the 16 november 2006 flank collapse of the south east crater at mount etna italy study of the deposit and hazard assessment 1 on 16 november 2006 a flank collapse affected the unstable eastern slope of the south east crater sec of mount etna the collapse occurred during one of the paroxysmal events with sustained strombolian activity that characterized the august december 2006 eruption and was triggered by erosion of loose hydrothermally altered material of the steep south east sector of sec from the outpour of lava the collapse produced a debris avalanche that involved both lithic and juvenile material and resulted in a deposit emplaced on the eastern flank of the volcano up to 1 2 km away from the source the total volume of the deposit was estimated to be in the order of 330 000 413 000 m3 the reconstruction of the collapse event was simulated using titan2d software designed to model granular avalanches and landslides this approach can be used to estimate areas that may be affected by similar collapse events in the future the area affected by the 16 november 2006 lateral collapse of sec was a small portion of the mount etna summit area but the fact that no one was killed or injured should be considered fortuitous the summit and adjacent areas of the volcano in fact are usually visited by many tourists who are not prepared to face this type of danger the 16 november 2006 collapse points to the need to be prepared for similar events through scientific investigation analysis of flank instability numerical simulation of flows and development of specific civil protection plans

effects of strait mixing on ocean stratification the density distribution in the abyssal atlantic ocean suggests that mixing associated with overflows across deep sills may account for substantial amounts of deep mixing estimates of the strait mixing are made from published estimates of the overflows and the difference between antarctic bottom water densities across the vema channel and the romanche fracture zone to demonstrate that the strait mixing is an order of magnitude larger than the abyssal mixing estimated for a standard diffusivity of 1 times 10 ndash 4 m2 s ndash 1

breaking internal lee waves at kaena ridge hawaii shallow water oscillatory flows and deep ocean steady flows have both been observed to give rise to breaking internal lee waves downstream of steep seafloor obstacles a recent theory also predicts the existence of high mode oscillatory internal lee waves in deep water but they have not previously been directly observed here we present repeated spatial transects of velocity isopycnal displacement and dissipation rate measured with towed instruments on the south flank of a supercritical ridge in hawaii known as kaena ridge and compare them with predictions from a 3 d numerical model with realistic tidal forcing bathymetry and stratification the measured and modeled flow and turbulence agree well in their spatial structure time dependence and magnitude confirming the existence and predicted nature of high mode internal lee waves turbulence estimated from thorpe scales increases 2 orders of magnitude following downslope tidal flow when the internal lee wave begins to propagate upslope and breaks

fine fracture structures in the geothermal region of hakone volcano revealed by well resolved earthquake hypocenters and focal mechanisms abstract we investigated precise hypocentral distribution and the mechanisms of small earthquakes in the geothermal region of hakone volcano central japan where swarm activity has been frequently observed earthquake swarms were remarkably prevalent in 2001 and 2006 and were accompanied by crustal deformation we first determined initial hypocenters using station corrections and one dimensional velocity structures as estimated by the joint hypocenter determination method then we applied the double difference method to relocate the initial hypocenters using the differential arrival time obtained by both manual picking and waveform cross correlation analysis subsequently we determined the focal mechanisms from the absolute p and sh wave amplitudes and p wave polarities from the relocated hypocenter distribution we found that most swarm earthquakes are distributed on thin plane like zones with width length of 100 m to 1 km we found that these plane like hypocentral distributions range from the e w to n s strikes and are consistent with one of the nodal planes of the focal mechanism it is likely that most swarm earthquakes occurred on pre existing fracture planes shaping the plane like hypocenter distributions previous studies suggested that a highly permeable fracture system has developed in the fault interaction area and these highly permeable fractures affect the occurrence of swarm earthquakes and surface geothermal activity since hakone volcano is located in the interaction area of the active tanna and hirayama faults it is suggested that the fracture planes revealed by the relocated hypocenter distribution have been developed by the activity of the two faults the fracture planes in the caldera might be channels for the hydrothermal water of hot springs in the caldera of hakone volcano which are rich in sodium chloride and considered to be composed of fluid heated by a deep seated magma the strike of the fracture plane on which the swarm earthquakes of the 2001 activity occurred is inconsistent with the orientation of open crack models estimated from geodetic data it is therefore possible that the hydrothermal fluid aseismically intruded the open cracks during the 2001 activity

quantitative analysis of abyssal hills in the atlantic ocean a correlation between inferred crustal thickness and extensional faulting a recent cruise to the office of naval research atlantic natural laboratory obtained 100 hydrosweep bathymetrie coverage 200 hawaii mrl hmrl side scan coverage gravity and magnetics over an area spanning three ridge segments along axis 25 25 n to 27 10 n and crustal ages from 0 to 26 30 ma 400 km on the west flank of the mid atlantic ridge this data set represents a first opportunity for an extensive regional analysis of abyssal hill morphology created at a slow spreading ridge the primary purpose of this work is to investigate the relationship between abyssal hill morphology and the properties of the ridge crest at which they were formed we apply the method of goff and jordan 1988 for the estimation of two dimensional statistical properties of abyssal hill morphology from the gridded hydrosweep bathymetry important abyssal hill parameters derived from this analysis include root mean square rms height characteristic width and plan view aspect ratio the analysis is partitioned into two substudies 1 analysis of near axis 7 ma abyssal hills for each of the three segments and 2 analysis of temporal variations 2 29 ma in abyssal hill morphology along the run of the south segment the results of this analysis are compared and correlated with analysis of the gravity data and preliminary determination of faulting characteristics based on hmrl side scan data principal results of this study are 1 abyssal hill morphology within the study region is strongly influenced by the inside outside corner geometry of the mid ocean ridge segments abyssal hills originating at inside corners have larger rms height and characteristic width and smaller plan view aspect ratio than those originating at outside corners 2 the residual mantle bouguer gravity anomaly is positively correlated with intersegment and along flow line variations in rms height and characteristic width and it is negatively correlated with plan view aspect ratio from this result we infer that lower relief narrower and more elongated abyssal hills are produced when the crust being generated is thicker 3 intersegment variations in near axis rms height negatively correlate with average fault density as determined from analysis of hmrl side scan imagery

strong transport and mixing of deep water through the southwest indian ridge theindianoceanharboursanimportantbutpoorlyunderstood part of the global meridional ocean overturning circulation which transports heat to high latitudes 1 understanding heat exchange in the indian ocean requires knowledge of the magnitudes and locations of both meridional deep water transport and mixing but in particular the latter is poorly constrainedatpresent 2 3 herewepresentdetailedmeasurements of transport and mixing in the atlantis ii fracture zone in the southwest indian ridge one of the main conduits for equatorward flowing deep water 4 5 we observe a northward jet of deep and bottom water extending 1 000m vertically with a transport rate of 3 10 6 m 3 s 1 turbulent di usivity within the jet was up to two orders of magnitude above typical deep ocean levels in our measurements our results quantify the flow through this narrow fracture zone to 20 to 30 of the total meridional overturning circulation in the indian ocean and provide an example of elevated turbulence in a deep shearedflow that is not hydraulically controlled in contrast to many other fracture zones 6 9 the lower limb of the indian ocean meridional overturning circulation moc consists of northward flowing deep and bottom water from the north atlantic and weddell sea that ultimately returns south as lighter deep and intermediate waters before continuing on a global trajectory 1 estimates of the total rate of overturning integrated across the basin vary widely ranging from 4sv ref 10 to 27sv ref 5 with rates from most recent studies clustering around 10 12sv refs 2 11 12

