late holocene terrestrial glacial history of miki and i c jacobsen fjords east greenland we present a late holocene glacial and environmental history of three valleys within miki and i c jacobsen fjords east greenland 68 n the fjords have no direct connection with the main ice sheet and are presently glacierized by a series of local ice caps and glaciers little sediment has been deposited within the study area but bedrock is distinctly glacially striated which suggests that extensive valley glaciers reached the present coastline in the past moraines are the prominent morphological features including distinct end and lateral moraines most of the moraines are related to the existing glaciers in the area apparent moraines extend as far as 2 to 2 5 km in front of present day glaciers based on morphological and stratigraphical studies of the sediments in these valleys five glacier advances during the late holocene are implied stabilization of the oldest moraines is lichenometrically dated to c 1450 to 1650 years ago younger moraines in both miki and i c jacobsen fjords are lichenometrically dated to c 1050 1100 years ago c 750 950 years ago and c 600 700 years ago the youngest moraines containing measurable lichens stabilized c 300 400 years ago the timing of this moraine formation correlates to marine records from previous research on the inner part of miki fjord where apparent intensification in sediment stratification is related to a glacier advance into the fjord c 290 years ago this glacial advance may correlate to the little ice age cooling observed in many records from the north atlantic region our glacial record from miki and i c jacobsen fjords also shows good correlation with temperature proxies within the grip ice core in greenland and foraminifera records from nansen fjord east greenland less pronounced correlation is observed with the icelandic sea ice index and records of glacier fluctuation in iceland during the last 1000 years these results suggest that widespread climatic cooling was the direct cause of many of the late holocene glacier variations documented in this study although the glacial advance at c 1050 1100 years ago coincides with the so called medieval warm period and could reflect the response of glaciers to increased precipitation within the area

holocene glacier advances in the headwaters of sredniaya avacha kamchatka russia abstract holocene glacial deposits in sredniya avacha headwaters are subdivided into three age groups events a b and c based upon geomorphic features tephrochronology and lichenometry tephras of opala volcano 1400 1500 yr b p ksudach volcano 1700 1800 and 6000 yr b p and zavaritskiy volcano 2800 yr b p are used as stratigraphic markers rhizocarpon geographicum l dc and rhizocarpon section alpicola growth curves are established using tephrochronologically dated and historical surfaces the age of event a pre hypsitermal moraines is constrained by an age of 6000 yr b p for overlying ksudach 2 tephra and an age of 7200 lichenometric l yr b p event b neoglaciation had a multiple nature with the most prominent advances at 4300 3500 3300 2800 2600 2100 1800 1400 and 1300 1100 l yr b p the culmination occurred before 2800 yr b p as suggested by a date for zavaritskiy volcano tephra found on the glacial and outwash deposits less extensive glacier advances of event c little ice age occurred at 800 600 500 200 180 110 and 90 40 l yr b p the ela depression was 200 250 100 150 30 70 m during the culmination of events a b and c respectively

rapid flooding of the sunda shelf a late glacial sea level record the increase in sea level from the last glacial maximum has been derived from a siliciclastic system on the tectonically stable sunda shelf in southeast asia the time from 21 to 14 thousand calendar years before the present has been poorly covered in other records the record generally confirms sea level reconstructions from coral reefs the rise of sea level during meltwater pulse 1a was as much as 16 meters within 300 years 14 6 to 14 3 thousand years ago

shedding dynamics and mass exchange by dry granular waves flowing over erodible beds abstract a continuous exchange of particles between an erodible substrate and the granular flow above it occurs during almost all geophysical events involving granular material such as snow avalanches debris flows and pyroclastic flows the balance between eroded and deposited material can drastically influence the runout distance and duration of the flow in certain conditions a perfect balance between erosion and deposition may occur leading to the steady propagation of material in which the flow maintains its shape and velocity throughout it is shown experimentally how the erosion deposition process in dense flows of sand 160 200 m on an erodible bed of the same material produces steadily propagating avalanches that deposit subtle levees at their lateral extent moreover it is shown in this paper by using two colours of the same sand that although the avalanche is propagating at constant velocity and maintaining a constant shape the grains that are initially released are deposited along the flow path and that the avalanche will eventually be composed entirely of particles that are eroded from the bed different steady travelling wave regimes are obtained depending on the slope angle thickness of the erodible layer and the amount of material released outside of the range of parameters where steady travelling waves form the avalanches loose mass and decay if the initial amount of material released is too small or if the initial release is too large they re adjust to a steadily propagating regime by shedding material and breaking into smaller avalanches at its rear side numerical simulations are performed using a shallow water like avalanche model together with a friction law that captures the erosion deposition process in flowing to static regimes and a transport equation for the interface between layers of the two colours the characteristic behaviours observed in the experiments are qualitatively reproduced specifically the complex processes such as the exchange of particles leading to a change in colour of the avalanche and the formation of lateral levees are captured by the model finally a comparison is made with deposits in lunar craters which are interpreted as closely analogous to the deposits formed in our laboratory experiments

holocene to modern fine grained sedimentation on a macrotidal shoreface to inner shelf setting eastern bay of the seine france abstract this paper presents the results of an investigation on different timescales of the main mechanisms governing fine grained sedimentation on a macrotidal sandy shoreface to inner shelf setting with a supply of terrigenous sediment the subtidal area of the southeastern bay of the seine calvados coast france interpretation and calibration of side scan sonar imagery clearly shows that compact clays crop out in water depths of 3 6 m radiocarbon dating and palynological studies of the material sampled using long cores from this subtidal area show that these relict sediments constitute the infilling of lateral valleys of the palaeo seine during the last 10 000 years the lower parts of these deposits consist of compact clays that accumulated in a floodplain setting later a salt marsh environment and are succeeded by sediment with sand mud couplets which formed in a tidal estuarine system the top of this sequence has been truncated by a wave erosion surface formed during the holocene transgression today the sediment accumulating is composed of fine sand mixed with fine grained sediment and sometimes temporarily covered by fresh mud the more recent sedimentological data compared with surveys in the 1960s 1970s demonstrate both an increase in the erosion of the submerged earlier holocene clays and an increase in the mud silt clay content of the superficial sediments on a seasonal timescale the seafloor is affected by high frequency variations in the nature of the contemporary sedimentary cover spatial and temporal observations of the seafloor composition have been undertaken during different seasons for four years 1998 2001 to study these sedimentation events the sedimentation on the inner shelf is at its maximum when veneers of fresh mud occur after some particular hydrological periods i e sustained high river outputs following several dry years i e prolonged weak river flows when significant volumes of mud have been stored within the seine estuary such mud veneers result from 1 the direct supply of river born material 2 the seaward shifting of the turbidity maximum and 3 the resuspension of mud from the lower estuary i e fluid mud and intertidal flats under wind waves and have been termed estuarine flood deposits on a longer timescale of at least the last decades the southeastern bay of the seine is an area of erosion but it is subjected to ephemeral fine grained sedimentation on a seasonal timescale

flow of variably fluidized granular masses across three dimensional terrain 2 numerical predictions and experimental tests numerical solutions of the equations describing flow of variably fluidized coulomb mixtures predict key features of dry granular avalanches and water saturated debris flows measured in physical experiments these features include time dependent speeds depths and widths of flows as well as the geometry of resulting deposits three dimensional 3 d boundary surfaces strongly influence flow dynamics because transverse shearing and cross stream momentum transport occur where topography obstructs or redirects motion consequent energy dissipation can cause local deceleration and deposition even on steep slopes velocities of surge fronts and other discontinuities that develop as flows cross 3 d terrain are predicted accurately by using a riemann solution algorithm the algorithm employs a gravity wave speed that accounts for different intensities of lateral stress transfer in regions of extending and compressing flow and in regions with different degrees of fluidization field observations and experiments indicate that flows in which fluid plays a significant role typically have high friction margins with weaker interiors partly fluidized by pore pressure interaction of the strong perimeter and weak interior produces relatively steep sided flat topped deposits to simulate these effects we compute pore pressure distributions using an advection diffusion model with enhanced diffusivity near flow margins although challenges remain in evaluating pore pressure distributions in diverse geophysical flows riemann solutions of the depth averaged 3 d coulomb mixture equations provide a powerful tool for interpreting and predicting flow behavior they provide a means of modeling debris flows rock avalanches pyroclastic flows and related phenomena without invoking and calibrating rheological parameters that have questionable physical significance

a novel dynamic impact pressure model of debris flows and its application on reliability analysis of the rock mass surrounding tunnels abstract assessing the influence of the impact pressure exerted on surrounding rock mass by potential debris flows is one of the challenges in a mountain tunnel construction project this paper proposes an effective mathematical model for the assessment of impact pressure exerted by debris flows on obstacles the characteristics of the new model are analyzed and the parameters determination method for the new model are deduced also a new method for dynamic reliability analysis of the rock mass surrounding tunnels is proposed and is constituted into three key steps first by inputting impact pressure of debris flows generated by the aforementioned new model the flac3d is used as the dynamic analysis engine to obtain the time varying stress distribution of surrounding rock mass during the impact of debris flow second the factor of safety fos contours of surrounding rock mass are generated based on element states using the maximum tensile stress criterion and the mohr coulomb yield criterion third by using the time varying contours of the fos a failure probability and a reliability index are obtained from a reliability perspective a case study shows the complete analysis process and confirms the effectiveness of the above methodology in sum this paper provides new ideas new methods and a reference example for evaluating the influence of dynamic impact exerted by debris flows on the rock mass surrounding tunnels

