79 ad vesuvius pdc deposits temperatures inferred from optical analysis on woods charred in situ in the villa dei papiri at herculaneum italy abstract determining the deposit temperature of pyroclastic density currents pdcs is a first order priority in the assessment of volcanic hazard for past eruptions in which no direct measurements are possible pdc deposit temperatures have been calculated mainly using magnetic proxies a more recent and innovative approach consists of the determination of the degree of charring of preserved wood fragments by optical analysis in this study we perform optical analyses on wooden beams belonging to the villa dei papiri at the archeological site of herculaneum which was destroyed by pdcs during the 79 ad eruption of vesuvius the new temperature data from this study range between 240 c and 370 c and are in good agreement with literature data for this eruption the large t variation measured can be interpreted as due to the interaction of the pdcs with the local environment i e the impacted buildings of the villa and the sea shoreline the study of in situ charred wood allows to constrain the charring kinetics and to evaluate the sensitivity of the reflectance proxy in recording pdc depositional features we demonstrate that the charcoal reflectance is an excellent proxy for the determination of the pdc deposit temperatures even at a local scale and it can be used in conjunction with or in alternative to other more traditional methodologies especially in case of pre heating effects which may alter the t determinations by thermoremanent magnetization

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

reply to comment on cobenas g thouret j c bonadonna c boivin p 2012 the c 2030 yr bp plinian eruption of el misti volcano peru eruption dynamics and hazard implications journal of volcanology and geothermal research 241 242 105 120 by harpel et al jvgr 2013 abstract the comment provided by harpel et al challenges our interpretation of the most recent plinian eruption of el misti c 2070 yr bp situated near the city of arequipa peru revised age from our previously stated date of c 2030 bp in our view the sequence of deposits points to another example of a plinian pumice rich tephra fall followed by lithic rich pyroclastic density currents pdcs locally late rockslide avalanches have emplaced mass flow deposits on top of pdcs while elsewhere post eruption lahars have led to their remobilization one of the main criticisms from harpel et al was in our interpretation of the deposits as being of pdc origin rather than post eruption lahars we revise each of the diagnostic features that harpel et al have used for attributing the deposits to lahars we present two tables of the revised age of the eruption and criteria based on lithofacies lithological components grain size distribution and statistical indices for each of the c 2070 yr bp old pdc lahar and mass flow deposits our maps and simulations of pdcs and lahars based on two numerical codes with volume inputs from identified deposits around el misti do not fall short of the hazard assessment goal

the effect of paleotopography on lithic distribution and facies associations of small volume ignimbrites the wtt cupa roccamonfina volcano italy abstract the distribution of lithic clasts within two trachytic small volume pumiceous ignimbrites are described from the quaternary white trachytic tuff cupa formation of roccamonfina volcano italy the ignimbrites show a downslope grading of lithics with a maximum size where there is a major break in the volcano s slope rather than at proximal locations this is also the location where ignimbrites are thickest and most massive the break in slope is interpreted to have reduced flow capacity and velocity increasing the sedimentation rate so that massive ignimbrite formed by hindered settling sedimentation ignimbrite cc exhibits no vertical grading of lithics though it does show downslope grading with maximum size at the major break in slope and a rapid decrease further downslope ignimbrite cc thins away from the break in slope and shows an upward fining of the grain size within the topmost few decimeters of the unit the ignimbrite is stratified proximally and grades to massive facies at the break in slope and distally to stratified facies with numerous inverse graded beds the simplest mechanism accounting for these downslope variations is progressive aggradation from a quasi steady nonuniform pyroclastic density current the changes in deposit thickness and facies are interpreted to record downcurrent changes in sedimentation rate the upward fining reflects waning flow inversely graded bedded depositional facies in distal areas is interpreted to reflect flow unsteadiness and a decrease in suspended sediment load ignimbrite cd shows vertical as well as downslope grading of lithics this characteristic coupled with the widespread massive facies of the deposit and the tabular unit geometry are features that can be reconciled with both the debris flow plug analogy for pyroclastic flows sparks 1976 and the progressive aggradation model branney and kokelaar 1992 however none of them appears to satisfy completely the field evidences implying that when dealing with massive ignimbrites other evidence than lithic grading needs to be presented to better understand the related transport and depositional processes

formation of lava tubes and extensive flow field during the 1991 1993 eruption of mount etna detailed mapping during the 1991 1993 eruption of mount etna has shown that there is a relationship between tumuli ephemeral vents lava tubes and their parent lava flows during this eruption many tubes formed in stationary inflated a a lava flows ephemeral vents at the fronts of these stationary flows and above lava tubes fed secondary lava flows many of which subsequently developed new tubes the resulting complex network of tubes ephemeral vents and secondary flows was responsible for most of the widening thickening and lengthening of the 1991 1993 etna lava flow field the supply of relatively uncooled lava via tubes to distal parts of this flow field allowed lava to flow 3 km farther from the vent than the longest channel fed lava flow our observations suggest that lava tubes play a more important role in the formation of extensive a a flow fields on etna than has previously been recognized

