the uwekahuna ash member of the puna basalt product of violent phreatomagmatic eruptions at kilauea volcano hawaii between 2800 and 210014c years ago abstract kilauea volcano s reputation for relatively gentle effusive eruptions belies a violent geologic past including several large phreatic and phreatomagmatic eruptions that are recorded by holocene pyroclastic deposits which mantle kilauea s summit area and the southeast flank of adjacent mauna loa volcano the most widespread of these deposits whose original distribution can be reconstructed is the uwekahuna ash member of the puna basalt a basaltic surge and fall deposit emplaced during two or more eruptive episodes separated by a few decades to several centuries the first episode occurred between 2770 70 and 2265 50 14 c yr ago it included two major pyroclastic surges each preceded by unusually vigorous lava fountaining from a vent near the volcano s summit before the second eruptive episode 2110 120 14 c yr ago plants had re colonized the rainforest environment northeast of the summit and at least two lava flows from mauna loa had buried parts of the first episode deposits the second episode also began with vigorous lava fountaining followed by widespread lithic ashfall a third major surge and finally a fourth fountaining event before the final pumice deposit could be significantly reworked it was partly buried by picritic basalt flows that are unusual in kilauea s summit area in proximal areas the uwekahuna ash member is more than 1 m thick locally 5 m and includes lithic blocks up to 0 8 m in diameter coarse primarily lithic debris was deposited around the vent by laterally expanding surges fallout deposits accumulated preferentially to the northeast under the influence of high altitude counter tradewinds the area devastated by surges and originally buried by at least 15 cm of the uwekahuna was about 420 km 2 the bulk volume of the deposits was approximately 0 3 km 3 including less than 0 1 km 3 of juvenile material juvenile constituents are olivine tholeiitic basalts similar in major element composition to typical kilauea summit lava flows but variations in both major elements and trace elements suggest that the eruptions tapped more than a single uniform source region we infer that the eruptions which produced the uwekahuna were driven by water interacting with a fluctuating magma column magma withdrawal episodes may have been accompanied by large volume submarine effusive eruptions and by summit collapse the volume extent and character of the uwekahuna deposits underscore the hazards posed by relatively infrequent but potentially devastating explosive eruptions at kilauea as well as at other basaltic volcanoes

clay mineral provinces in tidal mud flats at germany s north sea coast with illite k ar ages potentially modified by biodegradation abstract mineralogical studies chemical analyses and k ar dating were carried out on clay fractions from tidal mud flats along the lower saxony coast and its bays to identify material sources and sedimentary processes at this dynamic interface between air land and sea from the coast into the bays sediments are enriched in fine grained smectite relative to the coarser grained illite chlorite and kaolinite due to the weakening of the tidal current energy in the bays in addition the study area can be divided into two provinces on the basis of the illite k rb ratios and mg contents to the west schiermonnikoog dollart ley bay up to norderney island longshore currents carry suspensions from the belgian and dutch coasts to the east from langeoog island jade bay to the helgoland mud area suspensions from the elbe and weser rivers are mixed with submarine reworked glacial sediments whereas the portion of longshore current suspensions from the west decreases becoming negligible in the helgoland mud area off the elbe and weser estuaries the illite k ar data vary considerably and fail as source indicators due to differential settling and mixing of the clay material and probably to ar loss from illite by biodegradation during digestive processes only further offshore outside the zone of dynamic sediment dispersion do the k ar data fit provenance patterns

a reappraisal of the 1835 eruption of cosiguina and its atmospheric impact in the great january 1835 eruption of cosiguina volcano nicaragua andesitic magma and lithic material were erupted over a period of at least three days proximal facies consist of clastogenic lava scoria fall and lithic ash fall produced by phreatomagmatic to vulcanian or plinian activity together with surge deposits and lithic block falls pyroclastic flow deposits covered some flanks of the volcano and entered the sea in the gulf of fonseca little record exists of the distal ash fall thus the total bulk volume erupted can only be roughly constrained to 2 9 5 6 km3 furthermore the amount of juvenile material is thought to be small a recent study of volatiles in 1835 scoria suggests sulfur release from the magma was negligible this reappraisal indicates that the cosiguina eruption probably had little global climatic impact despite its violent nature the magnitude of the eruption was modest the eruption occurred too late to initiate the northern hemisphere cooling trend form 1828 1836 dry fogs and other atmospheric optical phenomena usually observed after eruptions that contribute significantly to the stratospheric aerosol burden were not recorded after 1835

transport of clay minerals and anthropogenic compounds into the german bight and the provenance of fine grained sediments se of helgoland a large mud body 500 km 2 and up to 21 m thick se of helgoland has been investigated using geochemical mineralogical and sedimentological methods the analysis of 27 sediment cores from this area revealed that overlying older fine grained sediments there is a 9cake9 of muddy polluted sediments up to 3 m thick which has accumulated over the last 100 years it is assumed that human activities like dredging and dumping are responsible for this rapid rate of deposition generally it has been estimated that all of this mud has been supplied by rivers entering this part of the north sea but analyses of sediments from the ems weser and the elbe rivers show that under normal conditions the river sediments do not enter the open sea but are trapped in the estuaries it may therefore be concluded that much of the underlying unpolluted sediments of the mud area were derived from elsewhere or were laid down during an earlier period one possibility is that the lower sediments were deposited when the german bight was a sheltered area protected by a barrier of morainic sediments in the north between helgoland and schleswig holstein this barrier must have been breached more than 2000 years ago

ignimbrites of basaltic andesite and andesite compositions from tanna new hebrides arc tanna island is part of a large volcanic complex mainly subsided below sea level on land two series of hydroclastic deposits and ignimbrites overlie the subaerial remains of a basal mainly effusive volcano the older tanna ignimbrite series oti late pliocene or pleistocene in age consists of ash flows and ash and scoria flow deposits associated with fallout tephra layers overlain by indurated pumice flow deposits phreatomagmatic features are a constant characteristic of these tuffs the younger late pleistocene pyroclastics the siwi sequence show basal phreatomagmatic deposits overlain by two successive flow units each comprising a densely welded layer and a nonwelded ash flow deposit whole rock analyses of 17 juvenile clasts from the two sequences vitric blocks from the phreatomagmatic deposits welded blocks scoriaceous bombs and pumices from the ignimbrites show basaltic andesite and andesite compositions sio2 53 60 in addition 296 microprobe analyses of glasses in these clasts show a wide compositional range from 51 to 69 sio2 dominant compositions at 54 56 58 5 and 61 62 sio2 characterize the glass from the oti glass compositions in the lower phreatomagmatic deposits from the siwi sequence also show multimodal distribution with peaks at sio2 55 57 5 61 62 and 64 whereas the upper ignimbrite has a predominant composition at 61 62 sio2 in both cases mineralogical data and crystal fractionation models suggest that these compositions represent the magmatic signature of a voluminous layered chamber the compositional gradient of which is the result of fractional crystallization during two major eruptive stages probably related to two caldera collapses the oti and siwi ignimbrites represent large outpourings from these magmatic reservoirs the successive eruptive dynamics from phreatomagmatic to plinian emphasize the role of water in initiating the eruptions without which the mafic and intermediate magmas probably would not have erupted

the volcano sedimentary succession of the archean sodium group ventersdorp supergroup south africa volcanology sedimentology and geochemistry abstract the volcano sedimentary succession of the sodium group in the south western corner of the kaapvaal craton rests unconformably on basement granites and is usually correlated with the middle ventersdorp supergroup this neoarchean 2700 ma large igneous province lip has been interpreted as deposited in a tectonic escape basin scenario following the collision of the zimbabwe and kaapvaal cratons or alternatively in a mantle plume induced cratonic rift basin the basaltic komatiitic to andesitic dacitic volcanic sequence and the accommodated sedimentary deposits developed in a graben to half graben setting within a cratonic failed rift system the sodium group sedimentary facies and geochemistry of volcanic rocks correlate well with the ventersdorp supergroup the major and trace element and ree geochemistry correspond with previously published results crow and condie 1988 grobler et al 1989 and the sr and nd isotopy confirms crustal contamination of the sodium group magmatic rocks a preliminary weighted mean 207 pb 206 pb zircon age of 2739 39 ma for a tuff in the upper ongers river formation is reported for the lower part of the sodium group the ongers river t kuip and omdraaivlei formations reflect sedimentation and volcanism in a rift induced graben setting with fast sedimentation from horst flanks and high burial rates in the graben valleys and subsequently a less pronounced topography post graben environment accompanying explosive phreatomagmatic and effusive mafic to acidic bimodal volcanism with abundant pyroclastics delivered ample material for graben fill deposits repeated horst reactivation has episodically exposed the basement to renewed erosion sedimentation along graben flanks comprised alluvial fans mass flow deposits braided river and related modes of deposition in distal shallow lakes volcaniclastic suspension and current sedimentation low density turbidites and stromatolitic reefs were accumulated

archaeological sedimentology of overbank silt deposits on the floodplain of the ohio river near louisville kentucky abstract the surface of the floodplain of the ohio river about 20km southwest of louisville kentucky is a series of linear ridges and swales that are subparallel to the channel of the river which here is relatively straight and flows southward numerous prehistoric occupational sites are located on these ridges the sediments that underlie the ridges which were examined in four archaeological excavations as deep as 8 m are predominantly sandy silt and silty fine to very fine sand and appear to be mainly the product of overbank deposition from suspended load abundant cultural material and occupational sites dating as early as 10 000 years bp are found in the sediments at depths as great as 6 5 m the fine sediments of the floodplain are underlain by sand and gravel the context of the cultural materials and the stratigraphy and morphology of the deposits indicate that the ridged deposits began as linear riverside sand and gravel bars these were succeeded upward by fine grained overbank deposits in which the ridged morphology was maintained because the overbank silt and fine sand were deposited as prograding elongate bars at high water as the floodplain ridge built upward the sedimentation rate decreased and the sand content of the sediments diminished and as the river channel occasionally shifted the ridged deposits were built in successive subparallel sequences two archaeological consequences are implicit in this depositional model of orderly growth of the floodplain first available archaeological data from floodplain segments along other parts of the river should confirm the model and second the model should make it possible to search the floodplains of the ohio river for stratified sites of any desired age

eruption of the dacite to andesite zoned mateare tephra and associated tsunamis in lake managua nicaragua the dacite to andesite zoned mateare tephra is the fallout of a predominantly plinian eruption from chiltepe peninsula at the western shore of lake managua that occurred 3000 6000 years ago it comprises four units unit a of high silica dacite is stratified ash rich lapilli fallout generated by unsteady subplinian eruption pulses affected by minor water access to the conduit and conduit blocking by degassed magma unit b of less silicic dacite is well sorted massive pumice lapilli fallout from the main steady plinian phase of the eruption unit c is andesitic fallout that is continuous from unit b except for the rapid change in chemical composition which had little influence on the ongoing eruption except for a minor transient reduction of the discharge rate and access of water to the conduit after this discharge rate re established to a strong plinian eruption that emplaced the main part of unit c this was again followed by water access to the conduit which increased through upper unit c the lithic rich lapilli to wet ash fallout of unit d is the product of the fully phreatomagmatic terminal phase of the eruption a massive well sorted sand layer the mateare sand replaces laterally variable parts of unit a and lowermost part of unit b in outcrops up to 32 m above present lake level the corresponding interval missing in the primary fallout can be identified by comparing the composition of pumice entrained in the sand and pumice from the local base of unit b on top of the sand with the compositional gradient in undisturbed fallout the amount of fallout entrained in the sand decreases with distance to the lake the mateare sand occurs at elevations well above beach levels and its widespread continuous distribution defies a fluviatile origin instead it was produced by lake tsunamis triggered by eruption pulses during the initial unsteady phase of activity such tsunamis could threaten areas not affected by fallout and represent a hazard of particular importance in nicaragua where two large lakes host several explosive volcanoes

