the benguela current and associated upwelling on the southwest african margin a synthesis of the neogene quaternary sedimentary record at dsdp sites 362 and 532

geochronological evidence supporting antarctic deglaciation three million years ago the response of the antarctic ice sheets to increased global temperatures is an important unresolved issue in the assessment of future climate change in particular considerable controversy exists as to whether the east antarctic ice sheet suffered extensive deglaciation during the mid pliocene epoch 3 myr ago when temperatures were only slightly warmer than today although the ice sheet is widely assumed to have existed in something like its present form for the past 14 myr ref 1 marine diatoms eroded from the antarctic interior have been found in glacial till deposits high in the transantarctic mountains2 3 and have been bio stratigraphically dated at 3 myr before present this age has been disputed4 because it implies marine deposition in the antarctic interior and hence substantial deglaciation at a time when other evidence has been marshalled for the persistence of cold polar conditions4 here we report k ar and 40ar 39 ar ages for a volcanic ash bed in diatom bearing glaciomarine strata cored in ferrar fiord east antarctica by the ciros 2 drill hole5 which confirm the age of the diatoms at 3 myr and hence also confirm the mid pliocene deglaciation

lessons from ontake san a comparative analysis of debris avalanche dynamics abstract dynamic aspects of the long runout ontake san debris avalanche are evaluated by a comparison of several models an unsteady numerical model assumes two dimensional flow of an incompressible biviscous or newtonian fluid represented as a continuum with a free surface internal deformation of the flowing mass is considered as well as boundary resistances thus flow thinning and deposit shape as well as flow kinematics may be modeled parameters are adjusted to match observed runout with additional constraints on velocity and emplacement time with abundant constraints for ontake san from careful field investigations by japanese research teams our analysis indicates that a substantial decrease in flow resistance occurred as a function of displacement constant property models that match runout tend to overestimate the peak velocities and to underestimate the emplacement times a staged increase in mobility in both constant volume and variable volume models leads to results consistent with field data runout in a channel overflow area was also modeled qualitatively similar results have been obtained by other researchers using simple sliding block models with empirical parameters a slide block model with rational parameter selection a modified flood simulation and a multi element frictional slide model the relative merits of these models are compared the field mechanisms associated with this mobility increase with displacement are poorly understood but the question is now identified as a target for future research at debris avalanche sites and some plausible mechanisms are considered the main reason probably involves the entrainment of river water and saturated sediment leading to enhanced efficiency of fluid pressure mechanisms with undrained shear in addition progressive shearing reduced the mean particle size and angularity and the cohesion and friction and apparent viscosity of avalanche debris near the wetted perimeter hydroplaning the shearing of water films and slurries may have occurred locally

a quasi three dimensional spring deformable block model for runout analysis of rapid landslide motion assessment of landslide hazard often requires a good knowledge of the landslide characteristics to investigate the dynamic runout process of the landslide across a 3d terrain a quasi three dimensional model using spring deformable block model is proposed on the assumption that the motion of landslides is continuous and variable the sliding body is divided into lots of columns the model is based on a stability analysis of landslides and allows the deformation of sliding body considering the force and moment equilibrium of deformable columns and the principle of conservation of energy a quasi three dimensional sliding body is simplified by a series of deformable blocks with different dimensions then the sliding body acceleration velocity and displacement formulas are established accordingly correlating relatively well with the discrete element method the present results are satisfactory in describing the dynamic process of landslides and predicting the impact areas of the post failure sliding body finally the present model is applied to analyze the sliding time the maximum velocity and displacement of the sliding body of jiweishan landslide in wulong chongqing southern china when comparing with distinct element method the model shows generally good agreement with them

a model for the analysis of rapid landslide motion across three dimensional terrain a new numerical model for the dynamic analysis of rapid flow slides debris flows and avalanches has been developed the model is an extension of an earlier algorithm and is implemented using a nu

paleoclimatic changes in southern africa during the intensification of northern hemisphere glaciation evidence from odp leg 175 site 1085 abstract pliocene age sediments from ocean drilling program leg 175 site 1085 a and b in the cape basin were analyzed to investigate the impact of the intensification of northern hemisphere glaciation inhg on the south atlantic benguela current system from 4 to 2 ma proxies for productivity concentrations and mass accumulation rates of total organic carbon carbon to nitrogen ratios percent calcium carbonate and percent biogenic silica as well as weight percent sand a proxy for preservation or winnowing peak at 3 2 3 0 2 4 and 2 25 ma normative calculations of allied trace and major elemental determinations indicate synchronous increases in productivity peaks as well as high concentrations and accumulations of terrigenous sediments coeval increases in hemipelagic sedimentation and productivity indicators could be the result of enhanced eolian sedimentation resulting from strengthened winds leading to elevated rates of upwelling and enhanced productivity however rapid burial as indicated by high sedimentation rates could also enhance preservation the very high concentrations 30 and accumulations up to 60 g cm 2 kyr limit the likelihood that eolian sedimentation was the only transport mechanism invoking an additional fluvial source rapid burial by either eolian or fluvial transport links these intervals of enhanced preservation and productivity with continental climate changes resulting from 1 increased winds and or dust availability due to higher aridity in the namibia northern south africa region 2 lowered sea level related to increased ice volume 3 increased sediment load due to wetter conditions in the continental interior or 4 some combination peaks at 3 2 2 4 and 2 25 ma are coincident with maximum precession suggesting a link between hemipelagic sedimentation and enhanced monsoonal circulation over southern africa the site 1085 sedimentary record during the inhg seems to be controlled by low latitude processes linked to precession rather than hig latitude processes

recent geomorphologic evolution of a glaciovolcanic active stratovolcano popocatepetl mexico abstract the recent geomorphologic evolution of the statovolcano popocatepetl 19 03 n 98 35 w including the volcanic activity and the evolution of the glacier that still exists on the north face was assessed most of the data were obtained from references in historical sources and aerial photographs dating from 1945 this information was supplemented with data from fieldwork conducted between 1992 and 1995 landform typology shows volcanic and glacial interactions the conclusions affirm that a geomorphologic evolution of the volcano occurred since the maximum glacier advance in the little ice age lia and the formation of a proglacial ramp later fluvioglacial gorges cut into the ramp especially during the 1921 27 eruption once the glacier had shrunk to a small size and was left hanging above the steep slope the streams disappeared and the gorges filled with blocks that fell in snow and ice avalanches

the sensitivity of a volcanic flow model to digital elevation model accuracy experiments with digitised map contours and interferometric sar at ruapehu and taranaki volcanoes new zealand abstract a growing trend in the field of volcanic hazard assessment is the use of computer models of a variety of flows to predict potential areas of devastation these can be compared against historic and geologic evidence of past events for model calibration or used to construct hazard zone maps for mitigation and planning purposes the accuracy of these computer models depends on two factors the nature and veracity of the flow model itself and the accuracy of the topographic data set over which it is run all digital elevation models dems contain innate errors the nature of these depends on the accuracy of the original measurements of the terrain and on the method used to build the dem in this paper we investigate the effect that these errors have on the performance of a volcanic flow model designed to delineate areas at risk from lahar inundation the model was run over two dems of southern ruapehu volcano derived from 1 digitised 1 50 000 topographic maps and 2 airborne c band synthetic aperture radar sar interferometry obtained using the nasa airsar system on steep slopes of 4 or more drainage channels are more likely to be incised deeply and flow paths predicted by the model are generally in agreement for both dems despite the differing nature of the source data over shallow slopes

volcaniclastic debris flows at la fossa volcano vulcano island southern italy insights for erosion behaviour of loose pyroclastic material on steep slopes abstract this paper describes a qualitative model of erosion of loose volcaniclastic material on steep slopes of la fossa cone vulcano island italy that generates small volume debris flows the loose volcaniclastic cover rests on an almost impermeable substratum which comprises a fine grained hydromagmatic tuff morphologically three sectors were distinguished 1 a water supply zone slope 32 where rain water is enriched in mud and concentrated in the initiation zone 2 an initiation zone or source area sensu stricto slope with 30 where debris flows form and 3 a transport and deposition zone where debris flows deposited levees and terminal lobes slope 30 main episodes of erosion of loose volcaniclastic cover and debris flow generation occur in response to thunderstorms the erosion of tuff from superficial water added a significant amount of fines mud fraction to the initiating flows debris flow stoppage on steep slopes was interpreted as the result of a loss of mass estimated between 35 and 53 of total mass to form levees from field and laboratory data the density of debris flows was estimated at about 1950 kg m3 morphological data matrix texture mass number nm and clay content of debris flow deposits suggest that they were deposited by saturated granular slurries

modelling tailings dams and mine waste dumps failures this paper presents a depth integrated model that can be used to simulate the flowslides mudflows and debris flows that are caused by the failure of tailing dams mining waste dumps and other similar structures the sliding mass is first determined using a coupled elastoplastic finite element code and a suitable constitutive equation once failure has been triggered propagation of the mobilised material is analysed considering flow properties averaged over depth a simple law of pore pressure dissipation is postulated for cases in which the consolidation and propagation times are of the same order of magnitude

excess pore pressure and grain crushing of sands by means of undrained and naturally drained ring shear tests an investigation of excess pore pressure generation of a weathered granitic sand taken from the source area of a typical landslide caused as a result of liquefaction and a fine silica sand was conducted in which grain crushing within the shear zone of ring shear test specimens was examined as the key phenomenon of rapid long runout motion of landslides in order to investigate and explain the low average apparent friction angle mobilized in a liquidized landslide speed controlled ring shear tests were conducted under undrained conditions on weathered granitic sand specimens formed under a wide range of initial void ratios it was revealed that very small steady state shear resistances were obtained irrespective of the initial void ratios which can explain the low average apparent friction angle in addition two series of ring shear tests on weathered granitic and fine silica sands were conducted under naturally drained conditions by keeping the upper drain valve of the shear box open during the tests the first series of tests was performed under differing total normal stresses but at the same shear speed and the second series was conducted at differing shear speeds but under the same total normal stress in order to investigate and analyze excess pore pressure generation and dissipation within the shear zone that is associated with grain crushing permeability analyses were conducted by passing water through the sample box of the ring shear test apparatus before and after shearing in addition grain size distribution analyses of samples taken from the shear zone after shearing were carried out for the weathered granitic sand samples a significant change in bulk permeability and large amount of grain crushing were observed in these tests on the above soil a considerable reduction of shear resistance which increased proportionally to the total normal stress and shear speed were obtained it was observed that due to grain crushing finer grains that lowered the permeability of the soil in the shear zone were formed it is likely that the decrease in permeability facilitated the generation of high excess pore pressures by reducing the pore pressure dissipation rate from the shear zone thus flow behaviour was exhibited even under naturally drained conditions

