eruptive history of earth s largest quaternary caldera toba indonesia clarified single grain laser fusion sup 40 ar sup 39 ar analyses of individual sanidine phenocrysts from the two youngest toba indonesia tuffs yield mean ages of 73 plus minus 4 and 501 plus minus 5 ka in addition glass shards from toba ash deposited in malaysia were dated at 68 plus minus 7 ka by the isothermal plateau fission track technique these new determinations in conjunction with previous ages for the two oldest tuffs at toba establish the chronology of four eruptive events from the toba caldera complex over the past 1 2 m y ash flow tuffs were erupted from the complex every 0 34 to 0 43 m y culminating with the enormous 2500 3000 km sup 3 youngest toba tuff eruption caldera formation and subsequent resurgence of samosir island timing of this last eruption at toba is coincident with the early wisconsin glacial advance the high precision sup 40 ar sup 39 ar age eruption of such magnitude may provide an important marker horizon useful as a baseline for research and modeling of the worldwide climatic impact of exceptionally large explosive eruptions

potential atmospheric impact of the toba mega eruption 71 000 years ago an approx 6 year long period of volcanic sulfate recorded in the gisp2 ice core about 71 000 5000 years ago may provide detailed information on the atmospheric and climate impact in the toba mega eruption deposition of these aerosols occur beginning of an approx 1000 year long stadial event but not immediately before the longer glacial period beginning approx 67 500 years ago total stratospheric loading estimates over this approx 6 year period range from 2200 to 4400 mt of h sub 2 so sub 4 aerosols the range in values is given to compensate for uncertainties in aerosol transport magnitude and longevity of the atmospheric loading may have led directly to enhanced cooling during the initial two centuries of this approx 1000 year cooling event 25 refs 2 fig 1 tab

sediment transport modelling in an alluvial river with artificial neural network abstract simulation of flow and transport of sediment in alluvial rivers particularly during release of water through dams is a complex problem such simulations are generally carried out using various numerical models subject to availability of requisite morphological and sediment data sets in addition various simplifying assumptions quite often are part and parcel of most of the available numerical sediment transport models as such non compliance of any of the assumptions or non availability of all the requite data sets restricts meaningful use of any numerical simulator in estimation of morphological changes in alluvial rives this study attempts to resolve such issues associated with numerical models by using artificial neural networks ann the primary objective of the study is to explore and identify best performing ann models in estimating morphological changes in alluvial rivers in the present study the one dimensional hydrodynamic modelling system hec ras hydrologic engineering centre s river analysis system is employed for generating database to train multilayer feedforward networks mlfn performance evaluations of all the developed mlfn models are made by using three statistical parameters i e mean square error mse mean absolute error mae and coefficient of determination r2 the study reveals that there are multiple ann models stretching across different training algorithms and transfer functions which can be reliably used in developing sediment transport models in alluvial rivers

a gravity and volcanostratigraphic interpretation of the lake toba region north sumatra indonesia abstract in northern and central sumatra a wide distribution of ignimbrite and volcanic sediments is observed some geologists consider that these volcanic products were erupted from lake toba the subduction of the indian ocean plate along the trench of central sumatra started at least as long ago as the late miocene fitch s model 1972 obtained the plate convergence vector 67 mm yr decomposed into its components perpendicular 58 mm yr and parallel 34 mm yr to the trench axis tears seaward of the mountain range created the sumatran fault about 2 ma ago at that time the edge of the plate reached a depth of almost 100 km and a large amount of dacite magma was generated the tuk tuk dacite a kind of ignimbrite was erupted along the sumatran fault and covered a broad area the age of this ignimbrite was obtained as 1 9 0 4 ma k arage and 2 0 0 3 ma fission track age since this eruption the hinterland of this fault has been changed to a tensional field forming a graben structure at the northern end of this graben west of harranggaoul the ignimbrite haranggaoul formation was erupted 1 3 0 3 ma ago forming a caldera the lacustrine sediments of samosir island have a normal magnetization and overlie the tuk tuk dacite unconformably from this we can conclude that the graben structure has been covered with water lake toba at 0 7 0 6 ma ago this tectonic movement has continued so that it is difficult to distinguish the caldera structure on the gravity anomaly map of the northern part of lake toba from the results of the gravity survey it can be concluded that at 0 1 ma ignimbrite flowed down along the asahan river and filled the old river along the lowland between parapat and porsea forming a caldera 30 000 years ago dacite and and esite eruptions have occurred around lake toba forming the volcanic cones

