exponent z is interpreted as an indication that the evolution of small channels in a braided river system is to a large extent forced by the evolution of bigger channels the presence of dynamic scaling is further interpreted as indicating that braided rivers may be in a critical state and behave as self organized critical systems in a recent paper sapozhnikov and foufoula georgiou 1996a evidence was presented that natural braided rivers ex hibit anisotropic scaling self affinity in their geometrical structure within a range of scales spanning the width of the narrowest channel to the width of the braid plain in simple words within these scales if a small part of a braided river is stretched in a certain way along the mainstream direction and a certain different way along the perpendicular direction then this stretched part looks statistically the same as a bigger part of the river such anisotropically scaled objects are called self affine fractals and are characterized by two fractal exponents nx and ny the ratio nx ny characterizes the scaling anisotropy and the fractal dimension d 5 ny 2 nx 1 1 ny e g see sapozhnikov and foufoula georgiou 1995 indicates how densely the object fills the space in sapozhnikov and foufoula georgiou 1996a three natu ral braided rivers of different scales and different hydrological and sedimentological characteristics aichilik and hulahula in alaska and brahmaputra in bangladesh were analyzed for spatial scaling using the logarithmic correlation integral lci method developed by sapozhnikov and foufoula georgiou 1995 interestingly enough it was observed that despite their different scales 0 5 15 km in braid plain width slopes 7 3 10 23 8 310 25 and types of bed material gravel to sand all three rivers exhibited anisotropic spatial scaling with almost the same fractal exponents nx 5 0 72 0 74 and ny 5 0 51 0 52 the x axis being oriented along the river and the y axis being in the perpendicular direction in simple terms this im plies that if parts of a braided river are stretched by l along the mainstream direction and by l n y n x l 0 7 along the perpen dicular direction the resulting images will look statistically similar to each other similarity within a braided river at the same time the invariance of nx and ny between braided rivers of different sizes and hydrology sedimentology suggests that the same anisotropic scaling as above applied to different riv ers will result in statistically similar images apart possibly from a normalization factor to account for the different mass of each river note that mass here refers to the area i e number of pixels covered with water the presence of such a statistical scale invariance in the spatial structure of braided rivers apart from being interesting in its own right might indicate the presence of universal features in the underlying mechanisms responsible for the formation of braided rivers and deserves further theoretical and experimental investiga tion braided rivers besides their complex geometry at any in stant of time are also highly dynamic systems characterized by intensive erosion sediment transport and deposition and fre quent channel shifting as they evolve predicting the evolution of braided rivers in terms of frequency and magnitude of chan nel shifting is of paramount importance where hydraulic struc tures or land developments are planned or where field use must be made of maps and air photos it is of great practical and theoretical value therefore to study the evolution of braided rivers in addition to their spatial structure in view of the evidence for spatial static scaling in braided rivers the question is asked here as to whether they also show dynamic scaling the presence of dynamic scaling would imply that space and time can be appropriately rescaled such that the evolution of the spatial structure of parts of the river of dif ferent size would be statistically indistinguishable the pres ence of dynamic scaling would also provide a highly desirable integrated framework for studying simultaneously the spatial and temporal structure of braided rivers

recent unrest of changbaishan volcano northeast china a precursor of a future eruption 1 over 12 years of continuous monitoring of changbaishan volcano in the border region of china and north korea by means of volcanic seismicity ground deformation and volcanic gas geochemistry yields new evidence for magmatic unrest of the volcano between 2002 and 2006 in this so called active period the frequency of volcanic earthquakes increased by about 2 orders of magnitude compared to that of the background inactive periods the active period was also accompanied by ground inflation high values of co2 he h2 and high ratios of n2 o2 and 3he 4he in volcanic gases released from three hot springs near the caldera rim the monitoring evidence implies pressurization of the magma chamber possibly caused by incremental magma recharge the ground deformation data from both gps and precise leveling are modeled to suggest the corresponding deformation source is at 2 60 km depth beneath the volcano s summit where earthquake swarms were detected in 2002 and 2003 our findings suggest that the magma chamber beneath changbaishan volcano has awakened and resumed activity after remaining dormant since ad 1903 there is an urgent need to keep close watch on this active and very hazardous volcano in northeast china

