nonexplosive and explosive magma wet sediment interaction during emplacement of eocene intrusions into cretaceous to eocene strata trans pecos igneous province west texas abstract eocene intrusion of alkaline basaltic to trachyandesitic magmas into unlithified upper cretaceous maastrichtian to eocene fluvial strata in part of the trans pecos igneous province in west texas produced an array of features recording both nonexplosive and explosive magma wet sediment interaction intrusive complexes with 40 ar 39 ar dates of 47 46 ma consist of coherent basalt peperite and disrupted sediment two of the complexes cutting cretaceous strata contain masses of conglomerate derived from eocene fluvial deposits that at the onset of intrusive activity would have been 400 500 m above the present level of exposure these intrusive complexes are inferred to be remnants of diatremes that fed maar volcanoes during an early stage of magmatism in this part of the trans pecos province disrupted cretaceous strata along diatreme margins record collapse of conduit walls during and after subsurface phreatomagmatic explosions eocene conglomerate slumped downward from higher levels during vent excavation coherent to pillowed basaltic intrusions emplaced at the close of explosive activity formed peperite within the conglomerate within disrupted cretaceous strata in the conduit walls and within inferred remnants of the phreatomagmatic slurry that filled the vents during explosive volcanism a younger series of intrusions with 40 ar 39 ar dates of 42 ma underwent nonexplosive interaction with upper cretaceous to paleocene mud and sand dikes and sills show fluidal billowed quenched margins against the host strata recording development of surface instabilities between magma and groundwater rich sediment accentuation of billowed margins resulted in propagation of intrusive pillows into the adjacent sediment more intense disruption and mingling of quenched magma with sediment locally produced fluidal and blocky peperite but sufficient volumes of pore fluid were not heated rapidly enough to generate phreatomagmatic explosions this work suggests that trans pecos texas may be an important locale for the study of subvolcanic phreatomagmatic processes and associated phenomena eocene intrusions in the study area underwent complex interactions with wet sediment at shallow levels beneath the surface in strata as old as maastrichtian which must have remained unlithified and rich in pore water for 20 25 ma

debris jets in continental phreatomagmatic volcanoes a field study of their subterranean deposits in the coombs hills vent complex antarctica abstract the ferrar large igneous province of antarctica contains significant mafic volcaniclastic deposits some of which are interpreted to fill large vent complexes such a complex was re examined at coombs hills to map individual steep sided cross cutting bodies in detail and we found several contrasting types two of which are interpreted to have filled subterranean passageways forcefully opened from below into existing non consolidated debris these transient conduits were opened because of the propagation of debris jets upward moving streams of volcaniclastic debris steam magmatic gases liquid water droplets following explosive magma aquifer interaction some debris jets probably remained wholly subterranean whereas others made it to the surface but the studied outcrops do not allow us to differentiate between these cases the pipes filled with country rock rich lapilli tuff or tuff breccia are interpreted to have formed following phreatomagmatic explosions occurring near the walls or floor of the vent complex causing fragmentation of both magma and abundant country rock material in contrast some of the cross cutting zones filled with basalt rich tuff breccia or lapilli tuff could have been generated following explosions taking place within pre existing basalt bearing debris well away from the complex walls or floor we infer that once focused jets were formed they did not incorporate significant amounts of existing debris while travelling through them instead incorporation of fragments from the granular host took place near explosion sites other basalt rich tuff breccia zones accompanied by domains of in situ peperite and coherent basalt pods are inferred to have originated by less violent processes

towards the reconstruction of the shallow plumbing system of the barombi mbo maar cameroon implications for diatreme growth processes of a polygenetic maar volcano abstract understanding the mechanisms involved in the formation of maars and their diatreme growth processes has been a subject of contention while there is no direct evidence of the presence of diatremes beneath most of the young maars their existence is inferred based on the amount and type of country rocks excavated at different depths and deposited as pyroclastic ejecta around their craters properly tracing fragmented country rocks in ejecta to interpret their depths of origin and thus the depths of phreatomagmatic explosions require good and detailed information on the substrate geology that is generally lacking at many maars as an alternative this paper explores the role of juvenile components in deposits of a maar for understanding the cratering and growth of diatremes during maar forming eruptions based on field investigations pyroclast distribution componentry and grain morphology examinations this study reports on the eruptive mechanisms that led to the formation of the barombi mbo maar bmm a polygenetic maar volcano in cameroon the bmm consists of three diatremes that formed during distinct eruptive events and coalesced to produce an amalgamated maar diatreme two end member types of eruption styles from the dry magmatic to the wet phreatomagmatic explosions governed the formation of the maar in total a minimum of 0 0658 km 3 of magma dense rock equivalent corrected was ejected based on calculation by applying interpolation techniques on digital elevation models obtained from srtm30m data corrected by rock textural data collected from the field the distribution of juvenile clasts throughout the stratigraphic sequence suggests a complex subsurface eruptive process which originated probably within the uppermost part of the diatreme from the distribution and morphology of juvenile clasts in the deposits it is inferred that cratering and country rock excavation during the growth of each of the small diatremes developed mainly from shallow level explosions sometimes with lateral and vertical variations in the position of the explosion loci a prospective juvenile based conceptual model is proposed for the formation of the bmm the model suggests that during maar forming eruptions explosions taking place at a deeper position might entrain extensive amount of lithics from the mostly lithic dominated upper crater infill to deposit juvenile poor 90 vol

unbedded diatreme deposits reveal maar diatreme forming eruptive processes standing rocks west hopi buttes navajo nation usa diatremes provide partial records of how dyke delivered magma periodically interacting with water produces the largest known cylindrical conduit structures of any volcano type we address how pre eruptive country rock is disrupted and redistributed to form the diatreme structure during an eruption by establishing the internal architecture of the unbedded diatreme at standing rocks west and the volumes and sources of wall rock within the diatreme and in a complementary tephra ring at teshim both in the hopi buttes volcanic field the unbedded diatreme is dominantly exposed as a massif comprising multiple subvertical columns interpreted as ephemeral conduit deposits of well mixed poorly sorted composite and juvenile pyroclast rich deposits that truncate marginal layered deposits plus a peripheral heterolithic country rock breccia wall rock clasts are scarce in the massif and were mainly sourced from 75 to 245 m depth below the paleosurface by contrast the tephra ring has abundant wall rock fragments dominantly from the upper 75 m of the pre eruptive sedimentary sequence the diatreme structure is interpreted to have been formed by many small volume explosions fed by a low flux of basaltic magma late stage explosive activity was rooted mostly within pyroclastic debris at shallow to intermediate depths within the diatreme structure this resulted in damped and shifting intra diatreme explosions and jets that facilitated gradual mixing recycling and remobilization of debris in the diatreme with incremental addition of juvenile material and possibly a local rise in the crater floor

transport and mixing dynamics from explosions in debris filled volcanic conduits numerical results and implications for maar diatreme volcanoes abstract most volcanoes experience some degree of phreatomagmatism during their lifetime however the current understanding of such processes remains limited relative to their magmatic counterparts maar diatremes are a common volcano type that form primarily from phreatomagmatic explosions and are an ideal candidate to further our knowledge of deposits and processes resulting from explosive magma water interaction due to their abundance as well as their variable levels of field exposure which allows for detailed mapping and componentry two conceptual models of maar diatreme volcanoes explain the growth and evolution of the crater maar and subsurface vent diatreme through repeated explosions caused by the interaction of magma and groundwater one model predicts progressively deepening explosions as water is used up by phreatomagmatic explosions while the other allows for explosions at any level in the diatreme provided adequate hydrologic conditions are present in the former deep seated lithics in the diatreme are directly ejected and their presence in tephra rings is often taken as a proxy for the depth at which that particular explosion occurred in the latter deep seated lithics are incrementally transported toward the surface via upward directed debris jets here we present a novel application of multiphase numerical modeling to assess the controls on length scales of debris jets and their role in upward transport of intra diatreme material to determine the validity of the two models the volume of gas generated during a phreatomagmatic explosion is a first order control on the vertical distance a debris jet travels unless extremely large amounts of magma and water are involved it is unlikely that most explosions deeper than 250 m breach the surface other factors such as pressure and temperature have lesser effects on the length scales assuming they are within realistic ranges redistribution of material within a diatreme is primarily driven by subsidence following debris jet passage natural debris jet deposits often contain wall rock material that originated above the explosion site likely this material was first transported downward by subsidence associated with preceding explosions and debris jets the length scales of debris jets decrease with increasing depth all other factors staying equal the characteristics of the domains formed from just one explosion along with the difficulty of erupting deep seated material indicate that erupted material at maar diatreme volcanoes has a complex history before it is erupted and is mostly sourced from the upper most part of the diatreme