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

glacially influenced basin plain sedimentation in the southern faeroe shetland channel northwest united kingdom continental margin abstract quaternary sediments at the southwest end of the faeroe shetland channel are preserved as a basin plain succession of variable fill geometry and lithology in high resolution seismic profiles the basin plain succession is characterised by laterally discontinuous and transparent mounded lensoid bodies interbedded with acoustically well layered sediments which display drape and onlapping reflection configurations the lensoid bodies comprise an up to 50 m thick amalgamated package of mass flow deposits consisting primarily of debris flow diamictons they represent resedimented glacigenic deposits derived from the west shetland shelf accumulation of these packages was episodic and related to specific rapid phases of downslope resedimentation most probably concomitant with ice marginal deposition on the west shetland slope the acoustically well layered sediments include glaciomarine hemipelagites and contourites these indicate phases of reduced sediment supply from the adjacent shelf and slope areas and probably represent the more pervasive background sedimentation in the basin although weak bottom current activity may have prevailed throughout the glacial episodes the onset of vigorous bottom current circulation occurred at the changeover from a glacial to an interglacial regime the debris flow packages form about 50 of the basin plain sediments in this part of the faeroe shetland channel thereby forming a significant component of the deep water succession

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

hydraulics of subaqueous ash flows as deduced from their deposits 2 water entrainment sedimentation and deposition with implications on pyroclastic density current deposit emplacement abstract turbidity currents are the most common flows of water and suspended and bed load sediment occurring in the relatively deep sea and lakes and act as large systems of sediment distribution due to the turbid nature of the flow they may impact subaqueous infrastructures as well as ecosystems during motion so quantifying the turbidity degree is important to predict the current impact a particular type of these currents is the so called volcaniclastic turbidity currents or subaqueous ash flows which are mostly composed of fine grained volcanic particles and are used here as synonymous sensu hydraulic with the meaning of secondary current in this paper a method to estimate the water entrainment column condition model as well as the sedimentation and deposition rates conveyer model in volcaniclastic turbidity currents is proposed by starting from the physical features of the deposits or inverse procedure some criteria of sediment mechanics are used to approximate the flow hydraulic parameters needed to quantify the water entrainment as well as the shear velocity in volcaniclastic turbidity currents the deposits used as case study are the impressive meters thick well sorted rhyolitic ash turbidites of late pliocene cropping out in southern italy particularly in the craco area matera the water entrainment coefficient of the currents is calculated in a range of particle concentration and slope angle whereas the slope angle giving the sedimentation rate is calculated in a range of flow shear velocity which in turns gives the deposition rate the results have a general validity for depositional turbidity currents laden with well sorted sediment and they show that the water entrainment is low for relatively dense slow moving subcritical flows but it increases as the richardson number decreases for relatively dilute fast supercritical flows moreover the sedimentation and deposition rates are high for relatively intense flows moving over gentle slopes but they decrease for relatively weak flows moving over steep slopes the deposit sedimentary structures thus infer sedimentation and particularly depositional processes finally the conveyer model is extended conceptually to pyroclastic density currents when approximating but not exclusively the column condition model in the flow above the flow boundary zone

columnar jointing in vapor phase altered non welded cerro galan ignimbrite paycuqui argentina columnar jointing is thought to occur primarily in lavas and welded pyroclastic flow deposits however the non welded cerro galan ignimbrite at paycuqui argentina contains well developed columnar joints that are instead due to high temperature vapor phase alteration of the deposit where devitrification and vapor phase crystallization have increased the density and cohesion of the upper half of the section thermal remanent magnetization analyses of entrained lithic clasts indicate high emplacement temperatures above 630 c but the lack of welding textures indicates temperatures below the glass transition temperature in order to remain below the glass transition at 630 c the minimum cooling rate prior to deposition was 3 0 10 3 8 5 10 2 c min depending on the experimental data used for comparison alternatively if the deposit was emplaced above the glass transition temperature conductive cooling alone was insufficient to prevent welding crack patterns average 4 5 sides to each polygon and column diameters average 75 cm are consistent with relatively rapid cooling where advective heat loss due to vapor fluxing increases cooling over simple conductive heat transfer the presence of regularly spaced complex radiating joint patterns is consistent with fumarolic gas rise where volatiles originated in the valley confined drainage system below joint spacing is a proxy for cooling rates and is controlled by depositional thickness valley width we suggest that the formation of joints in high temperature non welded deposits is aided by the presence of underlying external water where vapor transfer causes crystallization in pore spaces densifies the deposit and helps prevent welding

