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

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

identification of karst features using seismic p wave tomography and resistivity anisotropy measurements a football stadium with a capacity of a hundred thousand spectators is under construction over a karst terrain 10 km west of the old town of istanbul turkey a large cavity of approximately 30 m3 was detected beneath the sports field through a number of boreholes so that a geophysical survey was required to further investigate a portion of the sports field we utilized seismic refraction tomography and dc electrical method with rotated wenner array to delineate zones with solution voids and cavities total core recovery tcr was 5 15 from boreholes where zones with low velocities were identified through tomographic inversion whereas tcr values were above 60 in zones with higher velocities both low velocity zones in the tomographic images and increasing resistivity anisotropy with depth appear to indicate that the cavity extends toward the west and south at a depth of approximately 8 m although the southward and westward extension changes in character

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

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

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

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

an indian ocean tsunami triggered remotely by an onshore earthquake in balochistan pakistan this paper describes and documents instrumentally recorded tsunami waves that are interpreted as secondary effects of a 7 7 magnitude earthquake in southern pakistan on 24 september 2013 the tsunami waves were almost unnoticed because the wave heights were low and the tsunami occurred at low tide the historical record of tsunami events within the arabian sea northern indian ocean is fragmentary large tsunamigenic earthquakes are known to be generated in the makran subduction zone the area that forms the boundary of the arabian and eurasian plates submarine sliding is reported along the owen fracture zone which marks the boundary between the arabian and indian plates hence the tsunami hazard potential within the arabian sea is enigmatic our analysis is based on sea level oscillations recorded at various tide gauge stations along the coastlines of oman pakistan and iran as well as eyewitness accounts of the event in oman our results indicate that the waves were in the range of 1 m or less in height they were first recorded along the eastern coast of oman and propagated toward the west we suggest that the waves must have been triggered by a submarine slide on the makran margin cascading effects resulting in large submarine slope failures within the arabian sea are more frequent than postulated the hazard potential is underestimated as such secondary effects of distant ruptures onshore were previously not taken into account

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

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

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

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

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

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

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

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