predicting yield strengths and effusion rates of lava domes from morphology and underlying topography abstract to investigate the effects of slope on the morphology of lava domes laboratory experiments were conducted with a peg kaolin slurry erupted into cold water on slopes ranging from 0 to 60 in each experiment the slope effusion rate and water temperature were varied producing four distinct morphologies spiny lobate platy and no crust each morphology is correlated with b and slope where b is defined as the ratio of the timescale of solidification to the timescale of advection as the underlying slope increases from 0 to 40 each morphology forms at a lower value of b than it would on a horizontal surface above 40 the transitions between morphologies become independent of slope and the platy morphology is no longer observed once a range of b values for a dome is determined based on its morphology and slope its yield strength or effusion rate can be calculated in the case of active domes observations of the effusion rate can be used to calculate yield strength while for prehistoric domes an assumption of yield strength based on composition is used to determine the effusion rate for active domes we estimate yield strengths of 0 4 7 3 10 5 pa and effusion rate ranges for prehistoric domes of 0 1 330 m 3 s 1 these values compare well with yield strengths of 1 0 2 0 10 5 pa measured in the laboratory and effusion rates of 0 1 40 m 3 s 1 observed during historically active dome eruptions

new chronological constraints for middle palaeolithic mis 6 5 3 cave sequences in eastern transylvania romania abstract the middle to upper palaeolithic transition is one of the crucial periods of change in the prehistory of europe due to the full emergence continent wide of modern human lithic technologies and detrimental of neanderthal survival knowledge about the transition is growing however the evidence for cultural and technological developments for the middle palaeolithic in the carpathian lower danube basin is still rather sparse here we discuss latest findings arising from a chronological investigation of middle palaeolithic assemblages within the varghis karst eastern transylvania romania combining our first chronological results with information from previous excavations we can distinguish two main stages of habitation albeit middle palaeolithic lithics and faunal remains appear scattered throughout the investigated profile within the abri 122 rock shelter in order to augment the typological cultural considerations we applied direct radiocarbon dating on bones and charcoal from within the occupation layers radiocarbon dating of bones suggests that the middle palaeolithic sequence is older than the upper dating limit of the method whereas direct luminescence ages on the lowermost productive horizon and immediately above it indicate surprisingly old ages of ca 106 141 ka osl optically stimulated or 99 174 ka irsl infrared stimulated multiple protocol dating of charcoal found within the two habitation layers produced ages 38 14 c ka bp also suggesting that the lowermost lithic rich horizon pertains to the middle palaeolithic industries overall the recovered lithics currently forming one of the most significant collections for romania are fully consistent with two main habitation phases connected to middle palaeolithic cultural affinities the occurrence of a volcanic ash layer within ursului cave and originating from the ciomadul volcanic complex carpathians is first reported here recently dated to 43 50 ka it might represent an important marker horizon providing that it is identified within other palaeolithic cave assemblages

endogenous growth of dacite dome at unzen volcano japan 1993 1994 a dacite dome at unzen volcano grew mainly exogenously when it was small and the effusion rate was high but endogenously when the dome became large and the effusion rate declined the endogenous dome that has grown since late 1993 shows a shape classified as pelean whereas the earlier stage had a low lava dome shape the carapace of the endogenous dome moved like the crust of a basaltic lava pillow although the dome is several hundred times larger than such pillows the surface carapace was carried from the inside of the dome where it had been produced and it thickened as it cooled the crater floor was strongly deformed by the advancing endogenous dome the movement and crater floor deformation can be compared to that of a tractor tread moving on unconsolidated ground

effects of eruption history and cooling rate on lava dome growth to better understand the factors controlling the shapes of lava domes laboratory simulations measurements from active and prehistoric flows and dimensional analysis were used to explore how effusion history and cooling rate affect the final geometry of a dome fifty experiments were conducted in which a fixed volume of polyethylene glycol wax was injected into a tank of cold sucrose solution either as one continuous event or as a series of shorter pulses separated by repose periods when the wax cooling rates exceeded a critical minimum value the dome aspect ratios height diameter increased steadily with erupted volume over the course of a single experiment and the rate at which height increased with volume depended linearly on the time averaged effusion rate thus the average effusion rate could be estimated from observations of how the dome shape changed with time our experimental results and dimensional analyses were compared with several groups of natural lava flows the recently emplaced mount st helens and soufriere domes which had been carefully monitored while active three sets of prehistoric rhyolite domes that varied in eruptive style and shape and two sets of holocene domes with similar shapes but different compositions geometric measurements suggest that dome morphology can be directly correlated with effusion rate for domes of similar composition from the same locality and that shape alone can be related to a dimensionless number comparing effusion rate and cooling rate extrapolation to the venusian pancake domes suggests that they formed from relatively viscous lavas extruded either episodically or at average effusion rates low enough to allow solidified surface crust to exert a dominating influence on the final morphology

late quaternary productivity changes from offshore southeastern australia a biomarker approach reconstructions of primary productivity at low latitudes have been the focus of several studies to better understand how the export of nutrient rich intermediate southern ocean so waters influences productivity at these latitudes this was triggered by the general observation of minima in the planktonic foraminiferal delta c 13 values during deglaciations which was interpreted as an isotopic signal of intermediate so waters together with a concomitant increase in diatom productivity at some equatorial sites however the impact of these so waters on productivity at higher latitudes is not well constrained here we compare a high resolution planktonic foraminiferal delta c 13 record with total organic carbon and biomarker records for proboscia diatoms and haptophytes in marine sediments from offshore southeastern australia the planktonic foraminiferal delta c 13 record shows distinct minima during deglaciations and the marine isotope stage 4 3 transition tentatively suggesting that c 13 depleted so waters reached the coast of southeastern australia however it did not result in increased productivity during these periods instead the highest primary productivity period as indicated by total organic carbon and alkenone accumulation rates occurred during the last glacial maximum while proboscia diatoms mainly proliferated during interglacials and marine isotope stage 3 matching periods of increased diatom productivity in some sites of the eastern equatorial pacific our study suggests that increased primary productivity offshore southeastern australia was mainly due to stronger westerly winds during glacial periods while proboscia diatom productivity was probably controlled by the transport of silicic acid to this area

stress field and seismotectonics of northern south america we have integrated in situ stress neotectonic and global positioning system data to investigate the complex interactions among the south american caribbean and nazca plates and the costa rica panama microplate and to examine different seismotectonic models that have been proposed for the region the resulting data set was used to generate an integrated stress map of the region that shows that the stress field in northern south america varies systematically in both orientation and relative magnitude in the southwestern part of the study area the ecuadorian andes stress province exhibits strong e w compression resulting from the subduction of the nazca plate beneath the south american plate in the north andes stress province the observed nw se compression may result from the convergence between the caribbean and the south american plates and or the negative buoyancy of the already subducted caribbean plate beneath northwestern south america possible convergence between the costa rica panama microplate with respect to northwestern south america may also be a source of compression in this region in north and northeastern venezuela normal and strike slip faulting with a ne sw direction of extension characterizes the san sebastian el pilar stress province

geochemistry and tectonic development of cenozoic magmatism in the carpathian pannonian region this review considers the magmatic processes in the carpathian pannonian region cpr from early miocene to recent times as well as the contemporaneous magmatism at its southern boundary in the dinaride and balkans regions this geodynamic system was controlled by the cretaceous to neogene subduction and collision of africa with eurasia especially by adria that generated the alps to the north the dinaride hellenide belt to the east and caused extrusion collision and inversion tectonics in the cpr this long lived subduction system supplied the mantle lithosphere with various subduction components the cpr contains magmatic rocks of highly diverse compositions calc alkaline k alkalic ultrapotassic and na alkalic all generated in response to complex post collisional tectonic processes these processes formed extensional basins in response to an interplay of compression and extension within two microplates alcapa and tisza dacia competition between the different tectonic processes at both local and regional scales caused variations in the associated magmatism mainly as a result of extension and differences in the rheological properties and composition of the lithosphere extension led to disintegration of the microplates that finally developed into two basin systems the pannonian and transylvanian basins the southern border of the cpr is edged by the adria microplate via sava and vardar zones that acted as regional transcurrent tectonic areas during miocene recent times major trace element and isotopic data of post early miocene magmatic rocks from the cpr suggest that subduction components were preserved in the lithospheric mantle after the cretaceous miocene subduction and were reactivated especially by extensional tectonic processes that allowed uprise of the asthenosphere changes in the composition of the mantle through time support geodynamic scenarios of post collision and extension processes linked to the evolution of the main blocks and their boundary relations weak lithospheric blocks i e alcapa and western tisza generated the pannonian basin and the adjacent styrian transdanubian and z rand basins which show high rates of vertical movement accompanied by a range of magmatic compositions strong lithospheric blocks i e dacia were only marginally deformed where strike slip faulting was associated with magmatism and extension at the boundary of adria and tisza dacia strike slip tectonics and core complex extension were associated with small volume miocene magmatism in narrow extensional sedimentary basins or granitoids in core complex detachment systems along older suture zones sava and vardar accommodating the extension in the pannonian basin and afterward pliocene quaternary inversion magmas of various compositions appear to have acted as lubricants in a range of tectonic processes

eruptive history of the late quaternary ciomadul csomad volcano east carpathians part i timing of lava dome activity located at the southern tip of the intra carpathian volcanic range in romania and composed of a dozen dacitic lava domes the ciomadul csomad volcanic complex is the youngest eruptive centre of the carpatho pannonian region whereas in the last decade the explosive history of ciomadul since 50 ka has been well constrained by numerous studies the chronology of the dome sequence still lacks robust chronological constraints and an extended analysis of all available data here we apply a detailed k ar dating approach to refine the chronology of the lava dome eruptions using the unspiked k ar cassignol gillot technique our dating focused on the most voluminous central part of the lava dome complex new eruption ages were determined following a strict separation of 10 g of groundmass from about 3 kg of unaltered sample rocks thereby isolating material whose cooling was contemporaneous with the eruption the newly applied methodology mainly consisting of a double full preparation first at larger grain size 0 4 mm and then at 100 m provides an appropriate procedure to separate suitable material to obtain the k ar age of the eruption i e the sample s groundmass in which there is no risk of the presence of older inherited crystals our new geochronological data set gives an improved insight into the temporal construction of the ciomadul volcanic complex where due to the method applied here all ages are younger than those from previous studies that used whole rock k ar ages our new results show that ciomadul s volcanic activity began with the construction of the south eastern peripheral domes from ca 850 ka to 440 ka after a ca 250 ky long repose period the activity resumed in the northern part at around 200 ka with subsequent domes emplaced between 200 and 130 ka aligned roughly north south in the western central part of the complex following a 30 ky long quiescence period the eastern central domes formed between 100 and 60 ka in addition to the chronological history of lava dome volcanism we also investigated the sequence of crystallization of mineral phases present in the lavas with respect to the modification of eruption ages ages obtained on pure minerals plagioclase amphibole and biotite are systematically older than those obtained on groundmass showing that most of them formed up to 1 85 myr before eruption in a long lived pre ciomadul magmatic system crystal size distribution csd data support the age contrasts between juvenile groundmass and older inherited minerals after injection of new magma and convective mixing with crystal clots ascent of the resulting mixture led to eruptions of material representing contrasting ages

