geochemistry of oolitic iron ores an electron microprobe study oolitic iron ores are made up of silicate oxide and carbonate minerals that are part of solid solution series the compositions of the minerals can depart from pure end members and show variation among deposits this variability can be quantified using electron microprobe techniques iron silicates are represented by chamositic clays both berthierine and chamosite glauconite was not seen in any of these samples berthierine predominates in younger deposits whereas the paleozoic ores studied contained only chamosite compositions of the chamositic clays however were independent of age iron oxides are mostly goethite in younger deposits or hematite in older deposits both minerals lack appreciable al in solid solution most analyses show small amounts of al but usually balanced by si in the same proportion as in chamosite indicating a slight admixture of clay iron carbonates are siderite with appreciable substitution of ca and mg but not of mn apatite is common but no iron phosphates were found the compositions of the silicates and carbonates are close to those reported for early diagenetic minerals from other types of sedimentary rocks indicating that ironstone formation does not require unusual chemical conditions other than a large supply of iron the analytical results can be used to argue against several hypotheses of ironstone genesis the lack of al in the goethitic and hematitic ooliths is inconsistent with an origin either by redeposition of soil ooliths or by oxidation and leaching of earlier chamositic ooliths the presence of high al contents in the chamositic ooliths shows that they cannot have formed from earlier aragonitic ooliths and the presence of small amounts of chamositic clay and apatite as discrete laminae in goethitic and hematitic ooliths suggests that this type of oolith could also not have formed by replacement of aragonite times of ironstone deposition show a correlation with climate and sea level stands that suggests a mechanism for generating locally high iron concentrations in seawater a combination of a warm humid climate and low average continental relief would intensify lateritic weathering and the formation of iron enriched detritus coincidence of this increased detrital iron supply with intensification and shallowing of the oxygen minimum layer in the ocean could lead to mobilization of iron from offshore shelf clastics to be redeposited near the shoreline in intertidal to shallow subtidal environments

an analysis of the supply process of loose materials to mountainous rivers and gullies as a result of dry debris avalanches a dry debris avalanche will produce different volumes of colluviums or depositions loose materials which can have a significant impact on mountainous rivers or gullies the loose material supply process caused by a debris avalanche is an important issue for understanding secondary disasters that form via the coupling of water flow and loose materials two flumes were designed for laboratory tests of the loose materials supply process to rivers gullies and the related impact factors were analyzed experimental results show that the supply of loose materials is a continuous process that directly relates to the avalanche s mass movement processes the sliding masses with smaller particle sizes are more sensitive to the flume slope and exhibited a longer supply time the time consuming for the debris avalanche travel in the flume decreased with the increasing particle size such as flume b time consuming is decreased 0 2 s when the particle size increased from 1 0 to 20 60 mm landslide volume and flume slope flume a consuming 1 6 2 1 s when flume slope is 29 decreased to consuming 1 3 1 5 s when flume slope is 41 which means the increasing mobility of loose materials the total supply time increased with the increasing landslide volume or decreasing particle size and flume slope an empirical model for the process is presented based on numerous laboratory tests and numerical simulations which can successfully describe the supply process for loose materials to a river gully the supply process of loose materials to mountainous gully from a dry debris avalanche is controlled by the material compositions of sliding masses topographical conditions landslide volume and bed friction where large volume debris avalanches that occur in mountainous river regions are more likely to obstruct the river flow and form a landslide dammed lake

observation and analysis of pore pressure fluctuations in a thin colluvium landslide complex near cincinnati ohio abstract field observations in a thin colluvium landslide complex along the ohio river near cincinnati show that measurable late winter and spring pore water pressure increases occur when several centimetres of rain fall over a period of one or more days average pre storm fillable porosity of 9 suggests that the colluvium was near saturation during the period of record dimensional analysis of flow through a sloping homogeneous layer of uniform thickness shows that short term pore pressure fluctuations in very nearly saturated soils can be approximated by a one dimensional linear diffusion equation the concept of slope parallel and slope normal characteristic times is also introduced to determine the conditions under which slope parallel and slope normal flow will predominate analytical solutions to the diffusion equation are then used to investigate the effects of storm frequency and magnitude on pore pressure fluctuations comparison of solutions for layers of finite and infinite thickness shows that an impermeable substrate nearly doubles pore pressures along the substrate for storms of short duration however the effect of an impervious boundary vanishes with increasing duration finally measured rainfall values are incorporated into a finite difference simulation of the observed pore pressures with good results

