dynamical excitation of the tropical pacific ocean and enso variability by little ice age cooling tropical pacific ocean dynamics during the medieval climate anomaly mca and the little ice age lia are poorly characterized due to a lack of evidence from the eastern equatorial pacific we reconstructed sea surface temperature el nino southern oscillation enso activity and the tropical pacific zonal gradient for the past millennium from galapagos ocean sediments we document a mid millennium shift mms in ocean atmosphere circulation around 1500 1650 ce from a state with dampened enso and strong zonal gradient to one with amplified enso and weak gradient the mms coincided with the deepest lia cooling and was probably caused by a southward shift of the intertropical convergence zone the peak of the mca 900 1150 ce was a warm period in the eastern pacific contradicting the paradigm of a persistent la nina pattern

time resolved seismic tomography detects magma intrusions at mount etna the continuous volcanic and seismic activity at mount etna makes this volcano an important laboratory for seismological and geophysical studies we used repeated three dimensional tomography to detect variations in elastic parameters during different volcanic cycles before and during the october 2002 january 2003 flank eruption well defined anomalous low p to s wave velocity ratio volumes were revealed absent during the pre eruptive period the anomalies trace the intrusion of volatile rich 4 weight percent basaltic magma most of which rose up only a few months before the onset of eruption the observed time changes of velocity anomalies suggest that four dimensional tomography provides a basis for more efficient volcano monitoring and short and midterm eruption forecasting of explosive activity

fluid ascent during the 2004 2005 unrest at mt spurr inferred from seismic tomography 1 we present a seismic model of the crust beneath mt spurr volcano in alaska based on tomographic inversion of local earthquake data recorded by temporary seismic network during the unrest of mt spurr in 2004 2005 beneath the northern vent of mt spurr where the most intensive fumarolic activity was observed during the last unrest we observe a finger shaped anomaly with a higher p and lower s velocity which corresponds to high vp vs ratio another anomaly is located to the south of crater peak approximately beneath the same location where an explosive eruption occurred in 1992 we propose that these two finger anomalies represent separated conduits of magma and volatiles the ne conduit extends to the surface and enables free volatile flux the se conduit seems to be blocked at a ca 20 km depth and in case of continuous pressure build up may become a source of an explosive eruption citation koulakov i m west and p izbekov 2013 fluid ascent during the 2004 2005 unrest at mt spurr inferred from seismic tomography geophys res lett 40 4579 4582 doi 10 1002 grl 50674

crustal structure in the area of the cannon earthquakes of abu dabbab northern red sea egypt from seismic tomography inversion abstract abu dabbab seismogenic zone is located close to the egyptian red sea coast it is characterized by cannon earthquakes long continued seismic activity and frequent earthquake swarms earthquakes in this zone have occurred with high frequency over a long period of time in a confined linear zone that extends offshore in the red sea a unique property is that earthquake signals can be heard by humans most previous studies suggested a magmatic origin for this activity we perform a detailed earthquake tomography to image the crustal structure beneath abu dabbab and to explore the origin of its seismic activity and the cannon earthquakes based on the local and regional data we construct a large scale seismic tomography model for the entire region and then enhance it for the local area of abu dabbab we find the seismicity forms an arc shaped cluster that surrounds an aseismic block of high velocities and a low v p v s ratio according to the tomography results we developed a new schematic geodynamic model proposing that the confined linear seismic zone in abu dabbab is due to the location of an active fault below a large rigid nondeformed block of precambrian igneous rock which reaches a depth of 10 km the surface between this block and the moving parts of the fault are lubricated by fluids penetrating into the crust from the red sea as a result of combined strike slip and thrust displacements along the faults these results reveal strong arguments for the tectonic origin of the seismicity associated with an important role of the fluid contents in abu dabbab area

rapid changes in magma storage beneath the klyuchevskoy group of volcanoes inferred from time dependent seismic tomography abstract we present the results of time dependent local earthquake tomography for the kluchevskoy group of volcanoes in kamchatka russia we consider the time period from 1999 to 2009 which covers several stages of activity of kluchevskoy and bezymianny volcanoes the results are supported by synthetic tests that recover a common 3d model based on data corresponding to different time windows throughout the period we observe a robust feature below 25 km depth with anomalously high v p v s values up to 2 2 we interpret this feature as a channel bringing deep mantle materials with high fluid and melt content to the bottom of the crust this mantle channel directly or indirectly determines the activity of all volcanoes of the kluchevskoy group in the crust we model complex structure that varies over time during the pre eruptive period we detected two levels of potential magma storage one in the middle crust at 10 12 km depth and one close to the surface just below kluchevskoy volcano in 2005 a year of powerful eruptions of kluchevskoy and besymiyanny volcanoes we observe a general increase in v p v s throughout the crust in the relaxation period following the eruption the v p v s values are generally low and no strong anomalous zones in the crust are observed we propose that very rapid variations in v p v s are most likely due to abrupt changes in the stress and deformation states which cause fracturing and the active transport of fluids these fluids drive more fracturing in a positive feedback system that ultimately leads to eruption we envision the magma reservoirs beneath the kluchevskoy group as sponge structured volumes that may quickly change the content of the molten phases as fluids pulse rapidly through the system

automatic measurement of shear wave splitting and applications to time varying anisotropy at mount ruapehu volcano new zealand 1 we present an automatic shear wave splitting measurement tool for local earthquakes with the sole manual step of choosing an s arrival time we apply the technique to three data sets recorded on mount ruapehu volcano in new zealand that have previously been determined to have fast polarizations that vary in time and with earthquake depth the technique uses an eigenvalue minimization technique applied over multiple measurement windows the dominant period of each waveform sets minimum and maximum window lengths cluster analysis determines the best solution among all the windows and quality grading criteria assess the results automatically when the same filters are used for events determined to be high quality from manual studies the automatic technique returns virtually identical results scatter increases when the automatic technique chooses the best filter but the average automatic results remain consistent with the manual results when the automatic technique is used on sets that include data previously judged as poor quality some stations yield distributions of fast polarizations that include peaks that were not present in previously published results the difference may stem from two factors automatic grading lets through some measurements that independent analysts consider poor quality but also unconscious bias in the manual selection process may downgrade measurements that do not fit expectations nonetheless the new objective analysis confirms changes in the average fast polarizations between 1994 and 2002 and between shallow and deep events therefore this new technique is valuable for objective assessment of anisotropy and its variation in time

seismic evidence for a mantle plume oceanwards of the kamchatka aleutian trench junction summary a non linear iterative p wave traveltime tomography has revealed a mantle plume originating at a depth of nearly 1000 km rising across the 600 km discontinuity and deflecting subhorizontally in the uppermost mantle presumably by shear flow due to the overlying moving plate data from the geophysical survey of russia 1955 1997 were inverted jointly with the catalogues of international seismological centre and usgs national earthquake information centre 1964 1998 the result shows a 300 500 kmwide cylindrical low velocity anomaly yx2 per cent that extends from a depth of greater than 900 km to shallower than 200 km the anomaly is almost vertical at depths up to y400 km and rises obliquely to the north up to y200 km under the ocean floor near the northern end of emperor seamounts above y300 km depth a subsidiary anomaly extends subhorizontally to the nw in fair agreement with the direction of movement of the pacific plate the overlying seafloor is characterized by anomalously high heat flow which may be attributed to the thermal effect of the mantle plume

transient shallow reservoirs beneath small eruptive centres constraints from mg fe interdiffusion in olivine abstract small eruptive centres commonly have more primitive lavas than those associated with stratovolcanoes an observation that has been taken to indicate a short magma residence in the crust relative to those reservoirs below stratovolcanoes the caburgua cones of the andean southern volcanic zone from a basaltic small eruptive centre where this can be tested here we use melts simulations and the available thermobarometry data to determine the conditions of olivine crystal rim formation and the mg fe diffusion modelling to determine the magma residence times of those rims in the crust results yield timescales varying from a few days to dozens of days and if freezing is to be avoided can only be explained by some form of storage or slow transport through at least one shallow magma body the longest durations of magma residence seen in the olivine rim zones are up to 471 days these timescales are shorter than those estimated decadal from the nearby more differentiated and well established stratovolcano villarrica which has a dominantly basaltic andesite composition for caburgua cones we propose the existence of a transient reservoir in contrast to a long lived reservoir such as that inferred beneath the adjacent villarrica stratovolcano

three different types of plumbing system beneath the neighboring active volcanoes of tolbachik bezymianny and klyuchevskoy in kamchatka

