magmatic and hydromagmatic conduit development during the 1975 tolbachik eruption kamchatka with implications for hazards assessment at yucca mountain nv abstract xenoliths in pyroclastic fall deposits from the 1975 tolbachik eruption constrain the timing and development of subsurface conduits associated with basaltic cinder cone eruptions the two largest tolbachik vents contain xenoliths derived from magmatic and hydromagmatic processes which can be correlated with observed styles of eruption activity although many basaltic eruptions progress from early hydromagmatic activity to late magmatic activity transient hydromagmatic events occurred relatively late in the 1975 eruption sequence magmatic fall deposits contain 0 01 0 3 vol xenoliths from 500 m depth into the dry out zone around the conduit disrupting and ejecting 10 5 10 6 m 3 of wall rock through hydromagmatic processes with conduits widening to 8 48 m hydromagmatic falls contain 60 75 vol of highly fragmented xenoliths with juvenile clasts displaying obvious magma water interaction features during the largest hydromagmatic event unusual breccia bombs formed containing a wide range of fresh and pyrometamorphic xenoliths suspended in a quenched basaltic matrix hydromagmatic activity during the 1975 tolbachik eruption occurred below likely fragmentation depths for a basalt containing 2 2 wt magmatic water this activity is more likely related to conduit wall collapse rather than variations in conduit flow pressure in contrast larger volume silicic eruptions may have transient hydromagmatic events in response to conduit flow dynamics above the magma fragmentation depth the 1975 tolbachik volcanoes are reasonably analogous to quaternary basaltic volcanoes in the yucca mountain region and can guide interpretations of their poorly preserved deposits the youngest basaltic volcanoes near yucca mountain have cone deposits characterized by elevated xenolith abundances and distinctive xenolith breccia bombs remarkably similar to 1975 tolbachik deposits extrapolation of 1975 tolbachik data suggests conduits for some yucca mountain basaltic volcanoes may have widened locally on the order of 50 m in response to late stage hydromagmatic events

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

determining the effect of topography on isotherms in the shallow crust using low temperature thermochronometry in tunnels apatite u th he and fission track age determinations of samples from a 20 km long near horizontal tunnel in the hochalm ankogel dome eastern tauem window austria are presented in order to determine the role of paleo topography in perturbing isotherms in the shallow crust apatite fission track ages 26 8 ma show no systematic correlation with distance along the tunnel or elevation two age components in the fission track data indicate cooling through 120 c at approximately 20 ma and 80 c at approximately 6 ma surface and tunnel u th he ages 17 9 ma and 13 5 ma respectively are consistently younger than the equivalent fission track ages u th he ages vary systematically along the tunnel with older ages at the northern and southern tunnel portals and younger ages in the central section geological factors faulting lithology appear to have had little effect on this age distribution the u th he age pattern is inconsistent with rock cooling underneath the present day hochalm ankogel dome topography the age minimum is interpreted to coincide with a paleotopographic maximum in the hochalm ankogel dome and suggests that the 40 60 c isotherms were warped sufficiently to affect apatite u th he ages the tunnel apatite u th he ages match synthetic he ages derived from a two dimensional numerical model of landscape evolution integrating the thermal model results with the data allows the relief development to be constrained and we calculate that the present day hochalm ankogel dome topography was formed at 7 to 10 ma copyright 2007 by the american geophysical union

the variability and predictability of axisymmetric hurricanes in statistical equilibrium abstractthe variability and predictability of axisymmetric hurricanes are determined from a 500 day numerical simulation of a tropical cyclone in statistical equilibrium by design the solution is independent of the initial conditions and environmental variability which isolates the intrinsic axisymmetric hurricane variability variability near the radius of maximum wind is dominated by two patterns one associated primarily with radial shifts of the maximum wind and one primarily with intensity change at the time mean radius of maximum wind these patterns are linked to convective bands that originate more than 100 km from the storm center and propagate inward bands approaching the storm produce eyewall replacement cycles with an increase in storm intensity as the secondary eyewall contracts radially inward a dominant time period of 4 8 days is found for the convective bands which is hypothesized to be determined by the time scale over which subsidence from previous bands suppresses convection a

