the mechanism of surtseyan volcanism during eruption the vent of a surtseyan volcano is occupied by a highly mobile slurry of tephra hyaloclastite and water as magma ascends rapidly through the slurry mixing occurs due to velocity shear acceleration of the fluid fluid contacts and mass incorporation consequent expansion of the admixed water causes the jetting and continuous up rush activity that characterizes surtseyan volcanism there is no evidence of the widely accepted fuel coolant interaction mechanism

underwater observations of active lava flows from kilauea volcano hawaii underwater observation of active submarine lava flows from kilauea volcano hawaii in march june 1989 revealed both pillow lava and highly channelized lava streams flowing down a steep and unconsolidated lava delta the channelized streams were 0 7 1 5 m across and moved at rates of 1 3 m s the estimated flux of a stream was 0 7 m 3 s jets of hydrothermal water and gas bubbles were associated with the volcanic activity the rapidly moving channelized lava streams represent a previously undescribed aspect of submarine volcanism

crustal shortening in the palmyride fold belt syria and implications for movement along the dead sea fault system an edited version of this paper was published in tectonics by the american geophysical union agu copyright 1990 agu see also http www agu org journals tc http atlas geo cornell edu syria chaimov tectonics 1990 html

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

the 1891 submarine eruption offshore pantelleria island sicily channel italy identification of the vent and characterization of products and eruptive style high resolution bathymetry and seafloor sampling have been used to characterize the 1891 submarine eruption of the pantelleria volcanic complex this submarine eruption has been documented mainly by historical reports describing basaltic scoria bombs floating on the sea surface i e lava balloons in this study the 1891 eruptive vent has been identified as a small cone volume of 700 000 m3 rising 90 m from 350 m w d and located within a newly discovered submarine volcanic field covering a wide area offshore from the nw coast of pantelleria recently kelly et al 2012 confirmed this location by a multibeam and rov survey pyroclasts from the 1891 eruption crop out directly on the seafloor and are fresh scoria clasts i e small bombs bomb fragments and lapilli and glass ash sized grains both have been characterized in their morphology textures and geochemistry the distinctive vesicularity and crystallization characteristics displayed by the scoriaceous pyroclasts reflect modes of degassing in both syn and posteruptive regimes these characteristics along with the distribution of deposits suggest for the strongest eruptive phase of the 1891 eruption a style analogous to hawaiian fountaining glass grains from a buoyant plume were dispersed northward from the vent up to distances of 1 5 km redirected by the levantine intermediate water the identification of the 1891 submarine eruptive vent offshore pantelleria as well as the features of erupted pyroclasts improve our knowledge of submarine explosive eruptions that occur at shallow intermediate depths and among these of the rare eruptions producing lava balloons

volatiles in alkaline magmatism abstract gases extracted during fusion of volcanic glasses substantiate other sources of evidence that alkaline magmatism is distinguished from calc alkaline by higher co2 so2 contents with relatively smaller proportions of h2o in addition to higher c and s activity alkaline magmas are characterised by high cl and f which are released with alkalis during fusion experiments in a graphic reminder that alkalis should be regarded as mobile elements in magmatism the association of c s and halogens in alkaline magmatism is well shown in some high temperature residua characterized by assemblages such as calcite vishnevite calcium is an important cation in many aspects of alkaline magmatism and the links with carbonatite further emphasize the key position of c s cl and f throughout and the subordinate role of h2o

gas rich submarine exhalations during the 1989 eruption of macdonald seamount in january 1989 we observed submarine eruptions on the summit of macdonald volcano during a french german diving programme with the ifremer submersible cyana gas streaming of large amounts of ch4 co2 and so2 from summit vents inferred from water column anomalies and observed by submersible was accompanied on the sea surface by steam bursts turbulence red glowing gases and black bubbles comprising volcanic ash sulphur and sulphides chloride depletion of water sampled on the floor of an actively degassing summit crater suggests either boiling and phase separation or additions of magmatic water vapour submersible observations in situ sampling and shipboard geophysical and hydrographic measurements show that the hydrothermal system of this hotspot volcano is distinguished by the influence of magmatic gases released from its shallow summit

the submarine eruption of the bombarda volcano milos island cyclades greece the milos volcanic field includes a well exposed volcaniclastic succession which records a long history of submarine explosive volcanism the bombarda volcano a rhyolitic monogenetic center erupted 1 7 ma at a depth 200 m below sea level the aphyric products are represented by a volcaniclastic apron up to 50 m thick and a lava dome the apron is composed of pale gray juvenile fragments and accessory lithic clasts ranging from ash to blocks the juvenile clasts are highly vesicular to non vesicular the vesicles are dominantly tube vesicles the volcaniclastic apron is made up of three fades massive to normally graded pumice lithic breccia stratified pumice lithic breccia and laminated ash with pumice blocks we interpret the apron beds to be the result of water supported volcaniclastic mass how emplacement derived directly from the collapse of a small volume subaqueous eruption column and from syn eruptive down slope resedimentation of volcaniclastic debris during this eruptive phase the activity could have involved a complex combination of phreatomagmatic explosions and minor submarine effusion the lava dome emplaced later in the source area is made up of flow banded lava and separated from the apron by an obsidian carapace a few meters thick the near vertical orientation of the carapace suggests that the dome was intruded within the apron remobilization of pyroclastic debris could have been triggered by seismic activity and the lava dome emplacement

subaqueous eruption and emplacement of ot2 in the middle miocene iizuka formation noto peninsula japan abstract ot2 okada tuff 2 is one of six rhyolitic tuff beds that occur in a middle miocene marine diatomite lower iizuka formation and are known as the okada tuff ot2 is well sorted and thins and thickens infilling channels 1 3 m across and 0 30 cm deep with a thickness up to 30 cm small channels 10 30 cm across and 1 10 cm deep are commonly superimposed within wider channels a thin diatomite layer is ripped from the substrate up to a level immediately above the small channels the basal part beneath the ripped up diatomite layer is dominated by ash components with vague wavy stratifications above the ripped up diatomite layer diatomite clasts are dispersed and pumice lapilli increase upward in amount and size with local interruption at a middle lower level by a poorly defined pumice lapilli poor thin layer many glass and pumice shards are blocky with curviplanar surfaces and jigsaw cracks presumably produced by phreatomagmatic explosions the poorly defined two layers of ot2 are interpreted to be ash turbidites individually produced by discrete phreatomagmatic explosions lenticular bedforms and channels indicate that the currents were fully turbulent and unsteady fed by the submarine eruptions upward coarsening of pumice probably represents settling lag of hot pumice ot2 perhaps provides potential diagnostic features to identify eruption fed turbidites

northern east pacific rise evolution from 25 m y b p to the present the northeast pacific topography and magnetic lineations 25 m y b p to the present record the traces of three major spreading reorganizations only one spreading center is observed today but there is evidence for several ephemeral episodes of twin spreading accompanying the evolution from an extensive pacific guadalupe plate boundary to a much shortened pacific cocos and pacific rivera plate boundary the 25 m y b p plate reorganization culminated with the formation of the guadalupe plate bound by the murray fracture zone to the north and the cocos nazca spreading ridge to the south between 25 and 12 5 m y b p spreading continued while the plate retained the same general outline the 12 5 11 m y b p reorganization resulted in the creation of a much shortened pacific cocos plate boundary located in its early stages over the mathematician seamounts and a much reduced cocos plate the last reorganizaton 6 5 3 5 m y b p resulted in the abandonment of the mathematician spreading ridge as a pacific cocos plate boundary in favor of the east pacific rise

