unzipping long valley an explanation for vent migration patterns during an elliptical ring fracture eruption long valley caldera california formed during the cataclysmic pleistocene eruption of the bishop tuff previous stratigraphic and petrologic studies of this eruption deciphered an intriguing pattern of vent migration thought to mirror the lateral propagation unzipping of magma tapping ring fractures during caldera collapse from scaled analog models we show that this unzipping pattern was intrinsically related to the high plan view ellipticity of the precollapse magma chamber roof we also provide a first order kinematic explanation for the systematic location of initial elliptical roof failure and for the lateral propagation of highly elliptical ring fractures

the diversity of flow structures in felsic dykes abstract numerous structures and textures which can be related to magma flow were observed in felsic dykes intruding late mesozoic granitoid plutons in the jiaodong peninsula in eastern shandong province eastern china these flow structures may be classified into two categories interior and peripheral the former group includes magmatic bands various types of folds e g injection sheath similar and disharmonic folds rotation of phenocrysts magmatic foliation or lineation and crenulation whereas the latter includes hot tool marks and quarrying structures magmatic banding resulted from shearing of mingled magma during magma flow in the dykes the magma seemed to flow rapidly probably triggering turbulence in some thick dykes interaction at the contact between the hot moving magma and the cold stationary wallrock sometimes produced the peripheral structures a few measurements of hot tool marks and of magmatic lineation reveal a roughly horizontal flow of magma within these dykes for the dominant ne sw striking dyke set in the laoshan granitoid pluton the felsic magma probably ascended on or to the sw of the pluton to feed the dyke swarm and then flowed laterally to drive the horizontal propagation of dykes

is the valles caldera entering a new cycle of activity the valles caldera formed during two major rhyolitic ignimbrite eruptive episodes the bandelier tuff at 1 61 and 1 22 ma after some 12 m y of activity in the jemez mountains volcanic field new mexico several subsequent eruptions between 1 22 and 0 52 ma produced dominantly high silica rhyolite lava domes and tephras within the caldera these were followed by a dormancy of 0 46 m y prior to the most recent intracaldera activity the longest hiatus since the inception of the bandelier magma system at 1 8 ma the youngest volcanic activity at 60 ka produced the sw moat rhyolites a series of lavas and tuffs that display abundant petrologic evidence of being newly generated melts petrographic textures conform closely to published predictions for silicic magmas generated by intrusion of basaltic magma into continental crust the valles caldera may currently be the site of renewed silicic magma generation induced by intrusion of mafic magma at depth recent seismic investigations revealed the presence of a large low velocity anomaly in the lower crust beneath the caldera the generally aseismic character of the caldera despite abundant regional seismicity may be attributed to a heated crustal column the local effect of 13 m y of magmatism and emplacement of mid crustal plutons seismic signals of magma movement in the deep to mid crust may therefore be masked and clear seismic indications of intrusion may only be generated within a few kilometres of the surface we therefore encourage the establishment of a local dedicated volcanic monitoring system

calderas and caldera structures a review abstract calderas are important features in all volcanic environments and are commonly the sites of geothermal activity and mineralisation yet it is only in the last 25 years that a thorough three dimensional study of calderas has been carried out utilising studies of eroded calderas geophysical analysis of their structures and analogue modelling of caldera formation as more data has become available on calderas their individuality has become apparent a distinction between caldera caldera complex cauldron and ring structure is necessary and new definitions are given in this paper descriptions of calderas based on dominant composition of eruptives basaltic peralkaline andesitic dacitic rhyolitic can be used and characteristics of each broad group are given styles of eruption may be effusive or explosive with the former dominant in basaltic calderas and the latter dominant in andesitic dacitic rhyolitic and peralkaline calderas four end member collapse styles occur plate or piston piecemeal trapdoor and downsag but many calderas have multiple styles features of so called funnel and chaotic calderas proposed in the literature can be explained by other collapse styles and the terms are considered unnecessary ground deformation comprises subsidence or collapse essential characteristics of a caldera and uplifting doming and fracturing due to tumescence and or resurgence frequent but not essential collapse may occur on pre existing structures such as regional faults or on faults created during the caldera formation and the shape of the collapse area will be influenced by depth size and shape of the magma chamber the final morphology of a caldera will depend on how the caldera floor breaks up whether collapse takes place in one event or multiple events whether vertical movement is spasmodic or continuous throughout the eruptive sequence and whether blocks subside uniformly or chaotically at one or more collapse centres a meaningful description of any caldera should therefore include number of collapse events presence or absence of resurgence caldera floor coherency caldera floor collapse geometry and dominant composition of eruptives

