stratigraphy of the 1902 and 1929 nuee ardente deposits mt pelee martinique mild nuee ardentes in 1902 1903 and 1929 1930 at mt pelee formed high aspect ratio h a r deposits i e deposits with a high thickness extent ratio in the riviere blanche channel several violent nuees ardentes from may to august 1902 yielded low aspect ratio l a r deposits unevenly blanketing an area of 58 km2 on the southwestern flank of the volcano three closely spaced nuees ardentes on august 30 additionally affected 56 km2 on the southeastern flank the l a r deposits are divided into eight stratigraphic units u1 u8 either compound or consisting of a single flow unit the deposits of the largest nuees ardentes on may 8 20 and august 30 1902 are identified as u1 u3 and u8 respectively and can be traced over most of the area individual l a r flow units are lenticular and show large erratic lateral variations of thickness and grain size most flow units consist of three distinct beds bed 1 is a few centimeters thick lenticular fines depleted layer bed 2 is the thickest layer and contains more silt sized ash than bed 1 it is normally graded as a whole though reverse grading may occur in the lower part bed 2 generally consists of two parts bed 2a nonbedded and bed 2b finer grained and laminated with cross bedding and duned structures bed 3 is a thin silty capping layer which contains accretionary lapilli the distribution of the l a r flow units especially of the coarse grained facies suggests that they were formed from overpressured blast flows expanding radially from the vent at a high rate in the same manner as the laterally directed blast of mount st helens on may 18 1980 the transport system of the major 1902 nuees ardentes was an inflated relatively low concentration turbulent cloud as suggested by several lines of evidence 1 the transported material was able to cross ridges up to 300 m high 2 many scour and fill and other erosional features can be observed in the deposits at any distance from the vent 3 survivors within the devastated area on may 8 did not experience a dense low profile cloud but instead a choking hot ash laden cloud 4 many human corpses in st pierre remained where they fell instead of having floated away if the current flow surge terminology were to be used the 1902 blast flows would be better considered as pyroclastic surges the normally graded multi layered structure of the flow units is also consistent with deposits primarily formed from relatively low concentration flows

dune bedforms produced by dilute pyroclastic density currents from the august 2006 eruption of tungurahua volcano ecuador a series of pyroclastic density currents were generated at tungurahua volcano ecuador during a period of heightened activity in august 2006 dense pyroclastic flows were confined to valleys of the drainage network while dilute pyroclastic density currents overflowed on interfluves where they deposited isolated bodies comprising dune bedforms of cross stratified ash exposed on the surface here the description measurement and classification of more than 300 dune bedforms are presented four types of dune bedforms are identified with respect to their shape internal structure and geometry length width thickness stoss and lee face angles and stoss face length 1 elongate dune bedforms have smooth shapes and are longer in the flow direction than wide or thick internal stratification consists of stoss constructional thick lensoidal layers of massive and coarse grained material alternating with bedsets of fine laminae that deposit continuously on both stoss and lee sides forming aggrading structures with upstream migration of the crests 2 transverse dune bedforms show linear crests perpendicular to the flow direction with equivalent lengths and widths internally these bedforms exhibit finely stratified bedsets of aggrading ash laminae with upstream crest migration steep truncations of the bedsets are visible on the stoss side only 3 lunate dune bedforms display a barchanoidal shape and have stratification patterns similar to those of the transverse ones finally 4 two dimensional dune bedforms are much wider than long exhibit linear crests and are organized into trains elongate dune bedforms are found exclusively in proximal deposition zones transverse lunate and two dimensional dune bedforms are found in distal ash bodies the type of dune bedform developed varies spatially within an ash body transverse dune bedforms occurring primarily at the onset of deposition zones transitioning to lunate dune bedforms in intermediate zones and two dimensional dune bedforms exclusively on the lateral and distal edges of the deposits the latter are also found where flows moved upslope elongate dune bedforms were deposited from flows with both granular based and tractional flow boundaries that possessed high capacity and competence they may have formed in a subcritical context by the blocking of material on the stoss side we do not interpret them as antidune or chute and pool structures the dimensions and cross stratification patterns of transverse dune bedforms are interpreted as resulting from low competence currents with a significant deposition rate but we rule out their interpretation as antidunes a similar conclusion holds for lunate dune bedforms whose curved shape results from a sedimentation rate dependent on the thickness of the bedform finally two dimensional dune bedforms were formed where lateral transport exceeds longitudinal transport i e in areas where currents were able to spread laterally in low velocity zones we suggest that the aggrading ash bedsets with upstream crest migration were formed under subcritical flow conditions where the tractional bedload transport was less important than the simultaneous fallout from suspension this produced differential draping with no further reworking we propose the name regressive climbing dunes for structures produced by this process a rapid decrease in current velocity possibly triggered by hydraulic jumps affecting the entire parent flows is inferred to explain their deposition this process can in principle hold for any kind of particulate density current

hydraulic geometry change of a large river a case study of the upper yellow river study on hydraulic geometry can reveal the response of river systems to basin attributes and the trends in channel change based on 35 years of data collected at 10 hydrological stations cross sections the hydraulic geometry relations between cross sectional variables and discharge were established and the derived parameters were analyzed the channel behavior of the mountainous bedrock reach from riverhead to xunhua cross section and the alluvial reach from xunhua to toudaoguai cross sections differed significantly over the past decades in response to dramatic water and sediment changes the hydraulic geometry quasi equilibrium was achieved through equally adjusting water depth and flow velocity in the mountainous bedrock reach while primarily through flow velocity in the alluvial reach the change rate of river width with varying discharge was relatively small in the whole upper yellow river compared with the lower yellow river and other rivers in the world both similarity and differences existed indicating the general adjustment direction of hydraulic quasi equilibrium and also the importance of considering other influencing factors in hydraulic geometry studies in addition dams played an important role in affecting the changes of hydraulic geometry exponents

assessing pollen distribution patterns and provenance based on palynological investigation on surface sediments from laizhou bay china an aid to palaeoecological interpretation abstract assessing pollen distribution patterns in the sea is essential to understanding pollen provenance upon which subsequent interpretation of quaternary pollen data from marine sediments in the same study area should be soundly based here we present palynological data from seafloor sediments in laizhou bay and analogous samples from its inflowing rivers to elucidate the distribution patterns and provenance of modern palynomorphs our results demonstrate that the pollen assemblages of marine areas are dominated by arboreal pollen types especially pinus and herbaceous pollen types are dominated by chenopodiaceae and artemisia the higher pollen concentrations occur in the southwest area of laizhou bay and the lower pollen concentrations are mainly distributed in the nearshore area of the yellow river estuary such pollen distribution patterns are tightly correlated with the distribution features of grain size of the surface sediments specifically the sediments with higher pollen concentrations are of very fine and fine silts whereas those with lower pollen concentrations are of fine sands the results of pca analysis suggest that pollen grains in the nearshore areas are mainly transported by water flows of which herbaceous pollen show relatively higher concentrations while pollen grains in the offshore areas are largely carried by winds especially those pollen types with sacs such as pinus dissimilarity analysis between marine and alluvial samples indicates that the pollen spectrum show close linkage with the regional vegetation in the surrounding watersheds pollen quantitative characteristics and pollen assemblage changes in different parts of the marine areas indicate various pollen provenance and changing landscape of terrestrial vegetation particularly along the inflowing rivers our assessments on pollen distribution patterns and provenance based on palynological investigation would strongly aid quaternary palaeoecological and palaeoclimatological interpretation for our study area

depositional mechanics of turbulent nuees ardentes surges from their grain sizes the ability of turbulent nuees ardentes surges to transport coarse pyroclasts has been questioned on the basis that settling velocities of coarse fragments in the deposits are much too high for them to have been supported by turbulence in a dilute gas suspension a computer model is used to evaluate the settling velocity of pyroclasts in suspensions of varying concentration and temperature since suspension of grains in low concentration surges occurs if the shear velocity exceeds the settling velocity the shear velocities related to the 16th and 84th percentiles and the mean of the grain size distribution are compared in surge deposits of the vulsini with the shear velocity necessary to move the coarsest grain on the bed surface the shields criterion the results show that the settling velocities do not vary significantly in gaseous suspensions having volume concentrations lower than 15 and that an increase in concentration to 25 is not sufficient to decrease the settling velocity of the coarser fraction if it represents flow shear velocity it is shown that the settling velocity of the mean grain size m z best depicts the shear velocity of a dilute turbulent suspension applying the results to the may 1902 paroxysmal nuees ardentes of mount pelee shows that the estimated mean velocities are well within the observed velocities and sufficient to support all the clasts in dilute turbulent suspensions

outburst floods in china a review abstract outburst floods can have disastrous impacts on people and are an important driving force in landscape change and have been studied widely on earth in china although outburst floods have occurred frequently there has been relatively little systematic investigation of the controlling factor here we review outburst floods in china in terms of the characteristics distribution causes of dams and outburst floods in terms of natural dams landslides accounted for the majority 287 cases followed by moraine dams 33 cases which are mainly found on and around the tibetan plateau and although other types such as glacier and volcanic dams were historically rare many examples may be preserved in the geological record in addition there have been thousands of outburst floods from artificial constructed dams the majority of which were from small earth dams the largest reliably recorded peak discharge for an outburst flood was 1 24 105 m3 s which occurred in yigong tibet the peak discharge of the 1975 banqiao collapse was 7 9 104 m3 s the largest outburst flood of a man made dam our recent investigations on the yarlung tsangpo in southeast tibet have identified gravel deposits that probably record megafloods and offer great potential for paleoflood analysis

modeling flood dynamics along the superelevated channel belt of the yellow river over the last 3000 years the yellow river china experienced 1000 levee breaches during the last 3000 years a reduced complexity model is developed in this study to explore the effects of climate change and human activity on flood levels levee breaches and river avulsions the model integrates yearly morphological change along a channel belt with daily river fluxes and hourly evolution of levee breaches model sensitivity analysis reveals that under natural conditions superelevation of the channel belt dominates flood frequency when there is significant human accelerated basin erosion and breach repair the dominant factors shift to a combination of mean annual precipitation superelevation critical shear stress of weak channel banks and the time interval between breach initiation and its repair the effect of precipitation on flood frequency is amplified by land use changes in the hinterland particularly in the erodible loess plateau uncertainty analysis estimates the most likely values of the dominant factors for six historical periods between 850 b c and a d 1839 which are used to quantitatively reconstruct flood dynamics during 850 b c to a d 1839 when the sediment load increased fourfold the breach recurrence interval was shortened from more than 500 years to less than 6 years and the breach outflow rate increased 27 times river management practices during a d 1579 to a d 1839 focused on levees and triggered a severe positive feedback of increased levee heights and flood hazard exacerbation raising the levee heights proved to be ineffective for sustainable flood management