the 2011 2012 submarine eruption off el hierro canary islands new lessons in oceanic island growth and volcanic crisis management forty years after the eruption of the teneguia volcano on la palma 1971 the last volcanic event in the canary islands a submarine eruption took place in 2011 off shore el hierro the smallest an

asymmetry and basin migration in the dead sea rift the dead sea depression sensu stricto forms the deepest continental part of the dead sea rift a transfer which separates the levanthine and arabian plates it is occupied by three distinct sedimentary bodies deposited in basins whose depocenters are displaced northward with time they are the continental red beds of the hazeva formation miocene the bira lido gesher marls and the exceptionally thick rocksalt of the sedom formation pliocene early pleistocene and the successive amora lisan and dead sea evaporites and clastics early pleistocene recent lengthwise and crosswise asymmetries of these sedimentary basins and their respective depocenters are due to leftlateral shear combined with anticlockwise rotation of the arabian eastern plate steeper faulting of the crustal eastern margin than of the western sedimentary margin and modification of depositional pattern by twice filling up of basins by hazeva red beds during late miocene pause of shear and by sedom rocksalt during pliocene marine ingression

the concentration of co_ 2 in submarine tholeiitic basalts the concentrations of co 2 and h 2 o in glass separates from submarine tholeiitic basalts have been determined the presence of vesicles in samples precludes accurate determination of the co 2 concentration in glass unless steps are taken to analyze only uncontaminated vesicle free glass special care has been exercised during sample preparation to avoid these problems a new analytical technique for micro determination of h 2 o and co 2 has been applied to five mid ocean ridge and two kilauea submarine east rift zone basalts quenched at pressures as great as 0 5 kb the uncertainty of quenching pressure due to flow of lava subsequent to surface quenching global sea level variations and local deformation of the sea floor are discussed non tectonic uncertainties of quenching pressure have been estimated the concentration of co 2 in glass separates from submarine tholeiitic basalts increases linearly with quenching pressure the apparent solubility of co 2 in tholeiitic basalts

volcanosedimentary paleoenvironments of ediacaran fossils in newfoundland a new perspective on paleoenvironments of ediacaran fossils of the upper conception group newfoundland comes from geochemical and sedimentological study of volcanic tuffs and sedimentary rocks tuffs in the conception group have major and trace element compositions and u pb ages comparable with those of source volcanics on the nearby burin and bonavista peninsulas and the islands of st pierre and miquelon loss of silica and alkalies in some ashes indicates weathering on land not marine diagenesis volcanic crystal and lapilli tuffs fail to show grading and have lapilli and highly vesicular scoria scattered in a fine grained matrix and so they were deposited on land not in water these as well as block and ash flows volcanic spindle bombs and degassing features are evidence of eruptions from nearby subaerial volcanic edifices the fossiliferous conception group accumulated within a forearc basin formed on continental crust inboard of the holyrood horst and uplifted as part of an ancient subduction complex or accreted terrane like analogous forearc basins in oregon washington southern chile and japan the conception group includes not only marine bay turbidites but also a variety of intertidal and terrestrial tsunamites seismites tempestites and paleosols traditional marine turbidite models explain deposition of the mall bay lower drook and lower briscal formations of the conception group but the gaskiers upper drook upper briscal and mistaken point formations were deposited in coastal plains and intertidal zones paleoenvironments of vendobiont fossils preserved in life position in newfoundland were terrestrial to marginal marine not deep sea

syn and post fragmentation textures in submarine pyroclasts from lō ihi seamount hawai i abstract the extent and timing of vesiculation and microlite formation in ascending basaltic melts are relatively well understood for subaerial eruptions but they have not been studied thoroughly for submarine eruptions this is largely due to a lack of samples of appropriate volume and grain size we present a quantitative textural evaluation of coarse lapilli from two cone forming deposits at 1 km depth on l ihi seamount hawai i collected during a sampling intensive submersible dive series in 2006 lapilli from the deposits named the northern and southern cones have modal bulk vesicularities of 55 and 42 respectively and vesicle populations dominated by sub spherical non interconnected vesicles with number densities on the order of 10 4 to 10 5 cm 3 clasts of modal vesicularity have margin parallel zonation with seawater quenched rims interpreted to preserve syn fragmentation magmatic textures in microlite free sideromelane glass enclosing post fragmentation tachylitic interiors with vesicle and microlite textures that progressively coarsen from rim to core degassing scenarios are linked to syn fragmentation vesicle textures to demonstrate that both magmas degassed in dominantly closed systems diffusion controlled cooling rates of basaltic pyroclasts in contact with water are linked to post fragmentation evolution of vesicle and microlite textures to make inferences about transportation and dispersal of the pyroclasts in low submarine jets the textural analysis shows that the northern and southern cone eruptions were not strictly analogous to any classical subaerial eruption type they were uniquely submarine with ambient seawater playing a crucial role in the processes of degassing vesiculation crystallization and dispersal

cone morphologies associated with shallow marine eruptions east pico island azores eruptions in shallow water typically produce cones of volcaniclastic material in order to identify any systematic effects of water depth and other environmental parameters on cone morphology we have measured the heights and widths of cones in multibeam echo sounder data from a submarine ridge extending southeast from pico island azores xrf analyses of dredged samples show that lavas here vary compositionally from alkali basalt to trachybasalt and trachyandesite cones in deeper water are generally steep sided with upper flanks close to 30 the dip of talus at the angle of repose however height width ratios of cones vary more in shallow water 200 400 m summit depth with extreme values below 0 1 while some shallow water cones are steep sided as in deep water others are much flatter three such cones lie on a bench at 300 m depth immediately east of pico island and have flank slopes of only 10 20 we speculate that exceptionally shallow cone slopes here were produced by forced spreading of the erupting columns on reaching the water air density barrier

prolonged history of silicic peralkaline volcanism in the eastern pacific ocean socorro island mexico is an alkaline and peralkaline volcanic island located in the eastern pacific ocean on a mid ocean ridge spreading center that was abandoned at 3 5 ma silicic peralkaline rocks comprise up to 80 of the surface of the island rendering socorro virtually unique in the pacific ocean precise replicate 40ar 39ar ages of 21 peralkaline trachytes and rhyolites reveal a history of episodic volcanic activity from 540 to 370 ka that may have culminated with caldera formation repose periods between these episodes may have had maximum duration of 30 kyr after up to 200 kyr of quiescence 40ar 39ar ages indicate that postcaldera silicic peralkaline activity commenced by 180 ka forming the cerro evermann formation postcaldera mafic alkaline lavas of the lomas coloradas formation erupted dominantly between 70 and 150 ka based upon relative age relations the dominant lithology of precaldera and syncaldera silicic peralkaline deposits on socorro is nonfragmental and nonvesicular and lacks lithic fragments and fiamme despite this numerous lines of evidence including welding zonation presence of a proximal ignimbrite or co ignimbrite deposit association with a caldera and compositional heterogeneity within eruptive units suggest that they are dominantly ash flow tuffs a change in eruptive style from predominantly explosive to predominantly effusive followed caldera formation and suggests that a change in the efficacy of magma degassing may be linked to caldera formation on the basis of the presence of a caldera the magma chamber associated with socorro island is shallow and probably resides within the upper oceanic crust or the edifice this together with a prolonged history of silicic magmatism indicates that intrusion of mafic magma maintained thermal viability of the magmatic plumbing system the minimum calculated growth rate for the entire volcanic edifice 7 10 4 km3 yr exceeds those of nonhotspot off axis volcanoes in the pacific by almost an order of magnitude eruption rates for subaerial phases on socorro may be several orders of magnitude smaller than this growth rate and are comparable to subaerial eruption rates of isolated ocean islands related to mantle plumes

