effects of scoria cone eruptions upon nearby human communities scoria cone eruptions are typically low in volume and explosivity compared with eruptions from stratovolcanoes but they can affect local populations profoundly scoria cone eruption effects vary dramatically due to eruption style tephra blanket extent climate types of land use the culture and complexity of the affected group and resulting governmental action a comparison of a historic eruption paricutin mexico with prehistoric eruptions herein we primarily focus on sunset crater in northern arizona usa elucidates the controls on and effects of these variables long term effects of lava flows extend little beyond the flow edges these flows however can be used for defensive purposes providing refuges from invasion for those who know them well in arid lands tephra blankets serve as mulches decreasing runoff and evaporation increasing infiltration and regulating soil temperature management and retention of these scoria mulches which can open new areas for agriculture become a priority for farming communities in humid areas though the tephra blanket may impede plant growth and increase erosion cultural responses to eruptions vary from cultural collapse through fragmentation of society dramatic changes and development of new technologies to little apparent change eruptions may also be viewed as retribution for poor behavior and attempts are made to mollify angry gods

an approach to estimate the freshwater contribution from glacial melt and precipitation in east greenland shelf waters using colored dissolved organic matter cdom changes in the supply and storage of freshwater in the arctic ocean and its subsequent export to the north atlantic can potentially influence ocean circulation and climate in order to understand how the arctic freshwater budget is changing and the potential impacts it is important to develop and refine empirical approaches for tracing freshwater contributions this in turn can help develop and validate model simulations arctic rivers are an important source of freshwater and stable oxygen isotope measurements are used to separate contributions from meteoric water river glacial and precipitation and sea ice melt we develop this approach further and investigate the use of an additional tracer colored dissolved organic matter cdom which is largely specific to freshwater originating from arctic rivers a robust relationship between the freshwater contribution from meteoric water and cdom is derived from 4 years of measurements in fram strait 2009 2012 combined with measurements from the east greenland shelf and dijmpha sound ne greenland results confirm a high contribution of riverine cdom in arctic halocline waters with salinities 31 5 and indicate the importance of shelf processes riverine input and sea ice formation while previously these waters where thought to be derived from open sea processes cooling and sea ice formation in the northern barents and kara seas in greenlandic coastal waters the meteoric water contribution is influenced by greenland ice sheet meltwater and deviations from the cdom meteoric water relationships found are applied to quantify meltwater contribution along the east greenland shelf waters 0 13

risk perception and volcanic hazard mitigation individual and social perspectives this paper discusses how people s interpretation of their experience of volcanic hazards and public volcanic hazard education programs influences their risk perception and whether or not they adopt measures that can mitigate their risk drawing on four studies of volcanic risk perception and preparedness the paper first examines why experiencing volcanic hazards need not necessarily motivate people to prepare for future volcanic crises this work introduces how effective risk communication requires communities and civic agencies to play complementary roles in the risk management process next the findings of a study evaluating the effectiveness of a public volcanic hazard education program introduce the important role that social interaction amongst community members plays in risk management building on the conclusions of these studies a model that depicts preparing as a social process is developed and tested the model predicts that it is the quality of the relationships between people communities and civic agencies that determines whether people adopt measures that can reduce their risk from volcanic hazard consequences the implications of the model for conceptualizing and delivering volcanic hazard public education programs in ways that accommodate these relationships is discussed

understanding the storage conditions and fluctuating eruption style of a young monogenetic volcano blue lake crater 3 ka high cascades oregon abstract blue lake crater 13 m s this study illustrates the pre eruptive and eruptive complexities of monogenetic volcanoes and highlights the minimal warning that may precede future eruptions

origin of freshwater and polynya water in the arctic ocean halocline in summer 2007 extremely low summer sea ice coverage in the arctic ocean in 2007 allowed extensive sampling and a wide quasi synoptic hydrographic and 18o dataset could be collected in the eurasian basin and the makarov basin up to the alpha ridge and the east siberian continental margin with the aim of determining the origin of freshwater in the halocline fractions of river water and sea ice meltwater in the upper 150 m were quantified by a combination of salinity and 18o in the eurasian basin two methods applying the preformed phosphate concentration po and the nitrate to phosphate ratio n p were compared to further differentiate the marine fraction into atlantic and pacific derived contributions while po based assessments systematically underestimate the contribution of pacific derived waters n p based calculations overestimate pacific derived waters within the transpolar drift due to denitrification in bottom sediments at the laptev sea continental margin within the eurasian basin a west to east oriented front between net melting and production of sea ice is observed outside the atlantic regime dominated by net sea ice melting a pronounced layer influenced by brines released during sea ice formation is present at about 30 to 50 m water depth with a maximum over the lomonosov ridge the geographically distinct definition of this maximum demonstrates the rapid release and transport of signals from the shelf regions in discrete pulses within the transpolar drift the ratio of sea ice derived brine influence and river water is roughly constant within each layer of the arctic ocean halocline the correlation between brine influence and river water reveals two clusters that can be assigned to the two main mechanisms of sea ice formation within the arctic ocean over the open ocean or in polynyas at the continental slope where relatively small amounts of river water are found sea ice formation results in a linear correlation between brine influence and river water at salinities of about 32 to 34 in coastal polynyas in the shallow regions of the laptev sea and southern kara sea sea ice formation transports river water into the shelf s bottom layer due to the close proximity to the river mouths this process therefore results in waters that form a second linear correlation between brine influence and river water at salinities of about 30 to 32 our study indicates which layers of the arctic ocean halocline are primarily influenced by sea ice formation in coastal polynyas and which layers are primarily influenced by sea ice formation over the open ocean accordingly we use the ratio of sea ice derived brine influence and river water to link the maximum in brine influence within the transpolar drift with a pulse of shelf waters from the laptev sea that was likely released in summer 2005

toothpaste lava characteristics and origin of a lava structural type transitional between pahoehoe and aa toothpaste lava an important basalt structural type which illustrates the transition from pahoehoe to aa is particularly well displayed on the 1960 kapoho lava of kilauea volcano its transitional features stem from a viscosity higher than that of pahoehoe and a rate of flow slower than that of aa viscosity can be quantified by the limited settling of olivine phenocrysts and rate of flow by field observations related to the low angle slope on which the lava flowed much can be learned about the viscosity rheologic condition and flow velocity of lavas long after solidification by analyses of their structural characteristics and it is possible to make at least a semiquantitative assessment of the numerical values of these parameters

mechanisms for transition in eruptive style at a monogenetic scoria cone revealed by microtextural analyses lathrop wells volcano nevada u s a explosive activity at lathrop wells volcano nevada u s a originated with weak strombolian ws eruptions along a short fissure and transitioned to violent strombolian vs activity from a central vent with lava effusion during both stages the cause for this transition is unknown it does not reflect a compositional change as evidenced by the consistent bulk geochemistry of all the eruptive products however comparison of agglutinate samples from the early ws events with samples of scoria from the later vs events reveal differences in the abundance and morphology of groundmass phases and variable textures in the rims of olivine phenocrysts scanning electron microscope sem examination of thin sections from the ws samples show euhedral magnetite microlites in the groundmass glass and olivine phenocrysts show symplectite lamellae in their rims secondary ion mass spectrometry sims depth profiles of these symplectites indicate they are diffusion controlled the calculated dfe mg allows an estimation of the oxygen fugacity fo2 and indicates an increased fo2 during eruption of the ws products conversely the vs samples show virtually no magnetite microlites in the groundmass glass a lack of symplectites in the olivines and a lower calculated fo2 these microtextural features suggest that the lathrop wells trachybasalt experienced increased oxidation during ws activity as magma ascended through the original fissure exsolved bubbles were concentrated in the wider part s the protoconduit and this bubble flux drove convective circulation that oxidized the magma through exposure to atmosphere and recirculation this oxidation resulted in groundmass crystallization of magnetite within the melt and formation of symplectites within the olivine phenocrysts bubble driven convection mixed magma vertically within the protoconduit keeping it fluid and driving strombolian bursts while microlite crystallization in narrower parts of the fissure helped to focus flow development of a central conduit increased the magma ascent velocity due to a greater product volume in the later eruptive stages and caused the shift in eruption intensity consequently variations in microtextures of the lathrop wells products reveal how a combination of fluid dynamic and crystallization processes in the ascending magma resulted in different styles of activity while the products maintained a consistent bulk composition

