formation of an a ā lava delta insights from time lapse multibeam bathymetry and direct observations during the stromboli 2007 eruption five consecutive multibeam bathymetries collected before during and after the 2007 stromboli eruption combined with visual inspections allowed us to document the morphological evolution of an a lava fed delta and to reconstruct the main processes acting during its submarine emplacement the 2007 stromboli delta extended down to 600 m water depth and covered an area of 420 103 m2 with a maximum thickness of 65 m and a total estimated volume of 7 106 m3 i e three times larger than its subaerial counterpart the lava delta grew mainly through the emplacement of discrete lobes about 50 150 m in size lobes were fed from point sources along the paleoshoreline and their subaqueous pathways seem to be mainly controlled by the submarine morphology with flows mostly filling in depressions left by previous lobes the main controlling factors on the lobe morphology and thickness are the effusion rates and the pre eruption morphology i e the geometry and gradients of the basal surface data also shows that sudden slope failure of portions of the submarine delta may occur simultaneously with accretion implying that a significant part of the delta material can be transported to greater depths by submarine gravity flows the present study is relevant for future monitoring and hazard assessment during the growth of active lava fed deltas as well as for a better interpretation of ancient volcaniclastic successions inland

eruption and magma crystallization ages of las tres virgenes baja california constrained by combined 230th 238u and u th he dating of zircon las tres virgenes volcano is a calc alkaline composite cone located near the main gulf of california escarpment on the e coast of the baja california peninsula high sensitivity ion microprobe u series 230 th 238 u ages for zircon from la virgen tephra average 121 10 12 ka 1 mswd 2 7 with discrete age peaks at 100 and 160 ka the noble gas mass spectrometric u th he zircon age corrected for disequilibrium and pre eruptive storage is 36 3 ka this result for the eruption age of la virgen tephra is significantly older than previously postulated historic or holocene ages that were based on an 18th century map reference and 14 c dating of accidental charcoal respectively the new u th he zircon age is consistent with a n26 4 ka age derived from cosmogenic he exposure dating of an overlying basaltic lava flow hausback b p and abrams m j 1996 plinian eruption of la virgen tephra volcan las tres virgenes baja california sur mexico eos transactions american geophysical union 77 46 suppl 813 814 u pb zircon analysis of ignimbrites erupted from the adjacent early pleistocene la reforma and el aguajito calderas yielded ages of 1 38 0 03 ma n 12 mswd 1 0 and 1 17 0 07 ma n 23 mswd 1 3 respectively no evidence for these ages is found among la virgen zircons whereas pre quaternary zircon xenocrysts are common the la virgen magma therefore evolved unrelated to early pleistocene magmatism in adjacent calderas but assimilated local basement rocks a gap between average th u and u th he zircon ages suggests that zircon crystallization was discontinuous in the la virgen magma chamber in addition partial resorption of zircon suggests episodic thermal rejuvenation most likely by basaltic recharge based on the zircon record the n100 ka lifetime of the thermal anomaly that sustained repeated intrusive pulses significantly exceeds the age of the last eruption this strengthens the view that tres virgenes has a potential for future eruptions

prolonged residence times for the youngest rhyolites associated with long valley caldera 230th 238u ion microprobe dating of young zircons abstract we describe a new ion microprobe method for dating magmatic zircon growth that is based on in situ measurement of the magnitude of238u 230th disequilibrium our results support independent inferences that zircon can remain suspended for long periods 100 ka in the convecting potions of the magma from which it crystallizes because the crystallization ages date when the magma cooled to its zircon saturation temperature even when the zircons have long magmatic residence times 238u 230th zircon dating can be used to constrain the thermochemical evolution of silicic magmas 238u 230th ages have been determined for individual zircons from rhyolites associated with the long valley magmatic system of eastern california the samples are from deer mountain an 115 3 ka low silica moat rhyolite and from the coarsely porphyritic low silica rhyolite of south deadman dome one of the 0 6 ka inyo domes previous investigations have suggested that the two lavas were derived from the same magma reservoir a few of the zircon model ages calculated with respect to the isotopic characteristics of the whole rocks are within error of that for eruption of the deer mountain rhyolite however the majority of zircons from both lavas cluster around an age of 230 ka this common interval of zircon nucleation and growth for petrologically similar lavas suggests that the younger inyo dome lava may have tapped the same magma body from which the deer mountain rhyolite erupted more than 100 ka before on the other hand most of the zircon model ages are younger than previous episodes of silicic volcanism in the long valley caldera suggesting that the rhyolites may have been generated during development of a silicic upper crustal magma chamber in the western portion of long valley caldera zircon saturation temperatures for the rhyolites studied 795 810 c are the same as those obtained from coexisting fe ti oxides 809 4 c showing that the magma cooled to