petrologic evolution of large failed rifts in the eastern pacific petrology of volcanic and plutonic rocks from the mathematician ridge area and the guadalupe trough

northern east pacific rise magnetic anomaly and bathymetric framework the oceanic crust in the eastern pacific between 7on and 30on and east of 127ow contains a fairly complete history of the spreading centers associated with the east pacific rise since 25 m y b p late oligocene in this paper we have summarized the seafloor spreading magnetic anomaly data and the bathymetric data that reflect the record of this tectonic history the well defined magnetic lineations north of the clarion fracture zone in the mouth of the gulf of california and on the east flank of the east pacific rise epr are carefully examined and used to provide a guide for interpreting the spreading pattern between the clarion and clipperton fracture zones southward of the rivera fracture zone over the mathematician ridge and over the entire epr east of the mathematician ridge between the rivera and siqueiros fracture zones the bathymetric data provide a trace of the fracture zone pattern in each of the above mentioned areas the fracture zone bathymetry and the seafloor spreading magnetic lineations on the epr south of the rivera fracture zone have a distinctive fanning pattern caused by close poles of rotation and plate boundary reorganizations all these data provide a good record of the plate reorganizations in the middle miocene at magnetic anomaly 5a time 12 5 to 11 m y b p in the late miocene at magnetic anomaly 3 4 time 6 5 m y b p and in the pliocene at magnetic anomaly 2 3 time 3 5 m y b p several abandoned spreading centers including the mathematician ridge were left behind as a result of these reorganizations the mathematician ridge is shown to be a set of ridges and trough whose origin is related to the tectonic activity associated with each of the above mentioned reorganizations since anomaly 5a

the 1759 earthquake in the bekaa valley implications for earthquake hazard assessment in the eastern mediterranean region analysis of macroseismic data based on primary sources for large though infrequent historical earthquakes ms 6 5 that occurred along an approximately 350 km long segment of the northern part of the dead sea fault system primarily in lebanon and syria for the period 1100 1988 reveals the following 1 ten events occurred in three relatively short periods tens of years with repeat times of 200 350 years 2 the events most probably broke this north segment of the dead sea fault system possibly including the westernmost segment of the east anatolian fault system near the border between syria and turkey 3 the lack of such large events during the past 100 years should not be interpreted to minimize potential earthquake hazard in this region and 4 the ms 7 plus earthquake on november 25 1759 almost certainly produced surface faulting probably along the yammouneh fault in the bekaa valley and caused heavy destruction with great loss of life in numerous villages and towns including safad damascus beirut and baalbek this main event was preceded by a ms 6 plus foreshock on october 30 1759 in the southern part of the epicentral area of the main shock near the towns of safad and qunaitra which were almost totally destroyed with considerable loss of life

source fault of 19 august 1966 varto earthquake and its mechanism new field data eastern turkey abstract 19 august 1966 varto earthquake ms 6 8 io ix was sourced from varto fault zone vfz that caused 2529 deaths in the varto region just after the occurrence of the event some researchers have different ideas related to the source fault and mechanism of the earthquake the varto fault zone is a major nw se trending tectonic feature in eastern turkey new geological mapping and description of structures have been used to constrain the geometry surface deformations and geological history of the fault zone according to this extensive research the vfz consists of left lateral strike slip faults with minor amount of reverse component and has been divided into three fault segments varto leylekdag and caycati regarding as geological and morphological characteristics hence palaeostress configurations of the segments are reliable with the regional n s compression direction lastly the varto segment northern branch of vfz has been defined as the source of 19 august 1966 varto earthquake

the structural relationship between the east anatolian and dead sea fault zones in southeastern turkey abstract the complex structural relationship between the east anatolian and dead sea fault zones is examined mostly based on field observations in southeastern turkey where the two fault zones are close together several faults previously poorly documented can be traced to connect either to the east anatolian fault zone or to the dead sea fault zone one of these faults connects the dead sea fault zone to the east to the amanos fault to the west the amanos fault a n trending normal fault is a part of the east anatolian fault zone since it is apparently a left step fault between the main and southern strands of the east anatolian fault zone the dead sea fault zone also is connected to the east anatolian fault zone northeast of the town of narli and or northeast of the hazar lake therefore we suggest that the two fault zones can be considered as one broad fault system in southeastern turkey although they are well recognized as two different fault zones this fault system is responsible for several complex neogene structural features of the western part of the southeastern turkey one of these is the hatay graben which can be divided into southern central and northern parts the graben contains down to the west normal faults in its southern part the central part of the graben is a divergent strike slip basin and the northern part is a half graben

new field and laboratory evidence for the origin of hyaloclastite flows on seamount summits new field observations with the submersible alvin and photographic evidence from a study of the summits of seamounts near the east pacific rise show that hyaloclastite deposits occur commonly hyaloclastite outcrops were found on six volcanoes at depths from 1240 to 2500 m these new observations plus laboratory study of new hyaloclastite specimens extend the results of previous studies most of the hyaloclastite samples are of hydrovolcanic eruptive origin but a few show evidence of a predominantly sedimentary origin primarily from morphology we identify several vent areas from which hyaloclastite presumably erupted the surface appearance of the hyaloclastite deposits varies with distance to these vents leading us to propose a facies model for deep sea hyaloclastites on seamount summits hyaloclastites of hydromagmatic origin exhibit weak normal grading and bedding parallel alignment of platy shards they consist of blocky sliver and fluidal basalt glass shards and lithics in a matrix that contains pelagic sediment the shards themselves are remarkably free of even the tiniest crystals and are usually chemically homogeneous we propose that the shards form mainly by cooling contraction granulation but cannot rule out the possibility of limited steam explosivity hyaloclastites are closely associated with submarine pahoehoe and we propose that a very rapid eruption rate promoting clastic dominated versus flow dominated eruptive behavior is the dominant control on hyaloclastite formation we propose that shard formation occurs during submarine lava fountaining gravitational instability of the resulting slurry of shards sea water and possibly steam causes gravity flow that carries the shards outward from the vent further field and modelling studies are needed to test these ideas and more quantitatively constrain the ascent mechanism eruption dynamics and deposition of deep sea hyaloclastites

sea level changes from topex poseidon altimetry and tide gauges and vertical crustal motions from doris sea level difference topex poseidon minus tide gauge time series have been computed over 1993 1997 at 53 selected gauges sites comparison of these sea level differences with vertical crustal motions derived from the doris space geodesy system at 6 colocated sites shows good consistency at one site the socorro volcanic island a striking correlation is reported between sea level differences and doris height time series the observed trend likely reflects a post eruptive deformation associated with a volcanic eruption that occurred in early 1993 at several other gauge sites the sea level differences present large linear trends possibly bearing evidence of land motion this may be the case at rabaul papua new guinea where a volcanic eruption took place in autumn of 1994 the sea level differences at rabaul show a negative trend from this date likely related to the volcanic event

