southern kermadec submarine caldera arc volcanoes sw pacific caldera formation by effusive and pyroclastic eruption abstract three newly identified submarine caldera volcanoes brothers healy and rumble ii west of the southern kermadec arc within water depths 80 and low density 0 3 0 5 g cm 3 erupted pumiceous clasts these observations are interpreted as evidence of subaqueously quenched pyroclastic eruption s sheathed by ambient water flashing to steam discharging some 5 km3 of pyroclastic material from healy volcano caldera collapse is inferred to be penecontemporeous with the pyroclastic eruption s although it is possible formation as an explosive crater occurred but we consider the latter unlikely given the volume of erupted material and water depth extrapolation of these observations to other submarine arcs indicates pyroclastic eruption of silicic magmas and syn eruptive caldera collapse is possible within water depths of 500 1000 m

morphology and origin of the osbourn trough the osbourn trough is a 900 km long east west trending gravity low visible in satellite altimetry data which intersects the tonga trench at 25 30 s a recent survey collected gravity magnetic echo sounder and swath bathymetry data on three adjacent north south trending ship tracks centered on the trough the linear gravity low is 20 30 mgal less than the regional value and is accompanied by a flat lying 200 500 m deep sediment filled valley swath bathymetry images reveal several parallel east west trending linear ridges and valleys on either side of the main trough as well as other morphologic features characteristic of relict spreading centers including a prominent inside corner high and possible pseudo fault trace the presence of magnetic anomalies possibly anomalies 33 and 32 suggests that the seafloor here was formed after the end of the cretaceous normal superchron anomaly 34 these data support the conclusion that this trough is a spreading center which stopped spreading in late cretaceous time the existence of this feature has important implications for tectonic reconstructions in this region the osbourn trough could be part of the fossil spreading center between the pacific plate and a fragment of the phoenix plate the bellingshausen plate this would require the seafloor between the osbourn trough and the chatham rise to the south to be a remnant fragment of the bellingshausen plate this remnant may have joined to the pacific plate when the hikurangi plateau entered the gondwana subduction zone at the chatham rise possibly causing the cessation of spreading on the osbourn trough

backarc rifting constructional volcanism and nascent disorganised spreading in the southern havre trough backarc rifts sw pacific high resolution multibeam em300 and seabeam data of the southern havre trough sht combined with observations and sample collections from the submersible shinkai6500 and deep tow camera are used to develop a model for the evolution and magmatism of this backarc system the havre trough and the associated kermadec arc are the product of westward subduction at the pacific australian plate boundary detailed studies focus on newly discovered features including a seamount saito seamount and a deep graben ngatoroirangi rift 4000 m water depth floored with a constructional axial volcanic ridge 5 km in length and in excess of 200 m high both of which are characterised by pillow and lobate flows estimated at elongate volcanic ridges at 35 15 s and 34 30 s and backarc seamounts 35 30 s 178 30 e occur at the eastern margin of the sht similar seafloor morphology is observed in the central and western portions of the basin suggesting that recent volcanism may be broadly distributed across the backarc mass balance modelling indicates a maximum crustal thickness of 11 km to 4000 m spreading systems these discontinuous spreading systems are characterised by failed rifts rift segmentation and propagation successive episodes of magmatic intrusion into thinned faulted arc basement results in defocused asymmetrical accretion cross arc volcanic chains isolated volcanoes and underlying basement plateaus are interpreted to represent a cap of recent extrusives however they may also be composed entirely of newly accreted crust and the spatially extensive basement fabric of elongated volcanic ridges may be the surface expression of pervasive dike intrusion that has thoroughly penetrated and essentially replaced the original arc crust with newly accreted intrusives

estimating flow heterogeneity in natural fracture systems abstract examples of small to medium scale fault systems have been mapped in jurassic sedimentary rocks in north somerset england these examples include contractional and dilational strike slip oversteps as well as normal faults these maps form the basis of calculations performed to investigate heterogeneity in natural fracture systems with the aim of predicting fluid flow localisation in different fault styles as there is no way to measure fracture aperture directly we use vein thickness to represent an integrated flow path or palaeo aperture from which we derive a representation of the flow distribution three different methods are used to estimate flow heterogeneity based on 1 fracture density the ratio of fracture length to area 2 fracture aperture fracture porosity and 3 hydraulic conductance fracture permeability normalised to the pressure gradient and fluid properties our results show that fracture density and hydraulic conductance are poorly correlated and that fracture density does not fully represent the natural heterogeneity of fracture systems fracture aperture and hydraulic conductance indicate stronger degrees of flow localisation different types of structures also seem to display characteristic and predictable patterns of heterogeneity normal fault systems show the highest magnitude of localisation along the faults rather than in the relay ramps while contractional and dilational strike slip systems show very strong localisation in the faults and oversteps respectively in all cases the amount of damage in the oversteps can modify such patterns of heterogeneity

effect of stress fields on magma chamber stability and the formation of collapse calderas 1 the summits of many of the earth s and other planets larger volcanoes are occupied by calderas that formed by collapse into an evacuating underlying magma chamber these collapse calderas are typically several tens of square kilometers in area and are commonly elliptical in shape we show that the long axes of late quaternary collapse calderas in the kenya rift valley the western basin and range province the snake river yellowstone plateau and the iceland rift zone are parallel to the upper crustal minimum horizontal stress direction sh as determined by independent criteria we suggest that circular magma chambers beneath these volcanoes became elliptical by stress induced spalling of their chamber walls by a mechanism that is analogous to the formation of breakouts in boreholes and tunnels in breakouts the hole becomes elongate parallel to the far field minimum stress in the kenya rift late pleistocene caldera collapse was accompanied by a 45 rotation of sh and an increase in the magnitude of the maximum horizontal stress sh the breakout model predicts increasingly unstable caldera walls under these conditions a possible explanation for the sudden appearance of so many collapse events in a volcanic setting that had never experienced them before this mechanism of stress change induced collapse may have played a role in other caldera settings