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

thermohydraulic explosions in phreatomagmatic eruptions as evidenced by the comparison between pyroclasts and products from molten fuel coolant interaction experiments 1 thermohydraulic explosions were produced by molten fuel coolant interaction mfci experiments using remelted shoshonitic rocks from vulcano italy the fragmentation history and energy release were recorded the resulting products were recovered and analyzed with the scanning electron microscope fine particles from experiments show shape and surface features that result from melt fragmentation in brittle mode these clasts relate to the thermohydraulic phase of the mfci where most of the mechanical energy is released they are here called active particles the total surface area of such particles is proportional to the energy of the respective explosions other particles from experiments show shape and surface features that result from melt fragmentation in a ductile regime these fragments called passive particles form after the thermohydraulic phase during the expansion phase of the mfci in order to verify thermohydraulic explosions in volcanic eruptions we compared experimental products with samples from phreatomagmatic base surge deposits of vulcano ash particles from the experiments show features similar to those from the deposits suggesting that the experiments reproduced the same fragmentation dynamics to achieve discrimination between active and passive particles we calculated shape parameters from image analysis the mass of active particles in base surge deposits was calculated as the material properties for the natural samples are identical to the experimental ones the energy measurements and calculations of the experiments can be applied for a single phreatomagmatic eruption at vulcano a maximum mechanical energy release of 2 75 1013 j was calculated representing a tnt analogue of 6 5 kt

deep low frequency microearthquakes in or around seismic low velocity zones beneath active volcanoes in northeastern japan abstract precise hypocenter relocations have been made for shallow intraplate microearthquakes beneath northeastern japan by applying source region station corrections the relocated hypocenter distribution shows that most of the events are confined to the upper 15 km of the crust which forms the brittle seismogenic zone in this volcanic arc it also shows that exceptionally deep microearthquakes well below the base of the seismic aseismic boundary occur at twelve locations of northeastern japan they occur in the lowermost crust or in the uppermost mantle where rheological properties of rocks are presumed to be in the ductile regime all the 153 events presently detected in the lowermost crust or in the uppermost mantle have anomalously low predominant frequencies 1 5 5 hz both for p and s waves in contrast to those 8 20 hz of normal shallow events in the brittle seismogenic zone the magnitudes of these events are small m 2 2 moreover all of these events are located beneath active volcanoes and or near p wave low velocity zones in the uppermost mantle the proximity of these events to the active volcanoes and other anomalous features suggest that these deep low frequency events are generated by magmatic activity of mantle diapirs in the uppermost mantle

parameterizing tidal dissipation over rough topography the traditional model of tidal dissipation is based on a frictional bottom boundary layer in which the work done by bottom drag is proportional to a drag coefficient and the velocity cubed however away from shallow coastal regions the tidal velocities are small and the work done by the bottom boundary layer can account for only weak levels of dissipation in the deep ocean the energy flux carried by internal waves generated over rough topography dominates the energy transfer away from barotropic flow a parameterization for the internal wave drag over rough topography is included as a dissipative mechanism in a model for the barotropic tides model results suggest that the inclusion of this dissipation mechanism improves hydro dynamical models of the ocean tide it also substantially increases the amount of modeled tidal dissipation in the deep ocean bringing dissipation levels there into agreement with recent estimates from topex poseidon altimetry data

transport and dynamics of the panay sill overflow in the philippine seas abstract observations of stratification and currents between june 2007 and march 2009 reveal a strong overflow between 400 and 570 m depth from the panay strait into the sulu sea the overflow water is derived from approximately 400 m deep in the south china sea temporal mean velocity is greater than 0 75 m s 1 at 50 m above the 570 m panay sill empirical orthogonal function analysis of a mooring time series shows that the flow is dominated by the bottom overflow current with little seasonal variance the overflow does not descend below 1250 m in the sulu sea but rather settles above high salinity deep water derived from the sulawesi sea the mean observed overflow transport at the sill is 0 32 106 m3 s 1 the observed transport was used to calculate a bulk diapycnal diffusivity of 4 4 10 4 m2 s 1 within the sulu sea slab 575 1250 m ventilated from panay strait analysis of froude number variation across the sill shows that the flow is hydraulically controlled a suitable hydraulic control model

the search for hydrothermal sources on the mid atlantic ridge abstract in a search for hydrothermal vents in the median valley of the mid atlantic ridge twenty seven lowerings of a telemetering thermistor probe were made between 43 and 47 n no hot spots were detected below 3 000 m valleys were found filled with water of more or less uniform potential temperature indicating weak but efficient mixing the mechanisms for the renewal of the mixed water and the control exercised by the sill on them is reviewed sill locations and depths are identified for seven valley segments in the study area sill depths range from 2 100 to 2 850 m within the valleys the temperature at a depth of 3 000 m ranges from 3 56 to 3 17 c decreasing as the sill depth increases a strategy is proposed for exploring a series of such valleys in a systematic search for the presence of hydrothermal vents employing chemical sampling of mn ch4 or 3he sampling concentrated near the upper boundary of the mixed region and near the sill of a valley are novel features of the proposed method

fluid induced swarm earthquake sequence revealed by precisely determined hypocenters and focal mechanisms in the 2009 activity at hakone volcano japan 1 a swarm earthquake sequence is often assumed to be triggered by fluid flow within a brittle fault damage zone which is assumed to be highly permeable however there is little seismological evidence of the relation between the fluid flow within the fault damage zone and the occurrence of swarm earthquakes here we precisely determine the hypocenters and focal mechanisms of swarm earthquakes that occurred in the caldera of hakone volcano central japan using data from a dense seismic network we demonstrate that the swarm earthquakes are concentrated on four thin plane like zones each of which has a thickness of approximately 100 m one of the nodal planes of the focal mechanisms agrees with the planar hypocenter distribution the swarm earthquakes that occurred during the initial stage of the activity exhibited a migration of hypocenters that appears to be represented by the diffusion equation based on the spatiotemporal distribution of the earthquakes the hydraulic diffusivity is estimated to be approximately 0 5 1 0 m2 s the observations imply that swarm earthquakes were triggered by the diffusion of highly pressured fluid within the fault damage zone a burst like occurrence of the swarm earthquakes is also observed in the later stage these swarm earthquakes are thought to have been triggered primarily by local stress changes caused by the preceding activity the complicated spatiotemporal pattern is thought to have been caused by the effect of the fluid flow within the high permeability damage zones as well as the stress perturbations generated by the swarm earthquakes themselves

tectonic volcanic and semi volcanic deep low frequency earthquakes in western japan abstract in western japan relatively small m the present paper characterizes the seismicity of the three types of lfes in five regions based on a more complete catalog thanks to automated event detection and precise relocation using waveform correlation the results show that isolated intraplate lfes are more similar to volcanic lfes than to tectonic lfes the volcanic and isolated intraplate lfes are insensitive to tidal stress are characterized by power law magnitude frequency statistics such as the gutenberg richter relation and are distributed mainly in small vertical clusters while the tectonic lfes are modulated by tidal stress are limited in size and are distributed along the plate boundary hence we propose that isolated intraplate lfes should be named semi volcanic lfes since tectonic lfes and volcanic lfes are thought to be related to the fluid existence and fluid movements respectively isolated intraplate semi volcanic lfes may be related to crustal fluid movements in the source area