experimental studies of collapse calderas we present experiments to investigate the formation of calderas using inflatable balloons in a medium of fused alumina powder this system provides a model of a magma chamber in an homogeneous elastic media which scales to volcanic systems in terms of geometry and strength of the media three kinds of experiment were performed i the balloon was inflated and then deflated simulating pre emption tumescence and caldera collapse ii the balloon was deflated without prior inflation simulating caldera formation without pre eruption tumescence iii three balloons were inflated and deflated in a line simulating multiple magma chambers the influence of magma chamber shape was investigated using different shaped balloons balloon inflation formed a dome with a surface pattern of shallow polygonal fractures centrally and radial fractures peripherally uplift occurs along deep inward dipping concentric reverse faults deflation generated depressions with an outer set of concentric ring fractures surrounding a central funnel formed by sagging along numerous minor faults some of which formed during doming during collapse the concentric reverse faults were converted to normal faults and the radial normally faulted fractures were converted to reverse faults without prior tumescence an outer set of near vertical ring faults surround a flat central depression due to collapse of a coherent block an inner set of outward dipping reverse ring faults also develop the experimental caldera area increased with balloon size and increased as the balloon depth decreased for a given balloon volume and depth collapse area is significantly smaller if doming had occurred prior to collapse arcuate fractures can provide the pathways for magma ascent during pre emption tumescence smith bailey 1968 but the shallow radial and polygonal fracture systems may also influence vent location changes in fault geometry and sense of movement extension to compression and vice versa occur when subsidence initiates and can account for changes in vent location that occur in many eruptions multiple overlapping collapse calderas are associated with magma chamber migration whereas nested calderas can result from the activity of a single magma chamber

constraints on rheology of obsidian lavas based on mesoscopic folds the geometry of mesoscopic single and multiple layer folds in rhyolitic obsidian flows is investigated folds are composed of obsidian embedded in a matrix of pumice folds form by buckling processes as indicated by discontinuous deformation between obsidian and pumice layers and by the geometries of wavetrains buckling occurs through a continuum of styles controlled largely by the thickness ratio of pumice to obsidian n styles of folds include chevron harmonic polyharmonic disharmonic and single layer assemblages harmonic and chevron folds are observed for small values of n for large values of n folds buckle independently of one another and form disharmonic and single layer assemblages wavelength to thickness ratios of single layer folds are compared to theoretically predicted ratios for newtonian and power law fluids as a means of estimating shear viscosity ratios of obsidian and pumice while all folds indicate that bubble free rhyolite is more viscous during flow than bubbly rhyolite estimates of shear viscosity ratio based on newtonian theory 010 500 may exceed estimates based on power law rheologies by more than an order of magnitude newtonian buckling theory involves a number of simplifications and does not account for the possibly complex rheology of bubble bearing rhyolite 1999 elsevier science ltd all rights reserved