from rifting to active spreading in the lau basin havre trough backarc system sw pacific locking unlocking induced by seamount chain subduction associated with pacific australia plate convergence the lau basin havre trough is an active back arc basin that has been opened since 5 5 ma by rifting and southward propagating oceanic spreading current back arc opening rates decrease from 159 mm yr 1 in the northern lau basin to 15 mm y 1 in the southern havre trough major tectonic changes occur at the transition between havre trough rifting and full oceanic spreading of the eastern lau spreading center elsc where the oblique to trench westward subducting louisville seamount chain lsc sweeps southwards along the tonga trench new swath bathymetry seismic reflection data and limited rock sampling in this area constrain a tectonic and kinematic back arc model that incorporates the effects of lsc subduction the elsc which extends southward to 24 55 s forms a deep rift valley propagating southward through older rifted arc basement present day seismicity and fresh and fractured pillow lavas at 23 42 s are consistent with rift valley neovolcanism conversely the northern havre trough has low seismicity and rifted volcanic basement ridges trending 25 45 oblique to the basin axis consistent with low levels of extensional tectonism and volcanism this latter structural fabric is interpreted as an early stage of rifting that is now locked due to compression on the arc exerted by lsc subduction while in the lau basin such effects have passed as the lsc swept along the tonga trench it is proposed that the lau havre back arc opening is controlled by tectonic constraints exerted at the limits of the system by the lsc subduction which determines the southward migration of the tonga arc pole of rotation and associated lau basin opening a discrete three stage back arc opening evolution is proposed comprising 1 an initial phase of back arc rifting along the whole length of the plate boundary beginning at 6 5 ma 2 a subsequent phase mostly present in the southern part of the back arc domain and still active in the havre trough of transpression and transtension starting at 4 ma in the north as the lsc starts to subduct and sweeps southward along the tonga trench and 3 a renewed opening phase in the northern segment of the back arc domain with rifting and spreading starting at 3 5 ma as subduction of the lsc along the northern tonga trench is progressively completed

morphometric analysis of the submarine arc volcano monowai tofua kermadec arc to decipher tectono magmatic interactions morphometric analysis of multibeam bathymetry and backscatter data is applied to monowai a submarine volcano of the active tofua kermadec arc to map and document the structure and evolution of the volcanic centre low rates of erosion and sedimentation and pervasive tectonic and magmatic processes allow quantification through detailed structural analysis and measurement of deformation the slope aspect curvature rugosity and hydrology flow tools of arcgis provide a robust structural interpretation and the development of a model of monowai evolution a nested caldera structure with a volume of 31 km3 and a stratovolcano of 18 km3 dominate the magmatic constructs the outer caldera is elongate along 125 and the inner caldera along 135 numerous parasitic cones and fissure ridges are also observed oriented at 039 and 041 respectively northeast trending faults with a regional average strike of 031 are widespread within this part of the backarc forming a nascent rift graben to the west of the monowai caldera complex the distribution of throw varies spatially reaching a maximum total along rift of 320 m and across rift of 120 m with greater throw values measured in the west elongation directions of the two nested calderas are near perpendicular to the trends of faults and fissure ridges the inner caldera is more orthogonal to the magmatic constructs fissure ridges and aligned vent cones and the outer caldera is approximately orthogonal to the regional fault fabric suggesting a strong interaction between magmatic and tectonic processes and the directions of the horizontal principal stress we present a detailed morphometric analysis of these relationships and the data are used to interpret the spatial and temporal evolution of the tectono magmatic system at monowai and classify the type of rifting as transtensional similar analysis is possible elsewhere in the kermadec backarc and within other regions of submarine volcanism

oblique rifting along the central and southern kermadec arc front 30 36 s sw pacific we present a series of eleven structural maps of the central kermadec arc front between 30 s and 35 50s interpreted from multibeam bathymetric data these maps show the structural morphology of eighteen submarine arc volcanoes proximal to the havre backarc providing a critical window into the tectonomagmatic processes that operate at divergent arcs transitional to seafloor spreading each arc volcano unaffected by subaerial processes shows the structural imprint of oblique backarc rifting providing an exceptional opportunity to evaluate tectonic influences on edifice construction and destruction mapped seafloor structures include faults volcanic ridges aligned vents and cones cones aligned with faults elongate calderas and structurally controlled sector collapse in addition to the structural maps we present the results of quantitative analyses of fault orientation and growth behaviors we demonstrate that 50 of identified faults strike ne sw between 030 and 060 with a modal value of 047 evidence in support of an extension axis dextrally oblique to the nne trend of the rift further to this minimum and maximum values for the extension axis are calculated as 137 and 150 perpendicular to the modal strikes for all identified faults and for faults within the most oblique surveyed backarc rift domain respectively these values confirm moderate obliquity of opening along the havre rift with the sht opening slightly less obliquely than the nht consistent with accommodation of a lesser partitioned component of dextral pacific australian plate convergence

collapse and reconstruction of monowai submarine volcano kermadec arc 1998 2004 monowai submarine volcano is one of the three most historically active volcanoes of the kermadec arc repeat multibeam surveys of monowai cone from september 1998 and september 2004 and t wave data recorded by the reseau sismique polynesien network for the same period document the collapse and subsequent regrowth of the cone within this 6 a period grid differencing of the two bathymetric data sets acquired 6 a apart reveals that a landslide 2230 m long occurred between the surveys within which a postcollapse cone and talus ridge 0 023 km3 in volume subsequently formed the volume of this collapse minus postcollapse construction is 0 085 km3 we interpret an unusual strong amplitude t wave event on 24 may 2002 as recording hot landsliding where the 100 to 160 m thick collapse has unroofed the uppermost parts of the vent conduit with the subsequent explosive interaction and cooling of hot magma and volcaniclastic rubble with ambient seawater this interpretation is consistent with the lack of emergent events sharp onset and large amplitude of the 24 may 2002 t waves the subsequent 2500 t wave events between november 2002 and september 2004 occurred in swarms with emerging and waning activity and with typical explosive volcanic acoustic signatures which are interpreted as recording the regrowth of an 90 m high cone back to a near 1998 elevation at an average rate of 47 m a 1 this study provides 1 a lower bound for frequency magnitude relationships of landsliding for submarine arc volcanoes and 2 estimates of 0 013 km3 a 1 of submarine cone growth during eruptive cycles