the effects of secular disequilibrium on u th he systematics and dating of quaternary volcanic zircon and apatite the u th he dating method applied to u rich phases such as zircon and apatite has sufficient sensitivity and precision to be of potential use for dating relatively recent geologic events such as volcanic eruptions however in phases with crystallization ages less than 1 ma chemical fractionation within the 238 u decay series may modify the he ingrowth rate causing he ages computed from the secular equilibrium age equation to be incorrect the resulting systematic error depends on the 230 th 238 u activity ratio of the dated phase when it is erupted and on the eruption age zircons which exclude th relative to u will likely have secular equilibrium he ages that underestimate the eruption age by up to a few tens of decreasing with increasing eruption age apatites tend to accommodate u and th with little fractionation so apatite secular equilibrium he ages will be nearly concordant with eruption age if minerals are erupted immediately after crystallization the disequilibrium effect can be reasonably accounted for based on th u systematics however crystals are likely to reside for unknown but potentially long periods in a magma chamber such that the degree of secular disequilibrium will be reduced prior to the onset of he accumulation u th he analyses of co genetic phases that fractionate the u th ratio differently like apatite and zircon can be used to better constrain eruption age as well as to provide insights into magma chamber residence time we illustrate this approach with u th he analyses of zircons and apatites of the pleistocene age rangitawa tephra new zealand

eruptive history of a low frequency and low output rate pleistocene volcano ciomadul south harghita mts romania based on a new set of k ar age data and detailed field observations the eruptive history of the youngest volcano in the whole carpathian pannonian region was reconstructed ciomadul volcano is a dacitic dome complex located at the southeastern end of the c limani gurghiu harghita neogene volcanic range in the east carpathians it consists of a central group of extrusive domes the ciomadul mare and haramul mare dome clusters and the koves ponk dome surrounded by a number of isolated peripheral domes some of them strongly eroded balvanyos puturosul and others topographically well preserved haramul mic dealul mare one of the domes dealul cet ii still preserves part of its original breccia envelope a large number of bread crust bombs found mostly along the southern slopes of the volcano suggest that the dome building activity at ciomadul was punctuated by short vulcanian type explosive events two late stage explosive events that ended the volcanic activity of ciomadul left behind two topographically well preserved craters disrupting the central group of domes the larger diameter shallower and older mohos phreatomagmatic crater and the smaller deeper and younger sf ana sub plinian crater phreatomagmatic products of the mohos center including accretionary lapilli bearing base surge deposits and poorly sorted airfall deposits with impact sags are known close to the eastern crater rim a key section studied in detail south of b ile tusnad shows the temporal succession of eruptive episodes related to the sf ana sub plinian event as well as relationships with the older dome building stages the age of this last eruptive event is loosely constrained by radiocarbon dating of charcoal pieces and paleosoil organic matter at ca 27 35 ka the age of the mohos eruption is not constrained but we suggest that it is closely related to the sf ana eruption the whole volcanic history of ciomadul spans over ca 1 myr starting with the building up of peripheral domes and then concentrating in its central part ciomadul appears as a small volume ca 8 74 km3 and very low frequency and low output rate volcano ca 9 km3 myr at the terminus of a gradually diminishing and extinguishing volcanic range a number of geodynamically active features strongly suggest that the magma plumbing system beneath ciomadul is not completely frozen so future activity cannot be ruled out

late stage volcano geomorphic evolution of the pleistocene san francisco mountain arizona usa based on high resolution dem analysis and 40ar 39ar chronology the cone building volcanic activity and subsequent erosion of san francisco mountain az usa were studied by using high resolution digital elevation model dem analysis and new 40ar 39ar dating by defining remnants or planezes of the volcano flanks in dem derived images the original edifice can be reconstructed we propose a two cone model with adjacent summit vents which were active in different times the reconstructed cones were 4 460 and 4 350 m high a s l corresponding to 2 160 and 2 050 m relative height respectively new 40ar 39ar data allow us to decipher the chronological details of the cone building activity we dated the older and younger andesites of the volcano that according to previous mapping built the stage 2 and stage 3 stratocones respectively the new 40ar 39ar plateau ages yielded 589 556 ka for the older and 514 505 ka for the younger andesites supporting their distinct nature with a possible dormant period between the obtained ages imply an intense final 100 ka long cone building activity terminating 100 ka earlier than indicated by previous k ar ages moreover 40ar 39ar dating constrains the formation of the inner basin an elliptical depression in the center of the volcano initially created by flank collapse a 530 ka age with a 58 4 ka 2 error for a post depression dacite suggests that the collapse event is geochronologically indistinguishable from the termination of the andesitic cone building activity according to our dem analysis the original cone of san francisco mountain had a volume of about 80 km3 of this volume 7 5 km3 was removed by the flank collapse and subsequent glacial erosion creating the present day enlarged inner basin and 2 km3 was removed from the outer valleys by erosion based on volumetric analysis and previous and new radiometric ages the average long term eruption rate of san francisco mountain was 0 2 km3 ka which is a medium rate for long lived stratovolcanoes however according to the new 40ar 39ar dates for the last 100 ka period the final stratovolcanic activity was characterized by a greater 0 3 km3 ka rate

velocity field across the southern caribbean plate boundary and estimates of caribbean south american plate motion using gps geodesy 1994 2000 global positioning system gps observations between 1994 and 2000 at twenty two sites in the lesser antilles and northern south america indicate that the caribbean plate along its southern boundary slips at a rate of 20 5 2 mm a with an azimuth of n 84 2 e at 65 w relative to the south american plate east of 68 w 80 of the dextral slip is contained within a 80 km wide shear zone centered on the el pilar san sebastian fault system west of 68 w the plate boundary broadens to more than 300 km with dextral shear shared between the northeast trending bocono fault 9 11 mm a in western venezuelan and an offshore system near the northern coast

seismic strain rates and distributed continental deformation in the northern andes and three dimensional seismotectonics of northwestern south america abstract the seismic strain rates and configuration in the northern andes are estimated by summing the components of the centroid moment tensor cmt solutions for earthquakes with mw 5 0 and are compared with those predicted by various models of relative plate motions and gps data moment tensor components are summed linearly in four different regions with similar seismotectonics to infer changes in the regional strain patterns along the northern andes and to retrieve strain rates and relative plate velocities between this region and the stable south american plate the andean seismic strain rates are the result of east southeast directed contraction due to the collision of the nazca and caribbean plates with the south american plate and the collision of the panama block against central colombia with a component of northeast directed motion due to the obliquity of the eastern boundary of the northern andes with respect to the boundary of the nazca and caribbean plates with the south american plate along the colombia trench and the southern caribbean deformation zone respectively where the convergence is normal the present motion of the central andes towards the northeast does not require the plate boundary between the caribbean and south american plates to be along the eastern cordillera of colombia and the bocono fault in venezuela the seismic moment rates for the northern andes are small compared to the total expected seismic strain rates calculated from plate motion models and gps data suggesting that most of the strain is released aseismically and that is accommodated by folding fault creeping rigid block translation or other undetermined processes finally a three dimensional model of the cmt solutions and other seismicity in northwestern south america is presented where major subducting slabs including the peru flat slab and the ecuador and central colombia segments of the nazca and caribbean plates become more evident and easier to interpret the caribbean plate is interpreted to culminate at the location of the bucaramanga nest offering an explanation to this swarm of seismicity in the northern andes

morphometry of scoria cones located on a volcano flank a case study from mt etna italy based on high resolution lidar data abstract by using new high resolution 2 m digital elevation model derived from the 2005 lidar survey of mt etna volcano italy our study measured the classical morphometrical parameters for scoria cones i e w co cone width w cr crater diameter h cone height as well as volume inclination of cone slope and substrate and a number of other parameters for 135 scoria cones of mt etna volume and age distribution of cones shows that there is no direct structural control on their emplacement in terms of etna s rift zones the cones are progressively smaller in size toward summit which can be explained by the large volcano s feeding system and progressively frequent lava burial toward top a careful analysis of h w co ratio determined as 0 18 for other volcanic fields worldwide shows that this ratio strongly depends on 1 the calculation method of h and 2 lava burial of cone for etnean cones applying an improved method for calculating h relative to the dipping substrate results in a significantly lowered standard h w co ratio 0 137 which in turn questions the validity of the classical value of 0 18 in the case of large central volcanoes the reduction of the ratio is not only due to methodology but also to the common lava burial this can be expressed even better if h mean is used instead of h max h mean w co 0 098 using this measure at etna well formed cones have higher ratios than structurally deformed e g double or rifted cones furthermore although the sampled scoria cones at etna have formed in a relatively narrow time interval h w co corresponding to erosional changes detected globally h w co 0 143 0 135 and 0 115 for three age classes of etna s scoria cones corresponding to average slopes of 26 6 23 9 and 23 7 because the morphometrical effect of position on a dipping substrate as well as lava burial exceeds the effect of erosion we call attention to use caution in simply using the h w co ratio of scoria cones for detecting age especially on large active volcanoes

tectonic implications of tomographic images of subducted lithosphere beneath northwestern south america we used seismic tomography to investigate the complex structure of the upper mantle below northwestern south america images of slab structure not delineated by previous seismicity studies help us to refine existing tectonic models of subducted caribbean pacific lithosphere beneath the study area beneath western venezuela and colombia we distinguish two slabs a maracaibo and a redefined bucaramanga slab the maracaibo slab coinciding with most of the bucaramanga slab previously defined by w d pennington dips in a direction of 150 at an angle of 17 to a depth of 275 km and correlates to the subducted late cretaceous oceanic plateau of the caribbean plate farther south a second slab dips at an angle of 50 in a direction of 125 to a depth of at least 500 km and correlates to the subducted oceanic crust of the nazca plate and the downdip extension of the panama island arc we refer to this slab as the redefined bucaramanga slab because it is different from the bucaramanga slab segment defined by pennington the area of the south american plate overriding both slabs is characterized by the absence of an active volcanic arc an anomalously wide topographically uplifted and tectonically active area and the northward escape of the maracaibo block along active strike slip faults in support of earlier studies we attribute this to the underthrusting of the caribbean oceanic plateau our shallowly dipping maracaibo slab along the base of the south american lithosphere and to the recent collision of the panama island arc rafted in on more steeply dipping crust of the nazca plate our redefined bucaramanga slab

monitoring lava dome growth during the 2004 2008 mount st helens washington eruption using oblique terrestrial photography abstract we present an analysis of lava dome growth during the 2004 2008 eruption of mount st helens using oblique terrestrial images from a network of remotely placed cameras this underutilized monitoring tool augmented more traditional monitoring techniques and was used to provide a robust assessment of the nature pace and state of the eruption and to quantify the kinematics of dome growth eruption monitoring using terrestrial photography began with a single camera deployed at the mouth of the volcano s crater during the first year of activity analysis of those images indicates that the average lineal extrusion rate decayed approximately logarithmically from about 8 m d to about 2 m d 2 m d from november 2004 through december 2005 and suggests that the extrusion rate fluctuated on time scales of days to weeks from may 2006 through september 2007 imagery from multiple cameras deployed around the volcano allowed determination of 3 dimensional motion across the dome complex analysis of the multi camera imagery shows spatially differential but remarkably steady to gradually slowing motion from about 1 2 m d from may through october 2006 to about 0 2 1 0 m d from may through september 2007 in contrast to the fluctuations in lineal extrusion rate documented during the first year of eruption dome motion from may 2006 through september 2007 was monotonic 0 10 m d to gradually slowing on time scales of weeks to months the ability to measure spatial and temporal rates of motion of the effusing lava dome from oblique terrestrial photographs provided a significant and sometimes the sole means of identifying and quantifying dome growth during the eruption and it demonstrates the utility of using frequent long term terrestrial photography to monitor and study volcanic eruptions

