fault controlled soil co2 degassing and shallow magma bodies summit and lower east rift of kilauea volcano hawaii 1997 soil co2 flux measurements were carried out along traverses across mapped faults and eruptive fissures on the summit and the lower east rift zone of kilauea volcano anomalous levels of soil degassing were found for 44 of the tectonic structures and 47 of the eruptive fissures intercepted by the surveyed profiles this result contrasts with what was recently observed on mt etna where most of the surveyed faults were associated with anomalous soil degassing the difference is probably related to the differences in the state of activity at the time when soil gas measurements were made kilauea was erupting whereas mt etna was quiescent although in a pre eruptive stage unlike mt etna flank degassing on kilauea is restricted to the tectonic and volcanic structures directly connected to the magma reservoir feeding the ongoing east rift eruption or in areas of the lower east rift where other shallow likely independent reservoirs are postulated anomalous soil degassing was also found in areas without surface evidence of faults thus suggesting the possibility of previously unknown structures

enhanced diapycnal mixing in the south china sea profiles of current velocity temperature and salinity were obtained in the internal wave and mixing experiment in the south china sea scs the luzon strait and the north pacific the observations are examinedforevidenceofenhanceddiapycnalmixinginthescs whichreacheso 10 23 m 2 s 21 inmagnitude resultsfrom independent casts reveal that diapycnal diffusivity in the scs andthe luzon strait is elevatedby two orders of magnitude over that of the smooth bathymetry in the north pacific which are typical of background values in an open ocean the vertical distribution of diapycnal diffusivity is nonuniform in the scs exhibiting higher values at depths greater than about 1000 m this result compares favorably with the direct microstructure measurements at four stations in the scs velocity and density profiles are combined to estimatetheinternaltideenergyfluxgeneratedintheluzonstraitanddirectedintothescs theenergyamounts to 10 gw most of which is rationalized to be the potential energy source for enhanced mixing in the scs

tides and tidal energetics of the strait of gibraltar a modelling approach abstract the main semidiurnal m2 and s2 and diurnal o1 and k1 tidal waves in the strait of gibraltar are simulated by employing a 2d high resolution non linear boundary fitted coordinate model agreement between observational evidence and model results is good for the m2 and s2 tidal waves and satisfactory for the o1 and k1 tidal waves the model reproduces all the known features of the spatial structure of these waves and predicts some new ones namely the general direction of the m2 and s2 mean tidal energy fluxes to the west with a clear increase at the camarinal sill the o1 amphidrome with anticlockwise rotation of cotidal lines in the tarifa narrows and small scale eddies in the m2 s2 and o1 mean tidal energy flux fields in the vicinity of the western and eastern boundaries of the strait

sea level variations and their interactions between the black sea and the aegean sea abstract short tidal subtidal seasonal sea level variations sea level differences and interactions have been studied based on data collected at the stations located along the coasts of the south western black sea the strait of istanbul bosphorus the sea of marmara the strait of canakkale dardanelles and the north eastern aegean sea short period oscillations in the strait of istanbul the sea of marmara and the strait of canakkale were related to the natural periods of the straits and the sea of marmara itself tidal oscillations are small in amplitude and vary along the system tides are diurnal in the black sea and the strait of istanbul mixed but mainly diurnal at the south of the strait of istanbul and in the sea of marmara and semi diurnal in the strait of canakkale long period oscillations which are mainly governed by meteorological influences have a high correlation within a 3 14 day period seasonal sea level fluctuations are in accord with the black sea s hydrological cycle there is a pronounced sea level difference along the system the mean sea level at the black sea is about 55 cm higher than at the aegean sea but the slope along the system is non linear being much steeper in the strait of istanbul

soil co2 degassing along tectonic structures of mount etna sicily the pernicana fault abstract carbon dioxide emissions from the soil have been investigated along lines of equally spaced sampling points perpendicular to the pernicana fault on mt etna anomalous values of soil co2 have been found not only along the fault plane but also along directions parallel to it both to the n and to the s of the main fault the acquired data seem to reveal a shallow step like geometry of the pernicana fault system with parallel faults being generally not deeper than the interface between etna s volcanic cover and its sedimentary basement a few hundred meters the distribution of the anomalous co2 emissions has also revealed that the pernicana fault continues at least as far as the ionian sea in an area where only sedimentary rocks crop out this finding would suggest that the main structure is deeper than the base of the volcanic cover thus cutting at least the uppermost portion of etna s sedimentary basement isotopic analyses of c carried out in samples from locations of high co2 seem to indicate that the emitted co2 is a mixture of an organic shallow component and a minor deeper magmatic one both chemical and isotopic data on soil gases emitted in the easternmost part of the studied area distinguished another tectonic structure which seems to be much deeper than the pernicana fault and is roughly directed nne ssw this direction being coincident with an important structural trend of eastern sicily

fortnightly and monthly variability of the exchange through the strait of gibraltar the fortnightly and monthly variability of the exchange through the strait of gibraltar has been studied from two simultaneous five month long moored datasets at camarinal sill and the east section the study focuses on the msf and mm tidal components and their role for the subinertial exchange a significant monthly signal is observed in the upper layer transport also a significant fortnightly signal is observed in the lower layer transport which minimum maximum flow toward the atlantic takes place approximately on spring tides in consequence the net transport has both signals with maximum taking place during neap tides and a small monthly inequality fortnightly and monthly variability in the interface depth is also observed at camarinal sill the interface being deeper on neap and shallower on spring tides at the east section the interface depth signals are not significant the subinertial variability of the transports is separated in two contributions the first one is called quasistatic transport and arises from the subinertial fluctuations of currents the second contribution called tidally rectified transports arise from the non linear correlation of currents and interface depth at tidal frequencies the tidally rectified transports are important at camarinal but not at the east section an apparent contradiction between the fortnightly signals of the subinertial currents and subinertial transports is resolved when the fortnightly signal of the tidally rectified transports are considered the fortnightly signal of the quasistatic and tidally rectified transports mutually cancel in the upper layer but not in the lower layer where the rectified transports dominate a simple model for the spring tide mixing forcing accounts for the fortnightly variability of the lower layer quasistatic transports but underestimates it for the upper layer finally the observed lower layer transport is compatible with the hydraulic control condition at camarinal sill except for certain periods during intense spring tides 2006 elsevier ltd all rights reserved

a finite element model for tides and resonance along the north coast of british columbia a finite element barotropic tidal model is developed for the north coast of british columbia the model is run with eight tidal constituents and the results are compared with the flather 1987 finite difference model and with extensive tide gauge and current meter observations although the tidal potential earth tide and loading tide are included in the forcing their inclusion is shown to change the largest m2 amplitudes by only 2 5 and the largest k1 amplitudes by less than 1 root mean square differences between observed and calculated sea level amplitudes and phases are within 1 9 cm and 2 9 o for all but one constituent but the model currents do not in general compare as favourably the barotropic currents observed in hecate strait are reproduced well but elsewhere evidence is shown that model inaccuracies are due to baroclinic effects tidal residual currents calculated by the model suggest the existence of eddies off the tip of cape st james cape chacon and around goose island and learmonth banks the shallow water constituents in hecate strait are shown to have significant contributions from the constructive interference of signals propagating into dixon entrance and queen charlotte sound using the model the longest resonant period of the system is estimated to be 7 6 hours with an energy dissipation parameter q of 9 5

hydraulic adjustments of the bosphorus exchange flow 1 a three dimensional model elucidates connection between observed internal hydraulic characteristics of the bosphorus flow and channel configuration a typical two layer quasi steady exchange flow system is shown to be hydraulically adjusted within the strait by a series of morphological features three successive hydraulic controls occur within the southern 10 km zone first near the southern exit due to convex bending of the channel then at the southern sill and at the constriction finally the exchange flow system experiences another hydraulic control at the northern sill near the black sea entrance of the strait the upper and lower layer flows exiting from the strait at both ends with currents of 1 0 m s 1 layer depths of 10 m and g 0 1 ms 2 thus impose maximal exchange conditions

tides in the strait of gibraltar the strait of gibraltar is where the transition occurs between two distinct tidal regimes the north atlantic where tidal ranges are in excess of 2 m and the western mediterranean where tidal ranges are less than 1 m within the strait the tide is principally semidiurnal observations indicate that on average 96 of the bottom pressure and 74 of the current variability are contained in the semidiurnal band 2 cpd the structure of the local cotidal chart of the m2 tidal constituent is complicated but can be explained in terms of the along and across strait momentum balances along the strait the pressure gradient is mainly balanced by the acceleration of the flow although friction can be of appreciable magnitude corresponding to a decay time scale of 3 16 hours across the strait the momentum balance appears mostly geostrophic but better observations would be required to explain residual terms available observations indicate that the m2 tide has no net energy flux through the strait at the sill the tidal transport in the upper layer exceeds that in the lower layer by nearly a factor of 2 at the eastern end of the strait between algeciras and ceuta the tidal transport is larger in the lower layer this apparent shift in the location of maximum tidal transport is explained in terms of the kinematics of the interface between atlantic and mediterranean waters a mean transport of 0 21 sv due to subinertial and tidal flows carries atlantic water through the strait compensated by an approximately equal return in the lower layer