evaluation of aster and srtm dem data for lahar modeling a case study on lahars from popocatepetl volcano mexico abstract lahars are among the most serious and far reaching volcanic hazards in regions with potential interactions of lahars with populated areas and human structures the assessment of the related hazards is crucial for undertaking appropriate mitigating actions and reduce the associated risks modeling of lahars has become an important tool in such assessments in particular where the geologic record of past events is insufficient mass flow modeling strongly relies on digital terrain data availability of digital elevation models dems however is often limited and thus an obstacle to lahar modeling remote sensing technology has now opened new perspectives in generating dems in this study we evaluate the feasibility of dems derived from the advanced spaceborne thermal emission and reflection radiometer aster and the shuttle radar topography mission srtm for lahar modeling on popocatepetl volcano mexico two gis based models are used for lahar modeling laharz and a flow routing based debris flow model modified single flow direction model msf both predicting areas potentially affected by lahars results of the lahar modeling show that both the aster and srtm dems are basically suitable for use with laharz and msf flow path prediction is found to be more reliable with srtm data though with a coarser spatial resolution errors of the aster dem affecting the prediction of flow paths due to the sensor geometry are associated with deeply incised gorges with north facing slopes laharz is more sensitive to errors of the aster dem than the msf model lahar modeling with the aster dem results in a more finely spaced predicted inundation area but does not add any significant information in comparison with the srtm dem lahars at popocatepetl are modeled with volumes of 1 10 5 to 8 10 6 m 3 based on ice melt scenarios of the glaciers on top of the volcano and data on recent and historical lahar events as regards recently observed lahars the travel distance of lahars of corresponding volume modeled with laharz falls short by 2 to 4 km an important finding is that the travel distance of potential lahar events modeled with laharz may differ by about 2 km when using srtm or aster data because of varying lateral flow volume distribution as a consequence verification and sensitivity analysis of the dem is fundamental to deriving hazard maps from predicted modeled inundation areas because of the global coverage of this type of remote sensing data the conclusion that both srtm and aster derived dems are feasible for lahar modeling opens a wide field of application in volcanic hazards studies

source and behavior of pyroclastic density currents generated by vulcanian style explosions of popocatepetl volcano mexico on 22 january 2001 abstract since 1994 popocatepetl volcano has extruded 85 lava domes each of which has been destroyed by vulcanian style explosions the paroxysmal vulcanian explosion of 22 january 2001 has been unique by generating multiple pyroclastic density currents pdcs scientists and civil protection authorities have used those pdcs to remap the high risk hazard zone of the volcano although little study has been carried out to understand the generation and evolution of those pdcs here we examine 38 stratigraphic sections and analyze the granulometry componentry vesicularity and petrology glass melt inclusions in plagioclase of collected samples to interpret the origins of the vulcanian explosions and the pdc behavior the 22 january event generated two series of dense pdcs that detached from the base of the eruption column the first set of pdcs traveled northwest across a glacier on the volcano partially scouring and melting the ice that hours later generated a lahar two pulses of these pdcs were confined within a large ravine surpassed the slope break and traveled up to 3 km away from the vent the deposits are matrix supported throughout their extent the second set of pdcs traveled to the northeast mainly as unconfined currents that split into two lobes prior to the slope break the farthest traveled current followed a western ravine and reached the forest 3 5 km from the summit the eastern lobe buried a local hiking hut and reached 2 1 km the deposits from these northeastern currents are massive and block supported all deposits volume of 5 71 105 m3 have finger like morphology with levees and frontal snouts all pdcs flowed as a dense basal granular current with turbulent upper clouds at minimum speeds of 7 10 m s in terms of hazards pdcs that interact with glaciers on the volcano are expected to travel farther and potentially generate extensive lahars at present small intermittent patches of glacier occur on the northern upper slopes of the volcano the components of the deposits are in order of abundance black scoria 53 62 wt sio2 banded scoria pumice 63 wt sio2 dome lithics 60 61 wt sio2 accidental lithics and free crystals juvenile pumice and scoria contain phenocrysts of plagioclase an47 10 clinopyroxene en48 3 orthopyroxene en64 1 ilmenite and titanomagnetite set in a rhyolitic glass pumice clast 74 39 wt sio2 or microlite rich matrix scoria clast the dome lithics also contain these phenocrysts as well as rare olivine phenocrysts fe2 fe2 mg 0 1 dissolved h2o co2 contents in melt inclusions hosted by pumice plagioclase phenocrysts suggest the felsic magma was stored at depths of 2 4 km thus the 2001 event was triggered by the injection of mafic magmas into a small volume of felsic magma probably forming dikes left from the previous eruptive episode we propose that the vulcanian explosions tap a column of magma 2 km depth equivalent to the volume that contained the felsic dikes this mechanism has been acting during the destruction of all summit domes of the ongoing eruption of the volcano

late pliocene climate in the southeast atlantic preliminary results from a multi disciplinary study of dsdp site 532 abstract site 532 on the walvis ridge was sampled at 4000 to 800 year intervals from 2 24 to 2 60 ma spanning the three large glacial advances of the late pliocene an age model was created by correlating the oxygen isotope record to site 607 with linear interpolations between tie lines the resultant age model differs from that in the site reports by more than 800 000 years due to misidentification of a magnetic boundary sedimentation rates varied by an order of magnitude at this site with minimum accumulation during glacial events interglacial intervals were charactrized by high marine production and high summer precipitation on land while glacials had very low production and arid continental climate during the large glacial events stages 96 100 conditions of low production and continental aridity reached their greatest intensity but there is no evidence of a permanent mode shift in either marine or terrestrial records calcite concentration has a strong variation at obliquity frequencies with maxima during interglacials but occasionally shows a large amplitude at precessional frequencies as well so that high concentrations occur in a few glacial intervals as a result color variation is not a reliable guide to glacial scale cycles at this site composition of the phytoplankton assemblage is diverse and highly variable and we have not been able to distinguish a clear indicator of upwelling related production spectral analysis reveals obliquity and precessional signals in the pollen data while several diatom records contain combination tones indicating that these data represent a complicated response to both local and high latitude forcing

southeast atlantic marine and terrestrial response to middle pliocene climate change abstract analysis of planktic foraminifers and pollen from deep sea drilling project site 532 located on the continental margin of southwest africa provides information on the link between pliocene paleoceanographic conditions and paleoenvironments of southwest africa increased upwelling at site 532 correlates with southward migration of onshore vegetation regions both terrestrial and marine changes can be explained by changes in the southern hemisphere surface temperature gradient which affected the paleo position of subtropical high pressure cells and productivity of water masses during the pliocene when the subtropical high pressure cells were further south southern ocean waters were warmer contained less sea ice southern ocean diatom productivity was high and nutrient depleted water upwelled off southwest africa when the subtropical high pressure cells were in a configuration similar to the present southern ocean waters were cooler and contained more sea ice the aerial extent of southern ocean diatom productivity was limited and nutrient rich waters upwelled off southwest africa as the benguela upwelling system migrated closer to the position of site 532

a dislocation model of strain accumulation and release at a subduction zone strain accumulation and release at a subduction zone are attributed to stick slip on the main thrust zone and steady aseismic slip on the remainder of the plate interface this process can be described as a superposition of steady state subduction and a repetitive cycle of slip on the main thrust zone consisting of steady normal slip at the plate convergence rate plus occasional thrust events that recover the accumulated normal slip because steady state subduction does not contribute to the deformation at the free surface deformation observed there is completely equivalent to that produced by the slip cycle alone the response to that slip is simply the response of a particular earth model to embedded dislocations for a purely elastic earth model the deformation cycle consists of a coseismic offset followed by a linear in time recovery to the initial value during the interval between earthquakes for an elastic viscoelastic earth model elastic lithosphere over a viscoelastic asthenosphere the postearthquake recovery is not linear in time records of local uplift as a function of time indicate that the long term postseimic recovery is approximately linear suggesting that elastic earth models are adequate to describe the deformation cycle however the deformation predicted for amore simple elastic half space earth does not reproduce the deformation observed along the subduction zones in japna at all well if stick slip is restricted to the main thrust zone as recognized earlier by shimazaki seno and kato the uplift profiles could be explained if stick slips were postulated to extend along the plate interface beyond the main thrust zone to a depth of perhaps 100 km but independent evidence suggests that stick slip at such depths if unlikely less

the 1963 vajont landslide a numerical investigation on the sliding surface heterogeneity the 1963 vajont landslide is a key case in landslide literature because it was catastrophic and because a lot of accurate data were collected before and after its occurrence in this paper the main focus is on the possible heterogeneity of the sliding surface involved by the landslide motion which is reflected by a heterogeneous distribution of the dynamic basal friction coefficient assuming a given zonation of the sliding surface our strategy was to apply a 2d lagrangian model to compute the landslide motion and to find the values of for each zone leading to the best agreement between the computed and the observed final deposit following some hints from the literature we have explored heterogeneous configurations composed of up to four different zones including also the homogeneous case by means of a 2d numerical model ubo block2 that handles the landslide as a mesh of blocks and runs quickly enough to allow the computation of tens of thousands of simulations in a reasonable computing time it is found that the four zone zonation produces the best fit or the least misfit which is a strong hint that the gliding surface involved different geotechnical units

a smoothed particle hydrodynamic automaton of landform degradation by overland flow abstract a novel model for calculating hillslope degradation by overland flow is based on a coupling of the cellular automaton and smoothed particle hydrodynamics theories simulated debris laden floods were initiated on digital elevation models dems the flows were created by solving equations for diffusion routing and erosion and deposition we separated advection and diffusion terms using operator splitting then solved the advection term via automaton and the diffusion term via smoothed particle hydrodynamics the technique was tested on geometrically simple synthetic slopes against data for erosion and deposition by debris laden flows in a gully developing on a scoria cone arizona and against data on a recent moderate sized debris laden flood generated by possible partial glacier melting at popocatepetl volcano mexico the flow and erosion deposition patterns on the simple synthetic slopes appear intuitively reasonable on the synthetic scoria cone slope the model reproduced some of the observed spatial patterns of event scale erosion and deposition reasonable flow speeds runup heights and runout lengths were produced for the debris laden flood at popocatepetl the coupled cellular automaton smoothed particle hydrodynamics technique represents some advance in the modeling of landform degradation and channel development by cellular automata ca use of the technique may aid our understanding of the link between hillslope scale and landform scale degradation patterns