deep volcanic tremor and magma ascent mechanism under kilauea hawaii deep harmonic tremor originating at depths around 40 km under kilauea was studied using records accumulated since 1962 at the hawaii volcano observatory of the u s geological survey the deep source of the tremor was determined by onset times and confirmed by the relative amplitude across the island wide network of seismometers the period of tremor was conclusively shown to be determined by the source effect and not by the path or station site effect because the period would change considerably in time but maintained uniformity across the seismic net during the tremor episode the tremor appeared to be primarily composed of p waves we interpret the observed period and amplitude in terms of the stationary crack model of aki et al 1977 and find that the seismic moment rates for deep tremors are considerably larger than those for shallow tremors suggesting more vigorous transport for the former we propose a kinematic source model which may be more appropriate for deep tremor according to this model a measurable quantity called reduced displacement is directly proportional to the rate of magma flow a systematic search for deep tremor episodes was made for the period from 1962 through 1979 and the amplitude period and duration of the tremor were tabulated we then constructed a cumulative reduced displacement plot over the 18 year period the result shows a generally steady process which does not seem to be significantly affected by major eruptions and large earthquakes near the surface the total magma flow estimated from the reduced displacement is however one order of magnitude smaller than that estimated by swanson 1972 it may be that most channels transport magma aseismically and only those with strong barriers generate tremor

spatial variability of turbulent mixing in the abyssal ocean ocean microstructure data show that turbulent mixing in the deep brazil basin of the south atlantic ocean is weak at all depths above smooth abyssal plains and the south american continental rise the diapycnal diffusivity there was estimated to be less than or approximately equal to 0 1 x 10 4 meters squared per second in contrast mixing rates are large throughout the water column above the rough mid atlantic ridge and the diffusivity deduced for the bottom most 150 meters exceeds 5 x 10 4 meters squared per second such patterns in vertical mixing imply that abyssal circulations have complex spatial structures that are linked to the underlying bathymetry

identifying magma water interaction from the surface features of ash particles the deposits from explosive volcanic eruptions those eruptions that release mechanical energy over a short time span1 are characterized by an abundance of volcanic ash2 3 this ash is produced by fragmentation of the magma driving the eruption and by fragmenting and ejecting parts of the pre existing crust host rocks interactions between rising magma and the hydrosphere oceans lakes and ground water play an important role in explosive volcanism4 5 because of the unique thermodynamic properties of water that allow it to very effectively convert thermal into mechanical energy although the relative proportion of magma to host rock fragments is well preserved in the pyroclastic rocks deposited by such eruptions it has remained difficult to quantitatively assess the interaction of magma with liquid water from the analysis of pyroclastic deposits2 3 4 5 here we report the results of a study of natural pyroclastic sequences combined with scaled laboratory experiments we find that surface features of ash grains can be used to identify the dynamic contact of magma with liquid water the abundance of such ash grains can then be related to the water magma mass ratios during their interaction

intense mixing of lower thermocline water on the crest of the mid atlantic ridge the mixing of warm upper ocean water with the colder water beneath is an essential component of global ocean circulation because it increases the buoyancy of deep water but it is not clear where this mixing takes place louis st laurent and andreas thurnherr have measured the mixing that occurs as water flows through a narrow passage on the crest of the mid atlantic ridge the rates they observe are unusually high if similar mixing rates occur in the other narrow passages on the mid atlantic ridge in the north atlantic basin these sites could account for as much buoyancy flux at the depth of the passages as the rest of the basin combined so mixing in narrow passages on mid ocean ridges sites that have previously been overlooked may make a significant contribution to buoyancy flux at the global scale observations from the crest of the mid atlantic ridge suggest that passages in rift valleys and ridge flank canyons provide the most energetic sites for oceanic turbulence measurements show that large diffusivities characterize the mixing downstream of a sill in a well stratified boundary layer with mixing levels remaining of the order of 10 4m2 s 1 at the base of the main thermocline buoyancy exchange between the deep and the upper ocean which is essential for maintaining global ocean circulation mainly occurs through turbulent mixing1 2 this mixing is thought to result primarily from instability of the oceanic internal wave field3 but internal waves tend to radiate energy away from the regions in which they are generated rather than dissipate it locally as turbulence4 and the resulting distribution of turbulent mixing remains unknown another more direct mixing mechanism involves the generation of turbulence as strong flows pass through narrow passages in topography but the amount of turbulence generated at such locations remains poorly quantified owing to a lack of direct measurements here we present observations from the crest of the mid atlantic ridge in the subtropical north atlantic ocean that suggest that passages in rift valleys and ridge flank canyons provide the most energetic sites for oceanic turbulence our measurements show that diffusivities as large as 0 03 m2 s 1 characterize the mixing downstream of a sill in a well stratified boundary layer with mixing levels remaining of the order of 10 4 m2 s 1 at the base of the main thermocline these mixing rates are significantly higher than the diffusivities of the order of 10 5 m2 s 1 that characterize much of the global thermocline and the abyssal ocean5 our estimates suggest that overflows associated with narrow passages on the mid atlantic ridge in the north atlantic ocean produce as much buoyancy flux as has previously been estimated for the entire romanche fracture zone6 7 a large strait in the mid atlantic ridge that connects the north and south atlantic basins this flux is equivalent to the interior mixing that occurs in the entire north atlantic basin at the depth of the passages suggesting that turbulence generated in narrow passages on mid ocean ridges may be important for buoyancy flux at the global scale

flow and mixing in the rift valley of the mid atlantic ridge high levels of diapycnal mixing and geothermal heating near midocean ridges contribute to the buoyancy fluxes that are required to close the global circulation in topographically confined areas such as the deep median valleys of slow spreading ridges these fluxes strongly influence the local hydrography and dynamics data from a segment scale hydrographic survey of the rift valley of the mid atlantic ridge and from an array of current meters deployed there during an entire year are analyzed in order to characterize the dominant hydrographic patterns and dynamical processes comparison with historic hydrographic data indicates that the temporal variability during the last few decades has been small compared to the observed segment scale gradients the rift valley circulation is characterized by inflow from the eastern ridge flank and persistent unidirectional alongsegment flow into a cul de sac therefore most of the water flowing along the rift valley upwells within the segment with a mean vertical velocity 1025 ms 21 the observed streamwise hydrographic gradients indicate that diapycnal mixing dominates the rift valley buoyancy fluxes by more than an order of magnitude in spite of the presence of a large hydrothermal vent field supplying several gigawatts of heat to the water column hydrographic budgets in the rift valley yield diffusivity values of order 5 3 1023 m2 s 21 consistent with estimates derived from statically unstable overturns the largest of which were observed downstream of topographic obstacles in the path of the along segment flow this suggests vertical shear associated with cross sill flows as the dominant contributor to the mechanical mixing in the rift valley