facies distribution of ejecta in analog tephra rings from experiments with single and multiple subsurface explosions the volume grain size and depositional facies of material deposited outside an explosion crater ejecta are sensitive to the depth of the explosion the explosion energy and the presence or absence of a crater before the explosion we detonate buried chemical explosives as an analog for discrete volcanic explosions in experiments to identify unique characteristics of proximal medial and distal ejecta facies and their distribution from a range of scaled depths in undisturbed and cratered ground ejecta are here discussed in terms of three facies 1 proximal ejecta which form a constructional landform around a crater 2 medial ejecta which form a continuous sheet deposit that thins much more gradually with distance and 3 distal ejecta that are deposited as isolated clasts the extent of proximal ejecta away from the crater relative to crater size is not sensitive to scaled depth but the volume proportion of proximal ejecta to the total ejecta deposit is sensitive to the presence of a crater and scaled depth medial ejecta distribution and volume contributions are both sensitive to the presence of a crater and to scaled depth distal ejecta distance is dependent on scaled depth and the presence of a crater while the volume proportion of distal ejecta is less sensitive to scaled depth or presence of a crater experimental facies and deposit structures inferred from observations of jet dynamics are used to suggest facies associations anticipated from eruptions dominated by explosions of different scaled depth configurations we emphasize that significant differences in tephra ring deposits can result from the effects of scaled depth and preexisting craters on ejecta dynamics and are not necessarily related to fundamental differences in explosion mechanisms or degree of magma fragmentation

explosion depths for phreatomagmatic eruptions subsurface phreatomagmatic explosions can result from the interaction of ascending magma with groundwater experiments over a wide range of energies show that for a given energy there is a depth below which an explosion will be contained within the subsurface not erupt and there is a corresponding shallower depth that will optimize ejecta dispersal we combine these relationships with constraints on the energies of phreatomagmatic explosions at maar diatreme volcanoes and show that most eruptions are likely sourced by explosions in the uppermost 200 m and even shallower ones 100 m are likely to dominate deposition onto tephra rings most explosions below 200 m will not erupt but contribute to formation of and to the vertical mixing of materials within a diatreme vent structure with only rare very high energy explosions between 200 and 500 m erupting similar constraints likely apply at other volcanoes that experience phreatomagmatic explosions

topographic controls on a phreatomagmatic maar diatreme eruption field and numerical results from the holocene dotsero volcano colorado usa we analyze the eruptive products of holocene dotsero volcano colorado usa 4 15 ka which record evidence of a progression from effusive magmatic activity through explosive phreatomagmatic maar forming activity to a final explosive magmatic phase the nature of the deposits suggests that the irregular and mountainous pre eruptive topography strongly influenced the formation of directed pyroclastic density currents pdcs during the phreatomagmatic phase where the topographically high northern crater rim acted as a barrier and promoted transport to the south furthermore the crater shape strongly controlled the grain size of the final deposits providing further evidence that deposit grain size can be a misleading proxy for fragmentation or explosion intensity we test these hypotheses as gleaned from fieldwork by implementing a multiphase numerical model to simulate discrete explosions and their resulting pdcs at maar diatreme volcanoes we confirm that a crater shape where one rim is higher than the other promotes multiple pulses of particle transport in the direction of the lower rim the initial pdcs contain both coarse and fine particles whereas pdcs generated by later pulses contain predominately finer particles this mechanism provides an alternative explanation to the formation of lapilli tuff tuff couplets often found at maar diatreme tephra rings including dotsero volcano additional modeling shows how the crater depth can control grain size of the resulting pdc deposits in the case of a deep crater and a relatively weak explosion it is possible that only the fine particles escape following collapse of the eruptive column resulting in a fine grained deposit this work allows us to improve models developed to describe emplacement of pdcs for different crater geometries and informs on the dynamics of maar diatreme eruptions but also highlights the limitations of our knowledge of key parameters especially those related to the processes of magma water interaction and syn eruptive hydrogeology during such events

factors controlling the internal facies architecture of maar diatreme volcanoes most if not all kimberlite pipes show a multitude of facies types which imply that the pipes were emplaced under an episodic re occurrence of eruptive phases often with inter mittent phases of volcanic quiescence the majority of these facies can be related to either the fragmentation behaviour of the magma during emplacement or changing conditions dur ing sedimentation of volcaniclastic deposits as well as their alteration and compaction after deposition an additional factor controlling pipe facies architecture is the degree of mobility of the loci of explosions in the explosion chambers of the root zone or root zones at the base of the maar diatreme volcano in a growing pipe the root zone moves downward and with that movement the overlying diatreme enlarges both in size and diameter however during the life span of the volcano the explosion chamber can also move upward backintothelower diatreme where renewedexplosionsresult inthedestructionofolderdepositsandtheirstructures nextto vertical shifts of explosion chambers the loci of explosions can also move laterally along the feeder dyke or dyke swarm this mobility of explosion chambers results in a highly com plex facies architecture in which a pipe can be composed of several separate root zones that are overlain by an amalgam ated crosscutting diatreme and maar crater with several lobes pipe complexity is amplified by periodic changes of the fragmentation behaviour and explosivity of kimberlite mag ma recent mapping and logging results of canadian and african kimberlite pipes suggest that kimberlite magma frag mentation ranges from highly explosive with abundant entrained country rock fragments to weakly explosive spatter like production with scarce xenoliths on occasions spatter may even reconstitute and form a texturally coherent deposit on the crater floor in addition ascending kimberlite magma can pass the loci of earlier fragmentation events in the root zone and intrudes as coherent hypabyssal kimberlite dykes in high pipe levels or forms extrusive lava lakes or flows on the crater floor or the syneruptive land surface respectively this highly variable emplacement behaviour is typical for basaltic maar diatreme volcanoes and since similar deposits can also be found in kimberlites it can be concluded thatalsothevolcanologicalprocessesleadingtothesedeposits are similar to the ones observed in basaltic pipes

phreatomagmatic vs magmatic eruptive styles in maar diatremes a case study at twin peaks hopi buttes volcanic field navajo nation arizona the hopi buttes volcanic field hbvf is located on the colorado plateau northern arizona in this miocene volcanic field the erosion level increases southward allowing the study of maar diatreme volcanoes from top posteruptive crater infill and ejecta ring to bottom lower diatreme the twin peaks volcanic complex consists mostly of two hills north peak and south peak with thick lavas at their summits and pyroclastic rocks underneath in the hbvf such volcanic remnants have received little scientific attention so far despite their relative abundance our field observations allow us to interpret the north and south peaks as remnants of two maar diatreme volcanoes which evolved into lava lakes filling the craters within the complex we distinguish four volcanic units from unit 1 at the bottom to unit 4 at the top on the basis of the field description of the deposits and the componentry measurements we suggest that unit 1 is phreatomagmatic unit 2 is phreato strombolian with mixed phreatomagmatic and strombolian characteristics unit 3a is phreato hawaiian with mixed phreatomagmatic and hawaiian characteristics unit 3b is hawaiian formed by lava fountains and unit 4 consists of lava lakes filling the maar craters there is therefore a progressive evolution from a purely phreatomagmatic eruptive style which excavated the craters and diatremes and partly filled them to magmatic explosive to nonexplosive eruptive styles which filled the maar craters up to the pre eruptive surface we discuss traditional criteria used to distinguish phreatomagmatic from magmatic eruptive styles in ultramafic to mafic maar diatreme volcanoes

geology and eruptive history of bogoslof volcano bogoslof volcano is a shallow submarine subaerial volcano in the southern bering sea about 100 km west of the community of dutch harbor alaska the subaerial parts of the volcano consist of two small islands bogoslof island and fire island that together have a total area of about 1 6 km2 bogoslof was first depicted on a russian map in 1772 and since then has been observed and visited occasionally the volcano has had at least nine periods of eruptive activity since 1796 and all of its historical eruptions have been similar in style historical bogoslof eruptions involved the effusion of basalt trachybasalt basaltic trachyandesite and trachyandesite lava domes with above sea level relief of 100 200 m many of the eruptions are accompanied by the formation of tuff rings and ejection of ballistic particles historical observations suggest that eruption clouds are relatively ash poor minor ash fallout has typically occurred within about 100 km of the volcano many of the historical eruptions began at vents that were below sea level and thus seawater has played an important role in the style of eruptive activity exhibited by the volcano at times eruptive activity has been characterized by surtseyan style eruptions and magma interaction with wet vent fill deposits at other times the eruptive style has been more magmatically driven and has resulted in the formation of pyroclastic flows and small ash clouds preliminary studies of the deposits produced during the 2016 2017 eruption indicate vertical sequences of coarse grained horizontally bedded pyroclastic flow and fall deposits with numerous blocks bombs and lapilli of dense juvenile and accidental lithic material these deposits were emplaced by near vent pyroclastic flows surges and explosions some of which originated from shallow highly crystalline cryptodomes