the evolution of the equatorial thermocline and the early pliocene el padre mean state the tropical pacific thermocline strength depth and tilt are critical to tropical mean state and variability during the early pliocene 3 5 to 4 5 ma the eastern equatorial pacific eep thermocline was deeper and the cold tongue was warmer than today which resulted in a mean state with a reduced zonal sea surface temperature gradient or el padre however it is unclear whether the deep thermocline was a local feature of the eep or a basin wide condition with global implications our measurements of mg ca of globorotalia tumida in a western equatorial pacific site indicate pliocene subsurface temperatures warmer than today thus el padre included a basin wide thermocline that was relatively warm deep and weakly tilted at 4 ma thermocline steepening was coupled to cooling of the cold tongue since 4 ma the basin wide thermocline cooled shoaled gradually with implications for thermocline feedbacks in tropical dynamics and the interpretation of tex86 derived temperatures

the yellowstone magmatic system from the mantle plume to the upper crust the yellowstone supervolcano is one of the largest active continental silicic volcanic fields in the world an understanding of its properties is key to enhancing our knowledge of volcanic mechanisms and corresponding risk using a joint local and teleseismic earthquake p wave seismic inversion we revealed a basaltic lower crustal magma body that provides a magmatic link between the yellowstone mantle plume and the previously imaged upper crustal magma reservoir this lower crustal magma body has a volume of 46 000 cubic kilometers 4 5 times that of the upper crustal magma reservoir and contains a melt fraction of 2 these estimates are critical to understanding the evolution of bimodal basaltic rhyolitic volcanism explaining the magnitude of co2 discharge and constraining dynamic models of the magmatic system for volcanic hazard assessment

evolution of the eastern tropical pacific through plio pleistocene glaciation a tropical pacific climate state resembling that of a permanent el nino is hypothesized to have ended as a result of a reorganization of the ocean heat budget 3 million years ago a time when large ice sheets appeared in the high latitudes of the northern hemisphere we report a high resolution alkenone reconstruction of conditions in the heart of the eastern equatorial pacific eep cold tongue that reflects the combined influences of changes in the equatorial thermocline the properties of the thermocline s source waters atmospheric greenhouse gas content and orbital variations on sea surface temperature sst and biological productivity over the past 5 million years our data indicate that the intensification of northern hemisphere glaciation 3 million years ago did not interrupt an almost monotonic cooling of the eep during the plio pleistocene sst and productivity in the eastern tropical pacific varied in phase with global ice volume changes at a dominant 41 000 year obliquity frequency throughout this time changes in the southern hemisphere most likely modulated most of the changes observed

simulating pliocene warmth and a permanent el nino like state the role of cloud albedo available evidence suggests that during the early pliocene 4 5 ma the mean east west sea surface temperature sst gradient in the equatorial pacific ocean was significantly smaller than today possibly reaching only 1 2 c the meridional sst gradients were also substantially weaker implying an expanded ocean warm pool in low latitudes subsequent global cooling led to the establishment of the stronger modern temperature gradients given our understanding of the physical processes that maintain the present day cold tongue in the east warm pool in the west and hence sharp temperature contrasts determining the key factors that maintained early pliocene climate still presents a challenge for climate theories and models this study demonstrates how different cloud properties could provide a solution we show that a reduction in the meridional gradient in cloud albedo can sustain reduced meridional and zonal sst gradients an expanded warm pool and warmer thermal stratification in the ocean and weaker hadley and walker circulations in the atmosphere having conducted a range of hypothetical modified cloud albedo experiments we arrive at our pliocene simulation which shows good agreement with proxy sst data from major equatorial and coastal upwelling regions the tropical warm pool middle and high latitudes and available subsurface temperature data as suggested by the observations the simulated pliocene like climate sustains a robust el nino southern oscillation despite the reduced mean east west sst gradient our results demonstrate that cloud albedo changes may be a critical element of pliocene climate and that simulating the meridional sst gradient correctly is central to replicating the geographical patterns of pliocene warmth

hot fingers in the mantle wedge new insights into magma genesis in subduction zones abstract quaternary volcanoes in the northeast japan arc can be grouped into 10 volcanic clusters striking transverse to the arc these have an average width of 50 km and are separated by parallel gaps 30 75 km wide this clustering of volcanic centres topographic profiles low velocity regions in the mantle wedge and local negative bouguer gravity anomalies along the japan sea side of the volcanic arc are closely correlated all these observations may be related to locally developed hot regions within the mantle wedge that have the form of inclined 50 km wide fingers each of the 10 fingers recognised extends from deep mantle 150 km below the back arc region towards the shallower mantle 50 km beneath the volcanic front quaternary volcanoes are built immediately above the hot mantle fingers the volcanic basement along the fingers has been uplifted by repeated injection of magmas into the crust accompanied by quaternary volcanic activity at the surface although volcanic activity is rare along the japan sea coast tomographic results show that hot low velocity mantle fingers exist within the mantle wedge the negative bouguer anomalies at the rear of the volcanic arc could be caused by magmas supplied from the hot mantle fingers these have not yet been erupted but have accumulated at the moho discontinuity

accounting for centennial scale variability when detecting changes in enso a study of the pliocene the el nino southern oscillation enso is the dominant mode of interannual climate variability however climate models are inconsistent in future predictions of enso and long term variations in enso cannot be quantified from the short instrumental records available here we analyse enso behaviour in millennial scale climate simulations of a warm climate of the past the mid pliocene warm period mpwp 3 3 3 0ma we consider centennial scale variability in enso for both the mpwp and the preindustrial and consider which changes between the two climates are detectable above this variability we find that el nino typically occurred 12 less frequently in the mpwp but with a 20 longer duration and with stronger amplitude in precipitation and temperature however low frequency variability in enso meant that pliocene preindustrial changes in el nino temperature amplitude in the nino3 4 region 5 n 5 s 170 w 120 w were not always detectable the pliocene preindustrial el nino temperature signal in the nino4 region 5 n 5 s 160 e 150 w and the el nino precipitation signal are usually larger than centennial scale variations of el nino amplitude and provide consistent indications of enso amplitude change the enhanced mpwp temperature signal in the nino4 region is associated with an increase in central pacific el nino events similar to those observed in recent decades and predicted for the future this study highlights the importance of considering centennial scale variability when comparing enso changes between two climate states if centennial scale variability in enso has not first been established results suggesting changes in enso behaviour may not be robust

seismic tomography model reveals mantle magma sources of recent volcanic activity at el hierro island canary islands spain summary we present a 3 d model of p and s velocities beneath el hierro island constructed using the traveltime data of more than 13 000 local earthquakes recorded by the instituto geogr afico nacional ign spain in the period from 2011 july to 2012 september the velocity models were performed using the lotos code for iterative passive source tomography the results of inversion were thoroughly verified using different resolution and robustness tests the results reveal that the majority of the onshore area of el hierro is associated with a high velocity anomaly observed down to 10 12 km depth this anomaly is interpreted as the accumulation of solid igneous rocks erupted during the last 1 myr and intrusive magmatic bodies below this high velocity pattern we observe a low velocity anomaly interpreted as a batch of magma coming from the mantle located beneath el hierro the boundary between the low and highvelocityanomaliesismarkedbyaprominentseismicitycluster thoughttorepresentanomalous stresses due to the interaction of the batch of magma with crust material the areas of recent eruptions orchilla and la restinga are associated with low velocity anomalies surrounding the main high velocity block these eruptions took place around the island where the crust is much weaker than the onshore area and where the melted material cannot penetrate these results put constraints on the geological model that could explain the origin of the volcanism in oceanic islands such as in the canaries which is not yet clearly understood

changes in sea surface conditions in the equatorial pacific during the middle miocene pliocene as inferred from coccolith geochemistry abstract this study presents a new alkenone derived sea surface temperature sst record and 18onoelaerhabdaceae data of the 2 5 m carbonate fractions from the iodp site u1338 located in the eastern equatorial pacific eep over the miocene pliocene our data and those available from other sites of the same area show the establishment of a cold tongue during the early pliocene 4 4 3 6 ma sst and 18onoelaerhabdaceae time series indicate periods of significant salinity variations comparison with the 18obenthic curve from sediment cores of the equatorial pacific ocean allows us to distinguish between global changes and local surface salinity variations in the eep ice sheet growth and evaporation precipitation are then discussed as possible drivers of such changes along with the role of central american and the indonesian seaway restriction our data suggest a shallowing of the thermocline in the eep between 6 8 and 6 ma and its shoaling between 4 8 and 4 0 ma suggesting the appearance of the cold tongue steph et al 2010 the pliocene climate transition would therefore not be primarily driven by northern hemisphere glaciation