origin of ultramafic xenoliths containing exsolved pyroxenes from hualalai volcano hawaii hualalai volcano hawaii is best known for the abundant and varied xenoliths included in the historic 1800 kaupulehu alkalic basalt flow xenoliths which range in composition from dunite to anorthosite are concentrated at 915 m elevation in the flow rare cumulate ultramafic xenoliths which include websterite olivine websterite wehrlite and clinopyroxenite display complex pyroxene exsolution textures that indicate slow cooling websterite olivine websterite and one wehrlite are spinel bearing orthopyroxene olivine cumulates with intercumulus clinopyroxene plagioclase two wehrlite samples and clinopyroxenite are spinel bearing olivine cumulates with intercumulus clinopyroxene orthopyroxene plagioclase two pyroxene geothermometry calculations based on reconstructed pyroxene compositions indicate that crystallization temperatures range from 1225 to 1350 c migration or unmixing of clinopyroxene and orthopyroxene stopped between 1045 and 1090 c comparisons of the abundance of k2o in plagioclase and the abundances of tio2 and fe2o3in spinel of xenoliths and mid ocean ridge basalt and a single 87sr 86sr determination indicate that these hualalai xenoliths are unrelated to mid ocean ridge basalt similarity between the crystallization sequence of these xenoliths and the experimental crystallization sequence of a hawaiian olivine tholeiite suggest that the parental magma of the xenoliths is hualalai tholeiitic basalt xenoliths probably crystallized between about 4 5 and 9 kb the 155 230 c of cooling which took place over about 120 ka the age of the youngest hualalai tholeiitic basalt yield maximum cooling rates of 1 3 10 3 1 91 10 3 c yr hualalai ultramafic xenoliths with exsolved pyroxenes crystallized from hualalai tholeiitic basalt and accumulated in a magma reservoir located between 13 and 28 km below sealevel we suspect that this reservoir occurs just below the base of the oceanic crust at about 19 km below sealevel

a conceptual model for block and ash flow basal avalanche transport and deposition based on deposit architecture of 1998 and 1994 merapi flows the 1998 block and ash flow baf deposits on the western flanks of merapi were described both immediately following emplacement and after one and two wet seasons of erosion this afforded a unique combination of data on deposit morphology and internal structure from proximal to distal reaches the deposits of the basal avalanches from individual baf events were classified into three major and two minor facies in channelised reaches primarily resulting from effects of channel confinement and slope termination reaches were classified into three facies related to preevent topography the deposit facies architecture was interpreted to understand particle transport and deposition within the framework of granular flow systematics the transport model we propose for these basal avalanches involves unsteady flow conditions generated by pulses of collapse as the source and or by development of kinetic waves during the granular flow the coarsest clasts along with low density material migrated to the wave pulse fronts within these flows whereas in bulk flow grain dispersive pressures and kinetic sieving result in coarsest clasts being buoyed to the flow top with this tendency being greatest on higher slopes greater kinetic energy and with greater flow confinement maximising particle collisions deposition begins as the flow reaches near its full extent an initial pulse or flow wave freezes rapidly from its base upward and its rear forward as it looses kinetic energy and dispersive pressure such that an upper higher energy part of the flow is still able to move downstream over the frozen base later waves or pulses then accrete progressively horizontally upslope banking up onto or overtopping earlier deposited sediment hence the overall flow freezes from its front to its tail at termination reaches in unconfined areas the overflowing upper part of flow gradually deposits from its base upward resulting in a slightly tapering sheet formed deposit marked by a front made up of wood fragments and large boulders on sudden slope breaks in termination areas piling up of sediment occurs in flat reaches producing whaleback type forms as the flows rapidly lost competence one implication of this model is that each kinetic wave or flow pulse crest developed within the basal avalanche represents a portion of greater flow depth or stage height hence development of these crests control the ability of parts of the basal avalanche to escape from confined channels and generate unexpected hazards

development of lava tubes in the light of observations at mauna ulu kilauea volcano hawaii during the 1969 1974 mauna ulu eruption on kilauea s upper east rift zone lava tubes were observed to develop by four principal processes 1 flat rooted crusts grew across streams within confined channels 2 overflows and spatter accreted to levees to build arched roofs across streams 3 plates of solidified crust floating downstream coalesced to form a roof and 4 pahoehoe lobes progressively extended fed by networks of distributaries beneath a solidified crust still another tube forming process operated when pahoehoe entered the ocean large waves would abruptly chill a crust across the entire surface of a molten stream crossing through the surf zone these littoral lava tubes formed abruptly in contrast to subaerial tubes which formed gradually all tube forming processes were favored by low to moderate volume rates of flow for sustained periods of time tubes thereby became ubiquitous within the pahoehoe flows and distributed a very large proportionof the lava that was produced during this prolonged eruption tubes transport lava efficiently once formed the roofs of tubes insulate the active streams within allowing the lava to retain its fluidity for a longer time than if exposed directly to ambient air temperature thus the flows can travel greater distances and spread over wider areas even though supply rates during most of 1970 1974 were moderate ranging from 1 to 5 m3 s large tube systems conducted lava as far as the coast 12 13 km distant where they fed extensive pahoehoe fields on the coastal flats some flows entered the sea to build lava deltas and add new land to the island the largest and most efficient tubes developed during periods of sustained extrusion when new lava was being supplied at nearly constant rates tubes can play a major role in building volcanic edifices with gentle slopes because they can deliver a substantial fraction of lava erupted at low to moderate rates to sites far down the flank of a volcano we conclude therefore that the tendency of active pahoehoe flows to form lava tubes is a significant factor in producing the common shield morphology of basaltic volcanoes