collisional model for rapid fore arc block rotations arc curvature and episodic back arc rifting in subduction settings 1 we review geophysical and geological data from 23 active and ancient plate boundaries to document a compelling spatial and temporal relationship between collision plate boundary curvature rapid tectonic rotations and the occurrence of back arc rifting our observations support a conceptual model where the change from subduction to collision causes rapid fore arc rotation when viewed in a reference frame relative to the bounding tectonic plates leading to marked plate boundary curvature our global compilation reveals that most active back arc rifts are associated with rapidly rotating fore arcs and nearby collisions thus we propose that collision and rapid fore arc rotations play a major role in the evolution and kinematics of back arc basins we conduct numerical modeling to better understand the physical processes behind these observed rapid tectonic rotations at convergent margins our results suggest that the presence of an indentor or choke point in the subduction system e g collision can generate rapid rotation of the fore arc about a nearby pole and lead to back arc rifting the rate of fore arc rotation and back arc rifting depends on the incoming indentor velocity and can be greatly enhanced by slab rollback and the presence of a low viscosity back arc where viscosity of the back arc is low fore arc rotation dominates where back arc viscosity is high the formation of strike slip faults and tectonic escape dominates our observational and model derived results illustrate that shallow crustal forces produced by the entry of buoyant features into subduction zones are a fundamental mechanism for the generation of fore arc block rotations plate boundary curvature back arc rift evolution and tectonic escape in subduction systems rollback of the subducting slab within the mantle will certainly enhance the processes we describe but it is not the only driving force

cyclic eruptions and sector collapses at monowai submarine volcano kermadec arc 1998 2007 1 repeated multibeam bathymetric surveys at monowai cone a shallow submarine basaltic volcano and part of the monowai volcanic center in the northern kermadec arc were conducted in 1998 2004 and 2007 these surveys document dramatic depth changes at the volcano including negative changes up to 176 m from two sector collapses and positive changes up to 138 m from volcanic reconstruction near the summit and debris avalanche deposits downslope of the slide scars one sector collapse occurred on the se slope between 1998 and 2004 with a volume of 0 09 km3 and another occurred on the sw slope between 2004 and 2007 with a volume of 0 04 km3 the volume of positive depth change due to addition of volcanic material by eruption is of the same order 0 05 km3 between 1998 and 2004 and 0 06 km3 between 2004 and 2007 during these time intervals monitoring by the polynesian seismic network detected frequent t wave swarms at monowai indicative of explosive eruptive activity every few months an unusual t wave swarm on 24 may 2002 was previously interpreted as the collapse event between the 1998 and 2004 surveys but no similarly anomalous t waves were detected between 2004 and 2007 probably because the polynesian seismic network stations were acoustically shadowed from the second slide event we interpret that the sector collapses on monowai are caused by the unstable loading of fragmental erupted material on the summit and steep upper slopes of the volcano 20 moreover there appears to be a cyclic pattern in which recurrent eruptions oversteepen the cone and periodically lead to collapse events that transport volcaniclastic material downslope to the lower apron of the volcano volumetric rate calculations suggest that these two processes may be more or less in equilibrium the repeated collapses at monowai are relatively modest in volume involving only 0 1 0 5 of the edifice volume have occurred much more frequently than is estimated for larger debris avalanches at subaerial volcanoes and may be characteristic of how persistently active shallow submarine arc volcanoes grow

models of fracture orientation at oblique spreading centres three models are proposed for the orientation of extensional faults and dykes at mid ocean ridges based on their relationship to the ridge axis and the relative plate separation vector these models predict four ridge geometries allowing them to be tested by orientation data from 17 different sites within the earth9s oceans a transtensional model is shown to be generally applicable to the structure of mid ocean ridges with special conditions required for a departure from it spreading rate influences ridge geometry with intermediate and fast spreading ridges more likely to have an orthogonal spreading geometry which is an end member case of the transtensional model

magmatic and tectonic history of iceland s western rift zone at lake thingvallavatn high rates of holocene sedimentation in a lake spanning the thingvellir rift zone of western iceland provide an unusual opportunity to study the interaction of tectonic and magmatic processes on timescales of thousands of years lake thingvallavatn is oriented sw ne parallel to the trend of normal faults and fissures which extend northeast from hengill a central volcano system thingvallavatn s lake sediments provide a continuous high fidelity record of tectono magmatic processes chirp sub bottom profiler and sidescan records together with sediment core information enabled the lake stratigraphy to be constrained well since the emplacement of a post glacial lava at 9 1 0 3 ka this lava together with three younger horizons enabled detailed study of the main tectonic and magmatic events a major hengill volcanic event which controlled the development of the present day lake morphology occurred at 1 9 ka with the eruption of a scoria cone within the lake sandey during this event the nesjahraun lava was erupted into the southern part of the lake the sandey scoria cone was formed and major faulting and subsidence occurred in the northern part of the lake resulting in the formation of an asymmetrical rift within the southern part of the lake a deformed sequence of sediments of age 2 9 1 5 ka between undeformed younger and older sediments indicate that liquefaction phenomena are associated with the emplacement of the nesjahraun lava analysis of fault displacement reveals that the total throw summed over all faults across the width of the rift zone is approximately constant 110 130 m along the long axis of the rift we estimate an extension rate on the faults of 3 3 8 2 mm yr 1 since 9 1 ka assuming fault dips of 60 75 which represents 17 43 of the total plate boundary extension estimated from global plate motion inversion we speculate that the remaining extension must either be taken up elsewhere in iceland for example in the eastern rift zone or along the south island seismic zone or that extension estimated over the last 9kyr underestimates the long term extension rate due to incomplete sampling of the episodic magmatic component

neotectonics in central mexico regional neotectonic activity in central mexico was mapped through analysis of eleven landsat thematic mapper images the study area stretches from mexico city on the east to the gulf of california on the west between 17 and 21 n latitude fault scarps of plio quaternary age define several large scale tectonic features within the mexican volcanic belt dominated by rifting transtension and shear with probable sinistral components three large crustal blocks south of the mexican volcanic belt are separated from the north american plate and from each other by zones of neotectonic activity that express the relative motions between the adjacent blocks a simple vector diagram for plates and crustal blocks in central mexico has been constructed using information from the literature combined with the orientations of fault zones as mapped in this study the relative motion between the blocks varies from about 2 5 to 8 mm year 1 which is comparable to motions of crustal blocks in areas of active rifting in other parts of the world in the mexican volcanic belt there is a clear relationship between volcanism and neotectonic activity fault zones that traverse nearly the entire region have the same location and orientation as the volcanic belt this may indicate that deformation within the crust of the overriding slab plays a significant role in determining the unusual orientation of the mexican volcanic belt relative to the trench the ultimate factor controlling the location of plio quaternary volcanism and tectonism in central mexico may be large zones of crustal weakness formed during major mesozoic and cenozoic tectonic events