a multidisciplinary effort to assign realistic source parameters to models of volcanic ash cloud transport and dispersion during eruptions during volcanic eruptions volcanic ash transport and dispersion models vatds are used to forecast the location and movement of ash clouds over hours to days in order to define hazards to aircraft and to communities downwind those models use input parameters called eruption source parameters such as plume height h mass eruption rate duration d and the mass fraction m63 of erupted debris finer than about 4 or 63 m which can remain in the cloud for many hours or days observational constraints on the value of such parameters are frequently unavailable in the first minutes or hours after an eruption is detected moreover observed plume height may change during an eruption requiring rapid assignment of new parameters this paper reports on a group effort to improve the accuracy of source parameters used by vatds in the early hours of an eruption we do so by first compiling a list of eruptions for which these parameters are well constrained and then using these data to review and update previously studied parameter relationships we find that the existing scatter in plots of h versus yields an uncertainty within the 50 confidence interval of plus or minus a factor of four in eruption rate for a given plume height this scatter is not clearly attributable to biases in measurement techniques or to well recognized processes such as elutriation from pyroclastic flows sparse data on total grain size distribution suggest that the mass fraction of fine debris m63 could vary by nearly two orders of magnitude between small basaltic eruptions 0 01 and large silicic ones 0 5 we classify eleven eruption types four types each for different sizes of silicic and mafic eruptions submarine eruptions brief or vulcanian eruptions and eruptions that generate co ignimbrite or co pyroclastic flow plumes for each eruption type we assign source parameters we then assign a characteristic eruption type to each of the world s 1500 holocene volcanoes these eruption types and associated parameters can be used for ash cloud modeling in the event of an eruption when no observational constraints on these parameters are available

effect of sea ice melt on inherent optical properties and vertical distribution of solar radiant heating in arctic surface waters the inherent optical properties iops of polar waters pw exiting the arctic ocean in the east greenland current egc and of the inflowing atlantic waters aw in the west spitsbergen current wsc were studied in late summer when surface freshening due to sea ice melt was widespread the absorption and attenuation coefficients in pw were significantly higher than previous observations from the western arctic high concentrations of colored dissolved organic matter cdom resulted in 50 60 more heat deposition in the upper meters relative to clearest natural waters this demonstrates the influence of terrigenous organic material inputs on the optical properties of waters in the eurasian basin sea ice melt in cdom rich pw decreased cdom absorption but an increase in scattering nearly compensated for lower absorption and total attenuation was nearly identical in the sea ice meltwater layer this suggests a source of scattering material associated with sea ice melt relative to the pw in the aw melting sea ice forms a stratified surface layer with lower absorption and attenuation than well mixed aw waters in late summer it is likely that phytoplankton in the surface layer influenced by sea ice melt are nutrient limited the presence of a more transparent surface layer changes the vertical radiant heat absorption profile to greater depths in late summer both in egc and wsc waters shifting accumulation of solar heat to greater depths and thus this heat is not directly available for ice melt during periods of stratification

characteristics of colored dissolved organic matter cdom in the arctic outflow in the fram strait assessing the changes and fate of terrigenous cdom in the arctic ocean absorption coefficients of colored dissolved organic matter cdom were measured together with salinity delta o 18 and inorganic nutrients across the fram strait a pronounced cdom absorption maximum between 30 and 120 m depth was associated with river and sea ice brine enriched water characteristic of the arctic mixed layer and upper halocline waters in the east greenland current egc the lowest cdom concentrations were found in the atlantic inflow we show that the salinity cdom relationship is not suitable for evaluating conservative mixing of cdom the strong correlation between meteoric water and cdom is indicative of the riverine terrigenous origin of cdom in the egc based on cdom absorption in polar water and comparison with an arctic river discharge weighted mean we estimate that a 49 59 integrated loss of cdom absorption across 250 600 nm has occurred a preferential removal of absorption at longer wavelengths reflects the loss of high molecular weight material in contrast cdom fluxes through the fram strait using september velocity fields from a high resolution ocean sea ice model indicate that the net southward transport of terrigenous cdom through the fram strait equals up to 50 of the total riverine cdom input this suggests that the fram strait export is a major sink of cdom these contrasting results indicate that we have to constrain the c dom budgets for the arctic ocean much better and examine uncertainties related to using tracers to assess conservative mixing in polar waters citation granskog m a c a stedmon p a dodd r m w amon a k pavlov l de steur and e hansen 2012 characteristics of colored dissolved organic matter cdom in the arctic outflow in the fram strait assessing the changes and fate of terrigenous cdom in the arctic ocean j geophys res 117 c12021 doi 10 1029 2012jc008075

relating vesicle shapes in pyroclasts to eruption styles vesicles in pyroclasts provide a direct record of conduit conditions during explosive volcanic eruptions although their numbers and sizes are used routinely to infer aspects of eruption dynamics vesicle shape remains an underutilized parameter we have quantified vesicle shapes in pyroclasts from fall deposits of seven explosive eruptions of different styles using the dimensionless shape factor omega a measure of the degree of complexity of the bounding surface of an object for each of the seven eruptions we have also estimated the capillary number ca from the magma expansion velocity through coupled diffusive bubble growth and conduit flow modeling we find that omega is smaller for eruptions with rm ca ll 1 than for eruptions with ca gg 1 consistent with previous studies we interpret these results as an expression of the relative importance of structural changes during magma decompression and bubble growth such as coalescence and shape relaxation of bubbles by capillary stresses among the samples analyzed strombolian and hawaiian fire fountain eruptions have rm ca ll 1 in contrast to vulcanian plinian and ultraplinian eruptions interestingly the basaltic plinian eruptions of tarawera volcano new zealand in 1886 and mt etna italy in 122 bc for which the cause of intense explosive activity has been controversial are also characterized by rm ca gg 1 and larger values of omega than strombolian and hawaiian style fire fountain eruptions we interpret this to be the consequence of syn eruptive magma crystallization resulting in high magma viscosity and reduced rates of bubble growth our model results indicate that during these basaltic plinian eruptions buildup of bubble overpressure resulted in brittle magma fragmentation

thermohaline circulation hysteresis a model intercomparison we present results from an intercomparison of 11 different climate models of intermediate complexity in which the north atlantic ocean was subjected to slowly varying changes in freshwater input all models show a characteristic hysteresis response of the thermohaline circulation to the freshwater forcing which can be explained by stommel s salt advection feedback the width of the hysteresis curves varies between 0 2 and 0 5 sv in the models major differences are found in the location of present day climate on the hysteresis diagram in seven of the models present day climate for standard parameter choices is found in the bi stable regime in four models this climate is in the mono stable regime the proximity of the present day climate to the stommel bifurcation point beyond which north atlantic deep water formation cannot be sustained varies from less than 0 1 sv to over 0 5 sv

computer simulation models of scoria cone degradation abstract long term erosional modifications of the relatively simple morphology of scoria cinder cones are ideally suited for study by field and computer simulation methods a series of temporally distinct cones in the san francisco and springerville volcanic fields of arizona provides the foundation for documenting the degradational evolution of scoria cones in a semi arid climate progressive changes due to erosion are illustrated by the systematic decrease with increasing age of various morphometric parameters including scoria cone height cone height width ratio hco wco crater depth width ratio and slope angle for example holocene latest pleistocene cones in the san francisco field have a mean hco wco value of 0 178 0 041 a mean maximum slope angle of 29 7 4 2 and a mean average slope angle of 26 4 7 3 whereas the group of pliocene cones have values of 0 077 0 024 20 5 5 8 and 8 7 2 7 respectively comparative morphology of scoria cones is a potentially useful dating tool for mapping volcanic fields in order to better understand the degradational modifications of these volcanic landforms we have developed a numerical approach to simulate the surficial processes responsible for the erosion of a typical scoria cone the simulation algorithm can apply either a linear diffusion equation model or a model with a nonlinear transport law using a finite difference formulation the simulation operates upon a three dimensional scoria cone input as a matrix of elevation values utilizing both field and model results the correlation between changing hco wco value cone age and computer time step was expressed graphically to derive comprehensive values of the transport or diffusion coefficient df for both volcanic fields for the san francisco volcanic field df had a calculated value of 21 4 m2 kyr for the linear model and 5 3 m kyr for the nonlinear model while for the springerville volcanic field df had a calculated value of 24 4 m2 kyr for the linear model and 6 3 m kyr for the nonlinear model