catastrophic storm impact and gradual recovery on the mississippi alabama barrier islands 2005 2010 changes in vegetated and total land area and relationships of post storm ecological communities with surface elevation abstract one of the most destructive tropical cyclones ever to strike the u s hurricane katrina made landfall along the mississippi coast on 29th august 2005 the mississippi alabama ms al barrier islands were subjected to storm breaching area reduction and vegetation loss caused by a number of parameters including salt spray saltwater flooding mechanical damage e g ablation of bark from tree trunks removal of plants and their soil substrate by scouring burial under sand and a 10 month post storm period of low rainfall repeated acquisitions of remotely sensed data served as an essential tool in quantifying vegetated and total land area before and after the storm and post storm ecological community type and topographic elevation vegetated land area continued to decline on some islands in the first year following the storm however by november 2007 only 2 2 years after the storm total vegetated land area had recovered to 72 96 77 93 and 82 and total subaerial land area to 97 94 33 100 and 104 of pre katrina values on cat w ship e ship horn and petit bois islands by natural re growth and sediment accretion respectively comparing ecological community type maps that were developed from field and remotely sensed data with lidar derived digital elevation models determined that year 2010 ecological community type changed distinctively at the decimeter scale as mean surface elevation ranged from 0 1 m to 1 2 m storm related changes in ecological community type included subtidal to supratidal sand flat low marsh to wet or dry herbland and woodland to wet herbland shrubland

extensive ash falls in and around the sea of japan from large late quaternary eruptions abstract five widespread ashes of late quaternary age have been recognized on land and also in deep sea sediments in and around the sea of japan all are favorable for determining the magnitude and type of the great eruptions and for establishing a quaternary chronology around japan accurate determination of refractive indices of volcanic glass shards and phenocrysts together with chemical data have enabled successful characterization of the tephra layers and correlation between land and sea of the five tephras two are alkalic and are the products of major eruptions of two korean volcanoes the baegdusan tomakomai ash b tm and the ulreung oki ash u oki the b tm ash is recognized at the top of most cores in the northern part of the sea of japan and also on hokkaido and the northern part of honshu where a reliable archeological age is given around the 11th century the u oki ash occurs between the kikai akahoya and aira tn ashes in cores from adjacent to the ulreung do to central honshu where three radiocarbon ages of around 9300 yr b p were obtained the other three tephras are subalkalic and are correlated with large scale eruptions producing voluminous pyroclastic flows and calderas in kyushu the kikai akahoya k ah aira tn at and aso 4 ashes the former two have been well described already but their fallout areas are partly revised in this manuscript the at ash is the most prominent marker recognized not only on land of japan but also in cores from the whole area of the sea of japan and part of the pacific ocean the airfall aso 4 ash simultaneous with the aso 4 pyroclastic flow eruption is also described it mantles very extensive areas and serves as an important time marker about 70 000 years ago

chronology of tertiary fan deposits off the western barents sea implications for the uplift and erosion history of the barents shelf abstract a combined biostratigraphic and seismic study was performed on three holes drilled in the western barents sea two holes penetrate the thick sedimentary wedge which forms a large fan located off a trough on the barents sea shelf the bjornoyrenna fan the study shows that the fan was built over a short time span in the late pliocene pleistocene mainly due to glacial erosion of the barents shelf region this contrasts earlier age assignments which concluded that fan deposition started in the oligocene the results have a major impact on the understanding of trough mouth fan formation and has important bearing on the history of the sedimentary basins of the barents shelf

experimental craters formed by single and multiple buried explosions and implications for volcanic craters with emphasis on maars 1 craters at many volcanoes including most maars are formed by multiple subsurface explosions experiments compared the crater formed by a single large buried explosion with craters formed by multiple explosions with the same cumulative energy explosive charges were detonated in pads composed of layered aggregates in three configurations 1 a single large charge buried near its optimal crater excavation depth 2 three charges each with 1 3 the energy of the first one buried at approximately the same depth with respect to the original pad surface 3 the same three charges buried successively deeper final crater size in the multiple explosion cases is not a good indicator of the energy of individual explosions however crater morphology and ejecta volume and distribution can be good indicators of explosion energy and depth these results directly impact the estimate of the energy released by past maar eruptions and future hazard assessments

fumarolic pipes in the tshirege member of the bandelier tuff on the pajarito plateau jemez mountains new mexico the objective of this study is to demonstrate the relationships among devitrification vapor phase alteration localization of gas emanations into fumarolic pipes and initial deformation of the ash flow sheet during cooling and lithification utilizing a unique and temporary exposure of the tshirege member of the bandelier tuff near los alamos new mexico we identify several zones of distinctly preserved fossil fumarolic activity the fumarolic zones vary in width from a few centimeters to more than a meter almost ubiquitously these zones demonstrate fines depletion induration of the margins upward flaring geometries and intense fracturing of overlying geologic units the fumaroles were preferentially located on post welding early formed cooling joints that vented to the surface after the vapor phase alteration stage the pipes were regularly spaced at distances of approximately 4 5 m n s to 7 m e w in turn the pipes were covered by a surge deposit and overlying tuff which rapidly lithified the overlying tuff was then brecciated during continued fumarolic pipe emissions geochemical evaluations confirm the presence of high temperature mineral scapolite indicative of transport of hot volcanic gases through these zones the pipe centers and walls are depleted in sio2 and enriched in al2o3 and feo the overlying tuff breccia zones are enriched in al2o3 feo and mgo and depleted in sio2 nao and k2o from comparison to other ignimbrite cooling histories the fissures fumaroles and structures observed all likely formed in the first few decades after the deposition of the upper tshirege subunits this may have significant implications as to timing of initial cooling fractures and subsequent consolidation of gas emission pathways

