an early history of pure shear in the upper plate of the raft river metamorphic core complex black pine mountains southern idaho abstract although commonly obscured by simple shear pure shear fabrics occur locally within many metamorphic core complexes the cover rocks to the raft river metamorphic core complex exposed within the black pine mountains display an early coaxial strain history which developed prior to the formation of low angle fault bounded allochthons at higher structural levels this is documented by pressure shadows with straight sutures and oppositely rotated antitaxial calcite veins these rocks were sub horizontally extended parallel to bedding by up to 160 in an e w direction the marbles of the lowest exposed levels exhibit well developed crystallographic preferred orientation fabrics calcite c and a axis pole figures are symmetric to slightly asymmetric with obliquities ranging from 0 to 8 which indicate that the percent pure shear ranges between 100 and 76 initial constraints on the timing of this layer parallel extension suggest that extension was occurring locally within the sevier belt hinterland during the late cretaceous these data coupled with previous studies suggest that pure shear might be a much more common component of strain in rocks deformed in extensional environments than is generally acknowledged

lava fountain heights at pu u o o kilauea hawaii indicators of amount and variations of exsolved magma volatiles we review the factors determining lava fountain heights in hawaiian style basaltic eruptions such as those occurring during the recent series of eruptive episodes at the pu u o o vent east rift zone of kilauea volcano hawaii numerical solutions to the equations describing the fluid dynamics of such eruptions predict that lava fountain heights which are indicators of the velocity of magmas in vents should be controlled much more strongly by amounts of exsolved volatiles than by any other factors the next most important factor is the width of the conduit system which determines frictional losses and can be characterized by the volume flux of magma the diameter of the surface vent required to accommodate a given discharge i e instantaneous volume rate of eruption is also a function of exsolved magma volatile content but is less dependent on this factor than is the fountain height we simulate fountain heights for typical discharges at pu u o o and find implied exsolved gas contents very close to those determined by other methods the corresponding predicted vent diameters are comparable with and somewhat smaller than the observed diameter of the pu u o o vent the discrepancy is probably a consequence of processes occurring in the lava pond which is present over the vent during eruptions the variation of fountain height with time during eruptive episodes can be used as a measure of changing exsolved magma volatile content which can be related to processes occurring in the subsurface dike system

alligator ridge district east central nevada carlin type gold mineralization at shallow depths carlin type deposits in the alligator ridge mining district are present sporadically for 40 km along the north striking mooney basin fault system but are restricted to a 250 m interval of devonian to mississippian strata their age is bracketed between silicified ca 45 ma sedimentary rocks and unaltered 36 5 to 34 ma volcanic rocks the silicification is linked to the deposits by its continuity with ore grade silicification in devonian mississippian strata and by its similar 18 o values 17 and trace element signature as sb tl hg eocene reconstruction indicates that the deposits formed at depths of 300 to 800 m in comparison to most carlin type gold deposits they have lower au ag au grades and contained au more abundant jasperoid and textural evidence for deposition of an amorphous silica precursor in jasperoid these differences most likely result from their shallow depth of formation the peak fluid temperature 230 c and large 18 o h2o value shift from the meteroric water line 20 suggest that ore fluids were derived from depths of 8 km or more a magnetotelluric survey indicates that the mooney basin fault system penetrates to mid crustal depths deep circulation of meteoric water along the mooney basin fault system may have been in response to initial uplift of the east humboldt ruby mountains metamorphic core complex convection also may have been promoted by increased heat flow associated with large magnitude extension in the core complex and regional magmatism ore fluids ascended along the fault system until they encountered impermeable devonian and mississippian shales at which point they moved laterally through permeable strata in the devonian guilmette formation devonian mississippian pilot shale mississippian joana limestone and mississippian chainman shale toward erosional windows where they ascended into eocene fluvial conglomerates and lake sediments most gold precipitated by sulfidation of host rock fe and mixing with local ground water in zones of lateral fluid flow in reactive strata such as the lower devonian mississippian pilot shale

formation of lava tubes and extensive flow field during the 1991 1993 eruption of mount etna detailed mapping during the 1991 1993 eruption of mount etna has shown that there is a relationship between tumuli ephemeral vents lava tubes and their parent lava flows during this eruption many tubes formed in stationary inflated a a lava flows ephemeral vents at the fronts of these stationary flows and above lava tubes fed secondary lava flows many of which subsequently developed new tubes the resulting complex network of tubes ephemeral vents and secondary flows was responsible for most of the widening thickening and lengthening of the 1991 1993 etna lava flow field the supply of relatively uncooled lava via tubes to distal parts of this flow field allowed lava to flow 3 km farther from the vent than the longest channel fed lava flow our observations suggest that lava tubes play a more important role in the formation of extensive a a flow fields on etna than has previously been recognized

spatiotemporal gravity variations to look deep into the southern flank of etna volcano 1 a 14 year long microgravity data set october 1994 to september 2007 collected along a 24 km east west trending profile of 19 stations was analyzed to detect underground mass redistributions related to the volcanic activity involving the southern flank of mt etna italy a multiresolution wavelet analysis was applied to separate the volcano related anomalies from the unwanted components the residual image having both spatial extension and temporal duration evidenced two complete gravity increase decrease cycles mainly affecting the central and eastern stations of the profile the first gravity increase early 1995 to the end of 1996 and decrease end of 1996 to late in 1998 cycle reached a maximum amplitude of approximately 90 gal the second gravity increase mid 1999 to mid 2000 and decrease mid 2000 to early 2004 cycle attained an amplitude of about 80 gal after about 5 years of a persistent negative gravity anomaly a new semicycle started at the end of 2006 and continued during the last survey carried out in september 2007 the density changes modeled over time since 1994 using a quadratic programming algorithm are mainly located at a depth of 2 4 km bsl in a region recognized to be a preferential pathway of magma rising and an intermediate zone of magma storage withdrawal the computed positive mass variations of about 105 109 kg were interpreted as magma accumulation while negative mass changes of about 120 109 kg were associated with either magma drainage or opening of new voids by tectonic stresses within a source volume where tensional earthquakes occurred

comparison between the 1994 2006 seismic and gravity data from mt etna new insight into the long term behavior of a complex volcano abstract we investigate the relationship between changes of the gravity field and the release of the seismic energy at mt etna over a 12 year period 1994 2006 during which the volcano exhibited different eruptive patterns over the two sub periods when intense gravity decreases occur centered on the upper southeastern sector of the volcano late 1996 to mid 1999 and late 2000 to mid 2001 the strain release curve displays neat long term accelerations with many hypocenters clustered in the volume containing the gravity source various evidences suggest that since 1994 and until the breakout of the 2001 eruption the eastern flank of etna remained peripheral to the lines of rise of the magma from the deep storage to the surface accordingly we hypothesize that rather than being directly associated to the migration of the magma the joint anomalies we found image phases of higher tensile stress on the upper southeastern sector associated to increase in the rate of microfracturing along the nnw sse fracture zone such an increase implies a local density gravity decrease and an increase in the release of seismic energy thus explaining the correlation we observe the second period of gravity decrease strain release increase culminated in the breakout of the 2001 flank eruption as a pressurized deeper magma accumulation used the inferred zone of increasing microfracturing as a path to the surface this eruption marks an important modification in the structure of etna s plumbing system as also testified by the absence of post 2001 long term gravity changes and accelerations in the strain release curve and the neat modification of the seismicity and ground deformation patterns we prove that joint microgravity and seismic studies can allow zones of the medium experiencing an increase in the rate of microfracturing to be identified months to years before a magma batch is conveyed through them to the surface setting off a lateral eruption

intrusive mechanisms at mt etna forerunning the july august 2001 eruption from seismic and ground deformation data in this work we present seismological and ground deformation evidence for the phase preparing the july 18 to august 9 2001 flank eruption at etna the analysis performed through data from the permanent seismic and ground deformation networks highlighted a strong relationship between seismic strain release at depth and surface deformation this joint analysis provided strong constraints on the magma rising mechanisms we show that in the last ten years after the 1991 1993 eruption an overall accumulation of tension has affected the volcano then we investigate the months preceding the 2001 eruption in particular we analyse the strong seismic swarm on april 20 24 2001 comprising more than 200 events mmax 3 6 with prevalent dextral shear fault mechanisms in the western flank the swarm showed a ca ne sw earthquake alignment which in agreement with previous cases can be interpreted as the response of the medium to an intrusive process along the approximately nnw sse volcano genetic trend these mechanisms leading to the july 18 to august 9 2001 flank eruption are analogous to ones observed some months before the 1991 1993 flank eruption and more recently in january 1998 before the february november 1999 summit eruption