subplinian monogenetic basaltic eruption of sunset crater arizona usa sunset crater volcano located 25 km northeast of downtown flagstaff arizona usa in the san francisco volcanic field represents an interesting case of highly explosive monogenetic volcanism sunset crater is a young ca 1085 ce scoria cone 290 m high that produced 0 52 km3 dense rock equivalent dre of basaltic magma 0 16 0 12 and 0 24 km3 dre for the scoria cone lava flows and tephra deposit respectively the activity developed in three distinct phases an initial fissure phase followed by a highly explosive phase and a final low explosivity waning phase the first phase was characterized by the opening of a 10 kmlong fissure which produced the gyp crater spatter mounds and the vent 512 lava flow 10 km se of the main scoria cone followed by lava fountaining activity that produced the first tephra layer unit 1 0 01 km3 dre during the second highly explosive phase the activity migrated to the northwest to evolve into a single vent eruption which formed the main scoria cone the central vent activity was initially characterized by variable eruptive styles which started the process of cone building including deposition of a second tephra layer unit 2 0 01 km3 dre and the effusion of the two main lava flows bonito and kana a following the initiation of effusive activity the eruption increased in explosivity to produce three subplinian tephra layers from the central vent units 3 4 and 5 which emitted more than 0 22 km3 dre of basalt with associated eruption columns 20 km high by the end of this phase the kana a lava flow was almost completely emplaced but the bonito flow continued to grow forming a 3 km diameter flow field a final waning phase produced several tephra units commonly discontinuous and reworked with 0 01 km3 dre cumulative volume the comparatively large volume of tephra the high eruptive columns and high mass eruption rates make sunset crater the most explosive monogenetic eruption studied to date volcano explosivity index vei 3 4 sunset crater volcano represents an interesting case of monogenetic volcanism in that its activity was characterized by highly explosive eruptive phases up to subplinian in scale and intermittent episodes of lava effusion that heavily affected prehistoric communities in the area explosive basaltic volcanism should be considered when assessing volcanic hazards in continental settings such as in the western united states

the age of lathrop wells volcanic center an 40ar 39ar dating investigation the sup 40 ar sup 39 ar age spectrum analyses of basalt whole rock and partially degassed sanidine xenocrysts for the lathrop wells volcanic center nevada yield eruption ages of 77 3 plus minus 6 0 and 76 6 plus minus 4 9 ka 2 sigma for the ql sub 1 and ql sub 2 flows respectively basaltic samples were analyzed in four to six replicate runs and yield normally distributed plateau ages miocene ash flow tuff xenoliths were collected from the basaltic units with the majority of samples coming from the ql sub 2 the sanidines from the ql sub 2 xenoliths yielded apparent plateau ages n 10 ranging from 69 plus minus 17 to 309 plus minus 11 ka with a strong cluster n 6 at approximately 77 ka because the diffusion dimension of sanidine is approximated by the physical crystal size cracking of the sanidine following the development of an argon concentration profile may result in complex argon age spectra experimental studies exploring the natural and laboratory argon systematics of degassed sanidine reveal that crystal breakage and hf acid etching lead to anomalously old apparent ages these new ages for the ql sub 1 and ql sub 2 flows are analytically indistinguishable and agree well with published eruption ages determined by sup 3 he and sup 36 cl cosmogenic surface exposure dating methods we conclude that the ql submore 1 and ql sub 2 flows are temporally equivalent additionally the agreement between our eruption ages for these units and the published 76 plus minus 20 ka ital zreda ital et al 1993 sup 36 cl exposure age for the lathrop wells scoria cone qs sub 3 suggests that the cone may be temporally equivalent to the ql sub 1 and ql sub 2 flows we believe the simplest and most reasonable interpretation is that the volcanic center is monogenetic copyright 1999 american geophysical union less

tecolote volcano pinacate volcanic field sonora mexico a case of highly explosive basaltic volcanism and shifting eruptive styles abstract explosive basaltic eruptions have been documented in monogenetic volcanic fields and recognizing the scales of their explosivity is important for understanding the full range of basaltic volcanism here we reconstruct one of the youngest eruptions in the pinacate volcanic field sonora mexico and estimate the volumes of the lava flows scoria cone and tephra units the source vent of the eruption is tecolote volcano 27 6 ka 40ar 39ar there were two distinct episodes of tephra production tephra unit 1 t1 followed by tephra unit 2 t2 t1 and t2 show different dispersal patterns with t1 dispersed in an approximately circular pattern and t2 dispersed oblately trending se and nw of the vent based on column height reconstructions and deposit characteristics the t1 producing eruption was subplinian 15 18 km plume with a calculated mass eruption rate ranging between 1 0 0 6 107 kg s and 2 2 1 2 107 kg s and corresponding durations between 79 54 min and 38 26 min respectively the t2 producing eruption was violent strombolian 11 km plume with a calculated mass eruption rate of 3 2 1 4 106 kg s and resulting duration of 193 78 min in addition to the two tephra units tecolote volcano produced seven morphologically distinct lava flows the majority of lava volume production occurred before and partly contemporaneously with tephra production and five small volume lava flows were emplaced after pyroclastic activity terminated indicating shifting and simultaneous eruptive styles of the total 0 23 km3 dense rock equivalent dre erupted volume the lava flows constitute the majority 0 17 km3 dre with 0 041 km3 dre volume for the cone and a combined 0 026 0 005 km3 dre volume for the two tephra units the geochemistry of the samples is consistent with that determined for other pinacate rocks which show a trend most similar to that of ocean island basalts and appears characteristically similar to other volcanic fields of the basin and range province

freshwater balance and the sources of deep and bottom waters in the arctic ocean inferred from the distribution of h218o data from sections across the eurasian basin of the arctic ocean occupied in 1987 and 1991 are used to derive information on the freshwater balance of the arctic ocean and on sources of the deep waters of the nansen amundsen and makarov basins using salinity h218o and mass balances we estimate the river runoff and the sea ice melt water fractions contained in the upper waters of the arctic ocean and infer pathways of the river runoff signal from the shelf seas across the central arctic ocean to fram strait the average mean residence time of the river runoff fraction contained in the arctic ocean halocline is determined to be about 11 to 14 years pacific water entering through bering strait is traced using silicate and its influence on the halocline waters of the canadian basin is estimated water column inventories of river runoff and sea ice melt water are calculated for a section just north of fram strait and implications of these inventories for sea ice export through fram strait are discussed comparison of the 18o 16o ratios of shelf water atlantic water and the deep waters of the arctic ocean indicate that the sources of the deep and bottom waters of the eurasian basin are located in the barents and kara seas

geomorphology morphometry spatial distribution and ages of mafic monogenetic volcanoes of the peinado and incahuasi fields southernmost central volcanic zone of the andes abstract the back arc southern puna region south of 24 s in the central volcanic zone of the andes contains hundreds of miocene to quaternary mafic monogenetic volcanoes roughly distributed in several volcanic fields analysis of the geomorphology morphometry spatial distribution and age of 36 mafic monogenetic centers in the peinado and incahuasi fields at the southwestern margin of the puna plateau gives insights on the links that mafic monogenetic volcanism can have with main and secondary structures and the effects of degradation on scoria cone shape degree of preservation morphometry and six new unspiked k ar ages indicate two distinct age groups old centers 2 ma and young centers 1 ma the older mafic centers consist of degraded scoria cones and lava flows with an estimated cumulative bulk volume of 2 2 km3 the younger mafic centers display a variety of well preserved landforms scoria cones lava flows maars tuff rings domes and have an estimated cumulative volume of 6 2 km3 their distribution in a main nne ssw and secondary ene wsw trends suggests a control by the regional nne ssw striking peinado and san francisco fault systems in a dextral strike slip configuration scoria cone and lava flow morphometries are similar in both fields but a marked difference indicating hydrovolcanic activity is the presence of tuff rings maars and tephra fallout deposits only in the peinado field morphometric analysis of dated pristine and degraded scoria cones of the southern puna region shows that parameters related to crater depth and inner crater steepness decrease consistently with age suggesting that crater infilling is the degradation related process that is most sensitive to age at scoria cones in the southern puna high values of crater depth crater width crater depth cone height and mean inner crater slope are indicative of a young 1 ma age as young cones can have initially low values

the isotopic record of lunar volcanism abstract the timing and extent of lunar volcanism was determined primarily by the internal thermal evolution of the moon a late heavy bombardment produced most of the observable lunar basins easily recognized stratigraphic markers and also may have influenced lunar volcanism most of the nearside basins seem to have been produced 3 8 4 0 ga ago during a period often referred to as the lunar cataclysm the pre cataclysm period was characterized by formation of the lunar crust plutonic rocks within the crust and pre mare volcanism isotopic analysis of breccia clasts pre dating the cataclysm has yielded an outline of this period the isotopic record of post cataclysm mare volcanism is clear but incomplete because samples from the youngest mare areas are lacking specifically the isotopic data show that some lunar anorthosites formed 4 45 ga ago consistent with early formation of an anorthositic lunar crust some mg suite norites troctolites and dunites also formed approximately contemporaneously with the oldest anorthosites but others are up to 200 300 ma younger more evolved rocks granites and quartz monzodiorites also formed between 4 4 and 4 0 ga ago the earliest known pre mare volcanism at 4 25 ga ago included aluminous mare like basalts and an olivine gabbronorite similar to apollo 12 basalts kreep basalt volcanism began at least 4 1 ga ago approximately contemporaneously with that of the ancient mare like basalts and continued during the cataclysm recorded instances of high ti mare basalt volcanism began during or immediately after the cataclysm low ti mare basalt volcanism is the most recent for which samples are available the isotopic data record an early primary lunar differentiation during which mare basalt sources formed probably by crystallization of cumulus minerals from a lunar magma ocean the isotopic record of post cataclysm basalts indicates a heterogeneous lunar mantle and can be explained by partial melting of cumulate sources but more complex petrogenesis also has been suggested more complex petrogenetic processes including assimilation and assimilation fractional crystallization afc seem to be required for pre mare volcanics the isotopic data contain a hint that petrogenesis of the oldest pre mare volcanics may be linked to formation of the so called procellarum basin possibly the oldest and largest lunar basin such a basin would provide a geologic context for the pre mare volcanics and its formation may have been a defining moment in lunar history