temporal and spatial variation of catastrophic river floodings in the lower yellow river from ad 960 to 1938 this study is intended to investigate the patterns for the temporal and spatial changes of catastrophic river floodings which took place in the lower yellow river based on the available records co

thermodynamics of silicate liquids in the deep earth article i nfo we discuss the geophysical implications of recent first principles molecular dynamics simulations of mgsio3 liquid in particular the findings that the gruneisen parameter increases by a factor of three on two fold compression and the predicted melting curve the predicted melting temperature of mgsio3 perovskite at 136 gpa is 5400 600 k which if lowered by freezing point depression by 1300 k yields a mantle solidus temperature of 4100 k identical to recent estimates of the temperature at the base of the mantle we argue on this basis that partial melting at the base of the mantle is plausible while mgsio3 perovskite is denser than the isochemical liquid reasonable values of iron partitioning and bulk iron contents leads to the conclusion that a melt at the base of the multi component mantle would be denser than its surroundings and therefore buoyantly stable we predict the bulk sound velocity of this melt to be 10 9 km s 1 less than that of ultra low velocity zones and consistent with the explanation of these regions as being due to partial melting the increase on compression of the gruneisen parameter in the liquid state yields isentropes that are much hotter than previously thought a potential temperature of only 2450 k is sufficient to melt the entire mantle and a magma ocean will begin crystallization at mid mantle depths rather than at the base of the mantle

sediments at the top of earth s core unusual physical properties at the core mantle boundary have been inferred from seismic and geodetic observations in recent years we show how both types of observations can be explained by a layer of silicate sediments which accumulate at the top of the core as earth cools compaction of the sediments expels most of the liquid iron but leaves behind a small amount of core material which is entrained in mantle convection and may account for the isotopic signatures of core material in some hot spot plumes extraction of light elements from the liquid core also enhances the vigor of convection in the core and may increase the power available to the geodynamo

anthropocene archaeology of the yellow river china 5000 2000 bp in this paper we use geoarchaeological and paleoenvironmental data from three localities in the yellow river valley china taosi sanyangzhuang and the yiluo valley to argue that human activi

holocene environmental change inferred from the loess palaeosol sequences adjacent to the floodplain of the yellow river china abstract chinese loess deposits are generally considered to be the product of dust storms and dust falls from the central asia arid zones that were transported across china by the northwesterly continental monsoon in contrast the zhengzhou loess found southeast of the loess plateau adjacent to the floodplain of the yellow river records a different eolian regime and dust source the zhengzhou loess was investigated by field observations measurements of magnetic susceptibility particle size distribution loss on ignition caco3 and chemical contents both field observations and the laboratory results indicate that during the last glacial the zhengzhou loess was supplied by two different eolian regimes and dust sources one was from the fresh flood deposits of the yellow river driven by the northeast winds from the low lying floodplain and the other was from the dust storms and dust falls that traveled across the loess plateau driven by the northwesterly continental monsoon from the central asian arid lands the early holocene 11 500 8500 a bp was a transition during the change in eolian regime and dust source because of the weakened northwesterly monsoon along with the global climatic amelioration following the retreat of the northwesterly monsoon from the onset of the mid holocene climatic optimum at 8500 a bp dust supply from the drifting sand zone on the yellow river floodplain became dominant because of the intensified strength of the northeast winds from the bohai sea from 3100 a bp onwards climatic aridity and extensive human disturbance have resulted in intensive eolian processes causing the incursion of the drifting sand into the zhengzhou loess zone these results show that loess accumulation is more complex than traditionally assumed the origin of loess deposits elsewhere outside the loess plateau may be related to dust sources derived from alluvial sediments of major river systems

holocene aridification vegetation change sedimentation regime and limits of carbon isotope data as indicated by the alluvial pollen sites of arroyo grande and el molino in north central mexico abstract a multi proxy record of palynological sedimentological archaeological and carbon isotopic data of alluvial sites in the upper nazas basin arroyo grande durango 1855 m amsl and the parras basin el molino coahuila 1245 m amsl is introduced describing environmental changes across a short grassland desert ecotone from the eastern margins of the sierra madre occidental smo these sites reconstruct holocene vegetation history in semi arid north central mexico and integrate fluvial geomorphology and palynology data in particular pollen data links a rise of xeric flora with higher energy deposition and increased erosion in upland basins of the eastern smo according to archaeological finds at examined sites human occupation is linked to mesic or afforested conditions however limitations of carbon isotope data for environmental historical reconstruction are indicated by somewhat stable values at arroyo grande durango especially while pollen sites show a replacement of short grasses and park woodlands by a more xeric flora at higher elevations with a development of chihuahuan desert flora at low elevations el molino coahuila vegetation reconstructions are supported by pollen analog data collected from the cuatro cienegas region in coahuila mexico

paleoflood hydrology origin progress prospects from an origin in diverse studies of flood geomorphology and quaternary geology paleoflood hydrology emerged as a geophysical and an applied hydrological science during the 1970s and 1980s since acquiring its formal name in 1982 the most productive approach in paleoflood hydrology has become energy based inverse hydraulic modeling of discrete paleoflood events recorded in appropriate settings as slackwater deposits and other paleostage indicators swd psi or as various threshold indicators of non exceedence technological advances particularly in hydraulic modeling and geochronology were instrumental in moving the discipline to its present status the most recent advances include 1 new techniques for the accurate geochronology of flood sediments notably tams radiocarbon analyses and osl dating and 2 the phenomenal increase in computer power that allows complex hydraulic calculations to become feasible for routine studies from its initial demonstration in the southwestern united states swd psi paleoflood hydrology proved its widespread applicability to various landscape environments particularly important studies have been accomplished in australia china india israel south africa spain and thailand paleoflood hydrology has also generated its share of controversy in part because of the differing viewpoints and attitudes of the two scientific traditions from which it emerged quaternary geology geomorphology versus applied hydrologic hydraulic engineering nevertheless the future growth of the discipline is assured given the rapid pace of discoveries that it engenders indeed so many international studies exist that it is appropriate to pursue global syntheses to address interesting and timely questions of extreme flood phenomena in relation to global climatic change

diversity of eruptive styles inferred from the microlites of mt pelee andesite martinique lesser antilles abstract we have studied the compositional and textural characteristics of plagioclase microlites from several dome forming eruptions dome block and ash flows and surges and plinian fallouts of the recent period of activity of mt pelee in order to infer magma ascent dynamics dome forming and plinian samples display a wide range of plagioclase microlite compositions from an 35 to an 90 and an 55 to an 90 respectively microlites with compositions an 50 60 crystallized from a mafic melt that intruded the andesitic reservoir in proportion of 10 vol during magma ascent in the conduit the fraction number density and morphology of the decompression induced microlites compositions 50 60 suggest that the plinian magmas experienced a nucleation dominated crystallization regime with high undercooling in contrast magmas from domes and block and ash flows were dominated by a growth regime with low undercooling and the surges were influenced by both regimes according to these crystallization regimes and new experimental data on h 2 o content of the matrix glasses we propose magma relative ascent rates and fragmentation pressures for the different eruptive styles observed at mt pelee that may explain why surges are explosive events and why they may or may not be followed by a plinian event

implications of a long lived basal magma ocean in generating earth s ancient magnetic field 1 observations of earth s magnetic field extending back to 3 45 billion years ago indicate that generation by a core dynamo must be sustained over most of earth s history however recent estimates of thermal and electrical conductivity of liquid iron at core conditions from mineral physics experiments indicate that adiabatic heat flux is approximately 15 tw nearly three times larger than previously thought exacerbating difficulties for driving a core dynamo throughout earth history by convective core cooling alone here we explore the geomagnetic consequences of a basal magma ocean layer in the lowermost mantle hypothesized to exist in the early earth and perhaps surviving until well after the archean while the modern solid lower mantle is an electromagnetic insulator electrical conductivities of silicate melts are known to be higher though as yet they are unconstrained for lowermost mantle conditions we consider a range of possible electrical conductivities and find that for the highest electrical conductivities considered a long lived basal magma ocean could be a primary dynamo source region this would suggest the proposed three magnetic eras observed in paleomagnetic data originate from distinct sources for dynamo generation from 4 5 to 2 45 ga within a basal magma ocean from 2 25 to 0 4 ga within a superadiabatically cooled liquid core and from 0 4 ga to present within a quasi adiabatic core that includes a solidifying inner core

the 1984 nuee ardente deposits of merapi volcano central java indonesia stratigraphy textural characteristics and transport mechanisms for many centuries merapi volcano has generated hot avalanches of blocks lapilli and ashes derived from the destruction of partially solidified viscous lava domes merapi type nuees ardentes on 15 june 1984 at least four nuees ardentes came down the southwest slope of the merapi the first and the last being responsible for more than 99 of the deposits which are now exposed the first nuee ardente a merapi type nuee ardente was produced by the destruction of the dome travelled 7 km from the crater leaving a measured deposit 2 7 m thick 4 km from the crater near its upper depositional limit regularly increasing to a maximum measured thickness of 12 m at the front of the deposit the lower contact is sharp non erosive with pines still rooted in the underlying paleosol the deposit consists of 50 ash 33 lapilli and 17 blocks with two subpopulations one rosin and one normal and is finespoor with less than 4 of fine ash d finer than 4 the deposit displays reverse population grading of both vesiculated and massive clasts and of the maximum grain size the maximum size significantly increases regularly down current over most of the exposed length of unit 1 and bed thickness increases for the entire length of the deposit the deposit of the second nuee ardente is only 6 21 cm thick and of very limited lateral extent it is a normally graded coarse to fine ash with a finespoor base the third unit consists of fines poor normally graded coarse ash exposed in low amplitude 20 40 cm 12 m wavelength dunes the deposit of the fourth nuee ardente rests in sharp erosive contact on the underlying unit increasing in thickness down flow it consists of transitional coarse and fine grained strata 6 130 c cm thick dipping 5 10 down flow the deposit made up of two subpopulations one rosin and one normal is normally graded over the entire bed but coarsegrained strata are reversely graded the relative content of vesiculated clasts increases up bed in both strata types from 12 at the base to 40 at the top the characteristics of unit 1 suggest that it accumulated from a concentrated suspension of cohesionless solids exhibiting non newtonian behavior where dispersive pressure played an important role in the suspension of the clasts units 2 and 3 were probably deposited from dilute turbulent suspensions whereas the upper unit 4 is a classic example of deposition from a high density turbulent suspension leading to the formation of multiple traction carpets driven by the overlying lower density surge the horizontal distance travelled by a hot rock avalanche may be influenced by its transport mechanism debris flows are mobile on very low slopes as low as 1 whereas grain flows even density modified grain flows require relatively high slopes more than 6 at merapi to maintain their mobility if the present merapi dome were to collapse and produce a debris flow its present volume coupled with the minimal 1 5 km vertical drop could travel a distance ranging between 15 and 30 km however if transport were by grain flow mechanisms the mass could come to rest as it reaches a 5 10 slope