an insight into the bucaramanga nest abstract we used the local seismicity for the period of 1993 to 2001 in the northeast of colombia to show the existence of two slabs in the north and south of the bucaramanga nest the northern slab has a dip angle of about 25 and the southern slab has a 50 dip angle while the dip in the bucaramanga nest is about 29 in order to explain the nature of the bucaramanga nest we proposed the scenario of collision between these two slabs using a 3d finite element model fem we show that collision can concentrate modify and perturb the stress field the active process of dehydration embrittlement at intermediate depths and the concentrated stress field in the collision zone may explain the high rate of seismic activity inside the bucaramanga nest the perturbed and modified stress field resulting from the simultaneous effect of collision between two subducted slabs and subduction of the lithosphere under its own weight can explain the variation in the focal mechanism of micro earthquakes and the complexity in the source of the moderate size earthquakes in the bucaramanga nest

flexural and gravity modelling of the merida andes and barinas apure basin western venezuela abstract the kinematic evolution of the barinas apure basin and the southern merida andes from lower miocene to the present is numerically modelled using flexural isostatic theory and geophysical and geological data two published regional transects are used to build up a reference section which is then used to constrain important parameters e g shortenings and sedimentary thicknesses for the flexural modelling to control the location of the main fault system in the flexural model earthquake information is also used the estimated flexural elastic thickness of the south american lithosphere beneath the barinas apure basin and the merida andes range is 25 km the value for the final total shortening is 60 km the flexural isostatic model shows that the andean uplift has caused the south american lithosphere subsidence and the development of the barinas apure basin in addition gravity modelling was used to understand deep crustal features that could not be predicted by flexural theory consequently the best fit flexural model is used to build a gravity model across the merida andes and the barinas apure basin preserving the best controlled structural features from the flexural modelling e g basin wavelength and depth and slightly changing the main bodies density values and deep crustal structures the final gravity model is intended to be representative of the major features affecting the gravity field in the study area the predicted morphology in the lower crustal level of the final gravity model favours the hypothesis of a present delamination or megathrust of the maracaibo crust over the south american shield this process would use the conrad discontinuity as a main detachment surface within an incipient nw dipping continental subduction

70 m y history 139 69 ma for the caribbean large igneous province it is commonly accepted that large igneous provinces are formed through catastrophic volcanic events occurring over vast areas within a few million years at the initiation of hotspots mantle plumes new 40ar 39ar ages 111 139 ma and geochemical results from the nicoya peninsula costa rica extend the age range of volcanism in the caribbean large igneous province to 70 m y 69 139 ma our results are not consistent with the formation of this vast igneous province through a single plume head at the initiation of a mantle plume such as the galapagos instead we propose that multiple oceanic intraplate igneous structures such as plateaus and hotspot tracks were accumulated through the subduction process the igneous structures could be remnants of the earlier history of the galapagos hotspot making it one of the oldest active hotspots on earth alternatively they could have been derived from several spatially distinct mantle melting events that sampled similar source material e g oceanic lithosphere of similar age

microseismicity evidence for subduction of the caribbean plate beneath the south american plate in northwestern venezuela over 1100 microearthquakes with body wave magnitude mb 4 have been located in western venezuela and the southwestern caribbean region since the installation in 1980 of the venezuelan seismological array together with 120 events of mb 4 one of them with surface wave magnitude ms 6 this tectonically complex region is part of the boundary between the caribbean and the south american plates the main seismically active feature inland in western venezuela is the northeast striking 600 km long 100 km wide right lateral strike slip bocono fault zone along the venezuelan andes about 80 of the earthquakes located in the entire region in the period 1980 mid 1995 have occurred on this fault zone at focal depths 20 km microearthquake activity at lower rates also occurs northwest of the venezuelan andes both in the continental and caribbean sea regions part of this activity takes place at depths down to 150 km northwest oriented seismicity depth profiles show the existence of a benioff zone dipping to the southeast beneath northwestern venezuela and northern colombia this indicates the presence of a northeast striking southeast dipping subducted slab of the caribbean plate beneath the south american plate hypocentral locations show that the northeastern end of this subduction occurs northwest of the curacao aruba region in the vicinity of a northwest trending right lateral strike slip fault zone that joins up with the northeastern end of the bocono fault zone this latter place turns out to be the western end of the east west striking san sebastian fault along the venezuelan coast

morphometry of scoria cones and their relation to geodynamic setting a dem based analysis abstract the morphometry of a great number of scoria cones belonging to volcanic fields of various geodynamic settings has been measured and analyzed addressing the question whether there is a relation between the prevalent cone shape in a given field and the geodynamic setting of the field itself morphometric analysis was carried out on freely downloadable digital elevation models dems the accuracy of the used dems and the associated error in scoria cone morphometry were determined by cross comparing high resolution lidar derived dems usgs ned tinitaly dem and aster gdem the 10 m tinitaly 01 and usgs ned dems are proven to be suitable for scoria cone morphometry whereas aster gdem can be used reliably for cones with volume greater than 30 10 6 m 3 according to a detailed morphometry of all scoria cones we propose that the cones related to subductional setting show relatively higher values of h c o w co and lower values of w cr w co than the cones related to extensional setting the detected differences can be imputable to peculiar eruption dynamics resulting in slight but systematic changes in shape and differences in lithological and sedimentological characteristics that govern post eruptive erosion to constrain the pathway of scoria cone erosion the detected morphometric changes were also interpreted using a simple linear degradation model utilizing the obtained simulation results the inferred initial cone base and the age of scoria cones we calculated a diffusion coefficient k for several dated cones which are related to the prevalent climate our results despite the high error associated allow to assess the median k for all volcanic fields due to the complexity of the factors behind it is not easy to understand if the prevalent shape characterizing a certain volcanic field is due mainly to sin eruptive or post eruptive mechanisms however our distinction between the two main geodynamic settings may be the first step to decipher these factors

morphometrical and geochronological constraints on the youngest eruptive activity in east central europe at the ciomadul csomad lava dome complex east carpathians abstract the timing of late pleistocene volcanic activity of the ciomadul csomad dacitic lava dome complex site of the youngest eruptions in the carpathians has been constrained by morphometric analysis and radiometric chronology pelean domes and asymmetric domes coulees built up the volcano including the central edifice that hosts the youngest twin craters of mohos mohos peat bog and lake st ana szent anna a comparative digital elevation model dem based morphometric analysis of lava domes 29 worldwide examples including 5 domes from ciomadul shows that it is the mean slope of the upper dome flank that correlates best with age although the logarithmic relationship is only moderately strong r 0 80 slope characteristics of the ciomadul domes fit to those of 10 100 ka old domes these young ages contradict the previous k ar dates giving as old as 1 ma ages on a number of domes but are supported by ongoing u pb and u th he zircon dating the latter methods constrain the whole volcanic activity to the past 250 ka and the emplacement of most lava domes within the period of 150 100 ka the volcanism at ciomadul produced alternating effusive and explosive eruptions including lava dome collapses and successive crater formations the latest possibly subplinian explosive event formed the well preserved st ana crater radiocarbon dating of organic remains from a sediment core that reached 11 m into the lacustrine infill of st ana suggests that the crater was formed prior to 26 000 years bp

the latest explosive eruptions of ciomadul csomad volcano east carpathians a tephrostratigraphic approach for the 51 29 ka bp time interval abstract the most recent mainly explosive eruptions of ciomadul the youngest volcano in the carpatho pannonian region have been constrained by detailed field volcanological studies major element pumice glass geochemistry luminescence and radiocarbon dating and a critical evaluation of available geochronological data these investigations were complemented by the first tephrostratigraphic studies of the lacustrine infill of ciomadul s twin craters st ana and mohos that received tephra deposition during the last eruptions of the volcano our analysis shows that significant explosive activity collectively called eppa early phreatomagmatic and plinian activity started at ciomadul in or around the present day mohos the older crater at 51 ka bp these eruptions resulted in a thick succession of pyroclastic fall deposits found in both proximal and medial distal localities around the volcano characterized by highly silicic rhyolitic glass chemical compositions ca 75 2 79 8 wt sio 2 the eppa stage was terminated by a subplinian plinian eruption at 43 ka bp producing pumiceous pyroclastic fall and flow deposits of similar glass composition probably from a proto st ana vent located at or around the younger crater hosting the present day lake st ana after a quiescent period with a proposed lava dome growth in the st ana crater a new explosive stage began defined as mpa middle plinian activity in particular a significant two phase eruption occurred at 31 5 ka bp producing pyroclastic flows from vulcanian explosions disrupting the preexisting lava dome of sf ana and followed by pumiceous fallout from a plinian eruption column related pyroclastic deposits show a characteristic less evolved rhyolitic glass composition ca 70 2 74 5 wt sio 2 and occur both in proximal and medial distal localities up to 21 km from source the mpa eruptions that may have pre shaped a crater similar to but possibly smaller than the present day st ana crater was followed by a so far unknown but likewise violent last eruptive stage from the same vent creating the final morphology of the crater this stage referred to as lspa latest st ana phreatomagmatic activity produced pyroclastic fall deposits of more evolved rhyolitic glass composition ca 72 8 78 8 wt sio 2 compared to that of the previous mpa stage according to radiocarbon age constraints on bulk sediment charcoal and organic matter from lacustrine sediments recovered from both craters the last of these phreatomagmatic eruptions that draped the landscape toward the east and southeast of the volcano occurred at 29 6 ka bp some 2000 years later than the previously suggested last eruption of ciomadul

the onset of the volcanism in the ciomadul volcanic dome complex eastern carpathians eruption chronology and magma type variation abstract combined zircon u th pb and u th he dating was applied to refine the eruption chronology of the last 2 myr for the andesitic and dacitic pilisca volcano and ciomadul volcanic dome complex cvdc the youngest volcanic area of the carpathian pannonian region located in the southernmost harghita eastern central europe the proposed eruption ages which are supported also by the youngest zircon crystallization ages are much younger than the previously determined k ar ages by dating every known eruption center in the cvdc repose times between eruptive events were also accurately determined eruption of the andesite at murgul mare 1865 87 ka and dacite of the pilisca volcanic complex 1640 37 ka terminated an earlier pulse of volcanic activity within the southernmost harghita region west of the olt valley this was followed by the onset of the volcanism in the cvdc which occurred after several 100s kyr of eruptive quiescence at ca 1 ma a significant change in the composition of erupted magma occurred from medium k calc alkaline compositions to high k dacitic baba laposa dome at 942 65 ka and shoshonitic magmas malnas and bixad domes 964 46 ka and 907 66 ka respectively noteworthy eruptions of magmas with distinct chemical compositions occurred within a restricted area a few km from one another these oldest lava domes of the cvdc form a nne ssw striking tectonic lineament along the olt valley following a brief ca 100 kyr hiatus extrusion of high k andesitic magma continued at dealul mare 842 53 ka after another ca 200 kyr period of quiescence two high k dacitic lava domes extruded puturosul 642 44 ka and balvanyos 583 30 ka the turnul apor lava extrusion occurred after a ca 200 kyr repose time at 344 33 ka whereas formation of the haramul mic lava dome 154 16 ka represents the onset of the development of the prominent ciomadul volcano the accurate determination of eruption dates shows that the volcanic eruptions were often separated by prolonged ca 100 to 200 kyr quiescence periods demonstration of recurrence of volcanism even after such long dormancy has to be considered in assessing volcanic hazards particularly in seemingly inactive volcanic areas where no holocene eruptions occurred the term of volcanoes with potentially active magma storage illustrates the potential of volcanic rejuvenation for such long dormant volcanoes with the existence of melt bearing crustal magma body