tectonic stress controls on ascent and emplacement of magmas abstract the tectonic stresses can significantly affect the propagation of a magma filled crack it has been pointed out that the rheological boundaries control the emplacement of magmas through the effect of stress however it has not been clarified how the role of rheological boundaries depends on the regional tectonic and thermal states we have evaluated the role of rheological boundaries under various tectonic and thermal conditions and found that the level of magma emplacement may jump according to the changes in the tectonic force or the surface heat flow the stress profiles were estimated by a simple model of lithospheric deformation we employed a three layer model of the lithosphere the upper crust the lower crust and the upper mantle have different rheological properties a constant horizontal force is applied to the lithosphere and the horizontal strain is assumed to be independent of depth when realistic tectonic forces 10 11 n m are applied the rheological boundaries mainly control the emplacement of magma the emplacement is expected at the moho the upper lower crust boundary and the brittle ductile boundary for lower tectonic forces 11 n m the tectonic stress no longer plays an important role in the emplacement of magmas when the tectonic stress controls the emplacement the roles of rheological boundaries strongly depend on the surface heat flow when the surface heat flow is relatively high 80 mw m 2 the stress in the mantle is quite low and the moho cannot trap ascending magmas for relatively low heat flow 2 on the other hand the moho acts as a magma trap and the upper lower crust boundary acts as a magma trap only when the magma supply rate is sufficiently high our results suggest that the emplacement depth can change responding to the change in the tectonic force and or that in the surface heat flow this may provide us a key to understand the relation between the evolution of a volcanic region and its tectonic and or thermal history

structural control of volcanism and caldera development in the transtensional taupo volcanic zone new zealand abstract the taupo volcanic zone tvz new zealand comprises several segments with variable components of extension and is characterised by longitudinal segmentation into a central zone dominated by rhyolitic calderas and extremities with only andesitic composite volcanoes modern

the link between volcanism and tectonics in the southern volcanic zone of the chilean andes a review abstract the nature of the interplay between tectonics and volcanism is a major question in continental margin tectonics the southern andes volcanic zone svz located at the obliquely convergent nazca south america plate margin between 33 s and 46 s offers a unique opportunity to address this question because of along strike changes in crustal thickness tectonic style and well constrained long term and short term kinematic history the complex interaction between tectonic and magmatic processes is evidenced by both the architecture and geochemical signature of volcanic systems main first order factors accounting for the along strike variations in the nature and composition of volcanism are crustal thickness and the existence of a major intra arc fault system the liquine ofqui fault zone lofz second order factors include the local nature of the volcanic arc basement two main categories of volcano tectonic associations have been identified according to the spatial distribution and internal organization of individual volcanoes and clusters of volcanoes with respect to both the overall strike of the volcanic arc and the first and second order active inactive basement faults kinematically coupled associations those that are directly related to the current dextral transpressional tectonic regime include ne trending volcanic alignments of stratovolcanoes and or monogenetic cones kinematically uncoupled associations in which coupling with the current regime is not required include stratovolcanoes built on top of ancient reverse and strike slip faults of the volcanic arc basement and monogenetic cones lying along master faults of the lofz whereas mostly primitive magmas are found in the first category more evolved terms can occur genetically associated with the second category we propose a simplified three dimensional model for the magma plumbing system along and across the svz that integrates kinematically coupled and kinematically uncoupled volcano tectonic associations within the framework of first and second order geological and structural constraints

injection and arrest of dykes implications for volcanic hazards dykes are the principal channels through which magma reaches the surface in volcanic eruptions for this reason dykes observed in the field are commonly assumed to be feeders to lava flows the actual proportion of dykes reaching the surface is however poorly known in order to develop models for the purpose of estimating volcanic hazard this proportion must be known this follows because such models should not only consider the probability of dykes being injected from magma chambers during periods of unrest in the associated volcanoes but also the probability of the injected dykes being arrested this paper presents field data on several thousand dykes from iceland and tenerife canary islands indicating that many and probably most dykes become arrested at various crustal levels and never reach the surface to feed eruptions using the results of analytical and numerical models it is shown that for common loading conditions the stress field in the vicinity of a magma chamber may favour the injection and propagation of dykes while the stress field at a certain distance from the chamber favours dyke arrest this means that many dykes that are injected from the chamber propagate only for a very limited distance from the chamber to the point where they become arrested the implication is that during periods of unrest in volcanoes the probability of volcanic eruption is only a small fraction of the probability of dyke injection from the source magma chamber

submarine magmatic hydrothermal systems at the monowai volcanic center kermadec arc the monowai volcanic center is located at the midpoint along the 2 530 km long tonga kermadec arc system the monowai volcanic center is comprised of a large elongate caldera monowai caldera area 35 km2 depth to caldera floor 1 590 m which has formed within an older caldera some 84 km2 in area to the south of this nested caldera system is a large composite volcano monowai cone which rises to within 100 m of the sea surface and which has been volcanically active for the past several decades mafic volcanic rocks dominate the monowai volcanic center basalts are the most common rock type recovered from the cone whereas basaltic andesites are common within the caldera hydrothermal plume mapping has shown at least three major hydrothermal systems associated with the caldera and cone 1 the summit of the cone 2 low temperature venting 60 c mussel ridge on the southwestern wall of the caldera and 3 a deeper caldera source with higher temperature venting that has yet to be observed the cone summit plume shows large anomalies in ph a shift of 2 00 ph units and 3he 358 and noticeable h2s up to 32 m and ch4 up to 900 nm the summit plume is also metal rich with elevated total dissolvable fe tdfe up to 4 200 nm tdmn up to 412 nm and tdfe tdmn up to 20 4 particulate samples have elevated fe si al and ti consistent with addition to the hydrothermal fluid from acidic water rock reaction plumes extending from 1 000 to 1 400 m depth provide evidence for a major hydrothermal vent system in the caldera the caldera plume has lower values for tdfe and tdmn although some samples show higher tdmn concentrations than the cone summit plume caldera plume samples are also relatively gas poor i e no h2s detected ph shift of 0 06 ph units ch4 concentrations up to 26 nm the composition of the hydrothermal plumes in the caldera have higher metal contents than the sampled vent fluids along mussel ridge requiring that the source of the caldera plumes is at greater depth and likely of higher temperature minor plumes detected as light scattering anomalies but with no 3he anomalies down the northern flank of the monowai caldera most likely represent remobilization of volcanic debris from the volcano flanks we believe the monowai volcanic center is host to a robust magmatic hydrothermal system with significant differences in the style and composition of venting at the cone and caldera sites at the cone the large shifts in ph very high 3he values elevated tdfe and tdfe tdmn and the h2s and ch4 rich nature of the plume fluids together with elevated ti p v s and al in hydrothermal particulates indicates significant magmatic volatile metal contributions in the hydrothermal system coupled with aggressive acidic water rock interaction by contrast the caldera has low tdfe tdmn in hydrothermal plumes however elevated al and ti contents in caldera particulate samples combined with the presence of alunite pyrophyllite sulfide minerals and native sulfur in samples from mussel ridge suggest past and perhaps recent acid volatile rich venting and active fe sulfide formation in the subsurface