elastic properties of ferropericlase at lower mantle conditions and its relevance to ulvzs abstract the elasticity of fe x mg 1 x o was examined under lowermost mantle temperature and pressure conditions using density functional theory dft the addition of iron decreases the shear modulus of mgo but has varying effects on the bulk modulus depending on the spin state of the iron the spin state of iron in fe x mg 1 x o is dependent on pressure and temperature but also on the concentration of iron at 136 gpa fe in low concentrations 25 is nearly entirely low spin while at very high concentrations 75 it is nearly entirely in the high spin state there is as expected a large decrease in seismic velocities with iron substitution however the effect of fe is greater at high temperatures than at low temperatures meaning it is difficult to extrapolate low temperature experimental results we cannot simultaneously match the density and seismic velocities of ulvzs with fe enriched ferropericlase this is reflected in dln v s dln v p t p which in ulvzs is generally observed to be about 3 but does not exceed about 1 5 for fe enriched periclase a mixture of ferropericlase and ferrous perovskite can cause v s decreases of up to 45 which allows the range of ulvz v p v s and densities to be matched we also find that dln v s dln v p t p increases up to as much as 3 but this value is strongly dependent on the bounds of the mixing geometry we conclude therefore that the properties of ulvzs can be readily explained by a lower mantle with a single phase that is heavily enriched in fe

late quaternary linkage of sedimentary records to three astronomical rhythms and the asian monsoon inferred from a coastal borehole in the south bohai sea china abstract the bohai sea was formed by subsidence during the cenozoic some 2000 3000 m of fluvial lacustrine and marine sediments has been deposited in this basin previous studies focused mainly on the transgression history with little examination of orbital variation in relation to other areas within the asian monsoon domain here we present the late quaternary results of a new borehole in the south bohai sea optically stimulated luminescence and radiocarbon dating which provide concordant age estimates were employed to generate an initial chronology for the borehole after refining the chronology through astronomical tuning the results showed that 1 the grain size variation represents asian monsoon intensity which was dominated by both solar insolation major and global ice volume minor forcing 2 the magnetic susceptibility indicates river incision processes which were sensitive to orbital tilt with influence from solar insolation 3 the vegetation coverage responded to global ice volume coupled obliquity changes and that 4 neither external nor internal factors could dominate the paleoenvironmental evolution on orbital timescales in an independent way and they are both integrated in a complex pattern we conclude that three different astronomical rhythms have affected coastal evolution and that the sedimentary records in the south bohai sea china result from the nonlinear interaction and the complex response to driving processes

mt pelee martinique may 8 and 20 1902 pyroclastic flows and surges abstract the distribution stratigraphic relationships and fragmental components of the may 8 and 20 1902 pyroclastic flows from mt pelee martinique together with eyewitness accounts suggest the following explanation for those eruptions the eruptions were vertically directed magmatic perhaps initiated phreatically and contained abundant juvenile lithics from congealed magma of the dome and neck this resulted in a two part eruption column having 1 a dense lithic charged part which collapsed into the crater and flowed out of a pre existing notch in its side giving rise to pyrochlastic flows and 2 a magmatically derived column containing gases juvenile vitric material and crystals which largely by passed the neck and dome and escaped into the atmosphere all of the energy of the flows was apparently focused through the notch they emerged fully turbulent and flowed down riviere blanche gravity segregation of large and abundant fragments soon resulted in a dense high concentration poorly fluidized block and ash flow confined to the valley leaving above a fully turbulent high energy ash cloud surge as the ash cloud surge moved down the mountain it continued to expand outward the process of gravity segregation continued as the ash cloud surge expanded resulting in secondary block and ash underflows toward st pierre the secondary block and ash flows developed on a gently sloping upland surface 100 m or more above the valley of riviere blanche the turbulent fragment depleted surges above the secondary block and ash flows maintained sufficient energy to devastate the landscape outward to about 3000 m including st pierre the surges refracted around obstacles and in one place moved up a small valley in a direction opposite to the main flows

pyroclastic dune bedforms macroscale structures and lateral variations examples from the 2006 pyroclastic currents at tungurahua ecuador pyroclastic currents are catastrophic flows of gas and particles triggered by explosive volcanic eruptions for much of their dynamics they behave as particulate density currents and share similarities with turbidity currents they occasionally deposit dune bedforms with peculiar lamination patterns from what is thought to represent the dilute low concentration and fluid turbulence supported end member of the pyroclastic currents here we present a high resolution dataset of sediment plates lacquer peels with several closely spaced lateral profiles representing sections through single pyroclastic bedforms from the august 2006 eruption of tungurahua ecuador most of the sedimentary features contain backset bedding and preferential stoss face deposition from the ripple scale few cm to the largest dune bedform scale several m length similar patterns of erosive based backset beds are evidenced recurrent trains of sub vertical truncations on the stoss side of structures reshape and steepen the bedforms in contrast sporadic coarse grained lenses and lensoidal layers flatten bedforms by filling troughs the coarsest clasts up to 10 cm least sorted and massive structures still exhibit lineation patterns that follow the general backset bedding trend the stratal architecture exhibits strong lateral variations within tens of centimeters with very local truncations both in flow perpendicular and flow parallel direction we infer that the bedforms sedimentary patterns result from four formation mechanisms differential draping slope influenced saltation truncative bursts and granular based events whereas most of the literature makes a straightforward link between backset bedding and froude supercritical flows we reconsider this interpretation indeed features that would be diagnostic of subcritical dunes antidunes and chute and pools can be found on the same horizon and in a single bedform only laterally separated by short distances 10s of cm our data stress the influence of the pulsating and highly turbulent nature of the currents and the possible role of coherent flow structures such as gortler vortices backset bedding is interpreted here as a consequence of a very high sedimentation environment of weak and waning currents that interact with the pre existing morphology quantification of near bed flow velocities are made via comparison with wind tunnel experiments we estimate that shear velocities of ca 0 30 m s 1 equivalent to pure wind velocity of 6 to 8 m s 1 at 10 cm above the bed could emplace the constructive bedsets whereas the truncative phases would result from bursts with impacting wind velocities of at least 30 40 m s 1

spatially distributed erosion and sediment yield modeling in the upper indus river basin 1 spatially distributed erosion rates and sediment yields are predicted in the mountainous upper indus river basin with coupled models of erosion and sediment delivery potential erosion rates are calculated with the thornes model in combination with a surface runoff model sediment delivery ratios sdrs are hypothesized to be a function of travel time of surface runoff from catchment cells to the nearest downstream channel modeled monthly erosion rates for the upper indus river basin indicate that 87 of the annual gross erosion takes place in the three summer months the erosion risk map suggests that the areas with the greatest erosion potential are concentrated in subbasins with high relief and a substantial proportion of glacierized area lower erosion rates can be explained by the arid climate and low relief on the tibetan plateau and by the dense vegetation and lower relief in the lower monsoon subregion high erosion rates 1 0 mm a 1 occur over 66 4 of the basin area the model predicts an average annual erosion rate of 3 2 mm a 1 or 868 mt a 1 which is approximately 4 5 times the long term observed annual sediment yield of the basin the predicted annual basin sediment yield is 244 mt a 1 which compares reasonably well to the measured value of 195 1 mt a 1 the overall sediment delivery ratio in the basin is calculated as 0 28 model results indicate that higher delivery ratios sdr 0 6 are found in 18 of the basin area mostly located in the high relief subbasins the sediment delivery ratio is lower than 0 2 in 70 of the basin area the indus subbasins generally show an increase of sediment delivery ratio with basin area model evaluation based on accuracy statistics suggest very good to satisfactory performance ratings for predicted sediment yields the presented modeling framework requires relatively few data all of which can be derived from global data sets it therefore can be used to predict erosion and sediment yield in other ungaged or poorly gaged drainage basins

first principles calculations of the lattice thermal conductivity of the lower mantle abstract the temperature variations on top of the core mantle boundary are governed by the thermal conductivity of the minerals that comprise the overlying mantle estimates of the thermal conductivity of the most abundant phase mgsio3 perovskite at core mantle boundary conditions vary by a factor of ten we performed ab initio simulations to determine the lattice thermal conductivity of mgsio3 perovskite finding a value of 6 8 0 9 w m 1 k 1 at core mantle boundary conditions 136 gpa and 4000 k consistent with geophysical constraints for the thermal state at the base of the mantle thermal conductivity depends strongly on pressure explaining the dynamical stability of super plumes the dependence on temperature and composition is weak in the deep mantle our results exhibit saturation as the phonon mean free path approaches the interatomic spacing combining our results with seismic tomography we find large lateral variations in the heat flux from the core that have important implications for core dynamics

river sedimentation and channel adjustment of the lower yellow river as influenced by low discharges and seasonal channel dry ups fluvial sedimentation can be classified as one of the three types in terms of different morphological units i e vertical overbank deposition vertical deposition on the riverbed and lateral deposition on the riverbank with the example of the lower yellow river the three types of sedimentation have been studied in relation to channel adjustment since 1986 the lower yellow river has entered a new period that is characterized by small discharges with seasonal desiccations dry ups and strong sedimentation has occurred based on the measurement of 36 cross sections along the lower yellow river the rates of the three types of deposition have been calculated and are reported in this study multiple regression has been used to express the relationship between the three rates of deposition and the channel shape adjustment index influenced by the difference in channel sediment and by downstream variations in water discharge and sediment load the indices of channel deposition rate show a clear trend of downstream variation controlled by this the manner of channel adjustment also shows clear trends downstream under the hydrological regime dominated by small discharges the tendencies of adjustment of riverbed slope and bankfull slope are inverse i e the channel slope tends to decrease but the slope at bankfull stage to increase at present the former tendency is dominant thus the sediment carrying capacity of the lower yellow river tends to decrease which intensifies channel sedimentation

