descriptive nomenclature and classification of pyroclastic deposits and fragments recommendations of the iugs subcommission on the systematics of igneous rocks

syn and post eruptive volcanic processes in the yubileinaya kimberlite pipe yakutia russia and implications for the emplacement of south african style kimberlite pipes abstract the yubileinaya kimberlite pipe with a surface area of 59 ha is one of the largest pipes in the yakutian kimberlite province the devonian pipe was emplaced under structural control into lower paleozoic karstic limestone the pipe complex consists of several smaller precursor pipes which are cut by the large round main pipe while the precursor pipes show many features typical for root zones main pipe is younger cuts into the precursor pipes and exposes well bedded volcaniclastic sediments the maximum estimated erosion since emplacement is 250 m open pit mapping of a 180 m thick kimberlite sequence documents the waning phases of the volcanic activity in the kimberlite pipe and the onset of its crater infill by resedimentation three volcanic lithofacies types can be differentiated the deepest and oldest facies type is a massive volcaniclastic rock akb only accessible in drill core it is equivalent to tuffisitic kimberlite in south african pipes and thought to be related to the main volcanic phase which was characterized by violent explosions the overlying lithofacies type comprises primary and resedimented volcaniclastic sediments as well as rock avalanche deposits sourced from the exposed maar crater collar it represents the onset of sedimentation onto the crater floor during the waning phase of volcanic eruptions where primary pyroclastic deposition was contemporaneous with resedimentation from the tephra wall and the widening maar crater ongoing volcanic activity is also testified by the presence of a vertical feeder conduit marking the area of the last volcanic eruption clouds piercing through the diatreme this feeder conduit is overlain by the third and youngest lithofacies type which consists mainly of resedimented volcaniclastic material and lake beds during the sedimentation of this facies primary volcanic activity was only minor and finally absent and resedimentation processes dominated the crater infill the yubileinaya pipe complex exposes root zones contact breccias as well as diatreme and crater infill sediments it has all features typical of large south african style pipes and much can be learned from yubileinaya about the emplacement sequence and behaviour of these pipes emplacement of the pipe occurred over an extended time span with intermittent phases of volcanic quiescence and consolidation the akb reveals little direct evidence of what sort of emplacement process was dominant during the main period of volcanic activity there is neither textural evidence that violent degassing of a juvenile gas phase has caused pipe excavation nor that external water was present during the main phase of volcanic eruptions however there is clear evidence in rock textures that meteoric surface water was present during crater infill base surge deposits forming part of the bedded crater infill sequence indicate that water was present in the eruption clouds and hence the root zone of the pipe there is no reason to assume that groundwater did not also have access to the ascending magma during the main phase of volcanic activity that excavated the pipe and formed the akb

formation of tuffisitic kimberlites by phreatomagmatic processes the rock type tuffisitic kimberlite tk occurs in the deeper diatremes of some southern african canadian and siberian kimberlite pipes and has been considered a unique rock type related to a particular emplacement process the key features of this rock type are its fragmental nature its massive well mixed appearance and a specific matrix mineralogy characterized by the presence of serpentine and microlitic clinopyroxene and the absence or scarcity of carbonate historically all these features were thought to be related to a highly specific intrusive extrusive magmatic emplacement process in this process the expansion of magmatic volatiles drives the fluidization of a pre existing shallow crustal vertical magma reservoir the embryonic pipe and its consequent evolution into the final diatreme after breakthrough to the surface the specific matrix mineralization is explained by the dissociation of carbonate into co2 and cao while the expanding co2 drives the fluidization process cao reacts with sio2 released from xenolith and olivine alteration to form microlitic clinopyroxene with the phreatomagmatic process chain we offer an alternative model that can readily explain this specific rock type ongoing explosions in a downward penetrating root zone excavate a pipe consisting of a rather regular cone shaped diatreme underlain by the irregular root zone at this stage the pipe in its majority is infilled by warm to hot pyroclastic tephra during thermohydraulic explosions in the root zone the expansion of water vapor homogenizes the overlying diatreme tephra and mixes it with the adjacent country rock lithologies this result in the massive well mixed volcaniclastic rock type typical for tkbs post emplacement hydrothermal alteration and mineralization under epi to mesothermal conditions are considered responsible for the observed specific matrix mineralogy carbonate is frequently present in coherent root zone rocks but is rare or absent due to its dissolution in hot hydrothermal fluids ascending from the lower diatreme which in turn precipitate their dissolved carbonate higher up in the cooler bedded upper diatreme region clinopyroxene also grows under epi to mesothermal conditions for the crystallization of serpentine a x h2o x co2 ratio of 20 1 is required which suggests both a high availability of groundwater and a low abundance of co2 after and likely during emplacement isotope studies h c o sr of matrix minerals suggest participation of groundwater in the formation of these minerals

thermohydraulic explosions in phreatomagmatic eruptions as evidenced by the comparison between pyroclasts and products from molten fuel coolant interaction experiments 1 thermohydraulic explosions were produced by molten fuel coolant interaction mfci experiments using remelted shoshonitic rocks from vulcano italy the fragmentation history and energy release were recorded the resulting products were recovered and analyzed with the scanning electron microscope fine particles from experiments show shape and surface features that result from melt fragmentation in brittle mode these clasts relate to the thermohydraulic phase of the mfci where most of the mechanical energy is released they are here called active particles the total surface area of such particles is proportional to the energy of the respective explosions other particles from experiments show shape and surface features that result from melt fragmentation in a ductile regime these fragments called passive particles form after the thermohydraulic phase during the expansion phase of the mfci in order to verify thermohydraulic explosions in volcanic eruptions we compared experimental products with samples from phreatomagmatic base surge deposits of vulcano ash particles from the experiments show features similar to those from the deposits suggesting that the experiments reproduced the same fragmentation dynamics to achieve discrimination between active and passive particles we calculated shape parameters from image analysis the mass of active particles in base surge deposits was calculated as the material properties for the natural samples are identical to the experimental ones the energy measurements and calculations of the experiments can be applied for a single phreatomagmatic eruption at vulcano a maximum mechanical energy release of 2 75 1013 j was calculated representing a tnt analogue of 6 5 kt