lava flow shapes and dimensions as reflections of magma system conditions abstract the physical conditions producing variation in the shapes of lava extrusions from thin flows to domes to spines are investigated with focus on the influence of the lava thickness the accumulation of lava above the vent acts to increase the vent pressure and reduce the eruption rate in turn the eruption rate determines how the volume and thickness of erupted lava change with time the spreading of lava and the flow of magma from a deep reservoir through a conduit system are therefore coupled a fluid dynamical model is developed to evaluate the influence of magma chamber and conduit dimensions chamber overpressure magma viscosity and dome bulk viscosity on the eruption behaviour and dimensions of the lava flow the model assumes laminar flow of newtonian constant density magma from an overpressured reservoir with elastic walls up a vertical cylindrical conduit and onto a planar horizontal surface on which grows a radially symmetrical lava flow of constant bulk viscosity greater than the magma viscosity two dimensionless numbers characterize the resulting behaviour the ratio of a scale erupted lava volume to the total volume available for eruption and the ratio of the pressure due to a scale thickness of lava to the magma chamber overpressure the dimensionless numbers are used to map the flow behaviours and reveal two extreme extrusion regimes separated by a narrow transition zone one extreme corresponds to thin and voluminous flows and occurs for large deep strongly overpressured magma reservoirs narrow conduits and low viscosity contrasts between the magma and lava the other extreme corresponds to small volume domes and spines and is produced by shallow weakly overpressured chambers wide conduits and high viscosity contrasts near the transitional domain small changes of parameters are sufficient to cause major changes of eruption regime the model provides explanations for the variation in gross morphology of lava extrusions transitions between flow dome and spine eruptions and for long lived episodic extrusion of lava model predictions are consistent with features of the eruptions of montagne pelee 1902 1903 mount st helens 1980 1986 and montserrat 1995 1997 period the model is used to estimate the magnitude of overpressure driving eruptions and suggests that magma buoyancy is important in driving many terrestrial lava dome eruptions the model further suggests that thick extrusions on venus were driven primarily by buoyancy sourced at great depth

plate motions in the north andean region repeated geodetic measurements with the global positioning system gps provide direct measurements of displacements due to plate motions and active crustal deformation in central america and northern south america an area of complex interaction of the nazca cocos caribbean and south american plates the displacement rates for the period 1988 1991 obtained from the results of the first three central and south america casa gps campaigns are in general agreement with the predictions of the nuvel 1 plate motion model but there are differences in detail between the observations and the model the nazca north andes convergence rate vector measured by gps is different from the nuvel 1 vector at 95 confidence the difference implies that the north andes are moving northward relative to south america the measured convergence between the caribbean plate and the north andes suggests that the southern margin of the caribbean plate is located in the south caribbean deformed belt the april 1991 costa rica earthquake and the cocos caribbean convergence rate determined by gps suggest the possibility of significant ongoing deformation between central america and the stable interior of the caribbean plate our gps results are consistent with deformation of the overriding plates at the convergent margins of central and south america and confirm that active convergence is occurring around much of the southern margin of the caribbean plate from colombia west to costa rica costa rica and panama are not part of the stable caribbean plate instead the south caribbean deformed belt and the north panama fold belt probably represent the southern margin of the caribbean plate

exhumation and uplift of the sierras pampeanas preliminary implications from k ar fault gouge dating and low t thermochronology in the sierra de comechingones argentina the sierras pampeanas in central and north western argentina constitute a distinct morphotectonic feature between 27 s and 33 s the last stage of uplift and deformation in this area are interpreted to be closely related to the andean flat slab subduction of the nazca plate beneath the south american plate k ar fault gouge dating and low temperature thermochronology along two transects within the sierra de comechingones reveal a minimum age for the onset of brittle deformation about 340 ma very low exhumation rates since late paleozoic time as well as a total exhumation of about 2 3 km since the late cretaceous new ar ar ages 7 54 1 91 ma of volcanic rocks from the san luis volcanic belt support the eastward propagation of the flat slab magmatic front confirming the onset of flat slab related deformation in this region at 11 2 ma although low temperature thermochronology does not clearly constrain the signal of the andean uplift it is understood that the current structural relief related to the comechingones range has been achieved after the exhumation of both fault walls circa 80 70 ma

new seismic and tomography data in the southern part of the harghita mountains romania southeastern carpathians connection with recent volcanic activity the southern part of the southeastern carpathians represents the site of the most recent volcanic eruptions of the entire carpathian pannonian region the products of these eruptions range from 42 to 10 ka radiocarbon ages in the south harghita mountains high k calc alkaline rocks with adakite like features and at 1 2 0 6 ma k ar ages in the persani mountains alkali basalts they were emplaced in a post collisional regime ciomadul volcano is located at the southernmost part of the nw se oriented c limani gurghiu harghita range crossing the inner part of the southeastern carpathians and in the rough proximity of the vrancea seismic zone at ca 60 km toward nw its magma generation is attributed to geodynamic events closely related to the seismogenic area a number of particular geophysical and geochemical features located in the study region including 1 the abrupt attenuation of the seismic waves originating from the vrancea intermediate depth foci 2 the most intense heat flow anomaly in romania 3 the most prominent 3he 4he anomaly measured in natural postvolcanic gas emanations are all in favor of the hypothesis of a still existing hot local magma chamber data acquired during recent seismic monitoring of the vrancea zone and its neighborhoods suggest an enhancement of the local seismicity beneath the southern edge of the south harghita mts both at crustal and subcrustal levels at the same time recent tomography images obtained using local earthquake data correlate well with the presence of a vertically extended low velocity zone coming from the upper mantle to the assumed magmatic chambers located in the crust the present data supporting the presence of an active crustal magma chamber beneath ciomadul allow us to consider that future volcanic activity at this volcano cannot be discarded

growth and erosion rates of the east carpathians volcanoes constrained by numerical models tectonic and climatic implications abstract the east carpathian volcanic range experienced an along arc late miocene to quaternary migration of eruptive activity during its 11 ma long activity here a novel and complex methodology is presented that yields new geochronological and geomorphological constraints on the evolution of the 20 volcanic edifices new unspiked k ar ages either constrain their lifespan 6 79 0 10 6 47 0 09 ma for seaca t tarca 5 47 0 08 4 61 0 07 ma for v rghis or date the youngest volcanic activity central c limani in parallel numerical reconstructions of volcanic paleo topographies were performed to quantify their shape at the end of their construction stage the inferred initial volcano size shows a wide range 3 to 592 km3 making up the four main successive volcanic segments 910 880 279 and 165 km3 for c limani gurghiu north harghita and south harghita segment respectively totalizing 2200 km3 and an average growth rate of 200 km3 ma at range scale at the volcano scale with only consideration to their respective time spans i e avoiding repose periods growth rate is characterized by two major trends a moderate growth rate 137 km3 ma for the older volcanoes 11 3 6 ma followed by a lower growth rate 28 km3 ma obtained for the plio quaternary volcanoes comparing reconstructed and current topographies yielded a total eroded volume of 524 125 km3 defining averaged denudation of 22 and a 20 m ma erosion rate erosion rates for major climatic periods were computed which highlight the contrasting climatic contexts since 11 ma the highest erosion rate 38 m ma occurred during transitional moderate subtropical continental climate period 9 5 8 2 ma an intermediate erosion rate 14 m ma characterized a moderate continental climate period 8 2 6 8 ma when conditions became less humid the lowest erosion rate 7 m ma reflects the prevailing continental but occasionally semi arid climate 6 8 5 8 ma the highest erosion rate 28 m ma was obtained for plio quaternary times during the interglacial glacial cycles such a quantitative morphometric and geochronological approach demonstrates its efficiency to study volcanic dynamism including both constructional and erosional processes through time

re anchoring the late pleistocene tephrochronology of new zealand based on concordant radiocarbon ages and combined 238u 230th disequilibrium and u th he zircon ages abstract the caldera forming rotoiti eruption from okataina volcano was one of the largest rhyolite events of the last 100 ka in the taupo volcanic zone new zealand its associated widespread tephra layer rotoehu tephra is a significant time marker in terrestrial marine paleoclimate correlation studies in the sw pacific however the accurate and precise age of this eruption and of the subsequent smaller volume earthquake flat eqf eruption has been the subject of controversy despite numerous studies we have applied combined 238u 230th disequilibrium and u th he dating of zircon from rotoiti and eqf deposits and obtained overlapping ages of 45 1 7 3 3 ka and 45 1 6 2 9 ka respectively these results are supported by new and published high precision radiocarbon data bracketing the age of the rotoiti eruption between 44 8 0 3 and 47 5 2 1 ka cal bp these age data are also in good agreement with a range of previously published estimates based on paleoclimate palynology luminescence dating of enclosing sediment and sedimentation rates in terrestrial and marine settings however these results are at variance with a commonly quoted age of 60 ka largely constrained by a single 40ar 39ar age of an overlying glassy lava flow at a distal tephra site this study demonstrates the potential for combined 238u 230th disequilibrium and u th he dating of zircon in tephra and other volcanic deposits to provide age control in the 40 100 ka time interval a period difficult to constrain using more traditional radiocarbon k ar and 40ar 39ar methods

a geochemical traverse across the eastern carpathians romania constraints on the origin and evolution of the mineral water and gas discharges abstract the inner sector of the eastern carpathians displays a large number of na hco 3 co 2 rich meteoric originated cold springs soda springs and bore wells as well as dry mofettes they border the southern part of the pliocene quaternary calimani gurghiu harghita cgh calc alkaline volcanic chain both volcanic rocks and co 2 rich emissions are situated between the eastern part of the transylvanian basin and the main east carpathian range where active compression tectonics caused diapiric intrusions of miocene halite deposits and associated saline co 2 rich waters along active faults the regional patterns of the distribution of co 2 in spring waters as calculated p co 2 and the distribution pattern of the 3 he 4 he ratio in the free gas phases up to 4 5 r m r a show their maximum values in coincidence with both the maximum heat flow measurements and the more recent volcanic edifices moving towards the eastern external foredeep areas where oil fields and associated brines are present natural gas emissions become ch 4 dominated such a change in the composition of gas emissions at surface is also recorded by the 3 he 4 he ratios that in this area assume typical crustal values r m r a 0 02 in spite of the fact that thermal springs are rare in the harghita volcanic area and that equilibrium temperature estimates based on geothermometric techniques on gas and liquid phases at surface do not suggest the presence of shallow active hydrothermal systems a large circulation of fluids gases is likely triggered by the presence of mantle magmas stored inside the crust if total 3 he comes from the mantle or from the degassing of magmas stored in the crust co 2 might be associated to both volcanic degassing and thermometamorphism of recently subducted limestones