linking desert evolution and coastal upwelling pliocene climate change in namibia a late pliocene high resolution pollen record from the southeast atlantic ocean drilling program site 1082 registers vegetation development in southwest africa the marine record is continuous ranges from 3 5 to 1 7 ma and has a millennial resolution between 2 9 and 1 9 ma changes in climate and vegetation correspond to the matuyama diatom maximum of the namibian upwelling system and seem to be highly susceptible to latitudinal shifts in the polar front zone of the southern ocean a northward advance of the polar fronts is connected with an increase in winter rainfall in southwest africa rapid desiccation in namibia at 2 2 ma is associated with increasing upwelling and decreasing sea surface temperatures along the coast

a new view for the geodynamics of ecuador implication in seismogenic source definition and seismic hazard assessment a new view of ecuador s complex geodynamics has been developed in the course of modeling seismic source zones for probabilistic seismic hazard analysis this study focuses on two aspects of the plates interaction at a continental scale a age related differences in rheology between farallon and nazca plates marked by the grijalva rifted margin and its inland projection as they subduct underneath central ecuador and b the rapidly changing convergence obliquity resulting from the convex shape of the south american northwestern continental margin both conditions satisfactorily explain several characteristics of the observed seismicity and of the interseismic coupling intermediate depth seismicity reveals a severe flexure in the farallon slab as it dips and contorts at depth originating the el puyo seismic cluster the two slabs position and geometry below continental ecuador also correlate with surface expressions observable in the local and regional geology and tectonics the interseismic coupling is weak and shallow south of the grijalva rifted margin and increases northward with a heterogeneous pattern locally associated to the carnegie ridge subduction high convergence obliquity is responsible for the north andean block northeastward movement along localized fault systems the cosanga and pallatanga fault segments of the north andean block south american boundary concentrate most of the seismic moment release in continental ecuador other inner block faults located along the western border of the inter andean depression also show a high rate of moderate size earthquake production finally a total of 19 seismic source zones were modeled in accordance with the proposed geodynamic and neotectonic scheme

gravity currents descending a ramp in a stratified tank this paper describes experiments and numerical simulations of a gravity current flowing down a ramp in a tank stratied in two layers we study the dynamics of the conguration for dierent densities of the gravity current and dierent ramp angles the experiments show that waves of large amplitude can be generated easily and that depending on the density of the gravity current the initial gravity current splits into a gravity current along the interface of the stratied layers and a gravity current along the bottom of the tank we also describe numerical simulations which give results in agreement with the results of the experiments and enable us to study three fluid congurations with wider ranges of density than is possible in the laboratory

persistent warmth across the benguela upwelling system during the pliocene epoch a feature of pliocene climate is the occurrence of permanent el nino like or el padre conditions in the pacific ocean from the analysis of sediment cores in the modern northern benguela upwelling we show that the mean oceanographic state off southwest africa during the warm pliocene epoch was also analogous to that of a persistent benguela el nino at present these events occur when massive southward flows of warm and nutrient poor waters extend along the coasts of angola and namibia with dramatic effects on regional marine ecosystems and rainfall we propose that the persistent warmth across the pliocene in the benguela upwelling ended synchronously with the narrowing of the indonesian seaway and the early intensification of the northern hemisphere glaciations around 3 0 3 5 ma the emergence of obliquity related cycles in the benguela sea surface temperatures sst after 3 ma highlights the development of strengthened links to high latitude orbital forcing the subsequent evolution of the benguela upwelling system was characterized by the progressive intensification of the meridional sst gradients and the emergence of the 100 ky cycle until the modern mean conditions were set at the end of the mid pleistocene transition around 0 6 ma these findings support the notion that the interplay of changes in the depth of the global thermocline atmospheric circulation and tectonics preconditioned the climate system for the end of the warm pliocene epoch and the subsequent intensification of the ice ages

some aspects of the initiation of debris avalanches in the campania region the role of morphological slope discontinuities and the development of failure abstract in may 1998 a prolonged period of rainfall caused disastrous landslides in the sarno quindici area campania southern italy the landslides initiated as small debris slides and developed into debris avalanches and debris flows involving the shallow pyroclastic deposits that lie on the steep vegetated slopes of this area in view of the potential for such events to occur again in this area an understanding of the initial failure mechanism is crucial if assessments are to be made of the hazard levels in this paper the results of detailed surveys of the morphological characteristics of the source areas are presented statistical analyses and parametrical relationships have been performed on key parameters demonstrating that the initial failures were associated with the presence of morphological discontinuities such as limestone scarps and road cuts notably the presence of man made cuts appears to have been responsible for about the 60 of the initial debris slides morphometric analysis has shown that the debris avalanches are characterised by a typical triangular shape statistical analyses have been used to try to relate the apex angles to relevant geomorphological parameters allowing for differences in local morphology the findings show some significant correlation

a sliding consolidation model for flow slides a model is proposed for the behaviour of flow slides in loose cohesionless materials in which the debris spreads out as a uniform sheet excess pore fluid pressures are assumed to be generated for example by undrained loading arising from the collapse of metastable structure in the source area of the flow slide under the influence of these the leading element of the debris moves downslope by basal sliding consolidating as it does so by single upward drainage as a result the pore pressure at the base of the element eventually decays to a value that brings the element to rest hence defining the run out of the flow slide the model is applicable in principle to subaqueous and subaerial flow slides and to pore fluids consisting of water gas or both of these the predictions of the model are tested against the observed behaviour and measured properties of the 1966 flow slide at aberfan south wales the results show that a sliding consolidation model provides a possible mechanism for that event

smoothed particle hydrodynamic modeling of volcanic debris flows application to huiloac gorge lahars popocatepetl volcano mexico abstract lahars are among the most catastrophic volcanic processes and the ability to model them is central to mitigating their effects several lahars recently generated by the popocatepetl volcano mexico moved downstream through the huiloac gorge towards the village of santiago xalitzintla the most dangerous was the 2001 lahar in which the destructive power of the debris flow was maintained throughout the extent of the flow identifying the zone of hazard can be based either on numerical or empirical models but a calibration and validation process is required to ensure hazard map quality the geoflow sph depth integrated numerical model used in this study to reproduce the 2001 lahar was derived from the velocity pressure version of the biot zienkiewicz model and was discretized using the smoothed particle hydrodynamics sph method the results of the calibrated sph model were validated by comparing the simulated deposit depth with the field depth measured at 16 cross sections distributed strategically along the gorge channel moreover the dependency of the results on topographic mesh resolution initial lahar mass shape and dimensions is also investigated the results indicate that to accurately reproduce the 2001 lahar flow dynamics the channel topography needed to be discretized using a mesh having a minimum 5 m resolution and an initial lahar mass shape that adopted the source area morphology field validation of the calibrated model showed that there was a satisfactory relationship between the simulated and field depths the error being less than 20 for 11 of the 16 cross sections this study demonstrates that the geoflow sph model was able to accurately reproduce the lahar path and the extent of the flow but also reproduced other parameters including flow velocity and deposit depth

a fluid dynamics approach to modelling the 18th march 2007 lahar at mt ruapehu new zealand lahars are water sediment mass flows from a volcanic source they can be triggered by a variety of mechanisms and span a continuum of flow rheology and hydraulic properties even within the same event lahars are extremely powerful landscaping agents and represent a considerable hazard potential however this highly dynamic character and a lack of direct measurements has made modelling lahars difficult this study therefore applies a fluid dynamics model delft3d to analyse the 18th march 2007 dam break lahar at mount ruapehu new zealand the modelled lahar routed through the whangaehu gorge in 30 min crossed the whangaehu fan in 60 min and then over a further 3 h travelled an additional 22 km distance along the whangaehu river to the tangiwai bridge the modelled mean frontal velocity was 6 5 m s 1 along the gorge although peak velocity reached up to 19 6 m s 1 the modelled lahar flow front progressively slowed across the fan but along the river it accelerated from 2 1 3 3 m s 1 calculated peak velocity along the river was 4 5 m s 1 these results generally compare well with gauged records with historical records and with other modelling approaches however discrepancies in frontal velocity and time to peak stage arise due to 1 specifying roughness which arises from slope variations between adjacent computational nodes and which is stage dependant and 2 due to rapid topographic changes that produce frequent hydraulic jumps which are inadequately accommodated in the numerical scheme the overall pattern of discharge attenuation and of relationships between topographic and hydraulic variables is similar to that calculated for lahars on other volcanoes this modelling method could be applied at other similar sites where a likely source hydrograph and high resolution topographic data are available these results have important implications for hazard management at ruapehu and for examining geomorphic and sedimentary impacts of this lahar

benefits of freeze drying sediments for the analysis of total chlorins and alkenone concentrations in marine sediments abstract long chain alkenones and photosynthetic pigment derivatives chlorins are commonly employed biomarkers in the reconstruction of past sea surface temperatures ssts and organic carbon export from the surface to the deep ocean for these studies marine sediment samples are often available which have been air dried or freeze dried given that these are common methods for removing water from sediments prior to microfossil analysis we compared both drying procedures by analysing samples from two sediment cores odp 1087 southeast atlantic and m36 2 mc435 north atlantic we found that significant losses of chlorins 25 and alkenones up to 75 occur with air drying relative to freeze drying changes in the composition of pigments are also likely the alkenone unsaturation index u 37 k is sensitive to the drying method showing an increase of up to 0 02 units relative to freeze drying however this represents a maximum increase in sst estimates of only 0 5 c the tests suggest that freeze dried samples rather than air dried sediments should preferably be used to determine the sedimentary concentration of biomarkers however if chlorins are the main target compounds wet extraction with acetone of sediment results in ca 12 higher yield than the extraction of freeze dried sediments with acetone water