kinematic constraints on glacier contributions to 21st century sea level rise on the basis of climate modeling and analogies with past conditions the potential for multimeter increases in sea level by the end of the 21st century has been proposed we consider glaciological conditions required for large sea level rise to occur by 2100 and conclude that increases in excess of 2 meters are physically untenable we find that a total sea level rise of about 2 meters by 2100 could occur under physically possible glaciological conditions but only if all variables are quickly accelerated to extremely high limits more plausible but still accelerated conditions lead to total sea level rise by 2100 of about 0 8 meter these roughly constrained scenarios provide a most likely starting point for refinements in sea level forecasts that include ice flow dynamics

serpentinization and heat generation constraints from lost city and rainbow hydrothermal systems abstract the discovery of ultramafic hosted hydrothermal systems at rainbow 36 n mar and lost city a vent site approximately 15 km west of the mar at 30 n provides unique perspectives on chemical and heat generating processes associated with serpentinization at a range of chemical and physical conditions heat balance calculations together with constraints imposed by geochemical modeling indicate that significant changes in temperature are not likely to occur at either vent system as a result of the exothermic nature of olivine hydrolysis at rainbow the relatively high temperatures in subseafloor reaction zones in excess of 400 c which must be linked to magmatic processes inhibit olivine hydrolysis effectively precluding mineralization induced heating effects geochemical modeling of the lost city vent fluids indicates temperatures in excess of those measured 40 75 c the relatively high subseafloor temperatures 200 50 c requires conductive cooling of the fluids on ascent to the seafloor a scenario in keeping with the mineralization of chimney structures actually observed although the intermediate temperatures predicted for subseafloor reaction zones at lost city could be expected to enhance olivine to serpentine conversion dissolved cl k cl and na cl ratios of the lost city vent fluids are virtually unchanged from seawater values and indicate little hydration of olivine which is a necessary condition for exothermic heat generation by serpentinization apparently the fluid rock mass ratio is too high or fluid residence times too low for this to occur to any significant extent thus in spite of the off axis location of the lost city vents and apparent lack of a localized heat source mineralization reactions likely play an insignificant role in accounting for hydrothermal circulation it is more likely that tectonic processes associated with the slow spreading mar permit access of seawater to relatively deep and still hot lithospheric units and or near axis magmatic heat sources before venting additional chemical and physical temperature flow rate data for lost city and similar hydrothermal systems are needed to test key elements of the proposed model

on the first experimental phreatomagmatic explosion of a kimberlite melt abstract detailed field investigations of kimberlite pipes of the upper cretaceous gibeon kimberlite field in southern namibia revealed geologic features which do neither agree with extensive nor with explosive vesiculation in the pipe hanaus 2 vesicle free magmatic kimberlite intruded the diatreme as a plug here we report on the first experiments in which phreatomagmatic explosions were produced with remolten natural non fragmental magmatic kimberlite from the hanaus 2 central plug as a best fit model kimberlite magma system after water was injected into the melt under controlled conditions the resulting water melt mix was triggered by a low energy shock wave 400 m s

shallow shelf approximation as a sliding law in a thermomechanically coupled ice sheet model 1 the shallow shelf approximation a balance of membrane stresses for ice flow is an effective sliding law for ice sheet modeling our use of it as a sliding law becomes a standard model for ice stream flow when the sliding velocity is large 100 m a 1 and faster following schoof 2006a we describe the basal resistance as plastic till for which the yield stress is given by a mohr coulomb formula pore water pressure is related to basal melt rate the velocity field used in the mass continuity and conservation of energy equations is an average of velocities from the shallow shelf approximation and the nonsliding shallow ice approximation using this scheme our model has realistic time dependent ice streams which exhibit the range of surface velocities seen in actual ice streams we demonstrate the model at high spatial resolution 5 km grid over multiple millenia using its implementation in the parallel ice sheet model numerical experiments show that the entire scheme is stable with respect to many parameter changes some experiments reveal significant ice stream variability in a hypothetical steady climate with characteristic cycles on the order of 1000 years we believe this is the first practical whole ice sheet model with a unified treatment of vertical shear stresses and membrane stresses it is capable of high resolution thermomechanically coupled multimillenia simulations of ice sheets containing ice streams