local and regional scale impacts of the 74 ka toba supervolcanic eruption on hominin populations and habitats in india abstract the toba supervolcanic eruption of 74 000 years ago is argued to have devastated homo sapiens populations causing a human population bottleneck through a combination of rapid global climatic deterioration and ecological disruption following the widespread ash fall this dramatic eruption the largest in at least the last 2 million years is hypothesized to have shaped the genetic structure and diversity of human populations today past assessments of toba s human impacts however have been predominantly theoretical using archaeological and geological evidence from sites in india this study addresses toba s local scale impacts on hominin technology behavior demography and habitats in two valleys in india the jurreru and middle son valleys using paleoclimatological and volcanological data regional scale impacts throughout india are inferred a refugia hypothesis is presented that argues for variation in the scale of toba s impact throughout india driven by regional differences in monsoonal dynamics geography and topography areas of north west india the indo gangetic plain and parts of the deccan to the east of the western ghats are argued to have been the most affected whereas areas of southern and eastern india may have preserved the largest refugia for hominin populations

the regional geology and evolution of the toba volcano tectonic depression indonesia the late quaternary toba volcano tectonic depression in the sunda arc is the largest resurgent cauldron in the world and lies in one of the largest ignimbrite fields the toba tuffs although composed of at least 3000 km 3 of acid tuffs spread over 20000 km 2 of mainland sumatra the greater part of the toba tuffs is believed to be a single ignimbrite cooling unit formed about 100 000 years ago the toba tuffs also include a 30000 year old airfall tuff which was erupted from a centre just n of the toba depression the toba depression developed through the same stages as other resurgent cauldrons it formed after lithification of the toba tuffs by collapse along regional faults crossing an eastwards bulge in the sumatran geanticline resurgent uplift raised lake sediments within the depression by about 500 m the uplift which was not confined to the depression was probably caused by continuing influx of magma and it is possible that the toba depression is still in the stage of post resurgence volcanism the eruption of the toba tuffs and of all post ignimbrite volcanism took place on the line of the western marginal fault of the depression this marginal fault once extended northwards offshore into a zone of miocene back arc rifting

no short reversals of brunhes age recorded in the toba tuffs north sumatra indonesia paleomagnetic and 40ar 39ar data indicate that two tuffs are present at siguragura north sumatra indonesia a reversely magnetized tuff the earliest eruptive unit of the toba caldera of matuyama age 0 84 ma and a normally magnetized tuff the last eruptive unit of the toba caldera of late brunhes age no reversely magnetized tuffs of late brunhes age are present at this location as suggested by previous investigators

structural analysis of syn depositional hydrothermal veins of the 3 48 ga dresser formation pilbara craton australia abstract the lower chert unit of the 3 48 ga dresser formation pilbara craton western australia hosts earth s oldest convincing evidence of life in the form of stromatolites in a depositional setting that has been interpreted as either a shallow marine lagoon an active volcanic caldera or a basin deposited during regional extension understanding the environment where early life thrived is important not only for early life studies on earth but in the search for life on mars and for understanding the setting for the origin of life structural analysis of the extensive network of syn depositional hydrothermal chert barite veins that immediately underlies the dresser was undertaken in order to test if deposition occurred within an evolving caldera system or during regional extension over 190 hydrothermal veins were mapped for their geometry and relative age relationships bedding orientations were recorded within nine fault bounded structural sub blocks and used for back rotating the measured veins to their original orientation the results show that 1 there are four main vein systems including three that were emplaced during deposition of the dresser formation lower chert unit and a fourth that was emplaced within syn to post depositional listric growth faults 2 the majority of veins were sub vertical prior to regional tilting 3 the first three vein systems show mutually cross cutting relationships 4 vein densities and the number of vein systems vary between sub blocks 5 conjugate vein networks ne sw and nw se dominate two middle and northern sub blocks these results show that the first three vein systems were emplaced through fracturing under a stress regime with a vertical 1 vertical conjugate fractures are consistent with sandbox models of overburden fracturing during emplacement and discharge of a magma chamber in a volcanic caldera areas of single vein orientations reflect marginal areas of the caldera system dominated by radial or by ring faults the veins in late listric growth faults represent the final period of caldera collapse which controlled the depositional thicknesses of overlying strata possibly during subsequent regional extension these results document an unique setting for earliest life on earth within shallow water and terrestrial deposits of an active low eruptive caldera setting