feeding volcanoes of the kluchevskoy group from the results of local earthquake tomography 1 we present a seismic model of the area beneath the kluchevskoy volcano group kamchatka russia based on the tomographic inversion of more than 66000 p and s arrival times from more than 5000 local earthquakes that occurred in 2004 and that were recorded by 17 permanent stations below a depth of 25 km beneath the kluchevskoy volcano we observed a very strong anomaly in the vp vs ratio that reached as high as 2 2 this is a probable indicator of the presence of partially molten material with a composition corresponding to deeper mantle layers the upper part of this anomaly at a depth of 25 30 km coincides with a cluster of strong seismicity that can be explained by strong mechanical stresses in the lowermost crust due to magma ascension water release and or phase transitions in the crust we observed regular seismicity clusters that link the mantle anomaly with the kluchevskoy volcano and most likely indicate the paths of magma migration between depths of 8 and 13 km we see several patterns of high vp vs ratios interpreted as intermediate depth magma storages directly below the kluchevskoy volcano we observed a shallow body of high vp vs which probably represents the activated magma chamber just beneath the volcano cone which erupted in the beginning of 2005 the existence of three levels of magma storage based on results of local earthquake tomography may explain the variety of the lava composition and eruption regimes in different volcanoes of the kluchevskoy group

recent eruptions at bezymianny volcano a seismological comparison abstract for the past few decades bezymianny volcano has erupted once to twice per year here i examine eight eruptive events between 2006 and 2010 this is the first time period for which proximal or broadband seismic data have been recorded at bezymianny several recurring patterns are demonstrated in advance of eruptions eruptions are generally preceded by 12 36 h of tremor energy elevated by 2 to 3 orders of magnitude locatable earthquake activity is quite erratic in the days before eruptions for eruptions of juvenile magma however the cumulative moment magnitude increases with the repose time since the previous eruption though tenuous this relationship is statistically significant and could improve forecasts of bezymianny eruptions the most energetic eruptions demonstrate increasing multiplet activity in the run up followed by a rapid cessation at the time of eruption when present this behavior marks increasing pressure in the conduit system as degassing eclipses the capacity for venting very long period seismicity 20 s periods accompanies some eruptions these tend to be the same short lived high energy eruptions that exhibit multiplet precursors four eruptions are examined in detail to illustrate the variety in eruption mechanisms lava dome collapses sustained eruptions singular paroxysmal explosions and post explosion lava flows occur in different combinations demonstrating that more than one eruption trigger is regulating bezymianny compared to bezymianny s fifty year modern history recent eruptions have been shorter lived and separated by longer repose times some evidence suggests that these eruptions may be increasingly explosive a speculation that carries significant hazard implications if true however this threat is tempered by solid evidence that the most explosive eruptions are preceded by the clearest precursors suggesting an ability to improve the already excellent eruption forecasts available for bezymianny

planktic foraminifera shell chemistry response to seawater chemistry pliocene pleistocene seawater mg ca temperature and sea level change abstract foraminifera mg ca paleothermometry forms the basis of a substantial portion of ocean temperature reconstruction over the last 5 ma furthermore coupled mg ca oxygen isotope 18o measurements of benthic foraminifera can constrain eustatic sea level esl independent of paleo shoreline derived approaches however this technique suffers from uncertainty regarding the secular variation of the mg ca seawater ratio mg casw on timescales of millions of years here we present coupled seawater test mg ca temperature laboratory calibrations of globigerinoides ruber in order to test the widely held assumptions that 1 seawater test mg ca co vary linearly and 2 the mg ca temperature sensitivity remains constant with changing mg casw we find a nonlinear mg catest mg casw relationship and a lowering of the mg ca temperature sensitivity at lower than modern mg casw from 9 0 c 1 at mg casw 5 2 mol mol 1 to 7 5 0 9 c 1 at 3 4 mol mol 1 using our calibrations to more accurately calculate the offset between mg ca and biomarker derived paleotemperatures for four sites we derive a pliocene mg casw ratio of 4 3 mol mol 1 this mg casw implies pliocene ocean temperature 0 9 1 9 c higher than previously reported and by extension esl 30 m lower compared to when one assumes that pliocene mg casw is the same as at present correcting existing benthic foraminifera datasets for mg casw indicates that deep water source composition must have changed through time therefore seawater oxygen isotope reconstructions relative to present day cannot be used to directly reconstruct pliocene esl

permanent el nino like conditions during the pliocene warm period during the warm early pliocene 4 5 to 3 0 million years ago the most recent interval with a climate warmer than today the eastern pacific thermocline was deep and the average west to east sea surface temperature difference across the equatorial pacific was only 1 5 0 9 c much like it is during a modern el nino event thus the modern strong sea surface temperature gradient across the equatorial pacific is not a stable and permanent feature sustained el nino like conditions including relatively weak zonal atmospheric walker circulation could be a consequence of and play an important role in determining global warmth

driving magma to the surface the 2011 2012 el hierro volcanic eruption we reanalyzed the seismic and deformation data corresponding to the pre eruptive unrest on el hierro canary islands in 2011 we considered new information about the internal structure of the island we updated the seismic catalogue to estimate the full evolution of the released seismic energy and demonstrate the importance of non located earthquakes using seismic data and gps displacements we characterized the shear tensile type of the predominant fracturing and modelled the strain and stress fields for different time periods this enabled us to identify a prolonged first phase characterized by hydraulic tensile fracturing which we interpret as being related to the emplacement of new magma below the volcanic edifice on el hierro this was followed by post injection unidirectional migration probably controlled by the stress field and the distribution of the structural discontinuities we identified the effects of energetic magmatic pulses occurring a few days before the eruption that induced shear seismicity on pre existing faults within the volcano and raised the coulomb stress over the whole crust we suggest that these magmatic pulses reflect the crossing of the moho discontinuity as well as changes in the path geometry of the dyke migration towards the surface the final phase involved magma ascent through a pre fractured crust

studying deep sources of volcanism using multiscale seismic tomography abstract this paper presents an overview of several examples of multiscale studies of different volcanic systems including intracontinental collisional and subduction related volcanic areas regional tomographic models of the upper mantle are presented for three regions with the cenozoic intracontinental volcanism in eurasia namely europe southern siberia and eastern arctic in all cases recent volcanic fields correlate with low velocity anomalies in the mantle the modeling results show that these volcanic manifestations are related to large hot areas in the mantle and not to thin column shaped contrasted plumes as presumed by many collisional type volcanism is discussed with an example of the caucasus and the surrounding areas the regional tomographic model for this region reveals a lack of mantle lithosphere beneath the collision zone volcanism in this area is most likely due to the direct heating of the thick crust by the hot asthenosphere a dominantly felsic composition of the crust facilitates upward transport of the fluids and melts that leads to volcanic eruption subduction related volcanic systems are discussed for three different scale levels an example of a regional model of the mantle beneath the sunda arc reveals the general configuration of the slab middle scale tomographic models in areas of the toba caldera central java and central andes display feeding paths of the arc volcanoes from the slab the feeding paths are apparent in all of the considered cases but have different shapes depending on the unique features of the subduction regimes an example of a detailed local scale study of magmatic sources in the crust is discussed for the kluchevskoy volcano group it is found that the main volcano kluchevskoy is fed through a complex three layered system of magma sources another volcano of the same group bezymianny seems to be connected with the mantle through a direct short lived channel which appears only during the eruption periods a time dependent tomography study performed for this group over a period of ten years clearly reveals the correlation between the changes in the seismic structures and the stages of the volcanic process namely preparation activation and relaxation

andean elevation control on tropical pacific climate and enso late cenozoic marine proxy data record a long term transition in the tropical pacific from el nino like conditions with reduced zonal sea surface temperature sst gradient deepened thermocline and reduced upwelling in the eastern equatorial pacific eep to conditions similar to modern this transition coincides with kilometer scale uplift of the central andes to understand whether the rise of the andes contributed to tropical pacific climate evolution we performed experiments with the national center for atmospheric research s community climate system model version 4 to quantify changes in tropical pacific climate and el nino southern oscillation as a function of andean elevations our results demonstrate that uplift increases the equatorial east west sst gradient and walker circulation the rise of the andes from 1 to 3 km increases the sst gradient by 0 8 c and walker circulation by 60 due to strengthened radiative cooling by enhanced low cloud formation in the eep this cooling effect is largest in the southeastern tropical pacific and accounts for about one half of the reconstructed sst cooling along the peru coast the uplift also strengthens upwelling north of the eep consistent with documented increases in biological productivity in this region and decreases the frequency of el nino southern oscillation and the number of strong el nino events simulated responses to andean uplift are generally consistent with the late cenozoic proxy records but too small in magnitude taken together our results indicate that andean uplift was likely one of the multiple factors that contributed to the long term evolution of both the mean climate state and the interannual variability in the tropical pacific