high velocity ring shear tests on sand ring shear tests on sand materials have been carried out to show whether there is a change in the behaviour of these materials at high shearing rates and normal stresses this question is relevant to the problem of the mobility of large rock avalanches sturzstroms but is also of more general academic interest a ring shear apparatus of unusual although simple design has been constructed capable of achieving circumferential velocities of 2 m s at normal stresses of up to 200 kpa tests were carried out on two types of coarse sand wet or dry sand rock flour mixtures and polystyrene beads perfect frictional behaviour was observed in all the tests uninfluenced by either velocity or normal stress over the entire range of these variables change in frictional behaviour due to high rate of shearing therefore cannot be used to explain the high observed mobility of sturzstroms des essais de cisaillement circulaire par torsion ont ete effectes afin de decouvrir si un changement ait lieu dans le comportem

holocene glacial and climatic variations on spitsbergen svalbard holocene glacial and climatic variations have been inferred from investigations of sediment cores from the proglacial lake linnevatnet western spitsbergen a low content of glacially derived coal absence of regular laminations and a slow sedimentation rate in the lower part of the lacustrine sediments indicate that the former glaciers that existed within the catchment area during the last ice age melted quickly away as a result of the younger dryas holocene warming and during the next 6000 years there were no glaciers in the valley increasing coal content incipient laminations and rising sedimentation rates indicate that the glacier linnebreen started to form 4000 5000 years ago probably as a response to the late holocene cooling the holocene maximum extent of the glacier occurred during the little ice age starting with a pronounced ice advance in the thirteenth or fourteenth century a well dated core from billefjorden which is assumed to reflect glacial fluctuations in the inner part of the i

overrun length of avalanches overtopping catching dams cross comparison of small scale laboratory experiments and observations from full scale avalanches 1 results from small scale and full scale experiments on avalanche dam interactions are presented and compared these experiments were analyzed with respect to the overrun length i e the distance that the avalanche traveled beyond a catching dam the differences and similarities in the results are discussed through a cross comparison of the small scale experiments and by comparing them with observations from ryggfonn on avalanche dam interactions further we establish a simple relationship that appears to be valid for small scale experiments with granular materials as well as for full scale avalanche experiments the relationship relates the overrun length to the speed of the approaching avalanche and the effective height of the catching dam

a review on the provenance discrimination of sediments in the yellow sea the yellow sea has been extensively studied for the understanding of dispersal patterns and limits of sediments from neighboring countries including china and korea although sedimentological mineralogical and geochemical approaches have been tried to solve the problems especially including the identification of sediment sources in and around the yellow sea the published results are not enough for understanding them suggestions on sediment origins budgets sediment accumulation rates mineralogical and geochemical compositions are not coincident to each other and sometimes even controversial for example conflicts on the distribution patterns of smectite and calcium carbonate the provenance of the southeastern yellow sea mud and sedimentation rates in there the ratios of v al and mn al in korea and china river sediments the origin of ba and pb in sandy sediments of the northeastern yellow sea and so on various geochemical indicators from the literature for the provenance discrimination in the yellow sea are reviewed here in depth and corresponding discussions are described separately research topics for the future study also are suggested for the proper access to the understanding of the origin and dispersal patterns of the yellow sea sediments especially focusing on the geochemical approaches d 2003 elsevier science b v all rights reserved

the senegal river mud belt a high resolution archive of paleoclimatic change and coastal evolution abstract fine grained sediment depocenters on continental shelves are of increased scientific interest since they record environmental changes sensitively a north south elongated mud depocenter extends along the senegalese coast in mid shelf position shallow acoustic profiling was carried out to determine extent geometry and internal structures of this sedimentary body in addition four sediment cores were retrieved with the main aim to identify how paleoclimatic signals and coastal changes have controlled the formation of this mud depocenter a general paleoclimatic pattern in terms of fluvial input appears to be recorded in this depositional archive intervals characterized by high terrigenous input high sedimentation rates and fine grain sizes occur roughly contemporaneously in all cores and are interpreted as corresponding to intensified river discharge related to more humid conditions in the hinterland from 2750 to 1900 and from 1000 to 700 cal a bp wetter conditions are recorded off senegal an observation which is in accordance with other records from nw africa nevertheless the three employed proxies sedimentation rate grain size and elemental distribution do not always display consistent inter core patterns major differences between the individual core records are attributed to sediment remobilization which was linked to local hydrographic variations as well as reorganizations of the coastal system the senegal mud belt is a layered inhomogeneous sedimentary body deposited on an irregular erosive surface early holocene deceleration in the rate of the sea level rise could have enabled initial mud deposition on the shelf these favorable conditions for mud deposition occur coevally with a humid period over nw africa thus high river discharge sedimentation started preferentially in the northern areas of the mud belt during mid holocene a marine incursion led to the formation of an embayment afterwards sedimentation in the north was interrupted in association with a remarkable southward shift in the location of the active depocenter as it is reflected by the sedimentary architecture and confirmed by radiocarbon dates these sub recent shifts in depocenters location are caused by migrations of the senegal river mouth during late holocene times the weakening of river discharge allowed the longshore currents to build up a chain of beach barriers which have forced the river mouth to shift southwards

numerical modeling of self channeling granular flows and of their levee channel deposits when not laterally confined in valleys pyroclastic flows create their own channel along the slope by selecting a given flowing width furthermore the lobe shaped deposits display a very specific morphology with high parallel lateral levees a numerical model based on saint venant equations and the empirical variable friction coefficient proposed by pouliquen and forterre 2002 is used to simulate unconfined granular flow over an inclined plane with a constant supply numerical simulations successfully reproduce the self channeling of the granular lobe and the levee channel morphology in the deposits without having to take into account mixture concepts or polydispersity numerical simulations suggest that the quasi static shoulders bordering the flow are created behind the front of the granular material by the rotation of the velocity field due to the balance between gravity the two dimensional pressure gradient and friction for a simplified hydrostatic model competition between the decreasing friction coefficient and increasing surface gradient as the thickness decreases seems to play a key role in the dynamics of unconfined flows the description of the other disregarded components of the stress tensor would be expected to change the balance of forces the front s shape appears to be constant during propagation the width of the flowing channel and the velocity of the material within it are almost steady and uniform numerical results suggest that measurement of the width and thickness of the central channel morphology in deposits in the field provides an estimate of the velocity and thickness during emplacement citation mangeney a f bouchut n thomas j p vilotte and m o bristeau 2007 numerical modeling of self channeling granular flows and of their levee channel deposits

holocene development of the yellow river s subaqueous delta north yellow sea high resolution seismic profiles from the north yellow sea reveal a 20 40 m thick subaqueous clinoform delta that wraps around the eastern end of the shandong peninsula extending into the south yellow sea this complex sigmoidal oblique clinoform containing an estimated 400 km 3 of sediment overlies prominent relict transgressive surfaces the nearshore topset of the clinoform 50 m contain less than 1 m of holocene sediment with low sedimentation rates 1 mm year in contrast to other clinoforms the shandong clinoform appears to be a compound subaqueous deltaic system with what we interpret to be proximal and distal phases of clinoform development the underlying proximal sequence formed proximally between f11 and 9 2 ka in response to a temporary pause in the rapid postglacial sea level rise after the meltwater pulse 1b mwp 1b and increased discharge from the yellow river to the north yellow sea due to intensification of the summer monsoon a flooding surface appears to separate the proximal and distal phases corresponding to the next rapid sea level rise 9 5 9 2 ka bp mwp 1c since 9 2 ka bp an overlying distal sedimentary sequence has accumulated reflecting the backstepping and shifting river mouth westward to the gulf of bohai some inputs from coastal erosion and nearby small streams may be locally important along shore transport cross shelf advection and upwelling in the north yellow sea have reworked post lgm sediment and have helped maintain the morphology of the clinoform in the shandong mud wedge d 2004 elsevier b v all rights reserved

replicated proxy climate signals over the last 2000 yr from two distant uk peat bogs new evidence for regional palaeoclimate teleconnections ombrotrophic peat is an established source of proxy climate data but previous records have been produced by different methods and have been difficult to compare high resolution plant macrofossil analysis has been applied to a lowland raised bog at fallahogy northern ireland and a montane blanket bog moine mhor in the cairngorms scotland although the bogs are 300 km apart and differ floristically the results demonstrate parallel responses to climatic forcing especially that of the little ice age this approach provides a powerful tool for reconstructing proxy climate records wherever suitable peat deposits exist in contrast to the ocean and ice core records these proxies are from a terrestrial source and related to climate changes on land over most of the holocene

flux and fate of yangtze river sediment delivered to the east china sea numerous cores and dating show the yangtze river has accumulated about 1 16 x 10 12 t sediment in its delta plain and proximal subaqueous delta during holocene high resolution seismic profiling and coring in the southern east china sea during 2003 and 2004 cruises has revealed an elongated similar to 800 km distal subaqueous mud wedge extending from the yangtze river mouth southward off the zhejiang and fujian coasts into the taiwan strait overlying what appears to be a transgressive sand layer this distal clinoform thins offshore from similar to 40 in thickness between the 20 and 30 m water depth to 1 2 in between 60 and 90 m water depth corresponding to an across shelf distance of less than 100 km total volume of this distal mud wedge is about 4 5 x 10 11 m 3 equivalent to similar to 5 4 x 10 11 t of sediment most of the sediment in this mud wedge comes from the yangtze river with some input presumably coming from local smaller rivers thus the total yangtze derived sediments accumulated in its deltaic system and east china sea inner shelf have amounted to about 1 7 x 10 12 t preliminary analyses suggest this longshore and across shelf transported clinoform mainly formed in the past 7000 yrs after postglacial sea level reached its mid holocene highstand and after re intensification of the chinese longshore current system sedimentation accumulation apparently increased around 2000 yrs bp reflecting the evolution of the yangtze estuary and increased land erosion due to human activities such as fanning and deforestation the southward flowing china coastal current the northward flowing taiwan warm current and the kuroshio current appear to have played critical roles in transporting and trapping most of yangtze derived materials in the inner shelf and hence preventing the sediment escape into the deep ocean c 2006 elsevier b v all rights reserved