a magma hydrothermal system beneath hakone volcano central japan revealed by highly resolved velocity structures high resolution images of subsurface structures are necessary to understand the transport processes of crustal fluids from deep magma sources and their relationship to earthquake swarms in active volcanic regions based on a seismic tomography approach we have developed a new model for the magma hydrothermal system beneath hakone volcano central japan where shallow earthquake swarms and crustal deformation associated with inflation of an open crack source are often observed by applying travel time data for local earthquakes to a tomographic inversion we obtained highly resolved seismic velocity structures that show a region of low p wave velocity vp low s wave velocity vs and high vp vs ratios at depths of 10 20 km beneath the volcano corresponding to the location of the open crack source we suggest that the high vp vs ratios represent a deep magma chamber with a high concentration of melt and or fluids deep low frequency earthquakes located just beneath this high vp vs zone may indicate that magmatic fluids are supplied from below above the high vp vs zone a region of low vp low vs and low vp vs ratios exists at depths of 3 10 km suggesting the presence of crack filled water or co2 supplied from the inferred deep magma chamber many earthquake swarms occur in this low vp vs zone indicating that crustal fluids play an important role in generating the swarms similar relationships between magma reservoirs overlying hydrothermal systems and swarm activity have been reported from other volcanic areas and thus may be a ubiquitous feature beneath active volcanoes

a monochromatic earthquake suggesting deep seated magmatic activity beneath the izu ooshima volcano japan after a quiescence of 12 years the izu ooshima volcano located about 30 km east of the izu peninsula in central japan erupted on november 15 1986 on august 27 1985 about 1 year before the eruption a peculiar earthquake of magnitude 2 7 took place near the moho boundary just beneath the izu ooshima volcano where seismic activity is otherwise absent analysis of digital data obtained by the telemetered seismic network of the national research center for disaster prevention reveals the following distinctive features of the seismic waves 1 the main part of the wave train is composed of s waves and a small p phase precedes it 2 the spectral density has a sharp peak at 1 0 hz which is independent of the epicentral distance azimuth and time indicating a monochromatic spectrum at the source 3 ground motion for the initial part of the s wave is polarized in the n s direction at almost all the stations the amplitude ratios of s to p waves and the polarization pattern of s waves suggest that a traction force caused by magma flow is a more probable source than a double couple mechanism free oscillation of the magma reservoir or opening of a tensile crack we propose a traction force model for this earthquake in which magma flow through a conduit produces unidirectional viscous force on the conduit walls the observations imply a n s force direction and a maximum force of about 2 8 1010 n the pressure difference between the ends of the conduit is estimated as 6 1 107 pa 610 bar under the assumption of conduit dimensions of 2 km 1 km the monochromatic nature of the source spectrum is difficult to account for by the free oscillation of a magma reservoir we tentatively suggest the intermittent opening of a barrier in the conduit as a plausible mechanism of the periodic oscillation

boundary mixing and topographic blocking on the mid atlantic ridge in the south atlantic abstract it is commonly observed in hydrographic sections crossing midocean ridges that the isopycnals on the ridge flanks slope downward toward the crests although the observed vertical scales of isopycnal dipping are not consistent with steady diffusive boundary layers on slopes the cross flank density gradients can nevertheless be caused by diapycnal mixing acting on timescales of several years the corresponding pressure gradients are usually inferred to be associated with cyclonic along flank flows recent observations of southward flow along the highly corrugated western flank of the mid atlantic ridge near 20 s are inconsistent with this conceptual picture however data from seven zonal cross ridge sections and from four meridional along ridge sections were used to analyze the hydrography on the flanks of the mid atlantic ridge between 2 n and 30 s the majority of the hydrographic stations were occupied over deep cross flank canyons which extend over a total length of 90 000 km in the tropica

widespread intense turbulent mixing in the southern ocean observations of internal wave velocity fluctuations show that enhanced turbulent mixing over rough topography in the southern ocean is remarkably intense and widespread mixing rates exceeding background values by a factor of 10 to 1000 are common above complex bathymetry over a distance of 2000 to 3000 kilometers at depths greater than 500 to 1000 meters this suggests that turbulent mixing in the southern ocean may contribute crucially to driving the upward transport of water closing the ocean s meridional overturning circulation and thus needs to be represented in numerical simulations of the global ocean circulation and the spreading of biogeochemical tracers

remotely triggered seismic activity in hakone volcano during and after the passage of surface waves from the 2011 m9 0 tohoku oki earthquake abstract immediately after the march 11 2011 m9 0 tohoku oki earthquake seismic activity increased remarkably beneath hakone volcano central japan at an epicentral distance of 450 km the heightened seismicity was initiated during the passage of the large amplitude surface waves from the main shock and continued over the subsequent 2 months we obtained hypocenters and focal mechanisms of the seismic sequence with the aim of clarifying the physical mechanism responsible for the remotely triggered seismicity we used data from a dense seismic network containing 56 online permanent and offline temporary stations in and around the hakone volcano we found that the earthquakes that occurred during the passage of the surface waves are located at the lower depth limit of ordinary seismicity in the caldera these earthquakes have larger magnitudes than both the ordinary seismicity prior to the tohoku oki earthquake and the seismicity triggered after the passage of the surface waves the focal mechanism that we determined is a strike slip fault type with the p axis in the nw se direction which is consistent with the focal mechanisms of earthquakes that occurred after the passage of the surface waves and the tectonic stress field in the region we also tried to detect missing events that occurred immediately after the passage of the surface waves by using a waveform correlation technique the detected events are distributed near the hypocenters of the earthquakes that occurred during the passage of the surface waves the origin times of the first four events after the arrival of surface waves are consistent with the phases of the decrease in normal stress generated by the surface waves the results suggest that the changes in dynamic stress due to the surface waves from the 2011 tohoku oki earthquake contributed significantly to the initiation of the sequence of triggered seismic activity assuming that normal stress changes on the faults did play an important role in the triggering of earthquakes we propose that fluid flow induced by the oscillation of permeability on the faults is the main mechanism for the initiation of post tohoku oki earthquakes beneath the hakone volcano

hazards from pyroclastic density currents at mt etna italy abstract despite the recent recognition of mount etna as a periodically violently explosive volcano the hazards from various types of pyroclastic density currents pdcs have until now received virtually no attention at this volcano large scale pyroclastic flows last occurred during the caldera forming ellittico eruptions 15 16 ka ago and the risk of them occurring in the near future is negligible however minor pdcs can affect much of the summit area and portions of the upper flanks of the volcano during the past 20 years small pyroclastic flows or base surge like vapor and ash clouds have occurred in at least 8 cases during summit eruptions of etna four different mechanisms of pdc generation have been identified during these events 1 collapse of pyroclastic fountains as in 2000 and possibly in 1986 2 phreatomagmatic explosions resulting from mixing of lava with wet rock 2006 3 phreatomagmatic explosions resulting from mixing of lava with thick snow 2007 4 disintegration of the unstable flanks of a lava dome like structure growing over the rim of one of the summit craters 1999 all of these recent pdcs were of a rather minor extent maximum runout lengths were about 1 5 km in november 2006 and march 2007 and thus they represented no threat for populated areas and human property around the volcano yet events of this type pose a significant threat to the lives of people visiting the summit area of etna and areas in a radius of 2 km from the summit craters should be off limits anytime an event capable of producing similar pdcs occurs the most likely source of further pdcs in the near future is the southeast crater the youngest most active and most unstable of the four summit craters of etna where 6 of the 8 documented recent pdcs originated it is likely that similar hazards exist in a number of volcanic settings elsewhere especially at snow or glacier covered volcanoes and on volcano slopes strongly affected by hydrothermal alteration