global variations of thermospheric winds and temperatures caused by substorm energy injection two numerical simulations of the thermospheric response to magnetospheric energy injection have been performed using a zonally averaged time dependent model of neutral composition dynamics and energy budget the simulations are distinguished by the duration of the source the first simulation has an energy injection of 1 hour representative of substorm type forcing and the second one has a 12 hour energy injection representative of main storm type forcing they were performed under the condition of equinox at solar minimum in the first simulation large scale atmospheric gravity waves agws generated by the substorm energy via joule heating of ionospheric currents are clearly identified in the wind field in a meridional plane as well as in the temporal and spacial variations of the total energy density of air above about 130 km height these waves reach the equator after about 3 hours and propagate into the opposite hemisphere the horizontal propagation speed is close to the speed of sound for example roughly 440 m s at about 150 km altitude and 670 m s at about 260 km altitude snapshots of the wind system affected by the substorm energy injection show a four cell pattern between the poles above 260 km the cells have the opposite rotational direction to those below these small scale features in the wind system are indicative of the internal atmospheric gravity waves with the vertical phase propagation from a term analysis of the energy conservation equation it is identified that the dominant energy process associated with the propagation of agws is adiabatic compressional heating and or expansive cooling process it can be concluded that the energy oscillations at middle and low latitude are mainly produced by agws propagating from high latitude during the substorm the second simulation indicated that horizontal and vertical advections vertical heat conduction and infrared radiative cooling by nitric oxide are important in addition to adiabatic compressional heating and or expansive cooling it is suggested that short duration energy injection preferentially generates agws which dominate the energy oscillations at low latitudes through adiabatic heating and cooling long duration energy injection is more effective in generating a meridional circulation which transfers energy by both advective and adiabatic processes

single crystal 40ar 39ar dating of a late quaternary paroxysm on kos greece concordance of terrestrial and marine ages the late quaternary plinian eruption forming the kos plateau tuff on the island of kos greece was one of the largest in the mediterranean a precise date for this eruption would significantly improve the chronology of the deep sea tephra layer w 3 because reliable correlation of w 3 with the kos plateau tuff has been previously established we have dated sanidine from the eruption at 161 3 1 1 ka using the laser fusion single crystal 40ar 39ar technique this age represents a significant refinement over both conventional and highly precise cassignol method k ar ages and the 40ar 39ar age is shown to be in remarkably good agreement with the age of w 3 inferred from recent astronomically calibrated oxygen isotope chronologies

implications of pre eruptive magmatic histories of zircons for u pb geochronology of silicic extrusions zircons in silicic magmas begin to crystallize 10 s to 100 s of thousands of years ka prior to their eruption u pb and u th dating for zircons from 32 young extrusions indicate a range of mean pre eruption ages from 33 to 247 ka with a median of 92 ka explosive large volume widespread eruptions show a narrower range and a younger median of 70 ka these results indicate that the difference between initial zircon growth and eruption age measured by other e g 40ar 39ar techniques is in excess of the achievable analytical uncertainty for eruptions 30 million years ma and likely for eruptions of up to 300 ma protracted pre eruption zircon growth is well established by an increasing number of studies on magma process time scales but this source of eruption age bias has been largely ignored in chronostratigraphic applications of high precision u pb data until intrinsic properties of zircons or their host deposits enable a priori estimates of pre eruption age bias it is prudent to expand the uncertainties attending all u pb zircon ages interpreted as deposition ages in e g chronostratigraphic studies by 0 200 ka

thermospheric wind during a storm time large scale traveling ionospheric disturbance 1 a prominent large scale traveling ionospheric disturbance lstid was observed in japan during the major magnetic storm dst 358 nt of 31 march 2001 it was detected as enhancements of the 630 nm airglow and fof2 gps tec variations and a decrease in f layer virtual height at 1700 1900 ut 0200 0400 lt it moved equatorward with a speed of 600 m s the decrease in the f layer height was also detected by the mu radar at shigaraki thermospheric wind variations were observed by the mu radar through ion drift measurement and by a fabry perot interferometer fpi through a doppler shift of the 630 nm airglow line at shigaraki the wind data show a turn of the meridional wind from 94 m s equatorward to 44 m s poleward during the lstid indicating that an intense poleward wind in the thermosphere passed over shigaraki as an atmospheric gravity wave and caused the observed ionospheric features of the lstid intense poleward wind was also detected at mesospheric altitudes 95 100 km by the mu radar through meteor echoes and by the fpi through the 558 nm airglow with a delay of 2 hours from the thermospheric wind indicating downward phase progression of the wave generation of the observed poleward wind in the auroral zone was investigated using magnetic field data and auroral energy input estimated by the assimilative mapping of ionospheric electrodynamics amie technique we suggest that simple atmospheric heating and or the lorentz force in the auroral zone do not explain the observed poleward wind enhancement