dike induced faulting in rift zones of iceland and afar geodetic data and field observations demonstrate that the emplacement of dikes in volcanic rift zones frequently generates normal faulting and graben subsidence at the earth9s surface elastic modeling of the vertical ground surface displacements above dikes and faults indicates that the extent of graben subsidence can be achieved only if fault slip extends virtually to or beyond the dike plane at depth a mechanical model that includes dikes and frictional faults shows that dike opening tends to compress and lock faults located to either side of the dike therefore slip extending into or beyond the dike cavity must occur either 1 on faults that intersect the dike near its top above the zone of dike induced compression or 2 on faults that slip ahead of the dike as it propagates laterally data from iceland indicate that slip occurred on deep faults that presumably slipped in advance of the laterally propagating dike

evolution and interaction of migrating cross arc volcanism and backarc rifting an example from the southern havre trough 35 20 37 s the active southern havre trough 35 20 37 s backarc basin is interpreted to form from the evolution and interaction of migrating cross arc magmatism and the progressive development of longitudinal rift grabens the proposed migration of the proto kermadec arc front from the colville arc at 5 ma to the active kermadec arc margin is recorded by the construction of arc edifices trailed across the intervening and contemporaneously rifting backarc complex migration trails are identified for at least four arc volcano sources the rumble v arc migration trail is the most prominent forming a continuous high standing magmatic arc ridge these postulated arc trails segment the backarc region and initially limit rift development to the intervening proto arc crust blocks early rifting between the arc volcanoes forms fully developed rift grabens which with progressive basin widening propagate longitudinally across the trails of migrating constructional arc magmatism a model of the balance between rates of constructional arc magma production mr and destructive back arc rifting extension ve is proposed when ve is high mr is insufficient to keep abreast of destructional rifting resulting in small isolated arc massifs quickly dismembered by rifting conversely when ve is low mr is sufficiently greater than rifting to produce a continuous high standing cross arc ridge which segments longitudinal rift development migrating arc magmatism will be best observed and preserved in rifting backarc basins when mr is 600 km3 m y 1 100 km 1 of plate boundary and ve is 25 mm a 1

growth and mass wasting of volcanic centers in the northern south sandwich arc south atlantic revealed by new multibeam mapping new multibeam swath bathymetric sonar data acquired using an em120 system on the rrs james clark ross supplemented by sub bottom profiling reveals the underwater morphology of a not vert similar 12 000 km2 area in the northern part of the mainly submarine south sandwich volcanic arc the new data extend between 55 45 s and 57 20 s and include protector shoal and the areas around zavodovski visokoi and the candlemas islands groups each of these areas is a discrete volcanic center the entirely submarine protector shoal area close to the northern limit of the arc forms a 55 km long east west trending seamount chain that is at least partly of silicic composition the seamounts are comparable to small subaerial stratovolcanoes in size with volumes up to 83 km3 indicating that they are the product of multiple eruptions over extended periods zavodovski visokoi and the candlemas island group are the summits of three 3 3 5 km high volcanic edifices the bathymetric data show evidence for relationships between constructional volcanic features including migrating volcanic centers structurally controlled constructional ridges satellite lava flows and domes and mass wasting of the edifices mass wasting takes place mainly by strong erosion at sea level and dispersal of this material along chutes probably as turbidity currents and other mass flows that deposit in extensive sediment wave fields large scale mass wasting structures include movement of unconsolidated debris in slides slumps and debris avalanches volcanism is migrating westward relative to the underlying plate and major volcanoes are asymmetrical being steep with abundant recent volcanism on their western flanks and gently sloping with extinct eroded volcanic sequences to their east this is consistent with the calculated rate of subduction erosion of the fore arc

structure and petrology of newly discovered volcanic centers in the northern kermadec southern tofua arc south pacific ocean 1 the nzaplume iii expedition of september october 2004 to the northern kermadec southern tofua nkst arc between 28 52 s and 25 07 s resulted in the discovery of at least seven new submarine volcanic centers and a substantial caldera complex adjacent to the previously known monowai seamount the volcanic centers form a sublinear chain that coincides with the kermadec ridge crest in the south hinetapeka and diverges 45 km westward of the ridge crest in the north v just to the south of where the louisville ridge intersects with the arc all of the centers contain calderas or caldera like structures as well as multiple cones domes fissure ridges and vent fields all show signs of recent eruptive and current hydrothermal activity there are strong structural controls on edifice location with cones and fissure ridges typically associated with faulting parallel to the regional 12 strike of the arc front several of the calderas are ellipsoidal orientated northwest southeast in the general direction of least compressive stress sampled volcanic rocks representing the most recently erupted lavas are all low k tholeiites two of the centers gamble and rakahore yielded only high silica dacite to rhyolite 69 74 wt silica whereas two others monowai and v yielded only basalt to andesite 48 63 wt silica mineral assemblages are plagioclase pyroxene dominated with accessory fe ti oxides apatite olivine and quartz tridymite cristobalite typical of dry volcanic arc systems hornblende occurs only in a felsitic rhyolite from hinepuia volcanic center and zircon is absent glass contents range to 57 in basalts andesites mean 20 and 97 in andesites rhyolites mean 59 and other quench textures including swallow tailed plumose or dendritic crystal forms and crystallites are common most lavas are highly vesicular 63 mean 28 and have low volatile contents mostly 2 wt which together with the occurrence of tridymite or cristobalite indicates explosive eruption and rapid cooling exceptions are rocks from u volcanic center which have low vesicularity and low glass contents across a wide compositional range indicating effusive eruption disequilibrium mineral textures the frequent occurrence of xenoliths and xenocrysts and macroscopic evidence for magma mingling indicate that many of the lavas are hybrids having resided only a short time in upper crustal reservoirs prior to eruption silicic magmas are major components of nkst arc volcanism and caldera formation is the dominant eruptive style the scale of silicic magmatism is in marked contrast to the dominant basaltic andesitic magmatism in the southern kermadec arc with evidence from other arcs silicic magmatism is now recognized as a major feature of intraoceanic arcs globally