the effect of vertical shear on tropical cyclone intensity change abstract the effect of vertical shear on tropical cyclone intensity change is usually explained in terms of ventilation where heat and moisture at upper levels are advected away from the low level circulation which inhibits development a simple two layer diagnostic balance model is used to provide an alternate explanation of the effect of shear when the upper layer wind in the vortex environment differs from that in the lower layer the potential vorticity pv pattern associated with the vortex circulation becomes tilted in the vertical the balanced mass field associated with the tilted pv pattern requires an increased midlevel temperature perturbation near the vortex center it is hypothesized that this midlevel warming reduces the convective activity and inhibits the storm development previous studies have shown that diabatic heating near the storm center acts to reduce the vertical tilt of the vortex circulation these studies have also shown that there is an adiabatic process that acts to redu

idealized tropical cyclone responses to the height and depth of environmental vertical wind shear abstractthree sets of idealized cloud resolving simulations are performed to investigate the sensitivity of tropical cyclone tc structure and intensity to the height and depth of environmental vertical wind shear in the first two sets of simulations shear height and depth are varied independently in the third set orthogonal polynomial expansions are used to facilitate a joint sensitivity analysis despite all simulations having the same westerly deep layer 200 850 hpa shear of 10 m s 1 different intensity and structural evolutions are observed suggesting the deep layer shear alone may not be sufficient for understanding or predicting the impact of vertical wind shear on tcs in general vertical wind shear that is shallower and lower in the troposphere is more destructive to model tcs because it tilts the tc vortex farther into the downshear left quadrant the vortices that tilt the most are unable to precess upshear and realign resulting in their failure to intensify shear height appears to

kamafugitic diatremes facies characterisation and genesis examples from the goias alkaline province brazil abstract this paper describes the internal organisation of two diatremes aguas emendadas and neuzinha and one small breccia filled conduit tigre in the central portion of the late cretaceous goias alkaline province gap central brazil and explores the criteria for facies recognition the gap kamafugitic diatremes are emplaced into carboniferous sandstones of the aquidauana formation at the northern margin of the parana basin they are usually elliptical structures not longer than 900 m filled with breccia and partially covered by thin kamafugitic to basanitic lava flows the breccias are dominated by juvenile pyroclasts with subordinate amounts of cognate fragments and xenoliths in addition to variations in ash and lapilli proportions juvenile fragment types may be used to discriminate genetic processes and the corresponding pyroclastic deposits an extensive field textural and compositional dataset was analysed by multivariate statistical techniques combined with field observations this allowed us to define a set of facies for kamafugitic diatremes and more importantly to understand the internal structure of the studied bodies and to cross correlate them seven distinct facies were recognised the fluidised conduit facies fcf represents high energy strongly fluidised but only moderately fragmented systems it occurs in a confined environment and is typical of deeper parts of the conduit before the actual diatreme level is reached by the ascending fluidised magma large amounts of spinning droplets are formed within this region the fluidised conduit diatreme facies fcdf is characteristic of intermediate depths in the conduit where highly fluidised and highly fragmented systems produce large amounts of ash spinning droplets decrease in abundance ordinary juvenile fragments become very common and xenoliths from the country rock in the immediate vicinity of the diatreme are present the fluidised fragmented facies fff and the magmatic fluidised facies mff produce very heterogeneous deposits that dominate the shallower part of the system making up most of the diatreme filling materials the fluidised fragmented facies can be distinguished by much higher degrees of fluidisation fragmentation and system energy it occupies the internal part of the diatreme and is characterised by the common presence of tuff pockets tuff fragments and accretionary and armoured lapilli the magmatic fluidised facies typically occupies the outer portion of the diatreme and can be distinguished from the fluidised fragmented facies by the dominance of lapilli over ash and by the presence of abundant wrapped fragments the magmatic facies mf and the coherent magmatic facies cmf are volumetrically subordinate and represent late stages when less fluidised and less fragmented material or even coherent magma erupts relatively passively in the aftermath of the main explosive stage that generated the diatreme the border facies is defined by the increased abundance of material from the immediate country rock at aguas emendadas and neuzinha this facies is marked by the presence of fragments of peperite like rock formed by the interaction of the fluidised magma with friable sandstone