subsurface structure of a large basaltic maar volcano examined using geologically constrained potential field modelling lake purrumbete maar newer volcanics province southeastern australia abstract lake purrumbete maar lpm is situated in the late cenozoic intraplate basaltic newer volcanics province southeastern australia it is one of the largest maar volcanoes in the world with a near circular crater that is up to 2800 m in diameter containing a 45 m deep lake gellibrand marl accidental lithics which occurs to a maximum depth of 250 m below lpm represent the deepest excavated host rock unit present in the volcanic succession irregular clast shapes and peperitic textures observed in marl lithics suggest the host rock was poorly consolidated during the eruption high resolution lake and land based gravity and magnetic data were collected to conduct forward and inverse modelling of the subsurface architecture of the maar this is done to test the assumption based on lithics that the diatreme is limited to 250 m depth and identify the reasons behind lpm s large size the collection of gravity data presented a unique challenge due to the nature of measuring small changes in gravitational forces

effects of explosion energy and depth to the formation of blast wave and crater field explosion experiment for the understanding of volcanic explosion we made field explosion experiments as an analogue of volcanic explosion to understand the relationship between the explosion condition and the resultant surface phenomena the main parameters we employed were explosion depth and explosion energy through the experiments we confirmed that scaled depth which is the depth divided by cube root of energy is the main parameter determining the properties of explosive volcanism the energy assigned to blast wave decreased exponentially against the scaled depth the scaled crater diameter became maximum when the scaled depth was about 4 10 3 m j scaled crater diameters by nuclear chemical subsurface and some volcanic explosions were almost the same from the scaling law the overpressure at crater rim was estimated to be several mpa which corresponded to typical rock strength probably the ground forming materials were broken inside the area where overpressure exceeded their strength

insights into the dynamics of mafic magmatic hydromagmatic eruptions from volatile degassing behaviour the hverfjall fires iceland abstract the style and intensity of hydromagmatic activity is governed by a complex interplay between the relative volumes of magma and water that interact their relative viscosities the depth of subsurface explosions the substrate properties and the vent geometry fundamental questions remain however regarding the role of magmatic vesiculation in determining the dynamics of magma water interaction mwi petrological reconstructions of magmatic degassing histories are commonly employed to interpret the pre and syn eruptive conditions during dry magmatic eruptions but the application of similar techniques to hydromagmatic activity has not yet been fully explored in this study we integrate glass volatile measurements s cl h2o and co2 with field observations and microtextural measurements to examine the relationship between degassing and eruptive style during the hverfjall fires fissure eruption iceland here coeval fissure vents produced both dry magmatic jar ba sholar scoria cone complex and variably wet hydromagmatic hverfjall tuff ring activity generating physically distinct pyroclastic deposits with contrasting volatile signatures matrix glass volatile concentrations in hydromagmatic ash 883 172 1 ppm s 0 45 0 03 1 wt h2o 20 ppm co2 are consistently elevated relative to magmatic ash and scoria lapilli 418 93 1 ppm s 0 12 0 48 1 wt h2o co2 below detection and overlap with the range for co erupted phenocryst hosted melt inclusions 1522 127 1 ppm s 165 27 1 ppm cl measurements of hydromagmatic glasses indicate that the magma has degassed between 17 and 70 of its initial sulfur prior to premature quenching at variably elevated confining pressures by comparing volatile saturation pressures for both magmatic and hydromagmatic glasses and how these vary through the eruptive stratigraphy we place constraints on the conditions of mwi crucially our data demonstrate that the magma was already vesiculating when it encountered groundwater at depths of 100 200 m and that the external water supply was sufficient to maintain mwi throughout the eruption with no significant vertical or lateral migration of the fragmentation surface we propose that development of an in vent water sediment slurry provides a mechanism through which the elevated confining pressures of 1 6 2 6 mpa or up to 6 mpa accounting for uncertainty in co2 below analytical detection could be maintained and buffered throughout the eruption whilst enabling vertical mixing and ejection of fragmented juvenile and lithic material from a range of depths importantly these results demonstrate that the volatile contents of hydromagmatic deposits provide valuable records of 1 the environment of mwi e g groundwater versus surface water vertical migration of the fragmentation level and 2 the state of the magma at the time of fragmentation and quenching we further suggest that the volatile content of tephra glasses provides a reliable alternative or additional indicator of a hydromagmatic origin particularly for reduced ocean island basalts where late stage volatile saturation and degassing s h2o occurs over a pressure range relevant to typical mwi environments

evidence for the relative depths and energies of phreatomagmatic explosions recorded in tephra rings experimental work and field observations have inspired the revision of conceptual models of how maar diatreme eruptions progress and the effects of variable energy depth and lateral position of explosions during an eruption sequence this study reevaluates natural tephra ring deposits to test these new models against the depositional record two incised tephra rings in the hopi buttes volcanic field are revisited and published tephra ring stratigraphic studies are compared to identify trends within tephra rings five major facies were recognized and interpreted as the result of different transportation and depositional processes and found to be common at these volcanoes tephra rings often contain evidence of repeated discrete phreatomagmatic explosions in the form of couplets of two facies 1 massive lapilli tuffs and tuff breccias and 2 overlying thinly stratified to cross stratified tuffs and lapilli tuffs the occurrence of repeating layers of either facies and the occurrence of couplets are used to interpret major trends in the relative depth of phreatomagmatic explosions that contribute to these eruptions for deposits related to near optimal scaled depth explosions estimates of the mass of ejected material and initial ejection velocity can be used to approximate the explosion energy the 19 stratigraphic sections compared indicate that near optimal scaled depth explosions are common and that the explosion locations can migrate both upward and downward during an eruption suggesting a complex interplay between water availability and magma flux reverse to normal coarse tail graded tuff breccias inferred to be the product of closely timed phreatomagmatic explosions and deposits of magmatic gas driven explosions were observed interspersed with discrete explosion deposits this study not only provides a framework for more detailed interpretations of eruption sequences from tephra rings but also highlights the gap in our understanding of syn eruptive hydrology and variations in magma flux that enables phreatomagmatic explosions

simulating maar diatreme volcanic systems in bench scale experiments maar diatreme eruptions are incompletely understood and explanations for the processes involved in them have been debated for decades this study extends bench scale analogue experiments previously conducted on maar diatreme systems and attempts to scale the results up to both field scale experimentation and natural volcanic systems to produce a reconstructive toolkit for maar volcanoes these experimental runs produced via multiple mechanisms complex deposits that match many features seen in natural maar diatreme deposits the runs include deeper single blasts series of descending discrete blasts and series of ascending blasts debris jet inception and diatreme formation are indicated by this study to involve multiple types of granular fountains within diatreme deposits produced under varying initial conditions it is not possible to infer the energies of single blasts in multiple blast series from the final deposits the depositional record of blast sequences can be ascertained from the proportion of fallback sedimentation versus maar ejecta rim material the final crater size and the degree of overturning or slumping of accessory strata quantitatively deeper blasts involve a roughly equal partitioning of energy into crater excavation energy versus mass movement of juvenile material whereas shallower blasts expend a much greater proportion of energy in crater excavation supplementary materials five video files 12 figures and three tables are available at http www geolsoc org uk sup18890

the ilopango tierra blanca joven tbj eruption el salvador volcano stratigraphy and physical characterization of the major holocene event of central america abstract the ilopango caldera is the source of the large tierra blanca joven tbj eruption that occurred about 1 5 ka years ago between ca ad270 and ad535 the eruption dispersed volcanic ash over much of the present territory of el salvador and pyroclastic density currents pdcs extended 40 km from the volcano in this study we document the physical characteristics of the deposits from all over el salvador to further constrain the eruption processes and the intensity and magnitude of the different phases of the eruption the succession of deposits generated by the tbj eruption is made of 8 units the eruption started with pdcs of hydromagmatic origin unit a0 followed by fallout deposits units a and b that are