dynamics of degassing at kilauea volcano hawaii at kilauea volcano hawaii the recent long lived eruptions of mauna ulu and pu u o o have occurred in two major stages defining a characteristic eruptive pattern the first stage consists of cyclic changes of activity between episodes of fire fountaining and periods of quiescence or effusion of vesicular lava the second stage consists only of continuous effusion of lava we suggest that these features reflect the dynamics of magma degassing in a chamber which empties into a narrow conduit in the volcano chamber gas bubbles rise through magma and accumulate at the roof in a foam layer the foam flows toward the conduit and its shape is determined by a dynamic balance between the input of bubbles from below and the output into the conduit the foam thickness is proportional to lq e2 l g 1 4 where l and l are the viscosity and density of magma e is the gas volume fraction in the foam g is the acceleration of gravity and q is the gas flux the bubbles in the foam deform under the action of buoyancy and the maximum permissible foam thickness is hc 2 e lgr where is the coefficient of surface tension and r is the original bubble radius if this critical thickness is reached the foam collapses into a large gas pocket which erupts into the conduit foam accumulation then resumes and a new cycle begins the attainment of the foam collapse threshold requires a gas flux in excess of a critical value which depends on viscosity surface tension and bubble size hence two different eruption regimes are predicted 1 alternating regimes of foam buildup and collapse leading to the periodic eruption of large gas volumes and 2 steady foam flow at the roof leading to continuous bubbly flow in the conduit the essential result is that the continuous process of degassing can lead to discontinuous eruptive behavior data on eruption rates and repose times between fountaining phases from the 1969 mauna uiu and the 1983 1986 pu u o o eruptions yield constraints on three key variables the area of the chamber roof must be a few tens of square kilometers with a minimum value of about 8 km2 magma reservoirs of similar dimensions are imaged by seismic attenuation tomography below the east rift zone close to the roof the gas volume fraction is a few percent and the gas bubbles have diameters lying between 0 1 and 0 6 mm these estimates are close to the predictions of models for bubble nucleation and growth in basaltic melts as well as to the observations on deep submarine basalts the transition between cyclic and continuous activity occurs when the mass flux of gas becomes lower than a critical value of the order of 103 kg s in this model changes of eruptive regime reflect changes in the amount and size of bubbles which reach the chamber roof

the structure of basaltic scoria and reticulite and inferences for vesiculation foam formation and fragmentation in lava fountains in this investigation pyroclast structures are used to constrain degassing in basaltic lava fountains vesicle size shape number density interconnectedness and packing character are quantified and related to 1 the kinetics of bubble nucleation and growth 2 the structural evolution of magmatic foams and 3 the influence of vesiculation rate on magma fragmentation measurements made on a diverse suite of pyroclasts from kilauea volcano indicate that basaltic foams evolve through an initially disordered closed celled spherical state to a well ordered open celled polyhedral state as the vesicularity rises from 75 to 98 the structural changes occur rapidly 10 s in the conduit and fountain in response to an intense vesiculation burst vesicle size distribution systematics indicate bubble nucleation rates 2 104 events cm 3s 1 that are approximately three orders of magnitude greater than those found for effusive eruptive activity bubble growth rates 9 10 4 cm s exceed effusive estimates by a factor of 3 the observed runaway rate of bubble production indicates strong supersaturations at the onset of nucleation we speculate that the rise speed of the magma as it reaches the level where significant volatile exsolution begins determines the intensity of the vesiculation burst and hence the vigor of the eruption rapid expansion and acceleration of the magma under these conditions may provide the impetus for fragmentation

multimodal method for coseismic landslide hazard assessment abstract regional scale coseismic landslide hazard assessments have traditionally been based on infinite slope analyses considering only a single mode of failure inventories and landslide reconnaissance work have shown a diverse range of coseismic landslide modes with significantly different consequences of failure this paper presents a multimodal approach for regional scale coseismic landslide hazard assessment through a two step procedure the multimodal method explicitly accounts for four general landslide types commonly observed during earthquakes rock slope failures disrupted soil slides coherent rotational slides and lateral spreads first the susceptibility to each landslide mode is evaluated based on topography second coseismic landslide hazards are assessed using mode specific geotechnical models a trial multimodal landslide assessment is presented for the seismically active country of lebanon results show that the computed coseismic landslide hazard closely matches field verified slope activity across different regions of the country exhibiting a range of failure modes these results qualitatively demonstrate the efficacy of the procedure and suggest that multimodal coseismic landslide hazard analysis is especially well suited for regions with varying terrain and where landslide inventories are not available

tectonic isolation of the levant basin offshore galilee lebanon effects of the dead sea fault plate boundary on the levant continental margin eastern mediterranean abstract the continental margin of the central levant offshore northern israel and southern lebanon is characterized by a sharp continental oceanic crustal transition exhibited on the bathymetry as a steep continental slope at the base of the slope a narrow zone of faulting deforms the upper messinian recent sedimentary sequence further into the basin no major deformations are observed however onland a restraining bend along the dead sea fault plate boundary results in the formation of the lebanon and anti lebanon mountain ranges which exhibit a large positive isostatic anomaly not compensated at depth all these geologic features follow a nne ssw trend a dense network of multi channel and single channel seismic profiles covering 5000 km of ship track offshore northern israel and southern lebanon was analyzed for the purpose of characterizing the continental margin additional seismic surveys covering the area between the levant margin and the cyprean arc were examined data were then incorporated with magnetic gravity and earthquake measurements to reveal the deep crustal structure of the area and integrated with bathymetry data to describe the behavior of the young sedimentary basin fill results indicate that the levant basin offshore northern israel and southern lebanon up to beirut is more or less unaffected by the intense tectonic deformation occurring onland the transition between the deformed area onland and the undeformed levant basin occurs along the base of the continental slope along the base the upper messinian recent sedimentary sequence is cut by two sets of faults shallow growth faults resulting from salt tectonics and high angle faults marking the surface expression of a deeper crustal discontinuity the marine extension of the carmel fault zone the central levant continental margin is being reactivated by transpressional faulting of the marine continuation of the carmel fault at the base of the continental slope this fault system coincides with the sharp continental oceanic crustal transition and acts as an isolator between the levant basin and its land counterpart to the north this feature may initiate the formation of a new triple junction with the latakia ridge part of the eastern cyprean arc and the east anatolian fault

kinematic consistency between the dead sea fault zone and the neogene and quaternary left lateral faulting in se turkey a revised quantitative kinematic model has been determined for the dead sea fault zone dsfz and the left lateral fault zones in se turkey the relative motions of the african and arabian plates across the dsfz are represented by relative rotation about 31 1 n 26 7 e at 0 40 0 02 ma 1 the northern dsfz in syria and southern turkey is interpreted for the first time as a series of transpressional stepovers along which the left lateral slip rate is substantially less than the rate of relative plate motion because this slip is oblique to the plate motion the slip rate on the east anatolian fault zone eafz is estimated as 8 mm a 1 restoring its observed slip thus requires its age to be 4 ma the previous phase of deformation which involved slip on the malatya ovacik fault zone mofz before the eafz came into being is thus dated to 7 4 ma suggesting initiation of the north anatolian fault zone nafz at 7 ma not 5 ma as previously thought the total left lateral slip on the northern dsfz in southernmost turkey is estimated as at least 65 km partitioned with 45 km on the amanos fault 10 km on the east hatay fault and a further 10 km on the kirkpinar fault farther east much of this slip is inferred to have occurred during the miocene before the modern geometry of this plate boundary zone developed when it first formed the af ar plate boundary was relatively complex it initially reactivated preexisting structures in the palmyra foldbelt in syria and in the gaziantep region of southern turkey which were significantly misaligned relative to the plate motion requiring major components of shortening as well as left lateral slip the transition from this initial rather diffuse geometry to the present localised geometry of the dsfz across western syria occurred within the miocene the predicted rate of relative motion between the stable interiors of the turkish and african plates in the vicinity of their common boundary onshore of iskenderun gulf in southern turkey is estimated as westward at 9 mm a 1 however this promontory of the african plate is itself moving westward relative to the stable interior of this plate at 7 8 mm a 1 the rate of localised left lateral slip on the onshore part of this boundary the ne trending yakapinar goksun fault is thus estimated as only 2 mm a 1 this locality can also be regarded as within the distributed boundary zone between the turkish and arabian plates the estimated relative motion between these plates is at 8 7 mm a 1 towards the ssw partitioned between localised left lateral slip at 2 mm a 1 on the yakapinar goksun fault and at least 1 mm a 1 on the amanos fault and 2 5 mm a 1 on east hatay fault with at most distributed left lateral simple shear at 3 2 mm a 1 across the amanos mountains in between however the combined slip on left lateral faults east of the amanos mountains may be as high as 6 mm a 1 with slip at 1 7 mm a 1 on the amanos fault and at 4 3 mm a 1 on the east hatay fault and any active faults farther east this requires no more than 0 7 mm a 1 of distributed simple shear across the amanos mountains raising the possibility that this component of deformation may in fact be zero this small nonzero estimate possibly indicating a closure error arising from minor errors in predicted values of other relative motion vectors it is proposed that this boundary between the turkish and african plates first developed at the same time as the mofz and nafz but its original geometry involving left lateral slip on the karatas osmaniye fault has since become locked by the presence of relatively strong ophiolitic crust within this fault zone this quantitative kinematic model demonstrates for the first time how it is possible for the left lateral faulting accommodating the nnw sse relative motion between the arabian and african plates in nw syria to dovetail into the left lateral faulting accommodating the wsw ene relative motion between the turkish and arabian plates in se turkey