pyroclastic density currents resulting from the interaction of basaltic magma with hydrothermally altered rock an example from the 2006 summit eruptions of mount etna italy after 16 months of quiescence mount etna began to erupt again in mid july 2006 the activity was concentrated at and around the southeast crater sec one of the four craters on the summit of etna and eruptive activity continued intermittently for 5 months during this period numerous vents displayed a wide range of eruptive styles at different times virtually all explosive activities took place at vents at the summit of the sec and on its flanks eruptive episodes which lasted from 1 day to 2 weeks became shorter and more violent with time volcanic activity at these vents was often accompanied by dramatic mass wasting processes such as collapse of parts of the cone highly unusual flowage processes involving both old rocks and fresh magmatic material and magma water interaction the most dramatic events took place on 16 november when numerous rockfalls and pyroclastic density currents pdcs were generated during the opening of a large fracture on the se flank of the sec cone the largest pdcs were clearly triggered explosively and there is evidence that much of the energy was generated during the interaction of intruding magma with wet rocks on the cone s flanks the most mobile pdcs traveled up to 1 km from their source this previously unknown process on etna may not be unique on this volcano and is likely to have taken place on other volcanoes it represents a newly recognized hazard to those who visit and work in the vicinity of the summit of etna

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

comment on complex magma dynamics at mount etna revealed by seismic thermal and volcanological data by b behncke s falsaperla and e pecora

cooling magma model for deep volcanic long period earthquakes deep long period events dlp events or deep low frequency earthquakes deep lfes are deep earthquakes that radiate low frequency seismic waves while tectonic deep lfes on plate boundaries are thought to be slip events there have only been a limited number of studies on the physical mechanism of volcanic dlp events around the moho crust mantle boundary beneath volcanoes one reasonable mechanism capable of producing their initial fractures is the effect of thermal stresses since ascending magma diapirs tend to stagnate near the moho where the vertical gradient of density is high we suggest that cooling magma may play an important role in volcanic dlp event occurrence assuming an initial thermal perturbation of 400 c within a tabular magma of half width 41 m or a cylindrical magma of 74 m radius thermal strain rates within the intruded magma are higher than tectonic strain rates of 10 14 s 1 and produce a total strain of 2 10 4 shear brittle fractures generated by the thermal strains can produce a compensated linear vector dipole mechanism as observed and potentially also explain the harmonic seismic waveforms from an excited resonance in our model we predict correlation between the particular shape of the cluster and the orientation of focal mechanisms which is partly supported by observations of aso and ide 2014 to assess the generality of our cooling magma model as a cause for volcanic dlp events additional work on relocations and focal mechanisms is essential and would be important to understanding the physical processes causing volcanic dlp events

mixing associated with sills in a canyon on the midocean ridge flank to close the global overturning circulation the production and sinking of dense water at high latitudes must be balanced elsewhere by buoyancy gain and upward vertical motion hydrographic and microstructure observations from the brazil basin in the south atlantic ocean indicate that most of the abyssal mixing there takes place on the topographically rough flank of the midocean ridge in previous studies it has been suggested that the high level of abyssal mixing observed on the ridge flank is primarily caused by breaking internal waves forced by tidal currents here the results from a detailed analysis of velocity hydrographic and microstructure data from a ridge flank canyon are presented two year long current meter records indicate that within the canyon there is a significant along axial mean flow down the density gradient toward the ridge crest five hundred meters above the canyon floor the kinetic energy in the subinertial band exceeds that associated with the semidiurnal tides by approximately a factor of 2 the mean dissipation of kinetic energy inside the canyon exceeds that above the ridge flank topography by approximately a factor of 5 the largest dissipation values were observed downstream of a narrow 1000 m high sill that extends across the full width of the canyon along the entire canyon there is a strong association between the presence of sills and along axial density gradients while there is no similar association between the presence of depressions and density gradients together these observations suggest that sill related mixing contributes at least as much to the diapycnal buoyancy flux in the canyon as tidally forced internal wave breaking which is not expected to be associated preferentially with sills while only 15 of the interfacial area between antarctic bottom water and north atlantic deep water in the brazil basin lie inside canyons the available data suggest that approximately one half of the diapycnal buoyancy fluxes take place there in comparison the region above the ridge flank topography accounts for about one third of the buoyancy fluxes the apparent importance of sill related processes for mixing in ridge flank canyons is therefore of global significance especially considering that such canyons occur on average every 50 km along 2 3 of the global midocean ridge system and that sills partially block the canyon axes every few tens of kilometers

mixing in the romanche fracture zone the romanche fracture zone is a major gap in the mid atlantic ridge at the equator which is deep enough to allow significant eastward flows of antarctic bottom water from the brazil basin to the sierra leone and guinea abyssal plains while flowing through the romanche fracture zone bottom water properties are strongly modified due to intense vertical mixing the diapycnal mixing coefficient in the bottom water of the romanche fracture zone is estimated by using the finestructure of ctd profiles the microstructure of high resolution profiler data and by constructing a heat budget from current meter data the finestructure of density profiles is described using the thorpe scaleslt it is shown from microstructure data taken in the bottom water that the ozmidov scale lo is related to lt by the linear relationship lo 5 0 95lt similar to other studies which allows an estimate of the diapycnal mixing coefficient using the osborn relation the thorpe scale and the diapycnal mixing coefficient estimates show enhanced mixing downstream eastward of the main sill of the romanche fracture zone in this region a mean diapycnal mixing coefficient of about 1000 3 1024 m2 s21 is found for the bottom water estimates of cross isothermal mixing coefficient derived from the heat budgets constructed downstream of the current meter arrays deployed in the romanche fracture zone and the nearby chain fracture zone are in agreement with the finestructure estimates of the diapycnal mixing coefficient within the romanche fracture zone although the two fracture zones occupy only 0 4 of the area covered by the sierra leone and guinea abyssal plains the diffusive heat fluxes across the 1 4 8c isotherm in the romanche and chain fracture zones are half that found over the abyssal plains across the 1 88c isotherm emphasizing the role of these passages for bottom water property modifications

search for reliable precursors a case study of the seismic quiescence of the 2000 western tottori prefecture earthquake 1 how to search for reliable precursors is one of the key problems of the study on earthquake forecast in this paper a method is presented to judge whether or not a precursor is reliable before a potential anomaly can be nominated as a reliable precursor it should pass or be proved by the following tests or analyses whether or not it is an artificial anomaly whether or not it correlates with an investigated event whether or not it is a random anomaly as a case study i have investigated the reliability of seismic quiescence for an m 7 3 earthquake which occurred in the western region of tottori prefecture japan on 6 october 2000 the earthquake data 1975 2000 of the japan meteorological agency jma were used in this study after analyzing the completeness of the catalog and removing aftershocks a statistical method which is called the rtl region time length algorithm and takes into account the information of magnitude occurrence time and location of earthquakes was applied to the above preprocessed earthquake data a clear seismic quiescence anomaly was detected before the 2000 western tottori prefecture earthquake close investigation indicated that the above anomaly is not due to artifacts of the selections of model parameters after quantifying the anomaly and making statistical analysis over the whole investigated spatiotemporal domain reasonable correlation between the above anomaly and the main shock in 2000 was recognized the stochastic test using synthetic randomized catalogs showed the above anomaly is unlikely due to chance thus the above seismic quiescence anomaly before the 2000 main shock should be a significant and reliable precursor and the research method revealed in this study can enhance the reliability of precursors