alluvial pollen on the north china plain abstract mordern alluvial pollen varies with geomorphic setting and depositional facies in sediments of the yellow hutuo and luan rivers and in baiyangdian and hengshuihu lakes most of the arboreal pollen is derived from the mountains whereas most of the nonarboreal pollen is derived from the plain itself alluvium dominated bypinuspollen andselaginellaspores was deposited during a flood hydrodynamic sorting of alluvial pollen exists in the sediments of floodplain central bar natural levees and point bar in reconstructing the ancient vegetation and past climate based on pollen in alluvium it is important to consider sedimentary facies and geomorphologic setting

river mouth bar formation riverbed aggradation and channel migration in the modern huanghe yellow river delta china this paper addresses the recent 1970s 1990s processes of river mouth bar formation riverbed aggradation and distributary migration in the huanghe river mouth area in the light of station based monitoring field measurements and remote sensing interpretation the results show that the morphological changes of the river mouth bar have been closely associated with the largely reduced fluvial discharge and sediment load landforrn development such as bar progradation occurred in two phases i e before and after 1989 which correspond to faster and lower bar growth rates respectively fast riverbed aggradation in the mouth channel was strongly related to river mouth bar progradation during 1976 1996 about 2 8 of the total sediment loads were deposited in the river channel on the upper to middle delta therefore the river water level rose by a few meters from 1984 to 1996 the frequent distributary channel migration which switched the radial channel pattern into the se directed pattern in the mid 1980s was linked with mouth bar formation marine conditions also constrain seaward bar progradation furthermore the history of river mouth bar formation reflects human impacts such as dredging and dyking in order to stabilize the coastal area c 2005 elsevier b v all rights reserved

the past 5 000 years of volcanic activity at mt pelee martinique f w i implications for assessment of volcanic hazards the history of mt pelee martinique was subdivided into three stages based on field geology and 14c data the two first stages constructed an ancient mt pelee and an intermediate cone between 0 4 m y and 19 500 y b p the third or present stage started 13 500 years ago after a repose of 6 000 years this paper focuses on the activity of mt pelee during the past 5 000 years as a means to assess and zone volcanic hazards of the 23 magmatic eruptions during the past 5 000 years the ages of 21 eruptions of this period are based on 75 new 14c dates the types of phenomena and distribution of pyroclasts relate to four main types of activity the first type consists of pumice and ash flows that are not preceded by a plinian fall two eruptions named p6 and p4 illustrate this type for which the mixture of gas ash and pumice simply overflow the vent and flood several valleys the second type differs from the first by the occurrence of a preliminary moderate plinian fall stage four eruptions p5 p31 p2 and p1 illustrate this type two eruptions p32 and p33 experienced cataclysmic plinian explosions and pumiceous surges the third type is related to dome growth with the rise of viscous spines and the production of related block and ash flows five eruptions 1929 sept 1902 1904 npm nab2 and nmp illustrate this type the fourth type is characterized by violent ejection of more or less heterogeneous nuees ardentes the direction of the blast dictated by the morphology of the crater has been towards the south several times at mt pelee four eruptions may 1902 nab1 nrp2 and nrp3 belong to this type future magmatic eruptions at mt pelee will very likely belong to one of these four types assessment of hazards at mt pelee is based upon the behavior of the volcano during the past 5 000 years because 1 recognition of past magmatic eruptions is quite complete and well dated and 2 no structural change has occurred in the volcano a probabilistic and statistical approach has been tentatively followed stochastic models of wickman indicate a the chance that contemporary abnormal seismic and or phreatic activity at the volcano would signal an impending magmatic eruption is 20 percent b mt pelee exhibits a complex loading time behavior that may be related to the buffering effect of a magma chamber time is needed following a single or several closely spaced eruptions to establish conditions to initiate a new eruption and c if the 1929 event can be regarded as the last episode of the major 1902 eruption the volcano could remain in a dormant stage with respect to magmatic events for another century

depositional mechanics of the 1902 pyroclastic nueeardente deposits of mt pelee martinique abstract pyroclastic flows are believed to have a rheology similar to other gravity mass flows such as turbidity currents avalanches or debris flows gravity plays a major role in controlling the mobility of a nuee ardente the paroxismal nuees being differentiated by their larger mass by the initial direction of the trajectory produced by the explosion and by their higher velocity the 1902 deposits of mt pelee accumulated from primary flows the deposits may be grouped into two different facies 1 a coarse grained thick bedded agglomerate that has characteristics similar to debris flow deposits and 2 a well stratified lapilli tephra and ash that has characteristics of turbidity current deposits these deposits result from two different types of flow generally laminar for the agglomerate and turbulent for the lapilli tephra and ash the maximum grain size used previously as an indicator of flow competence is valid for the traction load of the turbulent suspension but is unrealistically high for a true suspension load the coarsest size in the turbulent flow deposits probably did not travel in true suspension and a value of 5 on the cumulative distribution is more realistic for the evaluation of the shear velocity needed for true suspension although representing a maximum size application of the reynolds number criteria to the may 8 and 20 1902 nuees that destroyed st pierre indicates that turbulence is their only possible physical state in agreement with the observed characteristics of the deposits mean flow velocity of pure air necessary to support the 5 size in true suspension 140 984 m s 1 is unrealistically high however increasing the density at the base of the turbulent flow to 0 01 or 0 05 g cm 3 decreases the settling velocity of the grains significantly and brings the mean flow velocity needed to support all grains except the largest down to the observed values of the 1902 eruptions the larger grains require a higher mean flow velocity and or a higher density increasing flow density provides a reasonable answer to the suspension problem of the coarse fraction in turbulent nuees ardentes

pollen plant macrofossils and microvertebrates from mid holocene alluvium in east central iowa usa comparative taphonomy and paleoecology abstract pollen plant macrofossils and micromammals are commonly used in paleoecological interpretations but rarely are found associated because of distinctly separate taphonomic pathways into the fossil record the lilienthal local biota dating between 5920 60 and 6300 80 14 c b p is a rare exception as the site contains all three proxies juxtaposed in alluvium impounded upstream from a fossil log near the headwaters of mud creek east central iowa u s a a variety of taphonomic processes can strongly influence the composition of fossil assemblages this paper compares the taphonomic framework for each fossil group interprets the paleoecologic signal from each and then compares the three interpretations pollen and plant macrofossils are found in organic silts indicating deposition in a quiet water environment microvertebrates ordinarily occur in sand sized sediments and show evidence of fluvial transport despite these different pathways all lilienthal assemblages indicate that a largely closed mesic deciduous forest grew along mud creek in mid holocene time therefore a narrow north south ecotone must have existed between the forest and tall grass prairie biomes in eastern iowa this robust data set provides a detailed picture of the paleoecology and paleogeography of this past environment

evolution of the fossa cone vulcano abstract in decreasing order of abundance the principal emplacement mechanisms for deposits of the fossa edifice of vulcano include dry surge wet surge pyroclastic fall lahar lava flow pyroclastic flow and epiclastic processes most samples from pyroclastic beds on fossa contain two grain size populations the coarser mode at 0 5 1 5 resulted from modified ballistic transport whereas the finer mode at 2 5 3 5 is related to surge transport reconstruction of the entire stratigraphy of the cone permits the beds to be grouped into five principal eruptive cycles all of which postdate the lower pilato ash of lipari dated at 11 000 to 8 500 y b p pte nere cycle palizzi cycle commenda cycle pietre cotte cycle and the modern cycle additional cycles may be present but exposures on the cone are insufficient for their adequate definition all cycles follow a similar stochastic pattern starting with surge eruptions and ending with effusion of lava from the crater rim the frequency of pyroclastic fall events increases with time throughout each cycle this progressive decrease in the efficiency of water melt interaction through the duration of each cycle may be due to a gradual rise of each new magma column coupled with an increase in magmatic volatiles tectonism and magma mixing both play a role in triggering eruptions on fossa the present crater lies at the intersection of two prominent tectonic trends a nnw fracture system parallels the main eruptive centers and an ene set aligns with the migration of minor vents the silicic lavas of fossa contain a mixture of two components xenocrysts of plagioclase augite and olivine surrounded by a dark glass are intimately dispersed into an evolved rhyolitic matrix

buried late holocene luvisols of the oka and moskva river floodplains and their anthropogenic evolution according to soil and pollen data abstract according to radiocarbon dating the ages of the four major soils developed on the floodplains are as follows 1 modern 2 2500 800 cal bp 3 4700 3000 cal bp and 4 7000 5300 cal bp the late holocene soil 2 is usually defined as albeluvisol or luvisol it has a developed profile with clearly expressed argic horizons bt it is markedly different from the underdeveloped soil 1 fluvisol and soil 4 phaeozem or chernozem that have a dark humus mollic chernic horizon soil 2 has a typical light gray color of the humus horizon and is characterized by the accumulation of clay fraction in the bt horizon as compared with the overlying e horizon micromorphological data indicate that the bt horizon has well developed clay films on pore walls and on the surface of aggregates cultural layers belonging to the iron age or early middle ages are sometimes located in soil 2 pollen analysis of this soil attests to its development under forest vegetation which corresponds to the genesis of luvisols and albeluvisols however in some places near ancient settlements characteristic features of the e and bt horizons become weakly pronounced and a well developed dark humus umbric horizon is diagnosed in the soil profiles these soils are marked by the abundance of pollen of herbs including cultivated cereals and weeds this is evidently related to the anthropogenic activity and the propagation of secondary grassy and ruderal vegetation that replaced forests on the floodplains floodplain environments are considered unsuitable for the development of luvisols and albeluvisols within a larger part of the holocene these soils appeared on the floodplains in the late holocene in relation to the propagation of forest vegetation and extremely low floods within a relatively long time