reconstructing eruptions from historical accounts makaturing c 1765 philippines abstract for some volcanoes the only evidence for past eruption is provided by historical accounts when interpreted carefully these have the potential to be a rich source of information and yet they have so far been under utilised in reconstructing eruption histories the navigator thomas forrest describes a large eruption at makaturing volcano southern philippines in approximately 1765 that he considers the catalyst for the local iranun population transitioning from an agrarian society to long distance piracy and slave raiding within the historical literature the eruption is attributed to large scale physical impacts around the volcano and disruptions to trading routes and livelihoods that ultimately changed the course of southeast asia s history however no such eruption or impacts are recognised in the scientific literature or in eruption databases and fieldwork to the region remains difficult here we reinterpret the account of forrest from a multi disciplinary perspective with a historian and physical volcanologists working together to incorporate the greatly needed local context into identifying credible volcanic processes and impacts associated with the reported activity we used a novel approach to eruption reconstruction by cross referencing deposits and impacts inferred from the historical record with stochastic tephra dispersal modelling that considered multiple eruption sources and characteristics we found that forrest s account was best characterised by an eruption of vei 4 between may and october with plume heights in the range of 12 to 16 km while at least one eruption of this size was required to reproduce the impacts described in the historical record it may have formed part of a longer sequence of multiple repeated eruptions in this way such an eruption could have acted as a tipping point for a local population already on the verge of socio political and economic collapse disproportionately affecting regions on a much larger scale than the reported deposits suggest there remains a disconnect between the eruption characteristics recorded in historical accounts and those reproduced by numerical modelling for which we propose alternative interpretations of the historical record unfortunately given the minimal details available about the eruption this discordance is unlikely to be resolved even when geological studies are possible however a valuable benefit of the probabilistic modelling approach presented here is that it highlights the likely direction of tephra dispersal and deposition during a future eruption of makaturing supporting rapid tephra hazard assessment in the event of future unrest

seismicity accompanying the 1999 eruptive episode at telica volcano nicaragua abstract telica volcano nicaragua is a persistently restless basaltic andesite stratovolcano located in the central american volcanic front a high rate of low frequency seismic events lfs has been recorded at telica since the installation of a single vertical component 1 hz seismic sensor teln near its summit in 1993 due to the high rate of lfs at telica traditional methods of forecasting volcanic activity based on increases in the overall rate of seismicity are not applicable therefore an understanding of the nature of precursory changes in telica s seismicity is necessary to forecast future volcanic activity in may 1999 a nine month eruptive episode started at telica consisting of phreatic to phreatomagmatic explosions here we analyse over 29 000 seismic events recorded during a fifteen month period of seismicity bracketing this eruptive episode in an attempt to retrospectively identify precursory changes in seismicity seismic event rates between january 1999 and march 2000 show a reduction in the lf event rate three months before the onset of eruptive activity closely followed by a short lived swarm of high frequency hf 5 hz events after a three month data gap a second reduction in the lf event rate started in august 1999 directly following eruptive activity in august and approximately two months before a series of explosions in october 1999 this reduction in the lf event rate was closely followed by a short lived swarm of hf events that was coincident with the onset of numerous 22 short lived but populous lf multiplets a further reduction in event rate for both lfs and hfs is evident in the months between the october 1999 explosions and explosions on the 29th of december 1999 we suggest that these changes in seismicity reflect a transition from open system degassing to closed system degassing at telica and could signify a change in the volcanic system preceding future episodes of phreatic to phreatomagmatic activity at telica and similar persistently restless volcanic systems worldwide we note that these signals are for phreatic to phreatomagmatic activity and thus may not pertain to magmatic volcanism or to other persistently restless volcanoes prior to their magmatic activity

changes in clay mineral content of tidal flat sediments resulting from dike construction along the lower saxony coast of the north sea germany the clay mineral content of the 2 m fraction in tidal flat sediments in the former harle bay on the lower saxony coast has changed considerably since the thirteenth century up to the present time the proportion of smectite has decreased from 29 to 11 wt whereas the proportion of illite has increased by about 10 wt and those of chlorite and kaolinite by about 3 wt each the chemical composition of the major clay mineral illite has also changed al2o3 has decreased by about 2 wt k2o by about 1 5 wt and sio2 by about 3 wt it can be concluded that the changes in the clay mineral content are mainly influenced by dike construction and sea level rise modifying flow pattern submarine morphology sedimentation and tidal range these processes cause smectite to settle less rapidly because of its small grain size and low density resulting from interlayer water so that the sediment becomes impoverished in this mineral

stability and instability of quiescently active volcanoes the case of masaya nicaragua quiescently active volcanoes are enigmatic due to their restlessness but lack of eruptive activity i present a model of coupled conduit convection and foam accumulation to explain degassing behavior of masaya an active volcano in nicaragua that is currently emitting large amounts of gas but not erupting gas rich magma is transported through a conduit 2 6 m in radius and then released into a shallow reservoir the magma is degassed in the reservoir and forms a foam 1 3 m thick at the top with bubbles 20 60 m in diameter the foam layer is stable because the input of gas into the foam is balanced by gas release through a vent to the surface if the foam layer is destabilized the volcano can erupt explosively the most likely cause of foam destabilization is a large injection of volatile rich magma from deeper levels into the shallow conduit reservoir system thereby increasing magma fluxes and gas fluxes exsolving large gas bubbles and reducing surface tension of the magma

volcanology and eruptive styles of barren island an active mafic stratovolcano in the andaman sea ne indian ocean barren island india is a relatively little studied little known active volcano in the andaman sea and the northernmost active volcano of the great indonesian arc the volcano is built of prehistoric possibly late pleistocene lava flows dominantly basalt and basaltic andesite with minor andesite intercalated with volcaniclastic deposits tuff breccias and ash beds deposited by pyroclastic falls and surges which are exposed along a roughly circular caldera wall there are indications of a complete phreatomagmatic tephra ring around the exposed base of the volcano a polygenetic cinder cone has existed at the centre of the caldera and produced basalt basaltic andesite aa and blocky aa lava flows as well as tephra during historic eruptions 1787 1832 and three recent eruptions 1991 1994 95 2005 06 the recent aa flows include a toothpaste aa flow with tilted and overturned crustal slabs carried atop an aa core as well as locally developed tumuli like elliptical uplifts having corrugated crusts based on various evidence we infer that it belongs to either the 1991 or the 1994 95 eruptions the volcano has recently 2008 begun yet another eruption so far only of tephra we make significantly different interpretations of several features of the volcano than previous workers this study of the volcanology and eruptive styles of the barren island volcano lays the ground for detailed geochemical isotopic and petrogenetic work and provides clues to what the volcano can be expected to do in the future

basaltic thermals and subplinian plumes constraints from acoustic measurements at shishaldin volcano alaska the 1999 basaltic eruption of shishaldin vol cano alaska usa included both strombolian and sub plinian activity as well as a pre subplinian phase inter preted as the local coalescence within a long foam in the conduit although few visual observations were made of the eruption a great deal of information regarding gas ve locity gas flux at the vent and plume height may be inferred by using acoustic recordings of the eruption by relating acoustic power to gas velocity a time series of gas velocity is calculated for the subplinian and pre subplinian phases these time series show trends in gas velocity that are inter preted as plumes or for those signals lasting only a short time thermals the subplinian phase is shown to be com posed of a thermal followed by five plumes with a total expelled gas volume of 1 5 10 7 m 3 the initiation of the subplinian activity is probably related to the arrival of a large overpressurised bubble close to the top of the magma column a gradual increase in low frequency 0 01 0 5 hz signal prior to this trigger bubble may be due to the rise of the bubble in the conduit this delay corresponds to a reservoir located at 3 9 km below the surface in good agreement with studies on other volcanoes the presence of two thermal phases is also identified in the middle of the pre subplinian phase with a total gas release of 4 3 10 6 m 3 and 3 6 10 6 m 3 gas veloc ity at the vent is found to be 82 m s 1 and 90 m s 1 for the subplinian plumes and the pre subplinian thermals respectively the agreement is very good between estimates of the gas flux from modelling the plume height and those obtained from acoustic measurements leading to a new method by which eruption physical parameters may be quantified fur thermore direct measurements of gas velocity can be used for better estimates of the so2 flux released during the eruption

quaternary volcanic stratigraphy of managua nicaragua correlation and source assignment for multiple overlapping plinian deposits a tephrochronological study that began as an active fault mapping program in managua nicaragua following the 1972 earthquake has yielded information with broader geologic relevance seven principal widespread quaternary air fall deposits the managua sequence have been defined the deposits are basaltic or rhyodacitic span probably 11 km 3 dense rock equivalent and are classified as plinian or phreatoplinian regardless of chemical composition two of the units were radiocarbon dated at 6 600 yr b p and 21 000 yr b p as a result of this study ages of the other layers are not as well constrained but are estimated on the basis of soil development and position in the section correlation and source assignment were particularly difficult because of incomplete exposure and similarity of physical and chemical features but they were accomplished with a combination of detailed measurement and sampling at managua reconnaissance mapping and sampling at potential vent areas and application of petrographic mineralogic and chemical correlation methods the close similarity among the rhyodacite pumices posed the greatest difficulty for correlation cluster analysis applied to multielement xrf chemical analyses of pure glass separates gave the best results the clarification of the managua sequence has revealed the local geologic history of managua has characterized the average largest recent nicaraguan eruptions and has defined time stratigraphic markers used for archaeologic and engineering purposes additionally it has provided a regional framework within which to interpret and correlate more detailed studies of individual nicaraguan volcanoes

kuwae 1425 a d the forgotten caldera in vanuatu tongoa and epi islands once formed part of a larger landmass kuwae which was partly destroyed during a cataclysmic seismo volcanic event that is recorded in local folklore it led to the formation of a 12 kmlong and 6 km wide oval shaped submarine caldera with two distinct basins and a total area of 60 km2 at the level of the rim the age ofthis eniption 1420 1430 a d and the structure of the related collapse are discussed and a composite log 143 m of the pyroclastics surrounding the caldera is presented they comprise thick hydromagmatic deposits belonging to a terminal hydromagmatic phase of the pre caldera edifice which grade upwards into two major sequences of pyroclastic flow deposits clearly related to the caldera event collapse near the caldera edge was at least in the range 650 to 950 m and may have been as much as 800 to 1100 m the volume of rocks engulfed during the caldera formation is 32 39 km3 suggesting the same volume of magma was erupted even if two coalescent collapse structures were formed it is worth noting that the kuwae caldera is not a reactivated structure but the result of a single event of short duration which occurred in the first half of the fifteenth century this event is one of the seven biggest caldera forming events during the last 10 000 years and is comparable with the santorini minoan eruption and the crater lake eruption