variable effects of cinder cone eruptions on prehistoric agrarian human populations in the american southwest abstract two 900 bp cinder cone eruptions in the american southwest affected prehistoric human populations in different ways mostly because of differences in the eruption styles and area affected primary pre eruption cultural factors that may have led to successful adaptation to the eruptions include decision making at the family or household level low investment in site structures dispersion of agricultural sites in varied environments and settlement spread over a large area so that those who were less affected could shelter and feed evacuees sunset crater near flagstaff arizona produced about 8 km 2 lava flow fields and a 2300 km 2 tephra blanket in an area that had been settled by prehistoric groups for at least 1000 years local subsistence relied on agriculture primarily maize and 30 cm tephra cover rendered 265 km 2 of prime land unfarmable this area was apparently abandoned for at least several generations a 500 km 2 area was probably marked by collapsed roofs and other structural damage from the fallout if the eruption occurred during the agricultural season the fallout would also have significantly damaged crops the eruption did have some benefits to local groups because lower elevation land which had previously been too dry to farm became agriculturally productive due to 3 8 cm of tephra mulch and some temporary soil nutrient improvements this previously uninhabited land became the site of significant year round settlement and farming eventually containing some of the largest pueblo structures ever built in the region new agricultural techniques were developed to manage the fallout mulch the eruption also affected ceramic production and trading patterns and volcano related ritual behavior the production of maize impressed lava spatter agglutinate was initiated little springs volcano about 200 km northwest of sunset crater is a small spatter rampart around a series of vents that produced about 5 km 2 of lava flow fields about 1 km 2 of land severely affected by ballistic fall and no significant tephra fall the small area affected resulted in much less disruption of human activities than at sunset crater farming was still possible right up to the edge of the lava flows which became attractive sites for settlements most sites along the lava flows have habitation and storage structures at the base of the flow and a series of small apparently little used structures on the blocky lava flow above these lava surface structures may have been defensive in nature in addition trails were constructed on the blocky lava flow surface these trails whose access points are difficult to recognize from below appear to have been used for rapid movement across the flows and may also have been defensive in nature spatter agglutinate blocks containing ceramic sherds within them similar to the maize impressed spatter agglutinate at sunset crater were made at little springs and carried to a nearby habitation site in arid and semiarid lands such as northern arizona tephra fall is a mixed blessing thick cinder blankets 20 30 cm render land uninhabitable but thinner 3 8 cm deposits can serve to conserve soil moisture regulate soil temperature thus lengthening the growing season and by lowering soil ph provide a temporary decades to a century or two increase in available phosphorus an important nutrient for growth the mulch opened up new lands for settlement but likely only lasted for a century or two before reworking reduced its effects

space time evolution of monogenetic volcanism in the mafic garrotxa volcanic field ne iberian peninsula we reconstructed the evolution of the volcanic activity within the central garrotxa monogenetic volcanic field the youngest volcanic area of the iberian peninsula by investigating the stratigraphy of the volcanic successions and the morphology of the monogenetic eruptive centres analysis of this volcanic succession has been conducted following the unconformity bounded stratigraphic units criteria the detailed stratigraphy of the volcanic successions shows that the central garrotxa volcanic field gvf evolved through four main periods of volcanic activity synthems represented by the eruptive products of the mafic monogenetic volcanoes and associated syn eruptive reworked deposits eruptive units and by the inter eruptive deposits epiclastic units the distribution and the morphologies of the monogenetic volcanoes suggest that feeder dykes were emplaced under influence of the present stress filed and along pre existing fractures of the basement our facies analysis of the deposits and their distribution shows that migration of volcanism toward the centre of the basin was accompanied by a trend of increasing explosivity episodic hydromagmatism in central garrotxa occurred without a specific geographic locus or obvious temporal correlation finally by integrating field data with the stratigraphy extracted from water wells we determined the volume of the volcanic deposits the small average volume of products emitted during each eruptive period and the long quiescence separating them allow us to classify the gvf as a low output rate volcanic field

eruption dynamics of hawaiian style fountains the case study of episode 1 of the kīlauea iki 1959 eruption hawaiian eruptions are characterized by fountains of gas and ejecta sustained for hours to days that reach tens to hundreds of meters in height quantitative analysis of the pyroclastic products from the 1959 eruption of k lauea iki k lauea volcano hawai i provides insights into the processes occurring during typical hawaiian fountaining activity this short lived but powerful eruption contained 17 fountaining episodes and produced a cone and tephra blanket as well as a lava lake that interacted with the vent and fountain during all but the first episode of the eruption the focus of this paper microtextural analysis of hawaiian fountaining products from this opening episode is used to infer vesiculation processes within the fountain and shallow conduit vesicle number densities for all clasts are high 106 107 cm 3 post fragmentation expansion of bubbles within the thermally insulated fountain overprints the pre fragmentation bubble populations leading to a reduction in vesicle number density and increase in mean vesicle size however early quenched rims of some clasts with vesicle number densities approaching 107 cm 3 are probably a valid approximation to magma conditions near fragmentation the extent of clast evolution from low vesicle to melt ratio and corresponding high vesicle number density to higher vesicle to melt ratio and lower vesicle number density corresponds to the length of residence time within the fountain

soluble chromophores in marine snow seawater sea ice and frost flowers near barrow alaska 1 we measured light absorption in 42 marine snow sea ice seawater brine and frost flower samples collected during the oasis field campaign between february 27 and april 15 2009 samples represented multiple sites between landfast ice and open pack ice in coastal areas approximately 5 km west of barrow alaska the chromophores that are most commonly measured in snow h2o2 no3 and no2 on average account for less than 1 of sunlight absorption in our samples instead light absorption is dominated by unidentified residual species likely organic compounds light absorption coefficients for the frost flowers on first year sea ice are on average 40 times larger than values for terrestrial snow samples at barrow suggesting very large rates of photochemical reactions in frost flowers for our marine samples the calculated rates of sunlight absorption and oh production from known chromophores are 0 1 1 4 1014 photons cm 3 s 1 and 5 70 10 12 mol l 1 s 1 respectively our residual spectra are similar to spectra of marine chromophoric dissolved organic matter cdom suggesting that cdom is the dominant chromophore in our samples based on our light absorption measurements we estimate dissolved organic carbon doc concentrations in barrow seawater and frost flowers as approximately 130 and 360 m c respectively we expect that cdom is a major source of oh in our marine samples and it is likely to have other significant photochemistry as well

new physical characterization of the fontana lapilli basaltic plinian eruption nicaragua the fontana lapilli deposit was erupted in the late pleistocene from a vent or multiple vents located near masaya volcano nicaragua and is the product of one of the largest basaltic plinian eruptions studied so far this eruption evolved from an initial sequence of fluctuating fountain like events and moderately explosive pulses to a sustained plinian episode depositing fall beds of highly vesicular basaltic andesite scoria sio2 53 wt samples show unimodal grain size distribution and a moderate sorting that are uniform in time the juvenile component predominates 96 wt and consists of vesicular clasts with both sub angular and fluidal elongated shapes we obtain a maximum plume height of 32 km and an associated mass eruption rate of 1 4 108 kg s 1 for the plinian phase estimates of erupted volume are strongly sensitive to the technique used for the calculation and to the distribution of field data our best estimate for the erupted volume of the majority of the climactic plinian phase is between 2 9 and 3 8 km3 and was obtained by applying a power law fitting technique with different integration limits the estimated eruption duration varies between 4 and 6 h marine core data confirm that the tephra thinning is better fitted by a power law than by an exponential trend