amphibole perspective to unravel pre eruptive processes and conditions in volcanic plumbing systems beneath intermediate arc volcanoes a case study from ciomadul volcano se carpathians ciomadul is the youngest volcano in the carpathian pannonian region produced crystal rich high k dacites that contain abundant amphibole phenocrysts the amphiboles in the studied dacites are characterized by large variety of zoning patterns textures and a wide range of compositions e g 6 4 15 wt al2o3 79 821 ppm sr often in thin section scale and even in single crystals two amphibole populations were observed in the dacite low al hornblendes represent a cold 900 c mafic magma amphibole thermobarometry suggests that the silicic crystal mush was stored in an upper crustal storage 8 12 km this was also the place where the erupted dacitic magma was formed during the remobilization of upper crustal silicic crystal mush body by hot mafic magma indicated by simple zoned and composite amphiboles this includes reheating by 200 c and partial remelting of different parts of the crystal mush followed by intensive crystallization of the second mineral population including pargasites breakdown textures of amphiboles imply that they were formed by reheating in case of hornblendes suggesting that pre eruptive heating and mixing could take place within days or weeks before the eruption the decompression rim of pargasites suggests around 12 days of magma ascent in the conduit several arc volcanoes produce mixed intermediate magmas with similar bimodal amphibole cargo as the ciomadul but in our dacite the two amphibole population can be found even in a single crystal composite amphiboles our study indicates that high al pargasites form as a second generation in these magmas after the mafic replenishment into a silicic capture zone thus they cannot unambiguously indicate a deeper mafic storage zone beneath these volcanoes the simple zoned and composite amphiboles provide direct evidence that significant compositional variations of amphiboles do not necessarily mean variation in the pressure of crystallization even if the al tschermak substitution can be recognized suggesting that amphibole barometers that consider only amphibole composition may often yield unrealistic pressure variation

systematic morphometric characterization of volcanic edifices using digital elevation models abstract quantitative characterization of the size and shape of volcanic edifices is an essential step towards the understanding of factors controlling volcano growth and morphology the recent advent of digital elevation models dems with worldwide coverage offers the opportunity to systematically document the morphometry of all types of volcanoes using quantitative well formalized methodologies we present a methodology for the morphometric characterization of volcanic edifices after reviewing previous studies on volcano morphometry and the various existing dem sources we describe an integrated procedure that uses a dem and its derived products slope curvature to extract a coherent set of morphometric parameters for a given volcanic edifice edifice boundaries are manually defined by searching for breaks in slope around the base the parameters describe the overall size basal and summit region area and widths height volume planar shape ellipticity and irregularity index of elevation contours profile shape height width ratios and slope of the edifice similar parameters for relatively large depending on dem spatial resolution summit craters calderas are also computed slope values and ellipticity and irregularity indexes are extracted for successive height intervals providing detailed information of volcano shape as a function of height the number of secondary peaks is also estimated the method is tested on thirteen composite volcanoes in nicaragua using three dem datasets 90 m srtm 30 m aster g dem and an 80 m topographic map derived dem and the resulting parameters are evaluated in terms of boundary delineation and dem source finally the parameters obtained for the nicaraguan volcanoes are discussed as an illustrative example of the type of data and information that can be extracted systematically for volcanoes worldwide

rapid dome growth at montagne pelee during the early stages of the 1902 1905 eruption a reconstruction from lacroix s data information obtained from various parts of the two books on montagne pelee by lacroix enables an estimate to be made of the size of l etang sec summit crater the volume of the 1902 1905 lava dome and its growth rate at various stages of development during the week preceding the 8 may nuee ardente dome growth was between 28 and 38 m3 s 1 leading to a volume of 17 23 106 m3 on the morning of the catastrophe considering that significant parts of the dome 1 3 were removed by the 8 and 20 may climactic eruptions a high magmatic flux could have continued until at least 27 may when the total remaining volume was estimated to 53 106 m3 after moderate activity in june july of order 10 m3 s 1 vigorous dome growth resumed dramatically leading to the third climactic eruption of 30 august a true calculation for this period being not feasible because of poor quality of the data from november 1902 to july 1903 most of the effusive activity was concentrated in the great spine erupted volume 15 106 m3 magma flux 1 2 m3 s 1 which was eventually destroyed by collapse and minor nuees ardentes the end of the eruption was characterized by a very low effusion rate 1 m3 s 1 in average from august 1903 to october 1905

loess accumulation during the last glacial maximum evidence from urluia southeastern romania abstract the eastern european loess steppe represents one of the most substantial landform types on the continent yet the impact on this region of the last glacial maximum lgm the coldest climatic episode during the last full glacial cycle is relatively poorly understood this is in part due to the comparatively small number of sites which have been reliably dated and in part due to the need to better elucidate depositional models for loess environments at both local and regional scales here we present a high frequency age depth profile for the last 40 ky from a loess deposit at urluia in southeastern romania using fine grained quartz optically stimulated luminescence osl dating and environmental magnetism analyses loess accumulation at the site for this period is well constrained by a clearly identifiable tephra deposit corresponding to the ca 39 ka campanian ignimbrite we show that the tephra is directly overlain by a relatively thin layer of loess corresponding to marine isotope stage mis 3 which is partially overprinted by a weakly developed paleosol the sequence is dominated by a 6 8 m package of primary loess of lgm age the eight osl samples from this package group together around a mean age of 21 6 1 5 ka and suggest rapid and substantial deposition during this phase the uppermost part of the section indicates significantly reduced loess accumulation during the deglacial period into the holocene less than 2 m in total thickness the rapid accumulation of loess during the lgm at urluia is consistent with increased sedimentation at other loess profiles in the lower danube basin although the variable thickness of these deposits across the catchment highlights the need to more explicitly investigate depositional models for loess the urluia record complements emerging data which suggests that the lower danube loess steppe was cold dry and windy during the lgm yet experienced milder climates than comparable latitudes further west and north and did not undergo periglacial activity

episodes of dormancy and eruption of the late pleistocene ciomadul volcanic complex eastern carpathians romania constrained by zircon geochronology abstract ciomadul is the youngest volcanic system in the carpathian pannonian region recording eruptive activity from ca 1 ma to 30 ka based on combined zircon u th and u th he geochronology ciomadul volcanism is divided into two main eruptive periods old ciomadul 1 ma 300 ka ocep and young ciomadul eruptive period 160 30 ka ycep ocep activity comprises eruptive epochs 1 3 whereas new ages for eight lava domes and four pyroclastic units belonging to the ycep lead to its further subdivision into two eruptive epochs eruptive epochs 4 and 5 the extrusion of most of the lava domes occurred between 160 and 90 ka eruptive epoch 4 during three eruptive episodes at ca 155 ka 135 ka and 95 ka eruptive episodes 4 1 4 2 and 4 3 respectively along a ne sw lineament which is perpendicular to the regional nw se trend of the c limani gurghiu harghita volcanic chain eruptive epoch 5 occurred after a ca 40 kyr of quiescence at ca 55 30 ka and is mainly characterized by explosive eruptions with a minor lava dome building activity all of the dated pyroclastic outcrops together with the lava dome of piscul pietros belong to the older eruptive episode 5 1 with an eruption age of 55 45 ka the eruption centers of eruptive epoch 5 are located at the junction of the conjugated nw se and ne sw lineaments defined by the older eruptive centers the whole rock geochemistry of all studied samples is fairly homogeneous sio2 63 69 wt k2o 3 4 wt it also overlaps with the composition of the lava domes of the old ciomadul eruptive period implying a monotonous geochemical characteristic for the past 1 myr the eruption rates for the ciomadul volcanism were determined based on the erupted lava dome volume calculations supplemented with the eruption ages the activity peaked during the eruptive epoch 4 160 90 ka having an eruption rate of 0 1 km3 kyr in comparison these values are 0 05 km3 kyr for the ycep 160 30 ka and 0 01 km3 kyr for the overall ciomadul volcanism 1 ma 30 ka based on the geochemical characteristics the quiescence periods and the lifetime of the complex as well as the relatively small amount of erupted material this volcanic system can be placed in a subduction related post collisional geodynamic setting which shows strong chemical similarities to continental arc volcanism the commonly found long repose times between the active phases suggest that the nature of a volcano cannot be understood solely based on the elapsed time since the last eruption instead comprehensive geochronology coupled with the understanding of the magma storage behavior could be a base of hazard assessment for volcanic fields where the last eruptions occurred several 10 s of thousand years ago and therefore they are not considered as potentially active

vegetation and environmental responses to climate forcing during the last glacial maximum and deglaciation in the east carpathians attenuated response to maximum cooling and increased biomass burning the carpathian mountains were one of the main mountain reserves of the boreal and cool temperate flora during the last glacial maximum lgm in east central europe previous studies demonstrated lateglacial vegetation dynamics in this area however our knowledge on the lgm vegetation compo sition is very limited due to the scarcity of suitable sedimentary archives here we present a new record of vegetation fire and lacustrine sedimentation from the youngest volcanic crater of the carpathians lake st anne lacul sf ana szent anna tto examine environmental change in this region during the lgm and the subsequent deglaciation our record indicates the persistence of boreal forest steppe vegetation with pinus betula salix populus and picea in the foreland and low mountain zone of the east carpathians and juniperus shrubland at higher elevation we demonstrate attenuated response of the regional vegetation to maximum global cooling between 22 870 and 19 150 cal yr bp we find increased regional biomass burning that is antagonistic with the global trend increased regional fire activity suggests extreme continentality likely with relatively warm and dry summers we also demonstrate xerophytic steppe expansion directly after the lgm from 19 150 cal yr bp and regional increase in boreal woodland cover with pinus and betula from 16 300 cal yr bp plant macrofossils indicate local 950 m a s l establishment of betula nana and betula pubescens at 15 150 cal yr bp pinus sylvestris at 14 700 cal yr bp and larix decidua at 12 870 cal yr bp pollen data furthermore support population genetic inferences regarding the regional presence of some temperate deciduous trees during the lgm fagus sylvatica corylus avellana fraxinus excelsior our sedimentological data also demonstrate intensified aeolian dust accumulation between 26 000 and 20 000 cal yr bp

rates and factors of stratovolcano degradation in a continental climate a complex morphometric analysis for nineteen neogene quaternary crater remnants in the carpathians abstract the systematic age progression of the neogene quaternary volcanic chain in the carpathians manifested in progressively degraded stratovolcanoes from south to north offers a great opportunity to calculate erosion rates and the factors that control degradation in a moderate continental climate using available and newly determined k ar ages for the cessation of volcanism of nineteen stratocones a great number of morphometric variables including crater diameter and perimeter intracraterial valley length valley order and density dip of internal and external crater rim cone diameter relative height cone diameter height above and distance from base level etc has been examined by regression and factor analyses on the one hand the erosion rates which are calculated from the regression equations of a given characteristic versus age seem to answer the question of to what extent the stratovolcanoes are degraded numerical values of crater enlargement 109 m ma internal valley growth 1 3 km ma average cone lowering 31 5 m ma etc are given moreover using multiple regression equations as age equations the age of any volcano in the same climate can be estimated from the measured characteristics on the other hand there are morphometric characteristics e g dip of crater rim crater circularity intracraterial valley density which are not functions of time three major factors i e the time factor about 40 the size depth factor about 24 and the erosional distance factor about 10 account for about 75 of the stratovolcano characteristics variance and two additional factors eruption style magma viscosity and the central manifestation of volcanism may be responsible for a further 13

mount st helens and santiaguito lava domes the effect of short term eruption rate on surface texture and degassing processes in order to assess the effect of eruption rate on the surface morphology and degassing mechanisms of silicic lava flows we studied surface characteristics and obtained water content and hydrogen isotopic values of samples from flows at the mount st helens and santiaguito lava domes we compared the surface textures and inferred degassing processes to short term extrusion rates and found that when domes are small and eruption rates are high lava will not completely degas in transit to the surface allowing additional volatile loss through surface vesiculation which results in the formation of a scoriaceous carapace when domes exceed a critical size and or their cooled crusts reach a critical strength emergence of new magma is impeded short term eruption rates decline and more thorough degassing can take place leading to smooth textured flows lacking scoria development at mount st helens this transition occurred during the dome s third year when it grew from 31 8 to 53 2 106 m3 santiaguito attained a comparable state after 2 3 years of growth and for most of its 70 year history has produced non vesicular lava degassing patterns that combine closed open and kinetic processes can be distinguished using isotope data obtained from samples whose positions on a flow and emplacement histories are well constrained evidence for these patterns is most clearly preserved in lavas erupted during early rapid stages of dome growth petrologists and volcanologists seeking to infer magma chamber conditions from the volatile contents of extruded lavas thus need to sample flows early in their emplacement while paying attention to surface texture position relative to the vent and flow front and time of emergence