flow of variably fluidized granular masses across three dimensional terrain 1 coulomb mixture theory rock avalanches debris flows and related phenomena consist of grain fluid mixtures that move across three dimensional terrain in all these phenomena the same basic forces govern motion but differing mixture compositions initial conditions and boundary conditions yield varied dynamics and deposits to predict motion of diverse grain fluid masses from initiation to deposition we develop a depth averaged three dimensional mathematical model that accounts explicitly for solid and fluid phase forces and interactions model input consists of initial conditions path topography basal and internal friction angles of solid grains viscosity of pore fluid mixture density and a mixture diffusivity that controls pore pressure dissipation because these properties are constrained by independent measurements the model requires little or no calibration and yields readily testable predictions in the limit of vanishing coulomb friction due to persistent high fluid pressure the model equations describe motion of viscous floods and in the limit of vanishing fluid stress they describe one phase granular avalanches analysis of intermediate phenomena such as debris flows and pyroclastic flows requires use of the full mixture equations which can simulate interaction of high friction surge fronts with more fluid debris that follows special numerical methods described in the companion paper are necessary to solve the full equations but exact analytical solutions of simplified equations provide critical insight an analytical solution for translational motion of a coulomb mixture accelerating from rest and descending a uniform slope demonstrates that steady flow can occur only asymptotically a solution for the asymptotic limit of steady flow in a rectangular channel explains why shear may be concentrated in narrow marginal bands that border a plug of translating debris solutions for static equilibrium of source areas describe conditions of incipient slope instability and other static solutions show that nonuniform distributions of pore fluid pressure produce bluntly tapered vertical profiles at the margins of deposits simplified equations and solutions may apply in additional situations identified by a scaling analysis assessment of dimensionless scaling parameters also reveals that miniature laboratory experiments poorly simulate the dynamics of full scale flows in which fluid effects are significant therefore large geophysical flows can exhibit dynamics not evident at laboratory scales

past environmental and circulation changes in the south china sea input from the magnetic properties of deep sea sediments abstract the south china sea located at the transition between the pacific and the indian ocean receives every year mainly during the rain season enormous amounts of river sediments originating from the erosion weathering of rocks in the catchment basins at sea these sediments are carried by different water masses to their deposition site and they constitute a unique archive for past environmental studies in this region the magnetic fraction of deep sea sediments though forming a minority in volume provides incredibly valuable information for paleoceanographic reconstructions as long as its provenance and source to sink processes are well constrained after a brief description of the climatic sedimentological and oceanographic context of the south china sea scs a review of the information available so far in the literature about the magnetic properties of scs sediments is presented it shows a large variety of interpretations conclusions that finally results in a rather unclear picture because in such a context the characterization of the sediment at the source is critical the magnetic properties recently obtained from a set of samples from rivers and marine surface sediments are summarized to describe the present day situation they are then used to interpret paleorecords from a set of seven marine cores distributed from the southern to the northern basins at different water depths and all covering at least the last climatic cycle the results reported here for the first time suggest that the magnetic mineralogy remains rather stable in time on land and that its time and spatial distribution at sea is an interplay of changes in sea level and deep sea circulation during low sea level periods bottom deep sea circulation is weak and the deposited sediment originates from the proximal rivers on the contrary during high sea level the circulation is enhanced transporting more sediment most likely from taiwan and luzon to the northwestern part of the scs and also in smaller proportion to the southern basin where it mixes with the local river borne sediment by comparing the two longest records we observe that this pattern is repeated over the last 900 ka superimposed to the 100 kyr cyclicity we also observe a longer term evolution with a maximum in the bottom current strength around 500 ka coinciding with global changes in the deep ocean circulation and carbon cycle these new results based on a wide spectrum of magnetic properties of numerous marine sedimentary cores from the scs show that the magnetic fraction yields important insights into past changes of the sedimentary pathways in particular the dynamic of the deep sea circulation depending on the global climatic context

the sedimentary and tectonic evolution of the yinggehai song hong basin and the southern hainan margin south china sea implications for tibetan uplift and monsoon intensification 1 the yinggehai song hong basin is one of the world s largest pull apart basins lying along the trace of the red river fault zone in the south china sea south of hainan island this basin crosscuts the rifted margin of the northern south china sea in this paper we present for the first time a regional compilation of multichannel seismic reflection data from both the strike slip and rifted margins the basins started to open after similar to 45 ma especially after similar to 34 ma the yinggehai basin was folded and inverted in the middle miocene after 21 ma in the north and 14 ma in the south before rapidly subsiding again after similar to 5 ma because of continued tectonism this subsidence has caused shale diapirism especially driven by associated sedimentation in the late pliocene 2 6 2 0 ma extension along the adjacent south hainan margin shows preferential lower crustal extension suggestive of lower crustal flow increasing toward the continent ocean transition during breakup sediment supply is reconstructed to peak in the middle miocene then falls between 14 and 10 3 ma to reach a low in the late miocene however rates rose again in the pliocene pleistocene the red river sediment budget is incompatible with climate models that propose stronger monsoon rains starting at 8 ma or with large scale river capture away from the red river after similar to 10 ma both lines of evidence point to major uplift in the red river drainage being middle miocene or older the recent preindustrial red river carried much more sediment than the average pleistocene accumulation rate indicating modest sediment buffering onshore at least in recent geologic time

the butterfly delta system of qiongzhou strait morphology seismic stratigraphy and sedimentation abstract analysis of high resolution sub bottom profiles topographical data and sediment samples reveals that the tidal delta system of qiongzhou strait is morphologically a butterfly delta system consisting of western mouth tidal delta wmtd and eastern mouth tidal delta emtd wmtd covers an area of about 11 000 km 2 and is more than two times larger than emtd 4000 km 2 wmtd is fan shaped with a tributary branch extending southwards along hainan island while emtd is typically fan shaped seismic architectures of wmtd and emtd are both characterized by a thick progradational unit overlying a thin transgression unit both wmtd and emtd start to develop at about 8 7 cal ka bp when qiongzhou strait completely opened and have the same three sedimentary facies tidal delta top tidal delta slope and tidal delta toe the formation of wmtd and emtd is attributed to qiongzhou strait s hydrodynamic regime which is dominated by the strong east west reciprocal tidal currents and influenced by the year round westward mean flow modified by the wind driven seasonal currents

volume change of mccall glacier arctic alaska usa 1956 2003 a long history of research documents that mccall glacier arctic alaska usa continues to lose mass at a rate that is likely increasing with time we present a photo comparison 1958 2003 that visually documents these volume changes along with survey measurements that quantify these losses measurements of longitudinal profiles initially acquired from airborne laser altimetry and repeated by ground based surveys indicate that the areally averaged rate of thinning increased between 1956 93 and 1993 2002 from 0 35 0 07 m a 1 to 0 47 0 03 m a 1 respectively total volume loss was 8 3 107 1 7 107 m3 and 2 7 107 0 2 107 m3 all in water equivalent for these two time periods these profiles also indicate that a 1 km stretch of the mid ablation area is behaving differently from this trend with a rate of thinning that is not changing with time lastly we present a comparison of several methods for calculating volume change and assess their relative errors

erosion deposition waves in shallow granular free surface flows debris flows can spontaneously develop regular large amplitude surge waves that are interspersed by periods in which the channel fill is completely stationary these are important because each individual surge is much more destructive than a steady uniform flow with the same mass flux in this paper small scale experiments that exhibit similar behaviour are described the flow consists of carborundum particles that flow down a rough inclined chute covered with a static erodible layer of the same grains for inflow conditions close to the minimum depth required for steady uniform flows to exist small disturbances are unstable creating waves that rapidly coarsen and grow in size as the waves become sufficiently large the troughs between the wave crests drop below a critical thickness and come to rest a series of steadily travelling waves develop which erode the static layer of particles in front of them and deposit grains behind them to form a layer that is again stationary this is in turn re eroded and deposited by the next wave we term these waves granular erosion deposition waves although erosion and deposition problems are notoriously difficult a simple model is developed which uses a depth averaged version of the i rheology and pouliquen and forterre s extended friction law the viscous dissipation combines with dynamic intermediate and static friction regimes to generate finite length waves with static and mobile regions the existence of stationary layers fundamentally distinguishes erosion deposition waves from granular roll waves which form in slightly deeper flows and are always completely mobilized numerical simulations show that the system of equations is able to model both erosion deposition waves and granular roll waves moreover the computed wave amplitude wavespeed and coarsening dynamics are in good quantitative agreement with experiments

chronology of holocene glaciation central brooks range alaska the central brooks range was glacierized in the highest north facing cirques during late middle to late holocene neoglacial time this neoglaciation involved at least 5 major cirque glacier expansions of similar magnitude as based on lichenometric mapping of more than 50 glaciers and radiocarbon dates directly associated with 5 moraines initial stabilization of debris covered glaciers took place by early holocene time but evidently no moraines formed during this interval few morainal ridges are preserved that date from the older expansions but they have been lichenometrically dated 20 age reliability to 3 separate intervals 4400 3500 and 2900 yr b p twelve morainal complexes have ridges indicative of glacial advance that lichenometrically date at 1800 500 yr b p relict lichens that are now emerging undisturbed from beneath a receding glacier toe imply that this time was one of prolonged recession in at least some parts of the brooks range however radiocarbon analysis of dead moss at this same site dates a subsequent neoglacial advance across the cirque floor at 1120 180 yr b p our data suggest that for the past 1 100 yr cirque glaciers have been continuously in more extended positions than they are today during this glaciologically favorable interval the last two major advances occurred at 800 150 and 390 90 yr b p a d 1410 1600 glaciers across the central brooks range stayed close to their maxima until a d 1640 1750 historical photographs and lichenometry show that retreat was most rapid after a d 1870 and decelerated after the mid 1900s recession from this most recent neoglacial maximum has amounted to 150 700 m and continues at present the cirque glacier advances were accompanied by equilibrium line altitude ela depressions of 100 to 200 m below levels maintained in the late 1970s environmental lapse rate estimates and 1977 1981 glaciologic meteorologic measurements suggest that summer air temperatures accompanying neoglacial maxima were respectively 1 c or 3 to 4 c cooler than those of the late 1970s across the central brooks range the neoglacial maxima elas rise northeastward and northward from 2 to 5 m km 1