hydrogen isotope systematics of submarine basalts the d h ratios and water contents in fresh submarine basalts from the mid atlantic ridge the east pacific rise and hawaii indicate that the primary d h ratios of many submarine lavas have been altered by processes including 1 outgassing 2 addition of seawater at magmatic temperature and 3 low temperature hydration of glass decreases in d and h2o from exteriors to interiors of pillows are explained by outgassing of water whereas inverse relations between d and h2o in basalts from the galapagos rise and the famous area are attributed to outgassing of ch4 and h2 a good correlation between d values and h2o is observed in a suite of submarine tholeiites dredged from the kilauea east rift zone where seawater added directly to the magma affected only the isotopic compositions of hydrogen and argon analyses of some glassy rims indicate that the outer millimeter of the glass can undergo lowtemperature hydration by hydroxyl groups having d values as low as 100 d values vary with h2o contents of subaerial transitional basalts from molokai hawaii and subaerial alkali basalts from the society islands indicating that the primary d values were similar to those of submarine lavas extrapolations to possible unaltered d values and h2o contents indicate that the primary d values of most thoteiite and alkali basalts are near 80 5 the weight percentages of water are variable 0 15 0 35 for mor tholeiites about 0 25 for hawaiian tholeiites and up to 1 1 for alkali basalts the primary d values of 80 for most basalts are comparable to those measured for deep seated phlogopites these results indicate that hydrogen in marked contrast to other elements such as sr nd pb and o has a uniform isotopic composition in the mantle this uniformity is best explained by the presence of a homogeneous reservoir of hydrogen that has existed in the mantle since the very early history of the earth

core top calibration of mg ca in tropical foraminifera refining paleotemperature estimation 1 optimal use of mg ca as a paleotemperature proxy requires establishing calibrations for different species of foraminifera and quantifying the influence of dissolution to achieve this goal we have measured mg ca and 18o in a series of tropical and subtropical core tops including four depth transects the ceara rise the sierra leone rise and the rio grande plateau in the atlantic and the ontong java plateau in the pacific focusing on spinose mixed layer dwelling species globigerinoides ruber and globigerinoides sacculifer and nonspinose thermocline dwelling neogloboquadrina dutertrei shell mg ca in g sacculifer is 5 15 lower than in g ruber while n dutertrei mg ca is 49 55 lower than in g ruber this statistically significant offset has allowed us to establish different calibrations for each species multilinear regression analysis was used to develop calibration equations that include a correction term for the dissolution effect on mg ca in foraminiferal calcite presented in this paper are two sets of calibrations one set using core depth as a dissolution correction and another using co32 as a dissolution parameter the calibrations suggest that g ruber is the most accurate recorder of surface temperature while g sacculifer records temperatures below the surface at 20 30 m the depth habitat of n dutertrei is more uncertain owing to the wide range in habitat depths depending on hydrographic conditions but on average mg ca and 18o data suggest it is at 50 m of the three species n dutertrei is the most sensitive to dissolution up to 23 decrease in shell mg ca per km while g sacculifer is the most resistant

bioturbational mixing depth and carbon flux at the seafloor radiocarbon dating series bulk sediment and organic carbon flux from various atlantic deep sea regions reveal that the thickness of the bioturbated zone increases by 2 cm if food supply increases by 1 gcm 2yr 1 r 0 8 bulk sediment accumulation rates do not influence the depth of bioturbational mixing under normal pelagic sedimentary conditions we believe that this relationship between nutrient supply and benthic mixing can be used for a quantitative and time variable unmixing procedure to improve high resolution stratigraphic correlations and paleoclimatic interpretations of deep sea records

tomographic imaging of the p wave velocity structure beneath the kamchatka peninsula summary a total of 5270 shallow and intermediate depth earthquakes recorded by the 32 stations of the regional seismic network of the geophysical service of russia are used to assess the p wave velocity structure beneath the kamchatka peninsula in the western pacific the tomographic inversion is carried out in three steps first a 1 d tomographic problem is solved in order to obtain an initial velocity model based on the 1 d velocity model 3 d tomographic inversions with homogeneous and heterogeneous starting models are obtained the conrad 15 km depth and moho 35 km depth discontinuities determined from the 1 d tomographic inversion and the upper boundary of the subducting slab are taken into account in the heterogeneous starting model for the traveltimes and ray path determinations both velocity structure and hypocentral locations are determined simultaneously in the inversion the spacing of the grid nodes is a half degree in the horizontal direction and 20 50 km in the vertical direction a detailed p wave tomographic image is determined down to a depth of 200 km the resulting tomographic image has a prominent low velocity anomaly that shows a maximum decrease in p wave velocity of approximately 6 per cent at 30 km depth beneath a chain of active volcanoes at depth low velocity anomalies are also observed in the mantle wedge extending down to a depth of approximately 150 km these anomalies are apparently associated with the volcanic activity the sedimentary basin of the central kamchatsky graben to the west of the volcanic front and the accretionary prism at the trench correlate with shallow low velocity anomalies highvelocity anomalies observed at a depth of 10 km may be associated with the location of metamorphic basements in the ganalsky valaginskoe uplift and upper crust of shipunsky cape the results also suggest that the subducted pacific plate has p wave velocities approximately 2 7 per cent higher than those of the surrounding mantle and a thickness of approximately 70 km

ground surface deformation patterns magma supply and magma storage at okmok volcano alaska from insar analysis 2 coeruptive deflation july august 2008 1 a hydrovolcanic eruption near cone d on the floor of okmok caldera alaska began on 12 july 2008 and continued until late august 2008 the eruption was preceded by inflation of a magma reservoir located beneath the center of the caldera and 3 km below sea level bsl which began immediately after okmok s previous eruption in 1997 in this paper we use data from several radar satellites and advanced interferometric synthetic aperture radar insar techniques to produce a suite of 2008 coeruption deformation maps most of the surface deformation that occurred during the eruption is explained by deflation of a mogi type source located beneath the center of the caldera and 2 3 km bsl i e essentially the same source that inflated prior to the eruption during the eruption the reservoir deflated at a rate that decreased exponentially with time with a 1 e time constant of 13 days we envision a sponge like network of interconnected fractures and melt bodies that in aggregate constitute a complex magma storage zone beneath okmok caldera the rate at which the reservoir deflates during an eruption may be controlled by the diminishing pressure difference between the reservoir and surface a similar mechanism might explain the tendency for reservoir inflation to slow as an eruption approaches until the pressure difference between a deep magma production zone and the reservoir is great enough to drive an intrusion or eruption along the caldera ring fracture system

robust enso across a wide range of climates abstractel nino southern oscillation enso is a pronounced mode of climate variability that originates in the tropical pacific and affects weather patterns worldwide growing evidence suggests that despite extensive changes in tropical climate enso was active over vast geological epochs stretching millions of years from the late cretaceous to the holocene in particular enso persisted during the pliocene when a dramatic reduction occurred in the mean east west temperature gradient in the equatorial pacific the mechanisms for sustained enso in such climates are poorly understood here a comprehensive climate model is used to simulate enso for a broad range of tropical pacific mean climates characterized by different climatological sst gradients it is found that the simulated enso remains surprisingly robust when the east west gradient is reduced from 6 to 1 c the amplitude of enso decreases only by 30 40 its dominant period remains close to 3 4 yr and the spectral peak stays above red noise t

seismically active subcrustal magma source of the klyuchevskoy volcano in kamchatka russia klyuchevskoy volcano in kamchatka russia is unique in the island arc systems of earth in having nearly continuous seismic activity beneath it at depths in excess of 20 km seismograms from these deep earthquakes carry an unmistakable signature of their tectonic nature we use p to s compressional to shear converted teleseismic waves to constrain the depth of the crust mantle transition beneath klyuchevskoy at 25 km and to delineate a deeper seismic boundary at 50 km earthquakes directly beneath klyuchevskoy have hypocentral depths of 25 35 km s p delays in records of these earthquakes are always larger than delay times of p tos converted waves originating at the crust mantle transition and traversing nearly identical paths thus deep seismic activity under klyuchevskoy is definitely beneath the crust mantle transition compositions of the klyuchevskoy parental melts inferred from melt inclusions and the most primitive lava interpreted using a barometer based on si activity in melts saturated with orthopyroxene olivine show that klyuchevskoy parental melts form at pressures within the range of 13 9 2 kbar at depths of 46 7 km together the estimates of melting depths the locations of seismic velocity features and the occurrence of tectonic earthquakes all point to the existence of a subcrustal volume beneath klyuchevskoy volcano where processes of magma accumulation are vigorous enough to promote brittle failure in mantle rock

three dimensional models of p wave velocity and p to s velocity ratio in the southern central andes by simultaneous inversion of local earthquake data the pisco 94 proyecto de investigation sismologica de la cordillera occidental 1994 seismological network of 31 digital broad band and short period three component seismometers was deployed in northern chile between the coastal cordillera and the western cordillera more than 5300 local seismic events were observed in a 100 day period a subset of high quality p and s arrival time data was used to invert simultaneously for hypocenters and velocity structure additional data from two other networks in the region could be included the velocity models show a number of prominent anomalies outlining an extremely thickened crust about 70 km beneath the forearc region an anomalous crustal structure beneath the recent magmatic arc western cordillera characterized by very low velocities and a high velocity slab a region of an increased vp vs ratio has been found directly above the wadati benioff zone which might be caused by hydration processes a zone of lower than average velocities and a high vp vs ratio might correspond to the asthenospheric wedge the upper edge of the wadati benioff zone is sharply defined by intermediate depth hypocenters while evidence for a double seismic zone can hardly be seen crustal events between the precordillera and the western cordillera have been observed for the first time and are mainly located in the vicinity of the salar de atacama down to depths of about 40 km