observed increases in bering strait oceanic fluxes from the pacific to the arctic from 2001 to 2011 and their impacts on the arctic ocean water column 1 mooring data indicate the bering strait throughflow increases 50 from 2001 0 7 sv to 2011 1 1 sv driving heat and freshwater flux increases increase in the pacific arctic pressure head explains two thirds of the change the rest being attributable to weaker local winds the 2011 heat flux 5 1020j approaches the previous record high 2007 due to transport increases and warmer lower layer ll temperatures despite surface temperature sst cooling in the last decade warmer ll waters arrive earlier 1 6 1 1 days yr though winds and sst are typical for recent decades maximum summer salinities likely set in the bering sea remain remarkably constant 33 1 psu over the decade elucidating the stable salinity of the western arctic cold halocline despite this freshwater flux variability strongly driven by transport exceeds variability in other arctic freshwater sources remote data winds sst prove insufficient for quantifying variability indicating interannual change can still only be assessed by in situ year round measurements

pacific freshwater river water and sea ice meltwater across arctic ocean basins results from the 2005 beringia expedition 1 pacific water sea ice meltwater and river water are the primary sources of freshwater in the arctic ocean we have determined their relative fractions on a transect across the arctic ocean section 2005 expedition onboard ib oden which took place from 21 august to 23 september 2005 the transect began north of alaska continued through the central canada basin to the alpha ridge and into the makarov basin and ended in amundsen basin pacific freshwater and river water were the major sources of freshwater throughout the central canada basin and into makarov basin with river water fractions sometimes considerably higher than pacific water in the top 50 m pacific freshwater extended to depths of about 200 m pacific water found over the alpha ridge and in the amundsen basin is suggested to have been transported there in the transpolar drift the inventories of pacific freshwater and river water were roughly constant along the section through most of the canada and makarov basins river water fractions were greater than those of pacific freshwater in the amundsen basin sea ice meltwater fractions were negative reflecting net ice formation or near zero throughout most of the section a comparison of freshwater inventories with those at stations occupied during expeditions in 1991 1994 and 1996 indicated an increase in river water inventories in the makarov and amundsen basins on the eurasian side of the arctic ocean

distribution of atlantic and pacific waters in the upper arctic ocean implications for circulation the atlantic and pacific oceans provide source waters for the arctic ocean that can be distinguished by their differing nitrate and phosphate concentration relationships using these relationships we estimate the amount of atlantic and pacific waters in the surface layer top 30 m of the arctic ocean atlantic source water is dominant in most of the eurasian basin and is present in significant amounts in the makarov basin north of the east siberian sea pacific source water is dominant in most of the canadian basin and is present in significant amounts in the amundsen basin north of greenland we deduce circulation patterns from the distributions of atlantic and pacific source waters in the surface layer of the arctic ocean and conclude that the flow within the surface layer differs from ice drift along the north american and european boundaries of the polar basin

freshwater composition of the waters off southeast greenland and their link to the arctic ocean 1 the freshwater composition of waters on the southeast greenland shelf and slope are described using a set of high resolution transects occupied in summer 2004 which included hydrographic velocity nutrient and chemical tracer measurements the nutrient and tracer data are used to quantify the fractions of pacific water sea ice melt and meteoric water present in the upper layers of the east greenland current egc and east greenland coastal current egcc the egc egcc system dominates the circulation of this region and strongly influences the observed distribution of the three freshwater types sea ice melt and meteoric water fractions are surface intensified reflecting their sources and generally increase southward from denmark strait to cape farewell as well as shoreward significant fractions of pacific water are found in the subsurface layers of the egcc supporting the idea that this inner shelf branch is directly linked to the egc and thus to the arctic ocean a set of historical sections is examined to investigate the variability of pacific water content in the egc and egcc from 1984 to 2004 in the vicinity of denmark strait the fraction of pacific water increased substantially in the late 1990s and subsequently declined to low levels in 2002 and 2004 mirroring the reduction in pacific water content reported previously at fram strait this variability is found to correlate significantly with the arctic oscillation index lagged by 9 years suggesting that the arctic ocean circulation patterns bring varying amounts of pacific water to the north atlantic via the egc egcc

dilution of the northern north atlantic ocean in recent decades declining salinities signify that large amounts of fresh water have been added to the northern north atlantic ocean since the mid 1960s we estimate that the nordic seas and subpolar basins were diluted by an extra 19 000 5000 cubic kilometers of freshwater input between 1965 and 1995 fully half of that additional fresh water about 10 000 cubic kilometers infiltrated the system in the late 1960s at an approximate rate of 2000 cubic kilometers per year patterns of freshwater accumulation observed in the nordic seas suggest a century time scale to reach freshening thresholds critical to that portion of the atlantic meridional overturning circulation

determination of the largest clast sizes of tephra deposits for the characterization of explosive eruptions a study of the iavcei commission on tephra hazard modelling the distribution of clasts deposited around a volcano during an explosive eruption typically contoured by isopleth maps provides important insights into the associated plume height wind speed and eruptive style nonetheless a wide range of strategies exists to determine the largest clasts which can lead to very different results with obvious implications for the characterization of eruptive behaviour of active volcanoes the iavcei commission on tephra hazard modelling has carried out a dedicated exercise to assess the influence of various strategies on the determination of the largest clasts suggestions on the selection of sampling area collection strategy choice of clast typologies and clast characterization i e axis measurement and averaging technique are given mostly based on a thorough investigation of two outcrops of a plinian tephra deposit from cotopaxi volcano ecuador located at different distances from the vent these include 1 sampling on a flat paleotopography far from significant slopes to minimize remobilization effects 2 sampling on specified horizontal area sections with the statistically representative sampling area depending on the outcrop grain size and lithic content 3 clast characterization based on the geometric mean of its three orthogonal axes with the approximation of the minimum ellipsoid lithic fragments are better than pumice clasts when present and 4 use of the method of the 50th percentile of a sample of 20 clasts as the best way to assess the largest clasts it is also suggested that all data collected for the construction of isopleth maps be made available to the community through the use of a standardized data collection template to assess the applicability of the new proposed strategy on a large number of deposits and to build a large dataset for the future development and refinement of dispersal models

the case for a younger imbrium basin new 40ar 39ar ages of apollo 14 rocks petrographically and chemically well characterized rocks of the apollo 14 landing site 12 impact melt breccias 3 clast free impact melt rocks 2 granulitic rocks 1 cataclastic noritic anorthosite 1 shocked gabbronorite 1 mare basalt and 1 plagioclase single crystal have been dated by the 40ar 39ar technique the samples represent two different formations at the apollo 14 site 1 small lithic clasts 10 specimens from fragmental breccia 14063 ejected from the 26 ma old cone crater and one clast mare basalt from cone crater soil 14140 and 2 large rock samples 10 specimens collected throughout the regolith of the landing site the first group of samples has exposure ages close to 26 ma and 40ar 39ar ages ranging from 3 86 to 4 09 ga which indicates that breccia 14063 was assembled 3 86 ga ago the second group of samples displays lower 40ar 39ar ages ranging from 3 73 to 3 85 ga we interpret breccia 14063 as part of a nectarian megabreccia unit which was incorporated into the fra mauro formation as a megablock by secondary mass wasting of the ejecta blanket of a local pre imbrian crater the remaining samples are thought to represent clasts of the apollo 14 subregolith basement megabreccia defined as the fra mauro formation consequently the reported ages of these clasts confirm previous suggestions that the fra mauro formation and therefore the imbrium basin is only 3 75 ga old and not 3 85 ga as commonly assumed

differentiating fluvial components of upper canada basin waters on the basis of measurements of dissolved barium combined with other physical and chemical tracers 1 the utility of dissolved barium ba as a quasi conservative tracer of arctic water masses has been demonstrated previously here we report distributions of salinity temperature and ba in the upper 200 m of the canada basin and adjacent areas observed during cruises conducted in 2003 2004 as part of the joint western arctic climate study and beaufort gyre exploration project a salinity oxygen isotope mass balance is used to calculate the relative contributions from sea ice melt meteoric and saline end members and ba measurements are incorporated to resolve the meteoric fraction into separate contributions from north american and eurasian sources of runoff large fractions of eurasian runoff as high as 15 5 were observed in the surface layer throughout the canada basin but significant amounts of north american runoff in the surface layer were only observed at the southernmost station occupied in the canada basin in 2004 nearest to the mouth of the mackenzie river smaller contributions from both eurasian and north american runoff were evident in the summer and winter pacific derived water masses that comprise the underlying upper halocline layer in the canada basin significant amounts of eurasian and north american runoff were observed throughout the water column at a station occupied in amundsen gulf in 2004 this suggests the export of runoff from both sources through the passages of the canadian arctic archipelago