refined models of the conductivity distribution at the transition from the bohemian massif to the west carpathians using stochastic mcmc thin sheet inversion of the geomagnetic induction data although volume 3d modeling solutions has become widespread in recent time thin sheet approximation of earth s conductivity distribution can still serve as a useful tool when quasi 3d conductivity structures in the heterogeneous subsurface are investigated and the available database of observations is limited to long period electromagnetic induction data from large scale deep sounding arrays we present results of stochastic monte carlo markov chains mcmc inversion of long period induction arrows based on the bayesian statistics strategy we concentrated on the different methodological aspects of mcmc for gibbs sampling and for adaptive metropolis algorithm together with convergence of these methods the results are presented on a case study from the transition zone between the bohemian massif and the west carpathians where a phantom effect caused by superposition of the prominent sw ne trending carpathian conductivity anomaly and nw se trending anomalous structure related to the fault system at the eastern boundary of the bohemian massif appears

characterization of river delta shorelines 1 coastline shape is among the basic geometric properties of the earth s surface yet defining and quantifying coastline shape precisely remains challenging here we propose new methods based on the dilation and erosion operators of mathematical morphology mm for the characterization of delta shorelines a class of open coasts we demonstrate the suitability of mm based methods for noise removal and shoreline identification from digital images of river deltas of varying geometric complexity we also show that a global a regional and a local shoreline parameter provide a first step in distinguishing among river wave and tidal dominated delta shapes

latest pleistocene crustal cannibalization at baekdusan changbaishan as traced by oxygen isotopes of zircon from the millennium eruption abstract the silicic volcanism of baekdusan changbaishan which is on the border between north korea and china was initiated in the late pleistocene and culminated in the 10th century with a powerful volcanic explosivity index 7 commendite trachyte eruption commonly referred to as the millennium eruption this study presents oxygen isotope data of zircon in trachydacitic pumices ejected during the millennium eruption together with whole rock geochemical and sr nd pb isotopic data that manifest once again the a type and em1 affinities of the millennium eruption magma the zircon crystals dated by previous studies at ca 12 9 ka show a moderate inter grain variation in 18o from 3 69 to 5 03 these values are consistently lower than the normal mantle range and interpreted to have resulted from the digestion of meteoric hydrothermally altered intracaldera rocks in the shallow magma chamber beneath baekdusan just prior to the crystallization of the zircons rather than from derivation from low 18o sources deep in the mantle the whole rock geochemical isotopic considerations suggest that the magma mainly self cannibalized the earlier erupted volcanic carapace around the magma chamber this study highlights the usefulness of zircon oxygen isotopes for characterizing past volcanic activity that has now been commonly eroded away and implies that the generation of yellowstone type low 18o magma is not a rare phenomenon in large volume silicic eruptions

subduction triggered magmatic pulses a new class of plumes article i nfo a variety of atypical plume like structures and focused upwellings that are not rooted in the lower mantle have recently been discussed and seismological imaging has shown ubiquitous small scale convection in the uppermost mantle in regions such as the mediterranean region the western us and around the western pacific we argue that the three dimensional return flow and slab fragmentation associated with complex oceanic subduction trajectories within the upper mantle can generate focused upwellings and that these may play a significant role in regional tectonics the testable surface expressions of this process are the outside arc alkaline volcanism topographic swell and low velocity seismic anomalies associated with partial melt using three dimensional simplified numerical subduction models we show that focused upwellings can be generated both ahead of the slab in the back arc region though five times further inward from the trench than arc volcanism and around the lateral edges of the slab in the order of 100 km away from slab edges vertical mass transport and by inference the associated decompression melting in these regions appears strongly correlated with the interplay between relative trench motion and subduction velocities the upward flux of material from the depths is expected to be most pronounced during the first phase of slab descent into the upper mantle or during slab fragmentation we discuss representative case histories from the pacific and the mediterranean where we find possible evidence for such slab related volcanism