the effects of topography on sedimentation from particle laden turbulent density currents abstract we present results from a series of laboratory experiments that illustrate the influence of changes in channel topography depth or width on the sedimentation patterns produced by steady particle laden currents on a planar surface in a channel with constant width such currents created deposits that thinned exponentially with distance as long as a current was not blocked to produce a bore topographic features consisting of constrictions ridges and sudden openings caused no significant deviation from exponential deposit thinning or discontinuity in thickness even when there was a transition in flow regime caused by the topographic feature changes in the channel width did affect the distance over which the deposit thinned with the deposits associated with wider parts of the channel thinning more rapidly with distance in contrast if the topographic change was large enough to partially reflect the flow producing an upstream propagating bore then the deposit did not thin exponentially the results are consistent with a model in which the current is assumed to be turbulent and well mixed in this case sedimentation occurs at a rate proportional to the channel width the settling speed of the particles and their concentration within the current and inversely proportional to the current discharge such a model predicts that as a flow passes through a topographic control that does not produce a bore the deposit continues to thin exponentially even if the flow undergoes a transition from the subcritical to the supercritical regime the results suggest that in natural systems changes in current speed and flow regime do not in themselves produce changes in deposit thickness or gradient in thickness unless the flow is partially blocked and a fraction of the flow is reflected upstream

the glacial north sea fan southern norwegian margin architecture and evolution from the upper continental slope to the deep sea basin abstract high resolution seismic data have been used to study the ice stream fed north sea fan deposited from approximately marine isotope stage mis 12 and onwards located at the outlet of the norwegian channel on the se nordic seas continental slope the 110 000 km2 fan is dominated by glacigenic debris flows and slide debrites the fan is divided in two provinces by the volcanic more marginal high the proximal province has been characterised by alternation between deposition and erosion while the distal province has been dominated by deposition from mis 12 until the present the fan has received 32 000 km3 of sediments age constraints on fan stratigraphy provided by core investigations indicate that the fennoscandian ice sheet advanced to the shelf edge during mis 2 6 8 10 and probably 12 the fan experienced megaslides in late mis 6 9 and during mis 11 12

two new end members of pyroclastic density currents forced convection dominated and inertia dominated abstract a great debate on the flow density of pyroclastic density currents pdcs in explosive eruptions has pervaded volcanology over the last decades dade and huppert 1996 dade and huppert 1996 dade and huppert 1997 wilson 1997 pdcs consist of gas particle flows that move for kilometers down the volcano and over the surrounding terrain they are generated because of vertical collapse of an eruptive column woods 1988 valentine and wohletz 1989 or explosion of a lava dome overpressure jet blast esposti ongaro et al 2008 2011 and they flow downstream as radial or unidirectional currents respectively radial currents are also generated because of collapse of an overpressurized mushroom like expanded column dellino et al 2010a pyroclastic fountaining woods and wohletz 1991 clarke et al 2002 or in ignimbrite forming eruptions fisher et al 1980 cas et al 2011 in this paper a new subdivision of pdcs forced convection dominated and inertia dominated is proposed based on flow property a simple pdc simulation and field evidences reveal that forced convection dominated flows may transport own density if they are continuously fed at source favored by steep volcano or channelized inertia dominated flows may leak the density floating over topography

submarine slope stability on high latitude glaciated svalbard barents sea margin abstract slope stability is evaluated at two locations on high latitude deep sea fans along the svalbard barents sea margin based on available samples and using an infinite slope analysis the stability evaluation uses the mohr coulomb failure criterion and a semi analytical approach based on gibson s formulation for determining the excess pore pressure build up due to sedimentation the main results are presented in the form of contour plots of slope safety factors in a diagram with axes of time and thickness of deposit the results show that during rapid sedimentation which mostly takes place during periods of maximum glaciation with the ice front located along the shelf edge slope failure will occur with a frequency varying between 95 and 170 years only part of the upper sedimented layer will be mobilised 10 30 m while the remaining thickness 40 70 m will remain at the initial sedimentation site these results may explain why the continental slope is characterised by relatively uniform sediment thickness from upper to lower slope