comparing the impacts of miocene pliocene changes in inter ocean gateways on climate central american seaway bering strait and indonesia changes in inter ocean gateways caused by tectonic processes have been long considered an important factor in climate evolution on geological timescales three major gateway changes that occurred during the late miocene and pliocene epochs are the closing of the central american seaway cas by the uplift of the isthmus of panama the opening of the bering strait and the closing of a deep channel between new guinea and the equator this study compares the global climatic effects of these changes within the same climate model framework we find that the closure of the cas and the opening of the bering strait induce the strongest effects on the atlantic meridional overturning circulation amoc however these effects potentially compensate as the closure of the cas and the opening of the bering strait cause similar amoc changes of around 2 sv strengthening and weakening respectively previous simulations with an open cas consistently simulated colder oceanic conditions in the northern hemisphere contrasting with the evidence for warmer sea surface temperatures 10 3 million years ago here we argue that this cooling is overestimated because a the models typically simulated too strong an amoc change not yet in equilibrium b used a channel too deep and c lacked the compensating effect of the closed bering strait a factor frequently ignored despite its potential influence on northern high latitudes and ice sheet growth further we discuss how these gateway changes affect various climatic variables from surface temperature and precipitation to enso characteristics

a deep eastern equatorial pacific thermocline during the early pliocene warm period abstract during the early pliocene warm period 4 6 4 2 ma in the eastern equatorial pacific upwelling region sea surface temperatures were warm in comparison to modern conditions warm upwelling regions have global effects on the heat budget and atmospheric circulation and are argued to have contributed to pliocene warmth though warm upwelling regions could be explained by weak winds and or a deep thermocline the temporal and spatial evolution of the equatorial thermocline is poorly understood here we reconstruct temporal and spatial changes in subsurface temperature to monitor thermocline depth and show the thermocline was deeper during the early pliocene warm period than it is today we measured subsurface temperature records from eastern equatorial pacific odp transect sites 848 849 and 853 using mg ca records from globorotalia tumida which has a depth habitat of 50 100 m in the early pliocene subsurface temperatures were 4 5 c warmer than modern temperatures indicating the thermocline was relatively deep subsurface temperatures steeply cooled 2 3 c from 4 8 to 4 0 ma and continued to cool an additional 2 3 c from 4 0 ma to present compared to records from other regions the data suggests the pronounced subsurface cooling between 4 8 and 4 0 ma was a regional signal related to restriction of the isthmus of panama while continued cooling from 4 0 ma to present was likely related to global processes that changed global thermocline structure additionally the spatial evolution of the equatorial thermocline along a n s transect across odp sites 853 849 and 848 suggests an intensification of the southeast trades from the pliocene to present large scale atmospheric and oceanographic circulation processes link high and low latitude climate through their influence on equatorial thermocline source water regions and consequently the equatorial thermocline through these low latitude high latitude linkages changes in the equatorial thermocline and thermocline source water played an important role in the transition from the warm pliocene to the cold pleistocene

the combined effects of water and fluorine on the viscosity of silicic magmas abstract the newtonian viscosity of water plus fluorine bearing silicate melt of haplogranitic composition hpg8 has been determined viscosities of hpg8 melt with addition of 3 11 and 4 25 wt of f and up to 3 wt h2o have been obtained using a micropenetration technique in the interval 109 74 to 1011 84 pa s and temperatures varying from 370 to 700 c at ambient pressure determination of the temperature dependence of viscosity from this and previous studies permits the parameterization of the viscosity of melts containing water and fluorine having similar composition within a 0 3 log units standard error the viscosity of water bearing f rich haplogranitic samples is represented by a modified vogel fulcher tammann vft equation which provides a non arrhenian description of the temperature dependence of the viscosity the results of this study indicate that taken individually or together both h2o and f have a strong and similar effect on the viscosity of sio2 rich compositions this similarity between f2o 1 and h2o greatly simplifies the task of predicting viscosity for volatile rich highly silicic magmas the low viscosities of hydrous fluorine bearing granitic melts favour efficient crystallization fractionaction paths for these liquids controlling degassing paths and consequently the eruptive behaviour numerical simulations of eruptive events normally do not take into account the contribution of fluorine this may introduce a significant error in the description of the fluid dynamic properties of magma and therefore in the accurate prediction of eruptive scenarios as well as in hazard assessment studies fluorine unlike water remains dissolved in the melt at high concentrations and low confining pressures the incorporation of fluorine data and the modelling of fluorine bearing viscosity data are therefore of fundamental importance for simulations of magma dynamics and prediction of eruptive scenarios

ground surface deformation patterns magma supply and magma storage at okmok volcano alaska from insar analysis 1 intereruption deformation 1997 2008 eruption magma storage had increased by 3 7 5 2 1 0 7 m 3 or 85 100 of the 1997 eruption volume we propose that the supply rate decreased in response to the diminishing pressure gradient between the shallow storage zone and a deeper magma source region eventuallytheeffectsofcontinuingmagmasupplyandvesiculationofstoredmagmacaused acriticalpressurethresholdtobeexceeded triggeringthe2008eruption asimilarpatternof initially rapid inflation followed by oscillatory but generally slowing inflation was observed prior to the 1997 eruption in both cases withdrawal of magma during the eruptions depressurized the shallow storage zone causing significant volcano wide subsidence and initiating a new intereruption deformation cycle

reduced el nino southern oscillation during the last glacial maximum el nino southern oscillation enso is a major source of global interannual variability but its response to climate change is uncertain paleoclimate records from the last glacial maximum lgm provide insight into enso behavior when global boundary conditions ice sheet extent atmospheric partial pressure of co2 were different from those today in this work we reconstruct lgm temperature variability at equatorial pacific sites using measurements of individual planktonic foraminifera shells a deep equatorial thermocline altered the dynamics in the eastern equatorial cold tongue resulting in reduced enso variability during the lgm compared to the late holocene these results suggest that enso was not tied directly to the east west temperature gradient as previously suggested rather the thermocline of the eastern equatorial pacific played a decisive role in the enso response to lgm climate

3 d seismic tomographic study of sinabung volcano northern sumatra indonesia during the inter eruptive period october 2010 july 2013 abstract we estimated 3d p wave velocity vp s wave velocity vs and vp vs tomographic structures in and around the sinabung volcano area northern sumatra indonesia during the intereruptive period between october 2010 and july 2013 using high quality p and s wave phases from 600 local volcano tectonic vt earthquakes and 5000 phase picks we used the iterative damped least squares method of simulps12 to simultaneously invert for the velocity structure and hypocenter relocations we find that the majority of the vt earthquakes locate beneath sinabung volcano to depths of about 8 km with distal hypocenters dominantly to the north and northwest of the summit we find six anomalous regions with the most notable including an area of low seismicity high vp vs and low vp at depths of around 5 km slightly south of the summit we believe this anomaly most likely represents hot material with some partial melt that may be the source for the 2010 phreatic eruptions and continued unrest throughout the study period we also find a region below the summit with high seismicity high vp high vs and low vp vs that we believe likely represents old intrusive material that has been fractured by the processes of the 2010 phreatic eruptions other shallow anomalous values of vp vs and vp vs are consistent with the known geology of sinabung anomalies of high vp and vs likely represent old well consolidated rock and are observed to the sw and ne of sinabung while low vp low vs and high vp vs likely represent increased fracture densities temperatures or gas contents in geothermal features to the west of the summit finally we compare our results to those of the tomographic study of the october to november 2013 eruptive period in nugraha et al 2019 and find evidence that suggests magma rose from the lower region imaged in our study to within a few kilometers of the surface

warm upwelling regions in the pliocene warm period 1 given the importance of upwelling processes to coastal productivity and regional climate it is critical to study the role of upwelling regions within the context of global climate change we generated sea surface temperature sst records for the last 5 million years in three important upwelling regions the eastern equatorial pacific the california margin and the peru margin prior to 3 0 ma ssts at all sites were significantly warmer than today by 3 9 c indicating that cold upwelling regions that characterize the modern pacific ocean did not exist in the early pliocene warm period 4 6 to 3 1 ma earth s most recent period of sustained global warmth alkenone phosphorus and organic carbon mass accumulation rate records indicate that changes in productivity and sst were decoupled and that upwelling of nutrient enriched water occurred even when ssts were warm during the early pliocene thus the long term trends in sst are likely explained by changes in the temperature of upwelled water rather than in the strength of upwelling favorable winds alone the fact that gradual cooling of upwelling regions began before the onset of significant northern hemisphere glaciation provides further evidence that the growth of ice sheets and their influence on atmospheric winds alone can not explain the cooling of upwelling regions our results suggest that the long term average ssts of upwelling regions are influenced by global changes in the depth and or temperature of the ventilated thermocline