volcanic eruptions in the longgang volcanic field northeastern china during the past 15 000 years the longgang volcanic field located in northeastern china is volcanically active with a number of eruptions during the quaternary but the chronology of the eruptions is poorly defined some tephra layers are well preserved in the annually laminated sediments of maar lakes in the region and facilitate the construction of a much improved chronological framework for the volcanic history of the area the results of our investigations reveal that three basaltic explosive eruptions occurred at ad 460 11460 cal yr bp and 14000 cal yr bp respectively the largest explosive basaltic eruption ad 460 produced a thick black scoria layer in the longgang volcanic field including lakes the tephra distribution and chronological data suggest that this eruption is likely to be from the jinlongdingzi volcano two basaltic flood eruptions occurred at jinlongdingzi the earlier basaltic eruption produced a lava flow that spread over a forest and encased standing trees two radiocarbon ages obtained from charcoal samples collected from the burned remains of these trees are 1828 1989 cal yr bp and 2164 2359 cal yr bp in the most recent stage of volcanism the lava flow extended only ca 2 km and flowed into lake dalongwan from the present status of the forest ecosystem which has not yet reached the fully mature successional stage we estimate that this lava is very young ca a few hundreds years old jinlongdingzi is a potentially dangerous volcano monitoring and assessment of the potential hazards in the longgang volcanic field should be carried out in the future

pyroclastic flow deposits on venus as indicators of renewed magmatic activity radar bright deposits on venus that have diffuse margins suggest eruptions that distribute debris over large areas due to ground hugging flows from plume collapse we examine deposits in eastern eistla western eistla phoebe and dione regiones using magellan data and earth based radar maps the radar bright units have no marginal lobes or other features consistent with viscous flow their morphology radar echo strength polarization properties and microwave emissivity are consistent with mantling deposits comprised of few cm or larger clasts this debris traveled downhill up to 100 km on modest slopes and blanketed lava flows and tectonic features to depths of tens of cm to a few meters over areas up to 40x103 km2 there is evidence for ongoing removal and exhumation of previously buried terrain a newly identified occurrence is associated with a ridge belt south of ushas mons we also note radar bright streaks of coarse material west of rona chasma that reflect the last traces of a deposit mobilized by winds from the formation of mirabeau crater if the radar bright units originate by collapse of eruption columns with coarse fragmental material entrained and fluidized by hot gases then their extent suggests large erupted volatile co2 or h2o amounts we propose that these deposits reflect the early stage of renewed magmatic activity with volatile rich disrupted magma escaping through vents in fractured regions of the upper crust rapidly eroding under venus surface conditions or buried by subsequent eruptions these markers of recently renewed activity have disappeared from older regions

preeruptive magma viscosity an important measure of magma eruptibility 1 using a compilation of melt compositions meltwater contents temperatures and phenocryst contents the preeruptive viscosities under magma reservoir conditions are calculated for 83 erupted magmas the basaltic to rhyolitic magmas have preeruptive viscosities over the range 101 to 108 pa s although bulk sio2 content has often been used as a qualitative measure of preeruptive magma viscosity the bulk sio2 content shows a weak correlation with magma viscosity correlation coefficient r 0 5 because of a wide range of phenocryst contents from 0 to 50 vol andesitic magmas have viscosities ranging from 102 to 107 pa s which are lower or higher than those of phenocryst poor rhyolitic magmas with 105 to 106 pa s focusing on andesitic to rhyolitic magmas the r between bulk sio2 contents and magma viscosities changes to 0 1 in contrast the melt only sio2 content from a basaltic to rhyolitic melt shows a good linear correlation with melt only viscosity r 0 9 although most of the calculated viscosities of erupted magmas fall below 106 pa s as consistent with the previous compilation study this paper describes 20 examples of highly viscous magmas with 106 pa s in most cases composed of mixtures of high silica rhyolitic melt 75 79 wt sio2 and abundant phenocrysts 30 55 vol in these highly viscous magmas 9 examples have erupted following the precursory eruption of less viscous magma suggesting that precursory dike propagation and conduit formation by the less viscous magma with 106 pa s induced the following eruption of less eruptible highly viscous magmas

compositional variation within some glauconites and illites and implications for their stability and origins textural mineralogical and chemical data are presented for glauconites and illites from the lower cretaceous glauconitic sand formation alberta canada single crystal analyses by scanning transmission electron microscopy stem indicate that both glauconite 29 analyses and illite 44 analyses correspond very closely to ideal dioctahedral structures al dominates the octahedral sheet in illite very extensive a1 for feiii substitution was also found in some of the glauconites much more than previously recorded the dioctahedral mica structure is clearly very stable and flexible with respect to a1 for feiii substitution iron poor glauconites were found associated with pyrite we believe that glauconites tend to lose iron progressively during burial diagenesis especially where pore water iron activities are low high hs activity and low eh it seems probable that a1 for si tetrahedral substitution also takes place during diagenesis with consequent loss of swelling properties this is the same trend which is responsible for conversion of smectite to illite glauconite forms only where sediments reside for lengthy periods at the interface between oxidizing and reducing environments where fe3 is transiently available in solution related marine and terrestrial nontronites also form only in similar interface environments

the k ar and 40ar 39ar methods revisited for dating fine grained k bearing clay minerals abstract the strengths and weaknesses of the two ar isotopic methods k ar and 40ar 39ar were evaluated on the basis of respective recent applications mainly on low temperature k bearing illite type clay minerals this review includes a presentation of basic analytical and technical aspects for both methods as well as a discussion of varied claims on the two methods and of requests about sample preparation and characterization whenever possible the advantages and weaknesses of each method were compared on coeval results obtained by both methods on the same mineral separates the comparative review examines stratigraphic dating of glauconites indirect dating of low temperature ore deposits dating of burial related illitization and dating of polyphased tectono thermal activity more specifically of fault gouges some pending questions such as the necessary encapsulation due to 39ar recoil and its restoration into step heating patterns are also raised together with the new potential of ar dating of nanometric illite crystals weakness of the k ar method is in its pioneering status that makes many believe that it is no longer accurate because of its traditional analytical aspects and of the k determinations leading to somewhat large uncertainties however precise evaluation of varied applications points to a k ar method having probably larger applicability in sedimentary to diagenetic environments than the 40ar 39ar method the drawbacks become less important if the method is applied to nanometer sized clay minerals in diagenetic to low grade metamorphic environments in this instance the extracted size fractions are generally homogeneous and the relative uncertainty given by the age calculations if mathematically justified can be reduced by duplicate analyses weakness of the 40ar 39ar method is in its basics such as the 39ar recoil the necessary encapsulation the reintegration of the 39ar into the step heating patterns and the meaning of the step heating patterns that are more suggestive of variable 39ar reservoirs created among the clay particles by irradiation than of meaningful geologic ages if the k ar method is the preferred method for dating diagenetic clay processes such as glauconitization illite crystal nucleation and growth or low temperature hydrothermal activities then the 40ar 39ar method has more potential in dating low temperature tectono thermal activities and in detailing mixtures of multi generation illite

delamination of smectite in river borne suspensions at the fluvial marine interface an experimental study abstract fine fractions the variations in fwhm d values and peak intensity of the smectitic material are assumed to be caused by an exchange of na for ca in the interlayer spaces and subsequent delamination of the particles along the na activated interlayers only those smectite particles in which adjacent sheets are still stabilized by the remaining ca are preserved after contact with seawater the experiments show that delamination of smectite and i s mixed layer minerals is likely to occur in the brackish environment at the mouth of a river however formation of these fine laminae is expected to be a transitional stage in the development of clay particle size owing to the formation of flocs and aggregates in the higher salt concentrations of seawater

petrology of tholeiitic lavas from tanna island new hebrides importance of cumulative processes in island arc magmatism tanna one of the southernmost islands of the new hebrides volcanic arc is made of late pliocene to recent island arc tholeiitic basalts and andesites with sio2 contents ranging from 45 to 57 these lavas are highly porphyritic 30 50 in volume phenocrysts of plagioclase are the most abundant together with olivine and clinopyroxene the groundmass contain plagioclase augite olivine magnetite and glass pigeonite tridymite sanidine and rarely biotite may also occur the olivines and clinopyroxenes show an iron enrichment from the cores of phenocrysts to their rims and the groundmass crystals but their compositional variations are not correlated with the mg fe ratio of bulk host rocks the most fe rich compositions being found in mg rich lavas plagioclase compositions range from an95 to an60 in the basalts and an60 to an50 in the andesites but within each group they are not correlated with sio2 or na2o contents of host lavas consequently the bulk major element compositions of tanna volcanic rocks cannot be considered as primarily controlled by crystal separation from successive liquids the oxyde sio2 variations diagrams and the modal compositions and mineral chemistry show that crystal accumulation is the predominant mechanism accounting for bulk rock compositions however this does not exclude fractional crystallization the variation of the calculated groundmass mineralogy strongly suggest the occurrence of crystal removal mainly clinopyroxene and magnetite

large volume basaltic hyaloclastite eruption along a propagating land lake lithosphere fracture at lake van eastern anatolia impact of volcanism on the evolution of lake van v the incekaya hyaloclastite cone eastern anatolia turkey the focal point along a major eruptive fissure was the main source of an unusually large explosive basaltic eruption the ca 80 ka old eruption began onshore with scoria cones from a 5 km n s fracture propagating toward lake van surface area of 3755 km2 at the intersection with the fault bounded lake basin a ca 400 m high subaerial hyaloclastite edifice formed which can be crudely subdivided into a main lower massive bulk of hydrothermally altered lithic rich hyaloclastites cl topped unconformably by a 30 m thick well bedded fallout tephra cu the cu tephras are correlated with 1 widespread onshore hyaloclastite fallout deposits mostly west southwest of the cone and 2 a ca 2 m thick ca 80 ka old bedded hyaloclastite v 60 part of a 220 m icdp international continental scientific drilling program core drilled in lake van 27 km n of incekaya the hyaloclastite unit was seismically identified as being the most widespread and well defined reflector throughout much of western lake van a minimum volume of 9 km3 fallout hyaloclastite tephra is estimated when the area of the seismic reflector is extrapolated to the coast and 2 km inland seismic reflectors also suggest at least two hyaloclastite intralake cones rising up to 388 m above the lake sediment surface 1 5 km nw off incekaya cone and were possibly erupted along the same fracture the total volume of hyaloclastites includes a subaerial incekaya cone b the inferred subaqueous continuation of the cone s c the bedded intralake and onshore deposits and tentatively d a widespread seismically defined mass flow deposits directly beneath incekaya reflector of roughly 20 km3 and may represent the deposits of explosively erupted basaltic magma sideromelane shards the main clast type are dominantly angular and most show 50 vol vesicles less common tachylite clasts are poorly vesicular 50 vol structural transitions and interlayering between tachylite and sideromelane are ubiquitous fluidal and pumiceous lapilli are present in the basal massive facies bulk rock and glass compositions indicate constant composition of the slightly evolved al rich basalt magma olivine fo78 82 and plagioclase an70 80 microphenocrysts many skeletal with growth features and microlites make up 1 vol and suggest rapid magma ascent the high explosive energy of the eruption is interpreted to be due to 1 high magma discharge rates and shearing in the eruptive jet and 2 magma water interaction conditions approximate temporal coincidences with the incekaya eruption include the following a an abrupt cessation in the supply of evolved tephra from the adjacent suphan volcano to the lake sediments which ended abruptly for ca 60 ky b an extreme fall in lake level by ca 150 m and c a drastic increase in pore water salinity na and cl g l and ph