diatreme evolution during the phreatomagmatic eruption of the songaksan tuff ring jeju island korea the songaksan tuff ring jeju island korea which erupted ca 3 7 ka bp in a coastal setting provides an unusual opportunity to study the processes of phreatomagmatic eruption and the formation of a diatreme because of the exceptionally well preserved ejecta beds and well known subsurface geology the tuff sequence can be divided into four units a to d which have distinctly different accidental componentry quartz rich vs quartz poor grain surface features abraded and ash coated vs unabraded and uncoated and chemical compositions of juvenile particles the basal tephra bed of unit a which probably erupted after the removal of the relatively hard shallow level 120 m deep accidental grains suggesting that the early erupted tephra had not yet experienced recycling and pre eruption mixing in the diatreme on the other hand the overlying tephra beds of units a b and d contain an abundance of abraded and ash coated juvenile accidental grains suggesting that the tephra comprised significant proportions of recycled or premixed materials from previous eruptions or subsurface explosions which participated in the explosion driven mixing in the diatreme before eventual ejection from the diatreme unit c is unusual in that it comprises extremely rare accidental grains and ash coated juvenile accidental grains we interpret that the supply of solid materials either accidental or juvenile to the diatreme was greatly reduced because of temporary stabilization of the diatreme and the reduction in magma flux to the diatreme the diatreme is therefore envisaged to have been filled with a water saturated slurry in which particle abrasion and adhesion were inhibited we also infer that the diatreme fill was temporarily removed by a powerful explosion before eruption of unit c on the basis of the near absence of the tephra grains from earlier eruptions throughout the tephra beds of unit c the ratio of tachylite to sideromelane grains generally increases up section of the tuff sequence with two abrupt drops across the tuff unit boundaries these variations are coincident with the changes in the chemical composition of juvenile particles suggesting an overall decrease in magma flux punctuated by brief increases in magma flux associated with the arrival of new magma batches the textural and compositional variations of the songaksan tuff ring suggest that there can be significant variability in diatreme processes even during a purely phreatomagmatic eruption of a tuff ring including removal and renewal of the diatreme fill and that there is still much room for further investigation of the diatreme processes from the ejecta beds in order to make the current diatreme model more robust

revised conceptual model for maar diatremes subsurface processes energetics and eruptive products diatremes are debris filled structures beneath maars that result from many magma water phreatomagmatic explosions during a monogenetic volcano s lifetime a long standing model requires deepening explosions due to water table drawdown that eject progressively deeper seated country rock from the explosion sites while the overlying diatreme and its surface crater widen due to subsidence a revised model is proposed wherein explosions can take place at any level within a diatreme at a given time most effectively venting material from near surface explosions deep seated country rock lithics in tephra deposits record stepwise vertical mixing of material by upward directed debris jets and downward subsidence rather than direct ejection from deep explosions juvenile and lithic clasts erupted during a given explosion may have had a complex history within the diatreme and need not directly reflect fragmentation or brecciation during the explosion that ejects them

reconstructing the eruptive history of a monogenetic volcano through a combination of fieldwork and geophysical surveys the example of puig d adri garrotxa volcanic field puig d adri is a complex volcano in the garrotxa volcanic field 0 7 0 01 ma the youngest part of the catalan volcanic zone ne iberian peninsula the construction of this volcano involved the superimposition of three volcanic edifices with five lithostratigraphic units in which several strombolian and phreatomagmatic episodes alternated geological and geophysical surveys performed using electrical resistivity tomography and self potential have contributed to revealing the internal structure of the volcano and the succession of deposits the ring cone morphology of the phreatomagmatic part of the structure shows how a number of variables including the way in which magma and water interacted greatly influenced the eruptive dynamics and the mechanisms of formation a further major issue reflected in the final structure of the edifice is the process of vent migration which was controlled by the characteristics of the substrate and its interaction with the magma as it rose supplementary material granulometric and component histograms of the samples not shown in figure 4 are available at http doi org 10 6084 m9 figshare c 3262498

deep sea rock record exhumed on oceanic volcanic islands the cretaceous sediments of maio cape verde abstract revising the deep water stratigraphy exposed on maio offers a key section recording the sedimentary evolution in the distal domain of the central atlantic and the related north west african atlantic margin nwaam the oceanic volcanic island is one of nine islands in the cape verde archipelago and is unique to the central atlantic due to the exposures of ophiolites and the overlying mesozoic deep water sediments uplifted during the cenozoic this provides the opportunity to assess at outcrop the exhumed sediments stratigraphy and palaeo environments of the early central atlantic and contribute towards the knowledge of passive margin evolution along the nwaam part of the largest continental remnant of gondwana combined with the previous recording of calpionellids the first collection of lower valanginian ammonites from the lowest sedimentary succession provides conclusive evidence that jurassic sediments are not present on maio bed by bed sampling and ensuing micro palaeontological analysis of these 71 samples together with a re interpretation of stahlecker s remaining historical palaeontological collection providing a comprehensive dataset to build a high resolution stratigraphic framework for the mesozoic sediments this reveals pelagic deep water limestones of the morro fm were deposited until the upper barremian a major lithological change from carbonate to siliciclastic dominated facies corresponding to the morro carquiejo fm boundary is recognised as a regional hiatus spanning part of the aptian identified across the central atlantic the overlying albian and younger carquiejo fm is seen as an equivalent to the albian cenomanian black shales of dsdp leg 41 yet organic content is absent due to degradation future studies can build on this multi disciplinary investigation revising the stratigraphy of maio

the erupted volumes of tephra from maar volcanoes and estimates of their vei magnitude examples from the late cenozoic newer volcanics province south eastern australia abstract calculating the volume of magma involved in an eruption of a maar volcano is often hindered by the uncertainty of the volumes of maar diatremes we calculate the eruptive volumes of several complex monogenetic volcanic centres utilising existing geophysical models to constrain the volumes of subsurface diatremes and conduits and digital elevation models and drill hole data to constrain the volume of the ejecta rims we focus our calculations on several maar volcanoes within the newer volcanics province of south eastern australia including ecklin maar and the red rock and mount leura volcanic complexes based on an average componentry of the ejecta rim we estimate a dense rock equivalent magma volume of 0 04 109 m3 0 17 109 m3 and 0 29 109 m3 for ecklin maar the red rock and mount leura volcanic complexes respectively the red rock and mount leura volcanic complexes have magma volumes that are an order of magnitude higher than ecklin maar and exhibit far more complex eruptive histories with multiple vents and transitions between explosive phreatomagmatic magmatic explosive and effusive styles based on the total tephra volume comparisons of observed eruptions we estimate a vei of 2 for ecklin mount leura and red rock

shallow plumbing systems for small volume basaltic volcanoes 2 evidence from crustal xenoliths at scoria cones and maars abstract monogenetic basaltic volcanoes record complex eruption processes and the relationships between those processes and shallow plumbing are poorly understood this paper explores these relationships building upon earlier studies of exposed shallow plumbing in the upper hundreds of meters of crust beneath volcanoes produced by magmatic eruption processes and those produced by phreatomagmatic processes such as scoria cones and maars respectively eruptive facies and xenolith abundances are described at three scoria cones and at tephra rings around two maars in the san francisco volcanic field arizona usa well constrained subvolcanic sedimentary stratigraphy provides constraints on the depths of origin of xenoliths of different types sedimentary xenolith contents at scoria cones are

arrested diatreme development standing rocks east hopi buttes navajo nation usa abstract maar diatreme volcanoes defined by their relatively large pyroclastic debris filled subsurface structures and craters that cut into the pre eruptive land surface are typically found in small volume mafic to ultramafic monogenetic volcanic fields diatremes are associated with strong explosions throughout most of their development focused along feeder dikes and generally attributed to magma water interaction or high magmatic volatiles detailed mapping of the magnificently exposed standing rocks east sre diatreme shows evidence of additional eruptive complexity and offers new insights into how the plumbing and vent structures of small volume volcanoes evolve during an eruption sre is part of a larger basanitic volcanic complex that includes several diatremes formed along a series of irregular offset nw se trending dikes exposed 300 m below the pre eruptive land surface its similarly oriented elliptical shaped diatreme structure comprises predominantly country rock lithic rich breccia of coarse inhomogeneously mixed wall rock blocks sourced from above and below the current surface plus sparse juvenile material domains of pyroclastic deposits crosscut the country rock breccia deposits and the best exposed is the nw massif rising 35 m above the current erosional surface it represents a cross section of an evolving crater floor and comprises matrix rich lapilli tuff and spatter deposits cut by irregularly distributed dikes some with very complex textures the most significant deposit in terms of volume is an unbedded lapilli tuff that is poorly sorted and has a well mixed population of wall rock and juvenile clast varieties thus resembling deposits typical of diatremes it is overlain by and locally intercalated with spatter deposits and this irregular contact demarcates the base of what was during eruption an uneven evolving crater floor the generally massive variably welded spatter deposits constitute mostly lapilli sized juvenile clasts with fluidal folded over shapes and ropy surfaces subordinate thermally altered wall rock and variegated domains of lapilli tuff sre shows a progressive transition from fissure to diatreme and overall evolution from more explosive to weakly explosive eruption styles recorded at the conduit crater transition diatreme development was initiated by deep quarrying explosive eruptions along a fissure to form the country rock rich breccia only parts of the fissure remained active as magma feeding the highly explosive eruptions along the fissure localized into discrete point sources forming the matrix rich lapilli tuff deposits these superimposed deposits record the passage of multiple debris jets and subvertical fallback from shallow cratering arising from explosions triggered by magma water interaction at numerous discrete sites however instead of continuing to build a well formed diatreme the system switched to weak spattering with intermittent explosive activity and near surface dike emplacement into the unconsolidated anisotropic pyroclastic debris of the crater floor dominant spatter from strombolian style bursts accumulated on the topographically varied evolving unstable syn eruptive crater floor and led to local failure and remobilization this study demonstrates how the combination of fissure behavior and sensitivity of the shallow plumbing system to local conditions during an eruption can lead to a decrease in eruptive footprint within the diatreme structure and an overall decrease in explosivity resulting in the arrested development of an immature diatreme