coupled textural and compositional characterization of basaltic scoria insights into the transition from strombolian to fire fountain activity at mount etna italy strombolian and fire fountain activities represent a common expression of explosive basaltic eruptions however the transition between these two eruptive styles and their source mechanisms are still debated we use textural and compositional studies to characterize pyroclastic material from both the strombolian and hawaiian style fire fountain phases of the january june 2000 etna activity we find that basaltic scoria presents distinctive textural and compositional features that reflect different modes of magma vesiculation and crystallization in the two eruptive regimes overall magma that forms strombolian scoria is far more crystallized less vesicular and more evolved indicating strong volatile depletion and longer residence time before being erupted fire fountain scoria indicates a fast rising magma with evidence of moderate syneruptive volatile exsolution the new textural and compositional data set is integrated with previous volcanological and geophysical investigations to provide further insights into the dynamics of fire fountains and to frame the transition from strombolian explosions to fire fountain activity into a model that may apply to future eruptions at mount etna as well as other active basaltic volcanoes

review of microgravity observations at mt etna a powerful tool to monitor and study active volcanoes microgravity observations at mt etna have been routinely performed as both discrete since 1986 and continuous since 1998 measurements in addition to describing the methodology for acquiring and reducing gravity data from mt etna this paper provides a collection of case studies aimed at demonstrating the potential of microgravity to investigate the plumbing system of an active volcano and detect forerunners to paroxysmal volcanic events for discrete gravity measurements results from 1994 1996 and 2001 are reported during the first period the observed gravity changes are interpreted within the framework of the strombolian activity which occurred from the summit craters gravity changes observed during the first nine months of 2001 are directly related to subsurface mass redistributions which preceded accompanied and followed the july august 2001 flank eruption of mt etna two continuous gravity records are discussed a 16 month october 1998 to february 2000 sequence and a 48 hour 26 28 october 2002 sequence both from a station within a few kilometers of the volcano s summit the 16 month record may be the longest continuous gravity sequence ever acquired at a station very close to the summit zone of an active volcano by cross analyzing it with contemporaneous discrete observations along a summit profile of stations both the geometry of a buried source and its time evolution can be investigated the shorter continuous sequence encompasses the onset of an eruption from a location only 1 5 km from the gravity station this gravity record is useful for establishing constraints on the characteristics of the intrusive mechanism leading to the eruption in particular the observed gravity anomaly indicates that the magma intrusion occurred passively within a fracture system opened by external forces

coupled conduit flow and shape in explosive volcanic eruptions volcanic conduit flow models generally utilise one of two conduit profile modes which are referred to as parallel sided typically surface choked or lithostatically pressure balanced their limitations in application to supersonically erupted basaltic and rhyolitic explosive eruptions are investigated likely changes in conduit profile over time due to catastrophic failure resulting from high wall stresses and abrasive erosion are investigated using a semi analytical model although time independent this model nonetheless reveals likely trends in shape from a simple parallel sided geometry it is found that for rhyolites early wall failure will occur in all but unusual circumstances resulting in expansion of the conduit a reduction in wall stresses and a trend towards a lithostatically pressure balanced solution at depth in both rhyolitic and basaltic eruptions abrasive erosion results in conduit flaring near the surface allowing the choking point to descent from the surface into the vent substantially changing exit conditions and resulting in a trend towards the a lithostatically pressure balanced solution at the surface although a truly lithostatically pressure balanced system can never be attained due to the effects of compressibility at supersonic velocities it is no less valid than the more commonly utilised parallel sided system for a variety of realistic eruption scenarios and can be a useful guide for potential steady states

spectroscopic evidence for a lava fountain driven by previously accumulated magmatic gas the eruption of mount etna in 2000 was notable for an exceptional series of 64 periodic lava fountains propelling lava fragments to heights of up to 900 metres it has been difficult to determine which of two suggested sources of power gas release from the magma itself during its rapid ascent or a build up of pressure from gas accumulated at depth is the driving force for these dramatic jets but one of the etna fountains provided volcanologists with the opportunity to use remote sensing not that remote see picture on the following page to determine the infrared spectra of the gas phase this revealed the chemical composition of the gas that powered this fountain as consistent with an origin in an accumulated gas layer lava fountains are spectacular continuous gas jets propelling lava fragments to heights of several hundred metres which occasionally occur during eruptions of low viscosity magmas1 2 3 4 5 whether they are generated by the effervescent disruption of fast rising bubbly melt2 3 4 5 or by the separate ascent of a bubble foam layer accumulated at depth6 7 still remains a matter of debate8 no field measurement has yet allowed firm discrimination between these two models a key insight into the origin of lava fountains may be gained by measuring the chemical composition of the driving gas phase this composition should differ markedly depending on whether the magma degassing occurs before or during eruption9 10 here we report the analysis of magmatic gas during a powerful 250 600 m high lava fountain measured with fourier transform infrared spectroscopy11 12 13 14 on mount etna sicily the abundances of volcanic gas species determined from absorption spectra of lava radiation reveal a fountain gas having higher co2 s and s cl ratios than other etnean emissions14 15 16 17 18 and which cannot derive from syn eruptive bulk degassing of etna basalt19 20 instead its composition suggests violent emptying of a gas bubble layer previously accumulated at about 1 5 km depth below the erupting crater

composite ground deformation pattern forerunning the 2004 2005 mount etna eruption 1 after the end of the 2002 2003 eruption mount etna activity was characterized only by gentle degassing at the summit craters and some earthquake swarms suddenly an eruption started on 7 september 2004 in complete absence of summit crater volcanic activity seismicity or seismic tremor and ground deformation this is the first time that magma poured out passively without preeruptive and coeruptive volcanic and or geophysical phenomena the primary key to understanding this event is represented by the ground deformation pattern recorded through gps measurements during the year before the eruption the ground deformation shows inflation superimposed by a predominant eastward movement of the eastern sector at a rate never observed before in a noneruptive period the images from satellite radar interferometry confirmed this pattern the deformation field clearly shows that the maximum tension in the eastern sector of the volcano caused the opening of the eruptive fracture which favored the silent pouring out of already resident magma

the effects of topography on magma chamber deformation models application to mt etna and radar interferometry we have used a three dimensional elastic finite element model to examine the effects of topography on the surface deformation predicted by models of magma chamber deflation we used the topography of mt etna to control the geometry of our model and compared the finite element results to those predicted by an analytical solution for a pressurized sphere in an elastic half space topography has a significant effect on the predicted surface deformation for both displacement profiles and synthetic interferograms not only are the predicted displacement magnitudes significantly different but also the map view patterns of displacement it is possible to match the predicted displacement magnitudes fairly well by adjusting the elevation of a reference surface however the horizontal pattern of deformation is still significantly different thus inversions based on constant elevation reference surfaces may not properly estimate the horizontal position of a magma chamber we have investigated an approach where the elevation of the reference surface varies for each computation point corresponding to topography for vertical displacements and tilts this method provides a good fit to the finite element results and thus may form the basis for an inversion scheme for radial displacements a constant reference elevation provides a better fit to the numerical results

molecular transformation and degradation of refractory dissolved organic matter in the atlantic and southern ocean more than 90 of the global ocean dissolved organic carbon doc is refractory has an average age of 4000 6000 years and a lifespan from months to millennia the fraction of dissolved organic matter dom that is resistant to degradation is a long term buffer in the global carbon cycle but its chemical composition structure and biochemical formation and degradation mechanisms are still unresolved we have compiled the most comprehensive molecular dataset of 197 fourier transform ion cyclotron resonance mass spectrometry ft icr ms analyses from solid phase extracted marine dom covering two major oceans the atlantic sector of the southern ocean and the east atlantic ocean ranging from 50 n to 70 s molecular trends and radiocarbon dating of 34 dom samples comprising 14c values from 229 to 495 were combined to model an integrated degradation rate for bulk doc resulting in a predicted age of 24 ka for the most persistent dom fraction first order kinetic degradation rates for 1557 mass peaks indicate that numerous dom molecules cycle on timescales much longer than the turnover of the bulk doc pool estimated residence times of up to 100 ka and the range of validity of radiocarbon dating changes in elemental composition were determined by assigning molecular formulae to the detected mass peaks the combination of residence times with molecular information enabled modelling of the average elemental composition of the slowest degrading fraction of the dom pool in our dataset a group of 361 molecular formulae represented the most stable composition in the oceanic environment island of stability these most persistent compounds encompass only a narrow range of the molecular elemental ratios h c average of 1 17 0 13 and o c average of 0 52 0 10 and molecular masses 360 28 and 497 51 da in the weddell sea doc concentrations in the surface waters were low 46 3 3 3 m while the organic radiocarbon was significantly more depleted than that of the east atlantic representing average surface water dom ages of 4920 180 a these results are in accordance with a highly degraded dom in the weddell sea surface water as also shown by the molecular degradation index ideg obtained from ft icr ms data further we identified 339 molecular formulae which probably contribute to an increased doc concentration in the southern ocean and potentially reflect an accumulation or enhanced sequestration of refractory doc in the weddell sea these results will contribute to a better understanding of the persistent nature of marine dom and its role as an oceanic carbon buffer in a changing climate