volcanic geomorphology an overview abstract the review examines the role of geomorphology in analyzing the volcanoes on earth five objectives are stressed first classifications of volcanic landforms should be improved to take care of the complexity in volcanic landform generation as magmatic systems style of eruption and the erupted material all influence the morphology second geomorphology should contribute to the science of volcanology through its capability in reconstructing growth stages in complex volcanoes and also in analyzing the structural factors which contribute to the catastrophic collapse of volcanoes third geomorphology can contribute to physical volcanology by assessing the effects of topography on transport erosion and deposition of volcanogenic flows and identifying the sources and climatic tectonic conditions which govern the emplacement of volcaniclastic deposits fourth volcanic geomorphology a identifies sedimentary facies associations b constructs facies models for dynamic volcano delivery systems and c analyzes the characteristics of sediment gravity flows in order to determine relevant parameters for modelling their behaviour fifth process oriented geomorphology is critical in developing accurate methods for measuring rates of geomorphic processes that shape ephemeral volcanic constructs and for evaluating and comparing geomorphic impacts on disturbed catchments and the related hydrologic response before during and after eruptions this should help to refine parameters for the exponential decay model finally volcanic geomorphology is essential for risk assessment through geomorphic hazard zonation and composite risk zonation such treatments are necessary in order to face the enhanced challenge posed by the combination of natural hazards and the increasing number of people who are at risk around volcanoes

geochemical response of magmas to neogene quaternary continental collision in the carpathian pannonian region a review the carpathian pannonian region contains neogene to quaternary magmatic rocks of highly diverse composition calcalkaline shoshonitic and mafic alkalic that were generated in response to complex microplate tectonics including subduction followed by roll back collision subducted slab break off rotations and extension major element trace element and isotopic geochemical data of representative parental lavas and mantle xenoliths suggests that subduction components were preserved in the mantle following the cessation of subduction and were reactivated by asthenosphere uprise via subduction roll back slab detachment slab break off or slab tearing changes in the composition of the mantle through time are evident in the geochemistry supporting established geodynamic models magmatism occurred in a back arc setting in the western carpathians and pannonian basin western segment producing felsic volcaniclastic rocks between 21 to 18 ma ago followed by younger felsic and intermediate calc alkaline lavas 18 8 ma and finished with alkalic mafic basaltic volcanism 10 0 1 ma volcanic rocks become younger in this segment towards the north geochemical data for the felsic and calc alkaline rocks suggest a decrease in the subduction component through time and a change in source from a crustal one through a mixed crustal mantle source to a mantle source block rotation subducted roll back and continental collision triggered partial melting by either delamination and or asthenosphere upwelling that also generated the younger alkalic mafic magmatism in the westernmost east carpathians central segment calc alkaline volcanism was simultaneously spread across ca 100 km in several lineaments parallel or perpendicular to the plane of continental collision from 15 to 9 ma geochemical studies indicate a heterogeneous mantle toward the back arc with a larger degree of fluid induced metasomatism source enrichment and assimilation on moving north eastward toward the presumed trench subduction related roll back may have triggered melting although there may have been a role for back arc extension and asthenosphere uprise related to slab break off calc alkaline and adakite like magmas were erupted in the apuseni mountains volcanic area interior segment from15 9 ma without any apparent relationship with the coeval roll back processes in the front of the orogen magmatic activity ended with oiblike alkali basaltic 2 5 ma and shoshonitic magmatism 1 6 ma lithosphere breakup may have been an important process during extreme block rotations 608 between 14 and 12 ma leading to decompressional melting of the lithospheric and asthenospheric sources eruption of alkali basalts suggests decompressional melting of an oib source asthenosphere mixing of asthenospheric

in situ u pb ages of zircons from the bishop tuff no evidence for long crystal residence times ion microprobe u pb isotope analyses of zircons from fallout and intercalated ash flow deposits of the early most chemically evolved bishop tuff east central california yield a weighted mean age of 823 11 ka mean square of weighted deviates mswd 0 8 n 22 a similar mean age of 839 36 ka mswd 0 6 n 15 obtained on unpolished zircon rims suggests that the difference between these ages and that of 760 ka for the bishop tuff obtained by recent ar isotope determinations may be largely analytical in origin considerations based only on the effect of 230 th 234 u disequilibria on the u pb ages yield an apparent maximum mean crystal residence time for zircon of 100 k y the zircon residence times are significantly shorter than those inferred from previous estimates for the timing of phenocryst growth and suggest that once evolved the early bishop tuff rhyolite was not stored for long before erupting

the crustal structure of the guayana shield venezuela from seismic refraction and gravity data abstract we present results from a seismic refraction experiment on the northern margin of the guayana shield performed during june 1998 along nine profiles of up to 320 km length using the daily blasts of the cerro bolivar mines as energy source as well as from gravimetric measurements clear moho arrivals can be observed on the main e w profile on the shield whereas the profiles entering the oriental basin to the north are more noisy the crustal thickness of the shield is unusually high with up to 46 km on the archean segment in the west and 43 km on the proterozoic segment in the east a 20 km thick upper crust with p wave velocities between 6 0 and 6 3 km s can be separated from a lower crust with velocities ranging from 6 5 to 7 2 km s a lower crustal low velocity zone with a velocity reduction to 6 3 km s is observed between 25 and 25 km depth the average crustal velocity is 6 5 km s the changes in the bouguer anomaly positive 30 mgal in the west and negative 20 mgal in the east cannot be explained by the observed seismic crustal features alone lateral variations in the crust or in the upper mantle must be responsible for these observations

evaluation of morphometry based dating of monogenetic volcanoes a case study from bandas del sur tenerife canary islands morphometry based dating provides a first order estimate of the temporal evolution of monogenetic volcanic edifices located within an intraplate monogenetic volcanic field or on the flanks of a polygenetic volcano two widely used morphometric parameters namely cone height width ratio hmax wco and slope angle were applied to extract chronological information and evaluate their accuracy for morphometry based ordering based on these quantitative parameters extracted from contour based digital elevation models dems two event orders for the bandas del sur in tenerife canary islands were constructed and compared with the existing k ar paleomagnetic and stratigraphic data the results obtained suggest that the commonly used hmax wco ratio is not reliable leading to inappropriate temporal order estimates while the slope angle gives slightly better results the overall performance of such descriptive parameters was however generally poor i e there is no strong correlation between morphometry and age the geomorphic morphometric mismatches could be the result of 1 the diversity of syn eruptive processes i e diverse initial morphologies causing geomorphic morphometric variability 2 contrasting edifice specific degradation that depends partly upon the inner facies architecture of the volcanic edifices 3 various external environmental controls e g tephra mantling from pyroclastic density currents unrelated to the edifice evaluated and 4 differences in the scale resolution of input data the observed degradation trend and changes in morphometric parameters over time do not support a simple degradation model for monogenetic scoria cones volcanoes

evaluation of aster and srtm dem data for lahar modeling a case study on lahars from popocatepetl volcano mexico abstract lahars are among the most serious and far reaching volcanic hazards in regions with potential interactions of lahars with populated areas and human structures the assessment of the related hazards is crucial for undertaking appropriate mitigating actions and reduce the associated risks modeling of lahars has become an important tool in such assessments in particular where the geologic record of past events is insufficient mass flow modeling strongly relies on digital terrain data availability of digital elevation models dems however is often limited and thus an obstacle to lahar modeling remote sensing technology has now opened new perspectives in generating dems in this study we evaluate the feasibility of dems derived from the advanced spaceborne thermal emission and reflection radiometer aster and the shuttle radar topography mission srtm for lahar modeling on popocatepetl volcano mexico two gis based models are used for lahar modeling laharz and a flow routing based debris flow model modified single flow direction model msf both predicting areas potentially affected by lahars results of the lahar modeling show that both the aster and srtm dems are basically suitable for use with laharz and msf flow path prediction is found to be more reliable with srtm data though with a coarser spatial resolution errors of the aster dem affecting the prediction of flow paths due to the sensor geometry are associated with deeply incised gorges with north facing slopes laharz is more sensitive to errors of the aster dem than the msf model lahar modeling with the aster dem results in a more finely spaced predicted inundation area but does not add any significant information in comparison with the srtm dem lahars at popocatepetl are modeled with volumes of 1 10 5 to 8 10 6 m 3 based on ice melt scenarios of the glaciers on top of the volcano and data on recent and historical lahar events as regards recently observed lahars the travel distance of lahars of corresponding volume modeled with laharz falls short by 2 to 4 km an important finding is that the travel distance of potential lahar events modeled with laharz may differ by about 2 km when using srtm or aster data because of varying lateral flow volume distribution as a consequence verification and sensitivity analysis of the dem is fundamental to deriving hazard maps from predicted modeled inundation areas because of the global coverage of this type of remote sensing data the conclusion that both srtm and aster derived dems are feasible for lahar modeling opens a wide field of application in volcanic hazards studies

receiver function study of the crustal structure of the southeastern caribbean plate boundary and venezuela 1 we have investigated crustal thickness and composition across the southeastern caribbean plate boundary with the receiver function technique we used teleseismic data recorded by a temporary broadband array deployed under the bolivar project and the permanent national seismic network of venezuela we used the primary p to s conversion and crustal reverberations to estimate crustal thickness and average crustal vp vs ratio over the region we observe large variations in crustal thickness and poisson s ratio estimated moho depth ranges from 16 km beneath the southeastern caribbean sea to 52 km beneath northeastern venezuela and the venezuelan andes there is a good correlation between crustal structure and tectonic terranes data from the precambrian guayana shield suggest that the underlying crustal structure is relatively uniform with a moderate thickness 37 km and an intermediate composition a thick crust is found below the foreland basins the two mountain systems in northern venezuela the serrania del interior and the serrania del falcon have a thin crust with arc composition and are likely dynamically supported by elastic rebound or underthrusting of the oceanic plateau that characterizes the southern caribbean on the other hand the venezuelan andes and perija range on the western side of the country are probably isostatically balanced by thick crustal roots

the roxolany tephra ukraine new evidence for an origin from ciomadul volcano east carpathians we present major element glass data and correlations for the roxolany tephra a so far geochemically unconstrained volcanic ash layer previously described in last glacial marine isotope stage 2 loess deposits of the roxolany loess palaeosol complex in south west ukraine this exceptionally well preserved 2 3 cm thick tephra layer is characterized by a rhyolitic glass composition that is comparable to that of proximal tephra units from ciomadul volcano in the east carpathians central romania the chemistry particularly matches that of the final latest st ana phreatomagmatic activity pyroclastic fall unit of st ana crater that is radiocarbon dated in the proximal mohos coring site moh 2 to 29 6 0 62 cal ka bp the age of the tephra correlative agrees with the newest radiocarbon and infrared optically stimulated luminescence age constraints from overlying palaeosols and tephra embedding loess of the roxolany sequence respectively which place the tephra between ca 33 and 24 cal ka bp and thus confirm the long debated chronostratigraphy of this important environmental archive the occurrence of a distal ciomadul tephra ca 350 km east of its source indicates great potential for further tephra and cryptotephra findings from this volcanic complex in the south eastern mediterranean and black sea region