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

transition zone between the upper diatreme and lower diatreme origin and significance at round butte hopi buttes volcanic field navajo nation arizona round butte is a small but complex miocene diatreme that crops out 190 m below the pre eruptive surface in the southeastern part of the hopi buttes volcanic field erosional remnants consist of a diatreme 170 190 m in diameter of which the central 130 150 m is well exposed in a massif featuring 20 30 m high sub vertical cliffs and a 50 cm thick basanite dike field mapping allowed us to define three main groups of pyroclastic rocks in the diatreme undisturbed beds disturbed beds and non bedded rocks pyroclastic rocks range in grain size from coarse tuff to tuff breccia and in componentry from juvenile rich to lithic rich with a dominance of heterolithic lapilli tuffs rocks from the undisturbed bedded pyroclastic group are present above an unconformity found all around the massif whereas the disturbed bedded and the non bedded pyroclastic groups are always found below it this unconformity was previously understood as the contact between the upper and the lower diatremes the undisturbed beds above the unconformity indeed compose the upper diatreme but the assemblage of non bedded rocks invasive columns and disturbed beds residual columns below it is not typical of the lower diatreme instead they represent a transition zone between the upper and lower diatremes such a transition zone also occurs in other diatremes it is important genetically and we propose to add it to the general model of maar diatreme volcanoes

the fekete hegy balaton highland hungary soft substrate and hard substrate maar volcanoes in an aligned volcanic complex implications for vent geometry subsurface stratigraphy and the palaeoenvironmental setting the fekete hegy volcanic complex is located in the centre of the bakony balaton highland volcanic field in the pannonian basin which formed from the late miocene to pliocene period the eruption of at least four very closely clustered maar volcanoes into two clearly distinct types of prevolcanic rocks allows the observation and comparison of hard substrate and soft substrate maars in one volcanic complex the analyses of bedding features determination of the proportion of accidental lithic clasts granulometry and age determination helped to identify and distinguish the two types of maar volcanoes ascending magma interacted with meteoric water in karst aquifers in mesozoic carbonates as well as in porous media aquifers in neogene unconsolidated wet siliciclastic sediments the divided basement setting is reflected by distinct bedding characteristics and morphological features of the individual volcanic edifices as well as a distinct composition of pyroclastic rocks country rocks in hard substrate maars have a steep angle of repose leading to the formation of steep sided cone shaped diatremes enlargement and filling of these diatreme is mainly a result of shattering material by fci related shock waves and wall rock collapse during downward penetration of the explosion locus country rocks in soft substrate maars have much shallower angles of repose leading to the formation of broad bowl shaped structures or irregular depressions enlargement and filling of these diatremes is mainly the result of substrate collapse for example due to liquefaction of unconsolidated material by fci related shock waves and its emplacement by gravity flows the fekete hegy is an important example illustrating that the substrate of a volcanic edifice has to be taken into account as an important interface which can have major control on phreatomagmatic eruptions and the resulting characteristics of the volcanic complex

the effects of the host substrate properties on maar diatreme volcanoes experimental evidence while the relationship between the host substrate properties and the formation of maar diatreme volcanoes have been investigated in the past it remains poorly understood in order to establish the effects of the qualitative host substrate properties on crater depth diameter morphological features and sub surface structures we present a comparison of four campaigns of experiments that used small chemical explosives buried in various geological media to simulate the formation of maar diatremes previous results from these experiments have shown that primary variations in craters and sub surface structures are related to the scaled depth physical depth divided by cube root of blast energy our study reveals that single explosions at optimal scaled depths in stronger host materials create the largest and deepest craters with steep walls and the highest crater rims for single explosions at deeper than optimal scaled depths the influence of material strength is less obvious and non linear for crater depth and non existent for crater diameter within the range of the experiments for secondary and tertiary blasts there are no apparent relationships between the material properties and the crater parameters instead the presence of pre existing craters influences the crater evolution a general weakening of the materials after successive explosions can be observed suggesting a possible decrease in the host substrate influence even at optimal scaled depth the results suggest that the influence of the host substrate properties is important only in the early stage of a maar diatreme neglecting post eruptive slumping into the open crater and decreases as explosion numbers increase since maar diatremes reflect eruptive histories that involve tens to hundreds of individual explosions the influence of initial substrate properties on initial crater processes could potentially be completely lost in a natural system

unconventional maar diatreme and associated intrusions in the soft sediment hosted mardoux structure gergovie france a miocene age volcanic hypabyssal structure comprising volcaniclastic deposits and mafic intrusions is exposed with vertical relief of 110 m on the side of gergovie plateau auvergne france three main volcaniclastic facies are 1 fluidal tuff breccia composed of juvenile basalt and sediment clasts with dominantly fluidal shapes with several combinations of basalt and sediment within individual clasts 2 thickly bedded lapilli tuff composed of varying proportions of fine grained sediment derived from oligocene miocene lacustrine marls and mudstones and basaltic lapilli blocks and bombs 3 planar bedded tuff forming thin beds of fine to coarse ash size sedimentary material and basalt clasts intrusive bodies in the thickly bedded lapilli tuff range from irregularly shaped and anastomosing dikes and sills of meters to tens of meters in length to a main feeder dike that is up to 20 m wide and that flares into a spoon shaped sill at 100 m in diameter and 10 20 m thick in the eastern part of the structure volcaniclastic deposits and structural features suggest that ascending magma entrained soft saturated sediment host material into the feeder dike and erupted fluidal magma and wet sediment via weak strombolian like explosions host sediment and erupted material subsided to replace the extracted sediments producing the growth subsidence structure that is similar to upper diatreme facies in typical maar diatremes but lacks evidence for explosive disruption of diatreme fill irregularly shaped small intrusions extended from the main feeder dike into the diatreme and many were disaggregated due to shifting and subsidence of diatreme fill and recycled via eruption the mardoux structure is an unconventional maar diatreme in that it was produced mainly by weak explosive activity rather than by violent phreatomagmatic explosions and is an example of complex coupling between soft sediment and ascending magma

spatter dike reveals subterranean magma diversions consequences for small multivent basaltic eruptions small volume short lived basaltic volcanoes earth9s most common subaerially are abundant and tractable in size thus offering opportunities for learning how magma behaves in the critical transition from coherent magma in dikes to pyroclastic dispersions spatter dikes at the castle butte trading post volcanic complex hopi buttes volcanic field arizona usa exposed 150 m below the paleosurface present an outstanding record of this transition they record pulsatory magma rise and eruption fissure extension vent stepping and conduit wall rock failure providing a critical link to activity witnessed and geophysically monitored during historic eruptions of well observed and monitored large volume basaltic volcanoes castle butte comprises four linked and closely spaced spatter dikes and maar diatremes the spatter dikes consist of bedded variably welded deposits plus wall rock debris in multiple sequences demarcated by truncation surfaces that indicate progressive southwest northeast emplacement they reveal a shallow plumbing cycle of pulsating weak hot spatter fragmentation concurrent wall rock failure and periodic slips that truncated and downdropped bedded deposits in addition to vertical pulsation we infer from the northeastward younging spatter succession that repeated magma diversions facilitated episodes of magma withdrawal that caused the slips during northeastward extension of the complex toward the large maar diatreme

el pozo volcanic complex evolution of a group of maars central mendoza province argentina abstract the el pozo volcanic complex in the south central mendoza province is formed by three maars the first to be described in the payenia volcanic province and one of the few examples in argentina the maars of el pozo volcanic complex 1 2 and 3 show large craters 0 97 km 1 2 km and 0 96 km respectively and their depth is between 10 and 57 m below the pre eruptive surface their deposits are described from the only outcrops that have been found called el pajarito and el visitante it was interpreted that the first maar to be formed would have been no 2 from which only the deposits corresponding to el pajarito 3 6 m and the lower section of el visitante 28 m are preserved we suggest that its shape is the result of lateral vent migration and coalescence of successive vents then after a short break represented by the angular unconformity in the el visitante section the active vent would have shifted more to the w and the maar no 3 is thought to have been formed the activity of this maar is represented in el visitante upper section with features resulting from the presence of water in the time of deposition maar no 1 was probably active simultaneously with maar no 3 with which coalesces but the lack of outcrops does not guarantee this affirmation towards the end of the eruptive cycle depletion of water produced a change in activity from phreatomagmatic to strombolian and effusive this gave rise to the nested pyroclastic scoria cone el pozo cone which lies in the maars 1 and 3 craters floors el pozo cone is related to lava flows with a tumulus and the deposit of a lapilli bearing tephra plume