the evolution of high alumina basalts of the klyuchevskoy volcano kamchatka russia based on microprobe analyses of mineral inclusions abstract the origin of calc alkaline high alumina basalts hab of the klyuchevskoy volcano kamchatka was examined using electron microprobe analyses of phenocrysts and mineral phases included in the phenocrysts continuous trends on major element variation diagrams suggest the hab were derived from high magnesia basalt hmb by fractional crystallization phenocrysts in the hab are strongly zoned olivine mg 91 64 clinopyroxene wo45 38en40 51fs5 20 and chrome spinel magnetite inclusions in them cr2o3 45 0 wt tio2 0 5 11 microprobe analyses of minerals included in the phenocrysts provide additional constraints on the mineral crystallization trends in the hab fe mg partitioning data when applied to the phenocrysts cores show they crystallized from a hmb the similarity of phenocryst core compositions in hab with those in hmb strongly suggests a genetic relationship between the two magma types

complex magma dynamics at mount etna revealed by seismic thermal and volcanological data 1 three eruptive episodes during the 2006 summit eruptions of mount etna were exceptionally well documented by visual seismic and thermal monitoring the first 16 november was strongly explosive with vigorous strombolian activity and ash emission from multiple vents lava emission and phreatomagmatic explosions generating pyroclastic density currents pdcs the second episode 19 november had a rather weakly explosive component with mild strombolian activity but more voluminous lava emission the third 24 november was a moderately explosive paroxysm with intermittent lava fountaining and generation of a tephra column as well as lava emission and pdcs data recorded by a thermal monitoring camera clearly document the different phases of each paroxysm weather clouds occasionally hampering thermal monitoring the images show a rapid onset of the volcanic activity which during each of the paroxysms reached a peak in eruptive and thermal intensity and then decreased gradually the stronger phreatomagmatic explosions and pdcs on 16 and 24 november did not yield any seismic signature linked to the opening of new vents nor were they associated with peculiar characteristics of the seismic signal nevertheless eruptive styles strombolian activity lava emission and different levels in the intensity of explosive activity were generally well reflected in the amplitude and frequency content of the seismic signal and in the source location of the volcanic tremor centroid throughout the three eruptive episodes this multidisciplinary study therefore not only provides a key to distinguish between endogenous and exogenous origins of the phenomena observed but also documents the complex magma dynamics within the volcano

evidence for enhanced mixing over rough topography in the abyssal ocean the overturning circulation of the ocean plays an important role in modulating the earth s climate but whereas the mechanisms for the vertical transport of water into the deep ocean deep water formation at high latitudes and horizontal transport in ocean currents have been largely identified it is not clear how the compensating vertical transport of water from the depths to the surface is accomplished turbulent mixing across surfaces of constant density is the only viable mechanism for reducing the density of the water and enabling it to rise however measurements of the internal wave field the main source of energy for mixing and of turbulent dissipation rates have typically implied diffusivities across surfaces of equal density of only approximately 0 1 cm2 s 1 too small to account for the return flow here we report measurements of tracer dispersion and turbulent energy dissipation in the brazil basin that reveal diffusivities of 2 4 cm2 s 1 at a depth of 500 m above abyssal hills on the flank of the mid atlantic ridge and approximately 10 cm2 s 1 nearer the bottom this amount of mixing probably driven by breaking internal waves that are generated by tidal currents flowing over the rough bathymetry may be large enough to close the buoyancy budget for the brazil basin and suggests a mechanism for closing the global overturning circulation

first detection of precursory ground inflation of a small phreatic eruption by insar abstract phreatic eruptions are caused by pressurization of geothermal fluid sources at shallow levels they are relatively small compared to typical magmatic eruptions but can be very hazardous however owing to their small magnitudes their occurrences are difficult to predict here we show the detection of locally distributed ground inflation preceding a small phreatic eruption at the hakone volcano japan through the application of interferometric synthetic aperture radar analysis the ground inflation proceeded the eruption at slow speed of 5 mm month with a spatial size of 200 m in the early stage and then it accelerated 2 months before the eruption that occurred for the first time in 800 900 yrs the ground uplift reached 30 cm and the eruption occurred nearby the most deformed part the deformation speed correlated well with inflation of spherical source located at 4 8 km below sea level thus suggesting that heat and or volcanic fluid supply from the spherical source maybe magma reservoir directly drove the subsurface hydrothermal activity our results demonstrate that high spatial resolution deformation data can be a good indicator of subsurface pressure conditions with pinpoint spatial accuracy during the preparatory process of phreatic eruptions

the millennium eruption of hekla in february 2000 the 18th historic eruption of hekla started on 26 february 2000 it was a short lived but intense event emitting basaltic andesitic 55 5 wt sio2 pyroclastic fragments and lava during the course of the eruption monitoring was done by both instruments and direct observations together providing unique insight into the current activity of hekla during the 12 day eruption a total of 0 189 km3 dre of magma was emitted the eruptive fissure split into five segments the segments at the highest altitude were active during the first hours while the segments at lower altitude continued throughout the eruption the eruption started in a highly explosive manner giving rise to a subplinian eruptive column and consequent basaltic pyroclastic flows fed by column collapses after the explosive phase reached its maximum the eruption went through three more phases namely fire fountaining strombolian bursts and lava effusion in this paper we describe the course of events of the eruption of hekla and the origin of its magma and then show that the discharge rate can be linked to different style of eruptive activity which are controlled by fissure geometry we also show that the eruption phases observed at hekla can be linked with inferred magma chamber overpressure prior to the eruption

buoyancy forcing by turbulence above rough topography in the abyssal brazil basin abstract observations of turbulent dissipation above rough bathymetry in the abyssal brazil basin are presented relative to regions with smooth bathymetry dissipation is markedly enhanced above rough topography of the mid atlantic ridge with levels above bathymetric slopes exceeding levels observed over crests and canyon floors furthermore mixing levels in rough areas are modulated by the spring neap tidal cycle internal waves generated by barotropic tidal flow over topography are the likely mechanism for supplying the energy needed to support the observed turbulent dissipation a model of the spatial and temporal patterns in the turbulent dissipation rate is used to constrain the diapycnal advection in an inverse calculation for the circulation in an area of rough bathymetry this inverse model uses both beta spiral and integrated forms of the advective budgets for heat mass and vorticity and contains sufficient information to resolve the full three dimensional flow the inverse model solution re

mixing and entrainment in hydraulically driven stratified sill flows author posting cambridge university press 2004 this article is posted here by permission of cambridge university press for personal use not for redistribution the definitive version was published in journal of fluid mechanics 515 2004 415 443 doi 10 1017 s0022112004000576