the july august 2001 eruption of mt etna sicily the july august 2001 eruption of mt etna stimulated widespread public and media interest caused significant damage to tourist facilities and for several days threatened the town of nicolosi on the s flank of the volcano seven eruptive fissures were active five on the s flank between 3 050 and 2 100 m altitude and two on the ne flank between 3 080 and 2 600 m elevation all produced lava flows over various periods during the eruption the most voluminous of which reached a length of 6 9 km mineralogically the 2001 lavas fall into two distinct groups indicating that magma was supplied through two different and largely independent pathways one extending laterally from the central conduit system through radial fissures the other being a vertically ascending eccentric dike furthermore one of the eccentric vents at 2 570 m elevation was the site of vigorous phreatomagmatic activity as the dike cut through a shallow aquifer during both the initial and closing stages of the eruption for 6 days the magma column feeding this vent was more or less effectively sealed from the aquifer permitting powerful explosive and effusive magmatic activity while the eruption was characterized by a highly dynamic evolution complex interactions between some of the eruptive fissures and changing eruptive styles its total volume 25 106 m3 of lava and 5 10 106 m3 of pyroclastics was relatively small in comparison with other recent eruptions of etna effusion rates were calculated on a daily basis and reached peaks of 14 16 m3 s 1 while the average effusion rate at all fissures was about 11 m3 s 1 which is not exceptionally high the eruption showed a number of peculiar features but none of these except the contemporaneous lateral and eccentric activity represented a significant deviation from etna s eruptive behavior in the long term however the 2001 eruption could be but the first in a series of flank eruptions some of which might be more voluminous and hazardous placed in a long term context the eruption confirms a distinct trend initiated during the past 50 years toward higher production rates and more frequent eruptions which might bring etna back to similar levels of activity as during the early to mid seventeenth century

analysis of simultaneous gravity and tremor anomalies observed during the 2002 2003 etna eruption abstract in this paper we discuss the data collected by a large aperture array of broadband seismometers and a continuously recording gravity station during the 2002 2003 eruption of etna volcano italy seismic signals recorded during the eruption are dominated by volcanic tremor whose energy spans the 0 5 5 hz frequency band on three different occasions 12 november 19 20 november and 8 9 december 2002 we observed marked increases of the tremor amplitude up to a factor of 4 which occurred simultaneously with gravity decreases up to 30 gal the three concurrent gravity tremor anomalies last 6 to 12 hours and terminate with rapid up to 2 hours changes after which the signals return back to their original levels based on volcanological observations encompassing the simultaneous anomalies we infer that the accumulation of a gas cloud at some level in the conduit plexus feeding a new eruptive vent could have acted as a joint source this study highlights the potential of joint gravity seismological analyses to both investigate the internal dynamic of a volcano and to improve the confidence of volcanic hazard assessment

an accurate and efficient method for including the effects of topography in three dimensional elastic models of ground deformation with applications to radar interferometry topography has a large effect on the results predicted by elastic surface deformation models in regions of significant relief in some cases topography may have more influence on the predicted deformation field than do model source parameters we have developed an approximate analytical technique for including topographic effects that retains most of the computational simplicity of elastic half space models while providing an accurate representation of topographic effects we use a series expansion of the elastic half space solution with a small slope approximation yielding a set of higher order corrections the integrated effect of these corrections is evaluated using fourier methods we investigate the effectiveness of our method by comparing predicted results for a tilted triaxial ellipsoid with those predicted by finite element models the resulting displacements and displacement gradients are in good agreement with finite element results both for relatively smooth topography synthetically generated and for the greater relief in the vicinity of mount etna volcano we then compare the results of our method with those predicted by traditional elastic half space models using different reference elevations and with a previously proposed method of estimating topographic effects our new method provides a significantly better fit to the finite element results than do the other methods our method is able to accurately portray both the number and the horizontal pattern of fringes in a synthetic interferogram when compared with finite element results in particular the method accurately represents the broadening of fringes that is observed in regions of high relief as well as reproducing the location of the fringe center and the topographically induced deviation of the fringes from a regular pattern elastic half space models typically show a fringe center that is displaced with respect to the finite element results indicating that parameter inversions based on such a model would provide incorrect estimates of the horizontal source position the lack of topographically generated fringe distortions in elastic half space results would also likely lead to inaccuracies in the predicted magnitude and orientation of proposed deformation sources our new technique over comes these limitations and should be useful when evaluating either traditional geodetic results or the greater areal coverage provided by interferometric observations

geochronology of intrusive and metamorphic rocks in the pilot range utah and nevada and comparison with regional patterns k ar and u pb isotopic studies demonstrate middle mesozoic metamorphism and plutonism followed by eocene plutonism in the pilot range northeastern great basin combined with field relations the age constraints indicate that local amphibolite facies and widespread greenschist facies metamorphism peaked between 165 and 150 ma and that plutons were emplaced early in the deformational and metamorphic history between 165 and 155 ma cenozoic plutons and widespread dikes that were emplaced at about 40 ma cut folds and faults including a major detachment fault that placed unmetamorphosed on metamorphosed rocks the mesozoic and early cenozoic history of metamorphism and plutonism in the pilot range is consistent with age data and field relations throughout the northeastern great basin that indicate late jurassic plutonism and metamorphism followed by eocene and oligocene plutonism and local metamorphism in many areas rocks that were metamorphosed during late jurassic time were cooled through ar blocking temperatures for micas between 85 and 60 ma the widespread occurrence of these mica ages suggests a regional mechanism for cooling

new insights into banded tremor from the 2008 2009 mount etna eruption 1 we investigated the banded tremor activity occurring at mt etna volcano between august october 2008 during the 2008 2009 eruption the banded tremor occurred in episodes lasting 25 30 min with intervals in between the episodes of about 25 min seismic signal analyses showed that the banded tremor was characterized by spectral contents wavefields and source locations that differed from the ordinary volcanic tremor the infrasound recordings exhibited an intermittent infrasonic tremor alternating with the banded tremor episodes finally nonlinear analyses suggested that a banded tremor system can be considered chaotic implying 1 sensitive dependence on initial conditions suggesting not only that a banded tremor system requires particular conditions to generate but also that slight variations of these conditions are able to greatly change the features of the banded tremor or even to stop it and 2 long term unpredictability that is the impossibility to forecast the long term evolution of the banded tremor on the basis of all these results and analogies with geyser models we suggest a model of banded tremor that invokes alternating recharge discharge phases banded tremor is due to perturbations in shallow aquifers such as fluid movement and bubble growth or collapse due to hydrothermal boiling triggered by the heat and hot fluid transfer from the underlying magma bodies this heat fluid transfer also causes an increasing pressure in the aquifer leading to fluid discharge during this process the seismic radiation decreases and if the fluid discharge is well coupled with the atmosphere acoustic signals are generated

triggering of volcanic eruptions although earthquakes and volcanic eruptions are each manifestations of large scale tectonic plate and mantle motions it is usually thought that the occurrences of these events are not directly related there have been some studies however in which triggering of volcanic eruptions by earthquakes remote from the volcano has been proposed1 2 the 1992 landers southern california earthquake caused triggered seismicity at very large distances3 including the magmatically active4 long valley caldera region which also experienced a significant coincident deformation transient5 motivated by this demonstration of the ability of a distant earthquake to disturb a volcanic system and the earlier studies of specific cases of eruption triggering we examine here the historical record of eruptions and earthquakes to see if there are indeed significantly more eruptions immediately following large earthquakes we find that within a day or two of large earthquakes there are many more eruptions within a range of 750 km than would otherwise be expected additionally it is well known6 that volcanoes separated by hundreds of kilometres frequently erupt in unison the characteristics of such eruption pairs are also consistent with the hypothesis that the second eruption is triggered by earthquakes associated with the first