mixing at camarinal sill in the strait of gibraltar during the gibraltar experiment in 1985 1986 observations of shear stratification microstructure and acoustic backscatter revealed a complex mixing regime at camarinal sill in the strait of gibraltar the mixing is forced by strong semidiurnal tidal currents and weaker but more steady baroclinic flows flows are characterized as outflow or inflow nearly equivalent to westward or eastward rising water at gibraltar coincides with outflow at all depths we observed two modes of outflow at the sill in may 1986 the transition layer separating atlantic and mediterranean water was between 0 75 mpa and 1 mpa when we sampled east of the sill near neap tide the transition turned down just before reaching the sill crest where the flow became critical increasing shear soon destabilized the transition producing billows which grew to 30 75 m on the west flank of the sill the overturning generated intense turbulence with peak dissipation rates e exceeding 10 2 w kg 1 this turbulence rapidly thickened the transition from z 30 50 m east of the sill to z 130 150 m within 1 2 km west of the sill from the rate of thickening we estimate the rate of formation of new transitional water during neap tide as 0 8 1 2 105 m3 s 1 this outflow mode did not release eastward propagating internal bores when outflow turned to inflow but the inflow did appear to arrest the deep outflow in may the largest average dissipation rate over and just west of the sill had the same magnitude as estimates of the net energy lost by adjustment of velocity and mass across the sill during outflow other averages are smaller than the energy loss presumably because the limited sampling severely underestimates the average dissipation rate during outflow strong shears were observed to rise to 100 times those in the background internal wave field however probably owing to spatial offsets between the ship s acoustic doppler current profiler and our tethered free fall profiler the only statistically significant correlations were found between overturning scales measured directly and those estimated from e in the same profile we observed the other outflow mode in october 1985 when we profiled over the sill near spring tide and the transition was east of the sill centered near 1 5 mpa after encountering the sill the transition rose sharply and remained within 10 20 m of the surface across the sill plunging steeply downward just past the west edge of the sill this was accompanied by intense turbulence and at least one rebound of the transition we did not observe release of eastward propagating bores when inflow turned to outflow but observations by armi and farmer 1988 in april 1986 found bores released at spring tide in regimes similar to the one we observed in october 1985

diffuse emission of carbon dioxide methane and helium 3 from teide volcano tenerife canary islands diffuse emission of co2 ch4 and he was investigated in the summit crater of teide volcano tenerife canary islands the results indicate that teide volcano releases abundant co2 not only from its active crater but also from its flanks as diffuse soil emanations the spatial distribution of these emanations correlates quite closely with that of geothermal anomalies and manifestations our flux measurements indicate a total output of 380 ton day 1 of co2 and 1 6 on day 1 of ch4 by diffuse degassing from the he co2 ratios and the co2 flux we estimate a diffuse he flux of 0 052 mol year 1 isotopic analysis of carbon in soil gas samples from sites of high soil co2 flux indicates a magmatic origin for the co2 also reported by high he 4he ratios of 5 50 and 5 87 ra the origin of methane is more uncertain with low 13c values suggesting a biogenic contribution

an experimental study of the upwelling response of stratified reservoirs to surface shear stress an experimental study of the dynamic response of non rotating stratified reservoirs to the application of surface shear stresses is presented the experiments were made using two layered and linear stratifications a moving belt was used to supply a shear stress to the fluid detailed measurements of the density field show that upwelling occurs at all values of the wedderburn number w rather than only occurring when w 1 differences between the two layer theory and the present observations are attributed to the fact that the experimental stratifications were continuous rather than layered shearflow dispersion is observed to be an important mechanism for distributing the effects of localized upwelling over the entire length of the mixed layer a model of mixed layer deepening based on upwelling and shearflow dispersion is presented and is compared to the observations of this and other experimental studies

observed volume fluxes and mixing in the dardanelles strait 1 pairs of moorings equipped with current profilers were deployed at each end of the dardanelles strait and remained in place for over 13 months current observations were able to resolve well the exchange flow and volume fluxes volume fluxes showed distinct temporal variability in upper and lower layers especially evident on synoptic time scales the synoptic flux variability in the upper layer was coherent with the local atmospheric forcing and the bottom pressure anomaly gradient while the flux variations in the lower layer were related to the bottom pressure anomaly gradient estimated volume flux values were often two or more times larger than their respective annual means annual upper layer flux means were 25 66 10 3 and 36 68 10 3 sv whereas the lower layer averages were 14 02 10 3 and 31 67 10 3 sv for the marmara and aegean sections respectively the fluxes also showed that there was a net low salinity water outflow to the aegean sea and that they varied weakly on longer time scales monthly to seasonal high salinity water fluxes 39 psu were used to calculate strait averaged vertical eddy diffusivities which ranged between 10 4 and 10 2 m2 s 1 additionally microstructure observations were used to evaluate vertical eddy diffusivities these estimates indicated that mixing in the strait varied spatially and temporarily and it was dependent on complex strait geometry exchange flow status and partially on meteorological conditions large values of eddy diffusivities with a depth averaged mean of 1 3 10 2 m2 s 1 and vigorous mixing were found in the nara pass the narrowest section in the dardanelles strait

block tectonics of the island of hawaii from a focal mechanism analysis of basal slip the southern third of the island of hawaii is composed of at least three rigid blocks kilauea volcano s south flank mauna loa volcano s southeast flank and mauna loa volcano s west flank analysis of earthquake focal mechanisms suggests that kilauea s south flank the most mobile of these blocks is moving seaward perpendicular to its east rift zone along a southeasterly course at an azimuth of 155 5 mauna loa s southeastern flank is also moving in a southeasterly direction although at a slightly more easterly azimuth of 140 5 although data are sparse on the western flank of mauna loa due to low seismicity and inadequate seismic network station density the available data suggest that this region is translating seaward along a generally westerly azimuth relative differences in these translational azimuths may represent oblique opening across the boundaries between these regions the active rift zones of kilauea and mauna loa volcanoes

neogene planktonic foraminifera and events in japan abstract the warm water constituents of successive neogene planktonic foraminiferal assemblages in japan are identified and expressed as percentages of the total planktonic fauna by this means five major events have been recognized 1 a marine temperature optimum in the earliest middle miocene zone n8b 2 an abrupt cooling since early middel miocene time 3 a rise in temperature culminating in latest miocene to earliest pliocene time zones n17b and n18 4 an accelerated evolutionary event during the early pliocene zone n19b n21a 5 a short warm episode in the early pliocene zone n21a

aegean sea water masses during the early stages of the eastern mediterranean climatic transient 1988 90 abstract the aegean water masses and circulation structure are studied via two large scale surveys performed during the late winters of 1988 and 1990 by the r v yakov gakkel of the former soviet union the analysis of these data sheds light on the mechanisms of water mass formation in the aegean sea that triggered the outflow of cretan deep water cdw from the cretan sea into the abyssal basins of the eastern mediterranean sea the so called eastern mediterranean transient it is found that the central aegean basin is the site of the formation of aegean intermediate water which slides southward and depending on their density renews either the intermediate or the deep water of the cretan sea during the winter of 1988 the cretan sea waters were renewed mainly at intermediate levels while during the winter of 1990 it was mainly the volume of cdw that increased this aegean water mass redistribution and formation process in 1990 differed from that in 1988 in two major aspects i during the winter of

meteorologically forced subinertial flows through the strait of gibraltar the observed transport due to subinertial flows with periods ranging from days to a few months through the strait of gibraltar reaches values up to 106 m3 s 1 and is well correlated with atmospheric pressure fluctuations over the mediterranean sea this transport is barotropic and accounts for 84 of the variance observed at these frequencies a second mode accounts for 12 of the variance and is characterized by a node zero amplitude located at the mean depth of the interface between atlantic and mediterranean waters this baroclinic mode is modulated by the spring neap tidal cycle corresponding to an increased exchange of waters between atlantic and mediterranean at neap tides a simple model of the mediterranean which includes two basins and two straits indicates that the system has two resonant frequencies at periods of 1 2 and 5 6 days the 1 2 day resonance corresponds to the eastern and western basins oscillating through the strait of sicily while that at 5 6 days is the resonance of the mediterranean sea with the north atlantic ocean a good approximation to the observed flows is obtained when this model is forced with the most energetic mode of the atmospheric pressure over the eastern and the western mediterranean and a friction term is included to limit the flow through the strait of gibraltar restricting the flow through the strait of sicily does not improve the agreement between the model and the observations for the flows at gibraltar

on the relevance of tidal forcing in modelling the mediterranean thermohaline circulation abstract the four dominant constituents of the semi diurnal and diurnal tides have been implemented in a regional eddy resolving mediterranean version of the massachusetts institute of technology general circulation model to assess the role played by tides on the simulated mediterranean thermohaline circulation to this aim we have compared two 10 year hindcast simulations differing only for the inclusion omission of tidal forcing following the recent recommendations suggested by sannino et al 2014 both simulations use the same model having a substantial increment of the horizontal resolution in the region of the strait of gibraltar the results suggest that application of explicit tidal forcing in a mediterranean model has non negligible effects on the simulated circulation in addition to the expected intensification of local mixing processes the western basin exhibits an immediate response to the different characteristics of the inflowing aw observable in the modified deep water convection processes in the gulf of lion the inclusion of tidal forcing also induces changes in the intermediate circulation of the tyrrhenian sea bringing to a better representation of local structures and a reinforcement of the global thermohaline cell liw dispersal paths in the eastern basin are also affected by tides