deep bedded ultramafic diatremes in the missouri river breaks volcanic field montana usa 1 km of syn eruptive subsidence the ultramafic eocene missouri river breaks volcanic field mrbvf montana usa includes over 50 diatremes emplaced in a mostly soft substrate the current erosion level is 1 3 1 5 km below the pre eruptive surface exposing the deep part of the diatreme structures and some dikes five representative diatremes are described here they are 200 375 m across and have sub vertical walls their infill consists mostly of 55 90 bedded pyroclastic rocks fine tuffs to coarse lapilli tuffs with concave upward bedding and 45 10 non bedded pyroclastic rocks medium lapilli tuffs to tuff breccias the latter zones form steep columns 15 135 m in horizontal dimension which cross cut the bedded pyroclastic rocks megablocks of the host sedimentary formations are also present in the diatremes some being found 1 km or more below their sources the diatreme infill contains abundant lithic clasts and ash sized particles indicating efficient fragmentation of magma and country rocks the spherical to sub spherical juvenile clasts are non vesicular they are accompanied by minor accretionary lapilli and armored lapilli the deposits of dilute pyroclastic density currents are locally observed our main interpretations are as follows 1 the observations strongly support phreatomagmatic explosions as the energy source for fragmentation and diatreme excavation 2 the bedded pyroclastic rocks were deposited on the crater floor and subsided by 1 0 1 3 km to their current location with subsidence taking place mostly during the eruption 3 the observed non bedded pyroclastic columns were created by debris jets that punched through the bedded pyroclastic material the debris jets did not empty the mature diatreme occupying only a fraction of its width and some debris jets probably did not reach the crater floor 4 the mature diatreme was nearly always filled and buttressed by pyroclastic debris at depth there was never a 1 3 1 5 km deep empty hole with sub vertical walls otherwise the soft substrate would have collapsed inward which it only did near the surface to create the megablocks we infer that syn eruptive subsidence shifted down bedded pyroclastic material and shallow sedimentary megablocks by 0 8 1 1 km or more after which limited post eruptive subsidence occurred this makes the mrbvf diatremes an extreme end member case of syn eruptive subsidence in the spectrum of possibilities for maar diatreme volcanoes worldwide

composition and emplacement of the benfontein kimberlite sill complex kimberley south africa textural petrographic and melt inclusion constraints abstract the benfontein kimberlite is a renowned example of a sill complex and provides an excellent opportunity to examine the emplacement and evolution of intrusive kimberlite magmas we have undertaken a detailed petrographic and melt inclusion study of the benfontein upper middle and lower sills these sills range in thickness from 0 25 to 5 m new perovskite and baddeleyite u pb dating produced ages of 85 7 4 4 ma and 86 5 2 6 ma respectively which are consistent with previous age determinations and indicate emplacement coeval with other kimberlites of the kimberley cluster the benfontein sills are characterised by large variations in texture e g layering and mineral modal abundance between different sill levels and within individual samples the lower sill is characterised by carbonate rich diapirs which intrude into oxide rich layers from underlying carbonate rich levels the general paucity of xenogenic mantle material in the benfontein sills is attributed to its separation from the host magma during flow differentiation during lateral spreading the low viscosity is likely responsible for non explosive emplacement of the benfontein sills while the rhythmic layering is attributed to multiple magma injections the benfontein sills are marked by the excellent preservation of olivine and groundmass mineralogy which is composed of monticellite spinel perovskite baddeleyite ilmenite apatite calcite dolomite along with secondary serpentine and glagolevite namg6 si3alo10 oh o 8 h2o this is the first time glagolevite is reported in kimberlites groundmass spinel exhibits atoll textures and is composed of a magnesian ulvospinel magnetite mum or chromite core surrounded by occasional pleonaste and a rim of mg al magnetite we suggest that pleonaste crystallised as a magmatic phase but was resorbed back into the residual host melt and or removed by alteration analyses of secondary inclusions in olivine and primary inclusions in monticellite spinel perovskite apatite and interstitial calcite are largely composed of ca mg carbonates and to a lesser extent alkali carbonates and other phases these inclusions probably represent the entrapment of variably differentiated parental kimberlite melts which became progressively more enriched in carbonate alkalis halogens and sulphur during crystal fractionation carbonate rich diapirs from the lower sill contain more exotic phase assemblages e g ba fe titanate barite ancylite pyrochlore which probably result from the extreme differentiation of residual kimberlite melts followed by physical separation and isolation from the parental carbonate rich magma it is likely that any alkali or halogen rich minerals crystallising in the groundmass were removed from the groundmass during syn post magmatic alteration or in the case of na remobilised to form secondary glagolevite the benfontein sill complex therefore provides a unique example of how the composition of kimberlites may be modified after magma emplacement in the upper crust

geology of the gahcho kue kimberlite pipes nwt canada root to diatreme magmatic transition zones abstract the cambrian gahcho kue kimberlite cluster includes four main pipes that have been emplaced into the archaean basement granitoids of the slave craton each of the steep sided pipes were formed by the intrusion of several distinct phases of kimberlite in which the textures vary from hypabyssal kimberlite hk to diatreme facies tuffisitic kimberlite breccia tkb the tkb displays many diagnostic features including abundant unaltered country rock xenoliths pelletal lapilli serpentinised olivines and a matrix composed of microlitic phlogopite and serpentine without carbonate the hk contains common fresh olivine set in a groundmass composed of monticellite phlogopite perovskite serpentine and carbonate a number of separate phases of kimberlite display a magmatic textural gradation from tkb to hk which is characterised by a decrease in the proportion of pelletal lapilli and country rock xenoliths and an increase in groundmass crystallinity proportion of fresh olivine and the degree of xenolith digestion the pipe shapes and infills of the gahcho kue kimberlites are similar to those of the classic south african pipes particularly those of the kimberley area similar intrusive magmatic emplacement processes are proposed in which the diatreme zone results from the degassing after breakthrough of the intruding magma column the transition zones represent frozen degassing fronts the style of emplacement of the gahcho kue kimberlites is very different from that of many other pipes in canada such as at lac de gras fort a la corne or attawapiskat