evolution of submarine eruptive activity during the 2011 2012 el hierro event as documented by hydroacoustic images and remotely operated vehicle observations submarine volcanic eruptions are frequent and important events yet they are rarely observed here we relate bathymetric and hydroacoustic images from the 2011 to 2012 el hierro eruption with surface observations and deposits imaged and sampled by rov as a result of the shallow submarine eruption a new volcano named tagoro grew from 375 to 89 m depth the eruption consisted of two main phases of edifice construction intercalated with collapse events hydroacoustic images show that the eruptions ranged from explosive to effusive with variable plume types and resulting deposits even over short time intervals at the base of the edifice rov observations show large accumulations of lava balloons changing in size and type downslope coinciding with the area where floating lava balloon fallout was observed peaks in eruption intensity during explosive phases generated vigorous bubbling at the surface extensive ash vesicular lapilli and formed high density currents which together with periods of edifice gravitational collapse produced extensive deep volcaniclastic aprons secondary cones developed in the last stages and show evidence for effusive activity with lava ponds and lava flows that cover deposits of stacked lava balloons chaotic masses of heterometric boulders around the summit of the principal cone are related to progressive sealing of the vent with decreasing or variable magma supply hornitos represent the final eruptive activity with hydrothermal alteration and bacterial mats at the summit our study documents the distinct evolution of a submarine volcano and highlights the range of deposit types that may form and be rapidly destroyed in such eruptions

active faulting in the dead sea rift abstract manifestations of late quaternary and holocene faulting were studied in a 500 km long segment of the dead sea transform rift most prominent are left slip faults whose characteristic physiographic features are recognizable along most of the studied segment where these faults bend or are stepped to the left rhomb shaped grabens or pull aparts are produced forming depressions in the reverse situation compressional features such as pressure ridges domes and folds form positive topographic features such structures are combined on a variety of scales ranging from a few hundred meters long to tens of kilometers normal faults sub parallel to the left slip faults produce a trough like valley along much of the dead sea transform but are most prominent along the margins of the large rhomb grabens e g the dead sea trough they apparently record a small component of transverse extension generally their motion is slow young slip did not occur along some segments during the last few 10 4 y elsewhere throws of 10 20 m at least occurred in this period the dead sea transform is seismically active the instrumental and historic records indicate a seismic slip rate of 0 15 0 35 cm y during the last 1000 1500 y while estimates of the average pliocene pleistocene rate are 0 7 1 0 cm y either much creep takes place or the slip rate varies over periods of a few 10 3 y

potential volcanological applications of the doris system a geodetic study of the socorro island mexico coordinate time series summary we analysed doris data from socorro island mexico providing weekly coordinates in itrf2000 from 1900 to 2006 careful analysis of this time series shows horizontal and vertical movements related to recent activity of the mt evermannn volcano a deflation of the volcano between 1993 and 1996 94 mm yr 1 in the n23 w direction directly pointing in the direction of the crater summit is observed we identify also a clear horizontal discontinuity of 81 mm and a significant change in velocity on 2002 october 3 we use a mogi formalism to provide constraints from our geodetic results on the successive locations and size of the depletion and inflation sources our model is consistent with a deflation source for the period 1993 1996 located beneath mt evermannn at a depth of about 6 2 km below sea level however our data constrain only the azimuth and dip angles of the source which could be located elsewhere along the azimuth of the summit depth and volume varying linearly with the distance

cosmogenic nuclides topography and the spatial variation of soil depth abstract if the rate of bedrock conversion to a mobile layer of soil depends on the local thickness of soil then hillslopes on uniform bedrock in a landscape approaching dynamic equilibrium should be mantled by a uniform thickness of soil conversely if the depth of soil varies across an actively eroding landscape then rates of soil production will also vary and consequently the landscape will not be in morphologic equilibrium the slow evolution of hillslopes relative to the tempo of climatic variations and tectonic adjustments would suggest that local morphologic disequilibrium may be expected in many landscapes here we explore this issue of equilibrium landscapes through a previously developed model that predicts the spatial variation in thickness of soil as a consequence of the local balance between soil production and erosion first we confirm the assumption in the model that soil production varies inversely with the thickness of soil using two independent methods one method uses the theoretical prediction that at local steady state soil production equals removal the depth of soil should vary inversely with hillslope curvature the second method relies on direct measurements of in situ produced concentrations of cosmogenic 10 be and 26 al in bedrock at the base of the soil column for our study site in northern california the two methods agree and yield the expression that the rate of soil production declines exponentially with the thickness of soil from 0 077 mm year with no soil mantle to 0 0077 mm year under 1 m of soil we then use this function of soil production in a coupled production and diffusive model of sediment transport to explore the controls on the spatial variation of the depth of soil on four separate spur ridges noses where we measured the data for the function of soil production model predictions are sensitive to boundary conditions grid scale and run time nonetheless we found good agreement between predicted and observed depths of soil as long as we used the observed function of soil production the four noses each have spatially varying curvature and consequently have varying depths of soil implying morphologic disequilibrium we suggest that our study site has been subjected to a wave of incision and varying intensities of erosion because of tectonic and climatic oscillations that have a frequency shorter than the morphologic response time of the landscape

some outstanding issues in the geology of lebanon and their importance in the tectonic evolution of the levantine region abstract the concept of pervasive and disruptive late neogene quaternary strike slip tectonics in lebanon has made establishing a satisfactory pre neogene palaeogeographic and palaeotectonic history for the area difficult research has allowed clarification of three fundamental issues that permit the setting of lebanon against its adjacent regions to be more firmly assigned the first issue is the identification of the significance of the 100 km long nne ssw trending monocline of the western lebanon flexure this feature is interpreted as a modified and rejuvenated early mesozoic hinge line that is presumed to be the northern continuation of the carmel sinai hinge line to the south the second issue is the correlation of the mount lebanon bekaa and anti lebanon complex with the adjacent intracontinental palmyride fold belt of syria through recognition in each of common divisions in structural style between a higher northern zone dominated by broadly spaced box folds and a lower southern zone with more numerous closely spaced and more internally complex folds the third issue involves the identification of major two stage late cretaceous to palaeogene syrian arc tectonism within lebanon resolution of these issues suggests a tectonic model for the region whereby the levantine region formed in two main phases the first of these was the multiphase late palaeozoic early mesozoic rifting of the area which imposed a fundamental extensional fabric over much of the region the second tectonic phase was the subsequent inversion of these extensional structures in the two stage syrian arc deformation of senonian and late palaeogene age which gave rise to the main lebanon structures it is this syrian arc tectonism rather than the late cenozoic strike slip that was probably the main structuring agent which affected the lebanon area the transpression from the braided dead sea fault motion although locally complex is an essentially neotectonic overprint on an already existing fabric offset of syrian arc structures in lebanon suggests that the total sinistral motion of the yammouneh fault segment of the dead sea fault is around 47 km