glacier retreat during the recent eruptive period of popocatepetl volcano mexico popocatepetl 19802 n 98862 w 5424 m is one of the largest active stratovolcanoes in the transmexican volcanic belt a glacier located on the north side has undergone severe ablation since the volcano reinitiated eruptive activity in december 1994 in our study we calculate the extent of the glacier recession and the loss in glacial mass balance during the period of greatest laharic activity 1994 2002 using photogrammetric treatment of 20 pairs of aerial photographs the results indicate that from november 1997 to december 2002 the glacier released approximately 3 967 000 m 3 of water a period of intense glacier melting occurred from 4 november 2000 to 15 march 2001 during which time 717 000 m 3 of water was released much of the melting was attributed to the pyroclastic flow that took place on 22 january 2001 and produced a 14 2 km lahar with 68 000 m 3 of water among the many types of volcanic events pyroclastic flows were the most effective in causing sudden snowmelt although small explosions were also effective since they deposited incandescent material on the glacier the collapse of the plinian columns covered the glacier with pyroclasts and increased its volume the existence of control points for georeferencing and a knowledge of the topography underlying the glacier previous to the eruption would have provided more accurate and useful results for hazard prevention

alkenone and coccolith records of the mid pleistocene in the south east atlantic implications for the u37k index and south african climate abstract successful application of the alkenone palaeothermometer the u 37 k index relies upon the assumption that fossil alkenone synthesisers responded to growth temperature changes in a similar manner to the modern producers chiefly the coccolithophores emiliania huxleyi and gephyrocapsa oceanica we compare coccolith and u 37 k data from odp site 1087 in the south east atlantic between 1500 and 500 ka and show that evolutionary events and changes in species dominance within the coccolithophore populations had little impact on the u 37 k record the relative abundances of the c37 and c38 alkenones also closely resembled those found in modern populations and suggest a similar temperature sensitivity of u 37 k during the early and mid pleistocene to that found at present these results support the application of the u 37 k index to reconstruct sea surface temperatures ssts throughout the quaternary the u 37 k record at odp site 1087 contains an sst signal that documents the emergence of the 100 kyr cycles that characterise the late quaternary ice volume records this is preceded by significant cooling at odp site 1087 marked by a negative shift in ssts and a positive shift in the planktonic 18o some 250 kyr earlier at ca 1150 1000 ka this results in a permanent fall in average ssts of around 1 5 c the predicted increase in aridity onshore as a result of this cooling can be identified in a number of published records from southern africa and may have played a role in some important evolutionary events of the mid pleistocene

estimation of lahar flow velocity on popocatepetl volcano mexico during 1997 and 2001 two lahars took place in the tenenepanco and huiloac gorges on the northeastern sector of the popocatepetl volcano in mexico these lahars were the result of volcanic activity characterized by a pyroclastic fall and flow the lahars were triggered by the mass failures produced hours after the eruption the well known superelevation technique commonly used in this kind of study was applied to infer the lahar s mean velocity estimations show a broad flow velocity range of 1 3 13 8 m s depending on the following geomorphological parameters channel depth and slope peak discharge and distance from the initial source these results were compared with lahar velocities from mount st helens 1980 and nevado del ruiz 1985 which were obtained by the same superelevation technique according to the data the lahars from nevado del ruiz and popocatepetl were triggered by similar conditions while at mount st helens they were the result of the conversion of a pyroclastic surge cloud actually the mount st helens lahars were almost twice as fast as the ones at nevado del ruiz and popocatepetl this observation shows the importance of the lahars genesis in that the pyroclastic surge clouds produce faster lahars than do pyroclastic falls such results should be taken into account in lahar risk assessment studies for communities located near active volcanoes 2007 elsevier b v all rights reserved

evaluation of titan2d modelling forecasts for the 2007 crater lake break out lahar mt ruapehu new zealand abstract following the 1995 1996 eruptions of mt ruapehu the hazard of a dam breakout lahar was immediately recognised because an unstable 7 9 m pile of volcaniclastic ejecta had accumulated over the former stable outlet of the normally 10 106 m3 crater lake prior to the dam breakout lahar of 18 march 2007 a range of flow scenarios down the eastern flanks of mt ruapehu were simulated using the titan2d mass flow numerical code to forecast flow travel times and inundation areas titan2d is a depth averaged code that solves the movement of a granular or two phase mass over digital representations of natural terrains we compared modelled scenarios run before the 18 march 2007 break out lahar of ruapehu to details from the actual event the titan2d models were accurate in predicting both the inundation areas and travel times of the lahar at various key points down the volcano s flanks to 9 km beyond 9 km and a major break in slope the initial model parameters did not cope with the fundamental change that occurred in flow rheology velocity and discharge predicted at a lahar deflection structure the bund at 9 km from the lake were up to 20 less than those of the actual 2007 flow but matched closely those of the largest 1995 lahar at this location predicted paths of flow including sites of avulsion correlated well with those in the march 2007 event in addition the simulations predicted dynamic behaviour such as super elevation of flow in corners and hydraulic ponding that corresponds to real event measurements this application shows that the titan2d model can be used to reliably forecast certain parameters of lahar flow however care must be taken when choosing parameters and flow length scales over which the comparison should be made

lahar hazard assessment in the southern drainage system of cotopaxi volcano ecuador results from multiscale lahar simulations abstract the ice capped cotopaxi volcano is known worldwide for the large scale catastrophic lahars that have occurred in connection with historical explosive eruptions the most recent large scale lahar event occurred in 1877 when scoria flows partially melted ice and snow of the summit glacier generating debris flows that severely impacted all the river valleys originating from the volcano the 1877 lahars have been considered in the recent years as a maximum expected event to define the hazard associated to lahar generation at cotopaxi conversely recent field based studies have shown that such debris flows have occurred several times during the last 800 years of activity at cotopaxi and that the scale of lahars has been variable including events much larger than that of 1877 despite a rapid retreat of the summit ice cap over the past century in fact there are no data clearly suggesting that future events will be smaller than those observed in the deposits of the last 800 years of activity in addition geological field data prove that the lahar triggering mechanism also has to be considered as a key input parameter and under appropriate eruptive mechanisms a hazard scenario of a lahar with a volume 3 times larger than the 1877 event is likely in order to analyze the impact scenarios in the southern drainage system of the volcano simulations of inundation areas were performed with a semi empirical model laharz using input parameters including variable water volume results indicate that a lahar 3 times larger than the 1877 event would invade much wider areas than those flooded by the 1877 lahars along the southern valley system eventually impacting highly urbanized areas such as the city of latacunga

lahars initiated by the 13 november 1985 eruption of nevado del ruiz colombia the eruption of nevado del ruiz in colombia on 13 november 1985 was accompanied by the formation of four lahars mud flows triggered by the melting of glacial ice near the summit of the volcano the lahars began as flows of water sand and gravel but they incorporated clay by eroding the soil along the steep valleys through which they passed the largest flow was a cohesive debris flow more than 45 m deep and moving at 12 ms 1 when it debouched from the canyon of the rio lagunilla 2 5 km from armero where it killed 25 000 people the continuing volcanic activity and abundant remaining glacial ice create an extremely high risk of future destructive flows

geology and paleontology of late cenozoic marine deposits in the sacaco area peru paleontologic stratigraphic and geochronologic k ar evidence demonstrate the presence of both late miocene and pliocene marine deposits in the pisco formation in the area of sacaco peru tuffaceous sandstone siltstone and shelly sandstone comprise the greater part of the ca 350 meters sequence the fine grained sediments have accumulated in large coastal lagoons while coarser sediments were deposited in semiprotected littoral and nearshore environments a rich marine vertebrate fauna from the sacaco basin includes fossil selachians teleost fishes marine birds cetaceans marine carnivores and a single edentate species a diverse invertebrate fauna consists principally of venerid and muricid molluscs five vertebrate levels have been correlated with five provisionally defined molluscan zones the vertebrate fauna has some affinity with faunas of the miocene yorktown formation at the lee creek mine of north carolina usa distinctive miocene and pliocene molluscan assemblages of the pisco formation and pleistocene molluscan assemblages from overlying terrace deposits become progressively more similar to chilean assemblages of equivalent age and less similar to tethyan faunas of the panamic and caribbean regions

diatom constraints on the position of the antarctic polar front in the middle part of the pliocene abstract the relative percentages of diatom taxa in 5 deep sea cores dsdp 266 odp 699a odp 747a odp 751 a and eltanin core 50 28 from the southern ocean are determined for an interval centered on 3 1 to 2 9 ma in the middle part of the pliocene this climatically warm interval which is being studied by the prism project of the u s geological survey coincides with a proposed interval of major deglaciation of east antarctica the maximum southerly position of the antarctic polar front between 3 1 and 3 0 ma is inferred from these diatom studies the presence of calcareous nannofossils in the sediments and sedimentologic and micropaleontologic information from the literature it is suggested that the antarctic polar front may have migrated by as much as 6 of latitude further to the south in the southeastern atlantic and indian oceans during this pliocene warm interval but probably lay close to its present day position in the southwest atlantic and drake passage summer sea surface temperatures are inferred to have been no more than 3 4 c warmer than present at latitudes between 55 and 60 s

middle pliocene vegetation reconstructions paleoclimatic inferences and boundary conditions for climate modeling abstract the general characteristics of global vegetation during the middle pliocene warm period can be reconstructed from fossil pollen and plant megafossil data the largest differences between pliocene vegetation and that of today occurred at high latitudes in both hemispheres where warming was pronounced relative to today in the northern hemisphere coniferous forests lived in the modern tundra and polar desert regions whereas in the southern hemisphere southern beech apparently grew in coastal areas of antarctica pliocene middle latitude vegetation differed less although moister than modern conditions supported forest and woodland growth in some regions now covered by steppe or grassland pliocene tropical vegetation reflects essentially modem conditions in some regions and slightly cooler than or warmer than modern climates in other areas changes in topography induced by tectonics may be responsible for many of the climatic changes since the pliocene in both middle and lower latitudes however the overall latitudinal progression of climatic conditions on land parallels that seen in the reconstruction of middle pliocene sea surface temperatures pliocene paleovegetational data was employed to construct a 2 2 global grid of estimated mid pliocene vegetational cover for use as boundary conditions for numerical general circulation model simulations of middle pliocene climates continental outlines and topography were first modified to represent the pliocene landscape on the 2 2 grid a modern 1 1 vegetation grid was simplified and mapped on this pliocene grid and then modified following general geographic trends evident in the pliocene paleovegetation data set