sedimentologic and stratigraphic constraints on emplacement of the star kimberlite east central saskatchewan abstract diamond bearing kimberlites in the fort a la corne region east central saskatchewan consist primarily of extra crater pyroclastic deposits which are interstratified with lower cretaceous albian and cenomanian marine marginal marine and continental sediments approximately 70 individual kimberlite occurrences have been documented the star kimberlite occurring at the southeastern end of the main fort a la corne trend has been identified as being of economic interest and is characterized by an excellent drill core database integration of multi disciplinary data sets has helped to refine and resolve models for emplacement of the star kimberlite detailed core logging has provided the foundation for sedimentological and volcanological studies and for construction of a regionally consistent stratigraphic and architectural framework for the kimberlite complex micropaleontologic and biostratigraphic analysis of selected sedimentary rocks and u pb perovskite geochronology on kimberlite samples have been integrated to define periods of kimberlite emplacement radiometric age determination and micropaleontologic evidence support the hypothesis that multiple kimberlite eruptive phases occurred at star the oldest kimberlite in the star body erupted during deposition of the predominantly continental strata of the lower mannville group cantuar formation kimberlites within the cantuar formation include terrestrial airfall deposits as well as fluvially transported kimberlitic sandstone and conglomerate successive eruptive events occurred contemporaneous with deposition of the marginal marine upper mannville group pense formation kimberlites within the pense formation consist primarily of terrestrial airfall deposits fine to medium grained cross stratified kimberlitic olivine dominated sandstone in this interval reflects reworking of airfall deposits during a regional marine transgression the location of the source feeder vents of the cantuar and pense kimberlite deposits has not been identified the youngest and volumetrically most significant eruptive events associated with the star kimberlite occur within the predominantly marine lower colorado group joli fou and viking formations kimberlite beds which occur at several horizons within these units consist of subaerial and marine fall deposits the latter commonly exhibiting evidence of wave reworking black shale encased resedimented kimberlite beds likely deposited as subaqueous debris flows and turbidites are particularly common in the lower colorado group during its multi eruptive history the star kimberlite body is interpreted to have evolved from a feeder vent and overlying positive relief tephra ring into a tephra cone initial early joli fou volcanism resulted in formation of a feeder vent 200 m diameter and tephra ring subsequent eruptions dominated by subaerial deposits partly infilled the crater and constructed a tephra cone a late joli fou eruption formed a small 70 m diameter feeder pipe slightly offset to the nw of the early joli fou feeder vent deposits from this event further infilled the crater and were deposited on top of early joli fou kimberlite proximal to the vent and sediments of the joli fou formation distal to the vent the shape of the tephra cone was modified during multiple marine transgression and regression cycles coeval with deposition of the lower colorado group resulting in wave reworked kimberlite sand along the fringes of the cone and kimberlitic event deposits tempestites turbidites debris flows in more distal settings

macrostructures vs microstructures in evaporite detachments an example from the salt range pakistan abstract the salt range pakistan is the surface expression of an evaporite detachment over which the potwar plateau fold thrust belt has moved whilst previous publications regarding this region have focused on the petroleum prospectivity deformation and large scale processes this paper characterises the salt range detachment at the meso 10 cm to 10s of metres and micro scale cm to m and examines correlations to the macro scale 10s of metres to kms two detailed scaled cross sections are analysed alongside structural measurements to characterise the detachment at the meso scale with optical analysis of microstructures that formed during deformation characterising the micro scale both ductile and brittle features observed in cross section indicate composite deformation processes acting simultaneously this contrasts with models of salt detachments behaving homogeneously microstructural analysis indicates processes of grain boundary migration and crystal lattice distortions the microstructurally revealed competition between intra crystalline deformation and recrystallization at shallow depths and low temperatures links passes up scale to mesoscale evaporite mylonites and progressively in the weaker units whereas more brittle processes operate in the stronger lithologies in this near unique outcrop of a the emergent toe of a major salt bearing detachment fault

fragmentation in kimberlite products and intensity of explosive eruption the explosive eruption of kimberlite magma is capable of producing a variety of pyroclast sizes shapes and textures however all pyroclastic deposits of kimberlite comprise two main types of pyroclasts 1 pyroclasts of kimberlite with or without enclosed olivine crystals and 2 olivine crystals which lack coatings of kimberlite here we propose two hypotheses for how kimberlite magmas are modified due to explosive eruption 1 olivine crystals break during kimberlite eruption and 2 kimberlite melt can be efficiently separated from crystals during eruption these ideas are tested against data collected from field study and image analysis of coherent kimberlite and fragmental kimberlite from kimberlite pipes at diavik nt olivines are expected to break because of rapid pressure changes during the explosive eruption disruption of kimberlite magma and pyroclast production is driven by ductile deformation processes rather than by brittle fragmentation the extent to which melt separates from olivine crystals to produce kimberlite free crystals is a direct consequence of the relative proportions of gas melt and crystals lastly the properties of juvenile pyroclasts in deposits of pyroclastic kimberlite are used to index the relative intensity of kimberlite eruptions a fragmentation index is proposed for kimberlite eruption based on a crystal size distributions of olivine and on b ratios of selvage free olivine pyroclasts to pyroclasts of kimberlite with or without olivine crystals