highly vesicular pumice generated by buoyant detachment of magma in subaqueous volcanism many submarine caldera volcanoes are blanketed with deposits of highly vesicular pumice typically attributed to vigorous explosive activity1 2 3 4 however it is challenging to relate volcanic products to specific eruptive styles in submarine volcanism5 6 here we document vesicularity and textural characteristics of pumice clasts dredged from the submarine macauley volcano in the kermadec arc southwest pacific ocean we find that clasts show a bimodal distribution with corresponding differences in vesicle abundances and shapes specifically we find a sharp mode at 91 vesicularity and a broad mode at 65 80 subordinate clasts show gradients in vesicularity we attribute the bimodality to a previously undocumented eruptive style that is neither effusive nor explosive the eruption rate is insufficient to cause magma to fragment explosively yet too high to passively feed a lava dome instead the magma foam buoyantly detaches at the vent and rises as discrete magma parcels or blebs while continuing to vesiculate internally the blebs are widely distributed by ocean currents before they disintegrate or become waterlogged this disintegration creates individual clasts from interior and rim fragments yielding the bimodal vesicularity characteristics we conclude that the generation and widespread dispersal of highly vesicular pumice in the marine environment does not require highly explosive activity

lava balloons peculiar products of basaltic submarine eruptions between december 1998 and april 2001 a submarine basaltic eruption occurred west of terceira island azores portugal in water depths between 300 and 1 000 m physical evidence for the eruption was provided by the periodic occurrence of hot lava balloons floating on the sea surface the balloons consisted of a large gas filled cavity surrounded by a thin shell a few centimetres thick the shells of the collected balloons are composed of two layers termed the outer layer and the inner layer defined by different bubble number density bubble sizes and crystal content the inner layer is further divided into three sublayers defined by more subtle differences in vesicularity the outer layer is glassy golden coloured and highly porous it shows signs of fluidal deformation and late stage extension cracks interstitial glass contains 0 29 wt h2o and co2 is below detection melt inclusions contain up to 1 18 wt h2o and 1 500 ppm co2 from different inclusions cooling rates of the outermost glass of the outer layer are found to be as high as 1 259 k s during ascent of low viscosity magma to the ocean floor volatiles dominated by co2 exsolved from the magma melt crystals the buoyancy of the vapour phase that accumulated below a thin crust on lava ponded at the vent caused bulging and ultimately cracking of the crust this allowed large bubbles central cavity surrounded by a film of vesicular magma balloon shell to leak into the water column on contact with the seawater the outermost part of the outer layer of the shell hyperquenched if an entirely closed shell was produced during detachment the trapped gas inside allowed buoyant rise only balloons with the right balance of physical properties e g size and bulk density rose all the way to the sea surface

the submarine eruption and erosion of surtla surtsey iceland abstract surtla is the site of a short lived submarine vent which built basaltic elastic deposits almost to sea level in 1963 early in the eruption of surtsey since then wave and current activity have eroded the volcanic pile such that in july 1981 its top was a fairly level plateau 45 m below sea level and its surface comprised a lag deposit of sparse blocks of lava in a bed mainly of glass granules this winnowed layer was underlain by a nonreworked poorly sorted and finer deposit of glassy clasts formed by a combination of disruption by magmatic volatiles steam explosions and quench brecciation during the eruption the explosion violence and associated comminution increased as the pile built up to shallower water depths it is argued that at times of continuous effusion a cupola of steam was situated over the vent as indicated by scoriaceous spatter which shows agglutination and bread crust features that can only have developed in conditions more akin to subaerial than hitherto envisaged in a subaqueous eruption

trace elements in anorthite megacrysts from the kurile island arc a window to across arc geochemical variations in magma compositions abstract anorthite megacrysts from twelve volcanic centers of the kurile island arc were analyzed by the ion microprobe for concentrations of li be b f mg p cl k ti fe co rb sr y zr nb cs ba la ce pr nd sm eu and pb these 1 2 cm megacrysts are mainly found as early phenocrysts in basalts but are also present in andesites rhyolites and hybrid rocks from almost every studied volcanic center both subaerial and submarine electron and ion microprobe studies show that the cores of these megacrysts are homogeneous and unzoned whereas rims often result from overgrowth of sodium richer plagioclase in equilibrium with its host silica richer melt the cores of these megacrysts can be used to see back through fractional crystallization and magma mixing and serve as a window into an earlier basaltic stage of magmatic evolution petrological observations and numerical crystallization modeling indicate that highly anorthitic plagioclase is the first or second after olivine liquidus phase in high al basalts regardless of varying k2o contents across the arc given the narrow compositional range of anorthite megacrysts the across arc chemical variations are well displayed by direct comparison of trace element concentrations in the megacrysts across the arc the concentration of k in megacrysts increases linearly by a factor of 11 ba 13 sr eu 4 be ti p 3 li 2 ree 5 2 whereas concentrations of pb b and halogens and their ratios to hfse either remain constant or decrease with deepening of the benioff zone from 110 to 220 km we used ion microprobe derived plagioclase basalt partition coefficients to convert trace element concentrations in megacrysts to parental magmatic values the reconstructed concentrations of several key trace elements and their correlation with benioff zone depth are consistent with whole rock basalt data but all give systematically more primitive compositions therefore anorthite megacrysts are helpful for retrieving the chemistry of parental basalts which have subsequently suffered variable differentiation and mixing they can be used to assess delicate variations in primary basaltic magma chemistry as a function of benioff zone depth we also report new results for sr nd and pb isotopes for anorthite bearing rocks and other rocks from the same volcanoes across arc zoning with respect to trace element concentrations ratios and isotopic values is largely linear and requires superposition of several petrogenetic processes trace element transfer by fluids variation in degree of partial melting and progressive change of the melting source

serreta 1998 2001 submarine volcanic eruption offshore terceira azores characterization of the vent and inferences about the eruptive dynamics abstract high resolution bathymetric data and seafloor sampling were used to characterize the most recent volcanic eruption in the azores region the 1998 2001 serreta submarine eruption the vent of the eruption is proposed to be an asymmetric topographic high composed of two coalescing volcanic cones underlying the location where lava balloons had been observed at the sea surface during the eruption the volcanic products related to the 1998 2001 eruption are constrained to an area of 0 5 km2 around the proposed vent position a submarine strombolian style eruption producing basaltic lava balloons ash and coarse scoriaceous materials with limited lateral dispersion led to the buildup of the cones the 1998 2001 serreta eruption shares many similarities with other intermediate depth lava balloon forming eruptions e g the 1891 eruption offshore pantelleria and the 2011 2012 eruption south of el hierro revealing the particular conditions needed for the production of this unusual and scarcely documented volcanic product