contrasting eruption styles of the 147 kimberlite fort a la corne saskatchewan canada abstract the cretaceous fort a la corne falc kimberlite field was active over a time span of 20 ma with contemporaneous terrestrial mannville group to marine lower colorado group background sedimentation steep sided pipes craters and positive landform volcanoes such as scoria or tuff cones are thought to have formed during that period the 147 kimberlite is located in the se section of the field s main cluster and is part of the large 377 5 ha orion north volcanic complex based on logging of 25 drill cores the morphology of the country rock kimberlite interface suggests excavation of a complex crater field down to the upper portion of the mannville group sedimentary deposits at least two types of volcaniclastic deposits are identified a main kimberlite unit that is typically characterized by crustal xenolith poor 1 2 normal graded beds possibly deposited as turbidites in a subaqueous environment originating from the nearby 148 tephra cone and infilling the adjacent 147 crater and a second unit located on the ne margin of the 147 kimberlite that represents a thick 60 m sequence of large up to 22 m sedimentary country rock blocks located at least 60 m above their original stratigraphic position we suggest the following time sequence of events crater excavation as a consequence of a shallow magma fragmentation level within the uppermost country rock sequences together with several closely spaced eruptive centres initially formed the complex intercalated crater field subsequently ongoing eruptions with a fragmentation level above the country rock produced the lithic fragment poor main infill of the 148 kimberlite resedimentation from the outer flanks of the 148 tephra cone resulted in the deposition of turbidites in the 147 area a consolidation phase solidified the lowermost portion of the main infill in 147 a subsequent explosion s occurred within the mannville group in the 147 area ejecting large blocks of sedimentary country rocks and fracturing the overlying volcaniclastic main infill finally blocks of the main infill tilted and possibly slumped into the subsidence structure developed above the emptied explosion chamber of 147 the different volcanic deposits reflect a change in eruption style and fragmentation level from highly explosive to spatter activity with little fragmentation potential cap rocks to build up the volatile overpressure necessary to blast the craters were not present at the time of emplacement no diatremes were observed in the study area assuming that the magma properties remained constant over time the change in eruption style has to be attributed to external factors such as water access to the rising magma the volcanic behaviour of the kimberlite magma appears to be comparable to that of other magmatic systems both in eruptive style and production rate no evidence was found for a high possibly plinian production rate or dispersion

alteration styles in the orion central volcanic complex fort a la corne kimberlite field saskatchewan and their effects on primary volcaniclastic textures implications for facies mapping and diamond exploration diamond grade distributions within individual kimberlite bodies are controlled by physical emplacement processes which are generally determined from volcaniclastic facies characteristics however the effects and distribution of secondary alteration styles which usually mask primary kimberlite facies have been given little attention at the fort a la corne kimberlite field saskatchewan complex overprinting alteration textures and mineral phases are recognized this study documents the characteristics overprinting relationships and spatial distribution of alteration styles within a crater filling volcaniclastic deposit body 219 of the orion central volcanic complex data were acquired from macroscopic drill core observations microscopic petrography sem imaging eds element mapping and xrd analyses olivine crystals display a mesh fracture pattern and have been replaced by multiple generations of serpentine and magnetite late stage serpentine has migrated into the interstitial medium bulk rock alteration textures include 1 fine grained crystal rich domains which are alteration pseudoclasts and or relict juvenile pyroclasts 2 a heterogeneous interstitial medium varying from early stage disseminated calcite rich serpentine to amorphous serpentine and crystalline calcite and 3 overprinting serpentine carbonate and magnetite veins and serpentine nodules alteration styles defined by unique alteration characteristics are spatially zoned through the body 219 volcaniclastic deposit and this is a result of multiple reaction fronts associated with the influx of fluids of varying composition over time and permeating different parts of the deposit recognition of alteration processes their paragenesis and spatial controls can assist in defining and constraining the distribution of primary kimberlite facies and by consequence the distribution of diamond grades

a new approach to kimberlite facies terminology using a revised general approach to the nomenclature of all volcanic rocks and deposits descriptive to genetic although kimberlite pipes bodies are usually the remains of volcanic vents in vent deposits and subvolcanic intrusions the terminology used for kimberlite rocks has largely developed independently of that used in mainstream volcanology existing kimberlite terminology is not descriptive and includes terms that are rarely used used differently and even not used at all in mainstream volcanology in addition kimberlite bodies are altered to varying degrees making application of genetic terminology difficult because original components and depositional textures are commonly masked by alteration this paper recommends an approach to the terminology for kimberlite rocks that is consistent with usage for other volcanic successions in modern terrains the eruption and emplacement origins of deposits can often be readily deduced but this is often not the case for old variably altered and deformed rock successions a staged approach is required whereby descriptive terminology is developed first followed by application of genetic terminology once all features including the effects of alteration on original texture and depositional features together with contact relationships and setting have been evaluated because many volcanic successions consist of both primary volcanic deposits as well as volcanic sediments terminology must account for both possibilities

committed sea level rise for the next century from greenland ice sheet dynamics during the past decade we use a three dimensional higher order ice flow model and a realistic initial condition to simulate dynamic perturbations to the greenland ice sheet during the last decade and to assess their contribution to sea level by 2100 starting from our initial condition we apply a time series of observationally constrained dynamic perturbations at the marine termini of greenland s three largest outlet glaciers jakobshavn isbrae helheim glacier and kangerdlugssuaq glacier the initial and long term diffusive thinning within each glacier catchment is then integrated spatially and temporally to calculate a minimum sea level contribution of approximately 1 0 4 mm from these three glaciers by 2100 based on scaling arguments we extend our modeling to all of greenland and estimate a minimum dynamic sea level contribution of approximately 6 2 mm by 2100 this estimate of committed sea level rise is a minimum because it ignores mass loss due to future changes in ice sheet dynamics or surface mass balance importantly 75 of this value is from the long term diffusive response of the ice sheet suggesting that the majority of sea level rise from greenland dynamics during the past decade is yet to come assuming similar and recurring forcing in future decades and a self similar ice dynamical response we estimate an upper bound of 45 mm of sea level rise from greenland dynamics by 2100 these estimates are constrained by recent observations of dynamic mass loss in greenland and by realistic model behavior that accounts for both the long term cumulative mass loss and its decay following episodic boundary forcing