song hong red river delta evolution related to millennium scale holocene sea level changes abstract the song hong red river delta occurs on the northwest coast of the south china sea its evolution in response to holocene sea level changes was clarified on the basis of sedimentary facies and 14 radiocarbon dates from the 40 m long duy tien core from the delta plain and using previously reported geological geomorphological and archaeological data the delta prograded into the drowned valley as a result of early holocene inundation from 9 to 6 cal kyr bp as sea level rise decelerated the sea level highstand at 2 3 m from 6 to 4 cal kyr bp allowed widespread mangrove development on the delta plain and the formation of marine notches in the ha long bay and ninh binh areas during sea level lowering after 4 cal kyr bp the former delta plain emerged as a marine terrace and the delta changed into the present tide and wave influenced delta with accompanying beach ridges delta morphology depositional pattern and sedimentary facies are closely related to holocene sea level changes in particular falling sea level at 4 cal kyr bp had a major impact on the evolution of the song hong delta and is considered to be linked to climate changes

quaternary stratigraphy and trace element indices of the yangtze delta eastern china with special reference to marine transgressions the quaternary stratigraphy of the yangtze delta has been revealed by a deep 344 64 m continuous borehole the sediments of which are divided into four sections the early q1 middle q2 and late pleistocene q3 and the holocene q4 six lithofacies include lacustrine fluvial coastal drowned river channel deltaic and shallow marine in these time periods the fluvial and lacustrine lithofacies prevailed during q1and q2 coastal and drowned river channel lithofacies periodically appeared in q1 q2 and q3 shallow marine lithofacies dominated q3 and deltaic lithofacies occurred in q4 based on stratigraphy four transgressive events are inferred trace element sr ba b ga v content and ratios of sr ba and b ga are considered with regard to their distribution in the various lithofacies geochemical facies criteria are established based on combined diagnostic indices sr 160 ppm b 90 ppm sr ba 0 35 b ga 4 0 for the shallow marine lithofacies sr 90 ppm b 50 ppm sr ba 0 2 b ga 2 5 for the terrigenous lithofacies these indices correspond well to paleosalinity data obtained using the sedimentary phosphate method ca ca fe transgressive events identified by the geochemical indices are mostly the same as reflected by marine fossils nevertheless geochemical indices can indicate the occurrence of a weak transgression where marine fossils are rare

gravity driven granular free surface flow around a circular cylinder snow avalanches and other hazardous geophysical granular flows such as debris flows lahars and pyroclastic flows often impact on obstacles as they flow down a slope generating rapid changes in the flow height and velocity in their vicinity it is important to understand how a granular material flows around such obstacles to improve the design of deflecting and catching dams and to correctly interpret field observations in this paper small scale experiments and numerical simulations are used to investigate the supercritical gravity driven free surface flow of a granular avalanche around a circular cylinder our experiments show that a very sharp bow shock wave and a stagnation point are generated in front of the cylinder the shock standoff distance is accurately reproduced by shock capturing numerical simulations and is approximately equal to the reciprocal of the froude number consistent with previous approximate results for shallow water flows as the grains move around the cylinder the flow expands and the pressure gradients rapidly accelerate the particles up to supercritical speeds again the internal pressure is not strong enough to immediately push the grains into the space behind the cylinder and instead a grain free region or granular vacuum forms on the lee side for moderate upstream froude numbers and slope inclinations the granular vacuum closes up rapidly to form a triangular region but on steeper slopes both experiments and numerical simulations show that the pinch off distance moves far downstream

the mass balance of mccall glacier brooks range alaska u s a its regional relevance and implications for climate change in the arctic mccall glacier has the only long term mass balance record in arctic alaska average annual balances over the periods 1958 72 and 1972 93 were 15 and 33cm respectively recent annual balances 1993 96 are about 60 cm and the mass balance gradient has increased for an arctic glacier with its low mass exchange rate this marks a significant negative trend recently acquired elevation profiles of mccall glacier and ten other glaciers within a 30 km radius were compared with topographic maps made in 1956 or 1973 most of these glaciers had average annual mass balances between 25 and 33 cm while mccall glacier averaged 28 cm for 1956 93 indicating that it is representative of the region in contrast changes in terminus position for the different glaciers vary markedly thus mass balance trends in this region cannot be estimated from fractional length changes at time scales of a few decades we developed a simple degree day accumulation mass balance model for mccall glacier the model was tested using precipitation and radiosonde temperatures from weather stations at inuvik canada and barrow kaktovik and fairbanks alaska and was calibrated with the measured balances the inuvik data reproduce all measured mass balances of mccall glacier well and also reproduce the long term trend towards more negative balances data from the other stations do not produce satisfactory model results we speculate that the arctic front oriented east west in this region causes the differences in model results

mid holocene sea level highstand along the southeast coast of china various sea level curves have been proposed for the coast of china in the past two decades these sea level curves indicate a complex history of holocene sea level and so the debate on whether or not a higher mid holocene sea level highstand exists in the coast of china has continued this paper aims to re examine the holocene sea level history for the low latitude part of the china coast between 18 n and 32 n by re assessing all the sea level data available from the east to south coasts and separating them according to geological settings in order to examine the influences of global and local factors the reconstructed sea level histories from different coastal sectors of the china coast reveal a certain degree of variability in the timing and height of mid holocene sea level highstand within large river deltas the mid holocene sea level highstand occurred earlier by almost 1000 years than that from other coastal sites the highstand from large river deltas appears also lower in altitude a few metres below the present day sea level due probably to the local factors of subsidence and sediment consolidation in geologically stable coastal sites the highstand is recorded at the same altitude as the present day sea level a 1 2 m higher highstand is found from sites where tectonic uplift is observed

on the accuracy of lichenometric dates an assessment based on the little ice age moraine sequence of nigardsbreen southern norway families of lichenometric dating curves are constructed using four historically dated moraine ridges on the glacier foreland of nigardsbreen jostedalsbreen ice cap southern norway a further 20 little ice age moraine ridges are dated in terms of median predicted dates derived from the families of curves four approaches are used to assess the accuracy of the median predicted dates 1 the extent to which the dates form a temporal sequence 2 the extent to which they agree with local independent evidence of glacier variations 3 the extent to which dates agree when the moraine sequences on the two sides of the glacier foreland are dated separately and 4 the extent to which they agree when section rhizocarpon is differentiated from lichens of the rhizocarpon subgenus as a whole it is concluded that under conditions favourable for lichenometric dating median predicted dates have attained an accuracy of 10 on the little ice age timescale realistic error limits are considered to be of the o

the role of qiongzhou strait in the seasonal variation of the south china sea circulation an analysis of the water level and current data taken in qiongzhou strait in the south china sea scs over the last 37 years 1963 to 1999 was made to examine the characteristics of tidal waves and residual flow through the strait and their roles in the seasonal variation of the scs circulation the observations reveal that qiongzhou strait is an area where opposing tidal waves interact and a source of water transport to the gulf of beibu gulf of tonkin scs a year round westward mean flow with a maximum speed of 10 40 cm s 1 is found in qiongzhou strait this accounts for water transport of 0 2 0 4 sv and 0 1 0 2 sv into the gulf of beibu in winter spring and summer autumn respectively the outflow from qiongzhou strait may cause up to 44 of the gulf water to be refreshed each season suggesting that it has a significant impact on the seasonal circulation in the gulf of beibu this finding is in contrast to our current understanding that the seasonal circulation patterns in the south china sea are primarily driven by seasonal winds several numerical experiments were conducted to examine the physical mechanisms responsible for the formation of the westward mean flow in qiongzhou strait the model provides a reasonable simulation of semidiurnal and diurnal tidal waves in the strait and the predicted residual flow generally agrees with the observed mean flow an analysis of the momentum equations indicates that the strong westward flow is driven mainly by tidal rectification over variable bottom topography both observations and modeling suggest that the coastal physical processes associated with tidal rectification and buoyancy input must be taken into account when the mass balance of the scs circulation is investigated especially for the regional circulation in the gulf of beibu

deflecting dams and the formation of oblique shocks in snow avalanches at flateyri iceland snow avalanches are a threat in many populated mountainous regions and deflecting dams are often built to divert them away from people and infrastructure into less harmful areas when an avalanche is deflected by a dam or wedge it often generates rapid changes in the flow thickness and velocity which can be modeled as an oblique shock wave this paper reviews classical oblique shock theory which was originally developed for shallow water flows and uses it to make predictions of the maximum runup height on a deflecting dam the downstream flow velocity and the width of the channelized stream the theory is used to investigate field observations of snow avalanches at flateyri in iceland where a dam has deflected two avalanches away from the town and produced a channelized stream that flowed parallel to the dam the results indicate that there is no one single set of upstream flow conditions that parameterizes the flow behavior but the solution evolves as the avalanche propagates along the dam in response to the deceleration imposed by the slope fully time dependent shock capturing numerical simulations of the skollahvilft avalanche which hit the dam on 21 february 1999 are used to show how the channelized stream widens as the avalanche slows down and thickens toward the end of the runout zone the oblique shock relations nevertheless provide useful local order of magnitude estimates for the flow conditions immediately upstream of the shock