volatiles and energy released by purace volcano total co2 output of purace volcano colombia was estimated on the basis of fluids discharged by fumaroles soil gases and dissolved carbon species in the aquifer the soil co2 emission was computed from a field survey of 512 points of co2 soil flux measurements at the main degassing areas of purace volcano the co2 flux from purace s plume was estimated using an indirect method that used the so2 plume flux and co2 so2 ratio of the main high temperature fumarole the total output of co2 was estimated at 1500 t day the main contribution of co2 comes from the plume summit degassing and from soil degassing that emit 673 and 812 t day respectively the contributions of summit and soil degassing areas are comparable indicating an intermediate degassing style partitioned between closed and open conduit systems the estimated water vapor discharge as derived from the chemical composition of the fumaroles the h2o co2 ratio and the so2 plume flux allowed calculation of the total thermal energy fumarolic soil degassing and aquifer released from the purace volcanic system this was 360 mw

soil gas geochemistry in relation to eruptive fissures on timanfaya volcano lanzarote island canary islands spain abstract we report herein the first results of an extensive soil gas survey performed on timanfaya volcano on may 2011 soil gas composition at timanfaya volcano indicates a main atmospheric source slightly enriched in co2 and he soil co2 concentration showed a very slight deep contribution of the timanfaya volcanic system with no clear relation to the main eruptive fissures of the studied area the existence of soil helium enrichments in timanfaya indicates a shallow degassing of crustal helium and other possible deeper sources probably form cooling magma bodies at depth the main soil helium enrichments were observed in good agreement with the main eruptive fissures of the 1730 36 eruption with the highest values located at those areas with a higher density of recent eruptive centers indicating an important structural control for the leakage of helium at timanfaya volcano atmospheric air slightly polluted by deep seated helium emissions co2 degassed from a cooling magma body and biogenic co2 might be the most plausible explanation for the existence of soil gas helium is a deep seated gas exhibiting important emission rates along the main eruptive fissure of the 1730 36 eruption of timanfaya volcano

summit outgassing as indicated by radon mercury and ph mapping kilauea volcano hawaii abstract surface geochemical mapping of rn hg and ph on the summit of kilauea volcano hawaii has shown some of the characteristics of outgassing rn concentrations measured in shallow ground gas are highest 10 to 155 units i e up to 0 016 nci l222rn over deep structures associated with the summit caldera low 1 to 5 units over the upper rift zones which are underlain by shallow intrusions and low to negative 1 to 3 units over most of the volcanically inactive peripheral areas high rn concentrations were measured over peripheral well developed structures such as the kaoiki and koae fault systems 45 and 12 units respectively the pattern of rn values broadly suggests the existence of a summit wide convection system interrupted locally by specific permeable structures the low ph 3 5 to 5 6 of soils over the caldera is suggested to be largely due to the sulfurous component of the ground gas the low concentrations of hg 5 to 80 ppb in these soils are postulated as being partly a function of subsurface complexing of hg with the abundant sulfur the shallow intrusions below the upper rift zones appear to have outgassed much of their sulfur content so soils in these areas are only slightly acid 5 6 to 6 2 allowing the accumulation of hg to concentrations of several thousands of ppb these conditions change during extrusive and intrusive events with the increases in shallow subsurface temperatures and volatiles in ground gas producing an increase in rn concentration and a decrease in soil hg due to volatilization after such events rn concentration decreases and soil hg increases significantly

the oceanic response of the turkish straits system to an extreme drop in atmospheric pressure moorings across all four entry exit sections of the dardanelles strait and the bosphorus strait simultaneously measured the response of the turkish straits system to the passage of a severe cyclonic storm that included an atmospheric pressure drop of more than 30 mbar in less than 48 h the bottom pressure response at the aegean sea side of the dardanelles strait was consistent with an inverted barometer response but the response at the other sections did not follow an inverted barometer leading to a large bottom pressure gradient through the turkish straits system upper layer flow toward the aegean sea was reversed by the storm and flow toward the black sea was greatly enhanced bottom pressure across the sea of marmara peaked 6 h after the passage of the storm s minimum pressure the response on the dardanelles side was a combination of sea elevation and pycnocline depth rise and the response on the bosphorus side was an even greater sea elevation rise and a drop in pycnocline depth the peak in bottom pressure in the sea of marmara was followed by another reverse in the flow through the dardanelles strait as flow was then directed away from the sea of marmara in both straits a simple conceptual model without wind is able to explain fluctuations in bottom pressure in the sea of marmara to a 0 89 0 96 level of correlation this stresses the importance of atmospheric pressure dynamics in driving the mass flux of the turkish strait system for extreme storms

dynamics of diffuse carbon dioxide emissions from cumbre vieja volcano la palma canary islands we report herein the results of 13 soil co2 efflux surveys at cumbre vieja volcano la palma island the most active basaltic volcano in the canary islands the co2 efflux measurements were undertaken using the accumulation chamber method between 2001 and 2013 to constrain the total co2 output from the studied area and to evaluate occasional co2 efflux surveys as a volcanic surveillance tool for cumbre vieja soil co2 efflux values ranged from non detectable up to 2442 g m 2 days 1 with the highest values observed in the south where the last volcanic eruption took place teneguia 1971 isotopic analyses of soil gas carbon dioxide suggest an organic origin as the main contribution to the co2 efflux with a very small magmatic gas component observed at the southern part of the volcano total biogenic and magmatic combined co2 emission rates showed a high temporal variability ranging between 320 and 1544 t days 1 and averaging 1147 t days 1 over the 220 km2 region two significant increases in the co2 emission observed in 2011 and 2013 were likely caused by an enhanced magmatic endogenous contribution revealed by significant changes in the 3he 4he ratio in a co2 rich cold spring the relatively stable emission rate presented in this work defines the background co2 emission range for cumbre vieja during a volcanic quiescence period

mediterranean climate and oceanography and the periodic development of anoxic events sapropels mediterranean sapropels are layers with elevated organic carbon concentrations that contrast with surrounding sediments which are organic poor sapropels occur quasi periodically in sedimentary sequences of the last 13 5 million years and exist both in the eastern and western mediterranean sub basins they have been the subject of extensive study based on records from both short conventional and long ocean drilling program sediment cores and from a wide variety of uplifted marine sediment sequences on the basin margins and islands previous syntheses in the 1990s and 2000s have discussed how the formation of sapropels is commonly ascribed to deep sea anoxia enhanced export productivity or a combination of these effects however a wealth of new evidence and insights has emerged during the past 1 2 decades based on traditional and novel proxy data as well as modelling which has revealed intriguing new aspects and nuances to the reconstructed conditions hence it is timely to present a new synthesis of current understanding of the processes behind the formation of sapropels which have over the past decade also become a matter of commercial interest in sub salt hydrocarbon exploration in this review we present a context of modern mediterranean climate and oceanography followed by an integrated assessment of the growing understanding of climatological and ocean circulation changes that were associated with sapropel deposition we find that sapropels predominantly formed during astronomically timed episodes when climatic and oceanographic conditions and ecological responses broadly preconditioned the basin for sapropel deposition there is strong correspondence with times of monsoon intensification fuelling runoff from north africa into the mediterranean sea while preconditioning due to sea level rise and regional precipitation and runoff may have contributed as well within these broad episodes of surface buoyancy gain and resultant decline in deep water ventilation specific deposition under dysoxic anoxic or even euxinic conditions occurred within a clearly dynamic system that was characterised by complex spatial and depth dependent patterns gradients with distinct temporal variability on at least decadal to centennial millennial timescales in the final section we evaluate the implications of different modes of deep water removal from silled basins to investigate why sapropels are more frequently and often more intensely developed in the eastern mediterranean than in the western mediterranean

tidal dynamics in the inter connected mediterranean marmara black and azov seas abstract in this study we investigated the tidal dynamics in a system of inter connected land locked basins formed by the mediterranean the marmara the black and the azov seas mmba system through the application of an unstructured grid hydrodynamic model to a unique domain representing the whole mmba system we simulated the tidal propagation and transformation inside each basin and in the straits connecting them the model performance was evaluated against amplitudes and phases of major tidal constituents from 77 tidal gauges the numerical results provided a description of the characteristics of the principal semi diurnal diurnal and long term tides over the entire system even if the narrow straits act as a barrier for the tidal sea surface oscillations our numerical results demonstrated that the along strait interface slope produces water fluxes between the adjacent basins of the same order of magnitude of the climatological transports estimated by several authors the long term tidal modulations of the water exchange between the mediterranean and the black seas resulted to be non negligible and may partially explain the monthly and fortnightly flow variability observed in the dardanelles and bosphorus straits

compositions and flux of soil gas in liu huang ku hydrothermal area northern taiwan abstract soil co 2 flux has been considered a useful proxy to remotely monitor volcanic activity in a hydrothermal area within a safe distance the liu huang ku lhk area which is close to the taipei basin and many existing active fumaroles and hot springs was chosen for the first systematic soil gas study in a hydrothermal area of taiwan in 2004 and 2006 the soil co 2 flux was measured by the closed chamber method with a non dispersive infrared detector soil co 2 emission rate was estimated 19 8 0 2 t day 1 and 582 t km 2 day 1 in 2004 and 22 4 0 2 t day 1 and 659 t km 2 day 1 in 2006 respectively these values are close to those reported for other active high co 2 flux hydrothermal areas of the world it implies that magmatic gases are actively degassing from subsurface in northern taiwan helium and carbon isotopic data reveal that soil gas in lhk is mainly derived from the mantle and is mixed with a small amount of crustal and air components the abundance of soil co 2 shows a positive correlation with the 3 he 4 he ratios and total sulfur contents which are considered as magmatic sensitive indicators for the fumarolic samples therefore soil co 2 could be used as a good proxy for future monitoring of magmatic activity in this area