degassing structures in volcaniclastic kimberlite examples from southern african kimberlite pipes kimberlite pipes are commonly filled with a distinctive structureless facies termed volcaniclastic kimberlite previously also termed tuffisitic kimberlite breccia tkb which constitutes a thorough mix of both juvenile material and lithic clasts derived from all stratigraphic levels within this facies at several kimberlite pipes we have identified steeply inclined segregation structures developed on length scales ranging from several centimetres to decimetres the structures are pipe like in 2d and characterised by a concentration of coarse crystals and lithic clasts and depletion of the fine components that characterise the host matrix they are interpreted as degassing structures generated by the passing of fluids through particulate deposits during the earliest or latest stages of fluidisation in this paper we identify three circumstances in which degassing structures are generated in volcaniclastic kimberlite emplacement 1 pyroclastic density current deposits 2 local segregations caused by degassing through pipe fill and 3 fluidisation during channelling of deep sourced gas particle dispersions to our knowledge these structures have not been described in kimberlites before and provide important evidence for the occurrence of gas fluidisation during the waning stages of kimberlite eruptions using examples from southern african kimberlite pipes we describe general aspects of their structure combined with particle size distributions clast fabric studies and petrographic compositions

on the welding of pyroclasts from very low viscosity magmas examples from kimberlite volcanoes abstract lithofacies in kimberlite pipes in southern africa exhibit features consistent with welded pyroclastic rocks these include flared conduit filling geometries abundant lithic clasts lithic clast layers subhorizontal clast fabrics gradational contacts with volcaniclastic rocks and sintered and coalesced globular ash and lapilli and melt coated particles the welding dynamics of kimberlite pyroclasts differ from those of glassy vesiculated pyroclasts in silicic volcanic systems low melt viscosity 0 1 pa s results in the efficient separation of volatiles and melt and the breakup of magma into nonvesicular spherical droplets the glassy state is difficult to form in silica deficient magmas because the crystallization kinetics are fast in low viscosity melts three pyroclastic lithofacies are recognized that primarily relate to the state of the initial melt phase in the pyroclasts on deposition 1 densely welded kimberlite forms where the initial melt phase in pyroclasts remains as pure mel

inertial waves in axisymmetric tropical cyclones abstractthe heat engine model of tropical cyclones describes a thermally direct overturning circulation outflowing air slowly subsides as radiative cooling to space balances adiabatic warming a p

concentric eye walls secondary wind maxima and the evolution of the hurricane vortex abstract research aircraft observations in recent hurricanes support the model of shapiro and willoughby 1982 for the tropical cyclone s response to circularly symmetric convective heat sources convective rings in both nature and the numerical model the tangential wind commonly increases rapidly just inside the radius of maximum wind and decreases inside the eye near the central axis of the vortex thus both secondary outer wind maxima and eyewall wind maxima often contract as they intensify this response is independent of the horizontal spatial scale of the maximum an outer maximum is frequently observed to constrict about a pre existing eye and replace it this chain of events often coincides with a weakening or at least a pause in intensification of the vortex as a whole the concentric eye phenomenon is a common but by no means universal feature of tropical cyclones it is most frequently observed in intense highly symmetric systems

prediction of nino 3 sea surface temperatures using linear inverse modeling abstract linear inverse modeling is used to predict sea surface temperatures ssts in the nino 3 region predictors in three geographical locations are used the tropical pacific ocean the tropical pacific and indian oceans and the global tropical oceans predictions did not depend crucially on any of these three domains and evidence was found to support the assumption that linear dynamics dominates most of the record the prediction model performs better when sst anomalies are rapidly evolving than during warm events when large anomalies persist the rms prediction error at a lead time of 9 months is about half a degree celsius