isotope fractionation and mixing in methane plumes from the logatchev hydrothermal field as methane is consumed in the deep sea its 13c 12c ratio progressively increases because of kinetic isotope fractionation many submarine hydrothermal vents emit methane with carbon isotope ratios that are higher than those of background methane in the surrounding ocean since the latter exists at low concentrations mixing of background methane with vent fluid tends to decrease the 13c 12c ratio as concentration decreases opposite to the trend produced by consumption we investigated ch4 concentration and 13c together with 3he in plumes from the logatchev hydrothermal field lhf located at 14 45 n 45 w which generates relatively heavy methane 13c 13 by serpentinization of ultramafic rock the measured methane and 3he were well correlated at high concentrations indicating a ch4 3he ratio of 1 108 in the vent fluids these tracer distributions were also simulated with an advection diffusion model in which methane consumption only occurs above a certain threshold concentration we utilized 3he to calculate the methane remaining in solution after oxidation f and the deviation of 13c from the value expected from mixing alone 13c both in the model and in the data the entire set of 13c values are not correlated with log f which is due to continuous oxidation within the plume while mixing with background seawater a linear relationship however is found in the model for methane at concentrations sufficiently above background and many of the samples with elevated ch4 north of lhf exhibit a linear trend of 13c versus log f as well from this trend the kinetic isotope fractionation factor in the lhf plumes appears to be about 1 015 this value is somewhat higher than found in some other deep sea studies but it is lower than found in laboratory incubation experiments

instabilities in the summit region of mount etna during the 1999 eruption during the 1999 eruption of mount etna sicily the summit of the volcano changed dramatically lavas erupted from a fissure on the southern flank of se cone formed a large compound flow field that buried a substantial part of the northern wall of valle del bove and the ground between there and se cone hot mass flow deposits formed on the eastern and western flanks of the chasm following a period of intense strombolian activity at the same time a new vent opened on the southern flank of se cone and there was a major rockfall from its summit seven weeks later part of the outer western rim of bocca nuova crater collapsed during another period of intense strombolian activity and lava emerged at a high effusion rate through the breached crater wall following a subsequent collapse of the bocca nuova crater rim a hot avalanche flowed a few hundred metres on top of the previous lava flow field similar deposits have been described on other volcanoes but their importance in the evolution of the summit of etna has not previously been recognised

generation of pyroclastic flows by explosive interaction of lava flows with ice water saturated substrate abstract we describe a new type of secondary rootless phreatomagmatic explosions observed at active lava flows at volcanoes klyuchevskoy russia and etna italy the explosions occurred at considerable up to 5 km distances from primary volcanic vents generally at steep 15 35 slopes and in places where incandescent basaltic or basaltic andesitic lava propagated over ice water saturated substrate the explosions produced high up to 7 km vertical ash steam laden clouds as well as pyroclastic flows that traveled up to 2 km downslope individual lobes of the pyroclastic flow deposits were up to 2 m thick had steep lateral margins and were composed of angular to subrounded bomb size clasts in a poorly sorted ash lapilli matrix character of the juvenile rock clasts in the pyroclastic flows poorly vesiculated with chilled and fractured cauliflower outer surfaces indicated their origin by explosive fragmentation of lava due to contact with external water non juvenile rocks derived from the substrate of the lava flows comprised up to 75 in some of the pyroclastic flow deposits we suggest a model where gradual heating of a water saturated substrate under the advancing lava flow elevates pore pressure and thus reduces basal friction in the case of frozen substrate water is initially formed by thawing of the substrate along the contact with lava on steep slope this leads to gravitational instability and sliding of a part of the active lava flow and water saturated substrate the sliding lava and substrate disintegrate and intermix triggering explosive fuel coolant type interaction that produces large volume of fine grained clastic material relatively cold steam laden cloud of the phreatomagmatic explosion has limited capacity to transport upward the produced clastic material thus part of it descends downslope in the form of pyroclastic flow similar explosive events were described for active lava flows of llaima chile pavlof alaska and hekla iceland indicating that this type of explosions and related hazard is common at snow ice clad volcanoes and sometimes happens also on fluid saturated hydrothermally altered slopes

hydrography and high temperature heat flux of the rainbow hydrothermal site 36 14 n mid atlantic ridge on the basis of an extensive set of conductivity temperature depth lowered acoustic doppler current profiler ladcp and nephelometry profiles and tow yos the hydrography flow field and particle plume of the rainbow hydrothermal site on the mid atlantic ridge are analyzed in the rift valley the water column is less dense and stratified than both eastern and western off ridge water with t s characteristics consistent with inflow across a sill from the east the buoyant hydrothermal plumes rise into a strong boundary current flowing along the slope of a topographic high which partially blocks the rift valley below 1950 m the bulk of the neutrally buoyant plume is advected across a sill which forms both the narrowest and the shallowest part of the valley and acts as a hydraulic control point for the flow below 2000 m large amplitude internal waves consistent with tidal forcing are observed near the sill but ladcp measurements suggest that the tidal signal is not strong enough to lead to flow reversal at plume depth above 2000 m the mean current across the topography generates lee waves which radiate energy upward and downstream density averaged light scattering profiles show the hydrothermal particle plume to be gaussian in depth even in the near field where many of the individual profiles are characterized by multiple peaks and the horizontal variability is highest the temperature anomalies associated with the mean near source particle plume are of order 5 10 3 c that is the plume is cold fresh as expected from the background hydrography of the deep atlantic using the flow field light scattering and hydrographic anomaly observations the heat flux associated with the hydrothermal particle plume at rainbow is estimated to lie between 1 and 5 gw

idealized solutions for the energy balance of the finescale internal wave field abstract recent fine and microstructure observations indicate enhanced finescale shear and strain in conjunction with bottom intensified turbulent dissipation above rough bathymetry in the brazil basin such observations implicate the bottom boundary as an energy source for the finescale internal wave field simple analytical and numerical solutions to an equation governing the spatial and temporal evolution of the finescale wave field are described here the governing equation implicitly treats the effects of wave breaking on the vertical propagation of internal waves through a flux representation of nonlinear transports associated with internal wave wave interactions these solutions identify the rate of dissipation of turbulent kinetic energy with downscale energy transports at high vertical wavenumber resulting in an estimate of dissipation versus depth the sensitivity of the turbulent dissipation depth profile to various environmental parameters is examined observed dissipation profiles and shear

intense mixing of antarctic bottom water in the equatorial atlantic ocean the spreading of antarctic bottom water the densest global scale water mass is highly constrained by ocean floor topography in the atlantic ocean the mid atlantic ridge confines this water mass mainly to the western basins the bottom waters in the eastern basins being renewed by flows through gaps in the ridge1 one such gap is the romanche fracture zone a large offset of the ridge which straddles the equator it has been observed2 that sills within this fracture zone block the passage of waters colder than 0 9 c warmer less dense waters passing over the sills appear to cascade downslope where they are modified by mixing here we present direct measurements which quantify these processes the flow is vertically sheared and exhibits remarkably intense turbulence comparable to that seen at the ocean surface in the presence of winds of l0ms 1 this turbulence mixes the densest waters passing through the fracture zone with the warmer overlying waters so that the coldest waters exiting this region have been warmed by 0 6 c during transit topographic obstructions and turbulent mixing together thus determine the properties of the flows renewing the deepest waters of the atlantic ocean s eastern basins

the zonal dimension of the indian ocean meridional overturning circulation abstract the three dimensional structure of the meridional overturning circulation moc in the deep indian ocean is investigated with an eddy permitting ocean model the amplitude of the modeled deep indian ocean moc is 5 6 sv 1 sv 106 m3 s 1 a broadly realistic but somewhat weak overturning although the model parameterization of diapycnal mixing is inaccurate the model s short spinup allows the effective diapycnal velocity the sum of model drift and the explicitly modeled diapycnal velocity to resemble the true real ocean diapycnal velocity for this reason the model is able to recover the broad zonal asymmetry in the turbulent buoyancy flux that is suggested by observations the model features a substantial deep depth reversing zonal circulation of nearly 50 of the moc the existence of this circulation brought about by the zonally asymmetric distribution of diapycnal mixing implies a much slower ventilation of the deep indian ocean by a factor of 5 6 than would be in place without zon