temporal change of upper crustal vp vs ratios with volcanic evolution in redoubt volcano abstract volcanic activities accompany changes in the physical and chemical properties of the medium the ratio between p and s wave velocities v p v s is sensitive to the medium property changes we investigate temporal variations of the v p v s ratios in the upper crust around redoubt volcano in the 1989 2014 time period using the traveltimes of local earthquakes the v p v s ratios reached 2 0 immediately prior to the 1989 1990 and 2009 eruptions these high v p v s ratios may be associated with partial melts in the edifice the v p v s ratios rapidly decreased to 1 7 during the 1989 1990 and 2009 eruptions due to decreasing temperatures fluids and pore pressures and increasing effective stresses after melt eruptions and gas emission the change rates of the v p v s ratios showed evident spatial distributions the v p v s ratios increased at a rate of 0 025 0 003 yr 1 below the 2009 vent during the inter eruption period between the 1989 1990 and 2009 eruptions due to an increase in the temperature which may be associated with the recharge of the magma in the lower crust the increase rate of the v p v s ratios was as low as 0 005 0 001 yr 1 in the regions located away from the eruption site the v p v s ratios appear to have increased consistently at a rate of 0 017 0 004 yr 1 since the 2009 eruption

anomalous seismic structure beneath the klyuchevskoy group kamchatka 1 the klyuchevskoy group is among the most active volcanic features on earth yet its position within the kamchatka subduction zone is hard to explain with a simple tectonic mechanism the geochemistry of klyuchevskoy group lavas is typical for volcanic products resulting from flux melting in the mantle wedge yet the depth to the subducting pacific plate beneath it is much larger than the average depth of volatile release in subduction zones we present new seismological constraints on the upper mantle structure beneath the klyuchevskoy group and identify a planar dipping seismic feature in the mantle wedge which is 100 km deep and appears to be sharply bounded we hypothesize that this upper mantle structure may be the true source of melts erupting at the klyuchevskoy group and that the presence of this feature may explain both the extraordinary productivity of the klyuchevskoy group and its unusual location

evidence for two upper mantle sources driving volcanism in central kamchatka article i nfo article history volcanoes of the central kamchatka depression ckd form the most active arc volcano system in the world volcanoes of the ckd are positioned 170 km above the subducting pacific plate in excess of the typical glob al value of 100 km for arc volcanism we present results of a combined geophysical and petrological study of the main volcanic center in the ckd and argue for the presence of a second contributing melt source within the mantle wedge this region of melt generation is separate from the fluid fluxed region above the subduct ing pacific plate it may explain the presence of the active ckd arc in its current location results of receiver function imaging of the upper mantle beneath ckd reveal a distinct area of low velocities at approximately 110 km depth that is clearly distinct from the crust of the subducting pacific plate results of petrological modeling suggest presence of pyroxenite source melt contribution to ckd lavas alongside pre viously described peridotite source melts we contend that our results advance the notion that melting at two separate sources rather than the simple flux induced melting within the mantle wedge drives volca noes of the ckd

the response of enso flavors to mid holocene climate implications for proxy interpretation the response of el nino southern oscillation enso to mid holocene boundary conditions remains an open question paleoclimate proxies and climate model simulations do not agree in the magnitude of the reduction of enso variability while recent proxy evidence from fossil corals from the central pacific show that the reduction in mid holocene enso variability compared to the end of the twentieth century is not different from the reduction during other holocene time intervals this is inconsistent with the interpretation of lake and ocean sediment records from the eastern pacific which show a significant reduction compared to all other holocene periods in order to reconcile the seemingly conflicting proxy evidence from the eastern and central pacific we hypothesize that enso remained active during the mid holocene however there was a change in the spatial pattern of the sea surface temperature anomalies also known as enso flavors using national center for atmospheric research s community climate system model version 4 forced with mid holocene orbital conditions we find that the frequency of occurrence of the strongest eastern pacific ep events decreases in the mid holocene and their variance is reduced by 30 while the frequency of central pacific cp events slightly increases and their variance does not change we also find a shift in the seasonality of ep events but not in that of cp events lastly mid holocene ep events develop more slowly and decay faster the differential response of enso flavors to mid holocene forcing is remotely forced by the west pacific where a weakening of the trade winds in early boreal spring in the mid holocene initiates an anomalous downwelling annual kelvin wave which reaches the eastern pacific during the enso development season weakens the upper ocean stratification and results in reduced enso upwelling feedback the simulated reduction in the ep flavor versus the cp flavor in the mid holocene is consistent with proxy evidence the teleconnection patterns of the two flavors with temperature precipitation and salinity are distinct and proxies from different regions of the pacific might be recording variability associated with only one of the flavors or some combination of their relative effects

the interaction between active crustal faults and volcanism a case study of the liquine ofqui fault zone and osorno volcano southern andes using magnetotellurics abstract the relationship between subduction in convergent margins crustal structures and magmatism is crucial to understand processes such as the type and frequency of volcanic activity in these areas although it is well known that the release of fluids by the subducting slab is the main cause of the arc volcanism in areas like the central and southern andes details such as the timing and pathways of magma ascent and storage are still not well understood a key factor that needs to be better studied in the southern volcanic zone of the andes of chile is the role of large tectonic features in fluid transport and magma ascent processes such as the liquine ofqui fault zone a n s strike slip crustal structure parallel to the main volcanic arc in this study we focus on osorno volcano a stratovolcano composed mainly by products of basaltic to basaltic andesite composition with minor dacites and with historical hawaiian strombolian eruptions through the measurement of magnetotellurics and the use of 3 d modeling tools and petrologic constraints two magmatic reservoirs have been inferred which suggest a complex magmatic system with reservoirs of different depths and compositions the shallowest magmatic reservoir 4 8 km has a dacitic composition while the deepest one 7 15 km has an andesitic composition instead the shallow reservoir is located 2 km to the e of the volcano and the deepest one is located 10 km to the e considering that the liquine ofqui fault zone is located 20 km to the e of the volcano we suggest that eruptions of osorno volcano are associated with the ascent of deep crustal basaltic magma enhanced by this master fault re activating the inferred reservoirs and the volcano

structural cause of a missed eruption in the harrat lunayyir basaltic field saudi arabia in 2009 harrat lunayyir is one of the most volcanically active recent basaltic fields in western saudi arabia a period of substantial seismic unrest featuring more than 30 000 local events occurred in harrat lunayyir in april june 2009 although this crisis was presumably related to ongoing magma activity it ended without any surface volcanic activity we create new tomographic models of p and s velocities v p and v s and use them to explain the causes of this unrest and the reasons the eruption failed a large seismic anomaly of high v p v s ratio below 7 km depth coincides with the locations of more than 50 recent cinder cones with ages of older than 100 ka and is interpreted as a steady state magma reservoir we also identify another seismic anomaly at depths below 15 km which is interpreted as a conduit for fluids and melts from deeper sources because the location of this conduit is slightly outside the main reservoir some of the incoming material was dispersed as a result the activation of the crustal reservoir was not sufficiently strong to pierce the rigid basaltic cover and cause an actual eruption dur ing the crisis in 2009

paleoceanographic changes in the eastern equatorial pacific over the last 10 myr to examine the late neogene evolution of tropical pacific oceanography we determined multiple geochemical proxy records for temperature u 37 k and tex86h indices and primary productivity algal biomarkers and diol indices in sediments recovered at odp site 1241 in the east equatorial pacific eep spanning a record of the last 10 myr the tex86h temperatures are lower than those recorded by u 37 k indices exhibiting large fluctuations and suggesting strong warming during the mid pliocene warm period mpwp 4 5 3 2 ma and significantly colder temperature during the late miocene cooling period 7 5 ma and after the middle pliocene warm period mpwp such variations could reflect changes in the eep thermocline temperatures but we suggest that they instead reflect changes in the depth of export production of glycerol dialkyl glycerol tetraether lipids in response to changes in the upper ocean structure a combination of temperature records inferred to represent different and likely varying depths in the water column as well as algal biomarker records for export production and ecosystem structure suggest that both productivity and inference upwelling were reduced in the eep during warmer periods such as the mpwp and prior to 7 ma in contrast stronger upwelling conditions and associated increased productivity likely prevailed from 7 to 5 ma and for the past 3 myr both corresponding to globally cool intervals a further increase in eep productivity occurred at ca 1 8 ma coincident with the development of the e w pacific sst gradient these results confirm previous work that protracted el nino like conditions prevailed during warmer intervals of the pliocene before ultimately descending into the current climate state