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

uncertainty propagation in coupled atmosphere wave ocean prediction system a study of hurricane earl 2010 abstractthis study focuses on understanding the evolution of hurricane earl 2010 with respect to random perturbations in the storm s initial strength size and asymmetry in wind distribution we

some major problems with existing models and terminology associated with kimberlite pipes from a volcanological perspective and some suggestions five significant problems hinder advances in understanding of the volcanology of kimberlites 1 kimberlite geology is very model driven 2 a highly genetic terminology drives deposit or facies interpretation 3 the effects of alteration on preserved depositional textures have been grossly underestimated 4 the level of understanding of the physical process significance of preserved textures is limited and 5 some inferred processes and deposits are not based on actual modern volcanological processes these issues need to be addressed in order to advance understanding of kimberlite volcanological pipe forming processes and deposits the traditional steep sided southern african pipe model class i consists of a steep tapering pipe with a deep root zone a middle diatreme zone and an upper crater zone if preserved each zone is thought to be dominated by distinctive facies respectively hypabyssal kimberlite hk descriptively called here massive coherent porphyritic kimberlite tuffisitic kimberlite breccia tkb descriptively here called massive poorly sorted lapilli tuff and crater zone facies which include variably bedded pyroclastic kimberlite and resedimented and reworked volcaniclastic kimberlite rvk porphyritic coherent kimberlite may however also be emplaced at different levels in the pipe as later stage intrusions as well as dykes in the surrounding country rock the relationship between hk and tkb is not always clear sub terranean fluidisation as an emplacement process is a largely unsubstantiated hypothesis modern in vent volcanological processes should initially be considered to explain observed deposits crater zone volcaniclastic deposits can occur within the diatreme zone of some pipes indicating that the pipe was largely empty at the end of the eruption and subsequently began to fill in largely through resedimentation and sourcing of pyroclastic deposits from nearby vents classes ii and iii canadian kimberlite models have a more factual descriptive basis but are still inadequately documented given the recency of their discovery the diversity amongst kimberlite bodies suggests that a three model classification is an over simplification every kimberlite is altered to varying degrees which is an intrinsic consequence of the ultrabasic composition of kimberlite and the in vent context few preserve original textures the effects of syn to post emplacement alteration on original textures have not been adequately considered to date and should be back stripped to identify original textural elements and configurations applying sedimentological textural configurations as a guide to emplacement processes would be useful the traditional terminology has many connotations about spatial position in pipe and of process perhaps the traditional terminology can be retained in the industrial situation as a general lithofacies mining terminological scheme because it is so entrenched however for research purposes a more descriptive lithofacies terminology should be adopted to facilitate detailed understanding of deposit characteristics important variations in these and the process origins for example every deposit of tkb is different in componentry texture or depositional structure however because so many deposits in many different pipes are called tkb there is an implication that they are all similar and that similar processes were involved which is far from clear

vortex rossby waves in a numerically simulated tropical cyclone part ii the role in tropical cyclone structure and intensity changes abstract in part i the author analyzed the asymmetric structure in the inner core of a numerically simulated tropical cyclone and found that the asymmetry near the eyewall in the mid lower troposphere is dominated by wavenumber 1 and 2 vortex rossby waves these waves are found to be well coupled with asymmetries in eyewall convection and thus may play an important role in the life cycle of a tropical cyclone in this paper analyses are extended to include the role of these vortex rossby waves in tropical cyclone structure and intensity changes the waves are found to transport angular momentum from the eyewall to the eye accelerating tangential winds in the eye at the expense of decelerating the tangential wind in the eyewall and thus they play an important role in the inner core dynamics of the tropical cyclone convection in the eyewall is enhanced between the downstream trough and upstream ridge in the vortex rossby waves but suppressed between the downstream ridge and upstream trough this close