triassic shoshonites and andesites lakmon mountains western continental greece differences in primary geochemistry and sheet silicate alteration products abstract shallow marine lavas and pyroclastic rocks several tens of metres thick outcrop at the base of thrust slices in the pindos nappe in the lakmon mountains of western continental greece these volcanic rocks are basalts and andesites formed during mid triassic subduction geochemically on the basis of the potassium content shoshonitic and calc alkalic groups are distinguished principally the shoshonitic rocks contain primary k feldspar the calc alkalic rocks contain complexly zoned feldspars and are depleted in intermediate ree this depletion could reflect a small degree of partial melting of amphibole or possibly phlogopite during petrogenesis these two characteristics are found in other examples of minor calc alkalic rocks associated with shoshonites described in the literature a petrogenetic model is developed involving deeper mantle enrichment in lile and partial melting of this enriched mantle rock containing amphibole calc alkalic rocks are the result of initial partial melting and may be mixed with small amounts of magma of deeper origin further partial melting produces the more voluminous shoshonites celadonite developed as a secondary mineral during burial beneath about 1 km of mesozoic to early tertiary sediments during nappe emplacement vermiculite formed in the calc alkalic rocks in contrast smectite developed in the shoshonites because the potassium was sufficient to immobilize all available fe in celadonite

paleobiological and sedimentological evidence of pleistocene holocene hiatuses and ironstone formation at the pontian islands shelfbreak italy abstract iron rich hardgrounds were grabbed near the shelfbreak ne ventotene and sw ponza at water depths of 119 and 141 m respectively these 1 to 3 cm thick ironstone layers formed at about the pleistocene holocene boundary during rapid sea level rise which began about 16 000 years ago and within about 8000 years brought the bottom of the shelf from a water depth of less than 30 100 m or more a rapid vertical transition from circalittoral deposits characterized by a coastal detritic community with calcareous algae to ironstones rich in iron managanese pisoids or glaucony and containing planktonic foraminifera siliceous sponge spicules and echinoderm remains indicates sediment starvation during rapid drowning of the shelf the crisis of the sedimentary system and the local ironstone formation at sites of favourable morphology were triggered by major paleogeographic changes during final deglaciation at the close of the pleistocene leading to modified circulation patterns and chemistry of sea water reduced carbonate productivity below the photic zone and strong activity of northward directed tyrrhenian currents intruding onto the outer shelf abundance of organic matter transported from the drowned volcanic islands and diminished oxygenation due to both increasing water depth and sluggish vertical circulation were responsible for local reducing micro environments as testified by the formation of pyrite leaching of carbonate bioclasts and growth of microbial mats offshore sedimentation did not resume until the last 2000 4000 years when the deeper water and finer grained ponza glauconitic ironstone was covered by a thin veneer of silty clay deposited on the uppermost slope beneath the mudline the shallower and coarser grained ventotene winnowed pisoidal hardground instead is probably still forming today under the action of strong northward directed marine currents sweeping the shelfbreak free of sediment

hydro mechanical analysis of volcanic ash slopes during rainfall rainfall induced landslides in volcanic ashes represent a major natural hazard in many regions around the world due to their loose structure volcanic ash slopes are prone to rainfall induced landslides the paper presents a continuum modelling approach for the analysis of wetting induced instability phenomena at the onset of failure in loose volcanic ash slopes a numerical simulation of a landslide prone volcanic slope in costa rica is carried out with a 2d hydro mechanical finite element slope model a constitutive model based on the effective stress concept extended to partially saturated conditions is used to reproduce the volcanic ash hydro mechanical behaviour the model parameters were calibrated through a previous extensive laboratory testing campaign simulation results allow to anticipate the behaviour of the slope during rainfall infiltration and to analyze the development of the failure mechanism results of the coupled numerical model demonstrate the important role of wetting and drying cycles slope geometry and bedrock on the timely evolution of matric suctions and wetting induced deformations moreover it is observed that the pore collapse upon wetting enhances the development of a localised shear failure mechanism in unsaturated conditions

instrumented laboratory flowslides flowslides have been induced in small instrumented coking coal stockpiles by slowly raising the water table these strongly resembled field cases showing sudden collapse rapid fluid like motion and very flat final slopes failure initiated under essentially static drained conditions and with a mobilized secant effective strength parameter d much less than the steady state value highspeed measurements showed that excess pore pressures were generated during rather than before movement and liquefaction was therefore a result of shear failure rather than the cause des glissements par liquefaction furent provogues dans de petites reserves de charbon cokeflant a instrumentation par elevations lentes de la nappe aquifere ils ressemblaient beaucoup a des cas sur chantier avec affaissement abrupt un mouvement rapide quasi fluide et des pentes finales tres plates la rupture commenca dans des conditions drainees essentiellement statiques et avec un parametre o de resistance effective secante mobilisee