an integrated model of kimberlite ascent and eruption diatremes are carrot shaped bodies forming the upper parts of very deep magmatic intrusions of kimberlite rock these unusual enigmatic and complex features are famous as the source of diamonds here we present a new model of kimberlite ascent and eruption emphasizing the extremely unsteady nature of this process to resolve many of the seemingly contradictory characteristics of kimberlites and diatremes dyke initiation in a deep co2 rich source region in the mantle leads to rapid propagation of the dyke tip below which co2 fluid collects with a zone of magmatic foam beneath when the tip breaks the surface of the ground gas release causes a depressurization wave to travel into the magma this wave implodes the dyke walls fragments the magma and creates a ringing fluidization wave together these processes form the diatreme catastrophic magma chilling seals the dyke no precursor to the eruption is felt at the surface and the processes are complete in about an hour

experimental birth of a maar diatreme volcano abstract maar diatreme eruptions are hazardous to people and infrastructure and are also linked to the formation of the kimberlitic variety of diatremes which is important economically processes occurring in the subsurface diatreme and their relation to surface eruptions are not yet well understood we conducted field scale experiments using analog materials to shed more light on these processes especially the formation of the proto diatreme during the first explosions of a maar eruption specifically a series of buried explosions in a prepared layered substrate pad produced craters extra crater deposits and sub crater deposits analogous to volcanic maar craters tephra rings and incipient diatremes post explosion substrate excavation revealed that single large explosions produce sub crater deposits extending nearly to the crater rim crest the same energy divided into three blasts either co located or at different depths with the same epicenter produced narrower and sometimes deeper sub crater deposits even though the final sizes of the craters were similar to that produced by the single large blast the sub crater deposits have an upper zone with domains from different substrate depths and an underlying zone distinguished primarily by being more loosely packed than the original substrate videos show surface motion extending beyond the post shot crater rim and largely vertical ejection and fallback of material into the footprint of these deposits especially for the explosions that occurred below optimal depth of burial we infer that much of the loosely packed material was disassembled vertically transported to different heights during the explosions then fell back without significant relative lateral movement of grains however subvertical fallback did produce apparent cross cutting structures in shallow sub crater deposits one explosion ejected material from the deepest substrate horizon but it was redeposited only within the crater and is unrepresented in the ejecta rim implications of the experiments for maar diatreme volcanoes including some kimberlite pipes are as follows 1 vertical focusing of deep explosions in the diatreme explains the deficit of deep wallrock lithics observed at maar volcanoes 2 direct vertical fallback is possibly an important process forming diatreme deposits especially during the earliest stages and 3 even in our limited simulation the number and scaled depth of explosions clearly affect proto diatreme size and structure

rapid bottom melting widespread near antarctic ice sheet grounding lines as continental ice from antarctica reaches the grounding line and begins to float its underside melts into the ocean results obtained with satellite radar interferometry reveal that bottom melt rates experienced by large outlet glaciers near their grounding lines are far higher than generally assumed the melting rate is positively correlated with thermal forcing increasing by 1 meter per year for each 0 1 c rise in ocean temperature where deep water has direct access to grounding lines glaciers and ice shelves are vulnerable to ongoing increases in ocean temperature

semiempirical and process based global sea level projections we review the two main approaches to estimating sea level rise over the coming century physically plausible models of reduced complexity that exploit statistical relationships between sea level and climate forcing and more complex physics based models of the separate elements of the sea level budget previously estimates of future sea level rise from semiempirical models were considerably larger than those from process based models however we show that the most recent estimates of sea level rise by 2100 using both methods have converged but largely through increased contributions and uncertainties in process based model estimates of ice sheets mass loss hence we focus in this paper on ice sheet flow as this has the largest potential to contribute to sea level rise progress has been made in ice dynamics ice stream flow grounding line migration and integration of ice sheet models with high resolution climate models calving physics remains an important and difficult modeling issue mountain glaciers numbering hundreds of thousands must be modeled by extensive statistical extrapolation from a much smaller calibration data set rugged topography creates problems in process based mass balance simulations forced by regional climate models with resolutions 10 100 times larger than the glaciers semiempirical models balance increasing numbers of parameters with the choice of noise model for the observations to avoid overfitting the highly autocorrelated sea level data all models face difficulty in separating out non climate driven sea level rise e g groundwater extraction and long term disequilibria in the present day cryosphere sea level system

root zone processes in the phreatomagmatic pipe emplacement model and consequences for the evolution of maar diatreme volcanoes abstract the understanding of processes within the root zone of maar diatreme volcanoes is important for the interpretation of the geology volcanology and even hazard assessment of these volcanoes in the phreatomagmatic model of pipe formation the irregularly shaped root zone is the site of the phreatomagmatic explosions and thus functions as the engine for pipe formation in this model the root zone grows over a period of time in a series of many single thermohydraulic i e phreatomagmatic explosions the explosions initially occur close to the surface and with ongoing explosive activity penetrate towards deeper levels the ejection of country rock clasts from the root zone results in a mass deficiency in the root zone that causes the overlying tephra and the adjacent country rocks to subside passively in a sinkhole like fashion into the root zone many phreatomagmatic eruptions consequently result in the formation of a cone shaped diatreme thus with ongoing eruptions the cone shaped diatreme has to grow systematically both in depth and diameter during its growth processes in the lower diatreme levels successively destroy the upper levels of the evolving root zone at the surface the maar crater in turn reacts to the underlying subsidence processes and also grows both in depth and diameter thermohydraulic explosions which fragment both magma and the surrounding country rocks mostly occur within the bottom part of the root zone violent explosions in small pipes may clear the overlying diatreme for a short period of time before tephra fall and collapse of the walls of the new crater refill the small initial diatreme in larger pipes via expansion of the mixture of highly pressurized water vapor juvenile gas phases and explosively produced tephra the confined and expanding eruption cloud has to pierce through the diatreme fill in a feeder conduit in order to erupt diatreme clearing events in large pipes are difficult or impossible to maintain since the explosive force in the root zone is only in exceptional instances strong enough to lift or entrain the entire diatreme tephra knowledge of the genetic relationships between root zones and diatremes is critical to understand pipe growth processes the combination of such processes can lead to substantial variation in volcanic behavior and thus produce fundamentally different volcano and rock types it is the purpose of this paper to outline important features of root zones and suggest their significance for the genesis and evolution of maar diatreme and related volcanoes