late pliocene vegetation and climate in namibia southern africa derived from palynology of odp site 1082 the present day condition of bipolar glaciation characterized by rapid and large climate fluctuations began at the end of the pliocene with the intensification of the northern hemisphere continental glaciations the global cooling steps of the late pliocene have been documented in numerous studies of ocean drilling program odp sites from the northern hemisphere however the interactions between oceans and between land and ocean during these cooling steps are poorly known in particular data from the southern hemisphere are lacking therefore i investigated the pollen of odp site 1082 in the southeast atlantic ocean in order to obtain a high resolution record of vegetation change in namibia between 3 4 and 1 8 ma four phases of vegetation development are inferred that are connected to global climate change 1 before 3 ma extensive rather open grass rich savannahs with mopane trees existed in namibia but the extension of desert and semidesert vegetation was still restricted 2 increase of winter rainfall dependent renosterveld like vegetation occurred between 3 1 and 2 2 ma connected to strong advection of polar waters along the namibian coast and a northward shift of the polar front zone in the southern ocean 3 climatically induced fluctuations became stronger between 2 7 and 2 2 ma and semiarid areas extended during glacial periods probably as the result of an increased pole equator thermal gradient and consequently globally enhanced atmospheric circulation 4 aridification and climatic variability further increased after 2 2 ma when the polar front zone migrated southward and the influence of atlantic moisture brought by the westerlies to southern africa declined it is concluded that the positions of the frontal systems in the southern ocean which determine the locations of the high pressure cells over the south atlantic and the southern indian ocean have a strong influence on the climate of southern africa in contrast to the climate of northwest and central africa which is dominated by the saharan low pressure cell

geohazards of slope mass movement and its prevention in hong kong rapid urban development in hilly terrain coupled with tropical storms with heavy rainfall has led to the frequent occurrence of disastrous landslides in hong kong this paper outlines several case histories of such disastrous landslides in hong kong and the major efforts that have been made to mitigate landslide hazards in hong kong since the mid 1970s factors that contributed to such landslides and their causative mechanisms are analyzed methods of predicting the runout distance and lateral extent of rainfall induced slope failures are summarized slope maintenance requirements and stabilization measures are delineated including the stabilization of loose fill slopes

evaluation of approaches to calculate debris flow parameters for hazard assessment abstract many different runout prediction methods can be applied to estimate the mobility of future debris flows during hazard assessment the present article reviews the empirical analytical simple flow routing and numerical techniques all these techniques were applied to back calculate a debris flow which occurred in 1982 at la guingueta catchment in the eastern pyrenees a sensitivity analysis of input parameters was carried out while special attention was paid to the influence of rheological parameters we used the voellmy fluid rheology for our analytical and numerical modelling since this flow resistance law coincided best with field observations the simulation results indicated that the basal friction coefficients rather affect the runout distance while the turbulence terms mainly influence flow velocity a comparison of the velocity computed on the fan showed that the analytical model calculated values similar to the numerical ones the values of our rheological parameters calibrated at la guingueta agree with data back calculated for other debris flows empirical relationships represent another method to estimate total runout distance the results confirmed that they contain an important uncertainty and they are strictly valid only for the conditions which were the basis for their development with regards to the simple flow routing algorithm this methods could satisfactorily simulate the total area affected by the 1982 debris flow but it was not able to directly calculate total runout distance and velocity finally a suggestion on how different runout prediction methods can be applied to generate debris flow hazard maps is presented taking into account the definition of hazard and intensity the best choice would be to divide the resulting hazard maps into two types final hazard maps and preliminary hazard maps only the use of numerical models provided final hazard maps because they could incorporate different event magnitudes and they supplied output values for intensity calculation in contrast empirical relationships and flow routing algorithms or a combination of both could be applied to create preliminary hazard maps the present study only focussed on runout prediction methods other necessary tasks to complete the hazard assessment can be looked up in the guidelines for landslide susceptibility hazard and risk zoning included in this special issue

high eustatic sea level during the middle pliocene evidence from the southeastern u s atlantic coastal plain the middle pliocene approximately 3 5 2 5 ma was a period of global warmth preceding the growth of major northern hemisphere ice sheets the authors report on eustatic sea level for the middle pliocene based on microspaleontologic study of marine deposits of the duplin formation of south carolina and north carolina the duplin was deposited during a middle pliocene marine transgression that formed the orangeburg scarp a prominent wave cut geomorphic paleoshoreline of the southeastern u s atlantic coastal plain they concluded that 1 the scarp in south carolina was formed mostly during the middle pliocene 3 5 3 0 ma 2 eustatic sea level was about 35 plus minus 18 m higher than modern sea level the scarp has been uplifted about 50 65 m since the middle pliocene and 3 ocean water temperatures along eastern north america were warmer when the scarp was formed that they are at present

pliocene sea surface temperature changes in odp site 1125 chatham rise east of new zealand abstract planktonic foraminiferal census counts were converted to sea surface temperature sst estimates using the modern analogue technique mat for the middle late pliocene 4 0 2 37 ma in odp site 1125 north side of chatham rise sw pacific ocean mat sstwarm records range between 8 c and 20 5 c and mat sstcold records parallel that pattern but with a temperature range of 5 15 c the modern position of site 1125 is just north of the subtropical front and has an annual temperature range of 14 18 c pliocene warmest temperatures are 1 2 warmer than modern summers whereas cold season sst records are up to 6 10 c cooler than modern winters overall average temperatures at the site are 2 3 c cooler than modern temperatures during a time of sustained global warmth three major cold excursions centred on 3 35 3 0 and 2 8 ma showed warm season temperatures over 5 c colder than the last glacial maximum experiencing temperatures typical of modern subantarctic waters two minor cold excursions at 2 7 ma and 2 4 ma experienced temperatures cooler than modern winters but not as cold as last glacial conditions cold season ssts show a shift to warmer climate upward through the study interval whereas warm season estimates remain essentially unchanged we interpret the strong regional cooling of subtropical southwest pacific water through the middle late pliocene as having been caused by increased upwelling it is also possible that the subtropical frontal zone moved north over the site in the pliocene however this is considered the least likely interpretation our record of cool conditions in the southwest pacific corroborate evidence of cooler than modern conditions in other regions of the western pacific through the mid pliocene despite overall global warming

upwelling intensification as part of the pliocene pleistocene climate transition a deep sea sediment core underlying the benguela upwelling system off southwest africa provides a continuous time series of sea surface temperature sst for the past 4 5 million years our results indicate that temperatures in the region have declined by about 10 c since 3 2 million years ago records of paleoproductivity suggest that this cooling was associated with an increase in wind driven upwelling tied to a shift from relatively stable global warmth during the mid pliocene to the high amplitude glacial interglacial cycles of the late quaternary these observations imply that atlantic ocean surface water circulation was radically different during the mid pliocene

holocene coastal uplift in the western pacific rim in the context of late quaternary uplift abstract this paper reviews recent studies of holocene coastal uplift in tectonically active areas near the plate boundaries of the western pacific rim emergent holocene terraces exist along the coast of north island of new zealand the huon peninsula of papua new guinea the japanese islands and taiwan these terraces have several features in common all comprise series of subdivided terraces the highest terrace is a constructional terrace underlain by estuarine or marine deposits and the lower terraces are erosional cutting into transgressive deposits or bedrock the highest terrace records the culmination of holocene sea level rise at ca 6 6 5 ka bp lower terraces were coseismically uplifted repeated major earthquakes have usually occurred at ka intervals and meter scale uplift the maximum uplift rate and number of terraces are surprisingly similar about 4 m ka and seven to four major steps in north island huon peninsula and japan taiwan especially along the east coast of the coastal range is different reaching a maximum uplift rate of 15 m ka with 10 subdivided steps they record a very rapid uplift comparison between short term holocene and long term since the last interglacial maximum sub stage 5e uplift rates demonstrates that a steady uplift rate huon peninsula or accelerated uplift toward the present several areas of japan and north island has continued at least since isotope sub stage 5e rapid uplift in eastern taiwan probably started only in the early holocene judging from the absence of any older marine terraces most of the causative faults for the coastal uplift may be offshore reverse faults branched from the main plate boundary fault but some of them are onshore faults which deformed progressively with time

the glaciers of popocatepetl volcano mexico changes and causes an updated inventory of popocatepetl volcano s glaciers and field observations for 1977 1992 is presented two glaciers 0 559 km 2 and four permafrost fields 0 239 km 2 are reported here comparing new descriptions of the glaciar del ventorrillo with previous descriptions a systematic retreat pattern is identified the average retreat rate in terms of terminus altitude for 1906 1968 is nearly 7 m year advance rate 10 m year for 1968 1978 and a response of glacier terminus is documented for 1978 1982 at 40 m year morphological changes are a reduction of 25 in the glaciated area and strong retreat of the tezcalco tongue glaciar noroccidental is a stationary glacierette whose area was reduced by 12 in 34 years total glaciated area was reduced by 22 permafrost fields are located around the glaciers and are the remains of larger glaciers fluctuations are explained in terms of a an increase of heat flow b local climatic changes c global climatic changes and d a combination of these further work is needed to evaluate the role of the glaciers in the local environment the impact of the local and global climate on them the role they would play in the case of explosive activity of popocatepetl and its consequences

precession forced changes in south west african vegetation during marine isotope stages 101 100 2 56 2 51 ma the intensification of northern hemisphere glaciation inhg is one of the critical climate thresholds in the cenozoic this study focuses on marine sediments recovered from marine isotope stages 101 100 at the ocean drilling program site 1083 to assesses the impact of the inhg on continental southern african vegetation through n alkane straight chain hydrocarbon abundance and delta 13 c values the n alkane abundance data yield a convoluted signal due to the number of controlling factors such as the source area transportation routes and vegetation type the c 31 n alkane delta 13 c values however exhibit a cyclic pattern with a periodicity of c 20 ka and are not correlated to the abundance data it is inferred that the signal does not represent a change in the geographical source of n alkanes instead we suggest that the variations are caused by water stress induced changes in either carbon isotope fractionation during c 3 photosynthesis or subtle changes in the proportion of c 3 and c 4 plants these changes unlike variations in oceanographic proxies closely track precessional forcing factors and are independent of the prevailing obliquity forced glacial interglacial cycles we conclude that the varying monsoon strength rather than pco 2 or temperature change forced changes in southern african vegetation during this period c 2005 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