temporal change of the magma plumbing system at galeras volcano colombia revealed by repeated seismic tomography in 2009 2018 abstract we performed repeated three dimensional seismic tomography in 2009 2018 for the area influenced by the intersection of the silvia pijao buesaco and cauca almaguer fault systems beneath galeras volcano colombia we analyzed two periods 2009 2012 and 2013 2018 which were characterized by explosive eruptive activity and relative quiescence at galeras respectively we used p and s wave arrival times of 2848 2009 2012 and 2289 2013 2018 earthquakes that occurred beneath the volcano p and s wave velocity vp and vs respectively anomalies and their changes between the two periods were interpreted to be associated with magma movement in the volcanic plumbing system which was controlled by the intersection of the faults two possible pathways of magma ascent and accumulation were identified in the fault systems one located sw of the active crater consisted of areas with high vp vs values 1 9 at depths of 2 to 4 km below sea level and the other located ne of the active crater with high and low vp vs values the low vp vs

seismic structure changes beneath redoubt volcano during the 2009 eruption inferred from local earthquake tomography we present seismic velocity models of the area beneath redoubt volcano alaska corresponding to two time periods before and after the strong eruption that occurred in march 2009 the calculations were based on tomographic inversion of p and s arrival time data recorded by 19 stations using the local earthquake tomography code lotos we performed thorough analysis of the results based on synthetic tests in each of the time periods that allow real time variations in structure to be distinguished from artifacts caused by changes in the observation system configurations in the resulting images corresponding to the period before the eruption the summit area is characterized by higher values of both p and s velocities and moderate values of the vp vs ratio this may correspond to the rigid igneous rocks composing the body of the volcano that lack significant liquid content in the second episode corresponding to the time of the eruption the p velocity remained high whereas the s velocity became very low the anticorrelation of p and s anomalies in the summit area produced a vp vs ratio as high as 2 2 which is seen down to 2 3 km depth this indicates presence of mobile phase at shallow depth beneath the volcano which can be either in the form of partial melt or fluid saturated rocks

vertically extensive and unstable magmatic systems a unified view of igneous processes volcanoes are an expression of their underlying magmatic systems over the past three decades the classical focus on upper crustal magma chambers has expanded to consider magmatic processes throughout the crust a transcrustal perspective must balance slow plate tectonic rates of melt generation and segregation in the lower crust with new evidence for rapid melt accumulation in the upper crust before many volcanic eruptions reconciling these observations is engendering active debate about the physical state spatial distribution and longevity of melt in the crust here we review evidence for transcrustal magmatic systems and highlight physical processes that might affect the growth and stability of melt rich layers focusing particularly on conditions that cause them to destabilize ascend and accumulate in voluminous but ephemeral shallow magma chambers

changes in equatorial pacific thermocline depth in response to panamanian seaway closure insights from a multi model study article i nfo the early pliocene warm phase was characterized by high sea surface temperatures and a deep thermocline in the eastern equatorial pacific a new hypothesis suggests that the progressive closure of the panamanian seaway contributed substantially to the termination of this zonally symmetric state in the equatorial pacific according to this hypothesis intensification of the atlantic meridional overturning circulation amoc in duced by the closure of the gateway was the principal cause of equatorial pacific thermocline shoaling dur ing the pliocene in this study twelve panama seaway sensitivity experiments from eight ocean climate models of different complexity are analyzed to examine the effect of an open gateway on amoc strength and thermocline depth all models show an eastward panamanian net throughflow leading to a reduction in amoc strength compared to the corresponding closed panama case in those models that do not include a dynamic atmosphere deepening of the equatorial pacific thermocline appears to scale almost linearly with the throughflow induced reduction in amoc strength models with dynamic atmosphere do not follow this simple relation there are indications that in four out of five models equatorial wind stress anomalies amplify the tropical pacific thermocline deepening in summary the models provide strong support for the hypothesized relationship between panama closure and equatorial pacific thermocline shoaling

mantle and crustal sources of magmatic activity of klyuchevskoy and surrounding volcanoes in kamchatka inferred from earthquake tomography

the three dimensional structure beneath the popocatepetl volcano mexico based on local earthquake seismic tomography abstract this paper presents a new seismic velocity model p and s wave velocities and vp vs ratio beneath the popocatepetl volcano to a depth of 4 km below sea level bsl this model is based on the tomographic inversion of p and s wave arrival time data from earthquakes in the region of the volcano these data were recorded by the 15 stations of a temporary seismic network that was deployed on the volcano in 1999 and 2000 the recording period was during a relatively quiet period between two strong eruptions which occurred before and after the experiment this period is characterized by low levels of volcano related seismicity most of the recorded events occurred across an area much larger than the network in this study we conducted several synthetic tests which validate the use of the out of network events to improve the resolution of the tomographic inversion beneath the stations in the resulting model we see that the main volcanic edifice is associated with high velocities that have a mushroom shape and that these high velocities are most prominent in the p wave model this feature may indicate the presence of overpressured solidified igneous rocks which comprise the edifice of popocatepetl below the summit of the volcano we observe a prominent high vp vs anomaly which reaches a value of 1 9 this anomaly probably indicates the existence of cracks and pores filled with melts and fluids and it may represent a fracture zone that serves as a conduit feeding the volcano this model characterizes the interior structure of the popocatepetl volcano prior to the strong september 2000 eruption which occurred a few months after the termination of the experiment

crustal exhumation during ongoing compression in the variscan maures tanneron massif france geological and thermo mechanical aspects abstract the maures tanneron massif mtm together with corsica and sardinia represent the southeastern branch of the huge european variscan belt a continuous evolution from continental collision to exhumation is described from ca 350 ma to ca 320 ma based on an extended compilation of available geological and geochronological data this geological compilation is complemented with thermo mechanical modelling that tests the conditions under which deep seated hp units can melt and exhume massively during continued convergence we simulate in two dimensions the development of gravitational instabilities in a partially melting crust depending on rheological layering and heat sources and accounting for temperature dependent elasto visco plastic rheologies in order to reproduce pt exhumation patterns in the mtm over the appropriate time scale 20 my and spatial extent 100 km a best fit was obtained with a convergence rate of 0 5 cm yr and moderate diffusive surface processes the contribution of radiogenic heating in the pre stacked felsic crustal units is crucial a lateral alternation with mafic units is also required in order to prevent lateral spreading of the orogen a low viscosity partially molten crust 1020 pa s thus rather felsic accompanies crustal exhumation in a decoupled mode from the deeper mantle a shallow asthenosphere below the orogen lab at 70 km depth e g shallow slab break off produces too warm and sudden exhumation as opposed to a competent mantle lithosphere 120 km depth lab that restrains it the mtm witnesses the typical competition between far field plate convergence and internal body forces and our study pleads for a progressive evolution of transpression towards perpendicular extension from ca 320 ma

early pliocene increase in thermohaline overturning a precondition for the development of the modern equatorial pacific cold tongue unraveling the processes responsible for earth s climate transition from an el nino like state during the warm early pliocene into a modern like la nina dominated state currently challenges the scientific community recently the pliocene climate switch has been linked to oceanic thermocline shoaling at 3 million years ago along with earth s final transition into a bipolar icehouse world here we present pliocene proxy data and climate model results which suggest an earlier timing of the pliocene climate switch and a different chain of forcing mechanisms we show that the increase in north atlantic meridional overturning circulation between 4 8 and 4 0 million years ago initiated by the progressive closure of the central american seaway triggered overall shoaling of the tropical thermocline this preconditioned the turnaround from a warm eastern equatorial pacific to the modern equatorial cold tongue state about 1 million years earlier than previously assumed since 3 6 3 5 million years ago the intensification of northern hemisphere glaciation resulted in a strengthening of the trade winds thereby amplifying upwelling and biogenic productivity at low latitudes

statistical constraints on el nino southern oscillation reconstructions using individual foraminifera a sensitivity analysis recent investigations of submillennial paleoceanographic variability have attempted to resolve high frequency climate signals such as the el nino southern oscillation enso using the population statistics of individual planktic foraminiferal 18o analyses this approach is complicated by the relatively short lifespan of individual foraminifers 2 4 weeks compared to the time represented by a typical marine sediment sample decades to millennia here we investigate the uncertainty associated with individual foraminiferal analyses ifa through simulations on forward modeled 18ocarbonate first focusing on the nino3 4 region of the tropical pacific ocean a bootstrap monte carlo algorithm is developed to constrain the uncertainty on ifa statistics subsequently to test the sensitivity of ifa to changes in seasonal cycle amplitude enso amplitude and enso frequency synthetic time series of 18ocarbonate with differing variability are constructed and tested with our algorithm the probabilities of the ifa technique in detecting changes in enso amplitude and seasonal cycle amplitude or a combination of both for the surface ocean and thermocline at different locations in the tropical pacific are quantified we find that the uncertainty in the standard deviation is smaller than the range that the ifa signal is insensitive to enso frequency and at certain locations the seasonal cycle may dominate enso ifa sensitivity towards enso is highest at the central equatorial pacific surface ocean and the eastern equatorial pacific eep thermocline whereas sensitivity towards the seasonal cycle is highest at the eep surface ocean our results suggest that rigorous uncertainty quantification should become standard practice for accurately interpreting ifa data