the emplacement of an obsidian dyke through thin ice hrafntinnuhryggur krafla iceland an eruption along a 2 5 km long rhyolitic dyke at krafla volcano northern iceland during the last glacial period formed a ridge of obsidian hrafntinnuhryggur the ridge rises up to 80 m above the surrounding land and is composed of a number of small volume lava bodies with minor fragmental material the total volume is 0 05 km3 the lava bodies are flow or dome like in morphology and many display columnar jointed sides typical of magma ice interaction quench fragmented lower margins indicative of interaction with meltwater and pumiceous upper surfaces typical of subaerial obsidian flows the fragmental material compromises poorly sorted perlitic quench hyaloclastites and poorly exposed pumiceous tuffs lava bodies on the western ridge flanks are columnar jointed and extensively hydrothermally altered at the southern end of the ridge the feeder dyke is exposed at an elevation 95 m beneath the ridge crest and flares upwards into a lava body using the distribution of lithofacies we interpret that the eruption melted through ice only 35 55 m thick which is likely to have been dominated by firn hrafntinnuhryggur is therefore the first documented example of a rhyolitic fissure eruption beneath thin ice firn the eruption breached the ice leading to subaerial but ice firn contact lava effusion and only minor explosive activity occurred the ridge appears to have been well drained during the eruption aided by the high permeability of the thin ice firn which appears not to have greatly affected the eruption mechanisms we estimate that the eruption lasted between 2 and 20 months and would not have generated a significant jokulhlaup 70 m3s 1

oblique back arc rifting of taupo volcanic zone new zealand taupo volcanic zone tvz is a back arc rift innorth island new zealand its geometry andkinematics are investigated using shaded reliefimages field examination of faults and offset streamchannels the results show that tvz trends nne is 250 km long by hikurangi margin in the north island of new zealand 20 km wide and consists of fivesegments extension is principally manifest as steeplydipping 60 90 normal faults parallel to tvz these in the last 300 kyr have experienced acomponent of dextral shear tvz is therefore anoblique back arc rift the dextral shear is 37 of thetotal displacement which for previously estimatedspreadingrates 7mm yr correspondsto 2 6mm yr thisvalueissimilartopreviousestimatesofthedextralshear from the back arc to the forearc domains in thenorthisland distributeddextralshearacrosstvzthussuggests that strain partitioning across the plateboundary at latitudes of tvz is less significant thanpreviously thought

insights into caldera and regional structures and magma body distribution from lava domes at rotorua caldera new zealand abstract lava domes emplaced after caldera forming eruptions are often the only clue to the structure of the caldera and to the regional structure at the time of caldera formation this is because the deposits from the subsequent eruptions commonly bury subsidence controlling caldera faults and regional cross faults within calderas other calderas and lava domes in the taupo volcanic zone tvz new zealand have been previously reported to show strong regional control at rotorua caldera there is a general lack of surface expression of faults but rhyolite lava domes are well exposed and aligned with regional structures that have been mapped outside of the caldera our summary of published data and new observations allows these lava domes to be subdivided into three groups based upon their petrology geochemistry relative age and spatial distribution 1 the kaikait huna group of pre collapse 451 ka crystal rich domes at the caldera boundary 2 the utuhina group of crystal poor high alkali post collapse domes c 200 ka surrounding the locus of collapse and directly related to the earlier 240 ka mamaku ignimbrite eruption and 3 the ruamata group of crystal rich more calcic less devitrified post collapse 60 36 ka domes further out from the collapse locus mapping of the morphology and internal structures of the utuhina group domes shows an ene wsw elongation direction and vent alignment which is parallel to and down strike of a the extensional rift orientation independently mapped either side of the caldera b the local caldera morphology and c structures mapped at nearby okataina caldera complex a second nw se trending orientation in the caldera morphology is parallel to a pre collapse basement fabric and has partially controlled the locations of the domes a third orientation is hinted at through consistent n s striking flow bands within ngongotaha dome which are parallel with a gravity anomaly we suggest that this orientation is a n s section of a caldera ring fault that links regional structures and was utilised during caldera collapse a subsequent dike intrusion also used this structure erupting a fissure style dome that contains radiating flow bands which mimic the orientation of the feeder dike however the structure morphology and location of post collapse lava domes generally echo the unburied regional structures outside the caldera indicating that dike intrusion also occurred along regional structures we suggest that the regional structures at rotorua caldera which are similar to those at okataina caldera complex show that the kink in the orientation of the rift across the tvz to the se of rotorua was active to at least 240 ka and possibly earlier this kink is significant due to its proximity and influence on both rotorua and okataina caldera systems and their associated geothermal fields we conclude that internal structures such as flow bands and morphology of lava domes are direct consequences of the shape and location of the feeder dike which in turn is controlled by the structure of the caldera and region we also suggest that lava dome eruptions at rotorua were from a series of small related nestled magma bodies a key outcome of this study is the reconstruction of the wider structure of the caldera and surrounding structure based upon the localised internal features distribution and morphology of related lava domes