collapse and reconstruction of monowai submarine volcano kermadec arc 1998 2004 monowai submarine volcano is one of the three most historically active volcanoes of the kermadec arc repeat multibeam surveys of monowai cone from september 1998 and september 2004 and t wave data recorded by the reseau sismique polynesien network for the same period document the collapse and subsequent regrowth of the cone within this 6 a period grid differencing of the two bathymetric data sets acquired 6 a apart reveals that a landslide 2230 m long occurred between the surveys within which a postcollapse cone and talus ridge 0 023 km3 in volume subsequently formed the volume of this collapse minus postcollapse construction is 0 085 km3 we interpret an unusual strong amplitude t wave event on 24 may 2002 as recording hot landsliding where the 100 to 160 m thick collapse has unroofed the uppermost parts of the vent conduit with the subsequent explosive interaction and cooling of hot magma and volcaniclastic rubble with ambient seawater this interpretation is consistent with the lack of emergent events sharp onset and large amplitude of the 24 may 2002 t waves the subsequent 2500 t wave events between november 2002 and september 2004 occurred in swarms with emerging and waning activity and with typical explosive volcanic acoustic signatures which are interpreted as recording the regrowth of an 90 m high cone back to a near 1998 elevation at an average rate of 47 m a 1 this study provides 1 a lower bound for frequency magnitude relationships of landsliding for submarine arc volcanoes and 2 estimates of 0 013 km3 a 1 of submarine cone growth during eruptive cycles

morphology of large scale traveling atmospheric disturbances in the polar thermosphere using a fully coupled thermosphere ionosphere plasmasphere model we investigate the morphology of modelled large scale traveling atmospheric disturbances ls tads hereinafter tads propagating both poleward and equatorward from auroral sources we confirm observational evidence of daytime ion drag reducing equatorward far field tad activity we further suggest an additional source dependent mechanism that associates tads propagating preferentially poleward with an auroral electric field burst that contains an eastward rather than a westward component these poleward tads are superimposed on the high speed neutral air winds in the polar cap originating from the day night plasma convection and exhibit speed and spatial resonance effects with the neutral wind the direction of propagation is affected by coriolis forcing due to the earth s rotation

identification of high latitude acoustic gravity wave sources using the goose bay hf radar observations of medium scale acoustic gravity waves using the goose bay hf radar are presented data were examined for the period of november and december 1991 and days that showed evidence of traveling ionospheric disturbances tids were selected for analysis tids were identified in the hf radar data by quasi periodic enhancements of the power in the ground scattered portion of the radar signal various parameters were determined from the data including the wave frequency the wavelength the propagation direction and the phase velocity it was found that multiple wave packets from multiple directions are often present simultaneously source times and locations were identified from data from 2 days december 5 and 6 1991 and these were compared with data from the greenland magnetometer chain the source times and locations were found to correspond to sudden magnetometer deflections indicating the correlation of gravity wave sources with the occurrence of ionospheric electrojet current surges finally the source times and locations were examined in local time and magnetic latitude and it was found that the sources were clustered in two locations near the magnetospheric cusp and near 1600 mlt at about 75 magnetic latitude

late pleistocene granodiorite source for recycled zircon and phenocrysts in rhyodacite lava at crater lake oregon abstract rhyodacite tephra and three lavas erupted 27 ka interpreted to be early leaks from the climactic magma chamber of mount mazama contain ubiquitous resorbed crystals antecrysts that were recycled from young granodiorite and related plutonic rocks of the same magmatic system the shallow composite pluton is represented by blocks ejected in the 7 7 ka climactic eruption that formed crater lake caldera plagioclase crystals in both rhyodacite and granodiorites commonly have cores with crystallographically oriented fe oxide needles exsolved at subsolidus conditions at least 80 of plagioclase crystals in the rhyodacite are antecrysts derived from plutonic rocks other crystals in the rhyodacite notably zircon also were recycled sims 238 u 230 th dating indicates that zircons in 4 granodiorite blocks crystallized at various times between 20 ka and 300 ka with concentrations of analyses near 50 70 110 and 200 ka that correspond to periods of dacitic volcanism dated by k ar u th ages of zircon from a rhyodacite sample yield similar results no analyzed zircons from the granodiorite or rhyodacite are pre quaternary zircon minimum ages in blocks from different locations around the caldera reflect ages of nearby volcanic vents and may map the distribution of intrusions within a composite pluton survival of zircon in zircon undersaturated hydrous magma and of fe oxide needles in plagioclase suggests that little time elapsed from entrainment of antecrysts to the 27 ka eruption of the rhyodacite the 27 ka rhyodacite is an example of young silicic magma that preserved unstable antecrysts from a known source early during growth of a large high level magma chamber in contrast the voluminous 7 7 ka climactic rhyodacite pumice is virtually lacking in zircon indicating dissolution of any granodioritic debris in the intervening period mineralogical evidence of assimilation may be destroyed in hot vigorously growing silicic magma bodies such as ultimately produced the climactic eruption of mount mazama

probing the accumulation history of the voluminous toba magma the age and compositional zonation in crystals from the youngest toba tuff record the prelude to earth9s largest quaternary eruption we used allanite crystals to date and decipher this zoning and found that the crystals retain a record of at least 150 000 years of magma storage and evolution the dominant subvolcanic magma was relatively homogeneous and thermally stagnant for 110 000 years in the 35 000 years before eruption the diversity of melts increased substantially as the system grew in size before erupting 75 000 years ago