the origin of ferro manganese oxide coated pumice from the central indian ocean basin pumice clasts partially and fully coated with ferro manganese oxide from the central indian ocean basin ciob were analysed for major trace and rare earth elements and glass and mineral grain chemistry to assess their possible source these pumice clasts have 95 glassy matrix with 5 of plagioclase ortho pyroxene amphibole and spinel mineral grains pumice is rhyolitic with high content of silica and total alkalis and show strong light rare earth element enrichment with la 100 times enriched compared to chondritic abundance and exhibits a pronounced negative eu anomaly both the partially and fully coated pumice clasts have a similar composition but this and their glass and mineral orthopyroxene chemistry differs from all tuffs known to have erupted from the toba caldera complex the partial to complete fe mn oxide coating suggests the pumice probably predates activity from the toba caldera their general composition is consistent with a volcanic arc origin and show similarities to rhyolitic eruptives from sumatra the distribution of partially and fully coated pumice in the ciob overlaps with that of uncoated pumice from the voluminous ytt eruption suggesting that other large rhyolitic calderas active in sumatra indonesia similarities in composition to ash layers from the ciob suggest a possible late miocene late pleistocene age for these pumices

studying deep sources of volcanism using multiscale seismic tomography abstract this paper presents an overview of several examples of multiscale studies of different volcanic systems including intracontinental collisional and subduction related volcanic areas regional tomographic models of the upper mantle are presented for three regions with the cenozoic intracontinental volcanism in eurasia namely europe southern siberia and eastern arctic in all cases recent volcanic fields correlate with low velocity anomalies in the mantle the modeling results show that these volcanic manifestations are related to large hot areas in the mantle and not to thin column shaped contrasted plumes as presumed by many collisional type volcanism is discussed with an example of the caucasus and the surrounding areas the regional tomographic model for this region reveals a lack of mantle lithosphere beneath the collision zone volcanism in this area is most likely due to the direct heating of the thick crust by the hot asthenosphere a dominantly felsic composition of the crust facilitates upward transport of the fluids and melts that leads to volcanic eruption subduction related volcanic systems are discussed for three different scale levels an example of a regional model of the mantle beneath the sunda arc reveals the general configuration of the slab middle scale tomographic models in areas of the toba caldera central java and central andes display feeding paths of the arc volcanoes from the slab the feeding paths are apparent in all of the considered cases but have different shapes depending on the unique features of the subduction regimes an example of a detailed local scale study of magmatic sources in the crust is discussed for the kluchevskoy volcano group it is found that the main volcano kluchevskoy is fed through a complex three layered system of magma sources another volcano of the same group bezymianny seems to be connected with the mantle through a direct short lived channel which appears only during the eruption periods a time dependent tomography study performed for this group over a period of ten years clearly reveals the correlation between the changes in the seismic structures and the stages of the volcanic process namely preparation activation and relaxation

on the mechanics of caldera resurgence the mechanisms suggested to cause caldera resurgence can be categorized as 1 viscous rebound of magma 2 regional detumescence and 3 pressure against the base of the caldera block due to magmatic vesiculation and convection or addition of new magma the critical observation that resurgence takes of the order of 103 105 years insists that the causative mechanism be regulated by a highly viscous e g 1022 pa s structural member of the crust the relatively low viscosity magma and a purely elastic crust cannot be important in achieving this time scale the most likely mechanism is the coupled effect of regional detumescence and magmatic vesiculation detumescence compresses the magma chamber squeezing magma upward against and through the caldera block vesiculation also compresses the chamber and tends to dome the caldera block the times of both detumescence and doming of the caldera block by magmatic pressure are probably inversely proportional to the size of the magma chamber but the rate of cooling of the chamber is proportional to its size because solidification spreads viscous relaxation over a wide region of the crust and curtails resurgence there is likely to be a minimum volume of magma that can undergo resurgent doming it is difficult to be exact about this critical size until more precise models have been developed