atmospheric dispersion environmental effects and potential health hazard associated with the low altitude gas plume of masaya volcano nicaragua masaya volcano 560 m a s l nicaragua re sumed its degassing activity in mid 1993 with the con tinuous emission of so 2 at rates increasing from 600 metric tons t day 1 7 0 kg s 1 in 1995 to 1800 t day 1 21 0 kg s 1 in 1999 the low altitude gas plume is typically blown westward by the prevailing wind across the masaya caldera and las sierras high lands which are at a higher elevation than the gas vent in this study the areal distribution of atmospheric so 2 concentrations was monitored within 44 km of the vent with a network of passive samplers measured so 2 air concentrations ranged from 2 to 90 ppbv in 1998 and from 2 to 230 ppbv in 1999 the data suggest that the volcanic emissions influenced air quality across a 1 250 km2 area downwind local topography exerts a strong control on plume dispersal and hilltops are particularly prone to fumigation and thus to high ambient so 2 lev els in a zone 22 km2 in size located within 15 km of the source the response of vegetation to sustained exposure to high atmospheric dose of volcanic so 2 and hf result ed in a strong reduction in the number of plant communi ties a transition zone of somewhat indefinite boundary surrounds the devastated zones and exhibits vegetation damage in the form of leaf injury in addition to the envi ronmental impacts of the volcanic emissions both short and long term public health hazards may exist in areas most exposed to the plume the harmful effects of the volcanic emissions on cultivated vegetation could be di minished by using windbreaks made of gas tolerant trees and shrubs such as eugenia jambos brosimum utile and clusia rosea the current gas crisis at masaya volcano provides an unique opportunity for investigating the at mospheric environmental and medical impacts of volca nic gases and aerosols

first insights into mid holocene environmental change in central vanuatu inferred from a terrestrial record from emaotfer swamp efate island abstract here we present the first terrestrial record of mid holocene environmental changes in vanuatu this preliminary multi proxy analysis of core tfer 06 from emaotfer swamp efate island indicates changes in environmental conditions are mainly related to variations in climate over the last 6500 cal yr bp drier periods are broadly correlated with an increase in sustained el nino events recorded in the pacific on a decadal timescale the earliest change is the disappearance of mangroves adjacent to the site around 3200 cal yr bp this could well be due to both local tectonic uplift with subsequent hydrostatic adjustment and the onset of a drier period from c 3250 2500 cal yr bp the prevailing drier conditions can be linked to more persistent el nino conditions local volcanic events had limited ecological impact on the area freshwater diatoms indicate a hydroseral succession species living on submerged plants being common in muds from c 3250 1500 cal yr bp but rare in fibrous peat deposited later palaeoecological indicators of human impact have not been identified throughout this work

geochemistry vs seismo tectonics along the volcanic new hebrides central chain southwest pacific abstract compositional variations major and trace element of pleistocene to present rocks along the volcanic new hebrides central chain southwest pacific are presented and discussed using a new set of analyses we focus in particular on the anomalous mg k lile and lree rich and al and si poor character of the basalts from aoba and santa maria volcanoes and to a lesser extent from ambrym volcano all located in the area where the d entrecasteaux zone collides with the arc in addition we note a compositional transition from normal arc basalts to boninite related high mg andesites at the southern termination of the nhcc the peculiar composition of the rocks of the volcanoes facing the d entrecasteaux zone has traditionally been related more or less directly to the collision subduction occurring in this area we present an alternative hypothesis of a strong geochemical anomaly under santa maria and aoba volcanoes unrelated to this collision in this model a westward and upward invasion of dupal type enriched mantle corroborated by the pattern of intermediate seismicity occurs under this part of the arc in strong contrast to the usual pacific type morb mantle source present under all other volcanoes of the nhcc such a dupal type source may explain the anomalous geochemistry of the resulting volcanic products

shallow magma mingling driven strombolian eruptions at mt yasur volcano vanuatu 1 mt yasur volcano vanuatu has been increasingly recognized for its high frequency strombolian eruptions strombolian activity is often regarded as a product of the rapid ascent of gas slugs originating from a deep magma which mingle with a batch of shallow magma upon eruption heterogeneous crystal distribution as well as bimodal bubble size distributions in the eruptive products generally supports this view here the strombolian activity at mt yasur is analyzed a rheological investigation indicates that the basaltic andesitic eruptive products contain an apparently homogeneous glass phase and yet exhibit evidence of a distinct range of glass transition temperatures with multiple peaks occurring in individual samples such anomalous behavior is proposed to result from the mingling of magmas with contrasting oxidation states the unstable nature of the measured glass transition behavior leads us to the inference that mingling is located in the shallow parts of the eruptive conduits partly driven by rejuvenation of material slumped from the crater walls into an open conduit system the dynamics of this process may expose the periodicity of the eruptions themselves

collecting field data in volcanic landscapes using small uas suas drones abstract the last several years have seen a very rapid increase in the development and availability of unmanned aerial vehicles systems uav or uas more commonly called drones uas are remotely operated aerial vehicles that can be fixed wing planes helicopters or aerial systems with multiple propellers small versions of uas here called suas in particular have become so prevalent that they can be easily purchased at general retail stores this paper seeks to review and summarize the use of suas in volcanic research given their size low cost and relative durability suas provide a light weight tool platform that is easy to transport to field locations quick to set up and easy to launch and control they require very little launch and recovery space because of these characteristics suas are useful in collecting immediate and real time aerial data especially in remote inaccessible dynamic and or hazardous volcanic environments in volcanic areas suas have been used for mapping sample collection thermal imaging magnetic surveys slope stability studies and as platforms for sensors to measure outgassing of co 2 and so 2 they are also becoming invaluable for real time hazard assessment during and after an eruption they are however limited by their flight time which is greatly affected by wind speeds since they are predominately made of plastic they are also impacted by the high thermal temperatures found in active volcanic areas which can degrade their structure and performance with continued technological improvement however suas have the potential to dramatically improve our ability to collect field data because of additional natural technological and legal challenges related to their use it is critical that users be aware of and adhere to all national and local laws associated with suas

rapid response of a hydrologic system to volcanic activity masaya volcano nicaragua hydrologic systems change in response to volcanic activity and in turn may be sensitive indicators of volcanic activity here we investigate the coupled nature of magmatic and hydrologic systems using continuous multichannel time series of soil temperature collected on the flanks of masaya volcano nicaragua one of the most active volcanoes in central america the soil temperatures were measured in a low temperature fumarole field located 3 5 km down the flanks of the volcano analysis of these time series reveals that they respond extremely rapidly on a time scale of minutes to changes in volcanic activity also manifested at the summit vent these rapid temperature changes are caused by increased flow of water vapor through flank fumaroles during volcanism the soil temperature response 5 c is repetitive and complex with as many as 13 pulses during a single volcanic episode analysis of the frequency spectrum of these temperature time series shows that these anomalies are characterized by broad frequency content during volcanic activity they are thus easily distinguished from seasonal trends diurnal variations or individual rainfall events which triggered rapid transient increases in temperature during 5 of events we suggest that the mechanism responsible for the distinctive temperature signals is rapid change in pore pressure in response to magmatism a response that can be enhanced by meteoric water infiltration monitoring of distal fumaroles can therefore provide insight into coupled volcanic hydrologic meteorologic systems and has potential as an inexpensive monitoring tool

likelihood of basaltic eruptions as a function of volatile content and volcanic edifice size a simple physical model is used to link eruption likelihood in continental regions to the size and shape of the volcanic edifice as well as to magma density and volatile content a volcanic edifice acts as a surface load and modifies the stress field in upper crustal levels including the magma chamber it affects the critical magma overpressure for reservoir failure as well as the conditions of dyke ascent from reservoir to surface calculations are made for dyke ascent in the stress field due to an overpressured reservoir beneath an edifice different edifice shapes are investigated from shield volcanoes with gentle slopes to stratovolcanoes with steeper flanks beneath a mature volcanic edifice magmatic overpressures required for reservoir failure are large but not large enough for a dyke to reach the central vent area at the summit thus basaltic summit eruptions can only occur if the amount of dissolved volatiles exceeds some threshold value which increases with edifice size and hence must be in explosive regimes unless magma is able to degas at shallow depths for mature volcanic systems edifice collapse or destruction may lead to renewed basaltic activity through the central vent area

proboscideans and paleoenvironments of the pleistocene great lakes landscape vegetation and stable isotopes abstract in this study we review the history of proboscideans in the great lakes region ontario and western new york in the context of local glacial and vegetational histories further we investigate mammoth mammuthus and mastodon mammut environmental niche partitioning using stable isotope analysis of bone and dentin collagen 13 c col 15 n col and structural carbonate in tooth enamel bioapatite 13 c sc 18 o sc and demonstrate that stable isotopes can be used to identify non locals among museum specimens with no contextual records new radiocarbon dates suggest that ontario mastodons lived in tundra like environments as well as their more common spruce forest habitat local ontario new york mammoths and mastodons consumed 100 c 3 plant diets and drank low 18 o waters consistent with colder than modern climates and proximity to glacial meltwater sources mammoths and mastodons occupied distinct environmental niches characterized by different oxygen and nitrogen isotope compositions and geographical locations this suggests that direct competition for resources was not a major factor in their local extinction we suggest that both mammoths and mastodons obtained water from sources formed primarily from precipitation rather than glacial meltwater we describe how high 15 n values in mammoths could have been caused by a combination of preferences for dry environments consumption of low nutrient forage particularly stems and stalks coprophagy geophagy and dung fertilization we argue that low 15 n values in mastodons could have been caused by consumption of trees and shrubs including nitrogen fixing taxa and a preference for recently deglaciated landscapes and or spruce environments finally we raise the possibility that mastodons contributed to the spruce pine transition by browsing directly on spruce trees

symmetrical and segmented variation of physical and geochemical characteristics of the central american volcanic front abstract the regional variation of physical and geochemical characteristics of central american volcanoes occurs in two fundamentally different patterns the first pattern is symmetrical about nicaragua crustal thickness silica contents of mafic lavas and volcanic edifice heights are lowest in nicaragua and increase smoothly toward costa rica to the south and guatemala to the north magma density is maximum in nicaragua and decreases smoothly outward the regional variation in crustal thickness is just enough so that magma densities calculated at appropriate moho pressures are the same at the base of the crust throughout the region this is consistent with magma ponding at the base of the crust the bulk compositions of central american basalts show the same symmetrical variation suites of nicaraguan basalts plotted in pseudo ternary cmas projections indicate large olivine and plagioclase primary phase volumes toward costa rica and guatemala the olivine and plagioclase fields inferred from suites of basaltic lavas are smaller which is consistent with fractionation at increasing depth the second pattern is the segmentation of the volcanic front and the plate margin in general the segmentation strongly affects the spacing and size of volcanic centers at segment boundaries volcanic centers are generally small and unusually widely spaced toward segment interiors volcano spacing and size increase systematically the lil element contents of lavas strongly reflect this pattern for lavas with similar silica contents the larger the volcano the higher the lil element contents the relationships between segmentation volcano spacing and volcano size are compatible with diapiric rise of magma accumulated in narrow ribbons near the upper surface of the underthrust slab the relationship between volcano volume and lil element content is qualitatively in agreement with an open system fractionation model

a global synthesis of lava lake dynamics abstract active lava lakes represent a variety of open vent volcanism in which a sizable body of lava accumulates at the top of the magma column constrained by the vent and or crater geometry the longevity of lava lakes reflects a balancing of cooling and outgassing occurring at the surface and input of hot and gas rich magma from below due to their longevity and relative accessibility lava lakes provide a natural laboratory for studying fundamental volcanic processes such as degassing convection and cooling this article examines all seven lakes that existed at the time of writing in 2018 located in the pacific antarctica africa and south and central america these lakes span all tectonic environments and a range of magma compositions we focus on analysis of the lake surface motion using image velocimetry which reveals both similarities and contrasts in outgassing and lake dynamics when comparing the different lakes we identify two categories of lake behavior organized erta ale nyiragongo k lauea after 2011 and erebus and chaotic villarrica masaya marum this division does not map directly to lake size viscosity gas emission rate or temperature instead when examined together we find that the lakes follow a linear relationship between average surface speed and the ratio of total gas flux to lake surface area this relationship points to the combined importance of both flux and lake size in addition to the total volume of gas emission and suggests that a shared deep mechanism controls the supply of heat and gas to all lakes on the other hand the differences between chaotic and organized lakes highlight the important role of the geometry of the conduit lake transition which superimposes a shallow signal on that of the deep circulation the spatial patterns of surface motion we document suggest that the release of gas bubbles at chaotic lakes is more efficient i e bubbles are less likely to be retained and recycled compared with organized lakes in addition the data presented here indicate that the solidified crust of organized lakes plays a role in regulating convection and outgassing in lava lakes