the importance of the transport system in shaping the growth and form of kimberlite volcanoes transport of kimberlite magma from the mantle to the surface is a complex process that involves many often sudden and dramatic changes in transport style the pace and magnitude of changes in the transport system acclerate as the magma nears the surface culminating in eruptions during which multiple transport events take place simultaneously as well as single transport events that change significantly from their point of origin to final deposition understanding the range of transport styles recorded by kimberlite deposits is key to describing the type and style of eruptions the growth of cones and craters and the distribution geometry and structure of the deposits that make up kimberlite volcanoes in an economic context building a clear picture of the processes that shape deposits is essential for selecting exploration targets and evaluating the grade and value of diamond bearing kimberlites variations in diamond grade reflect differences in the diamond content of different magma parcels erupted during the lifetime of the kimberlite volcano sorting during transport of eruption products or re working of diamonds during crater growth cone collapse and erosion deep transport systems control delivery of magma and diamonds to eruption sites the initial stages of kimberlite transport involve rise of magma in narrow interconnected networks of fluidfilled fractures there is compelling evidence that kimberlite magmas are extracted from their source region and erupted without significant residence times in the crust many single kimberlite volcanoes have significant variations in diamond grade between different kimberlite phases suggesting eruption of distinct perhaps unrelated magma parcels at the same site

antarctic ice sheet melting provides negative feedbacks on future climate warming we show by using a three dimensional climate model which includes a comprehensive representation of polar ice sheets that on centennial to millennial time scales antarctic ice sheet ais can melt and moderate warming in the southern hemisphere by up to 10 degrees c regionally in a 4 x co2 scenario this behaviour stems from the formation of a cold halocline in the southern ocean which limits sea ice cover retreat under global warming and increases surface albedo reducing local surface warming furthermore we show that ais melting by decreasing antarctic bottom water formation restrains the weakening of the atlantic meridional overturning circulation which is a new illustration of the effect of the bi polar oceanic seesaw consequently it appears that ais melting strongly interacts with climate and ocean circulation globally it is therefore necessary to account for this coupling in future climate and sea level rise scenarios

maar diatreme volcanoes a review maar diatreme volcanoes are produced by explosive eruptions that cut deeply into the country rock a maar is the crater cut into the ground and surrounded by an ejecta ring while the diatreme structure continues downward and encloses diatreme and root zone deposits here we attempt an evenhanded review of maar diatreme volcanology that extends from mafic to kimberlitic varieties and from historical maar eruptions to deeply eroded or mined diatreme structures we conclude that maar diatreme eruptions are episodic ejecta rings provide invaluable insight into eruption processes and sequence but are incomplete records of diatreme formation deposits within the diatreme structure include in varying proportions lower unbedded deposits sometimes typified by subvertical contacts among domains of debris emplaced sequentially and upper bedded deposits formed by sedimentation on surfaces open to the atmosphere a basal root zone comprises the transition from coherent magmatic feeder dike to clastic deposits formed by fragmentation of magma and enclosing country rock root zones are irregular in form and the clastic deposits are typically intruded by contorted dikes irregular root zone like chaotic breccias cut by contorted dikes are also present within diatreme deposits where they represent intra diatreme fragmentation zones and record changes in the location of the explosion locus during eruption

syn and posteruptive hazards of maar diatreme volcanoes abstract maar diatreme volcanoes represent the second most common volcano type on continents and islands this study presents a first review of syn and posteruptive volcanic and related hazards and intends to stimulate future research in this field maar diatreme volcanoes are phreatomagmatic monogenetic volcanoes they may erupt explosively for days to 15 years above the preeruptive surface a relatively flat tephra ring forms below the preeruptive surface the maar crater is incised because of formation and downward penetration of a cone shaped diatreme and its root zone during activity both the maar crater and the diatreme grow in depth and diameter inside the diatreme which may penetrate downwards for up to 2 5 km fragmented country rocks and juvenile pyroclasts accumulate in primary pyroclastic deposits but to a large extent also as reworked deposits ejection of large volumes of country rocks results in a mass deficiency in the root zone of the diatreme and causes the diatreme fill to subside thus the diatreme represents a kind of growing sinkhole due to the subsidence of the diatreme underneath the maar crater is a subsidence crater and also grows in depth and diameter with ongoing activity as long as phreatomagmatic eruptions continue the tephra ring grows in thickness and outer slope angle syneruptive hazards of maar diatreme volcanoes are earthquakes eruption clouds tephra fall base surges ballistic blocks and bombs lahars volcanic gases cutting of the growing maar crater into the preeruptive ground formation of a tephra ring fragmentation of country rocks thus destruction of area and ground changes in groundwater table and potential renewal of eruptions the main hazards mostly affect an area 3 to possibly 5 km in radius distal effects are comparable to those of small eruption clouds from polygenetic volcanoes syneruptive effects on infrastructure people animals vegetation agricultural land and drainage are pointed out posteruptive hazards concern erosion and formation of lahars inside the crater a lake usually forms and diverse types of sediments accumulate in the crater volcanic gases may be released in the crater compaction and other diagenetic processes within the diatreme fill result in its subsidence this posteruptive subsidence of the diatreme fill and thus crater floor is relatively large initially but will decrease with time it may last millions of years various studies and monitoring are suggested for syn and posteruptive activities of maar diatreme volcanoes erupting in the future the recently formed maar diatreme volcanoes should be investigated repeatedly to understand more about their syneruptive behaviour and hazards and also their posteruptive topographic limnic and biologic evolution and potential posteruptive hazards for future maar diatreme eruptions a hazard map with four principal hazard zones is suggested with the two innermost ones having a joint radius of up to 5 km areas that are potentially endangered by maar diatreme eruptions in the future are pointed out