constraints on magnetic energy and mantle conductivity from the forced nutations of the earth observations of the earth s nutations are used to explore the possible presence of a conducting layer at the base of the mantle the existence of such a layer is suggested by recent experiments on iron and silicate mixtures at high pressures and temperatures knittle and jeanloz 1986 1989 which indicate that iron may react with silicate minerals to produce metallic compounds nutations provide an ideal tool for investigating the existence of such a layer because they are sensitive to the electrical properties within a thin magnetic boundary layer along the core mantle boundary cmb evidence in favor of a conducting layer is found in the effects of ohmic dissipation which cause the amplitude of the earth s nutation to be out of phase with tidal forcings although out of phase components in the earth s nutations are conventionally attributed to the dissipative influences of ocean tides and mantle anelasticity these effects appear incapable of explaining nutation amplitudes determined from very long baseline interferometry vlbi observations the additional effects of ohmic dissipation enhanced by the presence of a thin conducting layer at the cmb are sufficient to reconcile theory and observation the largest mismatch between observations and theory taking account of ocean tides and mantle anelasticity is a discrepancy of 0 39 0 04 milliarcseconds in the out of phase component of the retrograde annual nutation this discrepancy can be eliminated if the lowermost 200 m of the mantle has a conductivity of 5 105s m 1 and the magnetic energy in the spherical harmonic components of the field at the cmb in degrees l 12 is approximately 4 times greater than the energy inferred in degrees l 12 from surface observations unfortunately the vlbi observations do not uniquely resolve the mantle conductivity and magnetic energy so that trade offs exist between these two parameters nevertheless a high mantle conductivity is favored on the grounds that the alternative involving high levels of magnetic energy yields an excessive amount of ohmic heating other interpretations of the vlbi discrepancy are also discussed one such alternative involves viscous dissipation at the cmb requiring a kinematic viscosity of 0 1m2s 1

thermal conductivity of ferropericlase in the earth s lower mantle abstract mg fe o ferropericlase fp is one of the important minerals comprising earth s lower mantle and its thermal conductivity could be strongly influenced by the iron content and its spin state we examined the lattice thermal conductivity of mg fe o fp containing 19 mol iron up to 111 gpa and 300 k by means of the pulsed light heating thermoreflectance technique in a diamond anvil cell we confirmed a strong reduction in the lattice thermal conductivity of fp due to iron substitution as reported in previous studies our results also show that iron spin crossover in fp reduces its lattice thermal conductivity as well as its radiative conduction we also measured the electrical conductivity of an identical fp sample up to 140 gpa and 2730 k and found that fp remained an insulator throughout the experimental conditions indicating the electronic thermal conduction in fp is negligible because of the effects of strong iron impurity scattering and spin crossover the total thermal conductivity of fp at the core mantle boundary conditions is much smaller than that of bridgmanite bdg our findings indicate that bdg and post perovskite is the best heat conductor in the earth s lower mantle and distribution of iron and its valence state among the lower mantle minerals are key factors to control the lower mantle thermal conductivity

the behavior of specific sediment yield in different grain size fractions in the tributaries of the middle yellow river as influenced by eolian and fluvial processes based on data from 35 stations on the tributaries of the yellow river annual specific sediment yield y s in eight grain size fractions has been related to basin averaged annual sand dust storm days d ss and annual precipitation p m to reveal the influence of eolian and fluvial processes on specific sediment yield in different grain size fractions the results show that y s in fine grain size fractions has the highest values in the areas dominated by the coupled wind water process from these areas to those dominated by the eolian process or to those dominated by the fluvial process y s tends to decrease for relatively coarse grain size fractions y s has monotonic variation i e with the increase in d ss or the decrease in p m y s increases this indicates that the sediment producing behavior for fine sediments is different from that for relatively coarse sediments the results all show that y s for relatively coarse sediments depends on the eolian process more than on the fluvial process and the coarser the sediment fractions the stronger the dependence of the y s on the eolian process the y s d ss and y s p m curves for fine grain size fractions show some peaks and the fitted straight lines for y d ss and y s p m relationships for relatively coarse grain size fractions show some breaks almost all these break points may be regarded as thresholds these thresholds are all located in the areas dominated by the coupled wind water process indicating that these areas are sensitive for erosion and sediment production to which more attention should be given for the purpose of erosion and sediment control a number of regression equations were established based which the effect of rainfall sand dust storms and surface material grain size on specific sediment yield can be assessed copyright 2007 john wiley sons ltd

characteristics of pyroclastic deposits at the margin of fond canonville martinique and implications for the transport of the 1902 nuees ardentes of mt pelee abstract the deposits which were studied at fond canonville represent a well defined record of the 1902 eruptions of the montagne pelee the sections are located at the margin of the valley where six eruption units with thicknesses ranging from 8 cm up to 2 m were identified overlying the pre 1902 paleosol the pyroclasts consist of lapilli coarse and fine ash composed of juvenile andesitic fragments of varying vesicularity dust free crystals dust free transparent vesicular glass and accretionary lapilli paleocurrent measurements on cross bedding support the stratigraphic evidence that the flows came down the valley of fond canonville rather than up as was previously proposed most eruption units are made of two or three beds always in sharp contact the basal bed relatively thin contains the coarsest grain size of the unit is massive or normally graded and fine depleted a thin division of parallel laminae may be present at the top the middle bed the thickest in all eruption units has a mean grain size which is intermediate between the lower and upper beds it may be simple or multiple normal grading is generally present on which may be superimposed in the upper portion of the bed 2 4 cm thick strata parallel to the upper bed surface or dipping from it at angles of less than 10 the upper bed the most regular in all units with thicknesses ranging from 2 to 8 cm is made of accretionary lapilli set in a matrix of fine ash a division of parallel and or oblique laminae is generally present at its top the characteristics of the deposits suggest that all three beds accumulated from a stratified turbulent flow normal grading of both coarsest and mean sizes sequences of internal structures including laminae evince that the flows were of relatively low concentration and that traction was an active process during the accumulation of the deposits for these structures to form the flows had to be turbulent for all three beds of the eruption units the thick strata superimposed on the graded middle bed are interpreted as having formed by the migration and aggradation of long wavelength antidunes the relationship between flow velocity and wavelength suggests that subaerial pyroclastic flows can only produce long wavelength antidunes with resulting internal stratification essentially parallel to bedding short wavelength antidunes in subaerial pyroclastic deposits require very high flow density at least close to the bed surface or low velocity which is unlikely considering the grain size present in the deposits

radionuclide dating of recent sediment and the validation of pollen environment reconstruction in a small watershed reservoir in southeastern china abstract a 76 cm sediment core was collected from the huangdong reservoir southeastern china the radionuclides 137 cs and 210 pb and sediment grain size analysis were applied to establish the chronology and modern sedimentation rates the chronology established by the 137 cs time markers was consistent with the constant flux constant sedimentation cfcs model and the known time of dam construction 1960 ad recognized from the curve of sediment grain size at the depth of 54 cm the results show that the sedimentation rate of the huangdong reservoir is relatively high implying that soil erosion and water loss were strong the sedimentation rate before the construction of the reservoir was approximately 1 5 cm a which belongs to the fluvial flooding deposit the rate decreased to approximately 1 0 cm a during the reservoir deposition since 1960s pollen and micro charcoal analysis were performed to test the reliability of pollen based environment reconstruction including vegetation cover deforestation planting and fire disasters the results of pollen and micro charcoal indicated that the herbs primarily gramineae ferns such as dicranopteris and several trees mainly pinus varied following chorography or historical records we discovered that the most important indicators for local forest cover changes are pollen concentration and the ap nap value ratio of arboreal pollen to non arboreal pollen human impact on forests is manifested by a sharp decrease in pollen percentage of trees and absolute pollen concentration forest fire events were recorded by the peaks of charcoal concentration and the c p value ratio of charcoal concentration to pollen concentration for example the massive deforestation and intensive fires during the great leap forward movement and the cultural revolution are reflected by pollen and micro charcoal spectra this work testifies that radionuclide use as a dating method is applicable in southern china and the 137 cs method has demonstrated its reliability in the small reservoir setting in spite of low absolute values the environmental proxies such as grain size pollen and charcoal are sufficiently sensitive to reveal local ecosystem changes caused by natural disasters or human activity

silicon isotopic composition of dissolved silicon and suspended particulate matter in the yellow river china with implications for the global silicon cycle abstract the silicon isotopic composition of dissolved silicon and suspended particulate matter spm were systematically investigated in water samples from the mainstem of the yellow river and 4 major tributaries the spm content of the yellow river varied from 1 4 to 38 560 mg l averaging 3568 mg l and the 30 si of suspended particulate matter 30 si spm varied from 0 3 to 0 4 averaging 0 02 the major factors affecting the spm content and the 30 si spm values in the yellow river were inferred to be the mineralogical chemical and isotopic characteristics of the sediments from the loess plateau and a combination of the climate and the flow discharge of the river the major ions in the yellow river water were na ca 2 mg 2 hco 3 so 4 2 and cl high salt concentration was observed in samples from the middle and lower reaches likely reflecting the effects of evaporation and irrigation because the na mg 2 so 4 2 and k concentrations were correlated with the cl concentration the dissolved si concentration d si increased downstream varying from 0 016 to 0 323 mm the 30 si of dissolved si 30 si diss varied from 0 4 to 2 5 averaging 1 28 the major processes controlling the d si and 30 si diss of the yellow river are a the weathering of silicate rocks b the formation of phytoliths in plants c the evaporation of water from and the addition of meteoric water to the river system which only affects concentrations d the adsorption and desorption of aqueous monosilicic acid on iron oxide and e the dissolution of phytoliths in soils the d si and 30 si diss values of global rivers vary spatially and temporally in response to changes in climate chemical weathering intensity and biological activity the moderately positive 30 si diss values observed in the yellow river may be attributed to the higher rates of chemical weathering and biological activities that have been observed in this catchment in comparison with those of other previously studied catchments excluding the yangtze river human activities may also potentially influence chemical weathering and biological activities and affect the d si and 30 si diss values of the major rivers of the world further river studies should be performed to gain a better understanding of the global si isotope budget