late cenozoic glacial history of the ross embayment antarctica abstract knowledge of the cenozoic terrestrial and marine glacial history of antarctica has been developed through studies of on land surface outcrops and subsurface drillcores and through examination of drillcores and piston cores obtained from a variety of offshore marine geological settings these field and laboratory endeavors have been a major target of the antarctic earth science community for more than thirty years the ross sea sedimentary basins including the byrd basin west antarctica wilkes and pensacola basins east antarctica and the transantarctic mountains provide significant data on the cenozoic glacial record a record that has been traced back to at least 38 ma close to the eocene oligocene boundary this paper reviews the late cenozoic history of the transantarctic mountains and flanking sedimentary basins with emphasis on the debate between the stabilist view of antarctic ice sheet history see clapperton and sugden 1990 and our favored multi glacial dynamic ice sheet model

reply to comment by k pedoja et al on tectonic record of strain buildup and abrupt coseismic stress release across the northwestern peru coastal plain shelf and continental slope during the past 200 kyr citation bourgois j d bourles and r braucher 2011 reply to comment by k pedoja et al on tectonic record of strainbuildup and abrupt coseismic stress release across the northwestern peru coastal plain shelf and continental slope during the past200 kyr j geophys res 116 b09402 doi 10 1029 2011jb008582

modelling the space time evolution of bed entrainment for flow like landslides abstract the paper discusses the space time evolution of bed entrainment for some typical flow like landslides in three different test areas first the attention is focused on debris avalanches da whose lateral spreading is highly affected by bed entrainment two cases of debris avalanches turning into debris flows df i e channelized flows are then investigated to discuss the potential occurrence of complex bed entrainment scenarios a quasi 3d depth integrated coupled sph smooth particle hydrodynamic model is used the numerical results show that i the eroded thicknesses have maximum values in the intermediate portion of the debris avalanche path and ii the computed time variations of eroded thicknesses and the entrainment rates are consistent with those indicated in recent literature for das at the studied areas in addition the computed scenarios are differentiated in terms of unitary flow discharge identifying the typical behaviour of small volume da landslides propagating inside gullies as dfs and combined dfs and das

lahar flow simulations using laharz program application for the popocatepetl volcano mexico lahars are a type of catastrophic event that is generated in volcanic environments due to the recent technological advances computer simulated models have become widely used by the scientific community to predict the distribution of catastrophic events such as floods debris avalanches earth landslides or lahars and to mitigate possible damage to populations located in a risk area our study risk area is located in the popocatepetl volcano a large and active stratovolcano in the trans mexican volcanic belt here lahars have been occurring during the last century and some of them have seriously affected nearby towns since one of the main input parameters into a lahar simulation is the digital elevation model dem this paper focuses on studying lahar simulations on popocatepetl using dems obtained from various sources with the aid of a popular package known as laharz the first simulations were performed using a 1 50 000 topographic map with 20 m contours interval the second set of tests used an enhanced dem with profiles measured during fieldwork in the lahar channel in the last set of tests we added lateral artificial barriers to the channel profiles used in the previous enhanced dem our results show that the use of high resolution and detailed dems does not necessarily guarantee a realistic lahar simulation as was previously thought and a detailed explanation as to why the laharz code computation creates ragged edges is offered our results also offer useful information on the level of detail necessary for an input dem into laharz in order to obtain lahar simulations closer to real lahars the minimum resolution for the dem used in simulations must be less than the width of the narrowest cross section of the channel to realistically reproduce the lahars for dems with lower resolution sometimes the modeled lahars are shorter in length and therefore underestimate real hazards to populations also the results show that lateral barriers are sometimes needed to obtain more realistic inundation areas

magnitude of climate variability during middle pliocene warmth a palaeoclimate modelling study abstract the nature and magnitude of climatic variability during the period of middle pliocene warmth ca 3 29 2 97 ma is poorly understood we present a suite of palaeoclimate modelling experiments incorporating an advanced atmospheric general circulation model gcm coupled to a q flux ocean model for 3 29 3 12 and 2 97 ma bp astronomical solutions for the periods in question were derived from the berger and loutre bl2 astronomical solution boundary conditions excluding sea surface temperatures ssts which were predicted by the slab ocean model were provided from the usgs prism2 2 2 digital data set the model results indicate that little annual variation 0 5 c in ssts relative to a control experiment occurred during the middle pliocene in response to the altered orbital configurations annual surface air temperatures also displayed little variation seasonally surface air temperatures displayed a trend of cooler temperatures during december january and february and warmer temperatures during june july and august this pattern is consistent with altered seasonality resulting from the prescribed orbital configurations precipitation changes follow the seasonal trend observed for surface air temperature compared to present day surface wind strength and wind stress over the north atlantic north pacific and southern ocean remained greater in each of the pliocene experiments this suggests that wind driven gyral circulation may have been consistently greater during the middle pliocene the trend of climatic variability predicted by the gcm for the middle pliocene accords with geological data however it is unclear if the model correctly simulates the magnitude of the variation this uncertainty is derived from a the relative insensitivity of the gcm to perturbation in the imposed boundary conditions b a lack of detailed time series data concerning changes to terrestrial ice cover and greenhouse gas concentrations for the middle pliocene and c difficulties in representing the effects of climatic history in snap shot gcm experiments

objective delineation of lahar inundation hazard zones a new method of delineating lahar hazard zones in valleys that head on volcano flanks provides a rapid objective reproducible alternative to traditional methods the rationale for the method derives from scaling analyses of generic lahar paths and statistical analyses of 27 lahar paths documented at nine volcanoes together these analyses yield semiempirical equations that predict inundated valley cross sectional areas a and planimetric areas b as functions of lahar volume v the predictive equations a 0 05v 2 3 and b 200v 2 3 provide all information necessary to calculate and plot in

a chronology of pliocene sea level fluctuations the u s middle atlantic coastal plain record abstract the sequence of marine and marginal marine silts and sands of the u s middle atlantic coastal plain preserves a relatively complete record of pliocene sea level highstands a general chronology for the deposition of these units has been developed previously from studies of the microfossil biostratigraphy complemented by a limited number of paleomagnetic and radiometric dates within this broad temporal framework it is currently difficult to assign ages to individual transgressive events with a resolution much better than 0 5 ma the age model proposed here attempts to refine the depositional history of the atlantic coastal plain by correlation with the more continuous deep ocean record the model assigns probable ages to the pliocene transgressions onto the atlantic coastal plain based on evidence for sea level highstands inferred from high resolution deep ocean 18 o records at least five major transgressive regressive events can be correlated with presumed eustatic fluctuations the temporal resolution for the timing of the transgressive events is greatly improved over that of the biostratigraphy alone many aspects of the proposed chronology require verification by more detailed field study but it is offered as a testable working hypothesis

comment on tectonic record of strain buildup and abrupt coseismic stress release across the northwestern peru coastal plain shelf and continental slope during the past 200 kyr by jacques bourgois et al citation pedoja k l ortlieb t j devries j machare l audin and v regard 2011 comment on tectonic record ofstrain buildup and abrupt coseismic stress release across the northwestern peru coastal plain shelf and continental slope duringthe past 200 kyr by jacques bourgois et al j geophys res 116 b09401 doi 10 1029 2011jb008321

quaternary coastal uplift along the talara arc ecuador northern peru from new marine terrace data marine terrace sequences have been investigated along the talara arc a 1000 km long stretch of the coast of ecuador and northern peru characterized by subduction with a concave plan view seven areas were investigated evidencing flights of up to seven marine terraces with elevations reaching up to 360 in above mean sea level amsl dating of the terraces was made using the infra red stimulated luminescence irsl technique on sands as old as mis 9 similar to 330 ka c 14 and u series dates were obtained from fossil shells for geochronological cross control mean uplift rates along the talara arc range from about 0 10 up to 0 50 mm yr the strongest uplift is observed in the manta peninsula of ecuador in front of the subduction of the carnegie ridge the uplift rate tends to slow down towards the northern and southern ends of the talara arc and then the transition toward the stable or subsiding coasts of central peru and northern ecuador and colombia is sharp the uplift appears to be homogeneous and related to 1 the map view curvature of the are 2 the concave subduction pattern and 3 the carnegie ridge subduction c 2006 elsevier b v all rights reserved

biogeochemical changes within the benguela current upwelling system during the matuyama diatom maximum nitrogen isotope evidence from ocean drilling program sites 1082 and 1084 1 the matuyama diatom maximum mdm is a time of peak opal accumulation from 2 6 to 2 0 ma within the benguela current upwelling system that was initiated by increased influence of southern ocean water on the eastern south atlantic we measured opal total organic carbon toc and caco3 fluxes and c and n stable isotopes in sediments deposited from 2 4 to 1 95 ma at sites 1082 and 1084 to explore the biogeochemical dynamics within the benguela region the infusion of southern ocean water delivered dissolved nutrients and southern ocean flora and fauna resulting in local opal accumulation increasing up to 8 g cm2ky and the production of diatom mats some 15n measurements of diatom bound organic matter indicate that the mats grew within the benguela region the bulk sediment 15n records are taken to reflect changes in the 15n of nitrate in the incoming water where lower values at 2 4 ma reflect less nitrate utilization in the antarctic a long term increase in relative nitrate uptake in the southern ocean is evidenced by the gradual increase in 15n toward 1 9 ma