asymmetric multiple block collapse at rotorua caldera taupo volcanic zone new zealand calderas worldwide have been classified according to their dominant collapse styles although there is a good deal of speculation about the processes involved recent laboratory experiments have tried to constrain these processes by modelling magma withdrawal and observing the effects on overlying materials however many other factors also contribute to final caldera morphology rotorua caldera formed during the eruption of the mamaku ignimbrite collapse structure and evolution of rotorua caldera is interpreted based its geophysical response geology and geomorphology and the stratigraphy of the mamaku ignimbrite rotorua caldera is situated at the edge of the extensional taupo volcanic zone in which major faults strike ne sw a second less dominant fault set strikes nw se these two fault sets have a strong influence on the morphology of rotorua caldera no one style of collapse can be applied to rotorua caldera it was formed during a single eruption but subsided as many blocks and shows features of trapdoor piecemeal and downsag types of collapse here rotorua caldera is described according to its composition activity and geometry as a rhyolitic single event asymmetric multiple block single locus collapse structure the mamaku ignimbrite is the only ignimbrite to have erupted from rotorua caldera extracaldera thickness of the mamaku ignimbrite is up to 145 m whereas inside the caldera it may be greater than 1 km thick the mamaku ignimbrite can be separated into a basal tephra sequence and main ignimbrite sequence the main ignimbrite sequence contains no observable flow unit boundaries but can be split into lower middle and upper parts lmi mmi umi respectively based on crystal content welding jointing devitrification and vapour phase alteration juvenile clasts within the ignimbrite comprise three consanguineous silicic pumice types and andesitic fragments only the most evolved pumice type occurs in the basal tephra sequence all three pumice types occur together throughout the main ignimbrite sequence whereas the andesitic fragments are only present in umi lithic lag breccias in umi indicate a late stage of caldera collapse concentration of lithic fragments increases towards the middle of the ignimbrite and may also reflect increased subsidence rate during an earlier stage collapse of rotorua caldera is thought to have occurred throughout the eruption of the main ignimbrite sequence of the mamaku ignimbrite allowing simultaneous eruption of all the different pumice types and causing the abrupt transition from deposition of the basal tephra sequence to the main ignimbrite sequence

the restless resurgent campi flegrei nested caldera italy constraints on its evolution and configuration abstract we have collected new stratigraphic data in the campi flegrei caldera through surface geological mapping and study of cores drilled to various depths we integrate these data with geological geochronological and geophysical constraints available in the literature to reconstruct the volcanic and deformational history of the caldera the caldera is a resurgent nested structure resulting from two main collapses related to the campanian ignimbrite 37 ka and the neapolitan yellow tuff 12 ka eruptions while the structure is affected by a broad subsidence ongoing local resurgence and unrest occur inside the younger nested caldera structure although most of the caldera floor consists of multiple structural blocks due to long term deformations magmas were able to erupt only in one sector of the resurgent part the caldera has shown signs of unrest during the past 25 years with short term deformations that have generated a net uplift of 3 5 m the short term deformations are related to the neapolitan yellow tuff caldera resurgence and interpreted as the net result of brittle and ductile components the long term deformations likely represent the sum of the permanent brittle component of each short term deformational event

sedimentology and allostratigraphy of post 240 ka to pre 26 5 ka lacustrine terraces at intracaldera lake rotorua taupo volcanic zone new zealand abstract lake rotorua partially occupies a nearly circular 20 km diameter volcano tectonic depression formed at c 240 ka by eruption of the voluminous mamaku ignimbrite three distinct lacustrine littoral terraces defined on the basis of contrasting geomorphology and field relations and separated by tephrostratigraphically dateable unconformities and basin floor disconformities fringe much of the lake basin they are here correlated with former high stands of the lake which resulted from the blockage and re establishment of a number of alternative outlets due to tectonic activity and volcanism at both the host and adjacent volcanic centres the unconformities allow division of the deposits into three allostratigraphic units each of which is then characterised by elevation and sediment provenance the