glacial cycles drive variations in the production of oceanic crust glacial cycles redistribute water between oceans and continents causing pressure changes in the upper mantle with consequences for the melting of earth s interior using plio pleistocene sea level variations as a forcing function theoretical models of mid ocean ridge dynamics that include melt transport predict temporal variations in crustal thickness of hundreds of meters new bathymetry from the australian antarctic ridge shows statistically significant spectral energy near the milankovitch periods of 23 41 and 100 thousand years which is consistent with model predictions these results suggest that abyssal hills one of the most common bathymetric features on earth record the magmatic response to changes in sea level the models and data support a link between glacial cycles at the surface and mantle melting at depth recorded in the bathymetric fabric of the sea floor

stratigraphy paleomagnetism and magnetic fabric of the toba tuffs constraints on the sources and eruptive styles the toba depression in north central sumatra is a complex of several overlapping calderas resulting from three major ignimbrite forming eruptions within the depression the upland masses of samosir and northern uluan consist of welded ignimbrite capped by coarse breccia and lacustrine sediment hitherto interpreted to be two parts of a single resurgent dome this study has demonstrated that the welded tuffs of samosir and uluan have different magnetic polarities and therefore at least two different ignimbrites are present the samosir uluan massif may consist of parts of two resurgent domes the first ignimbrite eruption occurred at 0 84 ma and produced a very thick 400 m densely welded unit having a reversed polarity anisotropy of magnetic susceptibility ams flow direction and lithic size data indicate that the source lies in the southern part of the toba depression and the thick deposit of uluan is thought to have ponded in a 40 km wide caldera the second ignimbrite is normally magnetized ams flow direction data indicate two separate source vents one to the north in the haranggaol caldera and another to the south the thick deposit at samosir is thought to have ponded in the southern caldera coarse sediments then accumulated over samosir and northern uluan and were capped by lacustrine deposits a renewed episode of resurgence then uplifted samosir island and possibly the northern part of uluan at approximately 0 075 ma the last and apparently largest ignimbrite eruption occurred from calderas in the north and south parts of the toba depression this ignimbrite is mostly nonwelded and normally magnetized part of the uluan dome was destroyed by collapse of the sibandung caldera and latung graben and concomitant with renewed subsidence of the haranggaol and porsea calderas

an experimental study of complex response in river channel adjustment downstream from a reservoir an experimental study is described which attempts to reveal the complex response process of river channel adjustment downstream from a reservoir a descriptive model has been established which identifies three adjustment stages in stage i following the change of water and sediment input the width depth ratio of river channel w d and the river channel gradient s both decrease but the river channel sinuosity r increases in stage ii because of feedback from the changing boundary conditions w d starts to increase r decreases and the rate of gradient decrease becomes very slow in stage iii equilibrium is reestablished w d r and s tend to constant values and the system recovers its stable state

an unusual bed of giant pumice in mexico we report here that a remarkable bed of giant sized pumice blocks occurs within an old caldera of the major late quaternary rhyolitic volcano of sierra la primavera mexico fig 1a the bed lies within a 100 m thick sedimentary sequence distributed over a near circular area 10km across the margin of this circular area closely parallels an incomplete ring of prophyritic comendite lava domes fig 1b some of which may be shallow intrusions emplaced into the sediments the vents of these domes are believed to lie on a ring fault fig 1b the sedimentary sequence now gently updomed fig 1c is believed to have accumulated in a caldera lake the shoreline of which lay up to 1 km outside the ring fault