long period 30 days 1 year electromagnetic sounding and the electrical conductivity of the lower mantle beneath europe the c response connects the magnetic vertical component and the horizontal gradient of the horizontal components of electromagnetic variations and forms the basis for deriving the conductivity depth profile of the earth time series of daily mean values at 42 observatories typically with 50 years of data are used to estimate c responses for periods between 1 month and 1 yr the z y method is applied which means that the vertical component is taken locally whereas the horizontal components are used globally by expansion in a series of spherical harmonics in combination with results from previous analyses the method yields consistent results for european observatories in the entire period range from a few hours to 1 yr corresponding to penetration depths between 300 and 1800 km 1 d conductivity models derived from these results show an increase in conductivity with depth z to about 2 s m 1 at z 800 km and almost constant conductivity between z 800 and z 2000 km with values of 3 10 s m 1 in good agreement with laboratory measurements of mantle material below 2000 km the conductivity is poorly resolved however the best fitting models indicate a further increase in conductivity to values between 50 and 150 s m 1

river pattern discriminant method based on resistance parameter and activity indicators abstract a new river discriminant system is presented based on resistance law a parameter characterizing river morphology and indicators reflecting activity of bed and bank are derived they are defined as river morphology parameter and river activity indicators respectively by relating river morphology to river activity through a comprehensive resistance factor the discriminant curves characterizing river patterns namely resistance thresholds were derived which make it possible to calculate the activity of bed and bank by just a few easy obtaining hydraulic variables in addition the effect of riparian vegetation on riverbank strength is incorporated into this study the discriminant method proposed in this paper has proved to be applicable in distinguishing river patterns by selected data sets of the model and natural rivers and in improving the understanding of patterning process

factors controlling specific sediment yield in the upper indus river basin northern pakistan estimates of sediment yield are essential in water resources analysis modelling and engineering in investigations of continental denudation rates and in studies of drainage basin response to changes in climate and land use the availability of high resolution global environmental datasets offers an opportunity to examine the relationships between specific sediment yield sysp and drainage basin attributes in a geographical information system gis environment this study examines sysp at 14 long term gauging stations within the upper indus river basin twenty nine environmental variables were derived from global datasets the majority with a 1 1 km resolution the sysp ranges from 194 to 1302 t km 2 yr 1 for sub basins ranging from 567 to 212 447 km2 the high degree of scatter in sysp is greatly reduced when the stations are divided into three groups upper glacierized sub basins lower monsoon sub basins and the main indus river percentage snow ice cover lcs emerges as the single major land cover control for sysp in the high mountainous upper indus river basin a regression model with percentage snow ice cover lcs as the single independent variable explains 73 4 of the variance in sysp for the whole indus basin a combination of percentage snow ice cover lcs relief and climate variables explains 98 5 of the variance for the upper glacierized sub basins for the lower monsoon region a regression model with only mean annual precipitation p explains 99 4 of the variance along the main indus river a regression model including just basin relief r explains 92 4 of the variance in sysp based on the r2adj and p value statistics the variables used are capable of explaining the majority of variance in the upper indus river basin copyright 2007 john wiley sons ltd

accretionary lapilli associated with archaean banded iron formations of the kraaipan group amalia greenstone belt south africa abstract the kraaipan group in the amalia greenstone belt south africa consists of an archaean volcano sedimentary assemblage of mafic metavolcanic rocks and banded iron formations together with subordinate greywacke slate and carbonate rocks the sequence is deformed and intruded by a variety of granites and gneisses interlayered with the volcano sedimentary rocks in close proximity to a small gold prospect are pyroclastic rocks in which are described well developed coated or rim type accretionary lapilli of a variety hitherto rarely if ever recorded in association with oxide facies banded iron formations the accretionary lapilli are discussed in terms of their significance and as palaeoenvironmental indicators it is concluded that the accretionary lapilli probably developed in a proximal setting with respect to an ancient eruptive centre and that the lapilli themselves do not constitute exceptional indicators of sedimentary environments but are useful mainly as time or stratigraphic markers their association with banded iron formations suggests the accretionary lapilli here described were deposited from volcanic centres close to some shallow marine or barred lagoonal basin the latter possibly analogous to a playa lake complex developed in a primitive inter arc or back arc basin setting in existence during the evolution of the kraaipan volcano sedimentary assemblage found in the amalia greenstone belt

study of sedimentation zones in a large sand bed braided river an example from the hanjiang river of china abstract the concept of sedimentation zone is applied to the study of spatial and temporal variations of mid channel bars in the middle hanjiang river a large sand bed braided river in china the river channel can be divided into alternating sedimentation zones and transport zones the formation of which is basically controlled by local channel boundary conditions such as natural and artificial bank controls bedrock outcrops local hill spurs terraces artificial dikes and influence of tributaries a systematic comparison between sedimentation and transport zones is made in this study including the flow shear stress stream power mid channel bar features and channel stability the results obtained indicate that different channel boundary conditions in sedimentation and transport zones control channel width and width depth ratio which in turn control the reach s hydraulic and sediment transport characteristics the storage and removal of sediment in sedimentation zones correspond to the increase and decrease of the degree to which mid channel bars develop when the sediment input of the channel system is altered by reservoir construction the bed load sediment historically accumulated is released by clear water scour thus a macroscopic bed load wave forms and moves gradually downstream associated with this is the complex response phenomenon of mid channel bar evolution

sediment budget as affected by construction of a sequence of dams in the lower red river viet nam abstract dam construction is one of the main factors resulting in riverine sediment changes which in turn cause river degradation or aggradation downstream the main objective of this work is to examine the sediment budget affected by a sequence of dams constructed upstream in the lower reach of the red river the study is based on the longer term annual data 1960 2010 with a complementary daily water and sediment data set 2008 2010 the results showed that the stretch of the river changed from sediment surplus suggesting possible deposition processes into sediment deficit possible erosion processes after the first dam thac ba dam was constructed in 1972 and changed back to deposition after the second dam hoa binh dam was constructed in 1985 the annual sediment deposition varied between 1 9 mt y and 46 7 mt y with an annual mean value of 22 9 mt y 1985 2010 the sediment deposition at the lower reach of the red river would accelerate river aggradation which would change river channel capacity in the downstream of the red river the depositional processes could be sustained or changed back to erosional processes after more dams the amount of sediment deposit was much less after the latest two dams tuyen quang dam in 2009 and sonla dam in 2010 are constructed depending on the water and sediment dynamics this study revealed that the erosional and depositional processes could be shifted for the same stretch of river as affected by a sequence of dams and provides useful insights in river management in order to reduce flood frequency along the lower reach of the red river

relation between the erosion and sedimentation zones in the yellow river china sedimentation in the lower reaches of the yellow river is a major problem requiring implementation of large scale control measures in the upper and middle drainage basin for maximum benefit major sediment generation areas must be delimited for this purpose the upper and middle drainage basin of the yellow river has been divided into four major sediment and water source areas a series of databases of runoff and sediment yields from these source areas and for the corresponding quantities of sedimentation in the lower yellow river channel have been established on this basis a set of multiple regression equations has been established that define the relationships between sedimentation in the lower yellow river and the yearly or event based runoff and sediment yields from the four source areas or subsystems based on the regression equations obtained the contribution of the four major source areas to the sedimentation in the lower yellow river channel can be estimated the results obtained indicate that given other factors for each ton of sediment reduced from the coarse sediment producing area csa the sediment deposited in the lower yellow river would be reduced by 0 455 ton for each ton of sediment reduced from the fine sediment producing area fsa the sediment deposited in the lower yellow river would be reduced by 0 154 ton only therefore if limited erosion control measures are applied to the coarse sediment producing area the benefits for sedimentation reduction in the lower yellow river will be much larger than if similar resources are applied to the fine sediment producing area c 2002 elsevier science b v all rights reserved

electrical conductivities of pyrolitic mantle and morb materials up to the lowermost mantle conditions abstract the electrical conductivities of natural pyrolitic mantle and morb materials were measured at high pressure and temperature covering the entire lower mantle conditions up to 133 gpa and 2650 k in contrast to the previous laboratory based models our data demonstrate that the conductivity of pyrolite does not increase monotonically but varies dramatically with depth in the lower mantle it drops due to high spin to low spin transition of iron in both perovskite and ferropericlase in the mid lower mantle and increases sharply across the perovskite to post perovskite phase transition at the d layer we also found that the morb exhibits much higher conductivity than pyrolite the depth conductivity profile measured for pyrolite does not match the geomagnetic field data below about 1500 km depth possibly suggesting the existence of large quantities of subducted morb crust in the deep lower mantle the observations of geomagnetic jerks suggest that the electrical conductivity may be laterally heterogeneous in the lowermost mantle with high anomaly underneath africa and the pacific the same regions as large low shear wave velocity provinces such conductivity and shear wave speed anomalies are also possibly caused by the deep subduction and accumulation of dense morb crust above the core mantle boundary

macroforms large bedforms and rhythmic sedimentary sequences in subglacial eskers south central ontario implications for esker genesis and meltwater regime abstract eskers of south central ontario were deposited in closed subglacial conduits which were continuous main conduits this interpretation is supported by the intimate association of eskers with an anastomosing network of tunnel channels relatively continuous esker ridges minimal post formational disturbance of esker sediments intercalation of till and stratified sand and gravel diapiric folding at an esker core low variability in palaeocurrent direction and upslope flow paths down esker trends in clast lithology roundness and sphericity indicate continuous conduits with sediment supply by subglacial deformation of adjacent material into the conduits melt out of sediment from the conduit walls and fluvial resedimentation esker ridge morphology is attributed to synchronous erosion transportation and deposition along the main conduits such that ridge discontinuities are primarily explained as zones of non deposition during esker formation composite pseudoanticlinal and oblique accretion avalanche bed macroforms are identified gravel facies within these macroforms were deposited from fluidal flows or hyperconcentrated dispersions progradation of macroforms or migration of constituent large bedforms through the main conduits may have temporarily blocked constricted portions of those conduits and acted as possible internal autogenic controls on sediment availability and flow resistance the location of macroforms within conduits was primarily controlled by conduit geometry and sediment availability and later by feedback between macroform and conduit geometries sand and gravel units alternate rhythmically in vertical section rhythmicity is interpreted as a response to episodic flood flows controlled by seasonal changes in water supply but not necessarily representing annual events fans beads anabranched reaches and extended hummocky deposits are intimately associated with the main esker ridges they are interpreted in terms of subglacial cavities and localized flotation zones connected to the main conduits during flood events in phase wave structures are the products of hydraulic jumps in hyperconcentrated flood flows at flow expansions into swells within the main conduits into cavities connected to the main conduits or at a grounding line esker ridges record only the most powerful flood events whereas fans and beads record flow events in finer detail being primarily depositional reservoirs laterally fining deposits record the waning stages of conduit operation