influence of the intertropical convergence zone on the east asian monsoon a palaeoclimate record spanning the past 16 000 years with nearly annual time resolution has been obtained from lake huguang maar in china the magnetic properties and titanium content of the lake sediments are thought to reflect changes in the east asian winter monsoon strength thus providing a complement to palaeoclimate archives that record the strength of the rain bearing summer monsoon the records point to an anti correlation between winter and summer monsoon strength best explained by migration of the intertropical convergence zone itcz a belt of low pressure air at the equator interestingly the decline of china s tang dynasty and the mayan civilization broadly coincide with drought periods recorded in lake huguang maar and cariaco basin sediments respectively did major shifts in the position of the itcz catalyse simultaneous events in civilizations on opposite sides of the pacific ocean the asian australian monsoon is an important component of the earth s climate system that influences the societal and economic activity of roughly half the world s population the past strength of the rain bearing east asian summer monsoon can be reconstructed with archives such as cave deposits1 2 3 but the winter monsoon has no such signature in the hydrological cycle and has thus proved difficult to reconstruct here we present high resolution records of the magnetic properties and the titanium content of the sediments of lake huguang maar in coastal southeast china over the past 16 000 years which we use as proxies for the strength of the winter monsoon winds we find evidence for stronger winter monsoon winds before the bolling allerod warming during the younger dryas episode and during the middle and late holocene when cave stalagmites suggest weaker summer monsoons1 2 3 we conclude that this anticorrelation is best explained by migrations in the intertropical convergence zone similar migrations of the intertropical convergence zone have been observed in central america for the period ad 700 to 900 refs 4 6 suggesting global climatic changes at that time from the coincidence in timing we suggest that these migrations in the tropical rain belt could have contributed to the declines of both the tang dynasty in china and the classic maya in central america

holocene climatic change in the alaskan arctic as inferred from oxygen isotope and lake sediment analyses at wahoo lake despite recent progress in understanding high latitude climate variability paleoclimate records are scarce from the alaskan arctic we conducted isotopic and sediment analyses at wahoo lake to infer holocene climate variability in northeastern alaska water 18o and d values from the lake and its inlet outlet streams suggest that winter precipitation dominates modern water inputs and that evaporation has limited influence on the lake s hydrological budget the isotopic composition of pisidium exhibits marked variations during the past 11 500 years with 18o ranging between 18 7 and 16 2 and 13c between 7 1 and 2 3 vienna pee dee belemnite vpdb elevated 18o and sediment composition from 11 5 to 8 9 kcal bp suggest evaporative 18o enrichment and arid conditions rising lake levels are evidenced by the disappearance of pisidium and a transition to low carbonate gyttja ca 6 3 kcal bp and by the onset of sediment deposition on an adjacent shelf by 5 3 kcal bp these changes coincided with

a 16 000 yr long sedimentary sequence from lakes peters and schrader neruokpuk lakes northeastern brooks range alaska sediments that accumulate in high latitude lakes serve as valuable environmental archives of changing conditions in a region currently undergoing rapid change a previously unexplored sedimentary sequence reaching back 16 000 years from lakes peters and schrader neruokpuk lakes in the northeastern brooks range 69 n alaska shows distinct changes in accumulation rates and biophysical properties including bulk density bd organic matter om content and grain size distribution at five widely distributed core sites the oldest sediments contain little om and accumulated rapidly as glaciers retreated around 15 ka om peaked between 12 and 10 ka along with northern hemisphere summer insolation bd increased and om decreased until around 5 ka possibly reflecting a decrease in river transported terrestrial om from 5 2 ka om consistently increased suggesting a rise in river discharge or a rise in summer temperatures which led to higher productivity or both after 2 ka sediments increased in bd and decreased in om suggesting glacier growth evidence for glacier expansion late during the little ice age is weak but increased sedimentation rates may reflect glacier retreat during the last century this study provides a framework for future paleoenvironmental research of a rare archive in a relatively pristine arctic setting

ten years of debris flow monitoring in the moscardo torrent italian alps abstract field data on debris flows are of utmost importance for improving knowledge of these hazardous phenomena and for the development of attenuation measures in alpine basins debris flows generally occur with a frequency high enough to create serious risk to human settlements and transportation routes but too low to justify monitoring activity capable of providing enough data in a sufficiently short time the moscardo torrent a small stream in the eastern italian alps is an exception to this general situation since it displays a high frequency of debris flows commonly at least one event per year in 1989 this torrent was instrumented and the results of the following 10 years 1989 1998 of debris flow monitoring are presented with an analysis of collected data the equipment installed allowed measurement of rainfall flow stage and ground vibrations caused by debris flows other important debris flow variables that is mean front velocity peak discharge and flowing volume were estimated from instrumental records video pictures have proved to be useful for the visual interpretation of debris flow waves and have made it possible to estimate the surface velocity of debris flows recorded data are compared with other experimental data sets collected and documented worldwide advantages and shortcomings of different types of sensors are discussed with relevance both for research monitoring purposes and for possible use in debris flow warning systems

holocene glacier fluctuations in alaska abstract this review summarizes forefield and lacustrine records of glacier fluctuations in alaska during the holocene following retreat from latest pleistocene advances valley glaciers with land based termini were in retracted positions during the early to middle holocene neoglaciation began in some areas by 4 0 ka and major advances were underway by 3 0 ka with perhaps two distinct early neoglacial expansions centered respectively on 3 3 2 9 and 2 2 2 0 ka tree ring cross dates of glacially killed trees at two termini in southern alaska show a major advance in the ad 550s 720s the subsequent little ice age lia expansion was underway in the ad 1180s 1320s and culminated with two advance phases respectively in the 1540s 1710s and in the 1810s 1880s the lia advance was the largest holocene expansion in southern alaska although older late holocene moraines are preserved on many forefields in northern and interior alaska tidewater glaciers around the rim of the gulf of alaska have made major advances throughout the holocene expansions were often asynchronous with neighboring termini and spanned both warm and cool intervals suggesting that non climatic factors were important in forcing these advances however climatic warming appears to have initiated most rapid iceberg calving retreats large glaciers terminating on the forelands around the gulf of alaska may have had tidewater termini early in the holocene but have progressively become isolated from the adjacent ocean by the accumulation and subaerial exposure of their own sediments

shock waves dead zones and particle free regions in rapid granular free surface flows shock waves dead zones and particle free regions form when a thin surface avalanche of granular material flows around an obstacle or over a change in the bed topography understanding and modelling these flows is of considerable practical interest for industrial processes as well as for the design of defences to protect buildings structures and people from snow avalanches debris flows and rockfalls these flow phenomena also yield useful constitutive information that can be used to improve existing avalanche models in this paper a simple hydraulic theory first suggested in the russian literature is generalized to model quasi two dimensional flows around obstacles exact and numerical solutions are then compared with laboratory experiments these indicate that the theory is adequate to quantitatively describe the formation of normal shocks oblique shocks dead zones and granular vacua such features are generated by the flow around a pyramidal obstacle which is typical of some of the defensive structures in use today

a late quaternary sedimentary shelf system under hyperarid conditions unravelling climatic oceanographic and sea level controls golfe d arguin mauritania nw africa abstract the sedimentation on the mauritanian shelf off the western saharan desert is strongly influenced by dust supply and is investigated in this study by combining surface mapping shallow acoustic profiling and the analysis of sediment cores coarse grained carbonates dominate wide areas of the open shelf at places where the shelf is exposed to the atlantic ocean the sheltered golfe d arguin in contrast is characterized by muddy shoals in its inner area and locally restricted and wedge shaped muddy depocenters which extend contour parallel in mid shelf settings in both cases cross shelf currents control sediment distribution and accumulation not location or amount of primary eolian input a major discontinuity on the outer shelf is located in 85 110 m water plus sediment depth and is refilled by a sedimentary facies succession of shoreface tidal and open shelf deposits this succession has formed during temporary lower sea levels along the last overall regression mis 4 and mis 3 the last glacial maximum and during the past deglacial sea level rise significant sediment deposition and preservation is limited to very restricted areas concerning the overall shelf architecture sea level was the main factor enabling or suppressing deposition in terms of 1 creating local erosional swales which have favored subsequent trapping and preservation of sediments 2 determining the type of sedimentary facies refilling these depressions under a variety of nearshore conditions 3 interacting with the seafloor morphology and by this controlling timing of initiation and growth geometry of mud wedges these mud wedges have formed since ca 9 cal ka under a continuous sedimentation regime these bodies must have formed in hydraulic equilibrium but they are detached from a defined sediment point source which is in contrast to common mudbelt formation on shelves in general sediment storage on shelves under hyperarid conditions seems to be very limited due to comparably low sediment input strong ravinement activity during changing sea levels significant bypassing and winnowing processes and a low preservation potential of the non cohesive materials these conditions lead to the development of almost sediment starved systems with low subsidence rates over longer geological timescales

reconstructing chemical weathering physical erosion and monsoon intensity since 25 ma in the northern south china sea a review of competing proxies reconstructing the changing strength of the east asian summer monsoon has been controversial because different proxies many being indirect measures of rainfall tell contrasting stories about how this has varied over long periods of geologic time here we present new sr isotope grain size and clastic flux data and synthesize existing proxies to reconstruct changing chemical erosion in the northern south china sea since the oligocene using the links between weathering rates and monsoon strength established in younger sediments as a way to infer intensity chemical proxies such as k rb l al and the chemical index of alteration cia together with clay proxies like kaolinite illite chlorite show a steady decline in alteration after a sharp fall following a maximum at the mid miocene climatic optimum mmco 15 5 17 2 ma probably as a result of cooling global temperatures in contrast physical erosion proxies including bulk ti ca and clastic mass accumulation rates mar show peaks at 21 23 ma similar to 19 ma and 15 5 17 2 ma implying faster run off in the absence of drainage capture rates increase again likely driven by slightly increased run off after 13 ma but decrease after 8 ma which is identified as a period of summer monsoon weakening sr isotope composition correlates with hematite goethite and the spectral proxy crat to show stronger weathering linked to more monsoonal seasonality these proxies argue for a strengthening of the east asian monsoon after 22 23 ma followed by an extended period of monsoon maximum between 18 and 10 ma then weakening there is some suggestion that the summer monsoon may have strengthened since 3 4 ma after reaching a minimum in the pliocene c 2014 elsevier b v all rights reserved