migration of early aftershocks following the 2004 parkfield earthquake a significant number of the early aftershocks following large shallow earthquakes are missing in existing earthquake catalogues an analysis of the waveforms of 3 647 relocated earthquakes along the parkfield section of the san andreas fault reveals 11 times more aftershocks within three days of the 2004 parkfield earthquake than listed in a standard catalogue large shallow earthquakes are immediately followed by numerous aftershocks a significant portion of these events is missing in existing earthquake catalogues mainly because seismicity after the mainshock can be masked by overlapping arrivals of waves from the mainshock and aftershocks1 2 3 4 however recovery of the missing early aftershocks is important for understanding the physical mechanisms of earthquake triggering2 3 4 and for tracking postseismic deformation around the rupture zone associated with the mainshock5 6 7 here we use the waveforms of 3 647 relocated earthquakes8 along the parkfield section of the san andreas fault as templates9 10 to detect missing aftershocks within three days of the 2004 magnitude 6 0 parkfield earthquake we identify 11 times more aftershocks than listed in the standard catalogue of the northern california seismic network we find that the newly detected aftershocks migrate in both along strike and down dip directions with logarithmic time since the mainshock consistent with numerical simulations of the expansion of aftershocks caused by propagating afterslip11 12 the cumulative number of early aftershocks increases linearly with postseismic deformation in the first two days supporting the view that aftershocks are driven primarily by afterslip13 14

explosive lava water interactions i architecture and emplacement chronology of volcanic rootless cone groups in the 1783 1784 laki lava flow iceland to determine the relationships between rootless cone emplacement mechanisms morphology and spatial distribution we mapped the hnuta and hrossatungur groups of the 1783 1784 laki lava flow in iceland we based our facies maps on differential global positioning system dgps measurements photogeological interpretations and supporting field observations the study area covers 2 77 km2 and includes 2216 explosion sites to establish the timing of rootless cone formation we incorporated tephrochronological constraints from eighty eight stratigraphic sections and determined that the hnuta and hrossatungur groups are composite structures formed by the emplacement of six geographically and chronologically discrete domains rootless eruptions initiated in domain 1 on the first day of the laki eruption june 8 1783 and lasted 1 2 days the second episode of rootless activity began in domain 2 on june 11 and lasted 1 3 days the four domains of the hrossatungur group dominantly formed after june 14 and exhibit a complex emplacement sequence that reflects interactions between the laki lava contemporaneously emplaced rootless cones and an existing topographic ridge in the study area we identify three distinct rootless cone archetypes i e recurring morphological forms that are related to tube channel and broad sheet lobe fed eruptions we assert that emplacement of lava above compressible substrates e g unconsolidated sediments may trigger rootless eruptions by causing subsidence induced flexure and failure of the basal crust thereby allowing molten lava fuel to come into direct contact with groundwater coolant and initiating analogs to explosive molten fuel coolant interactions mfcis

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

overturning and dissipation caused by baroclinic tidal flow near the sill of a fjord basin abstract dissipation time series and moored velocity and density time series on the inner slopes of the gullmar fjord sill showed that the internal tides generated at the sill radiated to the head of the fjord were reflected and then radiated back to the sill where they dissipated their energy mainly below sill level a large amount of the dissipation was caused by a transitional flow at a particular phase of the internal tide when the bottom layer descended down the sill slope and had to pass a constriction set up by a submarine hill the inward baroclinic bottom layer flow transformed into a supercritical bottom jet which separated from the bottom just downstream of the constriction a large fraction of the dissipation took place in the successive rebounding region the hydraulic jump above the bottom jet where overturns of the same size as the vertical extent of the rebounding region were observed more than half of the dissipation was happening in the bottom boundary layer below the jet durin

deep and shallow long period volcanic seismicity linked by fluid pressure transfer volcanic long period earthquakes are attributed to pressure fluctuations that result from unsteady mass transport in the plumbing system of volcanoes whereas most of the long period seismicity is located close to the surface the volcanic deep long period earthquakes that occur in the lower crust and uppermost mantle reflect the activity in the deep parts of magmatic systems here we present observations of long period earthquakes that occurred in 2011 2012 within the klyuchevskoy volcano group in kamchatka russia we show two distinct groups of long period sources events that occurred just below the active volcanoes and deep long period events at depths of 30 km in the vicinity of a deep magmatic reservoir we report systematic increases of the long period seismicity levels prior to volcanic eruptions with the initial activation of the deep long period sources that reflects pressurization of the deep reservoir and consequent transfer of the activity towards the surface the relatively fast migration of the long period activity suggests that a hydraulic connection is maintained between deep and shallow magmatic reservoirs the reported observations provide evidence for the pre eruptive reload of the shallow magmatic reservoirs from depth and suggest that the deep long period earthquakes could be used as a reliable early precursor of eruptions shallow volcanic earthquakes can aid eruption forecasts analysis of seismicity beneath the klyuchevskoy volcano group in russia reveals much deeper magma induced earthquakes that may serve as an early eruption indicator

diapycnal mixing associated with an overflow in a deep submarine canyon abstract in order to close the global overturning circulation the buoyancy loss to the atmosphere associated with the formation of deep and bottom water at high latitudes must be balanced by buoyancy gain elsewhere in case of water that is not in contact with the atmosphere except in its formation region the required buoyancy gain is accomplished primarily by diapycnal mixing recent observations suggest that a significant portion of the diapycnal buoyancy fluxes in the abyss is associated with overflows in submarine valleys or canyons especially on the flanks of slow spreading mid ocean ridges in the present study hydrographic and velocity data from an overflow across a sill rising 1000 m above the floor of the rift valley of the mid atlantic ridge near 36 n were used to infer the associated diapycnal mixing the cross sill density gradients are characterized by a vertical dipole with an upper layer of streamwise density increase overlying a lower layer where the density decreases along the flow this is qualitatively consistent with the effects of diapycnal mixing transferring buoyancy from the upper into the lower layer hydrographic and velocity profiles provide evidence for strong mixing associated with the overflow across the sill in addition to thick layers that are susceptible to shear instability there are numerous density overturns indicating a spatially averaged diffusivity of order 10 2 m 2 s 1 inversions of the density equation reveal that the cross sill gradients can be accounted for either by adiabatic vertical advection or by vertical eddy diffusion although the adiabatic solutions are considered energetically implausible because they require upwelling in the layer of cross sill density increase eddy diffusive solutions both with and without adiabatic downwelling are characterized by diffusivity profiles attaining local maxima of order 10 2 m 2 s 1 250 m above the sill depth the vertical structure of the inversion derived diffusivities is consistent with the thorpe scale based estimates and with observations from overflows in major ocean passages which also are often characterized by local diffusivity maxima of order 10 2 m 2 s 1 a few 100 m above sill depth combining the diffusivity profiles near the sill with budget derived bulk estimates for 150 km of rift valley implies that 50 of the mixing in the rift valley is associated with overflows while the remainder is caused by other processes including the breaking of tidally forced internal waves