analogue study of particle segregation in pyroclastic density currents with implications for the emplacement mechanisms of large ignimbrites analogue flume experiments were conducted to investigate the transport and sedimentation behaviour of turbulent pyroclastic density currents the experimental currents were scaled approximately to the natural environment in three ways 1 they were fully turbulent 2 they had a very wide range of particle sizes and associated rouse numbers the ratio of particle settling velocity to effective turbulent eddy velocity in the current and 3 they contained particles of two different densities two sets of surge type experiments were conducted in a 5 m long water filled lock exchange flume at five different volumetric particle concentrations from 0 6 to 23 in one set one component experiments the currents contained just dense particles in the other set two component experiments they contained both light and dense particles in equal volume proportions in both sets of experiments the population of each component had a log normal size distribution in the two component experiments the size range of the light particle population was selected in order to be in hydrodynamic equivalence with that of the dense particles dense particles were normally graded both vertically and downstream in the deposits from both sets of experiments the mass loading normalized to the initial mass of the suspension and grain size of the dense component in the deposits decreased with distance from the reservoir and were insensitive to initial total particle concentration in the currents on the other hand in the two component experiments the light particles were extremely sensitive to concentration they were deposited in hydrodynamic equivalence with the dense particles from dilute currents but were segregated efficiently at concentrations higher than a few per cent with increasing particle concentration the large light particles were carried progressively further down the flume because of buoyancy effects deposits from the high concentration currents exhibited reverse vertical grading of the large light particles efficient segregation of the light component was observed even if the bulk density of the current was less than that of the light particles in both sets of experiments marked inflexions in the rate of downstream decline in mass loading and maximum grain size of the dense component can be attributed to the presence of two different particle settling regimes in the flow 1 particles with rouse numbers 2 5 which did not respond to the turbulence and settled rapidly and 2 particles with rouse numbers 2 5 which followed the turbulent eddies and settled slowly the results are applied to the transport and sedimentation dynamics of pyroclastic density currents that generate large widespread ignimbrites field data fail to reveal significant departures from aerodynamic equivalence between pumice and lithic clasts in three such ignimbrites the particulate loads of some large ignimbrites are transported principally in turbulent suspensions of low concentration in some ignimbrites the well developed inflexions in curves of maximum lithic ml size vs distance can be attributed to the existence of distinct high and low rouse number particle settling regimes that mark the transition from an overcharged state to one in which the residual particulate load is transported more effectively by turbulence

youngest toba tuff in the son valley india a weak and discontinuous stratigraphic marker abstract investigation of the climatic and environmental impacts of the youngest toba tuff ytt 74 ka bp eruption of toba volcano sumatra is crucial for understanding the consequences of the eruption for contemporaneous human populations the middle son valley in india was the first locality on the indian subcontinent where the ytt was reported the ash bed forms a discontinuous layer stretching for over 30 km along the river here we report on the stratigraphic contexts of ytt ash layers in alluvial deposits of the middle son valley in order to reconstruct the taphonomy of the ash deposits and the dynamic of their deposition although the distal ash has been studied since the 1980s its stratigraphic integrity and the mechanisms and pathways involved in its transport and deposition have bit previously been assessed we find that the ytt occurrences in the middle son valley may not be reliable chronostratigraphical markers for millennial scale palaeoenvironmental reconstruction

geochemical fingerprinting of the widespread toba tephra using biotite compositions toba caldera sumatra is one of the largest and most explosive volcanoes on earth erupting some of the most voluminous volcanic deposits chronologically these eruptions are 790 ka older toba tuff 500 ka middle toba tuff and 74 ka younger toba tuff ash from these eruptions is dispersed over the entire region from india through malaysia to indonesia where it forms isochronous markers that have been documented in a variety of sedimentary sequences including palaeoclimate archives and archaeological sites the chemistry of the volcanic glass shards usually enables distal volcanic ash units to be correlated to a known eruption however the magmas involved in the three largest toba eruptions are compositionally similar and consequently the glass chemistry that is used to differentiate eruption units cannot be used to identify distal deposits here we show that the composition of biotite crystals which occur with glass in the distal deposits can be used to fingerprint the deposits of the younger toba tuff biotite in younger toba tuff has a lower feo mgo 2 1 2 6 than in the products of older eruptions 2 8 3 7 correlations using these distinct biotite compositions indicate that the ash found in malaysia and in archaeological sites in india was from the 74 ka younger toba tuff eruption