real time measurement and preliminary analysis of debris flow impact force at jiangjia ravine china impact forces associated with major debris flows jiangjia ravine china august 25 2004 were recorded in real time by a system consisting of three strain sensors installed at different flow depths this provides the first real time and long duration record of impact forces associated with debris flows a comprehensive approach including low pass filtering and moving average methods were used to preprocess the recorded signals the upper limit of impact frequency in the debris flows was estimated at 188 66 hz under the assumption that only coarse grains cause effective impact loadings thus a low pass filter with a 200 hz cut off frequency was needed to denoise the original data in order to extract the impact force then the moving average method was applied to separate long term and random components of the filtered data these were interpreted as respectively the fluid pressure and grain impact loading it was found that the peak grain impacts at different depths were non synchronous within the debris flows the impact loadings were far greater than and not proportional to the fluid pressures analysis of the impact force of 38 debris flow surges gives an empirical value for the ratio of the hydrodynamic pressure to the momentum flow density i e the product of debrisflow density and mean velocity square which provides a very valuable basis for understanding debris flow dynamics and designing debris flow management systems copyright c 2011 john wiley sons ltd

benthic foraminiferal evidence for the formation of the holocene mud belt and bathymetrical evolution in the central adriatic sea detailed analyses of modern and fossil benthic foraminiferal assemblages collected in the central adriatic sea are used as tools to reconstruct the environmental changes that occurred between the last deglaciation and the present last 14 kyrs in particular we focus on the timing and formation of the mud belt the modern benthic foraminiferal assemblages display a parallel zonation to the italian coast controlled by the interaction between food oxygen availability and water depth cluster analysis of 4 sediment cores separates the fossil foraminiferal assemblages in 6 groups cluster a is dominated by three ammonia species cluster b consists of ammonia papillosa nonionella turgida elphidium advenum and elphidium decipiens cluster c is composed of two taxa hyalinea balthica and trifarina angulosa cluster d is dominated by 5 species cibicides lobatulus buccella granulata reussella spinulosa textularia agglutinans and elphidium crispum cluster e contains bulimina spp gavelinopsis praegeri bolivina spp cassidulina neocarinata and asterigerinata mamilla and cluster f is dominated by bulimina marginata valvulineria bradyana globocassidulina subglobosa and melonis padanum the cluster analysis and contemporary distribution patterns of these taxa are used together with ecological preferences of the most frequent species to reconstruct the spatial and temporal distribution of the different biofacies in the past this reveals information about holocene palaeoenvironmental changes that are related to water depth fluctuations and the installment of the coast parallel mud belt the benthic assemblage records the transition from a infralitoral environment biofacies i to deeper marine condition biofacies iii after that the sea level reached about the modern level biofacies iv the benthic foraminiferal community evidences the development of the mud belt and the subsequent transformation of the ecological niches linked to the trophic evolution of the environment

introduction to the river dominated shelf sediments of the east asian seas peter d clift1 jan harff2 3 jiaxue wu4 yan qiu5 department of geology and geophysics louisiana state university baton rouge la 70803 usa university of szczecin institute of marine and coastal sciences mickiewicza 18 pl 70 383 szczecin poland leibniz institute for baltic sea research seestrasse 15 d 18119 rostock warnemunde germany centre of coastal ocean science and technology sun yat sen university guangzhou 510275 china guangzhou marine geological survey china geological survey guangzhou 510760 china

holocene delta plain development in the song hong red river delta vietnam abstract holocene delta plain development was investigated based on three sediment cores analyzed in detail from the song hong red river delta plain in vietnam two cores da and pd from the western delta plain showed both the landward limit of the transgressive estuarine system in the valley incised during the last glacial maximum and floodplain evolution since the middle holocene on the other hand a core tl from the eastern delta plain revealed a pleistocene terrace buried under the deltaic sediments and a slow accumulation rate compared with that in the west at 8 cal ky bp the shoreline migrated very close to the present hanoi city area and the sedimentary environment changed to tidal flat or salt marsh hanoi city marks the northern limit of shoreline transgression the mangrove swamp expanded from 8 to 5 cal ky bp to the landward limit of the delta plain subsequently the shoreline migrated seaward as a result of delta progradation and sea level lowering from 5 cal ky bp the emerged area evolved into a floodplain and natural levees formed along the abandoned river channels on the western delta plain but at 2 cal ky archeological sites indicate that the holocene terrace in the eastern delta plain was still inundated

experiments on the flow behaviour of granular materials at high velocity in an open channel a series of laboratory flume experiments has been conducted to investigate the flow behaviour of dry sand at high velocities the first incentive for this experimental programme was an attempt to explain the high mobility of apparently dry masses of rapidly moving broken rock during rock avalanches sturzstroms test velocities of over 5 m s and most other parameters of the tests were found to be dimensionally similar to those for a typical rock avalanche yet the conclusion was negative even the most rapid of the experiments indicated flow behaviour which is in conformity with the constant volume uniform coulomb friction relationship as applicable to slow shearing this conclusion was confirmed independently both by direct measurements of base friction and mean density of the flows and by detailed observations of flow uniformity acceleration and velocity profiles the surprising mobility of st umlrzstroms therefore requires a different explanation une serie de tests a canaux a ete entreprise dans le

maximum impact force of woody debris on floodplain structures we collided woody debris i e logs with structures using flume and test basin laboratory facilities to investigate the maximum impact force that floodplain structures are exposed to from floating woody debris the tests also investigated the influence of collision geometry determined by the debris orientation on impact on the maximum impact forces we reviewed the three approaches that represent the existing guidance for estimating maximum impact forces each approach estimates the maximum impact force based on the debris velocity and mass we show that all the existing approaches can be derived from a single degree of freedom model of the collision and can be considered to be equivalent the laboratory data show that the maximum impact force was associated with a log striking a rigid structure with its end oblique and eccentric collisions reduced the maximum impact load in a predictable and consistent manner the approach we refer to as contact stiffness a linear one degree of freedom model with no damping was able to reproduce the laboratory results over the entire range of data with an effective contact stiffness of 2 4 mn m

distribution of branched gdgts in surface sediments from the colville river alaska implications for the mbt cbt paleothermometer in arctic marine sediments significant climate fluctuations in the arctic over the recent past and additional predicted future temperature changes highlight the need for high resolution arctic paleoclimate records arctic coastal environments supplied with terrigenous sediment from arctic rivers have the potential to provide annual to subdecadal resolution records of climate variability over the last few millennia a potential tool for paleotemperature reconstructions in these marine sediments is the revised methylation index of branched tetraethers mbt cyclization ratio of branched tetraethers cbt proxy based on branched glycerol dialkyl glycerol tetraethers brgdgts in this study we examine the source of brgdgts in the colville river alaska and the adjacent simpson lagoon and reconstruct temperatures from simpson lagoon sediments to evaluate the applicability of this proxy in arctic estuarine environments the colville catchment soils fluvial sediments and estuarine sediments contain statistically similar brgdgt distributions indicating that the brgdgts throughout the system are soil derived with little alteration from in situ brgdgt production in the river or coastal waters temperatures reconstructed from the mbt cbt indices for surface samples show good agreement with regional summer june through september temperatures suggesting a seasonal bias in arctic temperature reconstructions from the colville system in addition we reconstruct paleotemperatures from an estuarine sediment core that spans the last 75 years revealing an overall warming trend in the twentieth century that is consistent with trends observed in regional instrumental records these results support the application of this brgdgt based paleotemperature proxy for subdecadal scale summer temperature reconstructions in arctic estuaries containing organic material derived from sediment laden episodic rivers

century scale solar variability and alaskan temperature change over the past millennium 1 correlation of geologic histories from 130 alaskan glaciers with a record of solar variation suggests that multi decadal to century scale temperature variations in the north pacific and arctic sectors have been influenced by solar forcing over the past thousand years mountain glacier fluctuations are primarily a record of summer cooling and the composite glacial history from three climatic regions across alaska shows ice expansions approximately every 200 years compatible with a solar mode of variability the modulating effects of the cold phases of the pacific decadal oscillation and the arctic oscillation may when in phase with decreased solar activity serve to amplify cooling forcing glacier advance

simulation of three dimensional rapid free surface granular flow past different types of obstructions using the sph method in nature when hazardous geophysical granular flows e g a snow avalanche impact on an obstacle as they stream down a slope rapid changes in flow depth direction and velocity will occur it is important to understand how granular material flows around such obstacles in order to enhance the design of defense structures in this study a three dimensional 3 d smoothed particle hydrodynamics sph model is developed to simulate granular flow past different types of obstacles the elastic perfectly plastic model with implementation of the mohr coulomb failure criterion is applied to simulate the material behavior which describes the stress states of soil in the plastic flow regime the model was validated by simulating the collapse of a 3 d column of sand with two different aspect ratios the results showed that the sph method is capable of simulating granular flow the model is then applied to simulate the gravity driven granular flow down an inclined surface obstructed by a group of columns with different spacing a circular cylinder and a tetrahedral wedge the numerical results are then compared with experimental results and two different numerical solutions the good agreements obtained from these comparisons demonstrate that the sph method may be a powerful method for simulating granular flow and can be extended to design protective structures