pluton emplacement within an extensional transfer zone during dextral strike slip faulting an example from the late archaean abitibi greenstone belt abstract the lake abitibi area within the late archaean abitibi greenstone belt exhibits an interlinked plutonic structural and metamorphic evolution that may characterize segmented strike slip faults at upper to mid crustal levels along the major southeastward propagating macamic d 2 dextral strike slip fault theological and preexisting d 1 structural heterogeneities induced the development of nnw trending dextral oblique splays which evolved into an extensional trailing fan and created an extensional nnw dipping stepover magma flowing upwards from deeper parts of the macamic fault spread towards the southeast at upper crustal levels along both the oblique slip and extensional d 2 splays and built several plutons in a pull apart domain between 2696 and 2690 ma different emplacement and material transfer mechanisms operated simultaneously in different parts of the system including fault dilation and wedging lateral expansion wall rock ductile flow and stoping transfer of movement between d 2 splays occurred under ductile conditions during syn emplacement amphibolite grade metamorphism 500 700 c during cooling d 2 faults appear to have been closely linked during the superior province wide late transpressional event

late cretaceous extension in the hinterland of the sevier thrust belt northwestern utah and southern idaho cover rocks of the raft river metamorphic core complex located in the sevier belt hinterland preserve a structural and metamorphic history that predates the middle tertiary extension of the region in the eastern raft river mountains cambrian permian rocks form two allochthons that occur in the hanging wall of the mid miocene raft river detachment fault dramatically attenuated metamorphosed cambrian pennsylvanian strata of the lower allochthon yield late cretaceous muscovite sup 40 ar sup 39 ar plateau ages ca 82 90 ma that are interpreted to date cooling during final stages of layer parallel extension devonian permian rocks exposed in the black pine mountains underwent east west extension approximately 160 associated with syntectonic growth of white mica along cleavage sup 40 ar sup 39 ar whole rock spectra of associated slates also indicate a late cretaceous metamorphism together field and sup 40 ar sup 39 ar results suggest that late cretaceous extension occurred in the sevier belt hinterland at the same time as shortening in the eastern foreland and at depth in the hinterland sufficient topography must have been present to drive upper crustal extension in the eastern hinterland

accelerating exhumation in the eocene north american cordilleran hinterland implications from detrital zircon u th he pb double dating

redox effects on organic matter storage in coastal sediments during the holocene a biomarker proxy perspective coastal margins play a significant role in the burial of organic matter om on earth these margins vary considerably with respect to their efficiency in om burial and to the amounts and periodicity of their om delivery depending in large part on whether they are passive or active margins in the context of global warming these coastal regions are expected to experience higher water temperatures changes in riverine inputs of om and sea level rise low oxygen conditions continue to expand around the globe in estuarine regions i e hypoxic zones and shelf regions i e oxygen minimum zones which will impact the amounts and sources of om stored in these regions in this review we explore how these changes are impacting the storage of om and the preservation of sedimentary biomarkers used as proxies to reconstruct environmental change in coastal margins

an investigation into shallow borehole tiltmeters shallow borehole tiltmeters are frequently used for ground deformation monitoring in volcanic areas where they are usually installed within a few meters of the surface a major problem concerns the noise affecting the installation at shallow depth where large tilt and strain are caused by temperature effects the long term stability of these instruments and the best shallow depth of installation in terms of best cost benefit are the crucial points we conducted an experiment in order to compare the signals of three shallow borehole electronic tiltmeters installed in the same place at different depths we verified the signal reliability in revealing the long term slow deformation and looked into the reduction of the temperature effects with depth we present three years of data and discuss the limits and the advantages of the different installation depths

alternating contraction and extension in the hinterlands of orogenic belts an example from the raft river mountains utah combined macroscopic to microscopic structural analyses detailed geologic mapping and thermochronology were used to study the structural evolution of midcrustal rocks of the sevier orogenic belt hinterland in northwestern utah these results when combined with previous studies provide new insight into the structural history of this region and suggest alternating tectonic contraction and extension during mesozoic to early cenozoic time two allochthons form the upper plate of the miocene raft river detachment fault in the eastern raft river mountains the lower allochthon comprises neoproterozoic ordovician and pennsylvanian strata and is bounded below by the raft river detachment fault and above by the middle detachment fault strata within the lower allochthon were dramatically attenuated by two episodes of ductile deformation the first deformation d1 took place at metamorphic temperatures of 500 c and resulted in penetrative fabrics throughout these rocks that record combined flattening and top to northeast shearing strains the second deformation d2 resulted in significant stratigraphic attenuation along discrete top to the west shear zones that are generally parallel to lithologic contacts separates of synkinematic muscovite from the penetrative fabric yield 40ar 39ar cooling ages that indicate that d1 deformation occurred prior to cooling ca 90 ma both fabrics were subsequently folded about d3 kilometer scale recumbent folds the areally extensive middle allochthon composed chiefly of pennsylvanian and permian rocks metamorphosed in the greenschist facies was emplaced d4 along the low angle middle detachment fault this fault cuts across various structural levels of the recumbently folded lower allochthon in its footwall and juxtaposes greenschist facies over amphibolite facies metamorphic rocks the lower and middle allochthon were subsequently deformed d5 into open folds with north trending axes neogene extension d6 produced an 200 m thick top to east ductile shear zone in precambrian rocks and formed the younger raft river detachment fault which forms the present upper contact of the ductile shear zone northeast vergent d1 fabrics probably record shortening deformation on the basis of fabric correlations with the grouse creek and albion mountains deformation kinematics and synkinematic prograde metamorphism d2 attenuation faults have been interpreted to record crustal extension of late cretaceous age if d3 recumbent folds developed during extension then the deformation sequence records early shortening followed by protracted extensional unroofing with variable structural styles the favored alternative is that d3 recumbent folds developed during shortening in this case d1 through d4 record episodic alternations of contraction and extension such alternations are consistent with observations from analog and theoretical models of contractional mountain belts and suggest that the hinterland of the sevier orogenic belt underwent dynamic adjustments in crustal thickness and deformation kinematics in response to changes in the boundary conditions of the orogenic belt

on the geophysical fingerprint of vulcanian explosions abstract extrusion of viscous magma and the subsequent formation of a lava dome is often interspersed by short lived vigorous vulcanian explosions the causes for and the timing of the transition from effusive to explosive activity during dome formation are poorly understood and forecasting this transition remains a challenge here we describe and interpret a robust and unique multi parameter data set documenting the subsurface processes associated with vulcanian explosions at soufriere hills volcano montserrat w i in july and december 2008 we quantify explosion priming by processes in either the shallow

seismic characteristics of variable convection at erta ʻale lava lake ethiopia abstract the active summit lava lake of erta ale volcano ethiopia offers a unique opportunity to study magma convection in february 2002 we collected a multiparametric set of seismic thermal and video data these data indicate that the lake cycled between periods characterized by low 0 01 0 08 m s 1 and high 0 1 0 4 m s 1 convection rates typically lasting tens to hundreds of minutes three seismometers placed around the active crater recorded continuous tremor with a dominant frequency of 2 hz and energy at frequencies from 0 8 to 12 hz here we characterize the seismic signature of each regime by its spectral content wavefield polarization and tremor source location for both regimes the wavefield is mostly rectilinear azimuths and incidence angles are consistent with p waves originating in one of two locations the north edge of the active lava lake or a region 100 150 m ene of the lava lake because both regimes are dominated by a low frequency rectilinearly polarized wavefield we investigate the source location using a method that solves for location and isotropic source power by a weighted least squares amplitude based inversion of seismic data we find that tremor source regions are unique to each convective regime although some location overlap exists when tremor is located in short time windows wavefield composition suggests that the convective phases may share a common source process but their differing locations indicate that either the source region is non stationary or a second source skews the location during the high convective phase tremor polarization and location suggests that the low frequency tremor is caused by bubble coalescence and bursting in a conduit whose surface is the lava lake the higher frequency signal associated with the high convective regime is associated with a scattered more complex wavefield superimposed on the low frequency background tremor caused by bubble bursting and cracking of cooled crust at the lava lake surface