the effects of secular disequilibrium on u th he systematics and dating of quaternary volcanic zircon and apatite the u th he dating method applied to u rich phases such as zircon and apatite has sufficient sensitivity and precision to be of potential use for dating relatively recent geologic events such as volcanic eruptions however in phases with crystallization ages less than 1 ma chemical fractionation within the 238 u decay series may modify the he ingrowth rate causing he ages computed from the secular equilibrium age equation to be incorrect the resulting systematic error depends on the 230 th 238 u activity ratio of the dated phase when it is erupted and on the eruption age zircons which exclude th relative to u will likely have secular equilibrium he ages that underestimate the eruption age by up to a few tens of decreasing with increasing eruption age apatites tend to accommodate u and th with little fractionation so apatite secular equilibrium he ages will be nearly concordant with eruption age if minerals are erupted immediately after crystallization the disequilibrium effect can be reasonably accounted for based on th u systematics however crystals are likely to reside for unknown but potentially long periods in a magma chamber such that the degree of secular disequilibrium will be reduced prior to the onset of he accumulation u th he analyses of co genetic phases that fractionate the u th ratio differently like apatite and zircon can be used to better constrain eruption age as well as to provide insights into magma chamber residence time we illustrate this approach with u th he analyses of zircons and apatites of the pleistocene age rangitawa tephra new zealand

40ar 39ar dating of latest pleistocene 41 ka marine tephra in the mediterranean sea implications for global climate records abstract fifty one 40 ar 39 ar laser heating analyses of sanidine crystals in the c 13 tephra layer recovered out of a piston core raised from 3000 m depth in the tyrrhenian sea yielded apparent ages between 25 and 112 ka twenty four of these measurements define an age probability maximum and generate an isochron of 41 1 2 1 ka 2 with a 40 ar 36 ar intercept of 288 21 that is indistinguishable from the modern atmosphere however the entire population is skewed toward older apparent ages with smaller peaks at 48 ka 55 ka 67 ka and 110 ka the composition of glass shards in the c 13 tephra overlaps that of the sio 2 rich phase of the 150 km 3 campanian ignimbrite which erupted from the campi flegrei caldera 130 km northwest of the core site although the 41 1 2 1 ka isochron is 15 older than k ar and 14 c ages for the campanian ignimbrite it is indistinguishable from recent 40 ar 39 ar age determinations the campanian ignimbrite eruptions were also chemically similar to and correlated with the y 5 ash layer the most voluminous and widely dispersed late pleistocene tephra in the mediterranean region the age of the y 5 layer was constrained originally at 38 0 2 5 ka on the basis of astronomical dating of o isotope stages the 40 ar 39 ar ages astronomical dating plus chemical similarities permit correlation of the c 13 tephra layer with both the campanian ignimbrite and the y 5 tephra layer the older ages preserved in the c 13 tephra layer may reflect xenocrysts incorporated during the explosive eruption accompanying collapse of the campi flegrei caldera 41 ka the c 13 tephra layer is correlated with a 10 be peak in an adjacent marine core o isotope stage 3 12 and immediately preceded a cooling episode corresponding to heinrich event 4 thus the age of these features is constrained by radioisotope dating the 41 ka peak in 10 be deposition is a global phenomenon whose age matches that of the laschamp geomagnetic excursion thus our results provide a new tie point among several polar ice core and marine proxy records of paleoclimate during the past 50 kyr precise age information independent of radiocarbon dating can be recovered from latest pleistocene marine tephra using the 40 ar 39 ar laser heating method despite the presence of multiple components that may have been incorporated during or after its deposition

crystallisation ages in coeval silicic magma bodies 238u 230th disequilibrium evidence from the rotoiti and earthquake flat eruption deposits taupo volcanic zone new zealand abstract the timescales over which moderate to large bodies of silicic magma are generated and stored are addressed here by studies of two geographically adjacent successive eruption deposits in the taupo volcanic zone new zealand the earlier caldera forming rotoiti eruption 100 km3 magma at okataina volcano was followed within months at most by the earthquake flat eruption 10 km3 magma from nearby kapenga volcano both generated non welded ignimbrite and coeval widespread fall deposits the rotoiti and earthquake flat deposits are both crystal rich high silica rhyolites with sparse glass bearing granitoid fragments also occurring in rotoiti lag breccias generated during caldera collapse here we report 238u 230th disequilibrium data on whole rocks and mineral separates from representative rotoiti and earthquake flat pumices and the co eruptive rotoiti granitoid fragments using tims and in situ zircon analyses by sims multiple grain zircon controlled crystallisation ages measured by tims from the rotoiti pumice range from 69 3 ka 350 ka with a pronounced peak at 70 90 ka the weighted mean of isochrons is 83 14 ka in accord with the tims data one glass bearing rotoiti granitoid clast yielded an age of 57 8 ka by tims controlled by th rich phases that however are not apparently present in the juvenile pumices another glass bearing rotoiti granitoid yielded sims zircon model ages peaking at 60 90 ka having a similar age distribution to the pumice age data from pumices are consistent with a published 64 4 ka eruptive age now modified to 62 2 ka but chemical and or mineralogical data imply that the granitoid lithics are not largely crystalline rotoiti rhyolite but instead represent contemporaneous partly molten intrusions reflecting different sources in their chemistries and mineralogies similarly although the earthquake flat eruption immediately followed and probably was triggered by the rotoiti event age data from juvenile material are significantly different a multiple grain zircon controlled crystallisation age measured by tims from a representative pumice is 173 5 ka while sims model ages range from 70 26 34 ka to 350 ka with a peak at 105 ka these age data coupled with previously published geochemical and isotopic data show that the rotoiti and earthquake flat deposits were erupted from independent unconnected magma bodies