fine and microstructure observations in the urup strait kuril islands during august 2006 1 for the first time we performed continuous observations of turbulent mixing upon the sill of the urup strait kuril islands for a period of 1 day during august of 2006 time series of velocity profiles water properties and isopycnal depths show variability with a period of about 1 day however the water mass variability is not explained by simple water exchange between the sea of okhotsk and the north pacific empirical orthogonal function eof analysis of isopycnal coordinates extracted variability presumed to represent tidal flows as major eofs in profiles of the residual flow after subtracting the mean flow and major eofs we detected phase propagations consistent with internal gravity waves with an approximate period of 9 1 11 4 h the turbulent energy dissipation rate and vertical diffusivity k ranged from 1 10 9 to 3 10 8 w kg 1 and from 3 10 5 to 2 10 3 m2s 1 respectively occurrences of high dissipation rates generally corresponded to either strong shear or weak stratification a significant contribution of shear s to the dissipation rate was indicated with a relationship of s1 4 s1 8 probably related to propagating internal waves a strong mixing event was observed within the water column with extremely weak stratification and a richardson number below the critical value of 0 25 when the flow direction changed from up sill to down sill

numerical modeling of the semidiurnal tidal exchange through the strait of gibraltar 1 a three dimensional sigma coordinate free surface model is used to investigate the semidiurnal tidal exchange through the strait of gibraltar the model makes use of a coastal following curvilinear orthogonal grid that includes the gulf of cadiz and the alboran sea with very high resolution in the strait 500 m a lock exchange initial condition is used the western part of the model domain is filled with atlantic water whereas the eastern part is filled with mediterranean water the model is forced at the open boundaries through the specification of the semidiurnal m2 and s2 tidal surface elevation the model is run over a spring neap cycle fortnightly period and the results are compared with available observed data simulated cotidal maps of the m2 and s2 tidal elevation components are in quantitative and qualitative good agreement with observed data as well as with the simulated major and minor axis of tidal ellipse the model reproduces the generation and the subsequent propagation of internal bores both eastward and westward showing that they are always generated during the fortnightly period however the principal aim of this work is to quantify the effects of tidal forcing on mean quantities entrainment and transport of atlantic and mediterranean water along the strait model results reveal that the contribution of the semidiurnal tidal component m2 to the transport is relevant over camarinal sill whereas it is negligible at the eastern end of the strait model results indicate also that the effect of the semidiurnal tide is to increment the mean transport by about 30 both for the inflow and the outflow

observations on the characteristics of the exchange flow in the dardanelles strait 1 a mooring section at each end of the dardanelles strait was deployed by the naval research laboratory on 28 29 august 2008 and maintained until 11 october 2009 each section was equipped with two bottom mounted barny moorings and a vertical string that together delivered concurrent bottom pressure temperature salinity and almost full water column current velocity observations these observations at the mooring sections indicated that on longer timescales monthly or longer the exchange through the dardanelles strait showed little variability and had a two layer structure with brackish waters moving approximately southward in the upper layer and more saline aegean waters flowing roughly northward underneath on shorter time scales synoptic there were pronounced fluctuations in both layers in the northern section some manifested as almost simultaneous reversals of the flow direction in both layers with lighter upper layer waters backing into the sea of marmara and dense lower layer waters moving toward the aegean sea in the southern section some of the exchange variability consisted of a three layer flow structure with upper brackish and bottom salty layers moving toward the aegean sea and a middle salty layer flowing toward the sea of marmara this three layer exchange persisted from a day to a week synoptic flow variability in the upper layer was partly related to both the along strait wind stress and the bottom pressure anomaly gradient while lower layer current fluctuations were coherent with the bottom pressure anomaly gradient

helium emission at cumbre vieja volcano la palma canary islands abstract we report herein the results of three soil helium surveys undertaken at cumbre vieja volcano la palma island canary islands helium content analyses at the surface environment of the volcano were carried out in the summers of 2002 2003 and 2004 to estimate the diffusion contribution of helium emission soil porosity was estimated indirectly from the granulometry data measured on a previous soil survey carried out in 1997 helium enrichments in the soil layer with respect to the air concentration measured on cumbre vieja indicate a strong structural control in the degassing processes of the volcano and the excess helium seems to be emitted mainly along both n s and n w rifts of the volcano 4 he flux values calculated following a pure diffusive model ranged between non detectable values and 1 0 mg m 2 d 1 in 2002 2003 and 2004 surveys total 4 he emission rate at cumbre vieja was estimated in the range of 18 38 kg d 1 isotopic composition of helium measured in soil gases along the n s volcanic rift of cumbre vieja showed small contributions of morb type helium increasing towards the southern part of the volcano a 3 he 4 he ratio of 9 95 0 12 r a was measured at a cold spring geothermal sample showing a 7 2 contribution of plume type helium 3 he emission results in the range of 0 6 0 7 mol yr support the hypothesis of contemporary degassing at cumbre vieja coming from magmas stored at different depths under la palma island

new evidence of co2 soil degassing anomalies on piton de la fournaise volcano and the link with volcano tectonic structures insu cnrs and la reunion prefecture projet pour la quantification de l alea volcanique a la reunion

three year decline of magmatic co2 emissions from soils of a mammoth mountain tree kill horseshoe lake ca 1995 1997 we used the closed chamber method to measure soil co2 efflux over a three year period at the horseshoe lake tree kill hltk the largest tree kill on mammoth mountain in central eastern california efflux contour maps show a significant decline in the areas and rates of co2 emission from 1995 to 1997 the emission rate fell from 350 t d 1 metric tons per day in 1995 to 130 t d 1 in 1997 the trend suggests a return to background soil co2 efflux levels by early to mid 1999 and may reflect exhaustion of co2 in a deep reservoir of accumulated gas and or mechanical closure or sealing of fault conduits transmitting gas to the surface however emissions rose to 220 t d 1 on 23 september 1997 at the onset of a degassing event that lasted until 5 december 1997 recent reservoir recharge and or extension enhanced gas flow may have caused the degassing event

a model of diffuse degassing at three subduction related volcanoes and 13c in soil gas were measured at three active subduction related stratovolcanoes arenal and poas costa rica galeras colombia in general rn co2 and 13c values are higher on the lower flanks of the volcanoes except near fumaroles in the active craters the upper flanks of these volcanoes have low rn concentrations and light 13c values these observations suggest that diffuse degassing of magmatic gas on the upper flanks of these volcanoes is negligible and that more magmatic degassing occurs on the lower flanks where major faults and greater fracturing in the older lavas can channel magmatic gases to the surface these results are in contrast to findings for mount etna where a broad halo of magmatic co2 has been postulated to exist over much of the edifice differences in radon levels among the three volcanoes studied here may result from differences in age the degree of fracturing and faulting regional structures or the level of hydrothermal activity volcanoes such as those studied here act as plugs in the continental crust focusing magmatic degassing towards crater fumaroles faults and the fractured lower flanks

modelling of seasonal exchange flows through the dardanelles strait abstract the dardanelles strait is a remarkable example of a long narrow shallow and strongly stratified strait with bidirectional exchange that is governed by both baroclinic and barotropic forcing with a wide spectrum of variability a three dimensional free surface primitive equation model is applied to study seasonal hydrodynamics variability in this strait the calculated vertical structure of temperature salinity and velocity fields agrees well with available survey data seasonal monthly values of the volume exchange at the aegean and marmara exits are estimated it is found that the seasonal exchange dynamics is governed by the turbulent friction and entrainment at the nara passage area the mean annual water transport in the upper layer is increased by 80 after the nara passage about 25 of water entering in the dardanelles bottom layer reaches the marmara sea in winter and 50 reaches it in summer the estimate of the dardanelles hydrodynamics according to hydraulic and viscous advective diffusive regime classification shows significant deviation from the two layer hydraulic asymptotic however according to three layer hydraulic theory the flow is found to be critical in the nara passage area

observed volume fluxes in the bosphorus strait 1 pairs of moorings containing acoustic doppler current profilers adcps were deployed at each end of the bosphorus strait as a part of the united states naval research laboratory s exchange processes in ocean straits epos project the moorings were deployed in september 2008 and remained in place for about half a year for the first time current velocity profiles were collected concurrently at both ends of the strait they well resolved the two layer exchange flow and were used to estimate volume flux time series these estimates clearly indicated that there was a mean net volume flux of over 100 km3 yr directed from the black sea to the sea of marmara over this period the upper layer fluxes showed distinct temporal variability whereas the lower layer fluxes varied less volume fluxes were maximized at over 1500 km3 yr in the upper layer and over 1100 km3 yr in the lower layer with an upper layer mean of about 400 km3 yr and a lower layer mean of about 300 km3 yr fluxes in both layers were highly coherent with the bottom pressure difference between the southern and northern ends of bosphorus strait and they can be fairly well predicted from this pressure difference the fluxes in the upper layer were also influenced by atmospheric forcing but generally less so than by the bottom pressure difference

climatology of cyclogenesis mechanisms in the mediterranean abstract a general climatology of the main mechanisms involved in mediterranean cyclogenesis is presented a diagnostic study of both composite means and case studies is performed to analyze processes occurring in different seasons and in different cyclogenetic regions within the same season it is shown that cyclones that developed over the three most active areas in winter the gulf of genoa the aegean sea and the black sea are essentially subsynoptic lows triggered by the major north atlantic synoptic systems being affected by local orography and or low level baroclinicity over the northern mediterranean coast it is also suggested that cyclones in two or all three of these regions often occur consecutively linked to the same synoptic system in spring and summer thermally induced lows become progressively more important despite the existence of other factors such as the atlas mountains contributing to lee cyclogenesis in northern africa or the extension of the asian monsoon into the eastern