the exceptional activity and growth of the southeast crater mount etna italy between 1996 and 2001 between 1971 and 2001 the southeast crater was the most productive of the four summit craters of mount etna with activity that can be compared on a global scale to the opening phases of the pu u k paianaha eruption of k lauea volcano hawai i the period of highest eruptive rate was between 1996 and 2001 when near continuous activity occurred in five phases these were characterized by a wide range of eruptive styles and intensities from quiet non explosive lava emission to brief violent lava fountaining episodes much of the cone growth occurred during these fountaining episodes totaling 105 events many showed complex dynamics such as different eruptive styles at multiple vents and resulted in the growth of minor edifices on the flanks of the southeast crater cone small pyroclastic flows were produced during some of the eruptive episodes when oblique tephra jets showered the steep flanks of the cone with hot bombs and scoriae fluctuations in the eruptive style and eruption rates were controlled by a complex interplay between changes in the conduit geometry including the growth of a shallow magma reservoir under the southeast crater magma supply rates and flank instability during this period volume calculations were made with the aid of gis and image analysis of video footage obtained by a monitoring telecamera between 1996 and 2001 the bulk volume of the cone increased by 36 106 m3 giving a total 1971 2001 volume of 72 106 m3 at the same time the cone gained 105 m in height reaching an elevation of about 3 300 m the total dre volume of the 1996 2001 products was 90 106m3 this mostly comprised lava flows 72 106 m3 erupted at the summit and onto the flanks of the cone these values indicate that the productivity of the southeast crater increased fourfold during 1996 2001 with respect to the previous 25 years coinciding with a general increase in the eruptive output rates and eruption intensity at etna this phase of intense summit activity has been followed since the summer of 2001 by a period of increased structural instability of the volcano marked by a series of important flank eruptions

response of mount etna to dynamic stresses from distant earthquakes 1 influences of distant earthquakes on volcanic systems by dynamic stress transfer are well documented we analyzed seismic signals and volcanic activity at mount etna during two periods january 2006 and may 2008 that clearly showed variations coincident with distant earthquakes in the first period characterized by mild volcano activity the effect of the dynamic stress transfer caused by an earthquake in greece m 6 8 was twofold 1 banded tremor activity changed its features and almost disappeared 2 a swarm of volcano tectonic vt earthquakes took place the changes of the banded tremor were likely due to variations in rock permeability caused by fluid flows driven by dynamic strain the vt earthquake swarm probably developed as a secondary process promoted by the dynamically triggered activation of magmatic fluids the second period may 2008 showed an intense explosive activity during this interval the dynamic stress transfer associated with the arrival of the seismic waves of the sichuan earthquake m 7 9 affected the character of the seismo volcanic signals and on the following day triggered an eruption in particular we observed changes in volcanic tremor and increases of both occurrence rate and energy of long period events in this case we suggest that dynamic stress transfer caused nucleation of new bubbles in volatile rich magma bodies with consequent buildup of pressure highlighted by the increase of long period activity followed by the occurrence of an eruption we conclude that stresses from distant earthquakes are capable of modifying the state of the volcano

dynamic stresses coulomb failure and remote triggering dynamic stresses associated with crustal surface waves with 15 30 sec periods and peak amplitudes 5 km the latter is consistent with the observation that extensional or transtensional tectonic regimes are more susceptible to remote triggering by rayleigh wave dynamic stresses than compressional or transpressional regimes locally elevated pore pressures may have a role in the observed prevalence of dynamic triggering in extensional regimes and geothermal volcanic systems

fault slip and exhumation history of the willard thrust sheet sevier fold thrust belt utah relations to wedge propagation hinterland uplift and foreland basin sedimentation

near infrared spectroscopy of lacustrine sediments in the great salt lake desert an analog study for martian paleolake basins the identification and characterization of aqueous minerals within ancient lacustrine environments on mars are a high priority for determining the past habitability of the red planet terrestrial analog studies are useful both for understanding the mineralogy of lacustrine sediments how the mineralogy varies with location in a lacustrine environment and for validating the use of certain techniques such as visible near infrared vnir spectroscopy in this study sediments from the pilot valley paleolake basin of the great salt lake desert were characterized using vnir as an analog for martian paleolake basins the spectra and subsequent interpretations were then compared to mineralogical characterization by ground truth methods including x ray diffraction automated scanning electron microscopy and several geochemical analysis techniques in general there is good agreement between vnir and ground truth methods on the major classes of minerals present in the lake sediments and vnir spectra can also easily discriminate between clay dominated and salt dominated lacustrine terrains within the paleolake basin however detection of more detailed mineralogy is difficult with vnir spectra alone as some minerals can dominate the spectra even at very low abundances at this site the vnir spectra are dominated by absorption bands that are most consistent with gypsum and smectites though the ground truth methods reveal more diverse mineral assemblages that include a variety of sulfates primary and secondary phyllosilicates carbonates and chlorides this study provides insight into the limitations regarding the use of vnir in characterizing complex mineral assemblages inherent in lacustrine settings

melt inclusions track pre eruption storage and dehydration of magmas at etna at mount etna italy vigorous gas rich eruptions in a d 2001 2002 and 2003 were followed by gas poor eruptions in 2004 2006 and 2007 analyses of volatile co2 h2o s cl f semivolatile cu and involatile nb la elements trapped in olivine hosted melt inclusions from these latest eruptions reveal the effects of the sustained interaction between a percolating gas phase and the stored magma melt inclusion compositions indicate that magmas erupted from 2004 to 2007 were residual from the 2001 2003 eruptions and show significant evolution in the volatile content of the melt these melt inclusion observations and variations in the c s of volcanic gases can be accounted for if melts reequilibrated with co2 rich gases during storage and prior to entrapment as melt inclusions sustained gas percolation caused loss of water and enhancement of co2 in the evolving melt and may strongly influence the behavior of cu which potentially partitions into the gas phase vapor melt interactions during magma storage are important controls on magma evolution at persistently degassing volcanoes

chemoautotrophy in the ocean are the most importantcontributors this input of new organic carbon to the oceanis similar to that supplied by world rivers and eventuallyburied in oceanic sediments chemoautotrophy driven byorganic carbon recycling is globally more important thanthat fuelled by water rock interactions and hydrothermalventsystems

an amagmatic origin of carlin type gold deposits carlin type deposits are major sources of gold yet their origins are enigmatic suggested genetic models make connections to magmatism regional metamorphism or regional extension depositional mechanisms are uncertain as well we propose on the basis of geologic physical and chemical reasoning a genetic model in which meteoric fluids were circulated by heat released during crustal extension these fluids interacted at depth with the sedimentary rock pile and scavenged gold upon upwelling these fluids interacted with various lithologies and or other fluids and produced the characteristic alteration and metal suites of these deposits to test the viability of this amagmatic model we have investigated certain physical and chemical constraints implicit to the model heat balance calculations indicate that ample surface waters could be heated to appropriate temperatures and circulated during rapid crustal extension mass balance calculations indicate that solution transport efficiencies of 10 percent can account for several times the amount of known alteration and mineralization in contrast magma driven or metamorphic fluids appear to be less adequate sources a two step source to deposit approach was used to simulate fluid rock interaction and mass transport implied in the amagmatic model fluids with a fixed sigma cl were first equilibrated with various potential source rocks arkose graywacke and pelite each with various f o2 and f s2 buffer assemblages at 300 degrees c and 1 kbar to simulate reaction at depth perhaps near the brittle ductile transition these fluids were then reequilibrated under conditions indicated for deposit formation 225 degrees 150 degrees c 0 5 kbars to investigate processes including cooling wall rock reaction and mixing which could be important to ore deposition gold transport was favored for low chlorinity intermediate oxidation state below pyrrhotite pyrite magnetite slightly acid fluids from sulfide bearing sources i e equilibration with arkosic rocks these conditions are not conducive to base metal transport and explain the rarity of base metals in carlin type systems when reacted under deposit level conditions these calculated ore fluids leach carbonate and deposit quartz the volume ratio of carbonate dissolved to quartz precipitated is approximately 0 2 to 2 5 and increases when mixing with a second fluid is considered arkose equilibrated source fluids can precipitate gold by combinations of wall rock reaction with a decarbonated host mixing with various sulfide poor fluids and reaction with iron rich host rocks cooling alone is ineffective over this temperature interval although most deposits are hosted by decarbonated marls geochemical calculations suggest that other depositional environments are feasible consistent with observation although here applied to the amagmatic hypothesis these chemical calculations are not mechanism specific and might also be appropriate to metamorphic or magma driven hydrothermal systems these results demonstrate that carlin type deposits can result from the coincidence of an effective driving force rapid major crustal extension a source of dilute fluids and chemically appropriate sets of both source and host rocks the aqueous chemistry involved is unexceptional and shares many features with other types of moderate to low temperature gold bearing hydrothermal systems it is the geologic setting and perhaps the fluid driving force that is unusual an amagmatic model is consistent with both deposit scale and regional scale observations it rationalizes carlin type systems in the framework of southwestern north american metallogeny and it implies multiple possible mechanisms for gold mineralization detachment type gold systems may be the high oxidation state high salinity analogues of carlin type systems formed by major extension but from contrasting lithologic and fluid sources