the role of sea ice and other fresh water in the arctic circulation salinity stratification is critical to the vertical circulation of the high latitude ocean we here examine the control of the vertical circulation in the northern seas and the potential for altering it by considering the budgets and storage of fresh water in the arctic ocean and in the convective regions to the south we find that the present day greenland and iceland seas and probably also the labrador sea are rather delicately poised with respect to their ability to sustain convection small variations in the fresh water supplied to the convective gyres from the arctic ocean via the east greenland current can alter or stop the convection in what may be a modern analog to the halocline catastrophes proposed for the distant past the north atlantic salinity anomaly of the 1960s and 1970s is a recent example it must have had its origin in an increased fresh water discharge from the arctic ocean similarly the freshening and cooling of the deep north atlantic in recent years is a likely manifestation of the increased transfer of fresh water from the arctic ocean into the convective gyres finally we note that because of the temperature dependence of compressibility a slight salinity stratification in the convective gyres is required to efficiently ventilate the deep ocean

estimating the volume of tephra deposits a new simple strategy volume determination of tephra deposits is necessary for the assessment of the dynamics and hazards of explosive volcanoes several methods have been proposed during the past 40 years that include the analysis of crystal concentration of large pumices integrations of various thinning relationships and the inversion of field observations using analytical and computational models regardless of their strong dependence on tephra deposit exposure and distribution of isomass isopach contours empirical integrations of deposit thinning trends still represent the most widely adopted strategy due to their practical and fast application the most recent methods involve the best fitting of thinning data using various exponential segments or a power law curve on semilog plots of thickness or mass area versus square root of isopach area the exponential method is mainly sensitive to the number and the choice of straight segments whereas the power law method can better reproduce the natural thinning of tephra deposits but is strongly sensitive to the proximal or distal extreme of integration we analyze a large data set of tephra deposits and propose a new empirical method for the determination of tephra deposit volumes that is based on the integration of the weibull function the new method shows a better agreement with observed data reconciling the debate on the use of the exponential versus power law method in fact the weibull best fitting only depends on three free parameters can well reproduce the gradual thinning of tephra deposits and does not depend on the choice of arbitrary segments or of arbitrary extremes of integration

sources and distribution of fresh water in the east greenland current abstract fresh water flowing from the arctic ocean via the east greenland current influences deep water formation in the nordic seas as well as the salinity of the surface and deep waters flowing from there this fresh water has three sources pacific water relatively fresh cf atlantic water river runoff and sea ice meltwater to determine the relative amounts of the three sources of fresh water in may 2002 we collected water samples across the east greenland current in sections from 81 5 n to the irminger sea south of denmark strait we used nitrate phosphate relationships to distinguish pacific waters from atlantic waters salinity to obtain the sum of sea ice melt water and river runoff water and total alkalinity to distinguish the latter river runoff contributed the largest part of the total fresh water component in some regions with some inventories exceeding 12 m pacific fresh water pacific source water s 32 cf atlantic source water s 34 9 typically provided about 1 3 of the river runoff contribution sea ice meltwater was very nearly non existent in the surface waters of all sections likely at least in part as a result of the samples being collected before the onset of the melt season the fresh water from the arctic ocean was strongly confined to near the greenland coast we thus conjecture that the main source of fresh water from the arctic ocean most strongly impacting deep convection in the nordic seas would be sea ice as opposed to fresh water in the liquid phase i e river runoff pacific fresh water and sea ice meltwater

total grain size distribution of a mafic subplinian tephra tb 2 from the 1986 izu oshima eruption japan an estimation based on a theoretical model of tephra dispersal abstract total grain size distribution was estimated using field data and theoretical modelling isopleth maps of each size were constructed at intervals of 1 phi based on the detailed sampling and analysis of a subplinian deposit tb 2 a product of the climatic phase of the 1986 eruption of the izu oshima volcano japan the umbrella spreading of the eruptive plume is analysed from isopleth maps based on a theoretical model of tephra dispersal bursik m i sparks r s j gilbert j s carey s n 1992 sedimentation of tephra by volcanic plumes i theory and its comparison with a study of the fogo a plinian deposit sao miguel azores bull volcanol 54 329 344 the dispersal of particles in the diameter range of 32 4 mm agrees with the model and the deduced column height is consistent with the visual observation using field data and the theoretical model the erupted mass of each size fraction is estimated and the total grain size distribution and total mass were obtained the observed mass loading decay as a function of the area enclosed by the isopleth is revised using the calculated terminal fall velocity and flux of the plume in the umbrella region the total grain size distribution of tb 2 indicates an intermediate nature between plinian and hawaiian eruption styles

freshwater budget of the canada basin arctic ocean from salinity δ18o and nutrients 1 the contribution of freshwater components e g meteoric sea ice and pacific water in the canada basin is quantified using salinity 18o and nutrient data collected in 2003 and 2004 the penetration depth of sea ice meltwater is limited to the upper 30 m and brine rejected during sea ice formation is observed from 30 to 250 m depth the fraction of meteoric water is high in the upper 50 m and decreases with depth pacific water entering via bering strait is the main source of freshwater below 50 m depth bering strait throughflow which transports pacific water with salinity 32 5 together with meteoric water supplied upstream of the bering strait contributes up to 75 of freshwater input 3200 km3 a 1 to the canada basin the mean residence time of pacific water in the canada basin is estimated to be 11 years precipitation and river runoff from both north american and eurasian continents add 800 km3 a 1 and sea ice formation removes 900 km3 a 1 0 6 m a 1 of fresh water the export of ice and liquid fresh water from the canada basin contributes 40 of the freshwater flux from the arctic ocean to the north atlantic ocean

the freshwater composition of the fram strait outflow derived from a decade of tracer measurements the composition of the fram strait freshwater outflow is investigated by comparing 10 sections of concurrent salinity 18o nitrate and phosphate measurements collected between 1997 and 2011 the largest inventories of net sea ice meltwater are found in 2009 2010 and 2011 the 2009 2011 sections are also the first to show positive fractions of sea ice meltwater at the surface near the core of the egc sections from september 2009 2011 show an increased input of sea ice meltwater at the surface relative to older september sections this suggests that more sea ice now melts back into the surface in late summer than previously comparison of april july and september sections reveals seasonal variations in the inventory of positive sea ice meltwater with maximum inventories in september sections the time series of sections reveals a strong anti correlation between meteoric water and net sea ice meltwater inventories suggesting that meteoric water and brine may be delivered to fram strait together from a common source we find that the freshwater outflow at fram strait exhibits a similar meteoric water to net sea ice meltwater ratio as the central arctic ocean and siberian shelves suggesting that much of the sea ice meltwater and meteoric water at fram strait may originate from these regions however we also find that the ratio of meteoric water to sea ice meltwater inventories at fram strait is decreasing with time due to an increased surface input of sea ice meltwater in recent sections

sources to the east greenland current and its contribution to the denmark strait overflow data from the east greenland current in 2002 are evaluated using optimum multiparameter analysis the current is followed from north of fram strait to the denmark strait sill and the contributions of different source waters in mass fractions are deduced from the results it can be concluded that at least in spring 2002 the east greenland current was the main source for the waters found at the denmark strait sill contributing to the overflow into the north atlantic the east greenland current carried water masses from different source regions in the arctic ocean the west spitsbergen current and the greenland sea the results agree well with the known circulation of the western nordic seas but also add knowledge both to the quantification and to the mixing processes showing the importance of the locally formed greenland sea arctic intermediate water for the east greenland current and the denmark strait

arctic ocean water mass balance from isotope data the distributions of the oxygen 18 and tritium isotopes and of salinity yield a residence time of 10 years for the surface and halocline waters of the arctic basin we find a yearly net production of 0 59 m of sea ice and an input of 1 16 m of freshwater from continental river runoff local precipitation and bering strait salinity deficiency using the basin area value with these numbers gives long term average total net production and transport rates of 0 15 sv of ice and 0 18 sv of meteoric component bering strait water not included if in addition a reasonable depth profile of relative current velocity is assumed for the outflow a yearly input of 2 8 sv of atlantic and bering strait water is needed to replenish the upper and halocline waters these numbers should be good to 20 and are multiyear averages the isotope data clearly indicate that the barents sea is an inflow area for atlantic water to the basin but that net export of ice occurs there

total grain size distribution and volume of tephra fall deposits on 17 june 1996 ruapehu volcano new zealand produced a sustained andesitic sub plinian eruption which generated a narrow tephra fall deposit extending more than 200 km from the volcano the extremely detailed data set from this eruption allowed methods for the determination of total grain size distribution and volume of tephra fall deposits to be critically investigated calculated total grain size distributions of tephra fall deposits depend strongly on the method used and on the availability of data across the entire dispersal area the voronoi tessellation method was tested for the ruapehu deposit and gave the best results when applied to a data set extending out to isomass values of 1 g m 2 the total grain size distribution of a deposit is also strongly influenced by the very proximal samples and this can be shown by artificially constructing subsets from the ruapehu database unless the available data set is large all existing techniques for calculations of total grain size distribution give only apparent distributions the tephra fall deposit from ruapehu does not show a simple exponential thinning but can be approximated well by at least three straight line segments or by a power law fit on semi log plots of thickness vs area 1 2 integrations of both fits give similar volumes of about 4 106 m3 integration of at least three exponential segments and of a power law fit with at least ten isopach contours available can be considered as a good estimate of the actual volume of tephra fall integrations of smaller data sets are more problematic