formation mechanism of volcanic reservoirs within a volcanostratigraphic framework the case of the wangfu fault depression in the songliao basin china abstract we discuss the reservoir formation mechanisms in volcanic gas reservoirs within a volcanostratigraphic framework with a focus on the huoshiling formation of the wangfu fault depression in the songliao basin china the volcanic sequences are divided from large to small into the volcanic cycle vc cooling unit set cus and cooling unit cu the cu is the basic volcanogenic stratigraphic unit and the cus is a superposition of cooling units which may be recognized on seismic profiles the huoshiling formation consists of two volcanic cycles and one volcanic sedimentary cycle the formation mechanisms of volcanic reservoirs include three processes based on the strata s evolution first cus formed and primary pore spaces developed near cooling surfaces second cuss and vcs formed and parasyngenetic and secondary pore spaces developed around the crater or caldera especially near the weathering surface lastly numerous dissolved pores and structural fractures formed during burial and concentrated near the fault belt cus volcanic edifices and structural systems controlled the formation of volcanic reservoirs the overlapping crater proximal crater region and the faulted area were centres of reservoir formation in the huoshiling formation cus 6 cus 8 and cus 13 are the major horizons where volcanic reservoirs developed forming dissolution reservoirs and structurally fractured reservoirs for natural gas accumulation

deposition of organic matter in the norwegian greenland sea during the past 2 7 million years abstract variations in the amount and composition of sedimentary organic matter in glacial and interglacial deposits of the last 2 7 myr correlate with late cenozoic climatic and oceanographic changes in the norwegian greenland sea these variations are predominantly caused by the changing supply of terrestrial and reworked organic matter the highest amounts of terrestrial organic particles macerals and of reworked coal clasts in glacial and early deglacial diamictons are closely related to glacial erosion of mesozoic strata that crop out along the scandinavian shelf the first occurrence of coal clasts at 2 53 myr demonstrates an initial advance of continental ice margins to these source areas the establishment of anoxic conditions at the sea floor during diamicton deposition probably reflects an increased vertical flux of labile organic matter due to lithogenic adsorbtion followed by an almost complete mineralization at the water sediment interface the content of marine organic matter was continuously low over the past 2 7 myr except for past interglacial highstands i e isotopic event 5 5 1 suggesting persistent diagenetic degradation of the labile organic fraction the marine organic matter exclusively consists of residual dinoflagellate cysts and fragments of them

the c 2030 yr bp plinian eruption of el misti volcano peru eruption dynamics and hazard implications abstract el misti volcano near the city of arequipa in south peru produced a plinian eruption c 2030 yr bp that resulted in a tephra deposit consisting of three fallout layers several pyroclastic density current pdc deposits a late stage small debris avalanche deposit and lahar deposits this vei 4 plinian eruption of el misti has been selected as one of the reference eruptions for the hazard assessment and risk mitigation plan for the city of arequipa the plinian column of this eruption rose up to 21 24 km and produced a tephra deposit over an area of at least 2580 km2 within the 5 cm isopach line the dispersal axis is oriented sw i e towards the area of the basin and city of arequipa later pumice and lithic rich pdc deposits were emplaced into radial valleys extending from the volcano up to a distance of at least 13 km the eruption produced a minimum total bulk volume of 1 2 km3 0 71 km3 dre volume of tephra and pdc deposits components of the tephra deposit consist of beige gray and banded pumices lithic fragments a minor amount of cogenetic dacite clasts and free crystals the minimum volume of the tephra deposit varies between 0 2 and 0 6 km3 exponential power law integration and inversion of tephra2 analytical model the tephra deposit is characterized by a bulk density of 1500 kg m3 which results in a mass of 2 5 9 0 1011 kg the maximum mass discharge rate mdr is 1 1 108 kg s based on a plume height of 24 km the estimated duration of the plinian eruption ranges between 0 6 and 2 3 h grain size distribution componentry and sem analyses of both the tephra and pdc deposits combined with the reconstructed stratigraphic sequence of the deposit suggest that the eruption took place in five stages 1 generation of a 21 24 km high eruptive column that deposited the lower tephra layer 2 collapse of the crater walls and partial obstruction of the vent during a period of decreased intensity which led to the formation of a thin sand sized lithic rich middle tephra layer 3 resurgence of a plinian eruption column that formed the upper tephra layer 4 subsequent collapse of the column that produced the pdc deposits and 5 failure of the hydrothermally altered part of the crater rim towards the s and se that resulted in a coarse lithic rich debris avalanche deposit geochemical and mineralogical data obtained from the banded pumices suggest a mechanical mixing between two magma batches of dacite 70 sio2 and andesite 61 7 64 1 sio2 prior to eruption the abundance of altered lithics in the uppermost tephra layer suggests that the hydrothermal system operating in the summit area of the volcano was partially disrupted and the vent enlarged just before the transition to the collapse of the column

effects of topography on pyroclastic density current runout and formation of coignimbrites laboratory experiments of dilute mixtures of warm talc powder in air simulate dilute pyroclastic density currents pdcs and show the effects of topography on current runout buoyancy reversal and liftoff into buoyant plumes the densimetric and thermal richardson froude stokes and settling numbers for our experiments match those of natural pdcs the laboratory currents are fully turbulent although the experiments have lower reynolds numbers than pdcs in sum our experiments are dynamically similar to natural currents comparisons of currents traversing flat topography or encountering barriers show that runout distance is not significantly reduced for currents that traverse barriers with height