early neogene biochemostratigraphy of pohang basin a paleoceanographic response to the early opening of the sea of japan east sea abstract the location of the pohang basin near the korea strait in the southwest of the sea of japan east sea makes this area appropriate for providing a record of paleoenvironmental biotic changes associated with the early neogene 16 5 ma opening of this gateway to the pacific ocean stable isotopic and planktonic foraminiferal records are presented that assist with the understanding of paleoenvironmental changes in the sea of japan resulting from the opening of the korea strait the oldest sediments of early neogene age of the pohang basin overlie cretaceous basement and are early miocene 16 5 ma shallow estuarine facies containing a benthic foraminiferal assemblage dominated by ammonia beccarii l the oldest early neogene planktonic foraminiferal assemblages in the basin are 16 5 ma in age latest early miocene foraminiferal zone n8 the migration of these planktonic assemblages to the sea of japan at that time appears to have resulted from the initial opening of the korea strait the overlying early neogene marine sequence of the pohang basin extends from 16 5 ma zone n8 through 14 ma zone n10 change in the oxygen isotopic record of the pohang basin sequence suggests strong local paleoenvironmental control related to the early opening of the korea strait early middle miocene isotopic temperatures of planktonic foraminifera are relatively cool at 15 ma at a time when global temperatures were high in the middle low latitude regions it was not until 14 8 ma that isotopic temperatures of planktonic foraminifera increased markedly this distinct warming is inferred to reflect the major intrusion of the kuroshio current into the sea of japan probably as a result of further critical opening and deepening of the korea strait at this time planktonic foraminifera increased in abundance reflecting expanding oceanic influence a cooling that followed at 14 5 ma when the strait was well open is unlikely to reflect local tectonic control on the paleoceanography but global cooling during the early middle miocene associated with the expansion of the east antarctic ice sheet

origin of hydrogen and carbon dioxide in fault gases and its relation to fault activity gases occluded in fracture zones of active faults are characterized by a high concentration of h 2 and or co 2 a predominant gas species h 2 or co 2 is related to the lithofacies which the fault cuts carbon dioxide concentration in sediments fluctuates with temperature this evidence and sigma 13 c of co 2 about 20 suggests that co 2 originates from organic materials carbon dioxide with sigma 13 c of 5 to 17 in brecciated gneiss containing marble may have been produced by interaction between organically derived co 2 and the marble or alternatively may have been magmatically derived hydrogen usually occurs in sheared silicate rocks and its concentration fluctuates a great deal the concentration of h 2 from active faults associated with historical earthquakes usually amounts to as high as several percent in maximum whereas the concentration of h 2 from quaternary faults not associated with historical earthquakes is at most 1

the role of the north aegean in triggering the recent eastern mediterranean climatic changes drastic changes have occurred in the vertical structure of the deep waters of the eastern mediterranean in the early 1990s as dense water of aegean origin has displaced lighter waters of adriatic origin at the bottom of the deep basins this work suggests that the initiation of this process took place in the north aegean in the winter of 1986 1987 and was intensified by another formation event in 1992 1993 the available observations from the north aegean support such a scenario furthermore we propose that the outflow of black sea waters into the aegean through the dardanelles could act as an insulator of the deeper layer from the atmosphere thus absorbing a large part of the heat and salt exchange despite this fact the existence of the densest bottom water of the mediterranean in the north aegean and the continuation of density increase for a large period of time suggests that it is a region of formation thus that the insulation layer may at times be penetrated we suggest that reduced black sea outflow into the north aegean could facilitate dense water formation during the passage of cold atmospheric fronts in the winter

marine climatic responses to neogene tectonics of the pacific ocean seaways abstract based upon surface marine climatic evolution on both sides of the pacific ocean recently revealed by biochronostratigraphy in japan and south america the tectonics of pacific ocean seaways and associated responses of adjacent seas and ocean currents are discussed the rapid opening of the sea of japan at about 15 ma in early middle miocene time mainly by the rotation of the southwest japan arc can be correlated with the abrupt appearance of a cold water fauna on the pacific coast of northeast japan beginning ca 15 ma and an extensive hiatus along the pacific coast of southwestern japan spanning 15 ma to 12 ma the abrupt and extensive development of biosiliceous lithofacies along the pacific coast of peru beginning about 14 ma might also represent a response to the tectonic anticlockwise rotation of the peruvian block of the andean mountain range estimated to have occurred sometime during the miocene as the tectonic closing of the indonesian seaway would have strongly intensified the warm kuroshio current in the northwest pacific it is most probable that this seaway was effectively closed just prior to 15 5 ma in the earliest middle miocene when tropical marine faunas were developed in most of the japanese islands the closing of the central american seaway is estimated to have been completed at 3 5 3 ma in pliocene time the closure of this seaway would likely have intensified the warm kuroshio current affecting the marine fauna along the pacific coast of southwestern japan it is also possible that a decrease in surface temperatures at about 3 ma along the pacific coast of ecuador was due to this pliocene tectonic event

continuous monitoring of hydrogen and carbon dioxide at mt etna article i nfo this study assessed the use of an h2 fuel cell as an h2 selective sensor for volcano monitoring the resolution repeatability and cross sensitivity of the sensor were investigated and evaluated under known laboratory conditions a tailor made device was developed and used for continuously monitoring h2 and co2 at mt etna throughout 2009 and 2010 the temporal variations of both parameters were strongly correlated with the evolution of the volcanic activity during the monitoring period in particular the co2 flux exhibited long term variations while h2 exhibited pulses immediately before the explosive activity that occurred at mt etna during 2010

the circulation and hydrography of the marmara sea abstract a comprehensive set of data collected during 1986 1992 reveal seasonal and interannual variability in the circulation and hydrography of the marmara sea waters which have contrasting properties and originate from the adjacent basins supply the two layer stratified flows in the sea of marmara turbulent entrainment into the upper layer in the exit region of the bosphorus jet and wind stirring in winter both contribute equally to the basin vertical mixing the upper layer circulation of the marmara sea is determined from adcp measurements and from dynamical calculations based on hydrographic data the mean upper layer circulation is anti cyclonic mainly driven by the southward flowing bosphorus jet in the enclosed domain the bosphorus inflow is well defined except during the periods of low discharge in autumn and winter when the jet becomes weaker and tends to become attached to the west coast near the exit mediterranean water entering from the dardanelles supply the suhalocline layer the negatively buoyant plume of well oxygenated water is the only means of renewal of the deep waters partially compensating for the oxygen consumed by the degradation of organic matter sinking from the upper layer into the lower layer yet the subhalocline waters remain permanently deficient in oxygen as a result of the internal balances of diffusion advection and consumption the depth to which the plume penetrates is a function of the seasonal characteristics of the inflow density modified in the strait and the weak interior stratification

fumarole plume and diffuse co 2 emission from sierra negra caldera galapagos archipelago measurements of visible and diffuse gas emission were conducted in 2006 at the summit of sierra negra volcano galapagos with the aim to better characterize degassing after the 2005 eruption a total so2 emission of 11 2 t day 1 was derived from miniature differential optical absorption spectrometer mini doas ground based measurements of the plume emanating from the mini azufral fumarolic area the most important site of visible degassing at sierra negra volcano using a portable multigas system the h2s so2 co2 so2 and h2o so2 molar ratios in the mina azufral plume emissions were found to be 0 41 52 2 and 867 9 respectively the corresponding h2o co2 and h2s emission rates were 562 394 and 3 t day 1 respectively the total output of diffuse co2 emissions from the summit of sierra negra volcano was 990 85 t day 1 with 605 t day 1 being released by a deep source the diffuse to plume co2 emission ratio was about 1 5 mina azufral fumaroles released gasses containing 73 6 mol of h2o the main noncondensable components amounted to 97 4 mol co2 1 5 mol so2 0 6 mol h2s and 0 35 mol n2 the higher h2s so2 ratio values found in 2006 as compared to those reported before the 2005 eruption reveal a significant hydrothermal contribution to the fumarolic emissions 3he 4he ratios measured at mina azufral fumarolic discharges showed values of 17 88 0 25 ra indicating a mid ocean ridge basalts morb and a galapagos plume contribution of 53 and 47 respectively

three dimensional velocity structure of the kilauea caldera hawaii high resolution velocity models 0 5 km resolution of the kilauea caldera region are obtained by the tomographic inversion of both p and s wave arrival times data are from the permanent hawaiian volcano observatory hvo seismic network a broadband seismic network and a temporary array of stations centered on the southern boundary of the caldera a low velocity p wave anomaly is imaged centered on the southeastern edge of the caldera with a velocity contrast of about 10 and a volume of 27 km the vp vs model mimics the spatial extent of the p wave anomaly but is partitioned into two discrete anomalous volumes centered on the southern boundary of the caldera and on the upper east rift of the volcano the corresponding poisson s ratio in these zones is high 0 25 0 32 which is consistent with a densely cracked hot volume which may contain partial melt the large scale features of the models are consistent with results obtained from an earlier larger scale 2 km resolution tomographic image of kilauea volcano based on hvo network data