δd and δ18o variations of the magmatic system beneath deception island volcano antarctica implications for magma ascent and eruption forecasting abstract geochemistry of volatiles in active volcanoes provides insights into the magmatic processes and evolution at depth such as magma evolution and degassing which can be implemented into volcanic hazards assessment deception island is one of the most active volcanoes in antarctica with more than twenty explosive eruptions documented over the past two centuries hydrogen and oxygen isotopic variations in the volatiles trapped in the deception island rocks glass and melt inclusions in phenocrysts provide essential information on the mechanisms controlling the eruptive history in this volcanic suite thus understanding the petrological and related isotopic variations in the island has the potential to foresee the possible occurrence and its main eruptive features of a future eruption the new isotopic results of this study combined with exhaustive petrologic knowledge reveal in deception island i fast ascent and quenching of most magmas preserving pre eruptive magmatic signal of water contents and isotopic ratios with local modification by rehydration due to glass exposition to seawater and by meteoric and fumarolic waters ii a plumbing system s variable with time and currently dominated by closed system degassing leading to explosive eruptions iii control on the interactions of ascending magmas with the surface waters producing hydrovolcanic activity throughout the two main fault systems in deception island and at different magma stagnation depths these results can be considered in further studies of volcanic monitoring to improve the capability to interpret geophysical data and signals recorded during volcanic unrest episodes and hence forecast volcanic eruptions and related hazards

using the characteristics of rootless cone deposits to estimate the energetics of explosive lava water interactions during volcanic eruptions the interaction of magma and groundwater can produce thermohydraulic explosions capable of significantly increasing the eruption energy the most well known mechanism by which explosive magma water interactions occur molten fuel coolant interaction mfci is a complex series of macro and microscale processes which have been simulated using laboratory scale experiments as a natural analog for mfci experiments we utilize rootless cone beds formed by lava water explosions to estimate explosion energy the specific mechanical energy of the lava water explosions studied here occurs over a broader range 4 to 178 kj kg than mfci experiments and includes estimates for the highest energy lava water explosions studied to date explosion energy is partitioned similarly over the two systems with kinetic transport and fragmentation energy making up 25 40 and 42 80 of the mechanical energy respectively which overlap the ranges estimated for mfci experiments our study of lava water explosions therefore provides a field scale analog of mfci laboratory experiments for understanding the energetics and therefore hazards of mfci in natural systems

low temperature emplacement of phreatomagmatic pyroclastic flow deposits at the monogenetic mt gambier volcanic complex south australia and their relevance for understanding some deposits in diatremes the occurrence of pyroclastic flow deposits is not restricted to polygenetic and or felsic volcanic systems but can also occur at mafic monogenetic volcanic centres at the c 5 ka mt gambier volcanic complex australia two small volume pyroclastic flow deposits resulted from phreatomagmatic eruptive phases of the blue lake east and the valley lake maar craters the facies descriptions of the two massive poorly sorted lapilli tuff and tuff breccia deposits are given low grade carbonized wood fragments in the deposits mark low emplacement temperatures 180 270 c for these deposits with only c 12 23 of the total thermal energy of the original magma preserved at the time of deposition the blue lake east vent erupted by forming a short lived vertical eruption column which could not be sustained and collapsed the valley lake pyroclastic flow deposit has a highly asymmetric dispersal to the west indicating that this deposit was formed during an eruptive phase with a large westward directed lateral component such massive poorly sorted deposits outside the maar crater indicate that some similar deposits in diatremes may have originated from surface eruptions and not just from subsurface debris jets

seismic imaging of santorini subsurface constraints on caldera collapse and present day magma recharge abstract volcanic calderas are surface depressions formed by roof collapse following evacuation of magma from an underlying reservoir the mechanisms of caldera formation are debated and predict differences in the evolution of the caldera floor and distinct styles of magma recharge here we use a dense active source seismic tomography study to reveal the sub surface physical properties of the santorini caldera in order to understand caldera formation we find a 3 km wide cylindrical low velocity anomaly in the upper 3 km beneath the north central portion of the caldera that lies directly above the pressure source of the 2011 2012 inflation we interpret this anomaly as a low density volume caused by excess porosities of between 4 and 28 with pore spaces filled with hot seawater vents that were formed during the first three phases of the 3 6 ka late bronze age lba eruption are located close to the edge of the imaged structure the correlation between older volcanic vents and the low velocity anomaly suggests that this feature may be long lived we infer that collapse of a limited area of the caldera floor resulted in a high porosity low density cylindrical volume which formed by either chaotic collapse along reverse faults wholesale subsidence and infilling with tuffs and ignimbrites phreatomagmatic fracturing or a combination of these processes phase 4 eruptive vents are located along the margins of the topographic caldera and the velocity structure indicates that coherent down drop of the wider topographic caldera followed the more limited collapse in the northern caldera this progressive collapse sequence is consistent with models for multi stage formation of nested calderas along conjugate reverse and normal faults the upper crustal density differences inferred from the seismic velocity model predict differences in subsurface gravitational loading that correlate with the location of 2011 2012 edifice inflation this result supports the hypothesis that sub surface density anomalies may influence present day magma recharge events we postulate that past collapses and the resulting topographical and density variations at santorini influence magma focusing between eruptive cycles a feedback process that may be important in other volcanoes

tsunamis generated by subaqueous volcanic explosions in taal caldera lake philippines volcanic subaqueous explosions can generate hazardous tsunamis especially in lakes in this paper we simulate different scenarios of subaqueous explosions and related tsunamis in taal caldera lake luzon philippines taal volcano is one of the most active volcanoes in southeast asia and eruptive processes are mostly explosive we test different energies of explosions at eight different explosion sites in the lake the initial water surface displacement 0 generated by the explosion is estimated as a function of explosion energy at a given depth we estimate the tsunami travel times maximum wave heights and wave periods at the shoreline this type of hazard is typically neglected and our work has important implications for hazard assessment around taal lake due to fast propagation of tsunamis in the lake waves typically crossing the lake in less than 10 min there is only a short time available for issuing a warning for 0 50 m wave heights at the shoreline are less than 2 m with a non dispersive numerical model and less than 0 5 m with a dispersive model whatever the explosion depth and location powerful explosions with 0 100 m generate wave heights greater than 2 m all around the lake and local peaks higher than 10 m

the polycyclic lausche volcano lausitz volcanic field and its message concerning landscape evolution in the lausitz mountains northern bohemian massif central europe abstract the tertiary lausitz volcanic field covers a broad area encompassing parts of eastern saxony germany lower silesia poland and north bohemia czech republic volcanism was predominantly controlled by the volcano tectonic evolution of the oh e rift and culminated in the lower oligocene this paper deals with the highest volcano of this area the lausche hill 792 6 m a s l situated in the lausitz mountains we offer a reconstruction of the volcanic edifice and its eruptive history its complex genesis is reflected by six different eruption styles and an associated petrographic variety furthermore the lausche volcano provides valuable information concerning the morphological evolution of its broader environs the remnant of an alluvial fan marking a middle paleocene lower eocene 62 50 ma palaeo surface is preserved at the base of the volcano the deposition of this fan can be attributed to a period of erosion of its nearby source area the lausitz block that has undergone intermittent uplift at the lausitz overthrust since the upper cretaceous the lausche hill is one of at least six volcanoes in the lausitz mountains which show an eminent low level of erosion despite their oligocene age and position on elevated terrain these volcanoes are exposed in their superficial level which clearly contradicts their former interpretation as subvolcanoes among further indications this implies that the final morphotectonic uplift of the lausitz mountains started in the upper lower pleistocene 1 3 ma due to revived subsidence of the nearby zittau basin it is likely that this neotectonic activity culminated between the elsterian and saalian glaciation 320 ka the formation of the low mountain range was substantially controlled by the intersection of the lausitz overthrust and the oh e rift