caldera development during the minoan eruption thira cyclades greece the well known caldera of thira santorini greece was not formed during a single eruption but is composed of two overlapping calderas superimposed upon a complex volcanic field that developed along a ne trending line of vents before the minoan eruption of 1400 b c thira consisted of three lava shields in the northern half of the island and a flooded depression surrounded by tuff deposits in the southern half andesitic lavas formed the overlapping shields of the north and were contemporaneous with and in many places interbedded with the southern tuff deposits although there appears to be little difference between the composition of magmas erupted differences in eruption style indicate that most of the activity in the northern half of the volcanic field was subaerial producing lava flows whereas in the south eruptions within a flooded depression produced a sequence of mostly phreatomagmatic tuffs many of these tuffs are plastered onto the walls of what appears to have been an older caldera most probably associated with an eruption of rhyodiacitic tephra 100 000 years ago the minoan eruption of about 1400 b c had four distinct phases each reflecting a different vent geometry and eruption mechanism the minoan activity was preceded by minormore eruptions of fine ash 1 the eruption began with a plinian phase from subaerial vent s located on the easternmost of the lave shields 2 vent s grew toward the sw into the flooded depression subsequent activity deposited large scale base surge deposits during vent widening by phreatomagnetic activity 3 the third eruptive phase was also phreatomagmatic and produced 60 of the volume of the minoan tuff this activity was nearly continuous and formed a large featureless tuff ring with poorly defined bedding less

la pacana caldera and the atana ignimbrite a major ash flow and resurgent caldera complex in the andes of northern chile the recently discovered la pacana caldera 60 35 km is the largest caldera yet described in south america this resurgent caldera of pliocene age developed in a continental platemargin environment in a major province of ignimbrite volcanism in the central andes of northern chile at about 23 s latitude collapse of la pacana caldera was initiated by the eruption of about 900 km3 of the rhyodacitic atana ignimbrite the atana ignimbrite was erupted from a composite ring fracture system and formed at least four major ash flow tuff units that are separated locally by thin air fall and surge deposits all four sheets were emplaced in rapid succession about 4 1 0 4 ma ago caldera collapse was followed closely by resurgent doming of the caldera floor accompanied by early postcaldera eruptions of dacitic to rhyolitic lava domes along the ring fractures the resurgent dome is an elongated asymmetrical uplift 48 5 12 km which is broken by a complex system of normal faults locally forming a narrow discontinuous apical graben later postcaldera eruptions produced large andesitic and dacitic stratocones along the caldera margins and dacitic domes on the resurgent dome beginning about 3 5 ma ago and persisting into the quaternary hydrothermally altered rocks occur in the eroded cores of precaldera and postcaldera stratovolcanoes and along fractures in the resurgent dome but no ore deposits are known a few warm springs located in salars within the caldera moat appear to be vestiges of the caldera geothermal system

build up and depositional dynamics of an arc front volcaniclastic complex the miocene tepoztlan formation transmexican volcanic belt central mexico volcanic terrains such as magmatic arcs are thought to display the most complex surface environments on earth ancient volcaniclastics are notoriously difficult to interpret as they describe the interplay between a single or several volcanoes and the environment the early miocene tepoztlan formation at the southern edge of the transmexican volcanic belt belongs to the few remnants of this ancestral magmatic arc and therefore is thought to represent an example of the initial phase of evolution of the transmexican volcanic belt based on geological mapping detailed logging of lithostratigraphic sections palaeocurrent data of sedimentary features and anisotropy of magnetic susceptibility mapping of two dimensional panels from outcrop to field scale and geochronological data in an area of ca 1000 km 2 three periods in the evolution of the tepoztlan formation were distinguished which lasted around 4 myr and are representative of a volcanic cycle edifice growth phases followed by collapse in a magmatic arc setting the volcaniclastic sediments accumulated in proximal to medial distances on partly coalescing aprons similar to volcanic ring plains around at least three different stratovolcanoes these volcanoes resulted from various eruptions separated by repose periods during the first phase of the evolution of the tepoztlan formation 22ae 8t o 22 ae2 ma deposition was dominated by fluvial sediments in a braided river setting pyroclastic material from small andesitic dacitic composite volcanoes in the near vicinity was mostly eroded and reworked by fluvial processes resulting in sediments ranging from cross bedded sand to an aggradational series of river gravels the second phase 22ae 2t o 21 ae3 ma was characterized by periods of strong volcanic activity resulting in voluminous accumulations of lava and tuff which temporarily overloaded and buried the original fluvial system with its detritus continuous build up of at least three major volcanic centres further accentuated the topography and in the third phase 21ae 3t o 18 ae8 ma mass flow processes represented by an increase of debris flow deposits became dominant marking a period of edifice destruction and flank failures

composition and origin of clay minerals in holocene sediments from the south eastern north sea the distribution of clay minerals varies systematically in sediments from holocene core material taken along a profile from the east frisian coast to the doggerbank the proportion of illite increases with distance from the coast at the expense of kaolinite whereas slight variations are seen in smectite and chlorite abundances the chemical composition changes and the k rb ratio and k ar isotopic age of illite increase seawards this trend results from progressive mixing processes of riverine detritus with pleistocene fluvioglacial material reworked during the holocene transgression however the clay fluvial flux only became dominant during the decreasing rate of sea level rise in the late holocene especially near the shore for example modern sediments in tidal flats contain 75 of river borne holocene supplied clay detritus whereas this amount is only 10 in modern marine sediments at the doggerbank

vegetation history in central kentucky and tennessee usa during the last glacial and deglacial periods abstract knowledge about vegetation dynamics during the last glacial and deglacial periods in southeastern north america is under constrained owing to low site density and problematic chronologies new pollen records from two classic sites anderson pond tn and jackson pond ky supported by ams 14 c age models span 25 2 13 7 ka and 31 0 15 4 ka respectively a transition from pinus dominance to picea dominance is recorded at jackson pond ca 26 2 ka coincident with heinrich event h2 anderson and jackson ponds record a transition from conifer to deciduous tree dominance 15 9 and 15 4 ka respectively marking the development of no analog vegetation characterized by moderate to high abundances of picea quercus carya ulmus fraxinus ostrya carpinus cyperaceae and poaceae and preceding by 2000 yr the advent of similar no analog vegetation in glaciated terrain to the north no analog vegetation developed as a time transgressive south to north pattern mediated by climatic warming sporormiella abundances are consistently low throughout the jackson and anderson pond records suggesting that megafaunal abundances and effects on vegetation varied regionally or possibly that the sporormiella signal was not well expressed at these sites additional records with well constrained chronologies are necessary to assess patterns and mechanisms of vegetation dynamics during the last glacial and deglacial periods

plinian airfall deposits of basaltic composition two widespread scoria fall deposits locally known as the fontana lapilli and san judas formation are demonstrated to have issued from masaya caldera complex nicaragua and to be the first documented plinian airfall deposit of basaltic composition data from maps of median grain size average maximum pyroclast diameter and average maximum diameter of lithic fragments provide conclusive evidence of the plinian nature of both deposits the volume within the 1 mm isopach of the fontana lapilli is 12 km3 3 4 km3 dense rock equivalent and within the san judas formation it is 1 2 km3 0 35 km3 dre theoretical eruption parameters calculated for the fontana lapilli and san judas formation respectively include muzzle velocity 170 m s and 150 m s column height 50 km and 18 km volume eruption rate 2 105 m3 s and 1 104 m3 s and duration 2 h and 10 h these are all similar to the calculated parameters for silicic plinian eruptions basaltic magmas are generally considered incapable of erupting in the manner characteristic of plinian eruptions recognition of them argues that factors other than high viscosity may be of fundamental importance

dispersal and characteristics of pyroclastic fall deposits from mt misery volcano west indies mt misery volcano near the northern end of the lesser antilles island arc produced late quaternary airfall layers that have different dispersal patterns these are controlled by a the style of explosive activity which determined the heights of the eruption columns and b a layered atmospheric system with contrasted bipolar wind directions at different altitudes isopach and isopleth maps are given for 10 eruptions belonging to the mansion series 41 730 1 750 yrs b p basaltic strombolian type scoria fall deposits were dispersed mainly by surface lower tropospheric winds to the nw and w in contrast green and brown andesitic sub plinian and plinian falls with higher eruption columns were dispersed to the se and e by upper tropospheric winds thinly laminated phreatomagmatic ashes within the mansion series are again dispersed to the nw and controlled by surface winds

giant tuff cone and 12 km wide associated caldera at ambrym volcano vanuatu new hebrides arc abstract ambrym in the new hebrides arc has been considered as an effusive basaltic volcano the present paper discusses the general structure of this edifice which consists of a basal shield volcano topped by an exceptionally large tuff cone surrounding a 12 km wide summit caldera dacitic pyroclastic flow deposits are exposed in the lower part of the tuff series they grade upward into composite sequences of bedded surtseyan type hyaloclastites ash flow deposits and fallout tephra which are essentially basaltic in composition in such a way that the tuff cone may be considered as mainly basaltic the relationship between the eruption of pyroclastics and the collapse event precludes a classical model of caldera formation at a basaltic volcano in which quiet subsidence i e kilauea type is the dominant mechanism interpretation of the tuff series implies intervention of external water and suggests both explosive and collapse mechanisms a model of caldera formation which assumes an enlargement of the ring fracture during a first plinian and dacitic then essentially hydrobasaltic eruption is proposed

sulfur and halogen gases at masaya caldera complex nicaragua total flux and variations with time santiago crater of masaya caldera complex near managua nicaragua entered a phase of intense magmatic degassing in late 1979 the flux of so2 increased rapidly from a previous average of 380 t d 1 to approximately 1200 t d 1 in february 1980 we report on results of a study of the gas flux and geochemistry conducted as part of a broader interdisciplinary study of the volcano and its impact on the adjacent environment masaya is an unusual volcano because of its low shield like form consistent tholeiitic basaltic composition frequent activity and especially because of the approximately 25 year cycle of major non eruptive degassing crises we have used a combination of techniques involving remote sensing using a correlation spectrometer cospec of the flux of so2 and direct filter sampling of the ratios of the sulfur and halogen gases and aerosols to quantify the flux of all of these species the three stage filters successively trap aerosols halogen acid gases and sulfur dioxide and are analyzed by ion chromatography we have used the ratios of various species with the cospec measurements of the flux of so2 to calculate that the average flux of so2 is 1275 t d 1 hcl is 830 t d 1 hf is about 16 t d 1 and hbr is at most 1 t d 1 h2s and so4 are only minor sulfur species the flux of so2 and hcl represents the largest reported noneruptive sustained volcanic release of these species in the world masaya contributed 7 of the total so2 estimated to have been released by volcanoes worldwide in 1981 the flux of so2 has declined by about 9 each year since 1979 and can be modeled as a first order kinetic rate law with a decay constant of approximately 0 04 yr 1 approximately 2 2 106 tons of so2 has been released between september 1979 and september 1985 the ratio s cl has declined more rapidly than the flux of so2 reflecting the greater solubility of hcl than so2 in the magma the so2 flux at santiago varies more widely within a single day than observed at other degassing volcanoes and may be controlled at least in part by effects of the solid earth tide an area larger than 500 km2 has been severely impacted downwind of the volcano downwind ground level concentrations of so2 of 0 25 ppm are frequently encountered acid rain unusually chloride rich has a ph as low as 2 63 s cl ratios in the gas plume increase downwind probably as a result of the high solubility and dry deposition velocity of hcl preliminary analyses of primary concentrations of sulfur and chlorine in the magma of the present lava lake are used to calculate that at least 1 2 km3 has been completely degassed with respect to sulfur to provide the observed flux this implies that 10 km3 have been degassed by previous crises in the past century and further suggests a magma supply rate of approximately 0 1 km3 yr comparable with kilauea or etna volcanoes during historic time only two lava flows have been extruded implying an unusually low ratio of extrusion intrusion of only 0 0007