explosive activity at mt etna summit craters and source modeling by using high precision continuous tilt we investigated the relationships between modelled strain produced by explosive activity through a volcanic conduit observed paroxystic episodes on mt etna and high precision continuous tilt signals recorded during such events from the tilt monitoring network the tilt changes detected during two different explosive episodes were compared with those calculated from analytical models of ground deformation in order to constrain source properties the july 22 1998 subplinian explosion from voragine crater produced small tilt changes order of 0 5 1 5 rad recorded over the entire volcano edifice implying a small storage at nearly 2 5 km below sea level the 1998 2000 period was characterized by tens of spectacular lava fountains from the south east crater very small tilt change 0 1 rad was recorded by a single station on the high north eastern flank of mt etna and indicated the action of a limited and shallow conduit with 1 5 1 9 km depth these results provide a contribution to better infer the shallow plumbing system beneath mt etna

evolution of lava flow fields at mount etna 27 28 october 1999 observed by landsat 7 etm landsat 7 enhanced thematic mapper etm data are presented which document the thermal characteristics of a series of lava flows emplaced at mount etna volcano sicily during 27 28 october 1999 by examining the composition of the short wave infrared swir signal emitted from the flow surface we identified distinctive flow units the first unit appears to comprise recently active lava flows with relatively cool crusts which by virtue of the integrity of this crust as determined from the etm data we infer are stationary or barely moving the second unit is characterized by much higher levels of swir radiance consistent with a channel fed active flow unit analysis of the swir data confirm that this is fed by a lava channel the properties of which are consistent with vigorously active channels observed on kilauea hawaii model predictions of the maximum length that such flows could attain compare favorably with the actual flow lengths observed in the etm data indicating that the cooler flows had indeed stopped advancing and may have attained a cooling limited rather than volume limited maximum length our observations and modeling provide a physical corroboration for the supposition made by wadge 1978 in his analysis of the shape of lava flow fields on mount etna which in the cooling limited case principal flows are active one after the other and not at the same time

factors influencing the height of hawaiian lava fountains implications for the use of fountain height as an indicator of magma gas content the heights of lava fountains formed in hawaiian style eruptions are controlled by magma gas content volume flux and the amounts of lava re entrainment and gas bubble coalescence theoretical models of lava fountaining are used to analyse data on lava fountain height variations collected during the 1983 1986 pu u o o vent of kilauea volcano hawaii the results show that the variable fountain heights can be largely explained by the impact of variations in volume flux and amount of lava re entrainment on erupting magmas with a constant gas content of 0 32 wt h2o however the gas content of the magma apparently declined by 0 05 wt during the last 10 episodes of the eruption series and this decline is attributed to more extensive pre eruption degassing due to a shallowing of the sub vent feeder dike it is concluded that variations in lava fountain height cannot be simply interpreted as variations in gas content as has previously been suggested but that fountain height can still be a useful guide to minimum gas contents where sufficient data are available on eruptive volume fluxes and extent of lava entrainment greatly improved estimates can be made of magma gas content from lava fountain height

the initial phases of the 2008 2009 mount etna eruption a multidisciplinary approach for hazard assessment accepted for publication in journal of geophysical research copyright 2010 american geophysical union

lava effusion rate definition and measurement a review measurement of effusion rate is a primary objective for studies that model lava flow and magma system dynamics as well as for monitoring efforts during on going eruptions however its exact definition remains a source of confusion and problems occur when comparing volume flux values that are averaged over different time periods or spatial scales or measured using different approaches thus our aims are to 1 define effusion rate terminology and 2 assess the various measurement methods and their results we first distinguish between instantaneous effusion rate and time averaged discharge rate eruption rate is next defined as the total volume of lava emplaced since the beginning of the eruption divided by the time since the eruption began the ultimate extension of this is mean output rate this being the final volume of erupted lava divided by total eruption duration whether these values are total values i e the flux feeding all flow units across the entire flow field or local i e the flux feeding a single active unit within a flow field across which many units are active also needs to be specified no approach is without its problems and all can have large error up to 50 however good agreement between diverse approaches shows that reliable estimates can be made if each approach is applied carefully and takes into account the caveats we detail here there are three important factors to consider and state when measuring giving or using an effusion rate first the time period over which the value was averaged second whether the measurement applies to the entire active flow field or a single lava flow within that field and third the measurement technique and its accompanying assumptions

precursory swarms of long period events at redoubt volcano 1989 1990 alaska their origin and use as a forecasting tool abstract during the eruption of redoubt volcano from december 1989 through april 1990 the alaska volcano observatory issued advance warnings of several tephra eruptions based on changes in seismic activity related to the occurrence of precursory swarms of long period lp seismic events dominant period of about 0 5 s the initial eruption on december 14 occurred after 23 years of quiescence and was heralded by a 23 hour swarm of lp events that ended abruptly with the eruption after a series of vent clearing explosions over the next few days dome growth began on december 21 another swarm with lp events similar to those of the first began on the 26th and ended in a major tephra eruption on january 2 eruptions continued over the next two weeks and then ceased until february 15 when a large eruption initiated a long phase of repetitive dome building and dome destroying episodes that continued into april warnings were issued before the major events on december 14 and january 2 but as the eruptive sequence continued after january 2 the energy of the swarms decreased and forecasting became more difficult a significant but less intense swarm preceded the february 15 eruption which was not forecast this eruption destroyed the only seismograph on the volcanic edifice and stymied forecasting until march 4 when the first of three new stations was installed within 3 km of the active vent from march 4 to the end of the sequence on april 21 there were eight eruptions six of which were preceded by detectable swarms of lp events although weak these swarms provided the basis for warnings issued before the eruptions on march 23 and april 6 the initial swarm on december 13 had the following features 1 short duration 23 hours 2 a rapidly accelerating rate of seismic energy release over the first 18 hours of the swarm followed by a decline of activity during the 5 hours preceding the eruption 3 a magnitude range from 0 4 to 1 6 4 nearly identical lp signatures with a dominant period near 0 5 s 5 dilatational first motions everywhere and 6 a stationary source location at a depth of 1 4 km beneath the crater this occurrence of long period events suggests a model involving the interaction of magma with groundwater in which magmatic gases steam and water drive a fixed conduit at a stationary point throughout the swarm the initiation of that sequence of events is analogous to the failure of a pressure relief valve connecting a lower supercharged magma dominated reservoir to a shallow hydrothermal system a three dimensional model of a vibrating fluid filled crack recently developed by chouet is found to be compatible with the seismic data and yields the following parameters for the lp source crack length 280 380 m crack width 140 190 m crack thickness 0 05 0 20 m crack stiffness 100 200 sound speed of fluid 0 8 1 3 km s compressional wave speed of rock 5 1 km s density ratio of fluid to rock 0 4 and ratio of bulk modulus of fluid to rigidity of rock 0 03 0 07 the fluid filled crack is excited intermittently by an impulsive pressure drop that varies in magnitude within the range of 0 4 to 40 bar such disturbance appears to be consistent with a triggering mechanism associated with choked flow conditions in the crack

chemoautotrophy in the redox transition zone of the cariaco basin a significant midwater source of organic carbon production during the cariaco time series program microbial standing stocks bacterial production and acetate turnover were consistently elevated in the redox transition zone rtz of the cariaco basin the depth interval 240 450 m of steepest gradient in oxidation reduction potential anomalously high fluxes of particulate carbon were captured in sediment traps below this zone 455 m in 16 of 71 observations here we present new evidence that bacterial chemoautotrophy fueled by reduced sulfur species supports an active secondary microbial food web in the rtz and is potentially a large midwater source of labile chemically unique sedimenting biogenic debris to the basin s interior dissolved inorganic carbon assimilation 27 159 mmol c m 22 d 21 in this zone was equivalent to 10 333 of contemporaneous primary production depending on the season however vertical diffusion rates to the rtz of electron donors and electron acceptors were inadequate to support this production therefore significant lateral intrusions of oxic waters mixing processes or intensive cycling of c s n mn and fe across the rtz are necessary to balance electron equivalents chemoautotrophic production appears to be decoupled temporally from short term surface processes such as seasonal upwelling and blooms and potentially is more responsive to longterm changes in surface productivity and deep water ventilation on interannual to decadal timescales findings suggest that midwater production of organic carbon may contribute a unique signature to the basin s sediment record thereby altering its paleoclimatological interpretation