field and laboratory analysis of the runout characteristics of hillslope debris flows in switzerland abstract hillslope debris flows are unconfined flows that originate by shallow failures in unconsolidated material at steep slopes in spite of their significant hazard for persons and infrastructure in mountainous regions research on hillslope debris flows is rather scarce in comparison to other landslide types this study focusses on the runout characteristics of hillslope debris flows applying two different approaches first detailed landslide inventories which include field measurements of 548 slope failures that occurred during the last two decades in seven parts of switzerland were analysed second laboratory tests were carried out to study the effect of the soil water content grain size distribution and mobilized volume on the runout behaviour of hillslope debris flows most of the failures in the field started as shallow translational slides at terrain slopes between 25 and 45 and involved volumes of some tens to a few hundred cubic meters an analysis of the runout distance of 117 hillslope debris flows showed that they normally travelled some tens of meters but sometimes the runout exceeded 300 m a positive relation between volume and runout distance and between volume and affected area was observed although there is considerable scatter in the data the affected area of 63 hillslope debris flows ranged from 100 to 1500 m2 based on the field data a 7 5 m long laboratory hillslope was designed with a geometrical scale factor of 20 a total of 75 runs with volumes from 4 to 20 dm3 water contents from 18 to 38 and four grain size distributions were carried out the laboratory tests revealed that water content is the dominant control but also the clay content strongly influences the runout distance and the affected area even a small increase in water or clay content produces a considerably larger or smaller runout distance respectively in contrast the influence of the volume on the runout was smaller and a positive relation was observed between these two parameters the field and laboratory results are in general agreement and consistent with the results of other studies the results of this work improve the understanding of hillslope debris flows and may aid in the hazard assessments of these processes

geochemistry tectonic setting and metamorphism of mid triassic volcanic rocks of greece abstract mid triassic volcanic rocks are preserved in about eight localities in the nappes of the external hellenides and are also widespread in the pelagonian zone of central greece most have suffered low grade metamorphism immobile trace elements from 35 samples 80 major element analyses and pyroxene analyses show that these rocks are the product of an eastward dipping subduction zone the subducted ocean was perhaps analogous to the pennine zone of the alps the othris and pindos ophiolites are probably contemporaneous products of related back arc extension metamorphic mineral assemblages in volcanic rocks of the phyllite series of the external hellenides indicate high pressure low temperature conditions probably related to a second subduction that occurred prior to the main phase of hellenide nappe emplacement in the miocene

fire related sedimentation events on alluvial fans yellowstone national park u s a abstract we document initiation and flow processes deposit facies and geomorphic effects of forest fire related sedimentation on small alluvial fans in yellowstone national park brief intense convective storm precipitation on steep basins burned in the 1988 fires produced sedimentation events involving a variety of depositional processes on fans over the course of all documented events flows on fans progressed from higher to lower sediment concentration events were often dominated by either debris flows or relatively sediment poor streamflow processes in some events however flows ranging a over wide spectrum of sediment concentration produced significant fan deposits debris flows were generated by progressive sediment bulking involving pervasive surface runoff and rill erosion on st ep upper basin slopes followed by deep incision as flows progressed down channels debris flow deposits show a marked decline in thickness and coarse gravel content downfan often with extensive distal gravel poor facies we recognized a relatively minor percentage of noncohesive debris flow and hyperconcentrated flow facies with sorting and stratification intermediate between muddy debris flow and streamflow facies these were deposited where dilute flows bulked with coarse sediment by eroding channel alluvium or earlier deposits of the event below incised fan channels streamflows expanded as sheetfloods which prograded lower fans with distally fining deposits basins 3 km2 typically produced streamflow events on fans but sediment texture and availability on slopes and in channels are primary factors determining flow processes on fans of smaller basins burned soil surfaces provided abundant silt and clay for debris flow generation but because soil surface sediment was stripped and or compacted over time the lack of available fines resulted in dominance of streamflow processes in later events

debris flows some physical characteristics and behaviour field observations on 449 debris flows in the queen charlotte islands british columbia are summarized movement of debris is classified according to seven characteristic types designated for the purposes of the study data on the physical characteristics of the events are presented an analysis of the data is made with reference to event initiation yield and deposition using both mechanistic and morphological criteria for those events which initiate on an open slope the infinite slope model is used to establish a relationship between field drainage class and slope angle for assumed frictional and cohesive soil strength parameters the field drainage classes are directly related to the postulated location of the groundwater surface within the depth of the rupture plane deposition of channelized events is found to be influenced by the ratio of channel width to channel gradient with the onset of deposition expected when the ratio exceeds unity five classes of depositional area are proposed the mag