isotopic paleoecology of clovis mammoths from arizona the causes of megafaunal extinctions in north america have been widely debated but remain poorly understood mammoths mammuthus spp in the american southwest were hunted by clovis people during a period of rapid climate change just before the regional onset of younger dryas cooling and mammoth extirpation thus these mammoths may provide key insights into late pleistocene extinction processes here we reconstruct the seasonal diet and climatic conditions experienced by mammoths in the san pedro valley of arizona using the carbon 13c 12c and oxygen 18o 16o isotope compositions of tooth enamel these records suggest that clovis mammoths experienced a warm dry climate with sufficient summer rainfall to support seasonal c4 plant growth monsoon intensity may have been reduced relative to the preceding time period but there is no isotopic evidence for severe drought however it is possible that the clovis drought inferred from stratigraphic evidence occurred suddenly at the end of the animals lives and thus was not recorded in the enamel isotopic compositions unlike mammoths that lived before the last glacial maximum clovis mammoths regularly increased c4 grass consumption during summer probably seeking seasonally green grasslands farther from the river valley this predictable seasonal behavior may have made mammoths easier to locate by clovis hunters furthermore clovis mammoths probably had no previous experience of such sudden climatic change as is believed to have occurred at the time of their extinction

a structural outline of the yenkahe volcanic resurgent dome tanna island vanuatu arc south pacific abstract a structural study has been conducted on the resurgent yenkahe dome 5 km long by 3 km wide located in the heart of the siwi caldera of tanna island vanuatu arc south pacific this spectacular resurgent dome hosts a small caldera and a very active strombolian cinder cone the yasur volcano in the west and exhibits an intriguing graben in its central part detailed mapping and structural observations make it possible to unravel the volcano tectonic history of the dome it is shown that following the early formation of a resurgent dome in the west a complex collapse caldera plus graben occurred and this was associated with the recent uplift of the eastern part of the present dome eastward migration of the underlying magma related to regional tectonics is proposed to explain this evolution

a geochemical and geophysical investigation of the hydrothermal complex of masaya volcano nicaragua abstract masaya volcano nicaragua is a persistently active volcano characterized by continuous passive degassing for more than 150 years through the open vent of santiago crater this study applies self potential soil co 2 and ground temperature measurements to highlight the existence of uprising fluids associated to diffuse degassing structures throughout the volcano the diffuse degassing areas are organized in a semi circular pattern and coincide with several visible and inferred surface volcanic structures cones fissure vents and likely consist of a network of buried faults and dykes that respectively channel uprising flow and act as barrier to gravitational groundwater flow water depths have been estimated by multi scale wavelet tomography of the self potential data using wavelets from the poisson kernel family compared to previous water flow models our water depth estimates are shallower and mimic the topography typically less than 150 m below the surface between 2006 and 2010 the depths of rising fluids along the survey profiles remained stable suggesting that hydrothermal activity is in a steady state this stable activity correlates well with the consistency of the volcanic activity expressed at the surface by the continuously passive degassing when compared to previous structural models of the caldera floor it appears that the diffuse degassing structures have an important effect on the path that shallow groundwater follows to reach the laguna de masaya in the eastern part of the caldera the hydrogeological system is therefore more complex than previously published models and our new structural model implies that the flow of shallow groundwater must bypass the intrusions to reach the laguna de masaya furthermore these diffuse degassing structures show clear evidence of activity and must be connected to a shallow magmatic or hydrothermal reservoir beneath the caldera as such the heat budget for masaya must be significantly larger than previously estimated

quaternary chronostratigraphy and stable isotope paleoecology of big bone lick kentucky usa abstract big bone lick bbl in northern kentucky usa has been a critical geologic site in the historical development of north american quaternary vertebrate paleontology since the 1700s sedimentology geoarcheology paleontology accelerator mass spectrometry radiocarbon and optically stimulated luminescence dating and stable carbon and nitrogen isotope analyses were undertaken to develop a chronostratigraphy and history of erosion and deposition for the site to provide a foundation for understanding taphonomy and species extinction and adaptation to periods of climatic and environmental change three geomorphic surfaces are recognized at bbl representing significant periods of floodplain aggradation since the last glacial maximum 26 5 19 ka dating to the oldest dryas tazewell 25 19 ka the older dryas cary 14 12 ka and late holocene 5 ka to the present unconformities suggest significant periods of degradation during the transitions from cold and dry to warm and moist climates from the oldest dryas tazewell to bolling oscillation from the older dryas cary to the allerod and from the younger dryas valders to the holocene climatic optimum increased anthropogenic activities since 5 ka may have increased soil upland erosion and floodplain aggradation stable isotopes demonstrate that the landscape has been dominated by c3 vegetation since the last glacial maximum

mafic pyroclastic flows at santa maria gaua volcano vanuatu the caldera formation problem in mainly mafic island arc volcanoes at santa maria volcano new hebrides island arc extensive ash and scoria flow deposits overlie the mainly effusive pre caldera cone hydromagmatic features characterize these deposits the composition of juvenile clasts ranges from basalt to acid andesite dacite sio2 51 63 6 with a dominant basaltic composition the stratigraphic position of this pyroclastic series and its spatial distribution around a 8 5 km 6 km wide caldera provide evidence of a relationship between this series and the caldera formation in addition these pyroclastic deposits are co genetic to parasitic cones and lava flows developed along faults concentric to the caldera both series result from a compositionally layered magma reservoir the subordinate differentiated magmas being the result of fractional crystallization from the basalts a model of caldera formation which implies a large hydromagmatic eruption at the central vent and minor magma withdrawal by flank eruptions is proposed this model emphasizes the importance of mafic hydroclastic eruptions in the caldera forming event and contradicts a model implying only quiet subsidence a process often proposed for the formation of calderas in island are volcanoes of mainly mafic composition

evaluating escarpment evolution and bedrock erosion rates in the western guadalupe mountains west texas and new mexico abstract the guadalupe mountains tower above surrounding plains and basins in western texas and southeast new mexico although this mountain range is extensively studied for the permian stratigraphy related to the petroleum reservoirs in the adjacent delaware basin little is known about the geomorphic history the western escarpment in particular rises abruptly from the salt basin to the west of the range and guadalupe peak rises 1600 m above the surrounding landscape this study investigates how geologic processes create and maintain the steep profile of the escarpment on the western boundary of the guadalupe mountain range in situ produced cosmogenic nuclides were used to quantify erosion rates across the steep western front of the range to assess how tectonic climatic and lithologic forces influence the escarpment profile erosion rates range from 1 to 73 m myr faster erosion rates in the southern area of the escarpment coincide with more frequently mapped faults higher elevations at the top of the rim and locations with colder temperatures and higher precipitation topographic profiles across the western escarpment surfaces indicate greater retreat from the original positions of fault surfaces at the north end of the mountain range faster erosion rates in the mountain range are linked to greater uplift and more recent activity in the southern end of the guadalupe mountains

late wisconsin periglacial environments of the southern margin of the laurentide ice sheet reconstructed from pollen analyses full glacial pollen assemblages from four radiocarbon dated interstadial deposits in southwestern ohio and southeastern indiana imply the presence of herbaceous vegetation tundra or muskeg with subarctic indicator selaginella selaginoides on the southern margin of the miami lobe of the laurentide ice sheet ca 20 000 14c yr bp scattered picea spruce and possibly pinus pine may have developed regionally ca 19 000 14c yr bp and ca 18 000 14c yr bp respectively spruce stumps in growth position support a local source of pollen prior to the ca 14 000 14c yr bp glacial advance small amounts of quercus oak and other deciduous pollen suggest development of regional boreal conifer hardwood forests copyright 2002 john wiley sons ltd

magma and volatile supply to post collapse volcanism and block resurgence in siwi caldera tanna island vanuatu arc v24c 04 allen s r 2005 complex spatterand pumice rich pyroclastic deposits from an andesitic caldera forming eruption the siwi pyroclastic sequence tanna vanuatu bulletin of volcanology 67

the phlegraean fields structural evolution volcanic history and eruptive mechanisms abstract the main event within the volcanic history of the phlegraean fields was the eruption about 35 000 years ago of a huge alkali trachytic ignimbrite 80 km 3 dre followed by caldera collapse the pre caldera activity evidence from geothermal wells and surface outcrops changed from submarine to subaerial shortly before the ignimbrite eruption the caldera was subsequently invaded by the sea and became progressively filled with tuffites and subordinate submarine flows in its northern half the last submarine explosive activity dates back to 12000 10500 yr with the eruption of mostly hydroplinian yellow tuffs recent mostly subaerial activity consists of a series of explosive eruptions whose volume decreases with time until the last eruption of mt nuovo in 1538 a d two peaks in recent activity occur at 10000 8000 and 4700 3000 years ago during post caldera activity eruptive vents migrated from the caldera rim toward the center where there are two distinct zones of recent vents minor collapses occurred within the caldera after the main eruptions often they are eccentric to the vent and displaced toward the caldera center phlegraean explosive activity is characterized by water magma interaction eruptive events without a hydromagmatic component are extremely rare in most cases the evolved trachytic magmas interacted with surface water either the sea or intracaldera lakes however there is evidence of interaction of magma with deep seated aquifers for some plinian events explosivity i e the efficiency of the transformation of thermal into kinetic energy during magma water interaction is largely controlled by the primary fragmentation of the magmatic melt

estimation of the near surface velocity structure of the yasur yenkahe volcanic complex vanuatu small aperture array measurements of seismic noise at seven sites around yasur volcano vanuatu are performed to estimate the vp and vs velocities of the shallow structure the spatial autocorrelation spac and the frequency wavenumber f k methods are used to determine rayleigh phase velocity dispersion curves phase velocities computed with the spac method vary between 580 m s and 960 m s at 1 hz and between 270 m s and 420 m s at 15 hz f k dispersion curves show velocities of 300 340 m s and 800 940 m s at 1 hz and 200 230 m s at 15 hz an inversion technique based on the use of the neighbourhood algorithm has been used to calculate the one dimensional velocity model at each site velocity models reach 200 m deep and mainly contain two layers and a half space for sites close to the siwi caldera rims comparisons with geology and hydrothermal system studies suggest that the two layers highlighted in models may correspond to two large pyroclastic sequences related to caldera collapses based on the flank of an old volcano results obtained for the other three sites located inside the caldera show the influence of the hydrothermal system on p and s wave velocities for these sites fluid circulation inside the volcanic deposits causes lower velocities at depth to obtain a near surface velocity model of the volcanic structure each 1d velocity model is spatially extrapolated according to the surface geology results highlight four distinct areas the siwi caldera edges with high velocities and the resurgent block the ash plain and the yasur edifice with lower velocities at depth