evolution of the norwegian current and the scandinavian ice sheets during the past 2 6 m y evidence from odp leg 104 biogenic carbonate and terrigenous records abstract records of biogenic and terrigenous components have been obtained from the interval corresponding to the last 2 6 m y of odp sites 643 and 644 in order to reconstruct surface and deep water regimes in the norwegian sea surface water regimes record long lasting moderate glacial conditions during the interval 2 6 1 0 ma small intrusions of atlantic water episodically penetrated into the norwegian sea forming a narrow tongue along the eastern margin which is documented at site 644 the polar front was most probably situated between the site 644 and 643 locations on the outer voring plateau during these time intervals deep water regimes reflect long term persistent corrosive bottom waters most probably due to a weakly undersaturated water column and a low rate of carbonate shell production in surface waters deep water production in the norwegian greenland sea may have operated in a different way e g brine formation during winter sea ice growth bottom waters were oxygenated throughout the entire period and deep water was exchanged persistently with the north atlantic increased glacial interglacial environmental contrasts are documented reflecting a strengthening of the norwegian current and intensified glaciations on the surrounding land masses during the interval 1 0 0 6 ma during this time a major shift in the mode of deep water production occurred the onset of large amplitudes in glacial interglacial environmental conditions with maximum contrasts in surface water regimes different modes of deep water production and intensified exchange with the north atlantic marks the last 0 6 ma a broad development of the norwegian current is observed during peak interglacials while during glacials seasonally variable sea ice cover and iceberg drift dominate surface water conditions

late pleistocene sedimentation on the norwegian continental slope between 67 and 71 n abstract the northern norwegian continental margin between 67 and 71 n comprises the gentle slope off the barents sea the relatively steep lofoten islands slope and the step like slope of the voring plateau during the late pleistocene these slopes received large amounts of terrigenous sediments from an extensively glaciated norwegian continental margin through the analyses of 17 gravity cores high resolution 3 5 khz and airgun seismic profiles and sea beam bathymetric data we have examined the late pleistocene sedimentation pattern of this region eight sedimentary facies from the gravity core analysis and seven types of 3 5 khz echo characters indicate that the slopes were moulded by hemipelagic sedimentation commonly associated with iceberg rafting slope failure slump slide and debris flow turbidity currents downslope bottom currents and contour following bottom currents ice rafted debris was dispersed over a broad area including the lower slopes off the barents sea and the lofoten islands and the voring plateau and its outer slope slope failures prevailed on the lofoten islands and voring plateau slopes where the broad glacial margin directly released unsorted glacial sediments during glacial periods on the barents sea slope glacial and reworked shelf sediments were supplied by underflows which were probably caused by cooling of surface shelf water during glacial periods on the upper slope sediments were further transported by turbidity currents and slope crossing bottom currents which excavated numerous small scale channels there are indications of deep sea contour currents at the base of slope and the upper slope off the barents sea and on the voring plateau these currents probably resulted from water exchange between the norwegian greenland sea and the north atlantic ocean during interglacial periods

a historical pyroclastic flow emplaced within a pre existing pleistocene lava tube silidong tianchi volcano changbaishan northeastern china pyroclastic flow deposits recently found within a pre existing lava tube at tianchi volcano represent to the best of our knowledge the only such reported occurrence worldwide in this case pyroclastic flow of tianchi s millennium eruption 1 ka traveled about 18 km from the summit eruptive source and poured successively into the 560 m long accessible segment of silidong lava tube mapping of tube morphology combined with detailed characterization of the features associated with the pumice flow deposits e g adhering of pyroclastic materials on tube walls fumarole pipes rootless vents and flow fronts of the deposit surface has enabled plausible inferences regarding the original within tube conditions and dynamic flow regime during emplacement we propose a model of an aggrading pyroclastic flow which locally varies its sedimentation rate the pyroclastic deposit is thicker in locations of reduced flow mobility and the resultant variations in deposit thickness appear to control the distribution of fumarole pipes and rootless vents

comment on cobenas g thouret j c bonadonna c boivin p 2012 the c 2030 yr bp plinian eruption of el misti volcano peru eruption dynamics and hazard implications journal of volcanology and geothermal research 241 242 105 120 abstract cobenas et al 2012 describe deposits from the 2 ka eruption of misti volcano southern peru they propose a tephra fall deposit overlain by voluminous pyroclastic flow and surge deposits which are overlain by proportionally minor lahar deposits and a debris avalanche deposit of limited distribution some of their data corroborate our earlier work harpel et al 2011 but three of their primary interpretations differ dramatically from ours and have important hazard implications voluminous flowage deposits crop out and we present evidence that the majority contain diagnostic features suggesting that they are lahar deposits rather than pyroclastic flow deposits their pyroclastic flow deposit volume is also unrealistically large and not consistent with the extant deposits the purported debris avalanche deposit is texturally identical to the lahar deposits and has none of the features typically associated with debris avalanche deposits associating such a unit with collapse and formation of a notch in the south crater rim lacks supporting data and disregards the myriad other reasons such notches can form they divide the tephra fall deposit into three beds suggest that it underlies the pyroclastic flow deposits and infer that the eruption ceased after pyroclastic flow formation we delineate six beds and present evidence that the upper beds persistently crop out between the pyroclastic flow and lahar deposits we infer from our eruption sequence that the eruption continued vigorously after pyroclastic flow formation