phanerozoic oolitic ironstones geologic record and facies model oolitic ironstonesl composed predominantly of ooidsl of ferric oxide and chamosite accumulated throughout much of phanerozoic time figure 1 and some of them have been important ore deposits they are built of two very common products of weathering iron oxide and clay but they constitute a distinctive and subordinate sedimentary facies for which there is no simple modem analogue as a result considerable disagreement has attended more than 125 years of discussion about their origin early analyses of these rocks for example the minette are of france focused mainly on their chemical and mineral composition and on processes of diagenesis more recent work has described their sedimentary textures and structures as well as their general facies and depositional environments ad eleye 1973 brookfield 1973 corbin 1980 hallam 1975 karpov et a11967

particulate iron and manganese in the santa barbara basin california abstract particulate fe and mn may be important trace metal scavengers in the water column as well as being probable indicators of biologically mediated redox processes a study has been made of suspended particulate composition in the santa barbara basin a shallow near shore basin off southern california with sub oxic conditions below sill depth observations have revealed several interesting phenomena relating to the geochemistry of fe and mn most striking is a profound enrichment of particulate fe in samples from the bottom two hundred meters these particulates have a constant fe p mole ratio of about three and may originate at the sediment water interface or may be transported to the basin from local marshes for particulate mn enrichments are observed both in the sub sill waters and near the base of the euphotic zone a consideration of particle removal rates suggests that the sub photic zone enrichment has a biogenic origin in the sub sill waters enrichment in mn is apparently due to the precipitation of dissolved mn diffusing from the anoxic basin sediments a simple mass balance suggests that most of the mn lost from the sediments is transported from the santa barbara basin in dissolved form

the mid triassic volcanic rocks of lakonia greece thick subaerial volcanic sequences of probable mid triassic age rest unconformably on permo carboniferous limestones in the phyllite series within the gavrovo tripolitsa zone of the external hellenide nappes the volcanic rocks are varied in character pyroclastic rocks often reddened predominate but minor basalt or andesite and rhyolitic hypabyssal intrusions and flows are also found the rocks have experienced low grade metamorphism and the only relict primary minerals are pyroxene and rare plagioclase in basic rocks and potash feldspar in acid rocks the most important metamorphic phases are albite chlorite potassium mica epidote hematite quartz and pumpellyite twenty seven whole rock major element analyses suggest that there has been some exchange of na 2 o and k 2 o for cao during metamorphism but that other elements have been relatively stable a genetic interpretation of the rocks is attempted using published geochemical discriminator diagrams the basic rocks are tholeiitic in major element chemistry and pyroxene composition trace element hf ta th ce yb distribution suggests magma generation at a destructive plate margin

identification of mechanisms for landslide type initiation of debris flows the modelling of debris flow initiation in slopes is addressed in this paper first possible factors governing debris flow initiation are established then a coupled hydro mechanical model for deformable porous media with two pore fluids that is used to assess the problem of the debris flow initiation in slopes is briefly outlined various ways to identify failure and to approach the transition of the failed mass into a debris flow are discussed in the framework of small strain theory and elasto plastic behaviour a parametric study was carried out to evaluate the relative importance of the most commonly cited parameters that are assumed to influence debris flow initiation it was found that the slope angle is of minor importance in the development of slope instability under loading due to internal water supply transient behaviour was found to be decisive and some critical combinations of water supply over time yielded situations that were likely to encourage the onset of debris flow the significant role of permeability as a function of the degree of saturation in relation to the water supply is demonstrated the proposed three phase model is shown to be an adequate and promising way to address debris flow initiation