tide at the eastern section of the strait of gibraltar from october 1995 to april 1996 three mooring lines were deployed at the eastern entrance of the strait of gibraltar the spatial coverage of the mooring array allows for a good description of the tides they exhibit a dominant semidiurnal nature and a noticeable baroclinic structure that matches the one of the mean exchange tidal currents in the upper layer are irregular and usually too weak to reverse the mean upper layer flow that keeps on flowing east lower layer flow reverses with semidiurnal periodicity because of the smallness of the mean flow and the appreciable amplitude of the regular semidiurnal oscillation of tidal currents in this layer tidal transports can be satisfactorily compared with previous estimates of bryden et al 1994 if we allow for strong internal divergences associated with the internal tide no significant eddy flux of water transport tidal rectification is observed at the eastern section contrary to the almost 50 of the total layer transport found by bryden et al 1994 in camarinal sill section time dependent hydraulic theory provides a good scenario for interpreting these two independent sets of observations despite the fact that the composite froude number does not reach the critical values predicted in the hydraulic models most of the time

flow water mass changes and hydraulics in the bosphorus 1 using average sections along the bosphorus taken in september 1994 with a loosely tethered profiler and an acoustic doppler current profiler gregg et al 1999 found the exchange flow between the sea of marmara and the black sea to be quasi steady but far from satisfying the hydraulic control conditions for two layered flows here we examine synoptic sections and use images from an acoustic backscatter system to provide the first detailed look at the flow and water mass changes in the bosphorus and to assess how well the flow satisfies the hydraulic assumptions thirty kilometers long 28 100 m deep and 0 75 3 km wide the bosphorus has bathymetry for more complex than that used in analytic or numerical models of exchange flows the particulars affect dynamics in important ways for instance owing to changes in channel shape the narrowest section known as the contraction is not also the minimum in cross sectional area rather it is a transition between the wider northern half and the narrower southern half of the strait and some places south of the contraction have slightly smaller areas sharp bends occur throughout the strait and often produce flow separations as well as directing upper and lower flows to opposite sides of the channel never 28 of the water column the interface thickens to 75 in the southern half of the strait as a result of intense mixing downstream of the contraction as a consequence of the strong mixing and numerous flow separations we conclude that the exchange flow may be at least partly controlled by friction instead of being a simple hydraulic flow

internal hydraulic flows on the continental shelf high drag states over a small bank observations of currents hydrography and turbulence provide unambiguous evidence for hydraulic control of flow over an isolated three dimensional topographic feature on oregon s continental shelf the flow becomes critical at the crest of the bank forming a strong supercritical downslope flow in the lower layer farther downstream internal hydraulic jumps form as the bottom flow becomes subcritical as a consequence turbulence is greatly enhanced in the bottom boundary layer in the sheared interface above the swiftly flowing bottom current and in the internal hydraulic jump the dissipation rate of turbulent energy is consistent with the mean energy removal rate for a hydraulic jump in an idealized two layer flow this enhanced turbulence constitutes a high drag state of the flow in which the form drag introduced by the topography exerts significant influence on the flow around it and mixing is increased 102 103 times the background values

exchange through the strait of gibraltar to measure the exchange between the atlantic and mediterranean through the strait of gibraltar an array of current meter moorings was deployed for a year in the strait during 1985 1986 a novel aspect of these measurements is the inclusion of conductivity as well as temperature and pressure sensors on each current meter so that the salinity of the flows could be monitored continuously these salinity measurements determine the water mass characteristics of the flows crossing the sill they allow definition of the 37 psu isohaline as the interface between inflowing fresher atlantic water and outflowing saltier mediterranean water and they enable time series to be developed for the depth of this interface for the upper layer inflow and for the lower layer outflow from these measurements the time averaged outflow of mediterranean water is estimated to be 0 68sv 1sv 1 106m3s 1 and the outflow salinity transport defined to be the outflow times the salinity excess above a basic atlantic water salinity of 36 1 psu is estimated to be 1 50 103m3s 1 1sv 1psu 1 103m3s 1 equivalent to a net evaporation over the mediterranean basin of 52cm y 1 extrapolated measurements of the inflow from current meters generally deployed below 100m depth yield an estimate for the time averaged inflow of 0 93sv which is believed to be unrealistically high in view of the better measured outflow and net evaporation thus a more realistic estimate of the inflow is 0 72sv equal to the sum of the outflow and net evaporation as required by the mass budget for the mediterranean sea such estimates of the exchange are smaller by almost a factor of 2 than previous values for the exchange by lacombe and richez 1982 the exchange across the gibraltar sill is found to be due in nearly equal parts to the mean currents and to the tidal fluctuations the mean currents are smaller than had been expected reaching a peak value of only about 60 cm s 1 in the deep outflow over the sill the tidal exchange is due to a strong correlation over the tidal period between the depth of the interface and the strength of the inflowing currents for the m2 tide at the sill the amplitude of the interface depth is 51 m and the amplitude of the tidal currents is 1 2m s 1 furthermore the inflow and interface depth have similar phases as a consequence the upper layer is deep on the inflowing tide so that a large slug of atlantic water crosses the sill into the mediterranean on the outflowing tide the interface is shallow so that a large slug of mediterranean water crosses the sill into the atlantic similar processes occur for the s2 o1 and k1 tides though the amplitude are smaller in this manner tidal oscillations lead to a time averaged exchange of water masses across the gibraltar sill the inflow and outflow defined to be the instantaneous transports above and below the 37psu isohaline interface exhibit m2 tidal amplitudes of 2 3 sv and 1 3sv respectively thus the tides are large enough to reverse the mean upper layer inflow and lower layer outflow daily averaged inflow and outflow transports exhibit low frequency fluctuations with standard deviations of 0 37sv and 0 22sv respectively such low frequency fluctuations have been shown previously to be associated with barotropic flows through the strait of gibraltar compensating for sea level variations over the mediterranean due to atmospheric pressure fluctuations candela winant and bryden 1989 finally from these measurements there appear to be little fortnightly or annual period fluctuations in the exchange through the strait of gibraltar

the role of straits and channels in understanding the characteristics of mediterranean circulation abstract straits in the mediterranean sea form an important network from which one can determine the characteristics of the water exchange between all the constituent sub basins this includes the definition of water masses and water transport and their time variability from 1994 all the major straits in the mediterranean sea gibraltar sicily otranto balearic sea straits cretan arc straits and corsica were subject to long term observations as part of various research projects besides adding new elements to the knowledge of internal strait conditions the data sets collected allow us to propose a fairly consistent representation of the mediterranean circulation and budgets in key points within the basin the amplitude of the annual water transport measured at these straits was about 1 sv and it appears to be modulated by a significant low frequency and seasonal variability for the first time a seasonal component was identified at gibraltar thus raising new questions on the actual state of the mediterranean also the very likely existence of a significant interannual component was documented in the corsica channel this component was found to be related to the interannual variability of the north atlantic oscillation the observations in the cretan arc straits have provided a more comprehensive representation of the recent changes in the eastern mediterranean thermohaline cell it is noteworthy that the effects of these changes have been observed both in the otranto and sicily straits and are now affecting the adjacent sea regions the presence of a stream of modified atlantic water in the balearic sea channels indicates that part of the atlantic inflow may be diverted directly into the northern region of the western mediterranean finally data gathered in the sardinia channel indicate that the central mediterranean region plays a critical role in controlling exchanges between the eastern and the western mediterranean while it is emphasized that the tyrrhenian sea area plays a role in strongly modifying some of the water masses that contribute to the large scale basin circulation their mixing creates new water types which modify the currently known pattern and composition of the mediterranean circulation

anomalous soil co2 degassing in relation to faults and eruptive fissures on mount etna sicily italy the relationships between soil gas emissions and both tectonic and volcano tectonic structures on mt etna have been studied the investigation consisted of soil co2 flux measurements along traverses orthogonal to the main faults and eruptive fissures of the volcano anomalous levels of soil degassing were found mainly in coincidence with faults whereas only 49 of the eruptive fissures were found to produce elevated co2 soil fluxes this result suggests that only zones of strain are able to channel deep gases to the surface according to this hypothesis several previously unknown structures are suggested based on our geochemical data new structural maps of different areas of etna are proposed the soil co2 fluxes observed in this study are higher than those measured in a 1987 study and they are consistent with the higher level of volcanic unrest during the current study

the importance of aspiration and channel curvature in producing strong vertical mixing over a sill on the basis of observations of the time dependent tidally forced flow over a long sill we find that aspiration and channel curvature set the flow structure and condition the flow to allow intense vertical mixing aspiration reduces the potential energy of the water column by thinning it while maintaining its density contrast channel curvature induces a cross channel circulation that can rapidly overturn a stratified flow eighteen along channel sections of density velocity and dissipation rate of turbulent kinetic energy were collected in and around the tacoma narrows of puget sound a site suspected of driving a strong vertical circulation in adjoining main basin rapid inflow to the narrows on flood from one channel of a triple junction reduces dynamic pressure allowing dense water from below sill depth to be uplifted or aspirated into the narrows we estimate water from below 150 m 3 times the sill depth is drawn into the narrows on a 3 m flood tide once in the narrows the flow remains stratified until it passes a 50 bend where a strong secondary circulation overturns the 50 m deep water column and generates intense turbulent mixing cross channel velocities of up to 0 4 m s 1 are observed and maximum values of exceed 10 3 w kg 1 upon leaving the sill stratification is reestablished and turbulence decays a similar set of sequences occurs on ebb except that the outflow bypasses the flood inflow channel and instead discharges into colvos passage the third branch of the triple junction colvos passage ultimately discharges the ebb effluent back into main basin enhancing the impact of mixing at the narrows by discharging the mixed product far from the source scaling of the cross channel momentum equation suggests that below a threshold value of along channel velocity stratification should suppress secondary circulation for a given vertical shear radius of curvature and channel width above the threshold velocity the magnitude of the cross channel velocity is roughly consistent with predictions for unstratified flow we estimate the maximum effective eddy diffusivity that aspiration and mixing in the narrows can produce in main basin to be 10 3 m2 s 1