archaeology of the anthropocene in the yellow river region china 8000 2000 cal bp although archaeological analysis emphasizes the importance of climatic events as a driver of historical processes we use a variety of environmental and archaeological data to show that human modif

the 1902 peleean deposits in the fort cemetery of st pierre martinique a model for the accumulation of turbulent nuees ardentes abstract the ancient fort cemetery located at the northwestern limit of st pierre has been left undisturbed since 1902 and therefore offers a unique opportunity to study the deposits of the eruptions that destroyed the city six eruption units were found overlying the floor of the cemetery leaving an average 1 6 m thick deposit the city was hit by four major nuees which occurred on may 8 20 june 6 and august 30 the may 20 and june 6 eruption units are each made of three beds the basal bed always lacks fines and is generally massive the middle bed is normally graded on which dune type cross bedding is superimposed in the may 20 deposit the upper bed the thinnest has the finest grain size of the eruption unit and is normally graded true parallel laminae were only observed in the upper bed the may 8 eruption unit is essentially made of fines depleted massive lapilli and tuff the evidence strongly suggests that the deposits of the middle and upper beds accumulated from turbulent suspensions the absence of structures in the basal bed is not conclusive evidence of laminar flow deposition and its characteristics are similar to deposits that have accumulated from highly concentrated turbulent suspensions the lack of fines observed only in the basal bed is attributed to gravity segregation helped by vaporization of water present in the underlying deposits and for the may 8 deposit to escaping gas produced by the destruction of the vegetation during or immediately after deposition which could explain the absence of primary structures in the basal bed the fine grained deposits of mt pelee show a primary structure sequence similar to the turbidite sequence and are therefore interpreted in terms of decreasing flow velocity and grain size with time at a fixed site

assessment of aeolian desertification trends from 1975 s to 2005 s in the watershed of the longyangxia reservoir in the upper reaches of china s yellow river abstract global climate change will affect the ecology and environment of the qinghai tibet plateau thus increasing attention is being paid to the aeolian desertification that is occurring in the watershed that supplies the longyangxia reservoir in the upper reaches of china s yellow river we must assess the aeolian desertification trends before developing a plan to restore the region s degraded eco environment in this study land suffered from aeolian desertification was classified into four levels slight moderate severe and extremely severe using a series of indices interpretation of landsat mss and tm data from 1975 s 1989 s and 2005 s was used to establish databases of aeolian desertified land at these three times we then derived the aeolian desertification trends during the study period by overlaying the consecutive databases and we analyzed the driving factors responsible for the observed aeolian desertification the results show a total of 1 721 478 02 ha of aeolian desertified land in 2005 s accounting for 13 of the region s total area from 1975 s to 1989 s the area of aeolian desertified land increased by 229 307 26 ha which represents a 15 increase compared to the 1975 s area and from 1989 s to 2005 s the area of aeolian desertified land decreased by 19 079 87 ha which represents a 1 decrease compared to the 1989 s area the main driving factors responsible for this increased aeolian desertification were climate factors high wind velocity and an increase in annual temperature combined with low precipitation and high evaporation as well as unsustainable human activities and inappropriate policy measures a series of key national projects initiated to combat degradation of the study area s eco environment led to a decrease of aeolian desertified land through obvious restoration of vegetation

meta analysis of holocene fluvial sedimentary archives a methodological primer this paper describes developments in the analysis and interpretation of holocene fluvial chronologies over the past 25 years particular consideration is given to meta analysis approaches pioneered by macklin and lewin 2003 using radiocarbon dated fluvial deposits in britain which have transformed fluvial geochronologies and correlations with climate and land use records worldwide during the last decade methodological developments have addressed issues such as correction for the shape of the radiocarbon calibration curve in the probability analysis of dated fluvial units and for variable alluvial unit preservation the number of regional database analyses of fluvial sedimentary archives has also expanded significantly during the past decade with studies now available for africa the mediterranean region india ireland new zealand poland the rhine catchment and the uk methods for incorporating optically stimulated luminescence ages in the probability analysis have also been developed and are illustrated using the database of eastern mediterranean dated fluvial deposits there is considerable potential for meta analysis research to inform long term flood risk assessment to evaluate short term climate and land use change impacts on flooding and river behaviour and to test landscape evolution models

a new indicator for dividing sedimentary rhythms in alluvial deposits a pollen based method abstract yellow river flooding has occurred many times near kaifeng city resulting in the formation of a relatively complete sedimentary sequence which provides a rare research carrier for exploring sedimentary rhythms in alluvium in this paper two 25 m long cores were respectively obtained from suburban jm core and urban sz core areas of kaifeng city china using detailed pollen data grain size and our previous studies we explore the effect of yellow river flood events on the characteristics of alluvial pollen assemblages through cluster analysis of the pollen assemblages and pollen concentrations we determined that there are 16 and at least 14 pollen zones subzones i e pollen rhythms in the jm core and sz core respectively to aid an objective analysis we define a comprehensive rhythm from three other indicators namely grain size black carbon and anthropogenic biological elements for the suburban jm core less disturbed by human activity each pollen rhythm has its corresponding comprehensive rhythm and the upper and lower boundaries are basically the same however the number of pollen rhythms is found to be greater than the number of comprehensive rhythms suggesting the precision of the pollen proxy is higher than the other three indicators similar phenomena were found in the sz core with significant human disturbance which also suggests that the pollen proxy is less susceptible to human disturbance and can accurately identify sedimentary rhythms furthermore the pollen concentration and its assemblage characteristics can indicate floods to some extent even small scale floods this is thought to be related to circumstances where some yellow river floods may have lasted for a long time during which time there were several relatively short flood intervals due to seasonal and flood path changes nevertheless pollen rhythms can also be identified consequently a pollen rhythm may not indicate a specific flood event

coarse grained nonmarine volcaniclastic sediment terminology and depositional process modern and ancient volcaniclastic sedimentary sequences contain depositional units whose features cannot be attributed to fully turbulent dilute stream flow or viscous debris flow the characteristics of these poorly sorted sediments suggest rapid deposition from high concentration dispersions but not en masse sedimentation thus appears related to high discharge flows intermediate in sediment water ratio between stream flow and debris flow the term hyperconcentrated flood flow is proposed for describing this intermediate condition hyperconcentrated flood flow deposits are distinguished from debris flow deposits by lack of matrix support or reverse grading and instead exhibit distribution normal grading and horizontal stratification these deposits are distinguished from normal dilute stream flow deposits by lack of cross stratification in sand facies and by very poor sorting poor imbrication and numerous clasts with long axes oriented parallel to flow direction in gravel facies the horizontal bedding that dominates sandy hyperconcentrated flood flow deposits consists of sediment too coarse grained and strata too thick to have been produced in the boundary layer of the upper flow regime and should not be confused with the more familiar thin graded laminae of fine to medium grained sand often associated with parting lineation hyperconcentrated flood flow deposits are not unique to volcanic settings they also occur in arid alluvial fan sequences debris flow and hyperconcentrated flood flow deposits however are much thicker and more extensive in volcanic regions than on alluvial fans because explosive volcanism leads to rapid mobilization of large volumes of sediment and water on a scale unparalleled in nonvolcanic settings in volcanic regions therefore these deposits have greater preservation potential show greater lateral variability and are more voluminous transformation of channelized debris flow to hyperconcentrated flood flow by dilution with stream water recently observed at mount st helens is recorded in ancient volcaniclastic sequences and may serve as the primary mechanism for generating hyperconcentrated flood flow

electronic conductivity of solid and liquid mg fe o computed from first principles ferropericlase mg fe o is an abundant mineral of earth s lower mantle and the liquid phase of the material was an important component of the early magma ocean using quantum mechanical finite temperature density functional theory calculations we compute the electronic component of the electrical and thermal conductivity of mg0 75 fe0 25 o crystal and liquid over a wide range of planetary conditions 0 200 gpa 2000 4000 k for the crystal and 0 300 gpa 4000 10 000 k for the liquid we find that the crystal and liquid are semi metallic over the entire range studied the crystal has an electrical conductivity exceeding 103 s m whereas that of the liquid exceeds 104 s m our results on the crystal are in reasonable agreement with experimental measurements of the electrical conductivity of ferropericlase once we account for the dependence of conductivity on iron content we find that a harzburgite dominated mantle with ferropericlase in combination with al free bridgmanite agrees well with electromagnetic sounding observations while a pyrolitic mantle with a ferric iron rich bridgmanite composition yields a lower mantle that is too conductive the electronic component of thermal conductivity of ferropericlase with xfe 0 19 is negligible 1 w m k the electrical conductivity of the crystal and liquid at conditions of the core mantle boundary are similar to each other 3 104 s m a crystalline or liquid ferropericlase rich layer of a few km thickness thus accounts for the high conductance that has been proposed to explain anomalies in earth s nutation the electrical conductivity of liquid ferropericlase exceeds that of liquid silica by more than an order of magnitude at conditions of a putative basal magma ocean thus strengthening arguments that the basal magma ocean could have produced an ancient dynamo

electrical conductivity as a constraint on lower mantle thermo chemical structure abstract electrical conductivity of the earth s mantle depends on both temperature and compositional parameters radial and lateral variations in conductivity are thus potentially a powerful means to investigate its thermo chemical structure here we use available electrical conductivity data for the major lower mantle minerals bridgmanite and ferropericlase to calculate 3d maps of lower mantle electrical conductivity for two possible models a purely thermal model and a thermo chemical model both models derive from probabilistic seismic tomography and the thermo chemical model includes in addition to temperature anomalies variations in volume fraction of bridgmanite and iron content the electrical conductivity maps predicted by these two models are clearly different compared to the purely thermal model the thermo chemical model leads to higher electrical conductivity by about a factor 2 5 and stronger lateral anomalies in the lowermost mantle 2000 2891 km the thermo chemical model results in a belt of high conductivity around the equator whose maximum value reaches 120 of the laterally averaged value and is located in the low shear wave velocity provinces imaged in tomographic models based on our electrical conductivity maps we computed electromagnetic response functions c responses and found again strong differences between the c responses for purely thermal and thermo chemical models at periods of 1 year and longer c responses based on thermal and thermo chemical models are easily distinguishable furthermore c responses for thermo chemical model vary geographically our results therefore show that long period 1 year and more variations of the magnetic field may provide key insights on the nature and structure of the deep mantle