u series and 40ar 39ar ages of holocene volcanic rocks at changbaishan volcano china accurately dating holocene volcanic rocks poses many challenges but is critical to assessing magmatic evolution and hazard risks at highly active volcanoes here we use ra th and 40 ar 39 ar geochronology to date very young eruptions at changbaishan volcano northeastern china a recently active stratovolcano responsible for one of the most voluminous eruptions in the past 2000 yr for holocene eruptions 40 ar 39 ar ages are consistently older than those of both independently determined ages and maximum ra th ages overall ra th ages are most consistent with historical accounts and indicate inaccurate 40 ar 39 ar ages that are due to extraneous argon in various forms ra th geochronology also confirms the highly active nature of changbaishan and supports the continued presence of trachytic magma residing under the volcano that appeared more than 1100 yr ago

in situ oxygen isotope records of crustal self cannibalization selectively captured by zircon crystals from high δ26mg granitoids zircon oxygen hafnium and biotite magnesium isotopic compositions of late cretaceous to oligocene 88 27 ma granitoids from the gyeongsang continental arc southeastern korea collectively provide a new insight into shallow magma petrogenesis zircon crystals extracted from eight calc alkaline or alkaline plutons commonly contain xenocrystic cores and typically show magmatic cathodoluminescence zonings and sharp raman spectra most zircons have positive ehf values plotting below the mid ocean ridge basalt evolution path indicating that the arc magmatism was dominated by the recycling of juvenile crustal materials zircon 18o values shifted upward or downward from the mantle range attest to the o isotopic exchange of crustal protoliths with surface waters at various temperature conditions small 1 but discernable core to rim decreases of 18o values are recognized selectively in magmatic zircon grains from four plutons possessing biotite 26mg values 0 07 to 2 32 distinctly higher than the mantle range such a concomitant o mg isotopic variation provides compelling evidence for a series of self induced hydrothermal alteration and assimilation processes i e crustal self cannibalization this study shows that the supracrustal input to magmas in a young and juvenile orogen can be traced effectively by the combination of stable isotope records from the plutonic root

magma plumbing system for the millennium eruption at changbaishan volcano china constraints from whole rock u th disequilibrium abstract a caldera forming eruption in 946 ce known as the millennium eruption me at changbaishan or baekdusan volcano located on the border between china and north korea was one of the largest explosive eruptions on earth in the last 2000 years in this study we obtained new whole rock sr nd and pb isotopic data and 238u 230th disequilibrium data of representative volcanic products of the me as well as those of a pre me 4 5 ka eruption to understand the evolution of the magma plumbing system related to the caldera forming eruption the volcanic products of the me have sio2 contents ranging from 54 to 75 wt and the whole rock 230th 232th ratios tend to decrease systematically from basaltic trachy andesite through trachyte to comendite the relatively high 230th 232th ratios of the felsic trachytic and comenditic volcanic products suggest that they were formed primarily from fractional crystallization of mafic magmas rather than from partial melting of crustal materials the basaltic trachy andesite sample has a distinctly high 230th 232th ratio and the least radiogenic pb isotopic ratios among me volcanic products suggesting that the mafic magma was recently introduced into the main felsic magma system and is hypothesized to have triggered the eruption the lower 230th 232th ratios of the comendite samples than those of the trachyte samples as well as published u series disequilibrium data suggest that the comendite magmas were produced by mixing old 23 ka and young

evidence of the theoretically predicted seismo magnetic conversion summary seismo electromagnetic phenomena in porous media arise from seismic wave induced fluid motion in the pore space which perturbs the equilibrium of the electric double layer this paper describes with details the original experimental apparatus built within the ultra shielded chamber of the low noise underground laboratory of rustrel france we measured seismo magnetic conversions in moist sand using two induction magnetometers and a pneumatic seismic source to generate the seismic wave propagation we ensured to avoid the magnetometer vibrations which could induce strong disturbances from induction origin interpretation of the data is improved by an analytical description of phase velocities for fast pf and slow ps longitudinal modes transverse mode s as well as the extensional mode due to the cylindrical geometry of the sample the purpose of this paper is to provide elements to measure correctly coseismic seismomagnetic fields and to specify their amplitude the seismic arrivals recorded in the sample showing a 1200 1300 m s 1 velocity have been associated to p and extensional waves the measured seismo magnetic arrivals show a velocity of about 800 m s 1 close to the calculated phase velocity of s waves therefore we show that the seismo magnetic field is associated to the transverse part of the propagation as theoretically predicted by pride 1994 but never measured up to now moreover the combined experimental and analytical approaches lead us to the conclusion that the measured seismo magnetic field is probably about 0 035 nt for a 1 m s 2 seismic source acceleration 0 1 g