fracture control on type morphology and distribution of parasitic volcanic cones an example from mt etna italy abstract this paper uses a coupled morphometric and stratigraphic analysis of several tens of parasitic pyroclastic cones of the se flank of mt etna volcano italy to explain the structure of a poorly understood actively deforming zone of the volcano moreover we present a new general classification of pyroclastic cones based on the parameterisation of coeval eruption points along the same magma feeding fracture each cone has been studied in detail in order to define its stratigraphic position morphometric characteristics growth evolution in relation to fracture distribution and orientation stress field and morphology of the substratum end members of this classification are at one side a simple circular or elongated edifice that grew around a single eruption point and can be related to a magma feeding fracture constrained by a relatively high confining stress in the substratum or a low magma pressure the other end member is a multiple rifted strongly elongated cone formed along multiple eruption points of a magma feeding fracture constrained by a relatively low confining stress or a high magma pressure lithostratigraphic and historical analyses demonstrate that the cones in this area developed between 15 ka bp and historical times the most recent one in 1669 ad testifying to a high rate of lateral eruption occurrence in the area these cones show n s elongated maximum crater axes n s trending axis of the depressed points of the crater rim and southward and southeastward breaching directions while coeval cones are n s aligned these morphometric characteristics reflect the geometry of n s magma feeding fractures the area can be regarded as a transitional weakness zone between the n s rift and the releasing system represented by the transtensional trecastagni and mascalucia faults indicating an e w oriented local component of extension possibly related to the interplay between the regional timpe fault system and the eastward gravitational spreading of the volcano the azimuth of breaching is controlled by magma feeding fracture orientation and substrate morphology especially in the eastern part of the area where it is influenced by the scarps related to the timpe regional fault system but it is also sensitive to cone development

widening of the krafla fissure swarm during the 1975 1981 volcano tectonic episode frequent distance measurements across the krafla fissure swarm north iceland recorded the extension accompanying the sequence of rifting events which started in december 1975 and lasted for 6 years an 80 to 90 km long section of the fissure swarm extended during this sequence of rifting and volcanic events maximum widening of about 8 m occurred 10 to 12 km north of leirhnjukur which is located above the center of the krafla magma reservoir from that location the amount of widening decreased north wards and is estimated to exceed 2 m where the seismicity indicated the northern termination of the present rifting off the north coast about 70 km north of leirhnjukur the amount of widening also decreased southwards and approached zero at 15 to 20 km south of leirhnjukur the ground deformation associated with these rifting events can be summarised as a narrow strip 1 to 2 km wide along the fissure swarm is heavily fractured with numerous open cracks parallel to the fissure swarm this fractured strip has subsided 2 to 3 m relative to its flanks the flanks of the fractured zone have been uplifted relative to regions farther away the uplift is not well constrained but tilt observations at several locations indicate about 1 m uplift the flanks of the rift zone have contracted perpendicular to the fissure swarm the maximum contractional strain exceeds 300 mm per km the amount of areal expansion windening of the fissure swarm times the length of the fractured zone associated with these rifting events is estimated to be about 0 30 km2 for individual events the area of expansion has been roungly proportional to the volume of subsidence above the krafla magma reservoir if the width of a new dike is equal widening of surface fissures the ratio of the subsidence volume to the area of expansion for the best observed events indicated a height of a new dike system as 2 4 to 2 8 km this ratio is significantly less for events of large lava production but even during these events the majority of magma leaving the krafla reservoir was apparently emplaced in subsurface fissures

comparison of methodological uncertainties within permeability measurements permeability measurements are critical to the calculation of water flow within hillslopes despite this errors in permeability measurements are often ignored and can be very large particularly in disturbance sensitive gley soils this work compares the uncertainties associated with six field methods of permeametry applied to a gleyed soil in upland britain slug tests constant head borehole permeametry and falling head borehole permeametry were undertaken on established piezometers additionally ring permeametry and two types of trench tests were evaluated method related uncertainty due to proximity of impeding layers of high sorptivity soils produces under and over estimates of permeability by a factor of up to 0 2 and 5 respectively this uncertainty band is smaller than the observed effects of anisotropy and temporal variability had smearing and soil ring leakage errors not been minimized the methodological uncertainties would have been so large that they would have distorted the true spatial field of permeability and its estimated impact on the balance of vertical and lateral flow

the lau havre taupo back arc basin a southward propagating multi stage evolution from rifting to spreading abstract the lau havre taupo lht system is an active 2000 km long back arc basin associated with pacific australian plate convergence in the sw pacific data from the lht back arc system include odp drillhole swath bathymetric and side scan imagery seismic reflection rock geochemistry magnetic anomaly heat flow shallow seismicity gravity and seismic refraction data the lht forms a longitudinal transect from southward propagating true oceanic spreading in the lau basin near tonga similarly southward propagating arc rifting in the havre trough and southward propagating continental rifting in the taupo volcanic zone tvz in northern new zealand four transitional tectonic settings are identified along the lht north to south between the continuum of spreading to rifting and comprise 1 oceanic spreading of the central lau spreading centre clsc propagating into oceanic crust formed by the eastern lau spreading centre elsc 2 oceanic spreading of the elsc propagating into rifted lau havre arc crust 3 rifting within havre arc crust propagating into rifting new zealand continental crust and 4 rifting of continental crust propagating into as yet non rifted but flexurally subsiding continental crust the enhanced spatial and temporal resolution of observed tectonic and magmatic processes along the strike of the lht is used to constrain a model for the evolution of back arc rifting to back arc spreading a sequence of five stages is identified and comprise 1 a combination of incipient simple and pure shear 2 early distributed and spatially heterogeneous half graben rifting with low angle synthetic and antithetic structures associated with rapid graben sediment infilling ephemeral early morb like rift magmatism and the initial trenchward migration of the arc front 3 a latter phase of half graben rifting mostly confined to a contiguous axial zone with continued ephemeral morb like rift magmatism and further trenchward migration of the arc front 4 initial oceanic spreading with evolving steady state morb magmatism along the axial rift graben system and 5 the reconfiguration of ridge geometry in response to changes in opening orientation leading to the development of ridge propagation into newly created oceanic crust rifting stages 2 and 3 can produce at least 120 km wide back arc crust by a balance of crustal extension with an estimated factor of 3 with rift and constructional arc magmatism in the lht system depending on latitude rates of widening during stages 2 and 3 vary between 15 and 45 mm yr 1 whilst stages 4 and 5 have full spreading rates of 90 mm yr 1