hotspot volcanism close to a passive continental margin the canary islands the canarian archipelago is a group of volcanic islands on a slow moving oceanic plate close to a continental margin the origins of the archipelago are controversial a hotspot or mantle plume a zone of lithospheric deformation a region of compressional block faulting or a rupture propagating westwards from the active atlas mountains fold belt have been proposed by different authors however comparison of the canarian archipelago with the prototypical hotspot related island group the hawaiian archipelago reveals that the differences between the two are not as great as had previously been supposed on the basis of older data quaternary igneous activity in the canaries is concentrated at the western end of the archipelago close to the present day location of the inferred hotspot this is the same relationship as seen in the hawaiian and cape verde islands the latter archipelago associated with a well defined but slow moving mantle plume shows anomalies in a plot of island age against distance which are comparable to those seen in the canary islands these anomalies cannot therefore be used to argue against a hotspot origin for the canaries individual islands in both archipelagoes are characterized by initial rapid growth the shield building stages of activity followed by a period of quiescence and deep erosion erosion gap which in turn is followed by a post erosional stage of activity the absence of post shield stage subsidence in the canaries is in marked contrast with the major subsidence experienced by the hawaiian islands but is comparable with the lack of subsidence evident in other island groups at slow moving hotspots such as the cape verdes comparison of the structure and structural evolution of the canary islands with other oceanic islands such as hawaii and reunion reveals many similarities these include the development of triple mercedes star rift zones and the occurrence of giant lateral collapses on the flanks of these rift zones the apparent absence of these features in the post erosional islands may in part be a result of their greater age and deeper erosion which has removed much of the evidence for their early volcanic architecture we conclude that the many similarities between the canary islands and island groups whose hotspot origins are undisputed show that the canaries have been produced in the same way

timing of the permian triassic biotic crisis implications from new zircon u pb age data and their limitations abstract the most profound biotic crisis in the earth s history causing the near extinction of both terrestrial and marine life occurred at the end of the permian period about 253 myr ago and marks the paleozoic mesozoic era boundary the cause of this event is still a matter of vigorous debate with both brief and catastrophic as well as gradual mechanisms having been proposed similar to a recent landmark study this study uses the u pb method on zircons from the uppermost permian lowermost triassic ash fall deposits at meishan zhejiang province se china in order to examine time and rate constraints for these events the results of both this study and previous work show that for these ash layers the effects of pb loss are combined with varying amounts and sources of inheritance resulting in an age scatter which prohibits the extraction of a statistically robust age in many cases though the effects of pb loss on the zircons analyzed in this study were reduced by leaching the grains in hydrofluoric acid as opposed to commonly applied air abrasion prior to analysis the presence within a single ash layer of multiple generations of older xenocrysts in many cases only slightly older than the depositional age has made quantitative interpretation even more difficult when these combined phenomena bias individual zircon ages by less than a percent they are extremely difficult to deconvolute and if multi grain analyses are used can become impossible to recognize because of the resulting age averaging monte carlo simulations using actual measurements of individual zircon crystals show that age excursions due to pb loss and xenocrystic contamination for the meishan bentonites are easily homogenized to the point of undetectability when replicate analyses of multi grain zircon samples are compared thus this study uses only high precision analyses of single crystals whether from our work or that of previous studies three main conclusions have emerged first our data require a significant increase in the age of the permian triassic boundary by more than 2 myr compared to the previous study which shifts the age to a value older than 253 ma second neither our data nor those from previous work can confirm or negate the possibility of a very abrupt biotic crisis third even large suites of very high quality single zircon u pb analyses for these tuffs cannot in most cases yield objective reliable and robust dates with accuracies at the sub myr level though the temptation to perform arbitrary selection of subsets of the analyses for that purpose is almost irresistible the last conclusion is not an indictment of zircon u pb dating in general other rocks and other zircon populations can and do behave very differently and further technical advances will likely improve our ability to prepare grains or sub grains of adequately enhanced quality for analysis consequently the results of the present study strongly suggest that for problems requiring time scale accuracy inferences from zircon u pb dating must be based on sufficiently large suites of single crystal or crystal domain high precision analyses