physical volcanology of a large crater complex formed during the initial stages of karoo flood basalt volcanism sterkspruit eastern cape south africa abstract the sterkspruit complex exposed at the base of the karoo flood basalts in south africa is a complex of mostly massive volcaniclastic rocks dikes and lava that fills a crater 45 km 2 cut into country rock and is surrounded by a blanket of more distal bedded volcaniclastic rocks the moderately to steeply inward dipping margins of the crater are delineated by country rock breccia that grades into rocks within the complex intra complex rocks are dominated by massive polymict lapilli tuff and tuff breccia 150 m thick with intercalated lavas and minor bedded volcaniclastic rocks pillow lava 50 m thick and thinly bedded inferred lacustrine deposits cap the complex succession and are in turn covered by subaerial karoo flood basalts beyond the crater a succession of bedded finer grained volcaniclastic rocks 100 60 m thick rests on country rock and thins distally over at least 5 km magma emplaced over a broad area through a network of feeder dikes and sheets created many small vents that grew into their neighbours through lateral quarrying and vent migration and whose deposits overlap both within and outside the complex an abrupt end to eruptions that formed volcaniclastic deposits is recorded by flooding of the lowest part of the crater by first water then lava then subsequently by inundation of the complex and the surrounding landscape by voluminous effusion of flood basalt formation of the sterkspruit complex and many others like it in south africa confirms that the opening phases of karoo flood basalt volcanism were partly explosive the abundant volcaniclastic products at sterkspruit and in other flood basalt provinces result from eruptions that disperse ash and volcanic aerosols differently than effusive eruptions of lava and thus may have important implications for climate change and landscape development associated with the initial stages of flood basalt provinces

maar diatreme geometry and deposits subsurface blast experiments with variable explosion depth basaltic maar diatreme volcanoes which have craters cut into preeruption landscapes maars underlain by downward tapering bodies of fragmental material commonly cut by hypabyssal intrusions diatremes are produced by multiple subsurface phreatomagmatic explosions although many maar diatremes have been studied the link between explosion dynamics and the resulting deposit architecture is still poorly understood scaled experiments employed multiple buried explosions of known energies and depths within layered aggregates in order to assess the effects of explosion depth and the morphology and compaction of the host on the distribution of host materials in resulting ejecta the development of subcrater structures and deposits and the relationships between them experimental craters were 1 2 m wide analysis of high speed video shows that explosion jets had heights and shapes that were strongly influenced by scaled depth physical depth scaled against explosion energy and by the presence or absence of a crater jet properties in turn controlled the distribution of ejecta deposits outside the craters and we infer that this is also reflected in the diverse range of deposit types at natural maars ejecta were dominated by material that originated above the explosion site and the shallowest material was dispersed the farthest subcrater deposits illustrate progressive vertical mixing of host materials through successive explosions we conclude that the progressive appearance of deeper seated material stratigraphically upward in deposits of natural maars probably records the length and time scale for upward mixing through multiple explosions with ejection by shallow blasts rather than progressive deepening of explosion sites in response to draw down of aquifers

monogenetic volcanism personal views and discussion monogenetic volcanism produces small volume volcanoes with a wide range of eruptive styles lithological features and geomorphic architectures they are classified as spatter cones scoria or cinder cones tuff rings maars maar diatremes and tuff cones based on the magma water ratio dominant eruption styles and their typical surface morphotypes the common interplay between internal such as the physical chemical characteristics of magma and external parameters such as groundwater flow substrate characteristics or topography plays an important role in creating small volume volcanoes with diverse architectures which can give the impression of complexity and of similarities to large volume polygenetic volcanoes in spite of this volcanic facies complexity we defend the term monogenetic volcano and highlight the term s value especially to express volcano morphotypes this study defines a monogenetic volcano a volcanic edifice with a small cumulative volume typically 1 km3 that has been built up by one continuous or many discontinuous small eruptions fed from one or multiple magma batches this definition provides a reasonable explanation of the recently recognized chemical diversities of this type of volcanism

planform channel dynamics of the lower colorado river 1976 2000 abstract in the past two decades major flood events have occurred on the lower colorado river a dramatic shift from the low flows and moderate floods associated with prior decades of river regulation this study uses repeat aerial photography and geographic information system analysis to examine the planform channel response of the upper colorado river delta limitrophe reach to this recently altered hydrology results indicate that channel contraction has been the dominant planform process in recent decades but periodic floods resulted in channel expansion 1981 1988 1997 2000 or likely reduced the channel contraction measured between successive aerial photographs 1976 1981 1988 1994 sinuosity adjustments were limited during the timeframe of the study range 1 31 to 1 38 but the channel did respond with large adjustments in channel width range 44 m to 355 m and changes in total mid channel bar area range 0 to 52 3 ha a channel probability model developed for this study provides a raster image of the channel changes and depicts areas modified to varying degrees by flood flows this historical study provides insight into how floods affect the channel system that provides the foundation for aquatic and riparian biodiversity this issue is of increasing relevance given growing international interest in rehabilitating the riparian and aquatic ecosystems of the colorado river delta through intentional flood flows

stratigraphy and evolution of the holocene aljojuca maar volcano serdan oriental basin eastern trans mexican volcanic belt and implications for hazard assessment abstract aljojuca maar is located in the eastern trans mexican volcanic belt within the serdan oriental basin which is characterized by quaternary bimodal monogenetic volcanism aljojuca maar has an irregular shape with an eastern embayment structure that forms an e w alignment with at least three older scoria cones to the east the crater walls expose a sequence of pre maar volcaniclastic deposits with a lava flow linked to the older scoria cones and a paleosol at its top the latter indicates that a significant hiatus occurred between the growth of the scoria cones and the eruption of the aljojuca maar whose deposits overlie the soil strong interactions of the ascending magma with groundwater led to the emplacement of a 30 m thick maar sequence our detailed stratigraphic study shows that the eruption can be grouped into two main stages comprising eight stratigraphic units deposited during five eruptive phases the first stage reflects the development of the main crater a maar sensu stricto and is recorded by six stratigraphic units from a to f the eruption began with a strombolian pulse followed by phreatomagmatic activity unit a forming dilute pyroclastic density currents in the second phase phreatomagmatic explosions prevailed with different degrees of fragmentation from juvenile and lithic rich lapilli fallout unit b to less diluted pyroclastic density currents unit c and a spatially restricted strombolian pulse the third phase includes a main vent enlargement event represented by a chaotic and heterolithic breccia unit d in the fourth phase dilute pyroclastic density current deposits unit e dominate with minor chaotic breccias unit f the second stage fifth phase includes the occurrence of a possibly fissural e w structure which formed a scallop in the eastern flank of the maar eastern embayment structure breaking the previously formed main crater s eastern flank and producing a 4 m chaotic breccia unit g followed by the occurrence of a dilute pyroclastic density current unit h whose energy enabled the current to climb to the closest scoria cone the migration of the explosive loci toward the eastern flank of the maar reflects a tectonic control by the dominant regional east trending structural pattern several radiocarbon ages support that the eruption of aljojuca took place between 2 7 ka age of charcoal fragments under the ejecta ring and 2 2 ka age of the oldest lake sediments in the maar crater this has important implications for the hazard assessment of volcanism in this area which had not been considered previously as a potentially active system

the effect of pre existing craters on the initial development of explosive volcanic eruptions an experimental investigation most volcanic eruptions occur in craters formed by previous activity the presence of a crater implies specific confinement geometries variably filled by loose fragmental deposits which are expected to exert a strong yet poorly studied control on the violent gas expansion that drives the eruption here we analyze patterns of ejection from buried explosions in analog experiments in order to investigate how the presence of a crater and changes in explosion depth and intensity may affect the formation of eruptive ejecta jets results show that scaled depth charge burial depth divided by the cubic root of charge energy controls the velocity and partly spread angle of eruptive jets independently of the presence of a pre existing crater conversely for a fixed scaled depth the presence of a pre existing crater limits the development of a laterally expanding annulus of the jet these results are directly applicable to interpretation of volcanic explosions key points analysis of ejection patterns from intra and extra crater buried explosions velocity and spread angle of ejecta jet are sensitive to explosion scaled depth radially expanding annulus of the jet is sensitive to pre existing crater