initiation process of debris flows on different slopes due to surface flow and trigger specific strategies for mitigating post earthquake in old beichuan county china the 12 may 2008 wenchuan earthquake ms 8 0 in china produced an estimated volume of 28 108 m3 loosened material which led to debris flows after the earthquake debris flows are the dominant mountain hazards and serious threat to lives properties buildings traffic and post earthquake reconstruction in the earthquake hit areas it is very important to understand the debris flow initiation processes and characteristics for designing debris flow mitigation the main objective of this article is to examine the different debris flow initiation processes in order to identify suitable mitigation strategies three types of debris flow initiation processes were identified designated as types a b and c by field survey and experiments in a type initiation the debris flow forms as a result of dam failure in the process of rill erosion slope failure landslide dam or dam failure this type of debris flow occurs at the slope of 10 2 with a high bulk density and several surges following dam failure b type initiation is the result of a gradual increase in headward down cutting bank and lateral erosion and then large amount of loose material interfusion into water flow which increases the bulk density and forms the debris flow this type of debris flow occurs mainly on slopes of 15 3 without surges c type debris flow results from slope failures by surface flow infiltration loose material crack slope failure and fluidization this type of debris flow occurs mainly on slopes of 21 4 and has several surges of debris flow following slope failure and a high bulk density to minimize the hazards from debris flows in areas affected by the wenchuan earthquake the erosion control measures such as the construction of grid dams slope failure control measures the construction of storage sediment dams and the drainage measures such as construction of drainage ditches are proposed based on our results it is recommend that the control measures should be chosen based on the debris flow initiation type which affects the peak discharge bulk density and the discharge process the mitigation strategies discussed in this paper are based on experimental simulations of the debris flows in the weijia huashiban and xijia gullies of old beichuan city the results are useful for post disaster reconstruction and recovery as well as for preventing similar geohazards in the future

evidence for very recent melt water and debris flow activity in gullies in a young mid latitude crater on mars abstract terrestrial debris flows and their deposits are mainly studied and monitored because of their hazardous nature on mars they may serve as geomorphologic indicators of transient liquid water we compared the morphology of debris flow like deposits within a young 0 2 ma mid latitude crater on mars with debris flow fans on svalbard as possible terrestrial analogues it was our objective to constrain whether dry granular flow or processes related to water saturation at or close to the surface were responsible for the formation of the deposits within the crater we found that the morphological attributes of the deposits on mars are very similar to debris flows in svalbard and include overlapping terminal lobes debris tongues and snouts debris flow fans scoured channels with medial deposits debris plugs and clearly defined lateral deposits levees furthermore the interior crater walls display a range of landforms indicating aspect dependent degradation ranging from debris flow dominated pole facing slopes to east and west facing single channel gullies and north facing talus cones granular flow our findings suggest that the debris flows are not related to impact induced heating and release of meltwater we further suggest that degradation of a latitude dependent dust ice mantling unit may only have played a minor role in this youthful terrain instead we propose that the debris flows are mainly formed by melting of very recent snow deposits after the termination of the last martian ice age as such they may represent some of the most recent geomorphological indicators of transient liquid water in the martian mid latitudes the distinct north south asymmetry in degradation further demonstrates that insolation controlled slope processes are surprisingly efficient on mars during the last

factors controlling debris avalanche initiation heavy rainfall during a january 1983 storm triggered numerous debris avalanches and associated debris torrents in the smith creek basin western whatcom county washington united states four classes of debris avalanches are recognized wedges drainage depressions logging roads and discontinuity surfaces nine different debris avalanche headscarps that are representative of these four classes are studied in detail the geometric configuration of each headscarp the properties of soils comprising the headscarps and water tables based on numerical models of hillslope hydrology are used in limit equilibrium slope stability analyses to back calculate root cohesion cr values at failure the calculated values are consistent with those reported by others four groups of cr values are proposed and correlated with forest vegetation group i understory cr range from 1 6 to 2 1 kpa group ii scrub forest cr range from 2 1 to 2 5 kpa group iii mixed forest cr range from 2 5 to 3 0 kpa and group iv old

pre quaternary sea level changes while the paramount importance of global sea level changes has been widely accepted by quaternary geologists throughout this century it is only within the last decade that such changes in the rest of the phanerozoic have received much attention there are two principal reasons for this arousal of interest first increased exploration of the stratigraphic record across the earth both on land and under the sea and significant improvement in biostratigraphic correlation have drawn attention to what appear to have been globally synchronous events second oceanographic research has demonstrated the importance of tectonically controlled changes in the cubic capacity of the ocean basins notably variations in ridge volume which provide a ready mechanism for sea level changes even at nonglacial times the adjective eustatic was first proposed for global changes of sea level by suess 1906 in his great treatise the face of the earth the corresponding noun is eustasy not eustacy as it is commonly misspelt the unconvinced reader need only think of ecstasy eustatic sea level changes can be inferred as suess recognized by a plotting the temporal spread of marine sediments over the continents and b estimating the depositional depth variations in marine stratal sequences which can be correlated across and between continents to these methods can be added seismic stratigraphy in which biostratigraphically age determined seismic sequences on the con tinental margins are analyzed in terms of cycles of coastal onlap and offiap when the results of these methods are broadly in accord confidence in a eustatic interpretation is increased but the range of confidence can vary considerably it is widely accepted that there was an exceptionally high sea