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

on the dynamics of large scale traveling ionospheric disturbances over europe on 20 november 2003 ionospheric disturbances often associated with geomagnetic storms may cause threats to radio systems used for communication and navigation one example is the super storm on 20th november 2003 when plenty of strong and unusual perturbations were reported this paper reveals additional information on the dynamics in the high latitude ionosphere over europe during this storm here analyses of wavelike travelling ionospheric distrubances tids over europe are presented based on estimates of the total electron content tec derived from ground based global navigation satellite system gnss measurements these tids are ionospheric signatures of thermospheric surges initiated by space weather events the source region of these tids is characterized by enhanced spatial gradients tec depression strong uplift of the f2 layer the vicinity of the eastward auroral electrojet and strong aurora e layers joule heating is identified as the most probable driver for the tids observed over europe during 20th november 2003 the sudden heating of the thermosphere leads to strong changes in the pressure and thermospheric wind circulation system which in turn generates thermospheric wind surges observed as tid signatures in the tec either the dissipation of the eastward auroral electrojet or particle precipitation are considered as the source mechanism for the joule heating in the course of the storm the tec observations show a southward shift of the source region of the tids these meridional dislocation effects are obviously related to a strong compression of the plasmasphere the presented results demonstrate the complex interaction processes in the thermosphere ionosphere magnetosphere system during this extreme storm

seismic hydraulic fracture migration originated by successive deep magma pulses the 2011 2013 seismic series associated to the volcanic activity of el hierro island in this manuscript we present a new interpretation of the seismic series that accompanied eruptive activity off the coast of el hierro canary islands during 2011 2013 we estimated temporal variations of the gutenberg richter b value throughout the period of analysis and performed high precision relocations of the preeruptive and syneruptive seismicity using a realistic 3 d velocity model our results suggest that eruptive activity and the accompanying seismicity were caused by repeated injections of magma from the mantle into the lower crust these magma pulses occurred within a small and well defined volume resulting in the emplacement of fresh magma along the crust mantle boundary underneath el hierro we analyzed the distribution of earthquake hypocenters in time and space in order to assess seismic diffusivity in the lower crust our results suggest that very high earthquake rates underneath el hierro represent the response of a stable lower crust to stress perturbations with pulsatory character linked to the injection of magma from the mantle magma input from depth caused large stress perturbations to propagate into the lower crust generating energetic seismic swarms the absence of any preferential alignment in the spatial pattern of seismicity reinforces our hypothesis that stress perturbation and related seismicity had diffusive character we conclude that the temporal and spatial evolution of seismicity was neither tracking the path of magma migration nor it defines the boundaries of magma storage volumes such as a midcrustal sill our conceptual model considers pulsatory magma injection from the upper mantle and its propagation along the moho we suggest within this framework that the spatial and temporal distributions of earthquake hypocenters reflect hydraulic fracturing processes associated with stress propagation due to magma movement

deep intrusions lateral magma transport and related uplift at ocean island volcanoes abstract oceanic intraplate volcanoes grow by accumulation of erupted material as well as by coeval or discrete magmatic intrusions dykes and other intrusive bodies within volcanic edifices are comparatively well studied but intrusive processes deep beneath the volcanoes remain elusive although there is geological evidence for deep magmatic intrusions contributing to volcano growth through uplift this has rarely been demonstrated by real time monitoring here we use geophysical and petrological data from el hierro canary islands to show that intrusions from the mantle and subhorizontal transport of magma within the oceanic crust result in rapid endogenous island growth seismicity and ground deformation associated with a submarine eruption in 2011 2012 reveal deep subhorizontal intrusive sheets sills which have caused island scale uplift of tens of centimetres the pre eruptive intrusions migrated 15 20 km laterally within the lower oceanic crust opening pathways that were subsequently used by the erupted magmas to ascend from the mantle to the surface during six post eruptive episodes between 2012 and 2014 further sill intrusions into the lower crust and upper mantle have caused magma to migrate up to 20 km laterally resulting in magma accumulation exceeding that of the pre eruptive phase a comparison of geobarometric data for the 2011 2012 el hierro eruption with data for other atlantic intraplate volcanoes shows similar bimodal pressure distributions suggesting that eruptive phases are commonly accompanied by deep intrusions of sills and lateral magma transport these processes add significant material to the oceanic crust cause uplift and are thus fundamentally important for the growth and evolution of volcanic islands we suggest that the development of such a magma accumulation zone in the lower oceanic crust begins early during volcano evolution and is a consequence of increasing size and complexity of the mantle reservoir system and potentially the lithospheric stresses imposed by increasing edifice load

40ar 39ar dating of quaternary feldspar examples from the taupo volcanic zone new zealand using a continuous laser and resistance furnace we have measured ages on quaternary plagioclase with an absolute precision of about 30 ka and on quaternary sanidine with a relative precision of better than 1 such precision was achieved by using low temperature heating steps to remove much of the nonradiogenic argon contamination plagioclase is one of the most common mineral phases in volcanic rocks thus these procedures will be widely applicable to many problems for which precise radiometric age control has not been available we studied plagioclase and plagioclase sanidine concentrates from the oldest and the three largest silicic ash flow deposits of the taupo volcanic zone new zealand one of the world9s largest and most active volcanic systems the results are in close agreement with new magnetostratigraphic data suggest that existing fission track age determinations significantly underestimate the age of older units and shift the inception of taupo volcanic zone volcanism back to at least 1600 ka the improved precision has permitted the first correlations between proximal and distal units previous correlations with deep sea ash flows in the western pacific require major revision