geochronology of age progressive volcanism of the oregon high lava plains implications for the plume interpretation of yellowstone 1 the high lava plains province hlp is a late cenozoic bimodal volcanic field at the northern margin of the basin and range province in southeastern oregon that hosts a westward younging trend of silicic volcanism that crudely mirrors northeastward migration of silicic volcanism along the yellowstone snake river plain ysrp trend we present 40ar 39ar ages for 19 rhyolite domes 5 rhyolite ash flow tuffs and 34 basaltic lavas from the hlp the previously identified trend of westward migration of hlp rhyolites is confirmed the rate of propagation is 33 km m y from 10 to 5 ma slowing to 13 km m y after 5 ma the duration of silicic volcanism at any locus is 2 m y three older hlp dacite domes yielded ages of 15 5 ma basalts are not age progressive we identify several episodes of increased basaltic activity at 7 5 7 8 5 3 5 9 and 2 3 ma with the younger episode likely continuing into the recent the hlp and ysrp trends emerged from the axis of middle miocene basaltic volcanism of the columbia river and steens basalts we propose a model in which 1 miocene flood basalts and widespread silicic rocks are the result of emplacement of a plume head near the craton margin enhanced by flow up a topographic gradient along the base of the lithosphere at the craton margin 2 the hlp trend is the result of westward flow originating at the craton margin and 3 the ysrp trend is the trace of the motion of the north american plate over the tail of the plume

hazard map of el chichon volcano chiapas mexico constraints posed by eruptive history and computer simulations abstract el chichon volcano consists of a 2 km wide somma crater compound cone 0 2 ma old with peripheral domes with a central crater reactivated several times during the holocene the most recent eruption at el chichon occurred from march 28 to april 4 1982 resulting in the worst volcanic disaster during historical times in mexico killing more than 2000 people and destroying nine towns and small communities the volcanic hazard map of el chichon is based on detailed field work that documented twelve eruptions during the last 8000 years and computer simulations to validate the results computer simulations were first performed over pre 1982 topography mimicking the extent of the actual deposits produced and afterwards run over post 1982 topography these eruptions have produced pyroclastic fall surge flow and lahar deposits pyroclastic flows have different volumes and heim coefficients varying from 0 2 pumice flows to 0 15 block and ash flows and 0 10 ash flows simulations using flow3d and titan2d indicate that pumice flows and block and ash flows can fill the moat area and follow main ravines up to distances of ca 3 km from the crater with no effect on populations around the volcano on the other hand more mobile ash flows related to column collapse events can reach up to 4 km from the vent but will always follow the same paths and still not affect surrounding populations the energy cone model was used to simulate the outflow of pyroclastic surges based on the 1982 event h l 0 1 and 0 2 and shows that surges may reach some towns around the volcano explosive activity also produced plinian columns higher than 27 km that were dispersed towards the ne by prevailing winds future fallout will seriously disturb the lives of more than 70 000 inhabitants of cities and towns located in a radius of 35 km from the volcano lahar events in the past originated from unconsolidated pyroclastic deposits with volumes varying from 1 to 4 10 6 m 3 for single pulses to a large one from dam breakout with a volume of 40 10 6 m 3 we used the laharz code to model future events with volumes of 1 2 and 3 10 6 m 3 that will reach as far as 10 14 and 16 km from the crater posing some danger to the communities of nicapa volcan and ostuacan even some time after the climax of the eruption

abrupt vegetation change after the late quaternary megafaunal extinction in southeastern australia the extinction of megafauna in australia about 43 000 years ago has been linked to both human arrival and vegetation change marine sediment analyses from the east coast of australia suggest that vegetation change was a result rather than cause of the extinction

microseismicity and focal mechanisms of the intermediate depth bucaramanga nest colombia the bucaramanga nest of intermediate depth seismicity in northern colombia was investigated from microearthquakes m sub b less than or equal to4 3 recorded from june 20 to july 6 1979 by a local array of 12 digital three component seismographs of 161 events studied 142 are from the nest and 19 define a thin wadati benioff w b zone mainly from 110 to 190 km depth the w b zone part of the bucaramanga segment strikes n10 sup 0 e with a dip increasing wtih depth from 30 sup 0 e to near vertical beneath the nest the 89 best located events from within the nest define a volume of about 8 km nw by 4 km ne by 4 km depth centered at 161 km depth with relative location accuracies of 0 5 to 1 0 km double couple fault plane solutions of 59 events were determined from an objective procedure using p wave polarities and s p amplitude ratios there is no dominant trend in focal mechanisms nor any reasonable correlation with regional stress patterns or previously determined mechanisms from teleseismic data the subduction and assimilation of a linear feature such as an island arc undergoing a phase transformation may explain the existence of the bucaramanga nest however the extraordinarilymore high rate of seismicity suggests that the nest may be moving rate several orders of magnitude faster than the rate of relative plate motion alone the intense seismicity and variation in focal mechanisms suggest that the nest represents some aspect of stress release associated with the ascent of fluids perhaps brine or magma that will ultimately result in the initiation of volcanic activity over this recently emplaced w b zone copyright american geophysical union 1987 less

the transition from endogenous to exogenous growth of lava domes with the development of shear bands the transition from an endogenous to an exogenous regime of lava dome growth must be achieved by the formation of discontinuities within the dome such transitions and vice versa are an important characteristic of most long lived lava domes and often coincide with significant changes in the dynamics of magma supply and lava dome collapse events for the purpose of this paper following recent experimental and observational evidence we assume that such a transition occurs when shear bands are generated a model for the formation of shear bands and therefore the growth transition within a dome and coupled conduit domain is presented shear bands are most likely to initiate at the junction of the conduit and base of the dome where the shear stress experienced between new lava entering the dome and existing lava is greatest stress accumulation within the shear bands is likely to lead to brittle shear resulting in the formation of fractures finite element modelling of lava flow shows that such shear bands only develop for certain extrusion rates and lava viscosities similarly the growth regime of the lava dome will depend upon the extrusion rate and viscosity within the conduit which is largely controlled by volatile loss and the growth of crystals in the upper part of the conduit we consider a simplified rheology during lava dome growth considering isothermal conditions with crystal growth the development of shear bands in the conduit is explored with a numerical model parameterized with values appropriate for soufriere hills volcano montserrat during october to december 1996 this lava dome forming eruption experienced a transition from endogenous to exogenous growth as it grew in height by about 90 m modelling indicates that the observed fall in magma extrusion rate from about 2 0 m3s 1 to 0 5 m3s 1 as a result of the increased pressure head from the dome and the evolution in viscosity could have subsequently changed the dome growth regime due to the development of shear bands our models provide insight into the shear stress fields possible within the conduit and the shear stresses required for shear band development

would the australian megafauna have become extinct if humans had never colonised the continent comments on a review of the evidence for a human role in the extinction of australian megafauna and an alternative explanation by s wroe and j field a critical comment on a review of the evidence for a human role in the extinction of australian megafauna and an alternative explanation by s wroe and j field is presented the authors have highlighted a range of ideas under consideration and provided a selective interpretation which does not come to terms with biology and ignores or misinterprets current evidence they rely heavily on the ages reported by roberts et al 2001 to argue for a gradual attenuation of the megafauna they propose a staggered series of extinctions throughout the middle and late pleistocene with many taxa lost during the penultimate glacial maximum pgm 140 130 ka and relatively few species persisting they ignore measurement uncertainties associated with the ages which when properly considered means that 20 rather than eight of the species they list have last appearance ages consistent with 45 ka

late miocene quaternary volcanism tectonics and drainage system evolution in the east carpathians romania abstract middle miocene sarmatian convergence created the fold and thrust belt of the eastern carpathians of romania which subsequently experienced post collisional crustal deformation combined with calc alkaline and alkalic basaltic volcanism in late miocene quaternary time this deformation led to the rise of the c limani gurghiu harghita volcanic mountains and to the subsidence of the n s oriented intramontane borsec bilbor gheorgheni ciuc and brasov pull apart basins and the e oriented monocline related f g ras basin the regional drainage network is the composite of 1 older e se and s flowing rivers which cross the carpathians radiate towards the foreland and were probably established during the middle miocene sarmatian collision event 2 a more recent drainage system related to the contemporaneous development of the volcanoes and intramontaneous basins which generally drains westward into the transylvanian basin since late miocene time and has been capturing the older river system the older river drainage system has also been modified by late pliocene quaternary folding thrusting and monoclinal tilting along the pericarpathian orogenic front and by reactivated transverse high angle basement faults which cross the eastern carpathian foreland

palaeontology extinction promoted fire the extinction of megafauna in australia roughly coincided with shifts in vegetation and fire regimes sediment geochemistry shows that the vegetation shift followed the extinction indicating that the loss of browsers promoted fire and altered plant composition

quantification of carbon dioxide emissions of ciomadul the youngest volcano of the carpathian pannonian region eastern central europe romania abstract we provide the first high resolution co 2 flux data for the neogene to quaternary volcanic regions of the entire carpathian pannonian region eastern central europe and estimate the co 2 emission of the seemingly inactive ciomadul volcanic complex the youngest volcano of this area our estimate includes data from focused and diffuse co 2 emissions from soil the co 2 fluxes of focused emissions range between 277 and 8172 g d 1 corresponding to a co 2 output into the atmosphere between 0 1 and 2 98 t per year the investigated areas for diffuse soil gas emissions were characterized by wide range of co 2 flux values at apor baths ranging from 1 7 10 1 to 8 2 10 4 g m 2 d 1 while at l z re ti ranging between 1 43 and 3 8 10 4 g m 2 d 1 the highest co 2 focused gas fluxes at ciomadul were found at the periphery of the youngest volcanic complex which could be explained either by tectonic control across the brittle older volcanic edifices or by degassing from a deeper crustal zone resulting in co 2 flux at the periphery of the supposed melt bearing magma body beneath ciomadul the estimate of the total co 2 output in the area is 8 70 10 3 t y 1 and it is consistent with other long 10 kyr dormant volcanoes with similar age worldwide such as in italy and usa taking into account the isotopic composition of the gases that indicate deep origin of the co 2 emissions this yields further support that ciomadul may be considered indeed a dormant or pams volcano volcano with potentially active magma storage rather than an inactive one furthermore hazard of co 2 outpourings has to be taken into account and it has to be communicated to the visitors finally we suggest that co 2 output of dormant volcanic systems has to be also accounted in the estimation of the global volcanic co 2 budget

eruptive history of the late quaternary ciomadul csomad volcano east carpathians part ii magma output rates this study which builds on high precision unspiked cassignol gillot k ar age determinations presents an advanced dem based volumetrical analysis to infer long term magma output rates for the late quaternary ciomadul csomad dacitic lava dome complex east carpathians romania the volcanic field of ciomadul developed on the erosional surface of lower cretaceous flysch and 2 ma old andesites and experienced an extended eruptive history from 850 to 30 ka predominantly effusive activity took place during the first stage 850 to 440 ka producing volumetrically minor isolated peripheral domes subsequently after a 250 ky repose interval a voluminous central dome cluster developed in the second stage 200 to 30 ka during the youngest phase of evolution 60 to 30 ka highly explosive eruptions also occurred resulting in the formation of two craters mohos and st ana the calculated 8 00 0 55 km3 total volume of the lava domes which includes the related volcaniclastic 1 57 km3 as well as erosionally removed 0 18 km3 material is in line with dimensions of other medium sized dacitic lava domes worldwide this volume was extruded at an average long term magma output rate of 9 76 km3 my 0 0098 km3 ky however most of the domes 7 53 0 51 km3 were formed in the 200 to 30 ka period implying a significantly increased magma output rate of 37 40 km3 my 0 0374 km3 ky more than 30 times higher than in the first stage within these long term trends individual lava domes of ciomadul e g those with volumes between 0 02 and 0 40 km3 would have been emplaced at much higher rates over a period of years to tens of years the active periods lasting up to hundreds of years would have been followed by repose periods 30 times longer the most recent eruption of ciomadul has been dated here at 27 7 1 4 ka this age which is in agreement with radiocarbon dates for the onset of lake sediment accumulation in st ana crater dates fragmented lava blocks which are possibly related to a disrupted dome this suggests that during the last typically explosive phase of ciomadul lava dome extrusion was still ongoing in a global context the analysis of the volumetric dynamism of ciomadul s activity gives insights into the temporal variations in magma output at lava domes short term day or week scale eruption rates smooth out in long term millenia scale output rates which are tens of times lower