mafic plinian volcanism and ignimbrite emplacement at tofua volcano tonga tofua island is the largest emergent mafic volcano within the tofua arc tonga southwest pacific the volcano is dominated by a distinctive caldera averaging 4 km in diameter containing a freshwater lake in the south and east the latest paroxysmal vei 5 6 explosive volcanism includes two phases of activity each emplacing a high grade ignimbrite the products are basaltic andesites with between 52 wt and 57 wt sio2 the first and largest eruption caused the inward collapse of a stratovolcano and produced the tofua ignimbrite and a sub circular caldera located slightly northwest of the island s centre this ignimbrite was deposited in a radial fashion over the entire island with associated plinian fall deposits up to 0 5 m thick on islands 40 km away common sub rounded and frequently cauliform scoria bombs throughout the ignimbrite attest to a small degree of marginal magma water interaction the common intense welding of the coarse grained eruptive products however suggests that the majority of the erupted magma was hot water undersaturated and supplied at high rates with moderately low fragmentation efficiency and low levels of interaction with external water we propose that the development of a water saturated dacite body at shallow 6 km depth resulted in failure of the chamber roof to cause sudden evacuation of material producing a plinian eruption column following a brief period of quiescence large scale faulting in the southeast of the island produced a second explosive phase believed to result from recharge of a chemically distinct magma depleted in incompatible elements this similar but smaller eruption emplaced the hokula ignimbrite sheet in the northeast of the island a maximum total volume of 8 km3 of juvenile material was erupted by these events the main eruption column is estimated to have reached a height of 12 km and to have produced a major atmospheric injection of gas and tephra recorded in the widespread series of fall deposits found on coral islands 40 80 km to the east in the direction of regional upper tropospheric winds radiocarbon dating of charcoal below the tofua ignimbrite and organic material below the related fall units imply this eruption sequence occurred post 1 000 years bp we estimate an eruption magnitude of 2 24 1013 kg sulphur release of 12 tg and tentatively assign this eruption to the ad 1030 volcanic sulphate spike recorded in antarctic ice sheet records

inverting the source mechanism of strombolian explosions at mt yasur vanuatu using a multi parameter dataset abstract the source mechanism of strombolian explosions at mt yasur vanuatu is analyzed using a unique data set which enables us to combine different methodologies the novelty of the approach presented here lies in the combination of seismic acoustic and doppler radar data thus using infrasound and doppler radar observations we are able to provide independent estimates of the volume of the eruptive source in the following we show that a correlation exists between source volume and the maximum particle velocity of the expelled volcanic products in order to determine the source location and the associated mechanism and to compare those two methods we use time reversal imaging and moment tensor inversion while the first method also applies to extended sources the latter might be biased by its intrinsic point source approximation we show that time reversal imaging can deliver an estimate of the source depth without any a priori assumptions even in an unfavorable scenario in terms of topography and receiver setup the inverted source mechanism retrieved from moment tensor inversion is found to be largely isotropic with minor deviatoric components the inverted source location points towards an area to the north west of the active craters indicative of a common feeder system of the activity at mt yasur however it is also evident that to fully locate the source of strombolian activity at yasur location precision must be enhanced

pyroclastic density currents at etna volcano italy the 11 february 2014 case study abstract on 11 february 2014 a considerable volume 0 82 to 1 29 106 m3 of unstable and hot rocks detached from the lower eastern flank of the new southeast crater nsec at mt etna producing a pyroclastic density current pdc this event was by far the most extensive ever recorded at mt etna since 1999 and has attracted the attention of the scientific community and civil protection to this type of volcanic phenomena usually occurring without any clear volcanological precursor and especially toward the mechanisms which led to the crater collapse the pdc flow dynamics and the related volcanic hazard we present here the results of the investigation carried out on the 11 february 2014 collapse and pdc events data were obtained through a multidisciplinary approach which includes the analysis of photograph images from visible and thermal surveillance cameras and the detailed stratigraphic textural and petrographic investigations of the pdc deposits results suggest that the collapse and consequent pdc was the result of a progressive thermal and mechanical weakening of the cone by repeated surges of magma passing through it during the eruptive activity prior to the 11 february 2014 events as well as pervasive heating and corrosion by volcanic gas the collapse of the lower portion of the nsec was followed by the formation of a relatively hot up to 750 c dense flow which travelled about 2 3 km from the source stopping shortly after the break of the slope and emplacing the main body of the deposit which ranges between 0 39 and 0 92 106 m3 this flow was accompanied a relatively hot cloud of fine ash that dispersed over a wider area the results presented may contribute to the understanding of this very complex type of volcanic phenomena at mt etna and in similar volcanic settings of the world in addition results will lay the basis for the modeling of crater collapse and relative pdc events and consequently for the planning of hazard assessment strategies aimed at reducing the potential risks to scientists and tens of thousands of tourists visiting etna s summit areas every year

the 1245 yr bp asososca maar new advances on recent volcanic stratigraphy of managua nicaragua and hazard implications abstract asososca maar is located at the western outskirts of managua nicaragua in the central part of the active n s trending and right lateral nejapa miraflores fault that marks an offset of the middle america volcanic arc it constitutes one of the 21 vents aligned along the fault between the chiltepe volcanic complex to the north and ticomo vents to the south asososca consists of an east west elongated crater filled by a lake which is currently used for supplying part of managua with drinking water 10 of the capital city demand the crater excavated the previous topography allowing the observation of a detailed holocene stratigraphic record that should be taken into account for future hazard analyses we present a geological map together with the detailed stratigraphy exposed inside and around asososca crater aided by radiocarbon dating of paleosols the pre existing volcanic sequence excavated by asososca is younger than 12 730 255 250 yr bp and is capped by the phreato plinian masaya tuff 2 are dominated by accidental clasts including basaltic to basaltic andesitic olivine bearing scoriae lapilli porphyritic and hypocrystalline andesite blocks and lapilli altered pumice lapilli and ash and ignimbrite fragments juvenile fragments were only identified in size fractions smaller than 1 in proportions lower than 25 and consist of black moss like fused shape and poorly vesiculated fresh glass fragments of basaltic composition sio2 48 the asososca tephra is interpreted as due to the emplacement of several pyroclastic surges originated by phreatomagmatic eruptions from asososca crater as suggested by impact sags geometry and dune crest migration structures according to radiocarbon dating these deposits were emplaced at 1245 125 120 yr bp the stratigraphic position of the asososca tephra and the well preserved morphology of the crater indicate that asososca is the youngest vent along the nejapa miraflores fault explosive eruptions might therefore occur again along this fault at the western outskirts of managua such kind of activity together with the strong seismicity associated to the active fault represents a serious hazard to urban infrastructure and a population of ca 1 3 million inhabitants

biodegradation of clay minerals laboratory experiments and results from wadden sea tidal flat sediments laboratory experiments indicate that clay particles of the 2 um fraction can be considerably degraded by the bivalve mytilus edulis dickite kaolinite smectite chlorite and illite particles are partially dissolved and rounded by the digestive processes structural changes and a decrease in crystallinity of kaolinites dickites and illites are striking investigations of clay minerals from tidal flat sediments highly populated by marine invertebrates from marine suspensions and samples from profiles across mytilis edulis beds on the north sea coast of germany show however that these materials have a uniform mineral composition this uniformity of clay mineralogy can be explained by the hydrodynamic conditions in the nearshore area where tidal currents and waves cause a periodic resuspension and transport of sediments introduced into the wadden sea from different sources glacial fluviatile processes of bioturbation also redistribute the sedimentary material these mixing processes effectively erase any evidence of local enrichment of the biogenically degraded clays however the disordered clays should react more sensitively i e have higher adsorption capacities for organic substances hydroxides and metals in sediments than untreated materials so that biodegradation is of basic importance for clay diagenesis during these processes pb v ni and fe are dissolved from the digested particles

the salazie cirque ignimbrite piton des neiges volcano reunion island chronostratigraphy description and significance of lithic fragments and eruptive mechanisms abstract an ignimbrite sequence in the salazie cirque is characterized by a pyroclastic flow unit composed of basal breccias layers a1 and a2 a welded tuff layer b and an upper ashy layer layer c this eruption began a new eruptive cycle in the piton des neiges volcanic complex the second stage of a differentiation series characterized by the emission of undersaturated lava the paleogeography of the volcano s eastern flank is reconstituted at about 150 000 y b p from the distribution of ignimbrite deposits that partially fill two large erosion cirques the salazie protocirque and the marsouins protocirque the total volume of these deposits is only a few km3 and no evidence indicates a related caldera collapse basal breccias are composed of 1 juvenile magmatic clasts yielding a mugearitic composition and normative nepheline and 2 xenoliths representative of the different units in a 1500 2000 m thick volcanic pile which include differentiated lavas first stage of differentiated series basaltic lava flows and plutonic rocks oceanite series the appearance of hydrothermal parageneses only in subsurface facies emphasizes the striking role of volcanotectonic structures in mineralized fluid circulation the common features of magma mixing abnormal mineralogical associations reverse zonings disequilibrium features in layer b are interpreted as resulting from the assimilation of highly differentiated foreign rocks by the mugearite magma during and after the course of the eruption the salazie cirque ignimbrite is of the overflowing type non plinian characterized by high emplacement temperatures a model is proposed for its formation 1 rising of a mugearitic eruption column 2 vesiculation of magma at shallow depth beneath the plug 3 increase of magma pressure and eruption of a mixture of gas magmatic blocks and xenoliths down slope deposition of fines depleted heterogenous lithic rich flow layer a1 4 explosion flashing of the gas rich upper part of the magma column and eruption of the main welded tuff unit with segregation of a basal non fines depleted lithic concentration zone during flow layer a2 and elutriation of an ash cloud fall layer c 5 effusive phase

a total volatile inventory for masaya volcano nicaragua nerc project magma dynamics at persistently degassing basaltic volcanoes a novel approach to linking volcanic gases and magmatic volatiles within a physical model ne f004222 1 and ne f005342 1

eruption transport and deposition of ignimbrite a case study from mexico abstract the acatlan ignimbrite covers 150 km 2 around a vent situated 40 km southwest of guadalajara mexico the upper and main ignimbrite flow unit is compositionally zoned and has white or pink rhyolitic pumice in its lower part and black andesite in its upper these parts are believed to have been erupted continuously from the same magma chamber this zonation has been important in correlating an extremely coarse lithic rich deposit a co ignimbrite lag fall deposit with this ignimbrite the co ignimbrite lag fall deposit indicates that the flow unit formed by continuous collapse of an explosive eruption column and enables the source vent to be located the vertical compositional grading of the flow unit also provides a means of testing the various proposed mechanisms of ignimbrite emplacement turbulent vs high concentration flow the preservation of compositional zonation and other features in the deposit indicate that flow was not turbulent details of the grain size distribution indicate that laminar flow was important early in the flow history when collapsing material from the eruption column was superimposed in stratigraphical sequence initial high gas flow rates associated with flow segregation and formation at the site of column collapse rapidly decayed away from vent and later in its history the flow degassed to a semi rigid plug overriding a sheared basal layer