origin of nonbedded pyroclastic rocks in the cathedral cliff diatreme navajo volcanic field new mexico cathedral cliff is a well exposed mid tertiary phreatomagmatic diatreme in the navajo volcanic field new mexico post eruptive erosion estimated between 500 and 1000 m exposes the deep part of the diatreme cathedral cliff provides an opportunity to examine the transition between the bedded pyroclastic rocks of an upper diatreme and the nonbedded pyroclastic rocks of the subjacent lower diatreme bedded pyroclastic rocks occupy 49 of the mapped diatreme area nonbedded pyroclastic rocks occupy 45 and the remaining 6 consist of sedimentary megablocks the bedded pyroclastic rocks range from coarse tuff to medium lapilli tuff and from lithic to juvenile rich they were emplaced during eruption at the bottom of the crater by pyroclastic density currents pyroclastic fallout and as ballistic bombs and blocks as the eruption continued they subsided into the diatreme to their current location bedding ranges from well preserved continuous beds to partially destroyed broken beds syn eruptive subsidence the passage of debris jets through the broken beds as well as a concentration of explosions nearby explains the partial destruction of the bedding the nonbedded pyroclastic rocks are massive and poorly sorted and consist of coarse tuff lapilli tuff and tuff breccia on average they are coarser grained and more juvenile rich than the bedded rocks nonbedded rocks form zones with steep contacts that cross cut each other and the bedded rocks in places they have gradual transitions into broken beds we interpret the nonbedded rocks as formed by the passage of debris jets through existing diatreme infill and from the destruction and recycling of the bedded deposits with juvenile clast enrichment due to dike fragmentation

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

three dimensional potential field modelling of a multi vent maar diatreme the lake coragulac maar newer volcanics province south eastern australia abstract high resolution gravity and magnetic data have been acquired across lake coragulac a quaternary maar volcano located in the newer volcanics province of south eastern australia a gravity low is observed across the maar crater with several local gravity highs identified in the centre of the crater often with corresponding magnetic anomalies geophysical data has been integrated with geologic observations and subjected to 2d forward and 3d inverse potential field modelling modelling has revealed a complex subsurface maar structure with four coalesced diatremes and several intrusive dykes identified the modelled diatremes are shallow maximum of 290 m deep with the margins having a similar density to the host rock while the diatreme centre is often denser indicating that higher volumes of volcanic debris are present deposits of the maar rim sequence show frequent transitions between phreatomagmatic and magmatic fragmentation styles a result of fluctuations in magma rise rate and interactions with external water the complex nature of the underlying maar diatreme suggests that the maar formed from at least four vents which migrated laterally during the eruption

discrete blasts in granular material yield two stage process of cavitation and granular fountaining a discrete blast within granular material such as a single subterranean explosion within a debris filled diatreme structure is typically considered to produce a single uprush of material our experiments demonstrate that apparent debris jet deposits can be formed by a two stage process of cavitation and subsequent granular fountaining bench scale experiments reported here demonstrate that for a range of overpressures and depths individual discrete buried gas blasts open space and expel particles from the blast site in two largely decoupled stages expanding gas initially pierces material nearest the blast source to open a cavity above it then a fountain of grains rises from the source into the cavity this staged motion dynamically segregates source grains from host material grains and the rates of cavity opening versus fountain rise show a power law decay relationship with initial pressure our experimental analysis has implications for maar diatreme systems field scale detonation experiments and underground nuclear testing

historic hydrovolcanism at deception island antarctica implications for eruption hazards deception island antarctica is the southernmost island of the south shetland archipelago in the south atlantic volcanic activity since the eighteenth century along with the latest volcanic unrest episodes in the twentieth and twenty first centuries demonstrates that the volcanic system is still active and that future eruptions are likely despite its remote location the south shetland islands are an important touristic destination during the austral summer in addition they host several research stations and three summer field camps deception island is characterised by a quaternary caldera system with a post caldera succession and is considered to be part of an active dispersed monogenetic volcanic field historical post caldera volcanism on deception island involves monogenetic small volume vei 2 3 eruptions such forming cones and various types of hydrovolcanic edifices the scientific stations on the island were destroyed or severely damaged during the eruptions in 1967 1969 and 1970 mainly due to explosive activity triggered by the interaction of rising or erupting magma with surface water shallow groundwater and ice we conducted a detailed revision field petrology and geochemistry of the historical hydrovolcanic post caldera eruptions of deception island with the aim to understand the dynamics of magma water interaction as well as characterise the most likely eruptive scenarios from future eruptions we specifically focused on the crimson hill estimated age between 1825 and 1829 and kroner lake estimated age between 1829 and 1912 eruptions and 1967 1969 and 1970 events by describing the eruption mechanisms related to the island s hydrovolcanic activity data suggest that the main hazards posed by volcanism on the island are due to fallout ballistic blocks and bombs and subordinate dilute pdcs in addition deception island can be divided into five areas of expected activity due to magma water interaction providing additional data for correct hazard assessment on the island

circum crater variability of deposits from discrete laterally and vertically migrating volcanic explosions experimental evidence and field implications abstract circumferential variation in sorting thickness granulometry and componentry of tephra ring deposits can result from instabilities in the eruptive jet and interactions with the confining crater jet instabilities result in fingers of high particle concentrations that form deposits radiating away from a crater referred to as rays two major types of rayed deposits are described from subsurface explosion experiments 1 symmetrical rayed deposits with an axisymmetric ejecta blanket which result from vertically directed eruptive jets and 2 zones of rays that extend out from sectors of a crater with an asymmetrical proximal ejecta skirt that result from inclined jets variations within each group are also associated with variations in the explosion depth relative to the energy of the explosion although the surface morphology of rays is likely to be lost in natural tephra rings due to overlapping deposits of numerous explosions rayed deposits are expected to be preserved in cross section as lenses of relatively coarse and poorly sorted material compared to surrounding deposits asymmetrical deposits of inclined jets are anticipated to be particularly distinctive the experimental facies associations indicate that these deposits would be easily distinguished given sufficient exposure from other heterogeneities caused by wind influence collapse of the crater rim or the influence of topography on density currents these experimental results can also be used to further the discussion of deposits from inclined jets from other explosion scenarios such as vulcanian blasts and hydrothermal explosions the experimental rayed deposits described here indicate that the classic interpretation of clast concentration zones in tephra ring deposits must be reevaluated

reconstructing the eruption magnitude and energy budgets for the pre historic eruption of the monogenetic 5 ka mt gambier volcanic complex south eastern australia understanding explosive volcanic eruptions especially phreatomagmatic eruptions their intensities and energy budgets is of major importance when it comes to risk and hazard studies with only a few historic occurrences of phreatomagmatic activity a large amount of our understanding comes from the study of pre historic volcanic centres which causes issues when it comes to preservation and vegetation in this research we show that using 3d geometrical modelling it is possible to obtain volume estimates for different deposits of a pre historic complex monogenetic centre the mt gambier volcanic complex south eastern australia using these volumes we further explore the energy budgets and the magnitude of this eruption vei 4 including dispersal patterns eruption columns varying between 5 and 10 km dispersed towards north east to south to further our understanding of intraplate monogenetic eruptions involving phreatomagmatic activity we also compare which thermodynamic model fits best in the creation of the maar crater of mt gambier the major explosion dominated model or the incremental growth model in this case the formation of most of the craters can best be explained by the latter model

compound maar crater and co eruptive scoria cone in the lunar crater volcanic field nevada usa abstract bea s crater lunar crater volcanic field nevada usa consists of two coalesced maar craters with diameters of 440 m and 1050 m combined with a co eruptive scoria cone that straddles the northeast rim of the larger crater the two craters and the cone form an alignment that parallels many local and regional structures such as normal faults and is interpreted to represent the orientation of the feeder dyke near the surface the maar formed among a dense cluster of scoria cones the cone cluster topography resulted in crater rim that has a variable elevation these older cones are composed of variably welded agglomerate and scoria with differing competence that subsequently affected the shape of bea s crater tephra ring deposits associated with phreatomagmatic maar forming eruptions are rich in basaltic lithics derived from

a new model for the fracture energy budget of phreatomagmatic explosions the fragmentation of magma and of the hosting country rocks is a major process in explosive eruptions it is important to quantify the mechanical energy needed for fragmentation in order to assess the physical processes of this volcanic phenomenon this paper presents a method to calculate the fragmentation energy of country rock using granulometry data of a typical phreatomagmatic eifel maar volcano explosion the total fracture area of country rock fragments in one tephra layer was quantified and related to the critical fragmentation energy of these country rocks the rock parameters critical shear stress and critical fragmentation energy were determined experimentally whereas the pre volcanic crack inventory was measured in the field the paper concludes with the calculation of the energy balance i e partitioning of thermal energy into kinetical energy and mechanical energy of the fragmentation of one eifel maar volcanic explosion