elliptical calderas in active tectonic settings an experimental approach abstract caldera volcanoes form due to collapse of a magma chamber roof into the underlying magma chamber many field theoretical and experimental studies have postulated that calderas are delimited by reverse ring faults and are surrounded by peripheral concentric normal faults in the simplest theoretical scenario circular magma chambers produce circular calderas many calderas however are elliptical in shape particularly those in extensional and compressive tectonic settings several factors may explain elliptical calderas the first is the presence of an elliptical magma chamber established by for instance preferential intrusion along pre existing basement structures or differential spalling of the magma chamber walls the second is the overlap nesting of several discrete calderas to form a single larger elliptical structure the third is asymmetric subsidence the fourth is variable pre collapse topography a fifth possible factor is distortion of the caldera faults by the regional stress field during caldera formation a sixth factor is the post collapse distortion of the caldera structure due to continued regional deformation to better understand relationships between caldera surface expression reservoir geometry and regional tectonic stresses we conducted scaled analogue experiments these experiments examined the impact of regional stress and associated structures on calderas formed during evacuation of reservoirs circular rubber balloons of known dimensions and depths the results show that in principle calderas produced in compression extension experiments are elongated parallel to the direction of minimum horizontal compressive stress despite the chamber beneath being circular in plan view as a consequence model ring fault orientation varied from steeply dipping where striking perpendicular to the minimum horizontal regional compressive stress to shallower dips where striking parallel to the minimum horizontal regional compressive stress this leads us to suggest that the influence of a regional stress field on caldera fault orientation during and or after caldera formation may be significant in the development of elliptical calderas in addition such variation of caldera ring fault dip from steep to relatively shallow could influence location and behaviour of ring fissure eruptions

volcanic and structural evolution of the okataina volcanic centre dominantly silicic volcanism associated with the taupo rift new zealand article the okataina volcanic centre ovc contains the northeasternmost caldera complex in onshore taupo volcanic zone tvz new zealand sited largely within the taupo rift pyroclastic fall deposits and ignimbrites deposited in the bay of plenty coast area between 420 and 625 ka were probably erupted from ovc and these provide a maximum age for the centre the earliest ignimbrite for which there is good evidence for eruption from ovc is the c 550 ka quartz biotite ignimbrite exposed to the west of lake okataina and to se of ovc this ignimbrite probably correlates with one of the early ignimbrites found in the kawerau geothermal wells and is large enough to have been accompanied by caldera collapse it was followed by extensive rhyolitic explosive eruptions of the murupara subgroup culminating with eruption of the matahina ignimbrite at c 325 ka this c 160 km 3 magma volume eruption was accompanied by caldera collapse to form the southern part of the present day okataina caldera complex a long duration sequence of rhyolite lavas and pyroclastics was then erupted on the southern and western sides of ovc before eruption of the 100 km

stability of dike intrusion along preexisting fractures we investigate the ability of magma to propagate along preexisting fractures oblique to the least compressive stress relaxation of the preexisting shear stress to zero over the portion of the fracture dilated by magma the dike results in slip for some distance along the closed portion of the fracture ahead of the dike tip and a stress concentration near the dike tip this could lead to the production of new tensile cracks oblique to the parent dike that could capture the flow if the shear stress resolved on the fracture plane is perpendicular to the fracture front mode i ii the front may deviate along its entire length if the shear stress is parallel to the fracture front mode i iii the front may splay into segments for mode i ii dikes the maximum tensile stress occurs at the dike tip and is parallel to the dike if the effective tensile stress exceeds the rock tensile strength then the intruding magma rather than dilating the existing fracture is expected to propagate into a self generated crack analogous to the wing cracks observed to form at the tips of pure mode ii fractures for mode i iii dikes the maximum tensile stress lies within the plane of the dike and is oriented at some angle that depends upon the far field boundary conditions even if the magma pressure exceeds the ambient normal stress it appears to be very difficult for dikes to intrude into preexisting fractures unless one or more of the following conditions is satisfied 1 the fracture is nearly perpendicular to the least compressive stress 2 the resolved shear stress on the fracture is small compared to the excess magma pressure i e the ratio of shear to opening of the dike walls is small 3 the effective ambient dike normal stress is small compared to the rock tensile strength this indicates that it may be quite difficult for dikes emerging from midcrustal to lower crustal depths to follow faults