holocene glaciation of alaska and adjoining yukon territory canada abstract holocene glacial fluctuations between arctic central interior and southern maritime alaska are broadly synchronous this synchrony is evident from a review of work in 11 study areas with varying numbers of glaciers 3 100 glacier types subpolar cirque temperate valley tidewater surging and dating methodologies the pattern is temporally and spatially consistent with vegetation data and generally with climatic deteriorations culminating in the little ice age early holocene glacial advances are confirmed for 7 6 5 8 lichen ka bp at 4 of 97 glaciers in the brooks range advances also occurred by 5 85 and 5 7 ka bp at separate glacier tongues in the northern alaska range at least by 6 5 ka bp in lituya bay and possibly also in the malaspina and aleutian islands areas a sharp increase in glacier activity began by 4 4 ka bp in the arctic and glacier bay areas and by about 3 ka bp major glacier advances probably were initiated or well underway throughout alaska during holocene glacial maxima ice filled glacier and lituya bays as well as fjords of prince william sound and massive moraines buried forests in the northeastern st elias mountains area minor recession is recorded directly or implied in most of alaska about 2 ka bp or locally through the following millennium subsequently distinct but locally weak advances occurred by about 1 2 ka bp in most areas again followed by intervals of glacier recession most pervasive and ubiquitous were the little ice age advances initiated about 700 bp these generally culminated in two major advances between about 400 and 50 bp in the arctic those of a d 1600 dominated those of the late 1800s in the gulf of alaska those of the middle 1700s or late 1800s dominated large scale asynchronous advances and retreats of calving tidewater glaciers have been recorded during the twentieth century but most such movements are only indirectly related to climate

middle holocene to present sedimentary environment in the easternmost gulf of finland baltic sea and the birth of the neva river abstract the easternmost gulf of finland is the recipient of the neva river the largest river draining to the baltic sea the depositional history and endozoobenthic activity in the area have not been studied before based long sediment cores although such studies are desirable to provide a paleoenvironmental context for the recent environmental changes and the ecosystem projections for the future baltic sea two replicate long sediment cores from the easternmost gulf of finland record brackish water mud accumulation beginning at 5900 60 calendar years before present cal bp the brackish water muds are characterized by thin beds with erosional bases fining upward grain sizes and increasing upward organic contents a storm induced flow origin is inferred for the thin mud beds contrasting with previous interpretations that these muds accumulate by quiescent suspension settling the bed primary microstructures are overprinted by biodeformation and burrow mottling by incipient small planolites and arenicolites polykladichnus ichnofossils of the continental skolithos ichnofacies left behind by endobenthic oligochaetes and chironomid larvae the depositional succession is cut by a strong erosional hyperpycnal flow event at 3320 40 cal bp caused by the birth of the neva river which is now documented offshore for the first time mineral magnetic properties show pseudosingle domain magnetite as the main magnetic mineral present increased magnetic grain sizes and reduced loi values indicate a strong lithic influx immediately after the neva river birth the dominance of riverborne material in the accumulating sediments ever since highlights the strong influence of reworking in the shallow sea area increased diameters and the deeper penetration of biogenic sedimentary structures demonstrate improved seafloor oxygenation after the river birth during the medieval warm period ca 1000 700 cal bp and the last century increased sedimentary lithic contents and magnetic grain sizes indicate an elevated riverine influx due to increased precipitation and or the increased reworking of sediments by storms the results provide a paleoenvironmental context for the study area and deepen the understanding of storm induced sediment dispersal and the formation of sedimentary fabric in shallow wave dominated sea areas

quantitative analysis of debris torrent hazards for design of remedial measures debris torrents which are rapid flows of soil and organic debris down steep mountain channels are a major natural hazard in many parts of british columbia a series of recent occurrences along the

late holocene glaciation and twentieth century retreat northeastern brooks range alaska lichenometric dating of moraines deposited by eight glaciers in the northeastern brooks range suggests major glacial advances or stillstands at about 2600 1000 450 and 60 lichenometric l years bp the latter two advances of the early middle and latest part of the little ice age respectively formed promi nent moraines at all glaciers studied in response to overall twentieth century warming these glaciers have retreated at average rates of 2 to 19 m yr 1 from the distinct ridges formed in ad 1890 glacier thinning at rates of 0 7 to 0 9 m yr 1 accounts for over 90 of the ice loss

pyroclastic flows generated by gravitational instability of the 1996 97 lava dome of soufriere hills volcano montserrat numerous pyroclastic flows were produced during 1996 97 by collapse of the growing andesitic lava dome at soufriere hills volcano montserrat measured deposit volumes from these flows range from 0 2 to 9 106 m flows range from discrete single pulse events to sustained large scale dome collapse events flows entered the sea on the eastern and southern coasts depositing large fans of material at the coast small runout distance 1 km flows had average flow front velocities in the order of 3 10 m s while flow fronts of the larger runout distance flows up to 6 5 km advanced in the order of 15 30 m s many flows were locally highly erosive field relations show that development of the fine grained ash cloud surge component was enhanced during the larger sustained events periods of elevated pyroclastic flow productivity and sustained dome collapse events are linked to pulses of high magma extrusion rates

channelized free surface flow of cohesionless granular avalanches in a chute with shallow lateral curvature received 29 november 1997 and in revised form 15 february 1999 a series of laboratory experiments and numerical simulations have been performed to investigate the rapid fluid like flow of a nite mass of granular material down a chute with partial lateral connement the chute consists of a section inclined at 40 to the horizontal which is connected to a plane run out zone by a smooth transition the flow is conned on the inclined section by a shallow parabolic cross slope prole photogrammetric techniques have been used to determine the position of the evolving boundary during the flow and the free surface height of the stationary granular deposit in the run out zone the results of three experiments with dierent granular materials are presented and shown to be in very good agreement with numerical simulations based on the savage hutter theory for granular avalanches the basal topography over which the avalanche flows has a strong channelizing eect on the inclined section of the chute as the avalanche reaches the run out zone where the lateral connement ceases the head spreads out to give the avalanche a characteristic tadpole shape sharp gradients in the avalanche thickness and velocity began to develop at the interface between the nose and tail of the avalanche as it came to rest indicating that a shock wave develops close to the end of the experiments

floods in mountain environments a synthesis floods are a crucial agent of geomorphic change in the channels and valley floors of mountains watercourses at the same time they can be highly damaging to property infrastructure and life because of their high energy mountain watercourses are highly vulnerable to environmental changes affecting their catchments and channels many factors have modified and frequently still tend to modify the environmental conditions in mountain areas with impacts on geomorphic processes and the frequency magnitude and timing of floods in mountain watercourses the ongoing climate changes vary between regions but may affect floods in mountain areas in many ways in many mountain regions of europe widespread afforestation took place over the twentieth century considerably increasing the amounts of large wood delivered to the channels and the likelihood of jamming bridges at the same time deforestation continues in other mountain areas accelerating runoff and amplifying the magnitude and frequency of floods in foreland areas in many countries in channel gravel mining has been a common practice during recent decades the resultant deficit of bed material in the affected channels may suddenly manifest during flood events resulting in the failure of scoured bridges or catastrophic channel widening during the past century many rivers in mountain and foreland areas incised deeply the resultant loss of floodplain water storage has decreased attenuation of flood waves hence increasing flood hazard to downstream river reaches on the other hand a large amount of recent river restoration activities worldwide may provide examples of beneficial changes to flood risk attained as a result of increased channel storage or reestablished floodplain water storage relations between geomorphic processes and floods operate in both directions which means that changes in flood probability or the character of floods e g increased wood load may significantly modify the morphology of mountain rivers but morphological changes of rivers can also affect hydrological properties of floods and the associated risk for societies this paper provides a review of research in the field of floods in mountain environments and puts the papers of this special issue dedicated to the same topic into context it also provides insight into innovative studies methods or emerging aspects of the relations between environmental changes geomorphic processes and the occurrence of floods in mountain rivers

effects of flow regime and sensor geometry on snow avalanche impact pressure measurements impact pressures of snow avalanches have been measured at the vallee de la sionne experimental test site using two kinds of sensors with different sizes placed at different locations in the avalanche flow pressures measured for a fast dry snow avalanche and a slow wet snow avalanche are compared and discussed the pressures recorded in the dense flow of a dry snow avalanche agree well for the two types of sensors used showing negligible dependence on the measurement device on the other hand significantly different pressures are measured in the slow dense flow of a wet snow avalanche this is attributed to the slow drag and bulk flow of this type of avalanche leading to the formation and collapsing of force chain structures against the different surfaces of the sensors at a macroscopic scale limit state analysis can be used to explain such a mechanism by a shear failure occurring between freely flowing snow and a confined snow volume against the sensor according to a mohr coulomb failure criterion the proposed model explains how impact pressure can be up to 8 times higher than the hydrostatic snow pressure in wet cohesive slow avalanches and its dependence on sensor geometry

grain size segregation and levee formation in geophysical mass flows 1 data from large scale debris flow experiments are combined with modeling of particle size segregation to explain the formation of lateral levees enriched in coarse grains the experimental flows consisted of 10 m3 of water saturated sand and gravel which traveled 80 m down a steeply inclined flume before forming an elongated leveed deposit 10 m long on a nearly horizontal runout surface we measured the surface velocity field and observed the sequence of deposition by seeding tracers onto the flow surface and tracking them in video footage levees formed by progressive downslope accretion approximately 3 5 m behind the flow front which advanced steadily at 2 m s 1 during most of the runout segregation was measured by placing 600 coarse tracer pebbles on the bed which when entrained into the flow segregated upwards at 6 7 5 cm s 1 when excavated from the deposit these were distributed in a horseshoe shaped pattern that became increasingly elevated closer to the deposit termination although there was clear evidence for inverse grading during the flow transect sampling revealed that the resulting leveed deposit was strongly graded laterally with only weak vertical grading we construct an empirical three dimensional velocity field resembling the experimental observations and use this with a particle size segregation model to predict the segregation and transport of material through the flow we infer that coarse material segregates to the flow surface and is transported to the flow front by shear within the flow head coarse material is overridden then recirculates in spiral trajectories due to size segregation before being advected to the flow edges and deposited to form coarse particle enriched levees