comparative lahar hazard mapping at volcan citlaltepetl mexico using srtm aster and dted 1 digital topographic data abstract in this study we evaluated and compared the utility of spaceborne srtm and aster dems with baseline dted 1 bald earth topography for mapping lahar inundation hazards from volcan citlaltepetl mexico a volcano which has had a history of producing debris flows of various extents in particular we tested the utility of these topographic datasets for resolving ancient valley filling deposits exposed around the flanks of the volcano for determining their magnitude using paleohydrologic methods and for forecasting their inundation limits in the future we also use the three datasets as inputs to a gis stream inundation flow model laharz and compare the results in general all three datasets with spatial resolution of 90 m or better were capable of resolving debris flow and lahar deposits at least 3 106 m3 in volume or larger canopy and slope related height errors in the aster and srtm dems limit their utility for measuring valley filling cross sectional area and deriving flow magnitude for the smallest deposits using a cross sectional area to volume scaling equation height errors in the aster and srtm dems also causes problems in resolving stream valley hydrography which controls lahar flow paths and stream valley morphology which controls lahar filling capacity however both of the two spaceborne dem datasets are better than dted 1 at resolving fine details in stream hydrography and erosional morphologies of volcaniclastics preserved in the valleys around the more humid eastern flanks of the volcanic range the results of laharz flow inundation modeling using all three dems as inputs are remarkably similar and co validate one another for example at citlaltepetl all lahar simulations show that the city of orizaba is the most vulnerable to flows similar in magnitude to or larger than one that occurred in 1920 many of the other cities and towns illustrated are built higher up on terrace deposits of older debris flows and are safe from all but the largest flows which occur less frequently finally asters 60 km swath width and 8 duty cycle presents a challenge for mapping lahar inundation hazards at e w oriented stream valleys in low latitude areas with persistent cloud cover however its continued operations enhances its utility as a means for updating the continuous but one time coverage of srtm and for filling voids in the srtm dataset such as those that occur along steep sided valleys prone to hazards from future lahars

the 1997 and 2001 lahars of popocatepetl volcano central mexico textural and sedimentological constraints on their origin and hazards abstract popocatepetl volcano is the most active volcano in central mexico and represents a high risk for more than 40 million people including mexico city in 1994 volcanic activity at popocatepetl renewed with the formation of ash rich plumes up to 7 km high in april 1996 lava emissions filled the crater and were accompanied by a series of explosions that produced eruptive columns up to 8 km high associated with explosive events in 1997 and 2001 two major lahars events occurred leaving debris flow deposits along huiloac gorge for as far as 15 km to the town of santiago xalitzinta the 1997 debris flow deposit originated after a prolonged emission of ash which caused glacier melt and a rapid release of water 1 107 m3 the amount of melting water was sufficient to gradually erode the river bed causing a flood that gradually transformed from a debris flow to a hyperconcentrated flow in contrast the 2001 debris flow that originated from a post depositional remobilization of a pumice flow deposit did not experience any flow transformation and carried 25 water at maximum the different behavior of these two lahars has important hazard implications both lahars reached xalitzintla town but at that point the 1997 lahar had already transformed into a sediment loaded stream flow the 2001 lahar by contrast maintained the characteristics of a debris flow being more competent and with greater destructive power what happened with these lahars demonstrates how important it is to take into consideration secondary volcanic phenomena even though they were not large flows they were capable of threatening populated areas even during periods of volcanic quiescence or reduced magmatic activity

impact of the eruptive activity on glacier evolution at popocatepetl volcano mexico during 1994 2004 abstract distribution rate and magnitude of the glacier changes caused by eruptive activity over 1994 2001 at popocatepetl volcano were determined digital elevation models computed by scanned photographs within a digital photogrammetric workstation and the subsequent dem comparison allowed the determination of glacial changes the results show that drastic changes occurred in glacier geometry and morphology over 1996 2001 53 of the glacier surface area was lost due to melting processes the most important loss occurred over 2000 2001 when 19 of the glacier covered area disappeared the glacier volume losses increased over time during 1999 2000 the largest loss was observed however in february 2001 the glacier showed an apparent small increase in volume volcanic processes disturbed the mass balance of the glacier thereby accelerating the ablation processes the eruptive behavior of popocatepetl was characterized during this time by alternating periods of explosive events and low activity pyroclastic flow generation ejection of incandescent material and tephra fall affected the glacier the tephra volume distribution and remobilization produced considerable changes on glacier evolution tephra deposition on the glacier surface was the most frequent process the irregular distribution and thickness of tephra provoked differential ablation and tephra remobilization processes took place on the glacier surface together these processes incised the glacier surface over time based on these results and observations a model of glacier evolution is proposed involving an adjustment phase thinning phase areal retreat phase and fragmentation phase a complex interplay of factors and processes took place between eruptive activity and the glaciers at popocatepetl volcano the glacier evolution and subsequent extinction were induced by the eruptive behavior over the years while not the only process at work eruptive activity played the primary role in accelerating retreat and as a consequence in glacier extinction

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

earthquake supercycles inferred from sea level changes recorded in the corals of west sumatra records of relative sea level change extracted from corals of the mentawai islands sumatra imply that this 700 kilometer long section of the sunda megathrust has generated broadly similar sequences of great earthquakes about every two centuries for at least the past 700 years the moment magnitude 8 4 earthquake of september 2007 represents the first in a series of large partial failures of the mentawai section that will probably be completed within the next several decades

planktonic foraminiferal assemblages in surface sediments from the southwest african continental margin abstract the relative abundance and distribution of planktonic foraminifera species on the southwest african continental margin have been determined from 152 surface sediment samples of the 23 recorded taxa only 8 make a significant contribution to the foraminiferal assemblages individual species proportions are closely related to the surface water hydrography of the benguela system and the associated upwelling phenomena three foraminiferal assemblages can be distinguished by correlation analysis on the abundances of the major taxa species composition of these assemblages range from polar taxa in the upwelling area left coiling neogloboquadrina pachyderma and globigerina quinqueloba to transitional taxa in the offshore oligotrophic environment globorotalia inflata and globorotalia truncatulinoides globigerina bulloides and right coiling neogloboquadrina pachyderma are preferentially distributed in the highly productive intermediate zone of the benguela system where upwelled and oligotrophic offshore waters mix variability of the hydrological processes upwelling intensity strength of the frontal features may be inferred from frequency variations of individual species and diversity patterns

middle pliocene sea surface temperatures a global reconstruction identification and analyses of pliocene marine microfossils from 64 globally distributed stratigraphic sequences have been used to produce a middle pliocene sea surface temperature reconstruction of the earth this reconstruction shows little or no change from current conditions in low latitude regions and significant warming of the ocean surface at mid and higher latitudes of both hemispheres this pattern of warming is consistent with terrestrial records and suggests a combination of enhanced meridional ocean heat transport and enhanced greenhouse effect were responsible for the middle pliocene warmth

the record of pliocene sea level change at enewetak atoll abstract detailed seismic stratigraphy lithostratigraphy and chemostratigraphy indicate that atoll wide subaerial exposure surfaces major disconformities developed during major sea level lowstands form prominent seismic reflectors and are coincident with biostratigraphic breaks in the plio pleistocene on enewetak atoll sea level models based on the stratigraphic position and age of major disconformities suggest a maximum sea level highstand elevation of 36 m above present sea level and a maximum sea level lowstand elevation of 63 m below present sea level for the pliocene

influence of the scar geometry on landslide dynamics and deposits application to martian landslides received 24 january 2011 revised 23 june 2011 accepted 30 june 2011 published 4 october 2011 1 landslides dynamics prediction remains difficult in spite of a considerable number of studies the runout distance is widely used in analysis of landslide dynamics and in the calibration of the rheological parameters involved in numerical modeling however the unknown impact of the significant uncertainty in the shape of the initial released mass on the runoutdistanceandontheoverallshapeofthedepositraisesquestionsabouttherelevanceof these approaches the impact of the initial scar geometry on flow and distribution of the deposits is studied here using satellite data and numerical modeling of theoretical landslides and martian landslides informed by geomorphological analysis by varying the initial scar geometry from spoon shaped to steep wall geometry our results show that the runout distance is a very robust parameter that is only slightly affected by the change in the geometry of the initial scar on the contrary the lateral extent of the deposit is shown to be controlled by the scar geometry providing unique insights into the initial landsliding conditionsonmarsandmakesitpossibletoaccuratelyrecoverthevolumeinitiallyinvolved an essential ingredient for volume balance calculation a feedback analysis of valles marineris landslides can be drawn showing good agreement between numerical results and geomorphological analysis the geometry of the initial scar inferred from numerical modeling is strongly correlated with the regional tectonic history in valles marineris area

an investigation of periglacial slope stability in relation to soil properties based on physical modelling in the geotechnical centrifuge results are presented from eight scaled centrifuge modelling experiments designed to investigate mass movement processes on thawing ice rich slopes four pairs of simple planar slope models were constructed one in each pair being of sufficient gradient to promote slope failure during soil thaw and the second having a gradient below the threshold for instability four frost susceptible soils were used three were normally consolidated and had different clay contents 2 12 and 20 and the fourth comprised the 20 clay soil but was over consolidated prior to model testing modelling protocols included freezing from the surface downwards under an open hydraulic system and thawing from the surface downwards under an enhanced gravitational field within the geotechnical centrifuge thereby utilising scaling laws to simulate correct prototype self weight stresses during thaw slopes below the stability threshold gradient were subjected to between 2 and 4 cycles of freezing and thawing simulating annual cycles those above the stability threshold were subjected to only one cycle since they failed during the first thaw phase thermal conditions pore water pressures surface movements and profiles of displacement are reported measured pore pressures are used in slope stability analyses based on a simple planar infinite slope model profiles of solifluction shear strain and mechanisms of slope failure are both shown to be sensitive to small changes in soil properties particularly clay content and stress history in all cases pore pressures rose rapidly immediately following thaw remained below the threshold for failure in low gradient models but exceeding the threshold to trigger landslides on steeper slopes upward seepage of melt water away from the thaw front contributed to loss of shear strength mechanisms of slope failure differed between test soils ranging from mudflow in non cohesive silt to active layer detachment sliding in over consolidated silt clay during solifluction shear strain was greatest at the surface in non cohesive silt and decreased rapidly with depth but in test soils containing clay the zone of maximum shear strain was located lower in the displacement profiles