electromagnetic fields induced in the world s oceans and the spatial distribution of electrical conductivity functions abstract the results of numerical simulation of electromagnetic fields induced in the world s oceans by solar daily variations are discussed some examples of apparent resistivity curves simulated for continental and ocean regions are demonstrated

changbaishan volcanism in northeast china linked to subduction induced mantle upwelling the changbaishan volcanic complex in china cannot be easily explained as the consequence of a mantle plume seismic images from the region identify buoyant mantle material that may have been entrained and dragged downwards by the subducting pacific plate but is now escaping upwards through a gap in the plate and producing the intraplate volcanism

seismic image and origin of the changbai intraplate volcano in east asia role of big mantle wedge above the stagnant pacific slab abstract we determined p wave tomography of the crust and upper mantle under the changbai volcanic area in northeast asia by using 289 318 arrival time data from 4802 local earthquakes and 9599 teleseismic events a prominent low velocity anomaly is clearly imaged in the crust and upper mantle down to about 410 km depth beneath the changbai volcano a broad high velocity anomaly is revealed in the mantle transition zone and deep earthquakes occurred actively there suggesting that the subducting pacific slab is stagnating in the mantle transition zone under east asia our results suggest that the formation of the changbai and other intraplate volcanoes in northeast asia is related to the upwelling of hot and wet asthenospheric materials in the big mantle wedge above the stagnant pacific slab hence the active intraplate volcanoes in northeast asia are not hotspots related to deep mantle plumes but are caused by plate tectonic processes in the upper mantle

reduced rapakivi type granites the tholeiite connection reduced rapakivi type granites are the most iron enriched and reduced i e least oxidized of the anorogenic granite association the low oxygen fugacity and chemical composition of these granites severely limit their sources in this paper we argue that reduced rapakivi type granites and their eruptive equivalents high potassium fayalite rhyolites are derived from mafic sources because tholeiitic magmas and their derivatives have the required low oxygen fugacity reduced rapakivi type granites are produced either by extreme differentiation of basaltic melts or by partial melting of underplated basalts and their differentiated equivalents they form in extensional environments where the asthenosphere is present at shallow depths we envision three stages in the origin of these rocks 1 tholeiitic melts are emplaced at the base of the crust 2 continued introduction of heat partially remelts these tholeiitic rocks and 3 the hot dry melts so produced migrate into the middle crust to produce rapakivi batholiths or erupt as rhyolites partial melting of felsic continental crust may accompany the intrusion of rapakivi type magmas thereby producing the other metaluminous and peraluminous granite compositions of the anorogenic suite

an image based method for shoreline mapping on complex coasts 1 the ready availability of satellite and other images of the earth together with increasing societal interest in coastal processes and morphology make it desirable to have a consistent way of defining and mapping shorelines from images the obvious choice the land water interface is inadequate because it includes the back sides of islands and the edges of river and tidal channels that are not directly exposed to open water on complex coasts inclusion of these portions of the land water interface would significantly affect quantitative measures of shoreline geometry here we propose a method to map shorelines consistently while accounting for ambiguity the opening anglemethod oam uses a visibility criterion to define the shoreline first a region of unambiguous open water is defined next the shoreline is defined as the locus of points for which the sum of viewing angles extending to open water unobstructed by land exceeds a specified critical value shorelines defined by the oam follow the land water interface where the shoreline is unambiguous and in more complex cases oam shorelines are consistent with the idea that the shoreline is that part of the land water interface that is directly exposed to open water

intensive hydration of the mantle transition zone beneath china caused by ancient slab stagnation the mantle transition zone beneath china is anomalously hydrated geochemical analyses of basalts erupted above the mantle transition zone in northeast china indicate that water may have been added to this zone during the dehydration of subducted slabs on two separate occasions over the past one billion years