sumatran granitoids and their relationship to southeast asian terranes abstract three subparallel n s trending granitoid provinces occur in southeast asia the eastern granitoid province of peninsular malaysia the central granitoid province extending from northwestern thailand to the western part of peninsular malaysia and to the tin islands indonesia and the western granitoid province in western thailand and burma it has been asserted that each of these granitoid provinces is restricted to one of the southeast asian terranes defined using gondwanan palaeozoic stratigraphic relations and faunal distributions very little is known about possible continuations of these terranes in sumatra and here we use the granite basement terrane concept and the geochemical and isotopic compositions of sumatran granitoids and fragmental rocks to extend the southeast asian terrane boundaries into sumatra and investigate the nature of the sumatran lithosphere granitoids west of the semangko fault and within the basement of the quaternary volcanic arc have low initial 87 sr 86 sr values granitoids in eastern sumatra east of the semangko fault including those of the tin islands of bukit batu close to palembang the hatapang pluton and granodiorites and fragmental volcanics of the lake toba area and possibly sijunjung pluton in central sumatra all share high 87 sr 86 sr values and other s type isotopic and compositional similarities and seem to be related to the central granitoid province s type granitoids of the sibumasu terrane siam burma malaysia sumatra metcalfe 1984 these similarities suggest that the granitoids define a granite basement terrane which may form the basement of the sibumasu terrane they also imply that the magmatism of the toba caldera was derived from the same crustal source granitoids that are geochemically and isotopically similar to those of the western province are not yet known in sumatra and granitoids similar to those of the eastern province are rare the distribution of sumatran granitoids suggests that the semangko fault and the sunda strait may mark the southwesternmost and southeasternmost limits of the sibumasu terrane and that the boundary between the central and the eastern granite provinces may run through the tin islands

toba ash layers in the south china sea evidence of contrasting wind directions during eruption ca 74 ka comment and reply buhring et al 2000 1 reported that the ash layers in two cores from the south china sea dated ca 74 ka are distinct from the volcanic glass supplied from the philippines and the northern south china sea but are almost identical in terms of the chemical compositions to the toba ash they

scale dependent location of hydrothermal vents stress field models and infrared field observations on the fossa cone vulcano island italy article i nfo hydrothermal venting occurs on numerous volcanoes of various age setting topographic and structural expression vent locations are commonly found not within volcanic craters only but predominantly at the crater margins and topographic highs a case example is vulcano island italy where the control on such vent locations along crater margins remained poorly understood however this paper describes numerical models combined with field observations and infrared imaging to explore the mechanisms that control the ascent paths of fluids in the fossa cone on vulcano using finite element modelling we calculate the gravitational stress in the volcanic edifice imposed by the topography results predict hydrofractures to be arranged in radial patterns at depth and in concentric patterns close to the surface furthermore low compressive stress values are found at the rims of the nested craters we compare the stress models to fumarole field data using a forward looking infrared camera we recorded images of the entire cone images were assembled to a mosaic and geocoded providing the first map of a remotely sensed temperature field in high resolution at la fossa the degassing and high temperature anomalies are found to be located mainly at the crests of the craters predominately in the northern and southern sector of the main crater therefore the stress distribution favours and indeed corresponds to the occurrence of fumaroles at la fossa the stress models also yield compression at the bottom of the crater where temperatures are cool thus we consider that the overall distribution of the fumaroles at the fossa cone is controlled by topography additional mechanisms contribute to the exact position of the degassing sites the influence of the lithological control seems to be strong in the southwestern part of the crater where the fumaroles are located 10 20 m below the inner crater rim in bedded strata in the northern part of the crater the exhalation sites can mainly be found at surface fractures and cracks emphasizing the structural control on the location of the fumaroles at this sector of the fossa cone using combined theoretical modelling and field observations this study helps to shed light into the processes directing fluids in volcanic edifices elsewhere and might contribute to the evaluation of upcoming hazard scenarios

lake toba volcano magma chamber imaged by ambient seismic noise tomography 1 for the first time ambient noise tomography is used to clearly image the magma chamber beneath lake toba caldera one of the largest quaternary calderas on earth using data from 40 seismic stations deployed between may and october 2008 around lake toba empirical green s functions are extracted from long term cross correlations of continuous records these functions are dominated by rayleigh waves whose group velocities can be measured in the period range from 2 5 to 12 seconds arrival times of these waves are picked for a given period and inverted using 2 d tomography to calculate lateral variations in velocity for the given period this was done for six different periods which all correspond to different sampling depths thus the six 2 d models presented together provide information on velocity variations with depth the results show a low velocity body coincident with the lake toba caldera representing the magma chamber under the volcano the chamber is observed to have a complex 3 d geometry with at least two separate sub chambers underlying the caldera other results include a deep low velocity body possibly another magma chamber south west of the lake with an upper limit of 7 km depth the maximum depth to which this body reaches could not be resolved the sumatra fault marks a velocity contrast but only down to depths not greater than 5 km the reliability of the results was further confirmed by checkerboard recovery tests