transition from contraction to extension in the northeastern basin and range new evidence from the copper mountains nevada abstract new mapping structural analysis and 40ar 39ar dating reveal an unusually well constrained history of late eocene extension in the copper mountains of the northern basin and range province in this area the northeast trending copper creek normal fault juxtaposes a distinctive sequence of metacarbonate and granitoid rocks against a footwall of upper precambrian to lower cambrian quartzite and phyllite correlation of the hanging wall with footwall rocks to the northwest provides an approximate piercing point that requires 8 12 km displacement in an ese direction this displaced fault slice is itself bounded above by another normal fault the meadow fork fault which brings down a hanging wall of dacitic to rhyolitic tuff that grades conformably upward into conglomerate these relationships record the formation of a fault bounded basin between 41 3 and 37 4 ma the results are consistent with a regional pattern in which volcanism and extension swept southward from british columbia to southern ne

magma dynamics in the shallow plumbing system of mt etna as recorded by compositional variations in volcanics of recent summit activity 1995 1999 describe the reactivation and the successive evolution of the shallow plumbing system of mt etna between the end of the largest flank eruption of the last three centuries 1991 1993 and the subterminal eruption from south east crater sec which occurred between february and mid november 1999 our analysis is based on observations of the volcanic activity and petrological studies of the erupted volcanics bulk rock mineral and glass compositions have been determined for more than 80 samples erupted from the four summit craters between october 1995 and february 1999 these data allow us to recognise significant compositional variations among the products of different craters in particular volcanics produced between 1995 and 1999 by bocca nuova bn voragine vor and north east crater nec show limited compositional variations and are similar to those observed during recent eruptions e g 1991 93 more primitive magmas have been produced during the more vigorous fire fountains episodes on the contrary the south east crater produced slightly more differentiated volcanics than those of the other summit craters following its reactivation november 1996 until the end of 1998 whole rock compositions of products from this crater show low cao al 2 o 3 whereas interstitial glasses have lower mgo and higher alkali contents than those from the other craters however since the beginning of 1999 and just before the start of the subterminal eruption from sec the volcanics erupted from this crater progressively changed in composition becoming similar to those of the other craters this trend indicates that within the conduits of the summit craters distinct thermal and fluid dynamical regimes can evolve controlling the cooling and crystallisation of etna magmas

a multiparameter approach to volcano monitoring based on 4d analyses of seismo volcanic and acoustic signals the 2008 mt etna eruption 1 volcanic tremor and low frequency events together with infrasound signals can represent important precursory phenomena of eruptive activity because of their strict relationship with eruptive mechanisms and with fluid flows through the volcano s feeding system important variations of these seismo volcanic and infrasound signals recorded at mt etna volcano occurred both in the medium and short term before the eruption that took place on 13 may 2008 the most significant changes were observed in the frequency content and location of lp events as well as in volcanic tremor location that allowed us to track the magma pathway feeding the 2008 eruptive activity the infrasound showed three different families of events linked to the activity of the three active vents north east crater south east crater and the eruptive fissure the seismic and infrasonic variations reported corroborated by ground deformations variations help to develop a quantitative prediction and early warning system for effusive and or explosive eruptions

iron and sulfide oxidation within the basaltic ocean crust implications for chemolithoautotrophic microbial biomass production microbial processes within the ocean crust are of potential importance in controlling rates of chemical reactions and thereby affecting chemical exchange between the oceans and lithosphere we here assess the oxidation state of altered ocean crust and estimate the magnitude of microbial biomass production that might be supported by oxidative and nonoxidative alteration compilations of fe2o3 feo and s concentrations from dsdp odp drill core samples representing upper basaltic ocean crust suggest that fe3 fe increases from 0 15 0 05 to 0 45 0 15 within the first 10 20 myr of crustal evolution within the same time frame 70 25 of primary sulfides in basalt are oxidized with an annual production of 4 0 1 8 1015 g of upper 500 200 m crust and average initial concentrations of 8 0 1 3 wt fe and 0 125 0 020 wt s we estimate annual oxidation rates of 1 7 1 2 1012 mol fe and 1 1 0 7 1011 mol s we estimate that 50 of fe oxidation may be attributed to hydrolysis producing 4 5 3 0 1011 mol h2 yr thermodynamic and bioenergetic calculations were used to estimate the potential chemolithoautotrophic microbial biomass production within ridge flanks combined aerobic and anaerobic fe and s oxidation may support production of up to 48 21 1010 g cellular carbon c hydrogen consuming reactions may support production of a similar or larger microbial biomass if iron reduction nitrate reduction or hydrogen oxidation by o2 aq are the prevailing metabolic reactions if autotrophic sulfate reduction or methanogenesis prevail the potential biomass production is 9 7 1010 g c yr and 3 2 1010 g c yr respectively combined primary biomass production of up to 1 1012 g c yr may be similar to that fueled by anaerobic oxidation of organic matter in deep seated heterotrophic systems these estimates suggest that water rock reactions may support significant microbial life within ridge flank hydrothermal systems these estimates suggest that water rock reactions may support significant microbial life within ridge flank hydrothermal systems

shallow magma pathway geometry at mt etna volcano 1 a fundamental goal of volcano seismology is to understand the dynamics of active magmatic systems in order to assess eruptive behavior and the associated hazard imaging of magma conduits quantification of magma transport and investigation of long period seismic sources together with their temporal variations are crucial for the comprehension of eruption triggering mechanisms at mt etna volcano several intense episodes of tremor activity were recorded during 2007 in association with strombolian activity and or intense fire fountaining episodes occurring from the south east crater sec the locations of the tremor sources and of the long period seismic events are used here to constrain both the area and the depth range of magma degassing highlighting the geometry of the shallow conduits feeding sec the imaged conduits consist of two connected resonating dike like bodies nnw sse and nw se oriented extending from sea level to the surface in addition we show how tremor long period lp and very long period vlp event locations and signatures reflect pressure fluctuations in the plumbing system associated with the ascent discharge of gas rich magma linked to the lava fountains the evidence here reported also corroborated by ground deformation variations can help develop a better prediction and early warning system for those eruptions effusive or explosive that apparently manifest no clear precursors

simultaneous magma and gas eruptions at three volcanoes in southern italy an earthquake trigger this study was partly funded by the deutsche forschungsgemeinschaft wa 1642 1 4 and protezione civile project ingv dpc v2

lava fountains during the episodic eruption of south east crater mt etna 2000 insights into magma gas dynamics within the shallow volcano plumbing system mt etna in sicily italy is well known for frequent effusive and explosive eruptions from both its summit and flanks south east crater se crater one of the four summit craters has been the most active in the last 20 years and often produces episodic lava fountains over periods lasting from a few weeks to months the most striking of such eruptive phases was in 2000 sixty four lava fountains separated by quiescent intervals and sometimes associated with lava overflows occurred that year between january and june a time period during which we consider the volcano to have been in episodic eruption this paper presents mainly results of petrochemical investigations carried out on both tephra and lavas collected during a number of the lava fountain episodes in 2000 the new data have been integrated with volcanological and seismic information in order to correlate the features of the eruptive activity with magma gas dynamics in the plumbing system of se crater the main findings allow us to characterise the 2000 episodic eruption in the framework of the recent se crater activity in particular we infer that the onset of the 2000 eruption was triggered by the ascent of new more primitive and volatile rich magma that progressively intruded into the se crater reservoir where it mixed with the resident more evolved magma furthermore we argue that the 2000 se crater lava fountains largely resulted from the instability of a foam layer accumulated at the top of the underlying reservoir and rebuilt prior to each episode in agreement with the collapsing foam model for lava fountains

comment on multidisciplinary investigation on a lava fountain preceding a flank eruption the 10 may 2008 etna case by a bonaccorso et al

reply to comment by d carbone and d patane on multidisciplinary investigation on a lava fountain preceding a flank eruption the 10 may 2008 etna case

patterns in the recent 2007 2008 activity of mount etna volcano investigated by integrated geophysical and geochemical observations 1 seismic deformation and volcanic gas observations offer independent and complementary information on the activity state and dynamics of quiescent and eruptive volcanoes and thus all contribute to volcanic risk assessment in spite of their wide use there have been only a few efforts to systematically integrate and compare the results of these different monitoring techniques here we combine seismic volcanic tremor and long period seismicity deformation gps and geochemical volcanic gas plume co2 so2 ratios measurements in an attempt to interpret trends in the recent 2007 2008 activity of etna volcano we show that each eruptive episode occurring at the southeast crater sec was preceded by a cyclic phase of increase decrease of plume co2 so2 ratios and by inflation of the volcano s summit captured by the gps network these observations are interpreted as reflecting the persistent supply of co2 rich gas bubbles and eventually more primitive magmas to a shallow depth of 1 2 8 km asl magma storage zone below the volcano s central craters ccs overpressuring of the resident magma stored in the upper ccs conduit triggers further magma ascent and finally eruption at sec a process which we capture as an abrupt increase in tremor amplitude an upward 2800 m asl and eastward migration of the source location of seismic tremor and a rapid contraction of the volcano s summit resumption of volcanic activity at sec was also systematically anticipated by declining plume co2 so2 ratios consistent with magma degassing being diverted from the central conduit area toward sec