gravity field over the sea of galilee evidence for a composite basin along a transform fault the sea of galilee lake kinneret is located at the northern portion of the kinneret bet shean basin in the northern dead sea transform three hundred kilometers of continuous marine gravity data were collected in the lake and integrated with land gravity data to a distance of more than 20 km around the lake analyses of the gravity data resulted in a free air anomaly map a variable density bouguer anomaly map and a horizontal first derivative map of the bouguer anomaly these maps together with gravity models of profiles across the lake and the area south of it were used to infer the geometry of the basins in this region and the main faults of the transform system the sea of galilee can be divided into two units the southern half is a pull apart that extends to the kinarot valley south of the lake whereas the northern half was formed by rotational opening and transverse normal faults the deepest part of the basinal area is located well south of the deepest bathymetric depression this implies that the northeastern part of the lake where the bathymetry is the deepest is a young feature that is actively subsiding now the pull apart basin is almost symmetrical in the southern part of the lake and in the kinarot valley south of the lake this suggests that the basin here is bounded by strike slip faults on both sides the eastern boundary fault extends to the northern part of the lake while the western fault does not cross the northern part the main factor controlling the structural complexity of this area is the interaction of the dead sea transform with a subperpendicular fault system and rotated blocks

the northern red sea and the dead sea rift abstract the results of geophysical measurements at sea when combined with mesostructural measurements on land demonstrate systematic extensional features in the region of the northern red sea and the dead sea rift rifts and diapirs were encountered in the northern red sea showing an arcuate trend whereas the faulted continental margins at that region are oriented nw se the rifts and the diapirs changed their trend northwards from nnw sse to n s systems of rifts and diapirs are considered to be extensional features therefore the tectonic extensional axis probably changed its orientation accordingly a series of rifts and diapirs was found also in the gulf of elat trending approximately parallel to the coastlines and is interpreted to be the northern extension of the red sea rift and diapir system mesostructural measurements that were carried out in the western flank of the dead sea rift indicated further evidence for structural extension trending e w to ene wsw in addition to measurements of left lateral offset of approximately 10 km all these data when combined with the geophysical measurements of the characteristics of the earth crust underneath the dead sea rift suggest a tectonic regime of oblique extension in the region of the red sea and the dead sea rift this tectonic regime indicates that the red sea spreading center extends northwards along the dead sea rift and the clockwise change of the axial trend imposed a sinistral offset to the tectonic extension thus it is suggested that the dead sea rift is an incipient oblique spreading center

fluidal clast breccia generated by submarine fire fountaining trooper creek formation queensland australia abstract a distinctive monomictic breccia composed of fluidal and blocky basaltic andesite clasts occurs in a cambro ordovician submarine volcanic succession in northern queensland australia associated with this fluvial clast buccia facies are coherent facies and coarse and fine breccia facies of the same composition the fluidal clast breccia facies is internally massive and 250 m thick varying only in the ratio of fluidal clasts to blocky clasts fluidal clasts range in size from 2 cm to 170 cm and have moderately to highly vesicular cores and thick up to 1 cm non vesicular formerly glassy rims blocky clasts are highly vesicular to non vesicular subaqueous fire fountain breccias are distinguished from subaerial fire fountain breccias by thick glassy margins on fluidal clasts the lack of welding and agglutination and the distinctive association of highly vesicular fluidal clasts with non vesicular angular blocky clasts recognition of submarine fire fountain breccias in volcanic successions constrains the eruption style proximity tens of metres to source and environment of deposition

inland jump of the arabian northwest plate boundary from the levant continental margin to the dead sea transform 1 while the breakup of arabia and africa began in the early oligocene the northwestern boundary of the arabian plate along the dead sea transform dst formed 10 15 myr later early middle miocene during the early stage of breakup the red sea rift continued propagating northwestward forming the suez rift the present 45 northward twist of the plate boundary from the red sea toward the gulf of eilat aqaba still did not exist what happened at the northern tip of the suez rift at that time how was strain distributed to its surroundings and where did the plate boundary continue from there here we describe an abandoned segment of the arabian northwestern plate boundary that extended from the northern tip of the suez rift northeastward along the levant margin seismic data collected offshore israel support a subsurface deep rooted fault zone running along the base of the continental slope these faults indicate oligocene transpressional lateral shearing we propose that during the early stage of continental breakup a left lateral strike slip motion of 10 km took place along this embryonic plate boundary such deep rooted tectonism implies that unlike the passive situation of the israel sinai continental margin witnessed presently and before the oligocene during the early stage of the africa arabia breakup this part of the continental margin was reactivated we further suggest that the inland jump of the plate boundary toward the dst was not immediate and that during the transitional period the israel sinai triangular block was an independent subplate with deformation all around it

geochemistry of hydrothermal fluids from an intraplate ocean island everman volcano socorro island mexico abstract socorro island mexico still volcanically active is an alkaline and peralkaline volcanic island in the eastern pacific ocean located on a mid ocean ridge spreading center that was abandoned at 3 5 ma gas and water samples collected on the island in 1999 from the dome fumaroles and hot springs of everman volcano have been analyzed for major components h o c s he and ar isotopic composition and noble gas abundances the boiling point temperature steam vents and low salinity thermal springs discharge cl free meteoric water and are typical surface manifestations of a high temperature hydrothermal system high h 2 and ch 4 contents up to 14 and 3 5 vol in dry gas respectively and an enrichment of ch 4 in 13 c 13 c ch 4 18 may suggest that these reduced gases were at least partially produced by the interaction of ultramafic rocks with water inside volcanic edifice due to serpentinization of olivine the 3 he 4 he ratios 6 0 6 6 r a which are lower than the morb values and the high he ne ratios 4000 and he ar ratios up to 4 indicate a contribution of radiogenic he from the oceanic crust or shallow magma chamber like at a low 3 he hot spot the maximum of the 40 ar 36 ar values 311 is close to the maximum value found in the socorro volcanic rocks noble gas abundances are close to values for the partially degassed air saturated water however with some excess ne concentrations an enrichment in 132 xe or depletion in 84 kr of the least air contaminated gas sample he ne 4000 relative to air saturated water can be related to the contribution of noble gases from a non atmospheric source probably oceanic crustal component assimilated in a shallow magma reservoir

continental margin evolution of the northern arabian platform in syria copyright aapg 1993 reprinted by permission of the aapg whose permission is required for further use see also http atlas geo cornell edu syria best 1993 html

submarine eruption near socorro island mexico geochemistry and scanning electron microscopy studies of floating scoria and reticulite abstract products of an underwater eruption near socorro island in the ne pacific were observed directly on january 29 1993 ten days after precursors were first recorded by sofar sound fixing and ranging hydrophones located in hawaii and tahiti eruptive activity was noticed from boats and ships as small steam plumes rising from the sea at an area centered at 18 48 n 111 05 w 2 4 km nw of punta tosca and 4 6 km ssw of cape henslow on socorro island the observed steam was produced by 1 3 m large blocks of hot dark grey highly vesiculated basalt rising buoyantly to the surface from two submarine shallow vents at 210 and 30 m depth tens of blocks accompanied by bubbles could be observed rising to the surface in irregular pulses these scoriaceous blocks remained floating at the surface until they would crack into smaller pieces by thermal contraction emitting hissing noises from vapourizing seawater in contact with the hot interior of the blocks steam jets several metres in height were produced and occasionally blocks were propelled laterally by the steam jet depending on vesicularity and permeability blocks remained floating and drifting with the surface current for 1 15 minutes before sinking back floating rocks covered an area of about 6000 m2 this intermittent activity has been observed ever since and has not stopped as of april 1994 buoyant scoria and reticulite are indicative of volatile mostly co2 supersaturation and exsolution in the magma prior to rapid quenching which inhibits loss of volatiles by bubble escape a high velocity ascent of low viscosity magma in a relatively narrow conduit is also required to prevent substantial gas escape and allow formation of reticulite the buoyant scoria is most probably ejected by intermittent lava fountaining at fixed vents as a result of changes in eruption velocities due to changes in the exsolved gas content of the lava between january and july 1993 floating blocks of scoria and reticulite were collected on several occasions from the surface of the sea for chemical and mineralogical analyses major and minor element analyses including ree as well as electron microprobe analyses of different phases revealed that the composition of the emitted lava has not changed through time blocks of basalt sio2 45 47 are highly vitric and vesicular with tabular anorthite phenocrysts up to 3 mm in length and minor grains of forsteritic olivine ree and trace element composition of these rocks suggest an anomalous mantle source for the erupted alkali basalt lava the ongoing eruption will either continue in a similar fashion as described and eventually cease or built up a mound that reaches the surface and forms an island with accompanying change in eruptive style