tracer derived freshwater composition of the siberian continental shelf and slope following the extreme arctic summer of 2007 we investigate the freshwater composition of the shelf and slope of the arctic ocean north of the new siberian islands using geochemical tracer data 18o ba and po 4 collected following the extreme summer of 2007 we find that the anomalous wind patterns that partly explained the sea ice minimum at this time also led to significant quantities of pacific derived surface water in the westernmost part of the makarov basin we also find larger quantities of meteoric water near lomonosov ridge than were found in 1995 dissolved barium is depleted in the upper layers in one region of our study area probably as a result of biological activity in open waters increasingly ice free conditions compromise the quantitative use of barium as a tracer of river water in the arctic ocean

tephra stratigraphy and eruptive volume of the may 2008 chaiten eruption chile on may 1st 2008 mount chaiten southern chile interrupted a long period of quiescence generating a sequence of explosive eruptions and causing the evacuation of chaiten town located a few kilometers south of the volcano the activity was characterized by several explosive events each associated with plumes which reached up to about 19 km above sea level the products were dispersed across a wide area with the finest ash reaching the atlantic coast of argentina our field observations in the proximal medial area 3 25 km from the vent indicate that the may 2008 tephra deposit consists of numerous layers most of which can be correlated with individual eruptive events these layers vary from extremely fine grained ash to layers of lapilli and blocks composed of both juvenile and lithic material here we describe the stratigraphy and physical characteristics of the may 2008 deposits and propose a reconstruction of the timing of the may 2008 events the deposits are mainly associated with the three main explosive phases which occurred on 1st 2nd may 3rd 5th may and 6th may with an estimated bulk tephra volume of 0 5 1 0 km3 integration of both exponential and power law fitting for the 6th may event represented by a layer composed mainly of lithic lapilli and blocks 2 mm an isopleth map was compiled from which a 19 km plume height was determined which is in good agreement with satellite observations

on the eruptive origins of lunar localized pyroclastic deposits abstract localized pyroclastic deposits lpds are low albedo accumulates of pyroclastic material with distinct positive topographic signatures that are found dominantly along highland mare boundaries previous workers hypothesized that lpds represent products of a lunar equivalent of vulcanian style eruptions based in part on the observation that some of the deposits in alphonsus crater have large vent volumes in comparison with their deposit volumes indicating a low proportion of juvenile material in the deposits the objective of this study is to better understand eruption mechanisms by determining how the proportion of juvenile material as calculated using deposit and vent volumes varies among lpds in alphonsus crater and elsewhere on the moon using contemporary data and methods deposit and vent volumes for 23 lpds from eleven sites were calculated by differencing current and modeled pre eruption surfaces using digital terrain models dtms derived from lunar reconnaissance orbiter camera narrow angle camera lroc nac results show that lpds have a wide range of juvenile proportions many of which are more juvenile rich than previously thought additionally there is a positive relationship between juvenile material proportion and deposit volume and thickness and a positive relationship between juvenile volume and dispersal area lpds also bear a broad range of thinning profiles which span a range of multiple eruption types on earth these findings along with previous studies employing spectroscopic analysis of these deposits indicate there is greater diversity among lpds in composition and morphometry than previously understood and that previously published simplified vulcanian models may apply only to the deposits containing the least amount of juvenile material with all others perhaps requiring a combination of multiple eruptive mechanisms furthermore dynamic model results suggest that the most widespread lunar deposits in this study were formed by magma containing 2000 5000 ppm of dissolved volatiles consistent with recent estimates via melt inclusion analysis but contrary to long held ideas that the moon was largely degassed during its formation

ocean circulation and freshwater pathways in the arctic mediterranean based on a combined nd isotope ree and oxygen isotope section across fram strait the water masses passing the fram strait are mainly responsible for the exchange of heat and freshwater between the nordic seas and the arctic ocean the arctic mediterranean am disentangling their exact sources distribution and mixing however is complex this work provides new insights based on a detailed geochemical tracer inventory including dissolved nd isotope end rare earth element ree and stable oxygen isotope 18o data along a full water depth section across fram strait we find that nd isotope and ree distributions in the open am primarily reflect lateral advection of water masses and their mixing seawater particle interactions exert important control only above the shelf regions as observed above the ne greenland shelf advection of northward flowing warm atlantic water aw is clearly reflected by an end signature of 11 7 and a nd concentration nd of 16 pmol kg in the upper 500 m of the eastern and central fram strait freshening and cooling of the aw on its way trough the am are accompanied by a continuous change towards more radiogenic end signatures e g 10 4 of dense arctic atlantic water this mainly reflects mixing with intermediate waters but also admixture of dense kara sea waters and pacific derived waters the more radiogenic end signatures of the intermediate and deep waters reaching 9 5 are mainly acquired in the sw nordic seas through exchange with basaltic formations of iceland and se greenland inputs of nd from svalbard are not observed and surface waters and nd on the svalbard shelf originate from the barents sea shallow southward flowing arctic derived waters 200 m form the core of the east greenland current above the greenland slope and can be traced by their relatively radiogenic end reaching 8 8 and elevated nd 21 to 29 pmol kg these properties are used together with 18o and standard hydrographic tracers to define the proportions of pacific derived 30 based on nd isotopes and atlantic derived waters as well as of river waters 8 shallow waters 150 m on the ne greenland shelf share some characteristics of arctic derived waters but exhibit less radiogenic end values reaching 12 4 and higher nd up to 38 pmol kg in the upper 100 m this suggests local addition of greenland freshwater of up to 6 in addition to these observations this study shows that the pronounced gradients in end signatures and ree characteristics in the upper water column provide a reliable basis for assessments of shallow hydrological changes within the am

a late holocene explosive mafic eruption of villarrica volcano southern andes the chaimilla deposit abstract villarrica chile is one of the most active volcanoes in south america having erupted about 60 times in the last 460 years although its historical eruptive activity has been mainly effusive and weakly explosive it had strong explosive behaviour in postglacial times chaimilla

timing of basaltic volcanism along the mesa butte fault in the san francisco volcanic field arizona from 40ar 39ar dates implications for longevity of cinder cone alignments using high precision stepwise heating 40ar 39ar methods we dated volcanic products of at least 12 vents cropping out along the northern segment of the mesa butte fault in the san francisco volcanic field arizona where the relationship between fault and vent alignment is unambiguous the 40ar 39ar isochron dates indicate that the mesa butte fault hosted five episodes of volcanism over a 1 million year interval from 1400 to 300 ka the first episode occurred 1 km northwest of the trace of the mesa butte fault whereas the next two episodes were centered near the intersection of the mesa butte and cedar ranch faults the final two episodes produced red mountain 750 100 ka and shadow mountain 300 100 ka respectively ages of vents representing the third mesa butte episode of volcanism 760 50 ka to 900 80 ka indicate a systematic southwestward shift in the locus of volcanism along the mesa butte fault that contrasts sharply with overall eastward younging of volcanism within the field these data demonstrate that structures in basaltic volcanic fields are capable of hosting multiple episodes of volcanism over periods of time comparable to duration periods of composite volcanoes 106 years but at significantly lower recurrence intervals these results suggest that probability models of spatiotemporal recurrence of volcanism within basaltic volcanic fields should incorporate mapped structures particularly where these structures have either hosted previous volcanic activity or are proximal to population centers or sensitive installations such as nuclear power plants or waste repositories