distribution of magma beneath the toba caldera complex north sumatra indonesia constrained by three dimensional p wave velocities seismicity and gravity data 1 we estimate the one and three dimensional p wave velocity structure beneath the toba caldera complex a 30 100 km topographic depression in north sumatra using arrival time data of local earthquakes recorded by a 40 station seismic network that operated for 4 months inversions reveal the presence of p velocities up to 37 below normal that likely map the distribution of magma within this subduction related volcanic system considered the world s largest in the upper 10 km of crust the largest low velocity region underlies the southern two thirds of the depression and coincides with a gravity low centered over the resurgent dome a smaller volume of low velocities is observed in the upper crust under the north end of the depression separating the two regions is a zone of locally high velocities indicating that the shallow subcaldera magma system is composed of two separate reservoirs not a single one that extends the entire length of the caldera complex above each low velocity region is a postcollapse volcano that erupted mostly mafic lavas after the last major caldera collapse 74 kyr ago a low velocity column below one of these volcanoes can be traced into the uppermost mantle and corresponds with a planar distribution of low frequency earthquakes in the 20 to 40 km depth range the low frequency earthquakes apparently record the migration of melt in the mafic roots of this large volume crustal magma system

limited global change due to the largest known quaternary eruption toba 74 kyr bp abstract the 74 kyr bp super eruption of toba volcano in sumatra is the largest known quaternary eruption on the basis of preserved deposits the eruption magnitude has been estimated at 7 10 15 kg 2800 km 3 of dense magma the largest sulphate anomaly in the greenland ice sheet project 2 core has been identified as fallout from toba s stratospheric aerosol veil correlation of the sulphate and oxygen isotope stratigraphy of the ice core suggests that the toba eruption might have played a role in triggering a millennium of cool climate prior to dansgaard oeschger event 19 although a comparable stadial preceded event 20 a possible 6 yr duration volcanic winter immediately following the eruption has also been proposed as the cause of a putative bottleneck in human population supporting in a general way the garden of eden model for the origin of modern humans however along with counter arguments regarding the timing of any demographic crash there remain major gaps in our understanding of the 74 kyr bp toba eruption that hinder attempts to model its global atmospheric and climatic and hence human consequences the tephra record reveals basic aspects of the eruption style but calculations of the duration and hence intensity and plume height of the event are poorly constrained furthermore estimates of the sulphur yield of the erupting magma central to predictions of its atmospheric and climatic impacts vary by two orders of magnitude 3 5 330 10 10 kg previous estimates of globally averaged surface cooling of 3 5 c after the eruption are probably too high a figure closer to 1 c appears more realistic the volcanological uncertainties need to be appreciated before accepting arguments for catastrophic consequences of the toba super eruption

stratigraphy of the toba tuffs and the evolution of the toba caldera complex sumatra indonesia during the past 1 2 m y a magma chamber of batholithic proportions has developed under the 100 by 30 km toba caldera complex four separate eruptions have occurred from vents within the present collapse structure which formed from eruption of the 2800 km3 youngest toba tuff ytt at 74 ka eruption of the three older toba tuffs alternated from calderas situated in northern and southern portions of the present caldera the northern caldera apparently developed upon a large andesitic stratovolcano the calderas associated with the three older tuffs are obscured by caldera collapse and resurgence resulting from eruption of the ytt samosir island and the uluan block are two sides of a single resurgent dome that has resurged since eruption of the ytt samosir island is composed of thick ytt caldera fill whereas the uluan block consists mainly of the oldest toba tuff ott in the past 74000 years lava domes have been extruded on samosir island and along the caldera s western ring fracture this part of the ring fracture is the site of the only current activity at toba updoming and fumarolic activity the toba eruptions document the growth of the laterally continuous magma body which eventually erupted the ytt repose periods between the four toba tuffs range between 0 34 and 0 43 m y and give insights into pluton emplacement and magmatic evolution at toba