low δ18o rhyolites from yellowstone magmatic evolution based on analyses of zircons and individual phenocrysts the yellowstone plateau volcanic field is one of the largest centers exchange time to form zoned zircons is between a few hundred and a few thousand years which reflects the residence time of lowo of rhyolitic magmatism on earth major caldera forming eruptions are followed by unusual lowo rhyolites new oxygen isotope magmas after formation and before eruption petrologic and geochemical data from rhyolites belonging to the 2 0 my eruptive history of yellowstone are presented with emphasis on the genesis of lowo magmas erupted after the huckleberry ridge tuff 2 0 ma 2500 km and lava creek tuff 0 6 ma

multifractal investigation of continuous seismic signal recorded at el hierro volcano canary islands during the 2011 2012 pre and eruptive phases abstract the multifractal detrended fluctuation analysis mf dfa is an effective method that allows detecting multifractality in non stationary signals we applied the mf dfa to the continuous seismic signal recorded at el hierro volcano canary islands which was affected by a submarine monogenetic eruption in october 2011 we investigated the multifractal properties of the continuous seismic signal before the onset of the eruption and after we analysed three frames of the signal one measured before the onset of eruption that occurred on october 10 2011 and two after but corresponding to two distinct eruptive episodes the second one started on november 22 2011 and lasting until late february 2012 the results obtained show a striking difference in the width of the multifractal spectrum which is generally used to quantify the multifractal degree of a signal the multifractal spectra of the signal frames recorded during the eruptive episodes are almost identical and much narrower than that of the signal frame measured before the onset of the eruption such difference indicates that the seismic signal recorded during the unrest reflects mostly the fracturing of the host rock under the overpressure exerted by the intruding magma while that corresponding to the eruptive phases was mostly influenced by the flow of magma through the plumbing system even some fracturing remains not being possible to distinguish among the two eruptive episodes in terms of rock fracture mechanics

comment on evidence from acoustic imaging for submarine volcanic activity in 2012 off the west coast of el hierro canary islands spain by perez nm somoza l hernandez pa gonzalez de vallejo l leon r sagiya t biain a gonzalez fj medialdea t barrancos j ibanez j sumino h nogami k and romero c bull volcanol 2014 76 882 896

pb u and th diffusion in natural zircon zircon zrsio4 is one of the most widely used minerals for determining the age origin and thermal history of rocks by u th pb geochronology but the parameters describing the solid state volume diffusion rates of these elements in natural zircon which are themselves important for establishing the limits on the applicability of zircon for geochronological studies have remained poorly quantified1 this is because of the measurement difficulties associated with the low p p m concentrations and low diffusion rates of these elements in natural zircon and the chemical and physical heterogeneity present in most crystals here we present direct measurements of the uranium thorium and lead loss from a thermally treated gem quality natural zircon and show that lead diffuses much faster than uranium or thorium we find that the u th pb isotopic system in natural zircon will typically have a closure temperature greater than 900 c which explains why zircon is apparently such a robust geochrometer and is capable of remaining isotopically closed through extended periods of high grade metamorphism and partial melting of the host rock

geomagnetic conjugate observations of large scale traveling ionospheric disturbances using gps networks in japan and australia 1 the geomagnetic conjugacy of large scale traveling ionospheric disturbances lstids was studied using total electron content tec data derived from gps networks in japan and australia the number of simultaneous occurrences of lstids within 1 hour in both hemispheres was 5 out of 20 21 events in japan australia when kp 5 and 0 out of 15 10 when kp 4 as for the lstids observed simultaneously in both hemispheres the propagation velocities of equatorward lstid were comparable between the two hemispheres with differences of 10 40 the crossing times at 30 geomagnetic latitude of the simultaneous lstids over japan and australia were also different by several tens of minutes for all five events these observational results indicate that the lstids observed almost simultaneously in both hemispheres are not connected electromagnetically through the geomagnetic field but are generated by atmospheric gravity waves propagating to the equator independently in the two hemispheres

rerewhakaaitu tephra a land sea marker for the last termination in new zealand with implications for global climate change abstract the rerewhakaaiutu tephra erupted from okataina volcanic centre north island new zealand at 14 700 95 14 c yr bp ca 17 600 cal yr bp at a time of rapid re organisation of earth s climate system at the end of the last glacial termination i it provides a distinctive isochron in a range of different environments in north island and in adjacent south pacific ocean sediments terrestrial evidence based on fluvial aggradation and downcutting relationships loess accumulation rates palaeovegetation patterns and buried soil development and mineralogy shows that marked amelioration of climate occurred shortly before the rerewhakaaitu tephra was deposited similarly marine evidence from around this time shows major changes in accumulation rates of sediment and aeolian quartz and in the abundance of various marine organisms while foraminiferal oxygen and carbon isotope records indicate that the arrival of the glacial meltwater signal occurred close to or just after the deposition of the rerewhakaaitu tephra these changes are discussed in relation to controls on climate by oceanic and atmospheric mechanisms the re organisation of climate commencing at ca 15 000 14 500 14 c yr bp ca 18 000 17 400 cal yr bp is detected elsewhere in the southern hemisphere and evidently was linked to orbitally forced warming which is thought to have initiated ice retreat in both hemispheres