barium as a tracer of arctic halocline and river waters dissolved barium ba concentrations are reported for water samples collected during six oceanographic cruises to the arctic in 1993 and during the 1994 arctic ocean section upper arctic 75 nmol ba 1 1 observed in the surface mixed layer of the arctic interior i e beyond the 200 m isobath occurred in the canada basin as a result of the biological removal of ba from surface waters of the chukchi sea and the tendency of the bering inflow to enter the arctic interior at depths below the relatively fresher mixed layer we hypothesize that the mackenzie river is the dominant source of the high ba observed in the surface waters of the canada basin features characterized by local salinity minima and ba maxima in surface waters down to depths of 30 50 m were observed over the arlis plateau and mendeleyev ridge in both 1993 and 1994 and over the makarov basin and lomonosov ridge in 1994 the physical and chemical properties of these waters suggest that they have been significantly influenced by fluvial discharge it could not be determined from available data whether these features arose from offshore transport of eurasian river discharge from the russian arctic seas meanders of the mackenzie river influenced beaufort gyre or a branch of bering inflow that crossed the chukchi shelf and entrained river water from north american and or eurasian sources in both 1993 and 1994 ba concentrations in the upper halocline layer as defined by a core salinity of 33 1 ranged between 42 and 77 nmol ba 1 1 with highest values observed in the canada basin the ba maximum and the related nutrient maxima and oxygen minimum that characterize the upper halocline in the canada basin suggest sources in the chukchi and beaufort seas and that the mechanism by which these waters are formed is linked with the influx of water through the bering strait the ba distributions for 1993 and 1994 delineate the lateral extent of upper halocline waters with canada basin character and show them to be chemically distinct from upper halocline waters in the eurasian basin the front separating these water types ran roughly along the mendeleyev and alpha ridges consistent with reports that the boundary between atlantic and pacific water mass assemblies in the arctic has recently been displaced from its historical position over the lomonosov ridge lateral gradients in both ba and the no parameter were observed within the lower halocline layer defined by an no minimum and core salinity of 34 2 34 4 along the 1994 arctic ocean section indicating that lower halocline waters receive additional inputs as they transit to the canadian basin from their region of formation in the eurasian sector of the arctic

formation and evolution of the surface mixed layer and halocline of the arctic ocean fresh water from summer ice melt and the total freshwater content of the arctic ocean water column above the thermocline are estimated from vertical profiles of temperature and salinity observed on the i b oden 1991 cruise the seasonal ice melt ranges from 0 5 m to slightly above 1 m and is moderately uniform over the observation area regions of lower melting are seen over the morris jesup plateau the freshwater content is calculated relative to the salinity just above the thermocline north of the barents sea the freshwater content increases toward the interior of the arctic ocean showing that fresh water is advected from other regions into the observation area regions of different freshwater content are separated by fronts over the nansen gakkel ridge over the lomonosov ridge and in the western eurasian basin between waters derived from the eurasian and canadian basins denser water homogenized north of the barents sea is recognized by a temperature minimum layer the absence of the temperature minimum near the nansen gakkel ridge indicates that heat is transferred from the atlantic layer over a longer time than the shortest route would allow this observation can be explained if the layer circulates together with the atlantic layer i e toward the east and returns above the nansen gakkel ridge and along the amundsen basin north of the laptev sea this water formed north of the barents sea becomes covered by low salinity shelf water the increased freshwater content limits the winter convection so it no longer reaches the thermocline and an intermediate halocline is formed the halocline in the eurasian basin consists of water originating from winter convection in the arctic ocean north of the barents sea which then circulates around the basin such a formation mechanism also explains the observed distribution of low no water the strong density increase limits vertical exchange and the vertical diffusion coefficient in the halocline is small 1 10 6 m2 s 1 the increased temperature of the halocline shows that the heat lost upward by the atlantic layer mainly by double diffusive convection is trapped below the mixed layer

tarawera 1886 new zealand a basaltic plinian fissure eruption abstract new zealand s biggest and most destructive volcanic eruption of historical times was that of tarawera in 1886 the resulting scoria fall has a dispersal very similar in extent to that of the vesuvius a d 79 pumice fall and is one of the few known examples of a basaltic deposit of plinian type a new estimate of the volume 2 km 3 is significantly greater than previous estimates the basalt came mainly from a 7 km length of fissure and emission and exit velocity were fairly uniform along at least 4 km of it this is one of the few documented examples of a plinian eruption from a fissure vent primary welding of the scoria fall resulted where the accumulation rate exceeded about 250 mm min 1 a model of the eruption dynamics is proposed which leads to an estimate of 28 km for the height of the eruption cloud and implies a magma volatile fraction of 1 5 3 violent phreatic explosions occurred in the southwestern extension of the fissure across the rotomahana geothermal field and it is thought that some of the water responsible for the power of the plinian eruption came from this source though its amount was not sufficient to turn the eruption into a phreatoplinian one

significance of agglutinate mounds on lava flows associated with monogenetic cones an example at sunset crater northern arizona large mounds of welded pyroclasts and rootless flows on top of mafic lava flows associated with symmetrical scoria cones may be evidence for breaching and subsequent restoration of the cones textures and bedding structures of the agglutinate mounds are distinctly different from those of hornitos and indicate deposition proximal to a major explosive vent breaching of a cone armored by an agglutinate carapace may cause the welded deposits to collapse onto the emerging lava which then rafts them away renewed or continued strombolian eruptions from the vent can restore the symmetry of the cone and conceal the disrupted structure rafted agglutinate mounds on the bonito lava flow at sunset crater a symmetrical holocene scoria cone in northern arizona extend in a belt from near the base of the cone toward the northwest the direction the lava flowed eye witness accounts of the eruption at paricutin mexico in 1943 record breaching and restoration events similar to the one inferred to have occurred at sunset crater and demonstrate that symmetrical monogenetic cones may have complicated histories

discovery of a plinian basaltic eruption of roman age at etna volcano italy basaltic plinian eruptions are rare and poorly known volcanic phenomena etna is an active basaltic volcano the activity of which is dominated by effusive eruptions that represent a continuous threat to a large populated area we report on a plinian eruption of basaltic composition that occurred in 122 b c lapilli fallout caused extensive damage to the southern flank of the volcano the discovery of this large explosive eruption raises important issues for previous hazard assessment at etna and other basaltic volcanoes an effusive basaltic volcano generally nonhazardous for humans can become very dangerous

isotopic studies of ferroan anorthosite 62236 a young lunar crustal rock from a light rare earth element depleted source isotopic analyses of mineral fractions and whole rocks from the ferroan anorthosite 62236 yield a sm nd isochron with an age of 4 29 0 06 ga and an initial end143 value of 3 1 0 9 we have also measured end142 anomalies of 0 25 on two fractions of 62236 these values are higher than the value of 0 1 predicted if 62236 was derived from a chondritic source at 4 29 ga but are consistent with the positive initial end143 value the sm nd isotopic composition of 62236 has been modified by the capture of thermal neutrons such that the 147sm 144nd 143nd 144nd and 142nd 144nd ratios measured on the mineral fractions and whole rocks must be corrected the corrections do not significantly alter the sm nd isotopic results determined on 62236 despite the fact that the ar ar and rb sr isotopic systematics of 62236 have been reset by impact metamorphism at 3 93 0 04 ga the sm nd systematics appear to have been unaffected the sm nd isotopic systematics of 62236 provide several constrains on models of lunar crustal differentiation provided they have not been reset since crystallization first the relatively young age of 62236 as well as the old ages determined on several crustal plutonic rocks of the mg suite require multiple sources of magmas on the moon very early in its history second positive end143 values determined on all analyzed ferroan anorthosites suggest that they were derived from sources depleted in light rare earth elements and third models based on initial end143 and present day end142 values suggest that the source of 62236 was depleted in light rare earth elements at 4 46 ga in order to reconcile these observations with the lunar magma ocean model 1 the magma ocean must have existed for a very short period of time and may have had a sub chondritic nd sm ratio and 2 the youngest ferroan anorthosites such as 62236 cannot be cumulates from the magma ocean but must form by other processes

highly explosive eruption of the monogenetic 8 6 ka bp la vache et lassolas scoria cone complex chaine des puys france abstract the eruption of the trachy basaltic la vache and lassolas cone complex was the youngest eruption ca 8 6 ka bp and one of the most violent in the chaine des puys france here we present field data and results of grain size componentry and clast density measurements of different layers of the widespread tephra deposit that is associated with this cone forming eruption our data indicates five main eruption phases comprising a vent opening phase a second sustained highly explosive phase a third and fourth violent strombolian phase and a fifth dominantly effusive phase the layer formed by the opening phase is rich in lithic material which was previously considered to be the result of phreatomagmatic activity the data presented here on the componentry and textures of the pyroclastic material contradict this hypothesis we propose instead that the material of the basal layer results from fragmentation caused by the explosion of a first arriving gas dominated phase the variations in eruption intensity during the main eruption phases are interpreted here to be the result of gas segregation within the plumbing system and fluxes in the magma ascent rate during the eruption significant amount of gas segregation is indicated by the deposition of both gas poor and gas rich material and by the presence of plate tephra this is also supported by the simultaneous ejection of tephra and lava from both cones during most of the explosive activity we suggest that gas segregation occurred within shallow intrusions and that fresh ascending material in the main conduit mixed with degassed material that flow back into the conduit from the intrusion before fragmentation the interaction of the ascending magma and the opening of intrusions may have controlled the evolution and explosivity of the eruption the high explosivity at the beginning of the eruption and the wide dispersal area demonstrate that scoria cone eruptions in monogenetic fields can impose a major threat to the population and infrastructures nearby as these events may occur with little warning and therefore research on this kind of eruptions is of a major importance to better understand the processes driving these events

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