pre spread rifting and heterogeneous volcanism in the southern havre trough back arc basin abstract the havre trough is an active back arc basin associated with pacific australian plate convergence two segments within the southern havre trough sht surveyed with gloria sea beam and sys09 swath data now provide the first detailed data to reliably document the structure and morphology of this complex back arc region at the southern segment 35 40 37 s along a strike length of some 120 km the sht structure comprises a series of segmented en echelon generally flat floored sediment filled axial rift grabens flanked by ridge and basin rift block topography prominent fault escarpments with relief of 500 1000 m and a marked zig zag arrangement mark the outer margins of the rift system within the rift grabens extensional tectonism is pervasive extensive shallow seismicity within the sht can only partly be associated with the rift graben system at present youthful constructional volcanic terrains within the rift grabens are not common and invariably have a restricted areal extent and a relief an identical rift morphology has been identified at the northern 33 34 s site data from both sites show individual rifts are 15 35 km in length 6 10 km wide and have axial depths of 3100 4000 m apart from at least one 15 20 km wide cross trough ridge available data indicate the rift graben system is contiguous between 33 s and 37 s this rift graben morphology by analogy with other known rifting back arc basins is considered here not to be consistent with true oceanic back arc spreading rather it is argued that the sht possibly indeed all of the havre trough is undergoing back arc rifting prior to true spreading further the rifting tectonic fabric within the sht and in the onshore taupo to the south extension is consistently dextrally oblique relative to the bounding colville and kermadec ridges the degree of obliquity increases from south to north if accepted that the sht is rifting rather than spreading magnetic anomaly data within the trough do not record the accretion of new oceanic crust and consequently can no longer be used to establish the spreading history of the sht the sht magnetic anomalies are here interpreted as pseudo linear magnetic anomalies resulting from the generally irregular spatial and temporal emplacement of magnetic sheeted lava and dike intrusives between older low magnetisation arc basement rift blocks flanking the axial rift proxy data from onshore north island new zealand and offshore sht suggest that the rate of extension and age of initiation of back arc rifting are between 35 and 37 s respectively 15 20 mm yr 1 and 5 ma

the effect of volcanic constructs on rift fault patterns volcanoes in rift situations often show distinctive hour glass fault patterns with increased fault throw as the volcano is approached we present analogue models that show that this is caused by an interaction of the regional stress field with that set up by the volcano mass for faults to be reorientated there must be a ductile layer below the volcano this can be hot crust at mid ocean ridges continental rifts or weak sedimentary strata increased volcano size or mass and lower brittle ductile ratios lead to increased fault curvature whereas an increased regional extension rate decreases the effect volcanoes on one side of a rift may capture it forming the axis of a new rift with curved or en echelon zones on either side by concentrating extension magma is more easily erupted so volcanoes may erupt more magma of less evolved composition a positive feedback between increased extension and magma eruption rate will lead to rift narrowing which can favor the formation of oceanic crust

strain accommodation by slow slip and dyking in a youthful continental rift east africa continental rifts begin and develop through repeated episodes of faulting and magmatism but strain partitioning between faulting and magmatism during discrete rifting episodes remains poorly documented in highly evolved rifts tensile stresses from far field plate motions accumulate over decades before being released during relatively short time intervals by faulting and magmatic intrusions1 2 3 these rifting crises are rarely observed in thick lithosphere during the initial stages of rifting here we show that most of the strain during the july august 2007 seismic crisis in the weakly extended natron rift tanzania was released aseismically deformation was achieved by slow slip on a normal fault that promoted subsequent dyke intrusion by stress unclamping this event provides compelling evidence for strain accommodation by magma intrusion in addition to slip along normal faults during the initial stages of continental rifting and before significant crustal thinning

new multibeam mapping and geochemistry of the 30 35 s sector and overview of southern kermadec arc volcanism new multibeam mapping and whole rock geochemistry establish the first order definition of the modem submarine kermadec arc between 30 degrees and 35 degrees s twenty two volcanoes with basal diameters 5 km are newly discovered or fully mapped for the first time giggenbacb macauley havre haungaroa kuiwai ngatoroirangi sonne kibblewhite and yokosuka for each large volcano edifice morphology and structure surficial deposits lava fields distribution of sector collapses and lava compositions are determined macauley and havre are large silicic intra oceanic caldera complexes for both concentric ridges on the outer flanks are interpreted as recording mega bedforms associated with pyroclastic density flows and edifice foundering other stratovolcanoes reveal complex histories with repeated cycles of tectonically controlled construction and sector collapse extensive basaltic flow fields and the development of summit craters and or small nested calderas combined with existing data for the southernmost arc segment we provide an overview of the spatial distribution and magmatic heterogeneity along similar to 780 km of the kermadec arc at 30 degrees 36 degrees 30 s coincident changes in arc elevation and lava composition define three volcano tectonic segments a central deeper segment at 32 degrees 20 34 degrees 10 s has basement elevations of 3200 m water depth and relatively simple stratovolcanoes dominated by low k series basalt basaltic andesite in contrast the adjoining arc segments have higher basement elevations typically 3 km coincide with the shallower arc segments the dominant mode of large caldera formation is interpreted as mass discharge pyroclastic eruption with syn eruptive collapse hence the shallower arc segments are characterized by both the generation of volatile enriched magmas from crustal melting and a reduced hydrostatic load allowing magma vesiculation and fragmentation to initiate and sustain pyroclastic eruptions proposed initiation parameters for submarine pyroclastic eruptions are water depths 70 wt sio2 and a high discharge rate c 2005 elsevier b v all rights reserved

structural controls of volcanism in transversal chains resheared faults and neotectonics in the cordon caulle puyehue area 40 5 s southern andes abstract the nature of the relationship between tectonics and volcanism in a specific area is the result of the interaction between the crustal structures of the basement and ongoing regional stress field in the southern andes different kinematic environments represented by two nearly orthogonal active fissure systems show apparently incompatible arrays of volcanic chains moreover a local quaternary compressive regime is inferred from basement faults however these mutually orthogonal chains which are also oblique to the volcanic front have contrasting magma evolution and eruptive styles that can be related with their tectonic setting whereas northeast trending monogenetic cones carran los venados can be interpreted as resulting from magma upwelling along regional tension cracks in a quaternary dextral transpressive compressive domain northwest striking fissure system cordon caulle volcanic complex can be the result of extensional fault reactivation and long magma residence in the upper crust different kinematic environments cause contrasting magma evolution and eruptive styles a two way coupling mechanism is suggested for to explain local depart of the regional stress field geometric array of extensional features and final magmatic evolution in these volcanic domains of the southern andes