distal mud deposits associated with the pearl river over the northwestern continental shelf of the south china sea abstract continental shelf mud deposits represent an important archive of the holocene earth history such deposits are usually associated with large rivers that transport a large quantity of suspended sediment the pearl river has formed a distal shore parallel holocene mud deposit on the northwestern continental shelf of the south china sea investigations into its spatial distribution and evolutionary history are necessary for an improved understanding of such sedimentary systems seabed sediment sampling in situ tidal cycle measurements seismic survey and the associated data analyses reveal that the distal mud deposit associated with the pearl river occupies an area of approximately 8 87 10 3 km 2 with a modern deposition rate of 1 27 to 5 66 mm yr 1 evidence from sediment balance environmentally sensitive components sediment transport processes and regional shelf circulation patterns indicates that the pearl river is a major sediment source for the mud deposit this distal mud deposit represents an initial stage of its development the fining upward pattern and the negative skewness values in the layer are indicative of the pearl river influence and the 210 pb age is younger than 10 2 yr the main body of the holocene deposit of the region is not related directly to the modern pearl river sediment for most of the holocene periods the pearl river has been trapping the sediment to fill its extensive estuarine waters and therefore the formation of the distal mud is a recent event a regional characteristic is that the timing of the formation of distal muds associated with large rivers depends on the estuarine morphological evolution and the quantity of sediment discharge

holocene paleoenvironmental implications of diatom and organic carbon records from the southeastern kara sea siberian margin diatom assemblages and organic carbon records from two sediment cores located within an estuarian bay of the inner kara sea trace changes in yenisei river runoff and postglacial depositional environments paleosalinity and sea ice reconstructions are based on modern relationships of local diatom assemblages and summer surface water salinity approximately 15 500 cal yr b p rivers and bogs characterized the study area when sea level reached the 38 to 40 m paleo isobath approximately 9300 cal yr b p the coring site was flooded from 9300 9100 cal yr b p estuarine conditions occurred proximal to the depocenter of fluvially derived material and salinity was 7 8 paleosalinity increased to 11 13 by 7500 cal yr b p following postglacial sea level rise and the southward shift of the siberian coast sharp decreases in diatom accumulation rates total sediment and organic carbon also occurred suggesting the presence of brackish conditions and greater distance between the coast and study site maximum paleosalinity up to 13 was recorded between 7500 and 6000 cal yr b p which was likely caused by the enhanced penetration of atlantic waters to the kara sea stepwise decreases to modern salinity levels happened over the last 6000 cal yr

holocene evolution of mud depocentres on a high energy low accumulation shelf nw iberia the high energy low accumulation nw iberian shelf features three confined holocene mud depocentres here we show that the evolution of such depocentres follows successive steps the flooding of inner shelf zones and river catchment areas by the late deglacial sea level rise provided the precondition for shelf mud deposition following this the holocene deceleration of the sea level rise caused a rapid refill of the accommodation space within river valleys subsequently the export of major amounts of fines was initiated the initial onset and loci of shelf mud deposition were related to deposition favouring conditions in mid shelf position or to the presence of morphological highs which act as sediment traps by providing protection against stronger hydrodynamic energy the detailed reconstruction of the holocene depocentre evolution shows for the first time that the expansion of such shelf mud deposits cannot only occur by linear growth off the associated sediment source rather they might develop around centres that are fully disconnected from the source of original sediment supply and expand later into specific directions based on these differences and on the connection of the individual mud depocentres to the material source we propose a conceptual subdivision of the group mid shelf mud depocentres

recent sedimentation and sediment accumulation rates of the ba lat prodelta red river vietnam abstract the ba lat river is the major distributary of the red river system in north vietnam to assess the recent to subrecent depositional processes in the ba lat prodelta a detailed sediment analysis was conducted bottom samples were collected during two field surveys one in the dry season winter and one in the wet season summer a steep frontal prodelta slope is characterized by very rapid sedimentation tens of cm per year of muddy sediments under influence of the turbid river plume beyond direct influence of the river plume the bottom slope decreases and bottom transport by the prevailing southward directed currents becomes important coarse grained tempestites alternate with the dominating muddy sediments downcore changes in the 234 th activities indicate that the subaqueous delta progrades to the southwest with erosion and reworking of older sediments occurring north of the present outlet the southwestward progradation is also encountered in the trend of 210 pb activities indicating that this process has continued for at least 100 years avulsion of the ba lat outlet in 1973 has led to a decrease in sedimentation rates north of the ba lat outlet

velocity and runout simulation of destructive debris flows and debris avalanches in pyroclastic deposits campania region italy the campanian apennines are characterized by the presence of monocline ridges mainly formed by limestone during the periods of volcanic activity of the somma vesuvius and phlegrean fields the ridges were mantled with pyroclastic materials in varying thickness the pyroclastics have been involved in destructive landslides both in historical time and in the recent past 1997 1998 1999 the landslides occur following intense and prolonged rainfalls in some cases landslides extended up to 4 km into the surrounding lowlands and reached towns causing severe destruction and over 200 deaths generally the landslides begin as small debris slides that develop into large shallow debris avalanches or debris flows involving pyroclastic horizons and colluvial soils 0 5 2 m thick on steep and vegetated slopes often at the heads of gullies during motion the landslide materials eroded vegetation and soils from the slope so that the moving material volume tended to increase then proceeding towards and beyond the base of the slopes the phenomena evolved into hyperconcentrated streamflow due to dilution by incorporating water the results of motion analyses are described an empirical rheological relationship was used including two principal terms that depend on the total normal stress and on the flow velocity on this basis the model has simulated the velocity and duration of debris avalanches and the distribution of the deposits the selected areas were those of sarno quindici and cervinara where a large amount of data is available both on the material properties and geomorphological setting it was found that the majority of the cases at the two sites can be simulated successfully with only one specific pair of rheologic parameters this provides the possibility for first order predictions to be made of the motion of future landslides such predictions will be a valuable tool for outlining potential hazard areas and designing remedial measures

flow of dense avalanches past obstructions one means of preventing areas from being hit by avalanches is to divert the flow by straight or curved walls or tetrahedral or cylindrical type structures thus there arises the question how a given avalanche flow is changed regarding the diverted flow depth and flow direction in this paper a report is given on laboratory experiments performed for gravity driven dense granular flows down an inclined plane obstructed by plane wall and tetrahedral wedge it was observed that these flows are accompanied by shocks induced by the presence of the obstacles these give rise to a transition from super to subcritical flow of the granular avalanche associated with depth and velocity changes it is demonstrated that with an appropriate shock capturing integration technique for the savage hutter theory the shock formation for a finite mass granular flow sliding from an inclined plane into a horizontal run out zone is well described as is the shock formation of the granular flow on either side of a tetrahedral protection structure

impact pressures and flow regimes in dense snow avalanches observed at the vallee de la sionne test site 1 a fundamental problem in avalanche engineering is to determine the impact pressures exerted on structures this task is complicated because snow avalanches flow in a variety of regimes primarily depending on snow temperature and moisture content in this paper we address this problem by analyzing measured impact pressures flow velocities and flow depths of five vallee de la sionne avalanches the measurements are made on a 20 m high tubular pylon instrumented with high frequency pressure transducers and optoelectronic velocity sensors in the observed avalanches we find both subcritical and supercritical flow regimes typical froude numbers were smaller than 6 the subcritical regime fr 1 is characterized by a flow plug riding above a highly sheared basal layer the measured pressures are large and velocity independent in contradiction to calculation procedures pressure fluctuations increase with flow depth indicating a kinematic stick slip phenomena which is largest at the basal layer supercritical flow regimes 1 fr 6 are characterized by a sheared flow all over the avalanche depth in this regime the impact pressure is velocity dependent we derive relationships governing impact pressure as a function of the froude number and therefore flow regime encompassing all the observed avalanches

acoustical facies analysis at the ba lat delta front red river delta north vietnam abstract a shallow penetrating high resolution acoustic study was performed in the ba lat delta the major distributary of the red river system in northern vietnam an acoustic facies map was constructed and the various facies types were validated through analysis of bottom sediments by a study of gravity cores collected at 22 stations analysis of the acoustic profiles and gravity cores revealed the presence of an asymmetrical s to sw prograding prodelta lobe in accordance with the prevailing longshore currents to the s the southern part of this prodelta is detached from the protruding ba lat delta front the prodelta is dominated by muddy sediments with minor thin

late pleistocene and holocene glaciation of the fish lake valley northeastern alaska range alaska we reconstructed a chronology of glaciation spanning from the late pleistocene through the late holocene for fish lake valley in the north eastern alaska range using 10 be surface exposure dating and lichenometry after it attained its maximum late wisconsin extent the fish lake valley glacier began to retreat ca 16 5 ka and then experienced a readvance or standstill at 11 6 0 3 ka evidence of the earliest holocene glacial activity in the valley is a moraine immediately in front of little ice age lia moraines and is dated to 3 3 3 0 ka a subsequent advance culminated at ca ad 610 900 and several lia moraine crests date to ad 1290 1640 1860 and 1910 our results indicate that 10 be dating from high elevation sites can be used to help constrain late holocene glacial histories in alaska even when other dating techniques are unavailable close agreement between 10 be and lichenometric ages reveal that 10 be ages on late holocene moraines may