thermal maturity evaluation of dispersed organic matter inclusions from kimberlite pipes lac de gras northwest territories canada abstract dispersed organic matter dom inclusions have been recovered from crater diatreme and diatreme xenoliths within hypabyssal facies of diamondiferous kimberlite pipes in the lac de gras region of northwest territories canada incident white and fluorescent light microscopy has been used to study vitrinite and liptinite dom xenoliths in the pipes percent reflectance in oil ro of wood derived vitrinite visible light region fluorescence properties of sporinite cutinite and resinite and changes in maceral morphology have been used to evaluate thermal alteration within the kimberlite pipes temperature estimates for different thermal zones in the kimberlite pipes have been inferred by comparing vitrinite reflectance with data from rapid pyrolysis experiments conducted on low rank vitrinites crater facies dom consists of very low reflecting 20 to 200 c to a maximum of 650 c the presence of petroleum derived cokes are consistent with estimates of 400 450 c for samples recovered close to and within hypabyssal dykes and macrocrystic breccia and massive hypabyssal facies below this zone tuffisitic kimberlites are marked by a reduction in vitrinite reflectance 0 5 to 1 8 ro and a lower inferred alteration temperature estimated at 200 to 450 c anomalous populations of very low reflecting partially devolatilized vitrinite 0 50 to 0 84 ro in this zone may have suppressed reflectance possibly a consequence of liquefaction like conditions and impregnation by oily bitumens produced during pyrolysis of associated liptinite macerals

internal vs external forcing in shallow marine diatreme formation a case study from the iblean mountains se sicily central mediterranean a model of diatreme evolution in a shallow marine setting is based on a multi disciplinary analysis of diatremes in the iblean mountains sicily the approach includes stratigraphic volcanological structural petrologic and compositional data we invoke a complex interplay of internal rapid ascent and pyroclastic fragmentation of a volatile co2 rich nephelinitic magma at depth and external factors these comprise hydroclastic explosions due to near surface interaction of the rising particle volatile mixture with seawater and water saturated lime mud other external factors contributing to diatreme formation include regional and local tectonics graben formation in pull apart motion combined with lateral pipe enlargement by bedrock spalling and radial block subsidence into the diatreme pipe we suggest that fragmentation of volatile rich magma due to internal eruption forcing was fundamental in the formation of the iblean shallow marine diatremes internal and external factors may act to a variable degree however during diatreme evolution in general

linear response functions to project contributions to future sea level we propose linear response functions to separately estimate the sea level contributions of thermal expansion and solid ice discharge from greenland and antarctica the response function formalism introduces a time dependence which allows for future rates of sea level rise to be influenced by past climate variations we find that this time dependence is of the same functional type r t t for each of the three subsystems considered here the validity of the approach is assessed by comparing the sea level estimates obtained via the response functions to projections from comprehensive models the pure vertical diffusion case in one dimension corresponding to 0 5 is a valid approximation for thermal expansion within the ocean up to the middle of the twenty first century for all representative concentration pathways the approximation is significantly improved for 0 7 for the solid ice discharge from greenland we find an optimal value of 0 7 different from earlier studies we conclude that solid ice discharge from greenland due to dynamic thinning is bounded by 0 42 m sea level equivalent ice discharge induced by surface warming on antarctica is best captured by a positive value of 0 1 which reflects the fact that ice loss increases with the cumulative amount of heat available for softening the ice in our model

new reconstruction of antarctic near surface temperatures multidecadal trends and reliability of global reanalyses a reconstruction of antarctic monthly mean near surface temperatures spanning 1958 2012 is presented itsprimarygoalistotakeadvantageofarecentlyrevisedkeytemperaturerecordfromwestantarctica byrd to shed further light on multidecadal temperature changes in this region the spatial interpolation relies on a kriging technique aided by spatiotemporal temperature covariances derived from three global reanalyses the european centre for medium range weather forecasts ecmwf interim re analysis erainterim modern era retrospective analysis for research and applications merra and climate forecast system reanalysis cfsr for 1958 2012 the reconstruction yields statistically significant annual warming in the antarctic peninsula and virtually all of west antarctica but no significant temperature change in east antarctica importantly the warming is of comparable magnitude both in central west antarctica and in most of the peninsula rather than concentrated either in one or the other region as previousreconstructions have suggested the transantarctic mountains act for the temperature trends as a clear dividing line between east and west antarctica reflecting the topographic constraint on warm air advection from the amundsen sea basin the reconstruction also serves to highlight spurious changes in the 1979 2009 time series of the three reanalyses that reduces the reliability of their trends illustrating a longstanding issue in high southern latitudes the study concludes with an examination of the influence of the southern annular mode sam on antarctic temperature trends the results herein suggest that the trend of the sam toward its positive phase in austral summer and fall since the 1950s has had a statistically significant cooling effect not only in east antarctica as already well documented and but also only in fall in west antarctica