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

seismicity and state of stress within the overriding plate of the tonga kermadec subduction zone 1 to reassess the main tectonic units and to quantify the slip partitioning within the overriding plate of the tonga kermadec subduction zone a seismotectonic study was performed using global seismicity and focal mechanisms catalogs 1 new tectonic features were identified within the lau basin and the volcanic arc by remarkable shallow hypocenters alignments 2 the centroid moment tensor solutions catalog was processed in order to map the stress tensor variation in the upper plate we found the tectonic features characterized by a diffuse seismicity are subjected to a composite stress regime and they are interpreted as diffuse immature plate boundaries controlled by the high thermal anomaly lying beneath the lau basin 3 we quantified the margin parallel rates of motion using the azimuth of the maximum compressive stress component computed within the interplate zone the results highlight a major tectono kinematic segmentation related to the subduction of the louisville seamount chain

bathymetry and magnetic anomalies in the havre trough and southern lau basin from rifting to spreading in back arc basins abstract the havre trough and lau basin are active back arc basins related to pacific australian plate convergence these back arc basins provide insight into the evolution of rifting through various stages including a final stage of oceanic spreading we carried out a swath bathymetry and magnetic anomaly survey focused on the less studied havre trough and southern lau basin the western portion of the whole havre trough is deeper and more thickly sedimented whereas shallow bathymetry and volcanic edifices are dominant in the east we suggest that crustal rifting progresses asymmetrically with respect to the trough axis the active tectono magmatic zone migrates trenchward during ongoing widening rifting along normal faults trending in the longitudinal trough strike occurs in the southern havre trough volcanism is restricted to a line along the normal faults circular or elongated knolls in the northern havre trough indicate that en echelon type segmented rifting of short strike length and successive volcanic intrusion takes place volcanism in this area is dominated by diapir like magma intrusion into an extended and thinned arc crust the southernmost tip of the spreading center of lau basin is defined by the deep graben striking at n20 e located at 24 00 s 177 10 w

usercalc a web based uranium series calculator for magma migration problems 1 measured departures from secular equilibrium in the uranium series decay chains provide important constraints on the rates of recent mantle and crustal processes nevertheless the inferences drawn from these observations depend upon the models used to interpret them while several useful models for u series exist they are not all equally easy to use and it is often the ease of use rather than the utility of the model that determines which models are applied the purpose of this paper is to level the playing field by making some of the more general u series transport models accessible to a wider community through the usercalc web site available from lamont doherty earth observatory at www ldeo columbia edu mspieg usercalc these models calculate the effects of both melting and melt transport on two u series chains 238u 230th 226ra and 235u 231pa and allow the user to input their own petrological insight and data to explore the behavior of this model the purpose of the site is to provide a tool that can spur additional collaborations between geophysicists and geochemists as well as drive more rapid exploration evolution of u series models

south arch volcanic field newly identified young lava flows on the sea floor south of the hawaiian ridge several young lava fields were imaged by gloria sidescan sonar along the hawaiian arch south of hawaii the largest 35 by 50 km across includes a central area characterized by high sonar backscatter and composed of several flow lobes radiating from a vent area reflection profiling and sea floor photography indicate that the central lobes are flat sheet flowsbounded by pillowed margins thin surface sediment and thin palagonite rinds on lava surfaces suggest ages of 1 10 ka vents are localized along the arch crest near bases of cretaceous seamounts two dredged flows are basanite and alkalic basalt broadly similar to rejuvenated stage and some pre shield alkalic lavas on the hawaiian ridge arch volcanism representsperipheral leakage of melt from the hawaiian hot spot over much larger areas than previously recognized

topographic analyses of k lauea volcano hawai i from interferometric airborne radar we analyze digital topographic data collected in september 1993 over a 500 km2 portion of k lauea volcano hawai i by the c band 5 6 cm wavelength topographic synthetic aperture radar topsar airborne interferometric radar field surveys covering an 1 km2 area of the summit caldera and the distal end of an 8 m thick a flow indicate that the 10 m spatial resolution topsar data have a vertical accuracy of 1 2 m over a variety of volcanic surfaces after conversion to a common datum topsar data agree favorably with a digital elevation model dem produced by the u s geological survey usgs with the important exception of the region of the ongoing eruption which postdates the usgs dem this dem comparison gives us confidence that subtracting the usgs data from topsar data will produce a reasonable estimate of the erupted volume as of september 1993 this subtraction produces dense rock equivalent dre volumes of 392 439 and 90 106 m3 for the pu u k pa ianah and episode 50 53 stages of the eruption respectively these are 124 89 and 94 of the volumes calculated by staff of the hawaiian volcano observatory hvo but do not include lava of k pa ianah and episodes 50 53 that flowed into the ocean and are thus invisible to topsar accounting for this lava increases the topsar volumes to 124 159 and 129 of the hvo volumes including the 2 m uncertainty derived from the field surveys produces topsar derived volumes for the eruption as a whole that range between 81 and 125 of the usgs derived values the vesicularity and ocean corrected topsar volumes yield volumetric eruption rates of 4 5 4 5 and 2 7 m3 s for the three stages of the eruption which compare with hvo derived values of 3 6 2 8 and 2 1 m3 s respectively our analysis shows that care must be taken when vertically registering the topsar and usgs dems to a common datum because c band topsar penetrates only partially into thick forest and therefore produces a dem within the tree canopy whereas the usgs dem is adjusted for vegetation

surface deformation in volcanic rift zones abstract the principal conduits for magma transport within rift zones of basaltic volcanoes are steeply dipping dikes some of which feed fissure eruptions elastic displacements accompanying a single dike emplacement elevate the flanks of the rift relative to a central depression concomitant normal faulting may transform the depression into a graben thus accentuating the topographic features of the rift if eruption occurs the characteristic ridge trough ridge displacement profile changes to a single ridge centered at the fissure and the erupted lava alters the local topography a well developed rift zone owes its structure and topography to the integrated effects of many magmatic rifting events to investigate this process we compute the elastic displacements and stresses in a homogeneous two dimensional half space driven by a pressurized crack that may breach the surface a derivative graphical method permits one to estimate the three geometric parameters of the dike height inclination and depth to center and the mechanical parameter driving pressure rock stiffness from a smoothly varying displacement profile direct comparison of measured and theoretical profiles may be used to estimate these parameters even if inelastic deformation notably normal faulting creates discontinuities in the profile geological structures open cracks normal faults buckles and thrust faults form because of stresses induced by dike emplacement and fissure eruption theoretical stress states associated with dilation of a pressurized crack are used to interpret the distribution and orientation of these structures and their role in rift formation