time dependent seismic tomography summary of methods for measuring temporal changes in seismic wave speeds in the earth seismic tomography is among those that offer the highest spatial resolution 3 d tomographic methods are commonly applied in this context by inverting seismic wave arrival time data sets from different epochs independently and assuming that differences in the derived structures represent real temporal variations this assumption is dangerous because the results of independent inversions would differ even if the structure in the earth did not change due to observational errors and differences in the seismic ray distributions the latter effect may be especially severe when data sets include earthquake swarms or aftershock sequences and may produce the appearance of correlation between structural changes and seismicity when the wave speeds are actually temporally invariant a better approach which makes it possible to assess what changes are truly required by the data is to invert multiple data sets simultaneously minimizing the difference between models for different epochs as well as the rms arrival time residuals this problem leads in the case of two epochs to a system of normal equations whose order is twice as great as for a single epoch the direct solution of this system would require twice as much memory and four times as much computational effort as would independent inversions we present an algorithm tomo4d that takes advantage of the structure and sparseness of the system to obtain the solution with essentially no more effort than independent inversions require

bubble growth during decompression of magma experimental and theoretical investigation a model of bubble growth during decompression of supersaturated melt was developed in order to explore the conditions for preservation of gas overpressure in bubbles or for maintaining supersaturation of the melt the model accounts for the interplay of three dynamic processes decompression rate of the magma deformation of the viscous melt around the growing bubble and diffusion of volatiles into the bubble generally these processes are coupled and the evolution of bubble radius and gas pressure is solved numerically for a better understanding of the physics of the processes we developed some analytical solutions under simplifying assumptions for cases where growth is controlled by viscous resistance diffusion or linear decompression rate we show that the solutions are a function of time and two dimensionless numbers which are the ratios of either the diffusive or viscous time scales over the decompression time scale the conditions for each growth regime are provided as a function of the two governing dimensionless parameters analytical calculations for some specific cases compare well with numerical simulations and experimental results on bubble growth during decompression of hydrated silicic melts the model solutions including the division to the growth regimes as function of the two parameters provide a fast tool for estimation of the state of erupting magma in terms of gas overpressure supersaturation and gas volume fraction the model results are in agreement with the conditions of plinian explosive eruption e g mount st helens 18 may 1980 where high gas overpressure is expected the conditions of effusion of lava domes with sudden onset of explosive activity are also in agreement with the model predictions mostly in equilibrium degassing and partly in overpressure conditions we show that in a situation of quasi static diffusion during decompression the diffusive influx depends on the diffusivity away from the bubble insensitive to the diffusivity profile

increase of shear wave velocity before the 1998 eruption of merapi volcano indonesia 1 we infer temporal changes in the elastic properties of the edifice of merapi volcano java indonesia before its eruption in 1998 by analyzing multiply scattered elastic waves excited by a repeatable controlled seismic source a pre eruptive increase of shear wave velocity which correlates well with pre eruptive seismicity and dome growth is revealed the method can be used as a pressure gauge for pressure changes inside of volcanoes because increasing pressures in rocks are known to cause proportionally increasing elastic wave velocities

surface deformation of bezymianny volcano kamchatka recorded by gps the eruptions from 2005 to 2010 and long term long wavelength subsidence abstract since bezymianny volcano resumed its activity in 1956 eruptions have been frequent recently with up to 1 2 explosive events per year to investigate deformation related to this activity we installed a gps network of 8 continuous and 6 campaign stations around bezymianny the two striking observations for 2005 2010 are 1 rapid and continuous network wide subsidence between 8 and 12 mm yr which appears to affect kamnet stations more than 40 km away where we observe 4 5 mm yr of subsidence and 2 only the summit station bz09 shows slight deviations from the average motion in the north component at times of eruptions the network wide subsidence cannot be explained by tectonic deformation related to the build up of interseismic strain due to subduction of the pacific plate a first order model of surface loading by eruptive products of the kluchevskoy group of volcanoes also explains only a fraction of the subsidence however a deep sill at about 30 km under kluchevskoy that constantly discharges material fits our observations well the sill is constrained by deep seismicity which suggests 9 5 km width 12 7 km length and a 13 dip angle to the south east we infer a closing rate of 0 22 m yr which implies a volume loss of 0 027 km 3 yr 0 16 m yr and 0 019 km 3 yr considering surface loading additional stations in the near and far field are required to uniquely resolve the spatial extent and likely partitioning of this source we explain the eruption related deformation at bz09 with a very shallow reservoir likely within bezymianny s edifice at a depth between 0 25 km and 1 5 km with a volume change of 1 4 10 4 km 3 much of the material erupted at bezymianny may be sourced from deeper mid crustal reservoirs with co eruptive volume changes at or below the detection limit of the gps network installation of more sensitive instruments such as tiltmeters would allow resolving of subtle co eruptive motion

error sources in basal yield stress inversions for jakobshavn isbrae greenland derived from residual patterns of misfit to observations the basal interface of glaciers is generally not directly observable geophysical inverse methods are therefore used to infer basal parameters from surface observations such methods can also provide information about potential inadequacies of the forward model ideally an inverse problem can be regularized so that the differences between modeled and observed surface velocities reflect observational errors however deficiencies in the forward model usually result in additional errors here we use the spatial pattern of velocity residuals to discuss the main error sources for basal stress inversions for jakobshavn isbrae greenland synthetic tests with prescribed patterns of basal yield stress with varying length scales are then used to investigate different weighting functions for the data model misfit and for the ability of the inversion to resolve details in basal yield stress we also test real data inversions for their sensitivities to prior estimate forward model parameters data gaps and temperature fields we find that velocity errors are not sufficient to explain the residual patterns of real data inversions conversely ice geometry errors and especially simulated errors in model simplifications are capable of reproducing similar error patterns and magnitudes we suggest that residual patterns can provide useful guidance for forward model improvements

seismicity and structure of akutan and makushin volcanoes alaska using joint body and surface wave tomography joint inversions of seismic data recover models that simultaneously fit multiple constraints while playing upon the strengths of each data type here we jointly invert 14 years of local earthquake body wave arrival times from the alaska volcano observatory catalog and rayleigh wave dispersion curves based upon ambient noise measurements for local vp vs and hypocentral locations at akutan and makushin volcanoes using a new joint inversion algorithm the velocity structure and relocated seismicity of both volcanoes are significantly more complex than many other volcanoes studied using similar techniques seismicity is distributed among several areas beneath or beyond the flanks of both volcanoes illuminating a variety of volcanic and tectonic features the velocity structures of the two volcanoes are exemplified by the presence of narrow high vp features in the near surface indicating likely current or remnant pathways of magma to the surface a single broad low vp region beneath each volcano is slightly offset from each summit and centered at approximately 7 km depth indicating a potential magma chamber where magma is stored over longer time periods differing recovery capabilities of the vp and vs data sets indicate that the results of these types of joint inversions must be interpreted carefully

4d seismic tomography of nevado del ruiz volcano colombia 2000 2016 abstract to track and analyze temporal changes in the volcanic system of nevado del ruiz colombia repeated three dimensional seismic tomography 4d seismic tomography for p and s wave velocities vp and vs respectively during the period 2000 2016 was performed p and s wave arrival time data were classified on the basis of changes in volcanic activity into five time periods 2000 2006 2007 2009 2010 2012 2013 2014 and 2015 2016 our results showed clear changes in 2013 2014 and 2015 2016 periods of heightened volcanic activity after an episode of unrest in 2010 regions of low vp low vs and high vp vs 1 9 were found beneath and northwest of the active crater at depths of 2 3 km below sea level the enhancement of those anomalies suggests that a new pulse of magma arrived in the volcanic system at that time regions with low vp vs values 1 3 1 6 in the upper part of the volcano at depths from 3 to 2 km are interpreted as the result of vapor accumulation within highly fractured zones of the hydrothermal system the ratios of fractional change of vp and vs in 2015 2016 suggest that partial melting zones were located beneath the active crater at depths of 2 to 0 km our results show that the volcanic system of nevado del ruiz has experienced changes associated with the input of new magma which ascended and interacted with preexisting magma bodies and led to the recent emplacement of a small dome at the bottom of the active crater we combined our results and evidence from previous studies to propose a model of the nevado del ruiz plumbing system from 1985 to 2016