sedimentology and flow behavior of a rain triggered lahar mangatoetoenui stream ruapehu volcano new zealand on october 28 1995 heavy rain triggered failure of approximately 3 3 10 5 m 3 of fall deposits on the mangatoetoenui glacier and generated a lahar event that flowed east northeast of ruapehu volcano down the mangatoetoenui stream and eventually entered the tongariro river 19 km downstream the lahar left multiple stacked deposits of at least three major flow surges or pulses which traveled down slope at calculated velocities of as much as 27 m s 1 and calculated maximum peak discharges of as much as 2900 m 3 s 1 the source area of the mangatoetoenui lahar is delineated by a thin furrowed lag of unsorted ash and lapilli margined by steep headwall scarps marking the edges of undisturbed fall deposits failure of fall deposits in the source area triggered debris flows down a north and south branch of the mangatoetoenui stream these two debris flows coalesced and ponded then flowed across seasonal snowpack covering the stream in the proximal zone to 5 km downstream of the source area the deposits of the individual constituent debris flows cannot be distinguished however in the medial zone between 5 and 16 km downstream of the source area and beyond the limit of the snowpack and the junction with perennial streamflow the depositional record of this lahar shows clear evidence for downstream transformation of individual peak flows from debris flow to hyperconcentrated flow transformation began at 5 km from source due to dilution 1 by each peak flow incorporating normal streamflow in the perennial mangatoetoenui stream and tributaries and 2 through deposition of part of each peak flow9s sediment load the hyperconcentrated flow deposits frequently may be subdivided into multiple units which is evidence that the lahar flowed as a series of surges or waves we consider that these were caused by episodic but contemporaneous inputs from a divergent flow from a single source area or by ponding and episodic release of debris within the channel estimated froude numbers for the mangatoetoenui lahar are greater than 3 implying supercritical flow and the development of fluid mechanical instabilities that enhanced these flow surges

the prism pliocene palaeoclimate reconstruction time for a paradigm shift global palaeoclimate reconstructions have been invaluable to our understanding of the causes and effects of climate change but single temperature representations of the oceanic mixed layer for dat

a gis based method to determine the volume of lahars popocatepetl volcano mexico abstract lahars are flows composed of water and volcanic sediment which are often dangerous for people living near volcanoes therefore a reliable estimation of lahar volume is needed to effectively assess the risk this paper proposes a new method to calculate the volume of lahar sediments found in channels of volcanic landscapes the method requires surveys of several cross sections along a gorge a digital elevation model of the study area and measurements of the thickness of the lahar deposits with these data and a geographical information system gis the volume is calculated for the erosive section where deposit volume is divided into oblique parallelepipeds and the sedimentary section where deposit volume is divided into polyhedrons this new method was applied to the 1997 and 2001 lahars that occurred in the channel of a gorge at popocatepetl volcano mexico the estimated volumes are 1 85 10 5 and 1 6 10 5 m 3 respectively which is about 40 less than those obtained by the traditional method that multiplies lahar flow path length sediment width and sediment depth this observation suggests that the traditional method tends to overestimate volumes

organic geochemical changes in pliocene sediments of odp site 1083 benguela upwelling system the intensification of the northern hemisphere glaciation inhg was a major event in the development of the current climate state and as one of the most productive regions in the world s oceans the behaviour of the benguela upwelling system bus following the inhg is of wide interest to investigate post inhg changes in productivity and organic matter accumulation total organic carbon and biomarker accumulation rates were determined for sediments from cop site 1083 and compared to alkenone derived sea surface temperatures and nitrogen isotopic compositions these data indicate that the interval between 2 6 and 2 4 ma was characterized by dramatic changes in upwelling intensity and organic carbon export on the northern edge of the modern bus the upwelling is reflected by significant changes in alkenone derived sst estimates between glacial and interglacial intervals with a total variability of 16 degrees c the studied interval is also characterized by large changes in organic matter export as reflected by changes in toc and biomarker accumulation rates which show maxima during ois 98 and during the transition from ois 97 to 96 intervals of elevated toc are also characterized by elevated concentrations of sedimentary microbial biomarkers and lower caco 3 suggesting that enhanced delivery of labile organic matter to the seafloor resulted in enhanced remineralisation with released co 2 being consumed by caco 3 dissolution however in apparent contrast to recent pleistocene sediments at the same site organic matter export after the inhg was not solely driven by upwelling intensity of the three pliocene glacial interglacial cycles examined ois 101 to 96 each is unique with respect to the timing and magnitude of changes in organic matter accumulation each is also characterized by different algal assemblages as inferred from biomarker distributions with ois 97 and 96 particularly dominated by diatoms we suggest that these differences reflect the important but evolving role of southern ocean waters in the pliocene bus nutrient depletion of so waters occurred during parts of pliocene glacial intervals such that even intense upwelling did not persistently result in enhanced organic matter accumulation rates c 2009 elsevier b v all rights reserved

interplay of rheology and entrainment in debris avalanches a numerical study flow type landslides are a major global hazard they occur worldwide and are responsible for a large number of casualties significant structural damage to property and infrastructure and economic losses the features of debris avalanches are particularly important as they involve open slopes and affect triangular source areas when initial slides turn into avalanches through further failures or eventual soil entrainment in this paper the propagation stage of debris avalanches is numerically modelled to provide information such as the propagation pattern of the mobilized material and its velocity thickness and run out distance the use of a depth integrated model has the following advantages i it adequately accommodates the irregular topography of real slopes which greatly affects the evolution of the propagation stage and ii it is less time consuming than full three dimensional approaches the model is named geoflow sph and has previously been applied to theoretical experimental and re

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

three and half million year history of moisture availability of south west africa evidence from odp site 1085 biomarker records ocean drilling program site 1085 provides a continuous marine sediment record off southern south west africa for at least the last three and half million years the n alkane 13 c record from this site records changes in past vegetation and provides an indication of the moisture availability of sw africa during this time period very little variation and no apparent trend is observed in the n alkane 13c record suggesting stable long term conditions despite significant changes in east african tectonics and global climate slightly higher n alkane 13c values occur between 3 5 and 2 7 ma suggesting slightly drier conditions than today between 2 5 and 2 7 ma there is a shift to more negative n alkane 13c values suggesting slightly wetter conditions during a 0 2 ma episode that coincides with the intensification of northern hemisphere glaciation inhg from 2 5 to 0 4 ma the n alkane 13c values are very consistent varying by less than 0 5 and suggesting little or no long term change in the moisture availability of south west africa over the last 2 5 million years this is in contrast to the long term drying trend observed further north offshore from the namib desert and in east africa a comparison of the climate history of these regions suggests that southern africa may have been an area of long term stability over the last 3 5 myrs

sph run out modelling of channelised landslides of the flow type abstract rainfall induced channelised landslides of the flow type may reach high velocities and travel large run out distances the proper modelling of the propagation stage is fundamental to risk analysis and management the correct selection of mass rheology is fundamental to this procedure and the variation of pore water pressures and bed entrainment along the landslide path must also be properly taken into account all of these processes can be consistently simulated through a quasi 3d depth integrated coupled sph model in this study such a model is applied to a relevant case history from southern italy for which an advanced dataset is available the numerical results provide a satisfactory back analysis of the case history and clearly indicate that the bed entrainment rate and the extent of the erodible areas affect the propagation paths the velocities and the deposition heights on the basis of the results general insights into this type of landslide are discussed with reference to different hypotheses for propagation modelling

evaluating titan2d mass flow model using the 1963 little tahoma peak avalanches mount rainier washington the titan2d geophysical mass flow model is evaluated by comparing its simulation results and those obtained from another flow model flow3d with published data on the 1963 little tahoma peak avalanches on mount rainier washington the avalanches totaling approximately 10 10 6 m 3 of broken lava blocks and other debris traveled 6 8 km horizontally and fell 1 8 km vertically h l 0 246 velocities calculated from runup range from 24 to 42 m s and may have been as high as 130 m s while the avalanches passed over emmons glacier titan2d is a code for an incompressible coulomb continuum it is a depth averaged dshallow watert granular flow model the conservation equations for mass and momentum are solved with a coulomb type friction term at the basal interface the governing equations are solved on multiple processors using a parallel adaptive mesh godunov scheme adaptive gridding dynamically concentrates computing power in regions of special interest mesh refinement and coarsening key on the perimeter of the moving avalanche the model flow initiates as a pile defined as an ellipsoid by a height z and an elliptical base defined by radii in the x and y planes flow parameters are the internal friction angle and bed friction angle results from the model are similar in terms of velocity history lateral spreading location of runup areas and final distribution of the little tahoma peak deposit the avalanches passed over the emmons glacier along their upper flow paths but lower in the valley they traversed stream gravels and glacial outwash deposits this presents difficulty in assigning an appropriate bed friction angle for the entire deposit incorporation of variable bed friction angles into the model using gis will help to resolve this issue d 2004 elsevier b v all rights reserved

tectonic record of strain buildup and abrupt coseismic stress release across the northwestern peru coastal plain shelf and continental slope during the past 200 kyr 200 kyr both segments uplifted at high rates of 10 to 20 mm yr 1 through tectonic pulses coeval with the eustatic deglacial sea level rises of isotope stage 1 and warm isotope substage 5e respectively the uplift and related extensive emersion of the coastal plain require high coupling along the subduction zone and or underplating at depth offshore industry acquired reflection seismic lines combined with em12 bathymetric data allow us to investigate the tectonic regime and deformation of the continental margin and shelf major dipping seaward detachments control the long term subsidence of this area these main tectonic features define a tectonic segmentation the talara paita and sechura segments are identified from north to south no clear tectonic correlation in time exists between the onshore and the continental margin segmentations or in space either the longterm subsidence of the offshore indicative of subduction erosion working at depth requires low coupling along the subduction channel at depth the distribution of permanent deformation along the northern peru forearc area includes long term uplift along the coastal plain and long term subsidence along the continental margin the neutral line being located within the 10 km seaward from the present coastline an extensive sequence of raised marine cliffs and associated notches evidences that the most recent uplift step 20 23 ka to present along the cabo blanco segment is related to a sequence of major earthquakes we infer that eustacy exerts important feedback coupling to the seismogenic behavior of the north peru subduction zone we speculate that during sea level fall pore fluid pressure diminishes along the subduction channel inducing a possible seaward migration of the locked zone i e migration of the updip limit reaching a maximum by the end of the eustatic low stand during eustatic sea level rise pore fluid pressure increases along the subduction channel this in turn is capable of weakening the previously locked zone along the plate interface beginning an earthquake sequence earth s orbital variations are a potential external cause that may control the physical processes at work along plate interface

flowslides in stockpiled coal abstract occasional deep seated flowslides in coking coal stockpiles at the north queensland port of hay point are described the flowslides result from particularly loose placement of the light cohesionless material and saturation of the lower levels of the stockpile due to rainfall infiltration and initial moisture at placement consolidated undrained triaxial testing has been used to define the density stress conditions at which liquefaction occurs the flowslide mechanism field verification and preventative measures are briefly discussed