origin of volcanic seamounts at the continental margin of california related to changes in plate margins volcanic samples collected with the monterey bay aquarium research institute s rov tiburon from eight seamounts at the continental margin offshore central to southern california comprise a diverse suite of mainly alkalic basalt to trachyte but also include rare tholeiitic basalt and basanite all samples experienced complex crystal fractionation probably near the crust mantle boundary based on the presence in some of mantle xenoliths incompatible trace elements poorly correlated with isotopic compositions suggest variable degrees of partial melting of compositionally heterogeneous mantle sources ranging from morb like to relatively enriched oib high precision 40ar 39ar ages indicate episodes of volcanic activity mainly from 16 to 7 ma but document one eruption as recent as 2 8 ma at san juan seamount synchronous episodes of volcanism occurred at geographically widely separated locations offshore and within the continental borderland collectively the samples from these seamounts have age ranges and chemical compositions similar to those from davidson seamount identified as being located atop an abandoned spreading center these seamounts appear to have a common origin ultimately related to abandonment and partial subduction of spreading center segments when the plate boundary changed from subduction dominated to a transform margin they differ in composition age and origin from other more widespread near ridge seamounts which commonly have circular plans with nested calderas and from age progressive volcanoes in linear arrays such as the fieberling guadalupe chain that occur in the same region each volcanic episode represents decompression melting of discrete enriched material in the suboceanic mantle with melts rising along zones of weakness in the oceanic crust fabric the process may be aided by transtensional tectonics related to continued faulting along the continental margin

upper crustal velocity structure and basement morphology beneath the intracontinental palmyride fold thrust belt and north arabian platform in syria an edited version of this paper was published in geophysical journal international by blackwell publishing copyright 1993 blackwell publishing see also http www blackwellpublishing com journal asp ref 0956 540xs http atlas geo cornell edu syria seber gji 1993 htm

a braided strike slip model for the northern continuation of the dead sea fault and its implications for levantine tectonics abstract the assumption that the 100 110 km sinistral displacement on the dead sea fault is transmitted northwards along a single structure the yammouneh fault which runs ne sw across lebanon is here reviewed a number of valid objections to this concept exist a more attractive model supported by the limited data available from the area is that the motion is transmitted along a number of faults on this basis the temporary rightward flexure of the levant fracture through lebanon has given rise to a braided strike slip fault complex the yammouneh serrhaya fault system this model overcomes the objections against the older concept and allows the explanation of the mt lebanon bekaa valley anti lebanon complex in terms of transpressive and transtensive blocks a tentative outline of the cenozoic structural evolution of the area in terms of two or more phases of motion along the levant fracture is presented

stability of foams in silicate melts bubble coalescence and the spontaneous disruption of high porosity foams in silicate melts are the result of physical expulsion of interpore melt syneresis leading to bubble coalescence and diffusive gas exchange between bubbles melt expulsion can be achieved either along films between pairs of bubbles or along plateau borders which represent the contacts between 3 or more bubbles theoretical evaluation of these mechanisms is confirmed by experimental results enabling us to quantify the relevant parameters and determine stable bubble size and critical film thickness in a foam as a function of melt viscosity surface tension and time foam stability is controlled primarily by melt viscosity and time melt transport leading to coalescence of bubbles proceeds along inter bubble films for smaller bubbles and along plateau borders for larger bubbles thus the average bubble size accelerates with time in silicate melts the diffusive gas expulsion out of a region of foam is effective only for water and even then only at small length scales as the diffusion of co2 is negligible the results of our analyses are applicable to studies of vesicularity of lavas melt degassing and eruption mechanisms

the palaeoecology of the callovian and oxfordian strata of majdal shams syria and its implications for levantine palaeogeography and tectonics abstract palaeoecological study of fossils from jurassic strata of majdal shams syria reveals a deepening and shallowing sequence of water conditions from callovian to tithonian time maximum water depth apparently occurred in the lower oxfordian where both fossils and lithology are typical of the deeper water parts of the tethys the contrast with very shallow facies nearby in lebanon is very marked the only acceptable palaeogeographic reconstruction of this region is obtained by accepting the widely proposed post jurassic 110 km sinistral strike slip movement on the dead sea fault on this reconstruction the majdal shams region becomes an extension of the basinal tethys along the nw se trending kishon jezreel graben this is strong evidence for tensional ne sw movements in the levantine area long before the miocene opening of the red sea

the mathematician paleoplate the pacific seafloor is littered with small fragments of lithosphere captured from adjacent plates by past plate boundary reorganizations one of the clearest examples of such a reorganization is documented in the mathematician seamounts region where a distinctive geomorphology and well developed magnetic anomalies are present this reorganization involved a short lived microplate between the failing mathematician ridge and a new propagating spreading center the east pacific rise it produced a transfer of a fragment of lithosphere from the farallon to the pacific plate and also created a number of landforms and magnetic patterns within and on the margins of the captured fragment these make up the mathematician paleoplate in many cases two sides of a microplate are active spreading ridges a microplate evolves into a paleoplate when dual spreading ceases and full spreading resumes at the prevailing spreading ridge we define a paleoplate as the area of the seafloor from the axis of a failed rift to the boundary of resumed full spreading it includes a fragment of captured lithosphere and the lithosphere slowly accreted to it during the period of dual spreading prior to complete abandonment of the failed rift the mathematician paleoplate has the following boundaries and components from west to east the axis of the mathematician failed rift the fragment of captured farallon plate a complex rift initiation site at the moctezuma trough a zone of slow spreading and an as yet ill defined eastern boundary where dual spreading stopped and full spreading resumed the northern boundary of the paleoplate is the rivera fracture zone its southeastern boundary a now inactive transform fault the west o gorman fracture zone in this case as well as in other more poorly documented ones relict landforms and magnetic patterns are carried on the aging lithosphere away from the spreading ridge recording a former geometry

structure and eruptive mechanisms at surtsey volcano iceland glassy basalt tuff was the primary material cored in 1979 from a 181 m deep drill hole on the east tuff ring of surtsey volcano despite the fact that the hole extends 122 m below sea level all the core is similar to the exposed tephra composing the two tuff rings of the island the tuff includes abundant accretionary lapilli and tuff vesicles indicating that it was all deposited subaerially during the growth of the tuff rings repeated hydromagmatic explosion cycles began with a series of intermittent tephra finger explosions leading up to continuous uprush explosions which lasted for several minutes to several hours this nozzle like continuous activity produced eruption columns 100 250 m in diameter and 500 2000 m in height which probably quarried several hundred metres below the ground surface the continuous uprush explosion type provides a reasonable mechanism to excavate a diatreme from the top down during construction of the tuff rings concentric faults repeatedly downdropped a funnel like structure 400 800 m in diameter several hundred metres thus accounting for the presence of subaerially deposited tephra in the drill core far beneath sea level ring dykes later intruded upward along these faults and fed small lava flows heat in the surface tephra probably originated primarily from these shallow intrusions