geology of a complex kimberlite pipe k2 pipe venetia mine south africa insights into conduit processes during explosive ultrabasic eruptions k2 is a steep sided kimberlite pipe with a complex internal geology geological mapping logging of drillcore and petrographic studies indicate that it comprises layered breccias and pyroclastic rocks of various grain sizes lithic contents and internal structures the pipe comprises two geologically distinct parts k2 west is a layered sequence of juvenile and lithic rich breccias which dip 20 45 inwards and k2 east consists of a steep sided pipe like body filled with massive volcaniclastic kimberlite nested within the k2 pipe the layered sequence in k2 west is present to 900 m below present surface and is interpreted as a sequence of pyroclastic rocks generated by explosive eruptions and mass wasting breccias generated by rock fall and sector collapse of the pipe walls both processes occurred in tandem during the infill of the pipe several breccia lobes extend across the pipe and are truncated by the steep contact with k2 east dense pyroclastic rocks within the layered sequence are interpreted as welded deposits k2 east represents a conduit that was blasted through the layered breccia sequence at a late stage in the eruption this phase may have involved fluidisation of trapped pyroclasts with loss of fine particles and comminution of coarse clasts we conclude that the k2 kimberlite pipe was emplaced in several distinct stages that consisted of an initial explosive enlargement followed by alternating phases of accumulation and ejection

post eruptive development of the ukinrek east maar since its eruption in 1977 a d in the periglacial area of south west alaska maar eruptions form small initially steep walled basins that contain important archives for the climatic and palaeoenvironmental history in continental areas the two ukinrek maars in south western alaska erupted between 30 march and 9 april 1977 and are the best documented maars that have erupted in historical time this study presents a preliminary analysis of geomorphology hydrology magnetic susceptibility geochemistry and sedimentology data of a field study in august 2004 these results photographs and topographic surveys are combined for reconstructing the post eruptive evolution of ukinrek east maar within less than 30 years the initially polygonal shape of the crater with nearly vertical crater walls has developed into an almost elliptic form with slopes of 35 inclination on debris fans between a few escarpments the water table and the crater floor have risen significantly and the crater diameter depth ratio increased from 3 4 to 5 7 whereas the average height of the crater rim remained almost constant the main sub aerial resedimentation process is formation of rock falls rock slumps and scree resulting in debris flows and turbidites within the lake that is ice covered throughout about half of the year distal lake sediments consist of laminated minerogenic clayey sandy silts that document frequent turbidity currents from the linear sedimentation rate of only ca 5 mm year 1 in 17 cm long cores it may be concluded that the largest portion of the crater sediments formed within the first few months of the maar history however this has to be confirmed by future studies

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

eruption of kimberlite magmas physical volcanology geomorphology and age of the youngest kimberlitic volcanoes known on earth the upper pleistocene holocene igwisi hills volcanoes tanzania the igwisi hills volcanoes ihv tanzania are unique and important in preserving extra crater lavas and pyroclastic edifices they provide critical insights into the eruptive behaviour of kimberlite magmas that are not available at other known kimberlite volcanoes cosmogenic 3he dating of olivine crystals from ihv lavas and palaeomagnetic analyses indicates that they are upper pleistocene to holocene in age this makes them the youngest known kimberlite bodies on earth by 30 ma and may indicate a new phase of kimberlite volcanism on the tanzania craton geological mapping global positioning system surveying and field investigations reveal that each volcano comprises partially eroded pyroclastic edifices craters and lavas the volcanoes stand 102 to 106 pa s for kimberlite attributed to degassing and in vent cooling each volcano is inferred to be the result of a small volume short lived days to weeks monogenetic eruption the eruptive processes of each igwisi volcano were broadly similar and developed through three phases 1 fallout of lithic bearing pyroclastic rocks during explosive excavation of craters and conduits 2 fallout of juvenile lapilli from unsteady eruption columns and the construction of pyroclastic edifices around the vent and 3 effusion of degassed viscous magma as lava flows these processes are similar to those observed for other small volume monogenetic eruptions e g of basaltic magma

temporal changes of the primary circulation in tropical cyclones abstract more than 900 radial profiles of in situ aircraft observations collected in 19 atlantic hurricanes and tropical storms over 13 years confirm that the usual mechanism of tropical cyclone intensification involves contracting maxima of the axisymmetric swirling wind radar shows that annuli of convective echoes accompany the wind maxima these features called convective rings exist and move inward because latent heat released in the rings leads to descent adiabatic warming and rapid isobaric height falls in the area they enclose the radial change in rate of isobaric height fall is concentrated at the inner edge of the wind maximum causing the gradient wind to increase there and the maximum to contract vigorous convection organized in rings invariably causes well defined inward moving wind maxima but when convection is weak the rings are also weak or even absent in this case the swirling wind may be nearly constant with radius and change slowly in time hurricanes that have a single vigor