scale effect on sediment yield from sloping surfaces to basins in hilly loess region on the loess plateau in china based on data from two runoff plots and ten stations in hilly loess region dalihe drainage basin ranging in area from 0 0006 to 3983 km2 on the loess plateau the relationship between mean annual specific sediment yield ys and drainage area a is studied which is different from those for many other drainage areas of the world neither at the scale of whole basin nor at local scale on the loess plateau with increasing drainage area the mean annual specific sediment yield experiences two peak values the first peak value appears at 0 00408 km2 in area corresponding to the whole slope surface and the second peak value appears at 96 1 km2 in area the non linear variation in the ys a can be explained as follows the first peak value can be explained by the abrupt increase in slope gradient and flow shear stress resulting in highly increased sediment concentration and specific sediment yield and the second peak value can be explained by the combined influence of flow shear stress and drainage density represented by dimensionless variable

anthropogenic origins of a late holocene basin wide unconformity in the middle reaches of the yellow river the luoyang basin henan province china we evaluate the relative importance of climate change fluvial dynamics and anthropogenic environmental modification in forming the holocene sedimentary record of the luoyang basin a tributary drainage basin of the yellow river located in western henan province china our 2011 fieldwork south of the erlitou site in the luoyang basin indicates that an unconformity dating to ca ad 1100 is roughly coincident with a major southward shift in the lower course of the yellow river in ad 1128 the governor of kaifeng breached the dikes of the yellow river to impede an advancing army causing the yellow river to flow south out to the yellow sea we argue that the dike breach not only changed the fluvial dynamics of the yellow river but also switched the rivers in the luoyang basin from an aggrading to an incising system the resumption of sedimentation in the luoyang basin is roughly coincident with the next major shift of the yellow river s main course northward to the bohai sea in ad 1855 the unconformity found in the luoyang basin may be a legacy of historically contingent human agency rather than climatic shifts or gradual environmental modification

reconstructing the suspended sediment load of the yellow river since 1470 ce using the drought and flood index abstract the yellow river of china is well known around the world for its large sediment yield and suspended sediment load ssl to better understand the cause of ssl variability we need long term perspectives that go back 100 1000 yr however few long term reconstructions have been published especially with high temporal resolution in this study we show that the drought and flood index idf based on historical document analysis can be used as a proxy to reconstruct the ssl the high flow season june october stream flow and the annual precipitation of the middle yellow river from 1470 1919 the calibration equation explains 57 6 of the variance in the ssl produced from the drainage area between the hekouzhen and longmen stations on the yellow river variation in the idf reflects the variation in the summer monsoon in china that causes the variation in water vapor transport precipitation and soil erosion these links explain the mechanism of reconstructing the ssl based on the idf the reconstructed 450 yr series shows that the ssl responds sensitively to el nino events the reconstructed ssl may be used as a baseline to assess the effects of human activity on the ssl for the period after 1970 and the reduction in ssl for the period 1971 2013 was estimated as 4 09 108 t yr accounting for 48 9 of the annual ssl induced by only climate

the geology of mount hasan stratovolcano central anatolia turkey mount hasan is a double peaked stratovolcano located in central anatolia turkey the magmas erupted from this multi caldera complex range from basalt to rhyolite but are dominated by andesite and dacite two terminal cones big mt hasan and small mt hasan culminate at 3253 m and 3069 m respectively there are four evolutionary stages in the history of the volcanic complex stage 1 kecikalesi volcano 13 ma stage 2 palaeovolcano 7 ma stage 3 mesovolcano and stage 4 neovolcano the eruptive products consist of lava flows lava domes and pyroclastic rocks the later include ignimbrites phreatomagmatic intrusive breccias and nuees ardentes sometimes reworked as lahars the total volume is estimated to be 354 km 3 the area extent 760 km 2 textural and mineralogical data suggest that both magma mixing and fractional crystallization were involved in the generation of the andesites and dacites the magmas erupted from the central volcanoes show a transition with time from tholeite to calc alkaline three generations of basaltic strombolian cones and lava flows were emplaced contemporaneously with the central volcanoes the corresponding lavas are alkaline with a sodic tendency

a multi index analysis of the extraordinary paleoflood events recorded by slackwater deposits in the yunxi reach of the upper hanjiang river china abstract paleoflood investigations were carried out on the first river terrace along the upper reaches of the hanjiang river a major tributary of the yangtze river in china several bedsets of paleoflood slackwater deposit swd were found within the eolian loess soil profiles in the yunxi reach of the upper hanjiang river the pedo stratigraphic sequences were studied using a multi index approach including magnetic susceptibility particle size distribution loess on ignition chemical elements and micro morphology both the sedimentary criteria and the analytical results show that the paleoflood swds were clearly differentiated from eolian loess and paleosol in the same profile by their abrupt vertical change in the pedo stratigraphy the studies indicate that these paleoflood swds were deposited from the suspended sediment load in floodwaters and hardly affected by the subsequent weathering and pedogenesis we have identified four episodes of extraordinary paleoflood events occurred on the hanjiang river during the last 18 000 years the paleoflood events were dated to 12 500 12 000 a b p 7500 7000 a b p 3100 3000 a b p and 1000 900 a b p respectively by using the osl method in combination with archeological dating of anthropogenic remnants and with pedo stratigraphic correlation with well dated profiles in the upper hanjiang river the flooding events are considered to respond to climate variability in relation with the monsoonal shift and coincide with the global climatic events recorded by other climatic proxies in different regions of the world this study is of great significance for understanding the interactions between hydro climatic systems and global change in sub humid regions

electrical conductivity model of al bearing bridgmanite with implications for the electrical structure of the earth s lower mantle electrical conductivity measurements of bridgmanite with various al contents and a constant mg of 90 were performed at temperatures ranging from room temperature up to 2000 k at pressures of 26 28 gpa in a kawai type multianvil apparatus by impedance spectroscopy analysis the incorporation of al into bridgmanite raises its electrical conductivity significantly but it is a small conductivity variation with respect to the quantity of al synchrotron mossbauer spectroscopy of recovered samples showed significant amounts of ferric iron in aluminous bridgmanite the mobility of the charge carriers in bridgmanite was calculated based on the conductivity and the fe3 fe ratio the relationship between the logarithm of the electrical conductivity and the reciprocal temperature is consistent with fe2 fe3 electron hopping small polarons as the dominant conduction mechanism at low temperatures 1600 k by taking various conduction mechanisms into account we develop an electrical conductivity model for aluminous bridgmanite as a function of the al and fe contents the small polaron conduction model indicates that the electrical conductivity of aluminous bridgmanite has a maximum at around 0 06 al atoms per formula unit and any further increase in the al content in bridgmanite reduces the conductivity in contrast the ionic conduction model indicates that the electrical conductivity simply increases with increasing al content the resulting conductivity of al bearing bridgmanite first increases up to 0 06 al atoms per formula unit and then remains constant or increases with increasing al content at higher temperatures the increase in conductivity observed in the uppermost part of the lower mantle by electromagnetic studies can be explained by the gradual decomposition of majorite garnet the deeper lower mantle conductivity would be controlled by small polaron conduction because of the large positive activation volume required for ionic conduction

lower mantle electrical conductivity based on measurements of al fe bearing perovskite under lower mantle conditions abstract laboratory measurements of the electrical conductivities of minerals provide important constraints on the chemistry and structure of the earth s interior we have measured the electrical conductivity of al fe bearing perovskite pv the most abundant lower mantle phase using a laser heated diamond anvil cell lhdac the sample with composition mg 0 83 fe 0 21 al 0 06 si 0 91 o 3 fe 3 fe ratio 0 4 was synthesized at 26 gpa and 2073 k using a multianvil press sample resistance was measured in situ at high pressure and high temperature up to 82 gpa and 2000 k respectively results show a continuous increase in electrical conductivity with increasing pressure in contrast to some previous studies of mg fe sio 3 perovskite and a pyrolite assemblage where a decrease in conductivity was observed at higher pressure our results suggest that 1 incorporation of aluminum in pv has a strong effect on its electrical conductivity and evolution with pressure 2 spin crossover of fe 3 does not occur or its effect on the conductivity is small in al fe bearing pv and 3 the contribution of ferropericlase to the electrical conductivity of pyrolite may be significant the electrical conductivity profile of the earth s lower mantle derived from geomagnetic data can be better explained by a pyrolitic bulk chemical composition rather than a non pyrolitic model such as one based solely on perovskite

sedimentary laminae in muddy inner continental shelf sediments of the east china sea formation and implications for geochronology abstract the sedimentary rhythm is well developed in the environment which is controlled by strong seasonal climate changing condition this rhythm is important for sediment core dating purpose in this study we examine muddy sediments on the inner continental shelf of the east china sea that are influenced under seasonal change of the east asian monsoon we use ensemble empirical mode decomposition eemd method to process sediment grain size and x radiograph negatives grayscale value data in three sediment cores from this area and use the results to analyze the patterns of sedimentary variability and the causes of cyclic variability of the sedimentary process the variability in the grain size and grayscale values of the core sediments has three components the high frequency variability low frequency variability and a secular trend among these components the high frequency component reflects variability on annual time scale can be well recognized we suggest that the annual variability is derived from seasonal variation in the sediment flux from the yangtze river to the sea as well as the east asian monsoon s impact on the sedimentary dynamics of the east china sea s inner continental shelf however the other variability is hard to identify which cycles there are this variability may reflect decadal winter monsoon oscillation and human activity of dam construction in the yangtze river each annual variability presents a varve in the sediment sequence which can be used to determine the sediment deposition rate and accurately date the core sediment we found that the average deposition rates of the three cores from north to south on the inner shelf were 3 1 cm yr 1 0 cm yr 0 9 cm yr indicating that the yangtze derived sediment decreased with the increasing distance from the yangtze estuary to the shelf the deposition rate of each core varies over time and the maximum deposition rate can be 3 5 times greater than the minimum rate the sediment ages obtained from varve chronology and radiometric dating are fairly consistent on a centennial scale differing only by 2 5 years thus varve counting is a useful supplementary approach to radiometric age dating for constructing chronologies for core sediment in shelf seas influenced by monsoons

venus a thick basal magma ocean may exist today basal magma oceans develop in earth and venus after accretion as their mantles solidify from the middle outwards fractional crystallization of the basal mantle is buffered by the core and radiogen