chemical mass transfer modelling of ore forming hydrothermal systems current practise and problems abstract chemical mass transfer modelling is a numerical approach to predicting the progress of multicomponent fluid rock reactions in natural hydrothermal systems based on thermodynamic data for minerals and fluid species quantitative simulations of hydrothermal wall rock alteration and ore mineral deposition can be used to develop and test geological models for ore formation which are a basis for mineral exploration and resource assessment in practice the application of thermodynamic mass transfer modelling to specific ore forming systems faces two main problems even for the limiting assumption of local equilibration between fluids and minerals the first problem relates to the geometry of fluid rock interaction where the scheme of the model must be adjusted to the geological question of interest one dimensional reactor models defining reaction progress as a function of integrated fluid flux along a path through a chemically reactive rock do not necessarily provide a more realistic description of chemical mass transfer than simple titration models without temporal and spatial dimension because in most ore depositing systems the fluids are partially channelized by structures like veins or faults the efficiency of metal extraction at the ore deposition site is commonly determined by a sensitive balance between fluid focusing on one hand and wall rock reaction promoting ore mineral precipitation on the other an example of gold and scheelite mineralization associated with mesothermal quartz veins illustrates how ore deposition and alteration zoning parallel to the main fluid flow direction in partially channelized systems can be described by a two dimensional multibox model the second problem relates to the extent and quality of thermodynamic data explicit consideration of fe bearing silicate solid solutions is essential for predicting realistic mass balance in complex fluid silicate sulphide reactions associated with hydrothermal ore formation although a high level of internal consistency of multicomponent data sets has been achieved by simultaneous fitting of multiple thermodynamic and equilibrium measurements significant inconsistencies persist among the most comprehensive data compilations published for the three main groups of species relevant to hydrothermal ore deposits aqueous species in high temperature aqueous brines silicate oxide carbonate minerals including fe mg silicates and sulphur bearing minerals including sulphides and sulphates discrepancies between thermodynamic predictions and observed brine composition and mineral assemblages in the salton sea geothermal system suggest that the redox scale for rock forming silicates may be inconsistent with that of sulphides and aqueous s c o h species this analysis is preliminary but illustrates the importance of field testing of thermodynamic data particularly for hydrothermal conditions between 150 and 450 c which lie between the high temperatures of reliable equilibrium experiments among rock forming minerals 500 c and the low temperatures of many experiments defining the thermodynamics of aqueous species mostly

caldera resurgence during magma replenishment and rejuvenation at valles and lake city calderas a key question in volcanology is the driving mechanisms of resurgence at active recently active and ancient calderas valles caldera in new mexico and lake city caldera in colorado are well studied resurgent structures which provide three crucial clues for understanding the resurgence process 1 within the limits of 40ar 39ar dating techniques resurgence and hydrothermal alteration at both calderas occurred very quickly after the caldera forming eruptions tens of thousands of years or less 2 immediately before and during resurgence dacite magma was intruded and or erupted into each system this magma is chemically distinct from rhyolite magma which was resident in each system 3 at least 1 km of structural uplift occurred along regional and subsidence faults which were closely associated with shallow intrusions or lava domes of dacite magma these observations demonstrate that resurgence at these two volcanoes is temporally linked to caldera subsidence with the upward migration of dacite magma as the driver of resurgence recharge of dacite magma occurs as a response to loss of lithostatic load during the caldera forming eruption flow of dacite into the shallow magmatic system is facilitated by regional fault systems which provide pathways for magma ascent once the dacite enters the system it is able to heat remobilize and mingle with residual crystal rich rhyolite remaining in the shallow magma chamber dacite and remobilized rhyolite rise buoyantly to form laccoliths by lifting the chamber roof and producing surface resurgent uplift the resurgent deformation caused by magma ascent fractures the chamber roof increasing its structural permeability and allowing both rhyolite and dacite magmas to intrude and or erupt together this sequence of events also promotes the development of magmatic hydrothermal systems and ore deposits injection of dacite magma into the shallow rhyolite magma chamber provides a source of heat and magmatic volatiles while resurgent deformation and fracturing increase the permeability of the system these changes allow magmatic volatiles to rise and meteoric fluids to percolate downward favouring the development of hydrothermal convection cells which are driven by hot magma the end result is a vigorous hydrothermal system which is driven by magma recharge