three dimensional density model of the nazca plate and the andean continental margin 1 we forward modeled the bouguer anomaly in a region encompassing the pacific ocean 85 w and the andean margin 60 w between northern peru 5 s and patagonia 45 s the three dimensional density model that reproduces the gravity field is a continental scale representation of density structure to 410 km depth that characterizes the mantle and crust of the oceanic nazca plate subducted slab and continental margin with a minimum number of bodies we predefined the density of each body after studying the dependency of density on composition of crustal and mantle materials and pressure temperature conditions appropriate for the andean setting a database of independent geophysical information constrains the geometry of the top of the subducted slab locally the moho of the oceanic and continental crusts and indirectly the lithosphere asthenosphere boundary underneath the continental plate other boundaries notably the intracrustal density discontinuity separating upper from lower crust below the continent were not constrained and their geometry is the result of fitting the observed and calculated bouguer anomaly during forward modeling this contribution presents the model to the andean geoscientific community and contains some tools like a sensitivity analysis that helps potential users of the model to interpret its results we describe and discuss some of these results in order to illustrate the application of the model to the study of a wide range of phenomena e g modification of oceanic plate structure by hot spots shape of the subducted slab thermal structure of the continental lithosphere compensation mechanism and formation of orogenic relieve causes of andean segmentation

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

geodynamics of the northern andes subductions and intracontinental deformation colombia new regional seismological data acquired in colombia during 1993 to 1996 and tectonic field data from the eastern cordillera ec permit a reexamination of the complex geodynamics of northwestern south america the effect of the accretion of the baudo panama oceanic arc which began 12 myr ago is highlighted in connection with mountain building in the ec the istmina and ibague faults in the south and the santa marta bucaramanga fault to the northeast limit an e se moving continental wedge progressive indentation of the wedge is absorbed along reverse faults located in the foothills of the cordilleras northward of 5 n and transpressive deformation in the santander massif crustal seismicity in colombia is accurately correlated with active faults showing neotectonic morphological evidences intermediate seismicity allows to identify a n ne trending subduction segment beneath the ec which plunges toward the e se this subduction is interpreted as a remnant of the paleo caribbean plateau pcp as suggested by geological and tomographic profiles the pcp shows a low angle subduction northward of 5 2 n and is limited southward by a major e w transpressive shear zone normal oceanic subduction of the nazca plate np ends abruptly at the southern limit of the baudo range northward the np subducts beneath the choco block overlapping the southern part of the pcp cenozoic shortening in the ec estimated from a balanced section is 120 km stress analysis of fault slip data in the ec northward of 4 n indicates an e se orientation of 1 in agreement with the pcp subduction direction northward near bucaramanga two stress solutions were observed 1 a late andean n80 e compression and 2 an early andean nw se compression

the regular shape of stratovolcanoes a dem based morphometrical approach abstract we studied the shape of the most regular shaped stratovolcanoes of the world to mathematically define the form of the ideal stratovolcano based on the shuttle radar topographic mission data we selected 19 of the most circular and symmetrical volcanoes which incidentally all belong to subduction related arcs surrounding the pacific the selection of volcanoes benefitted from the introduction of a new definition of circularity which is more robust than previous definitions being independent of the erosional dissection of the cone our study on the shape of stratovolcanoes was based on the analysis of the radial elevation profiles of each volcano the lower half section of the volcanoes is always well fitted by a logarithmic curve while the upper half section is not and falls into two groups it is fitted either by a line c type conical upper part or by a parabolic arc p type parabolic concave upper part a quantitative discrimination between these groups is obtained by fitting their upper slope with a linear function c type volcanoes show small whereas p type volcanoes show significant negative angular coefficient the proposed threshold between the two groups is 50 10 4 m chemical composition of eruptive products indicates higher sio 2 and or higher h 2 o content for c type volcanoes which could imply a higher incidence of mildly explosive e g strombolian eruptions we propose that this higher explosivity is responsible for forming the constant uppermost slopes by the deposition of ballistic tephra and its subsequent stabilisation at a constant angle by contrast p type volcanoes are characterized by a smaller sio 2 and h 2 o content which can be responsible for a higher incidence of effusive events and or a lower incidence of upper flank forming i e mild explosive eruptions therefore the concave upper flanks of these volcanoes may be shaped typically by lava flows based on this hypothesis we propose that the morphometric analysis of the elevation profile of stratovolcanoes can provide insights into their dominant eruptive style

crustal density structure in northwestern south america derived from analysis and 3 d modeling of gravity and seismicity data abstract this paper presents a three dimensional 3 d interpretation of new gravity and seismicity datasets for northern south america a 3 d forward density model was constructed on the basis of deep wide angle seismic refraction sections moho depth from receiver functions and surface geology density values were estimated from published borehole data for sediments by using empirical velocity density functions and considering mineralogical chemical composition variations under typical pressure temperature conditions for upper and lower crustal rocks the modeled 3 d density structure was kept as simple as possible the continental and oceanic plates were formed by two sedimentary bodies one crustal body and one mantle lithosphere body overlying a sub lithospheric mantle the caribbean plate was modeled with an atypical crustal thickness of 18 km including sediments the geometry of the caribbean plate was modeled using a combination of gravity modeling and analyses of the seismicity and focal mechanism solutions intermediate seismicity and the orientation of the t axes appeared aligned along the predicted position of the slab as a result the estimated slab dip angle under maracaibo and the merida andes was 15 and increases up to 20 after 100 km depth the model shows two orientations in the slab strike n150 e 5 in western colombia and southward underneath the maracaibo block the modeling results suggest that the northern south american upper and lower crusts are relatively light and the density of the caribbean crust is typical for an oceanic crust

heinrich events massive late pleistocene detritus layers of the north atlantic and their global climate imprint 1 millennial climate oscillations of the glacial interval are interrupted by extreme events the so called heinrich events of the north atlantic their near global footprint is a testament to coherent interactions among earth s atmosphere oceans and cryosphere on millennial timescales heinrich detritus appears to have been derived from the region around hudson strait it was deposited over approximately 500 250 years several mechanisms have been proposed for the origin of the layers binge purge cycle of the laurentide ice sheet jokulhlaup activity from a hudson bay lake and an ice shelf buildup collapse fed by hudson strait to determine the origin of the heinrich events i recommend 1 further studies of the timing and duration of the events 2 further sedimentology study near the hudson strait and 3 greater spatial and temporal resolution studies of the layers as well as their precursory intervals studies of previous glacial intervals may also provide important constraints

an assessment of shuttle radar topography mission digital elevation data for studies of volcano morphology the shuttle radar topography mission has provided high spatial resolution digital topographic data for most of earth s volcanoes although these data were acquired with a nominal spatial resolution of 30 m such data are only available for volcanoes located within the u s a and its territories for the overwhelming majority of earth s volcanoes not contained within this subset dems are available in the form of a re sampled 90 m product this has prompted us to perform an assessment of the extent to which volcano morphologic information present in the raw 30 m srtm product is retained in the degraded 90 m product to this end we have a applied a simple metric the so called dissection index di to summarize the shapes of volcanic edifices as encoded in a dem and b using this metric evaluated the extent to which this topographic information is lost as the spatial resolution of the data is reduced calculating di as a function of elevation a di profile allows us to quantitatively summarize the morphology of a volcano our results indicate that although the re sampling of the 30 m srtm data obviously results in a loss of morphological information this loss is not catastrophic analysis of a group of six alaskan volcanoes indicates that differences in di profiles calculated from the 30 m srtm product are largely preserved in the 90 m product this analysis of resolution effects on the preservation of topographic information has implications for research that relies on understanding volcanoes through the analysis of topographic datasets of similar spatial resolutions produced by other remote sensing techniques e g repeat pass interferometric sar optical stereometry

constraints on the timing of quaternary volcanism and duration of magma residence at ciomadul volcano east central europe from combined u th he and u th zircon geochronology article i nfo high spatial resolutionzircon geochronologywas applied to constrain thetimescalesof volcaniceruptions of the youngest mostly explosive volcanic phase of ciomadul volcano carpathian pannonian region romania com bined u th and u th he zircon dating demonstrates that intermittent volcanic eruptions occurred in a time range of 56 32 ka the reliability of the eruption dates is supported by concordant ages obtained from different dating techniques such as zircon geochronology radiocarbon analysis and infrared stimulated luminescence dating for the same deposits the new geochronological data suggest that volcanism at ciomadul is much youn ger bca 200 ka than previously thought up to 600 ka a dominantly explosive volcanic phase occurred after an apparent lull in volcanism that lasted for several 10 s of ka after a period of lava dome extrusion that defines the onset of the known volcanism at ciomadul at least four major eruptive episodes can be distinguished within the 56 32 ka period among them relatively large sub plinian to plinian explosive eruptions produced distal tephra covering extended areas mostly southeast from the volcano the 38 9 ka tephra overlaps the age of the campanian ignimbrite eruption and has an overlapping dispersion axis towards the black sea region the wide range of u th model ages of the studied zircons indicates prolonged existence of a low temperature b800 c silicic crystal mush beneath ciomadul the main zircon crystallization period was between ca 100 and 200 ka coeval with the older mostly extrusive lava dome building stage of volcanism even the youngest u th model ages obtained for the outermost 4 m rim of individual zircon crystals predate the eruption by several 10 s of ka the zircon age distributions suggest re heating above zircon saturation temperatures via injection of hot mafic magmas prior to eruption intermittent intrusions of fresh magma could play a significant role in keeping the intrusive silicic magmatic reservoir in a partially melted for prolonged period the previous history of ciomadul suggests that melt bearing crystal mush resided beneath the volcano and was rapidly remobilized after a protracted several 10 s of ka lull in volcanism to trigger several eruptions in a comparatively short time window this classifies ciomadul as a volcano with potentially active magma storage pams which we propose to be common among the seemingly inactive volcanoes in volcanic arc regions the potential for reacti vation of these systems should be included into volcanic hazard assessments

erosion rates and erosion patterns of neogene to quaternary stratovolcanoes in the western cordillera of the central andes an srtm dem based analysis abstract erosion patterns and rates of 33 stratovolcanoes in the arid to hyperarid central andean volcanic zone 14 s to 27 s have been constrained by morphometric modelling all selected volcanoes belong to the short lived symmetrical circular andesitic stratocone type with ages spanning 14 ma to recent starting from the initial youthful volcano morphology of this type represented in our study by parinacota volcano and comparing reconstructed volumes of progressively eroded volcanoes such a time span allows us to infer long term erosion rates typical erosion rates of