stratigraphy sedimentology and eruptive mechanisms in the tuff cone of el golfo lanzarote canary islands the tuff cone of el golfo on the western coast of lanzarote canary islands is a typical hydrovolcanic edifice along with other edifices of the same age it was constructed along a fracture oriented nee sww that coincides with the main structural trend of recent volcanism in this part of the island we conducted a detailed stratigraphic study of the succession of deposits present in this tuff cone and here interpret them in light of the depositional processes and eruptive dynamics that we were able to infer the eruptive sequence is represented by a succession of pyroclastic deposits most of which were emplaced by flow plus a number of air fall deposits and ballistic blocks and bombs we distinguished five different eruptive depositional stages on the basis of differences in inferred current flow regimes and fragmentation efficiencies represented by the resulting deposits the different stages may be related to variations in the explosive energy eight lithofacies were identified based on sedimentary discontinuities grain size components variations in primary laminations and bedforms the volcanic edifice was constructed very rapidly around the vent and this is inferred to have controlled the amount of water that was able to enter the eruption conduit the sedimentological characteristics of the deposits and the nature and distribution of palagonitic alteration suggest that most of the pyroclastic succession in el golfo was deposited in a subaerial environment this type of hydrovolcanic explosive activity is common in the coastal zones of lanzarote and the other canary islands and is one of the main potential hazards that could threaten the human population of this archipelago detailed studies of these hydrovolcanic eruptions such as the one we present here can help volcanologists understand the hazards that this type of eruption can generate and provide essential information for undertaking risk assessment in similar volcanic environments

valley pond and ignimbrite veneer deposits in the small volume phreatomagmatic peperino albano basic ignimbrite lago albano maar colli albani volcano italy influence of topography abstract the ca 23 ka small volume basic phreatomagmatic peperino albano ignimbrite from the polygenetic albano maar colli albani volcano central italy shows valley pond facies as well as veneer deposits along the maar rim and along topographic ridges valley pond facies is characterised mainly by massive structure and chaotic texture and can be up to 30 m thick veneer deposit facies is characterised by parallel to low angle cross stratified bedforms alternating fines depleted lapilli sized layers and massive matrix supported beds occurrence of uncharred wood remains and accretionary lapilli suggests temperature of emplacement comprised between 246 and 100 c we have interpreted the lateral facies variations in terms of temporal and spatial variations of the sediment supply from the transport system to the depositional system of the pyroclastic flow ignimbrite veneer facies at the maar rim may reflect pulsatory eruption dynamics whereas valley pond facies may reflect the bulking of the pyroclastic flow inside the valleys and consequent high sedimentation rates ignimbrite veneer facies at topographic ridges has been interpreted to reflect detachment processes of more concentrated undercurrents draining within valleys from the more dilute upper part of the pyroclastic flow that climbs the ridges the present interpretation suggests that processes of pyroclastic flow transformation downcurrent and induced by topography are not necessarily peculiar of hot high mobility pyroclastic density currents the more likely source of water interacting with magma is interpreted to be groundwater contained within the karstic aquifer located at approximately 1 km below the ground level this is inferred by both the large amount of limestone xenoliths present in the peperino albano and the absence of vesicular juvenile clasts the latter implying that magma water interaction occurred before gas exolution processes were significant

late cenozoic prograding wedges on the nw european continental margin their formation and relationship to tectonics and climate abstract during late pliocene to pleistocene times prominent prograding wedges were deposited along the continental margin of nw europe resulting in seaward shelf break migration of up to 150 km much of the sediment accumulation occurred marginal to the former mid to high latitude ice sheets the geographical distribution and stratigraphical and chronological data may suggest that the instigation of the wedges was variously related to tectonic uplift as well as a response to the late pliocene to pleistocene climate deterioration and onset of major northern hemisphere glaciations the onset of wedge growth on the nw uk and irish margins was initiated at about 4 ma in response to tectonic tilting of the margin in that region however glacially derived sediments here comprise a significant proportion of the wedges especially since 0 44 ma for the faroe margin no detailed chronology is available however it may be inferred that onset of glacigenic wedge growth here did not post date that observed on the nw uk and irish margins offshore norway wedge growth has largely occurred since ca 2 7 ma in response to northern hemisphere glaciations also recording a major change in sediments transport routes at 0 8 1 1 ma reflecting larger fennoscandian ice sheets presently it is uncertain whether the glacigenic wedge growth was preceded by a fluvial phase in response to uplift in this area in the western barents sea an early phase of wedge growth was glacio fluvial in character off western spitsbergen the development was similar to that of the barents sea although the glacigenic wedge growth phase may have started somewhat earlier the wedges commonly display gently inclined seaward prograding clinoforms and transparent to chaotic internal acoustic facies sampling of their sediments reveals that they are mainly composed of glacigenic diamicton interbedded with marine and glaciomarine sediments that to various extents have been affected by bottom current action the clinoforms of these wedges vary in geometry from oblique to sigmoidal and they also show varying degrees of aggradation throughout their development the resulting stratal stacking pattern can be attributed to a combination of variations in sediment supply sedimentary processes and accommodation space the latter being a function of tectonic movements and or loading induced subsidence as well as eustatic sea level fluctuations