the role of fluidisation in the formation of volcaniclastic kimberlite grain size observations and experimental investigation abstract deep steep sided kimberlite pipes in southern africa are normally partially filled with multiple units of a characteristically massive structureless volcaniclastic rock here termed massive volcaniclastic kimberlite mvk these units can be arranged in a pseudo concentric nested pipes within pipes structure several key observations on typical mvk from the venetia kimberlite pipes south africa indicate that fluidisation may have been an important process during its emplacement these include 1 the thorough mixing together of juvenile components and of lithic components derived from all stratigraphic levels of the country rock and 2 a matrix composed of void filling minerals related to hydrothermal metamorphism mainly diopside and serpentine which indicates that the primary deposit had a high porosity 50 and 3 particle size distributions poor in fine ash 10 cm analogue experiments utilising a sand bed laced with marker horizons were conducted in order to investigate the role of fluidisation in the formation of mvk high pressure gas fed through the bed from a point source resulted in the formation of an upwardly diverging pipe structure of thoroughly mixed fluidised material bounded by undisturbed sand strong upward gas flow along the centre of the pipe is characteristically bubbly and results in internal circulation with downward moving regions at the pipe margins analysis of the experimental results suggests that the gas velocity decreases linearly with height and has a gaussian distribution of vertical velocity in the cross flow direction a decrease in the gas flow rate resulted in the development of nested pipes reminiscent of the pipes within pipes structures in kimberlite pipes the results suggest that fluidisation could be a major control on the structure and sorting of deposits in kimberlite pipes we propose that the fluidisation of particles in a kimberlite pipe occurs during the final stages of the eruption when erupting pyroclasts and incorporated fragmented lithic material can no longer be ejected out of the deep wide conduit this bed is subject to quasi sustained fluidisation by the erupting gas particle flow which imparts on it the distinctive characteristics of a massive well mixed poorly sorted deposit

lithofacies characteristics of diatreme deposits examples from a basaltic volcanic field of sw sardinia italy abstract a deeply eroded diatreme field consisting in several decametric sized vertical mainly clastic volcanic bodies of basaltic composition is described for the first time in the variscan basement of sw sardinia the recognition and description of four different lithofacies in these diatremes allowed discussion of the role of the different processes which control magma eruption and conduit infilling and making general inferences about diatremes the studied diatremes have a cross sectional shape from elliptical to sub triangular and are slightly elongated nearly parallel to the main foliation of the intruded meta sedimentary rocks foliation of host rocks is locally reoriented or folded close to the contact with the diatremes suggesting that magma possibly rose to the surface through fissures oriented nearly parallel to host rock foliation textural features of the volcanic bodies show many analogies with kimberlitic diatremes despite the difference in petrography and composition juvenile lapilli are mainly made by ghosts of mafic phenocrysts olivine and clinopyroxene set in a groundmass formed by plagioclase microlites immersed in a cryptocrystalline chlorite rich matrix the four lithofacies were described mainly based on the shape and physical features of the clasts and textural anisotropy a globular juvenile rich lapilli tuff facies gjlt an angular juvenile rich lapilli tuff facies ajlt a lithic rich lapilli tuff facies lirlt and a coherent lava like facies coh all the clastic lithofacies are generally well sorted and typically lack a fine grained matrix juvenile fragments are lapilli sized and from equant to oblate in axial ratio and from rounded globular to very angular in shape conversely lithic clasts are largely variable in shape and size and are mainly represented by basement derived clasts the absence of bedding the scarcity of the coherent facies and the dominance of clast supported structureless volcaniclastic facies suggest that the outcropping portion of these volcanic bodies represents the lower diatreme zone the presence of diffuse welding and the globular shapes of some juvenile fragments together with their vesicularity suggest that magma fragmentation was mainly driven by magmatic gas exsolution occurring at a deeper level respect to classical basaltic explosive activity textural features facies association and facies architecture of the studied deposits are suggestive of an important affinity with kimberlitic and other ultramafic diatremes

thermal aureoles of igneous intrusions some possible indications of hydrothermal convective cooling the size and shape of metamorphic aureoles is investigated as a possible indicator of hydrothermal convective cooling of epizonal igneous intrusions a simple family of numerical models illustrates the effect of convective cooling on maximum temperatures attained in the country rock surrounding an intrusion boundary layer approximations have also been applied to describe convection of vaporizing groundwater near the contact of an intrusion early in its cooling history maximum temperature isotherms are taken to reflect the width and shape of thermal aureoles defined by preserved mineral assemblages as appears to be reasonable based on several well studied conductively cooled intrusions the thermal aureoles of intrusions for which oxygen and hydrogen isotope data indicate convective groundwater circulation have been examined on the basis of the simple numerical and boundary layer models the shape of the low temperature alteration aureole of the well mapped el salvador porphyry copper deposit suggests co

glaciers dominate eustatic sea level rise in the 21st century ice loss to the sea currently accounts for virtually all of the sea level rise that is not attributable to ocean warming and about 60 of the ice loss is from glaciers and ice caps rather than from the two ice sheets the contribution of these smaller glaciers has accelerated over the past decade in part due to marked thinning and retreat of marine terminating glaciers associated with a dynamic instability that is generally not considered in mass balance and climate modeling this acceleration of glacier melt may cause 0 1 to 0 25 meter of additional sea level rise by 2100