volumetric observations during paroxysmal eruptions at mount etna pressurized drainage of a shallow chamber or pulsed supply abstract the october 17 to november 5 1999 eruption of mount etna s bocca nuova crater emplaced a 15 10 6 m 3 flow field the eruption was characterized by 11 paroxysmal events during which intense strombolian and lava fountain activity fed vigorous channelized a a flows at eruption rates of up to 120 m 3 s 1 each paroxysm lasted between 75 and 450 min and was separated by periods of less intense strombolian activity and less vigorous 3 s 1 effusion ground based satellite and model derived volumetric data show that the eruption was characterized by two periods during which eruption rates and cumulative volume showed exponential decay this is consistent with a scenario whereby the system was depressurized during the first eruptive period october 17 23 repressurized during an october 24 pause and then depressurized again during the second period october 25 28 the imbalance between the erupted and supplied volumes mean that the two periods involved the collection of 1 5 5 7 10 6 m 3 and 1 2 3 6 10 6 m 3 respectively or an increase in the time averaged supply to 11 6 13 6 m 3 s 1 and 12 5 14 9 m 3 s 1 two models are consistent with the observed episodic fountaining derived volumetric trends and calculated volume imbalance a magma collection model and a pulsed supply model in the former case depressurization of a shallow reservoir cause the observed volumetric trends and foam collapse at the reservoir roof powers fountaining in the pulsing case variations in magma flux account for pressurization depressurization and supply the excess volume increases in rise rate and volatile flux coupled with rapid exsolution during ascent trigger fountaining limiting equations that define critical foam layer volumes and magma rise rates necessary for hawaiian style fountaining favor the latter model

long period and very long period events at mt etna volcano characteristics variability and causality and implications for their sources abstract almost 50 000 long period lp events were recorded at mt etna from november 2003 to may 2006 we analysed these events as well as very long period vlp events which were associated with some of them during some intervals the spectral and wavefield features of lp events remained steady with significant changes occurring between the intervals based on the times of the changes we distinguish five different sub periods in particular during sub period iii june november 2005 the wavefield at the stations nearest to the summit area was composed of p waves locations for 150 lp events occurring in sub period iii determined using radial semblance changed at the same time as the events spectral features changed it was during this sub period that many of the lp events were associated with vlp events based on similarity of the waveforms we distinguished two families of vlp events with gradually evolving waveforms the two families are located in slightly different places but near the sources of the lp events the change between the families occurred at the same time as the spectra of the lp events changed finally the source of the vlp events was investigated by performing complete waveform moment tensor inversion of stacks of the two families synthetic green s functions for the full moment tensor were calculated for a homogeneous half space for both families the source region with the highest variance reduction lies approximately beneath the active craters at 500 m below the altitudes of the stations the solutions for both families are very similar with sources that are between 60 and 70 isotropic attempts to determine deviatoric moment tensors produced consistently poorer fits the remaining energy is poorly constrained and is likely to be noise in conclusion these results highlight changes in the lp and vlp events at mt etna over time and the causal relationship between them

activity of mount etna preceding the february 1999 fissure eruption inferred mechanism from seismological and geochemical data abstract the february 1999 eruption of mt etna took place through a fissure on the sse flank of the cone of the summit se crater this event was preceded by continuous activity since 1995 sometimes accompanied by violent outbursts from one or more of the three other summit craters ne crater voragine or chasm and bocca nuova and finally by a series of 20 short lived eruptions from the se crater between september 1998 and january 1999 these phenomena could be accounted for by invoking gradual invasion of a shallow small reservoir by more primitive basic and gas rich magma coming from depth the shallow chamber is more likely to be a plexus of dikes which had developed during the previous years 1995 1997 following variations of the local stress field owing to enhanced magma generation and accumulation at the top of the mantle magma injection and mixing is evidenced through geochemistry whereas the state of stress of the volcanic pile and underlying crust is determined using earthquake distributions and focal mechanisms the behaviour of the seismic tremor amplitude appears to be a good indicator of the state of unrest of the volcano although not always directly linked to the relative energy of degassing phenomena

the 4 5 september 2007 lava fountain at south east crater of mt etna italy abstract continuous monitoring of paroxysmal eruptions at mt etna italy is performed from the istituto nazionale di geofisica e vulcanologia sezione di catania in recent years this activity has allowed us to study fallout deposits and track the evolution of eruptive phases this communication reports on the paroxysm that occurred in the afternoon of 4 september 2007 when a powerful lava fountain started from south east crater at the summit of etna the fountaining formed a plume up to 2 km high for almost 12 h causing abundant tephra fallout in the eastern sector of the volcano and emplacement of a thick about 4 km long clastogenic lava flow extensive area collection of tephra samples from the fallout deposit was performed within a few hours after the end of the paroxysm we calculated a total erupted volume of 3 92 4 9 10 5 m 3 and a total grain size fitted by a gaussian distribution with the mode of 0 and equal to 1 3 the total volume of the clastogenic lava flow deposit that resulted was 2 4 10 6 m 3 the systematic study of paroxysms at etna helps to better investigate etnean type lava fountains and to improve the classification of explosive activity on basaltic volcanoes

multidisciplinary investigation on a lava fountain preceding a flank eruption the 10 may 2008 etna case a multidisciplinary approach integrating a wide data set ranging from bulk rock compositions of the erupted products to volcanic tremor long period events and tilt and gravity signals is used to investigate the source depth and magma dynamics of the 10 may 2008 lava fountain at southeast crater sec of mount etna the investigation was undertaken in the framework of the previous 2007 explosive activity as well as the subsequent effusive eruption beginning 13 may 2008 and lasting up to july 2009 all the data concur in indicating that the 10 may lava fountain was generated by the fragmentation of a foam layer trapped at the top of a shallow reservoir about 1500 1700 m below the summit of sec the shift from the episodic strombolian lava fountain activity occurring in 2007 at sec to the more powerful 10 may 2008 lava fountain is explained by the intrusion of a new more primitive magma into the shallow reservoir data also indicate that an attempted magma intrusion east of the summit area occurred during the 10 may fire fountain this event caused the fracturing and weakening of the surrounding rocks and created a preferential pathway for the penetration of the magma that only 3 days later started to feed the 2008 2009 effusive eruption

volcanic tremor at mt etna inferences on magma dynamics during effusive and explosive activity abstract during 1999 the volcanic activity at mt etna was both explosive and effusive at the summit craters strombolian activity lava fountains and lava flows affected different areas of the volcano involving three of the four summit craters results from analysis of the 1999 volcanic tremor features are shown at two different time scales first the long term time variation of the features of the volcanic tremor including spectral and polarization parameters during the entire year was compared with the evolution of the eruptive activity this approach demonstrated the good agreement between tremor data and observed eruptive activity the activation of different tremor sources was suggested then a more refined analysis of the volcanic tremor recorded during 14 lava fountain eruptions was performed in particular a shift of the dominant frequencies towards lower values was noted which corresponds with increasing explosive activity similar behaviour in the frequency content has already been observed in other explosive eruptions at mt etna as well as on other volcanoes this behaviour has been explained in terms of either an increase in the tremor source dimension or a decrease in the sound speed in the magma within the conduit these results confirm that the volcanic tremor is a powerful tool for better understanding the physical processes controlling explosive eruptions at mt etna volcano

buoyancy controlled eruption of magmas at mt etna buoyancy controls the ability of magma to rise its ascent rate and the style of the eruptions geophysical geological and petrological data have been integrated to evaluate the buoyancy of magmas at mt etna the density difference between host rocks and magmas is mainly related to the amount of h2o dissolved in the magma and to the bubble liquid separation processes in the depth interval 22 2 km b s l highly hydrated h2o 3 basaltic magmas or mixtures of bubbles liquid have positive buoyancy and rise rapidly conversely bubble depleted liquids with an intermediate h2o content 1 5 having neutral buoyancy will spread out and form magmatic reservoirs at different depths until cooling crystallization further modify composition and density these different processes account for the magma compositions location of magmatic reservoirs as determined by geophysical methods and the complex eruptive cycles slow effusions fire fountains and plinian eruptions that have been observed in the history of the volcano