formation of the maturin foreland basin eastern venezuela thrust sheet loading or subduction dynamic topography 1 the maturin basin in eastern venezuela is considered a good example of a peripheral foreland basin earthquake and tomographic data indicate that eastern venezuela is affected by the oblique subduction of the south american plate underneath the caribbean plate new forward flexural isostatic modeling of eastern venezuela has been carried out in order to determine whether the maturin basin was generated purely by thrust sheet loading from the serrania and monagas foreland thrust belts a sequence of forward models from middle miocene to present was generated for 3 profiles across the serrania del interior thrust belt the monagas foreland thrust belt and the maturin foreland basin the predictions of these models are constrained using seismic reflection and well data the flexural isostatic modeling shows that thrust sheet loading associated with the serrania del interior and monagas foreland thrust belts is insufficient to generate the observed subsidence within the maturin basin dynamic fluid flow modeling of subduction related dynamic topography of eastern venezuela has been used to investigate the influence of south american plate subduction on the generation of the accommodation space observed in the maturin basin fluid flow modeling of subduction related dynamic topography suggests that the subduction of the south american lithospheric mantle caused downward deflection of the south american crust affecting the maturin basin and the serrania thrust belt this modeling suggests that the maturin basin subsidence has two components 55 related to thrust sheet loading and 45 driven by continental subduction

a geophysical study of the taupo volcanic zone new zealand the taupo volcanic zone is a region of intense volcanic activity from which over 16 000 km3 of lavas and pyroclastics have been erupted since the late pliocene analysis of gravity and magnetic anomalies over the zone has revealed the presence of five major centers each associated with an approximately circular negative gravity anomaly and a positive pseudogravity anomaly these centers are interpreted as collapse features resulting from large scale withdrawal of magma from the upper crust four of the depressions occur beneath recognized volcanic centers or calderas the fifth kapenga is inferred to underlie an extinct hidden volcanic center three dimensional models of the thicknesses of low density and magnetized rocks in the taupo volcanic zone have been determined by inversion of gravity and magnetic anomalies beneath three of the centers the thicknesses of low density and magnetized rocks are approximately equal 2 3 km that is the collapse structures are infilled by magnetized volcanics however there is a significant discrepancy between the thicknesses of the gravity 5 km and magnetic models 1 5 km in the region of the okataina volcanic centre it is therefore suggested that a significant volume of low density nonmagnetic rock possibly acidic magma underlies okataina

runup of tsunami waves in u shaped bays the problem of tsunami wave shoaling and runup in u shaped bays such as fjords and underwater canyons is studied in the framework of 1d shallow water theory with the use of an assumption of the uniform current on the cross section the wave shoaling in bays when the depth varies smoothly along the channel axis is studied with the use of asymptotic approach in this case a weak reflection provides significant shoaling effects the existence of traveling progressive waves propagating in bays when the water depth changes significantly along the channel axis is studied within rigorous solutions of the shallow water theory it is shown that traveling waves do exist for certain bay bathymetry configurations and may propagate over large distances without reflection the tsunami runup in such bays is significantly larger than for a plane beach