experimental production of clay rims by macrobiotic sediment ingestion and excretion processes using controlled experiments that simulate interlayered sand and mud in marine conditions it is shown that clay rims develop on sand grains during the digestive processes of the polychaete worm arenicola marina the clay size minerals also undergo accelerated weathering and mineral authigenesis synthetic mud crushed slate and clean eolian sand of known composition and texture were horizontally layered in experimental and control tanks natural seawater was added to these tanks along with several a marina fecal casts were collected at regular time intervals and these were analyzed texturally using electron microscopy and mineralogically using x ray diffraction xrd total bioturbation of the sand and mud layering by a marina was achieved after only eight weeks of feeding activity sand grains in the fecal casts developed clay mineral rims a feature absent in the original material and not found in the control tanks thin composite curvilinear structures assumed to be detached clay rims were also produced over a period of many months the synthetic mud proved to be unchanged in the control tank but it was significantly different in the fecal casts from the experimental tank that contained the worm a marina the original minerals were degraded and new authigenic clay minerals formed it is postulated that a combination of low ph and the biologically active microenvironment in the guts of annelid worms may radically accelerate mineral dissolution and clay mineral precipitation processes during digestion it is likely that mucous produced by the worms not only led to the aggregation of the fine grained material into fecal casts but also adhered the fine sediment onto sand grains thus creating clay mineral rims in this case the solid part of the clay rim will be a combination of the primary material crushed slate and the neoformed clay minerals

degassing driven crystallisation in basalts abstract syn eruptive crystallisation can drastically increase magma viscosity with profound implications for conduit dynamics lava emplacement and volcanic hazards there is growing evidence that crystallisation is not only cooling driven but can also occur almost isothermally during decompression induced degassing on ascent from depth here we review field and experimental evidence for degassing driven crystallisation in a range of magma compositions we then present new results showing for the first time experimental evidence for this process in basaltic magma our experiments use simultaneous thermogravimetric analysis and differential scanning calorimetry coupled with mass spectrometry tga dsc ms to monitor degassing patterns and thermal events during heating and cooling of porphyritic basaltic samples from mt etna italy the partly degassed samples which contained 0 39 0 81 wt total volatiles in the glass fraction were subjected to two cycles of heating from ambient to 1250 c on the first heating tga data show that 30 60 of the total volatiles degassed slowly at

varied pathways of river borne clay minerals in a near shore marine region a case study of sediments from the elbe and weser rivers and the se north sea abstract the the results outline significant systematic changes in the proportions of clay minerals in the k rb ratios the k ar data and in the heavy metal contents at the fluvial estuarine transition and towards the marine environment these changes result from a progressive mixing of suspended fluvial material with reworked pleistocene sediments at the bottom of the north sea near shore the proportion of reworked pleistocene sediment amounts only 20 30 the mixture is distributed within a 100 km wide zone mainly by currents parallel to the coast it is also transported during flood tide into the estuaries where it is mixed further with suspended fluvial material the k rb ratios and k ar dates obtained from illite prove to be particularly useful for modeling the mixing of the clay minerals as well as their distribution patterns and origin

families of similar events and modes of oscillation of the conduit at yasur volcano vanuatu abstract we examined one year of seismic recordings collected in 2008 during a temporary experiment at yasur volcano vanuatu the volcano has a permanent strombolian activity that was at a relatively high level during most of our experiment with commonly at least one explosion per minute associated with this activity the network recorded intense seismicicity with hundreds of transients per day video recordings indicate that most of the high frequency transients are directly related to the strombolian explosions they also outline the presence of fewer signals which are not accompanied by any surface activity the classification of transient events recorded at a station close to the summit indicates that a significant part of the events exhibit waveform similarity this technique allows the identification of characteristic repeating events among the hundreds of thousands of transients recorded during the experiment most of the families of similar events are groups of explosion quakes eqs but a few are groups of long period events related to deeper processes by scanning the 9 months of continuous data available at the summit station with master events extracted from these families we reconstruct their temporal evolution our results show that several families dominate the activity with a few of them lasting for several months we show that their temporal evolutions can be used to probe changes in the structure or activity of the volcano we observe that a major change was induced by a m 7 3 subduction earthquake which occurred on april 9 2008 about 80 km from the volcano while this event did not change significantly the surface morphology of the volcano nor the intensity of the eruptive activity it interrupted the families as none of them is present both before and after the event this change in the waveforms can be explained by a drop in the seismic velocity of the volcano caused by the distal event numerous other transitions between families are observed sudden or progressive these can be interpreted as representative of changes in the eruptive dynamics the presence of similar eqs especially for impulsive explosions indicates that the source mechanism is reproducible and has a stable location for some periods this favors a source process based on the oscillation of the conduit or oscillation of the edifice in response to the explosive decompression of gas slugs at the free surface of the conduit our results suggest that the seismic activity of yasur is characterized by the presence of dominant modes of resonance of the conduit which may be influenced both by external and internal factors

strombolian eruptions and dynamics of magma degassing at yasur volcano vanuatu abstract open vent basaltic volcanoes account for a substantial portion of the global atmospheric outgassing flux largely through passive degassing and mild explosive activity we present volcanic gas flux and composition data from yasur volcano vanuatu collected in july 2018 the average volcanic plume chemistry is characterised by a mean molar co2 so2 ratio of 2 14 h2o so2 of 148 and so2 hcl of 1 02 the measured mean so2 flux in the period of 6th to 9th july is 4 9 kg s 1 therefore the mean fluxes of the other species are 7 5 kg s 1 co2 208 kg s 1 h2o and 4 8 kg s 1 hcl the degassing regime at yasur volcano ranges from passive to active styles with the latter including strombolian activity and spattering gases emitted during active degassing are enriched in so2 over hcl and co2 over so2 relative to passive degassing with co2 so2 ratios of 2 85 0 17 so2 hcl of 1 6 0 22 and h2o so2 of 315 78 8 gases emitted during passive degassing have co2 so2 ratios of 1 96 0 12 so2 hcl of 0 50 0 07 and h2o so2 of 174 43 5 we use a model of volatile degassing derived from melt inclusion studies metrich et al 2011 combined with our observations of chemical variations in the outgassing bubbles to propose a mechanism for magma degassing in the conduit at yasur we envisage a shallow conduit filled with crystal rich magma forming a viscous and mobile plug that develops an effective yield strength from the surface to a depth of at least 2000 m in which bubbles are trapped grow ascend towards the surface and burst in a typical strombolian eruption deeper bubbles released during active degassing are enriched in co2 and so2 compared to bubbles released during passive degassing which are sourced from close to the surface and are consequently hcl rich

strombolian surface activity regimes at yasur volcano vanuatu as observed by doppler radar infrared camera and infrasound abstract in late 2008 we recorded a continuous multi parameter data set including doppler radar infrared and infrasound data at yasur volcano vanuatu our recordings cover a transition in explosive style from ash rich to ash free explosions followed again by a phase of high ash discharge to assess the present paradigm of strombolian behavior in this study we investigate the geophysical signature of these different explosive episodes and compare our results to observations at stromboli volcano italy to this end we characterize yasur s surface activity in terms of material movement temperature and excess pressure the joint temporal trend in these data reveals smooth variations of surface activity and regime like persistence of individual explosion forms over days analysis of all data types shows ash free and ash rich explosive styles similar to those found at stromboli volcano during ash free activity low echo powers high explosion velocities and high temperatures result from the movement of isolated hot ballistic clasts in contrast ash rich episodes exhibit high echo powers low explosion velocities and low temperatures linked to the presence of colder ash rich plumes furthermore ash free explosions cause high excess pressure signals exhibiting high frequencies opposed to low amplitude low frequency signals accompanying ash rich activity to corroborate these findings we compare fifteen representative explosions of each explosive episode explosion onset velocities derived from doppler radar and infrared camera data are in excellent agreement and consistent with overall observations in each regime examination of infrasound recordings likewise confirms our observations although a weak coupling between explosion velocity and excess pressure indicates changes in wave propagation the overall trend in explosion velocity and excess pressure however demonstrates a general correlation between explosive style and explosion intensity and points to stability of the uppermost conduit on timescales shorter than at stromboli volcano

formation of the mid fifteenth century kuwae caldera vanuatu by an initial hydroclastic and subsequent ignimbritic eruption in the mid fifteenth century one of the largest eruptions of the last 10 000 years occurred in the central new hebrides arc forming the kuwae caldera 12x6 km this eruption followed a late maar phase in the pre caldera edifice responsible for a series of alternating hydromagmatic deposits and airfall lapilli layers tuffs related to caldera formation 120 m of deposits on a composite section from the caldera wall were emitted during two main ignimbritic phases associated with two additional hydromagmatic episodes the lower hydromagmatic tuffs from the precaldera maar phase are mainly basaltic andesite in composition but clasts show compositions ranging from 48 to 60 sio2 the unwelded and welded ashflow deposits from the ignimbritic phases and the associated intermediate and upper hydromagmatic deposits also show a wide compositional range 60 73 sio2 but are dominantly dacitic this broad compositional range is thought to be due to crystal fractionation the striking evolution from one eruptive style hydromagmatic to the other magmatic with emission of a large volume of ignimbrites which occurred either over the tuff series as a whole or at the beginning of each ignimbritic phase is the most impressive characteristic of the caldera forming event this strongly suggests triggering of the main eruptive phases by magma water interaction a three step model of caldera formation is presented 1 moderate hydromagmatic sequences hd 1 4 and magmatic fallout deposits activity from a central vent probably over a period of months or years affected an area slightly wider than the present caldera at the end of this stage intense seismic activity and extrusion of differentiated magma outside the caldera area occurred 2 unhomogenized dacite was released during a hydromagmatic episode hd 5 this was immediately followed by two major pyroclastic flows pfd 1 and 2 the vents spread and intense magma water interaction at the beginning of this stage decreased rapidly as magma discharge increased subsequent collapse of the caldera probably commenced in the southeastern sector of the caldera 3 dacitic welded tuffs were emplaced during a second main phase wfd 1 5 at the beginning of this phase magma water interaction continued producing typical hydromagmatic deposits hd 6 caldera collapse extended to the northern part of the caldera previous c14 dates and records of explosive volcanism in ice from the south pole show that the climactic phase of this event occurred in 1452 a d

rapid clay transformations in delaware salt marshes abstract salt marshes are the major areas for net sedimentation in many estuaries such as the delaware bay and their diagenetic chemistry is harsh and extreme with large seasonal excursions in chlorinity 1 50 ppt ph 4 6 and eh 240 120 such diagenesis is driven by organic matter decomposition using redox cycles of s and fe materials imported primarily as tidal sea water so 4 and fe silicates respectively important and quantitative changes in clay mineralogy occur within a decade at the redox boundary in a high marsh sediment near lewes delaware the clay mineralogy consists initially of a micaceous illite and chlorite mixture accumulating at the salt marsh surface it is comprised of relic glacial sediments deposited on the continental slope during their net tidal movement from the sea to land once buried these detrital clays are transformed into a new assemblage containing an illite smectitic mixed layer mineral of poor crystallinity using curve decomposition techniques on complex x ray traces it is estimated that this new phase constitutes 45 55 of the clay fraction the redox boundary where the sharp transition occurs is only about 20 a old as determined by 210 pb and 137 cs geochronology and thus the clay mineral transformation is rapid the occurrence of the new abundant clay mineral is very abrupt less than 1 cm at 12 cm in depth and thus may itself occur in as little as three years once formed the new mixed layer phase remains stable during the subsequent 40 a of burial from the time of formation at the oxic anoxic boundary slow transformations of unstable primary clay reactants such as illite and chlorite are a common process of soil formation however such rapid clay reactions have rarely been documented in either subaerial or submerged soil settings the formation of a smectite mineral product of high chemical reactivity for a significant portion of the clays in a soil is unusual in fact the abrupt change in clay mineralogy in the salt marsh occurs precisely at the sharp evolution in salt marsh geochemistry from oxidized to reducing conditions where there is extensive redox cycling of fe and s phases a large seasonal oscillation in interstitial ph and eh probably contributes to the rapid clay transformation such clay transformations may have important implications for the retention of other trace elements entering the salt marsh by atmospheric fallout and tidal cycles or the release of such metal inventories after burial