mixing in a coastal environment 1 a view from dye dispersion 1 dye release experiments were performed together with microstructure profiling to compare the two methods of estimating diapycnal diffusivity during summer and fall stratification on the continental shelf south of new england the experiments were done in 1996 and 1997 as part of the coastal mixing and optics experiment during the 100 hours or so of the experiments the area of the dye patches grew from less than 1 km2 to more than 50 km2 sundermeyer and ledwell 2001 diapycnal diffusivities inferred from dye dispersion range from 10 6 to 10 5 m2 s at buoyancy frequencies from 9 to 28 cycles hour diffusivities estimated from the dye and those estimated from dissipation rates in the companion paper by oakey and greenan 2004 agree closely in most cases estimates of diffusivities from towed conductivity microstructure measurements made during the cruises by duda and rehmann 2002 and rehmann and duda 2000 are fairly consistent with the dye diffusivities the dye diffusivities would be predicted well by an empirical formula involving shear and stratification statistics developed by mackinnon and gregg 2003 from profiling microstructure measurements obtained at the same site in august 1996 all of the measurements support the general conclusion that the diffusivity averaged over several days is seldom greater than 10 5 m2 s in the stratified waters at the site and usually not much greater than 10 6 m2 s severe storms such as a hurricane that passed over the cmo site in 1996 can dramatically increase the mixing at the site however

modeling the mediterranean sea interannual variability during 1961 2000 focus on the eastern mediterranean transient 1 this work is dedicated to the study of the climate variability of the mediterranean sea in particular the study of the eastern mediterranean transient emt which occurred in the early 1990s simulations of the 1961 2000 period have been carried out with an eddy permitting ocean general circulation model of the mediterranean sea driven by realistic interannual high resolution air sea fluxes using different databases for the river runoff black sea inflow and atlantic thermohaline characteristics at climatological or interannual scales we assess the effects of the non atmospheric hydrological forcings on the simulation of the interannual variations of the mediterranean circulation the evolution of the basin scale heat content is in very good agreement with the observations especially in the surface and intermediate layers while the agreement is lower for the evolution of the salt content convection events in the aegean sea are noticed in the simulations between 1972 and 1976 in the late 1980s and around the emt period the formation rates of cretan deep water cdw are different during these periods allowing or preventing the spreading of cdw into the eastern mediterranean the sequence of the emt events is well reproduced the high winter oceanic surface cooling and net evaporation over the aegean sea in the early 1990s the high amount of dense cdw formed during these winters and then the overflow and the spreading of this cdw in the eastern mediterranean among the preconditioning processes suggested in the literature we find that changes in the levantine surface circulation possibly induced by the presence in the cretan passage of anticyclonic eddies and a lasting period with reduced net precipitation over the eastern mediterranean lead to an increase of the salt content of the aegean sea changes in the black sea freshwater inflow or in the characteristic of the atlantic water entering at the gibraltar strait also modify the thermohaline state of the aegean sea before the emt but as none of these preconditioning factors has a lasting impact on lowering the vertical stratification of the aegean sea we conclude that concerning the emt the major triggering elements are the atmospheric fluxes and winds occurring in winters 1991 1992 and 1992 1993

a two dimensional tidal model for the mediterranean sea the tidal propagation in the mediterranean sea is described through a high resolution two dimensional hydrodynamic model forced by the equilibrium tide and the incoming tide at the strait of gibraltar the four most significant constituents m2 s2 k1 and o1 are included in the model good agreement with a set of 63 coastal gauges is achieved the significance of the equilibrium tide and the forcing at the open boundary is investigated the incoming wave from the strait of gibraltar is important in tuning the tides in the whole of the mediterranean for the north aegean sea the solution without the forcing at gibraltar results in a doubling of the amplitudes of the semidiurnal tides the estimated energy dissipation due to bottom friction is 8 8 108 w the major area of dissipation is the gulf of gabes energy fluxes through the major straits are calculated

imaging the crustal magma sources beneath mauna loa and kilauea volcanoes hawaii three dimensional seismic p wave traveltime tomography is used to image the magma sources beneath mauna loa and kilauea volcanoes hawaii high velocity bodies 6 4 km s in the upper 9 km of the crust beneath the summits and rift zones of the volcanoes correlate with zones of high magnetic intensities and are interpreted as solidified gabbro ultramafic cumulates from which the surface volcanism is derived the proximity of these high velocity features to the rift zones is consistent with a ridge spreading model of the volcanic flank southeast of the hilina fault zone along the south flank of kilauea low velocity material

investigating the deepest part of a volcano plumbing system evidence for an active magma path below the western flank of piton de la fournaise la reunion island abstract peripheral diffuse degassing of co 2 from the soil occurs across the western flank of piton de la fournaise volcano la reunion island indian ocean along a narrow zone in this area carbon isotopic analysis on soil gas samples highlights significant mixing between magmatic and organic end members the zones with the strongest magmatic signature highest 13 c overlap spatial distribution of hypocenters recorded shortly before and during volcano reactivation and allow discriminating a n135 degassing lineament with a minimum length of 11 km and 140 20 m width such orientation is in accordance with that of an old dyke network along the rift zone and with n120 130 and n140 155 lineaments related to the inheritance of oceanic lithosphere structures our findings show that this n135 lineament represents a preferential magmatic pathway for deep magma transfer below the volcano flank moreover spatial distributions of recent eccentric cones indicate a well founded possibility that future eruptions may by pass the shallow plumbing system of the central area of the volcano taking a lateral pathway along this structure our results also confirm that piton de la fournaise activity is linked to a laterally shifted plumbing system and represent a major improvement in identifying the main high risk area on the densely populated western flank of the volcano

oceanography of the black sea a review of some recent results abstract a new synthesis of the black sea oceanography is presented primarily based on studies carried out in the southern black sea as well as on some recent work covering the entire basin obtained in a new era of increasing cooperation between the riparian countries a review of the physical environment is given seasonal and interannual climatic variability of the system are discussed in relation to its hydrology water mass variability and formation are studied with emphasis on the inflow of mediterranean waters pycnocline variability shelf and internal mixing and double diffusive convection the general circulation of the basin and the roles of stratification topography and coastline variations in determining the behaviour of the rapid unstable boundary currents and upwelling along the coast are discussed based on hydrographic data and satellite observations impacts of the physical processes on the ecosystem are discussed

soil co2 degassing on mt etna sicily during the period 1989 1993 discrimination between climatic and volcanic influences wide variations were measured in the diffuse co2 flux through the soils in three selected areas of mt etna between august 1989 and march 1993 degassing of co2 from the area of zafferana etnea s venerina on the eastern slope of the volcano has been determined to be more strongly influenced by meteorological parameters than the other areas the seasonal component found in the data from this area has been excluded using a filtering algorithm based on the best fitting equation calculated from the correlation between co2 flux values and those of air temperature the filtered data appear to have variations temporally coincident with those from the other areas thus suggesting a common and probably deep source of gas the highest fluxes measured in the two most peripheral areas may correlate well with other geophysical and volcanological anomalous signals that preceded the strong eruption of 1991 1993 and that were interpreted as deep pressure increases anomalous decreases in co2 fluxes accompanied the onset and the evolution of that eruption and have been interpreted as a sign of upward migration of the gas source the variations of co2 flux at the 1989 se fracture have also given interesting information on the timing of the magmatic intrusion that has then fed the 1991 1993 eruption

paratethys pacing of the messinian salinity crisis low salinity waters contributing to gypsum precipitation during the so called messinian salinity crisis msc 5 97 5 33 myr ago reduced exchange with the atlantic ocean caused the mediterranean to develop into a saline giant wherein 1 million km3 of evaporites gypsum and halite were deposited despite decades of research it is still poorly understood exactly how and where in the water column these evaporites formed gypsum formation commonly requires enhanced dry conditions evaporation exceeding precipitation but recent studies also suggested major freshwater inputs into the mediterranean during msc gypsum formation here we use strontium isotope ratios of ostracods to show that low saline water from the paratethys seas actually contributed to the precipitation of mediterranean evaporites this apparent paradox urges for an alternative mechanism underlying gypsum precipitation we propose that paratethys inflow would enhance stratification in the mediterranean and result in a low salinity surface water layer with high ca cl and so4 cl ratios we show that evaporation of this surface water can become saturated in gypsum at a salinity of 40 in line with salinities reported from fluid inclusions in msc evaporites

sea level response to pressure forcing in a barotropic numerical model abstract a barotropic shallow water model is used to study the large scale sea level response to realistic barometric forcing at periods ranging from 1 day to 1 year results are presented from coarse resolution open ocean experiments i e no shallow continental shelf regions or marginal seas with coastal geometries and bottom topography representative of the north atlantic and pacific basins the validity of the inverted barometer ib approximation is examined in detail including nonlocal effects which result from taking into account the constant volume of the ocean these effects are found to be important at low latitudes where a considerable part of the sea level variability is related to pressure forcing over higher latitudes root mean square deviations from an ib response in the range of 1 3 cm are typical with most of the variance occurring at high frequencies basin averaged estimates yield ib deviations of only a few percent at time scales longer than 1 week increasing to 5 20 over the