paleomagnetic observations from lake sediments on samosir island toba caldera indonesia and its late pleistocene resurgence approximately 74 ka toba caldera in sumatra indonesia erupted in one of the most catastrophic supereruptions in earth s history resurgent uplift of the caldera floor raised samosir island 700 m above lake toba exposing valuable lake sediments to constrain sediment chronology we collected 173 discrete paleomagnetic 8 cm 3 cubes and 15 radiocarbon samples from six sections across the island bulk organic 14 c ages provide an initial chronostratigraphic framework ranging from 12 to 46 ka natural and laboratory magnetizations were studied using alternating field demagnetization a generally well defined primary magnetization is isolated using principal component analysis comparison of inclination and to a lesser degree declination across independently dated sections suggests paleomagnetic secular variation psv is recorded average inclination of 6 is more negative than a geocentric axial dipole would predict but consistent with an eastward extension of the negative inclination anomaly observed in the western equatorial pacific the 14 c and psv derived age model constrains resurgent uplift confirming faster uplift rates to the east and slower rates to the west while suggesting that fault blocks moved differentially from each other within a generally trapdoor type configuration

the taupo eruption new zealand i general aspects the ca a d 186 taupo eruption was the latest eruption at the taupo volcanic centre occurring from a vent at horomatangi reefs now submerged beneath lake taupo in the central north island of new zealand minor initial phreatomagmatic activity was followed by the dry vent 6 km 3 hatepe plinian outburst large amounts of water then entered the vent during the 2 5 km 3 hatepe phreatoplinian ash phase eventually stopping the eruption though large amounts of water continued to be ejected from the vent area causing gullying of the ash deposits after a break of several hours to weeks phreatoplinian activity resumed generating the 1 3 km 3 rotongaio ash notable for its fine grainsize and for containing significant quantities of non or poorly vesicular juvenile material the vent area then became dry again and eruption rates and power markedly increased into the 23 km 3 taupo ultraplinian phase which is the most powerful plinian outburst yet documented synchronous with this ultraplinian activity lesser volumes of non to partially welded ignimbrite were generated by diversion of ejecta from or partial collapse of the eruption column the rapid rate of magma withdraw al during this phase removed support from the vent area to trigger local vent collapse and initiate the catastrophic eruption of the ca 30 km 3 taupo ignimbrite finally after some years lava was extruded on to the floor of the reformed lake taupo and floating fragments derived from the lava carapace were driven ashore the known eruption volume is more than 65 km 3 while additional volumes are represented by primary material now beneath lake taupo and layer 3 to the ignim brite phases a total volume of more than 105 km 3 is likely equivalent to more than 35 km 3 of magma plus more than 3 km 3 of lithic debris airfall deposits more than 10 cm thick blanketed 30000 km 2 of land east of the vent while ignimbrite covers a near circular area of 20000 km 2 widespread and locally severe ground shaking occurred during but mostly after the eruption associated with subsidence in the lake taupo basin secondary deposits are abundant above and extending beyond the taupo ignimbrite consisting of the products of surface water interacting with the still hot ignimbrite and subsequent water reworking of the light pumiceous materials the complexity and size of this eruption preclude accurate forecasting of the size nature and return period of the inevitable next eruption from the taupo volcanic centre

case study finite element method and artificial neural network models for flow through jeziorsko earthfill dam in poland a finite element method fem and an artificial neural network ann model were developed to simulate flow through jeziorsko earthfill dam in poland the developed fem is capable of simulating two dimensional unsteady and nonuniform flow through a nonhomogenous and anisotropic saturated and unsaturated porous body of an earthfill dam for jeziorsko dam the fem model had 5 497 triangular elements and 3 010 nodes with the fem network being made denser in the dam body and in the neighborhood of the drainage ditches the ann model developed for jeziorsko dam was a feedforward three layer network employing the sigmoid function as an activator and the back propagation algorithm for the network learning the water levels on the upstream and downstream sides of the dam were input variables and the water levels in the piezometers were the target outputs in the ann model the two models were calibrated and verified using the piezometer data collected on a section of the jeziorsko dam the water levels computed by the models satisfactorily compared with those measured by the piezometers the model results also revealed that the ann model performed as good as and in some cases better than the fem model this case study offers insight into the adequacy of ann as well as its competitiveness against fem for predicting seepage through an earthfill dam body