fluid flow and water rock interaction in the east rift zone of kilauea volcano hawaii the east rift zone of kilauea volcano in hawaii represents a major area of geothermal activity fluid inclusion and stable isotope analyses of secondary hydrothermal minerals in core samples from three scientific observation holes soh drilled into the rift zone indicate that the geothermal system is dominated by meteoric waters to depths of as much as 1500 m below sea level calculated 18o and d values for fluids on the north side of the rift zone indicate that the deep meteoric fluids may be derived from precipitation on the upper slopes of mauna loa volcano in the interior of the rift zone recharge is dominated by seawater mixed with local meteoric water water rock ratios in the rift area are approximately 2 but strongly 18o enriched fluids in the deeper parts of the soh 2 and soh 4 drill holes on the north side of the rift indicate that the fluids underwent extensive interaction with rocks prior to reaching this part of the rift zone marine carbonates at the subaerial to submarine transition between 1700 and 1780 m depth in soh 4 have not fully equilibrated with the fluids suggesting that the onset of hydrothermal activity in this area was relatively recent 2000 years this may represent increased volcanic activity along the rift after the end of the ai la au phase of eruptive activity at the kilauea summit approximately 1000 years ago or it may reflect progressive evolution of the hydrothermal system in response to southward migration of intrusive activity within the rift

geochemical investigations applied to active fault detection in a volcanic area the north east rift on mt etna sicily italy geochemical investigations were performed on the northeast rift of mt etna a prominent volcanic structure of this volcano low temperature fumaroles were found on the upper part of this area and the isotopic compositions of c co2 and he suggest a likely magmatic origin of the emitted gases on the contrary very low degassing was found in the lower part of the ne rift with co2 concentrations generally very close to those in air this pattern is probably due to sealing of the eruptive fissures by the repeated injections of magma solidified into dikes and by consequent shallow hydrothermal alteration of the fissured rocks due to residual magma degassing high soil co2 concentrations were also found in an elongated area parallel to the ne rift and located immediately to the east of it the geometry of these anomalies suggests the existence of several hidden faults sub parallel to the ne rift and likely connected to the pernicana fault system this latter structure seems to merge with the ne rift at the altitude where the fumarole emissions are located the hidden structures together with the pernicana system and the ne rift represent the western and northern boundaries of a large eastward collapsing sector of mt etna

ten years of soil co2 continuous monitoring on mt etna exploring the relationship between processes of soil degassing and volcanic activity 1 the measurement of soil co2 flux variations is a well established practice in many volcanic areas around the world until recently however most of these were made using direct sampling methods these days a variety of automatic devices providing real time data now make the continuous monitoring of volcanic areas possible a network of automatic geochemical monitoring stations etnagas network was developed by ingv palermo and installed at various sites on the flanks of mt etna here we present a large set of soil co2 flux data recorded by the network dating back 10 years a period in which several noteworthy eruptive phenomena occurred our statistical analysis strongly suggests that anomalous measurements of soil co2 flux are attributable to volcanic origin and in almost all cases precede volcanic activity here we present the actual data series recorded by etnagas and an interpretative model of the expected behavior of soil co2 flux in terms of increase decrease cycles which corresponded well with the volcanic activity during this period through the use of a comparative approach incorporating both volcanological and geochemical data the global soil co2 flux trends are put into a coherent framework highlighting close links between the time flux variations and volcanic activities these insights made possible from 10 years of uninterrupted data confirm the importance of continuous monitoring of volcanic soil degassing and may contribute in the forecasting of imminent eruptive activity or the temporal evolution of an in progress eruption therefore facilitating civil defense planning in volcanic areas under high hazard conditions

comparative hydrodynamics of 10 mediterranean lagoons by means of numerical modeling a comparison study between 10 mediterranean lagoons has been carried out by means of the 3 d numerical model shyfem the investigated basins are the venice and marano grado lagoons in the northern adriatic sea the lesina and varano lagoons in the southern adriatic sea the taranto basin in the ionian sea the cabras lagoon in sardinia the ganzirri and faro lagoons in sicily the mar menor in spain and the nador lagoon in morocco this study has been focused on hydrodynamics in terms of exchange rates transport time scale and mixing water exchange depends mainly on the inlet shape and tidal range but also on the wind regimes in the case of multi inlet lagoons water renewal time which is mostly determined by the exchange rate is a powerful concept that allows lagoons to be characterized with a time scale in the case of the studied lagoons the renewal time ranged from few days in the marano grado lagoon up to 1 year in the case of the mar menor the analysis of the renewal time frequency distribution allows identifying subbasins the numerical study proved to be a useful tool for the intercomparison and classification of the lagoons these environments range from a leaky type to a choked type of lagoons and give a representative picture of the lagoons situated around the mediterranean basin mixing efficiency turns out to be a function of the morphological complexity but also of the forcings acting on the system

maximal two layer exchange over a sill and through the combination of a sill and contraction with barotropic flow the analysis of two layer exchange flow through contractions with a barotropic component treated by armi farmer 1986 is extended to include exchange flows over sills and through a combination of a sill and contraction it is shown that exchange over a sill is fundamentally different from exchange through a contraction control at the sill crest acts primarily through the deeper layer into which the sill projects and only indirectly controls the surface layer this asymmetry in the control results in asymmetrical flows the interface depth above the crest is not one half the total depth as assumed in other studies by analogy with flow through contractions but is somewhat deeper the maximal exchange rate is less than for flow through a contraction of equal depth when both a sill and a contraction are present the contraction influences control at the sill crest only if it lies between the sill and the source of denser water the response to barotropic flow is also asymmetrical the transition to single layer flow occurs at much lower speeds for a barotropic component in one direction than the other results of the analysis are applied to exchange flow through the strait of gibraltar which includes both a sill and a contraction it is shown that maximal exchange conditions apply throughout part of the tidal cycle and observations illustrate several of the analytical predictions for barotropic flows including the formation of fronts single layer flow submaximal exchange and reverse flow

tides and sea level variability at the strait of euripus abstract the strong tidal currents in the strait of euripus are one of the first recorded observations of tidal phenomena the analysis of sea level time series from tide gauges located near the narrowest part of the strait show that the amplitude of the semi diurnal tides at the north side of the strait is four times the amplitude at the south side of the strait the two tide gauges are located a few hundred metres apart two dimensional depth averaged tidal modelling of the area shows that the m 2 and s 2 tides are enhanced as they travel through the straits of oreon and trikeri which are the communication of the north evvoikos gulf to the aegean sea the tidal propagation through the strait of euripus itself is severely restricted owing to its small cross section therefore the tides measured at the two tide gauges represent the independent propagation of the tide from the aegean sea through the north and south evvoikos gulfs respectively to the north and south sides of the strait the strong currents are driven by the gradient in sea level across the strait the natural modes of the basins are determined but are not detectable in the records 1997 academic press limited

deep co2 emitted at furnas do enxofre geothermal area terceira island azores archipelago an approach for determining co2 sources and total emissions using carbon isotopic data abstract quantification of the co2 released by the volcanoes to the atmosphere is relevant for the evaluation of the balance between deep derived biogenic and anthropogenic contributions the current study estimates the co2 released from furnas do enxofre degassing area terceira island azores archipelago by applying an approach that integrates the flux of co2 from the soil with the 13c co2 values a deep derived co2 output of 2 54 t d 1 is estimated for an area of 23 715 m2 high biogenic derived co2 flux values 45 g m 2 d 1 associated with light carbon isotopic content 13c 28 1 1 are detected and explained by the type of vegetation that characterizes the study site carbon isotopic compositions of the co2 6 4 1 2 measured in olivine hosted fluid inclusions of the terceira basalts are presented for the first time and contribute to defining the mantle co2 signature differences between these values and heavier carbon isotope values from gas in fumaroles at furnas do enxofre 4 66 to 4 27 are explained by the carbon isotopic fractionation occurring when co2 reacts to form calcite in the geothermal reservoir at temperatures 180 c a clear correlation between the soil temperature and deep co2 fluxes is observed and the integration of the diffuse degassing information with the composition of the fumarolic emissions allows estimating a thermal energy flux of 1 1 mw

soil co2 emissions at furnas volcano sao miguel island azores archipelago volcano monitoring perspectives geomorphologic studies and land use planning application accepted for publication in journal of geophysical research copyright 2010 american geophysical union

the character of long term eruptions inferences from episodes 50 53 of the pu u ō ō kūpaianaha eruption of kīlauea volcano the pu u k paianaha eruption on the east rift zone of k lauea began in january 1983 the first 9 years of the eruption were divided between the pu u 1983 1986 and k paianaha 1986 1992 vents each characterized by regular predictable patterns of activity that endured for years in 1990 a series of pauses in the activity disturbed the equilibrium of the eruption and in 1991 the output from k paianaha steadily declined and a short lived fissure eruption broke out between k paianaha and pu u in february 1992 the k paianaha vent died and 10 days later eruptive episode 50 began as a fissure opened on the uprift flank of the pu u cone for the next year the eruption was marked by instability as more vents opened on the flank of the cone and the activity was repeatedly interrupted by brief pauses in magma supply to the vents episodes 50 53 constructed a lava shield 60 m high and 1 3 km in diameter against the steep slope of the pu u cone by 1993 the shield was pockmarked by collapse pits as vents and lava tubes downcut as much as 29 m through the thick deposit of scoria and spatter that veneered the cone as the vents progressively lowered the level of the pu u pond also dropped demonstrating the hydraulic connection between the two the downcutting helped to undermine the prominent pu u cone which has diminished in size both by collapse as a large pit crater formed over the conduit and by burial of its flanks intervals of eruptive instability such as that of 1991 1993 accelerate lateral expansion of the subaerial flow field both by producing widely spaced vents and by promoting surface flow activity as lava tubes collapse and become blocked during pauses