construction of an oceanic island insights from the el hierro canary islands 2011 2012 submarine volcanic eruption eight consecutive swath bathymetry data sets were obtained to monitor the submarine eruption that occurred from 10 october 2011 to 5 march 2012 south of el hierro island in the canary islands an increase in seismic activity since july 2011 preceded the onset of the eruption which was marked by seismic tremor and stained waters the first bathymetry 15 d after the eruption started depicts a cone topping at 205 m depth growing on a preexisting valley recurrent mapping shows changes in the morphology and depth of the cone allowing us to identify collapses and calculate eruptive volumes and rates which peaked at 12 7 10 6 m 3 d 1 of non dense rock equivalent ndre on 29 30 october the final cone consists of at least four vents along a north northwest south southeast lineation with the shallowest summit at 89 m depth the total accumulated volume was 329 10 6 ndre m 3 of which one third formed the cone similar cones have been identified on the submerged flanks of the island with volumes ranging from 6 to 1000 10 6 ndre m 3 as in many other volcanic islands large scale landslides play an important role in the evolution of el hierro a giant flank landslide el golfo 13 134 ka 150 180 km 3 mobilized in a single event a volume equivalent to 450 550 eruptions of the size of the reported one showing striking differences in the construction and destruction rates of the island this study is relevant for future monitoring programs and geohazard assessment of new submarine eruptions

geochemical signals related to the 2011 2012 el hierro submarine eruption abstract on 10 october 2011 a submarine volcanic eruption began 2 km south of the island of el hierro canary islands spain it was the first eruption after 40 years of quiescence in the canarian archipelago since mid july 2011 a multiparametric network has been deployed by the instituto geografico nacional hereinafter ign to monitor volcanic processes the data recorded by five stations measuring the air and soil temperature co2 and radon concentration in the air inside four galleries and one well are the focus of the present paper two important anomalies were found that improve comprehension of the volcanic process first a clear increase in co2 concentration in one gallery from 825 19 to 2305 35 ppm which seems to be mainly controlled by ground deformation measured during the unrest period preceding the eruption second a relationship between radon concentration in air in a well located in the northern side of the island with seismic energy release several peaks with up to 115 increase and ground deformation 50 growth in background level also before the eruption onset lastly changes in radon concentration during eruptive period seem to be modulated by seismic activity increases up to 233 which in turn is likely related to variations in magma rheology

comparing the cross polar cap potentials measured by superdarn and amie during saturation intervals 1 assimilative mapping of ionospheric electrodynamics amie and super dual auroral radar network superdarn are two commonly used techniques to measure cross polar cap potential pc in this study i compare pc inferred from amie with that inferred from superdarn during saturation intervals measurements from defense meteorological satellite program dmsp and polar cap pc index are also used to help estimate true pc seven saturation events in 2000 were selected for each event i ran the amie software driven by magnetometer data only by magnetometer data and superdarn data and by superdarn data only then i compared pc obtained from amie with that from superdarn i found that 1 pc inferred from superdarn is significantly lower than that inferred from other techniques including amie when pc is large e g greater than 150 kv 2 pc inferred from amie with superdarn input is much higher than pc inferred from superdarn 3 pc inferred from amie with magnetometer input tends to give the same results as that inferred from amie with magnetometer and superdarn input 4 pc inferred from amie with magnetometer input is in general in agreement with pcinferred from amie with superdarn input it is suggested that reason for the low values of superdarn derived pc during saturation intervals is that the superdarn algorithm to compute pc from measurements is not applicable to such intervals

assimilative mapping of ionospheric electrodynamics in the thermosphere ionosphere general circulation model comparisons with global ionospheric and thermospheric observations during the gem sundial period of march 28 29 1992 satellite and ground based observations from march 28 to 29 1992 were combined in the assimilative mapping of ionospheric electrodynamics amie procedure to derive realistic global distributions of the auroral precipitation and ionospheric convection which were used as inputs to the national center for atmospheric research ncar thermosphere ionosphere general circulation model tigcm comparisons of neutral model winds were made with fabry perot measurements and meridional winds derived from ionosondes the peak equatorward winds occurred 1 2 hours later in the model gravity waves launched from high latitude joule heating sources reached the equator in about 2 hours and agreed with observed variations in the height of the maximum electron density hmf2 and in the meridional winds joule heating events produced minima in the o n2 ratio that moved equatorward and usually westward in longitudinal strips which lasted about a day changes in the o n2 ratio and in the peak electron density nmf2 were strongly correlated so the observed daytime nmf2 values for stations near 50 magnetic latitude were generally reproduced by amie tigcm on the second day of the simulation the amie tigcm underestimated the electron density after midnight by up to a factor of 2 in midlatitudes while the modeled f2 layer was about 35 km lower than the observations at midnight shifting the model winds 2 hours earlier at night could double the nmf2 at 0400 lt and increase hmf2 by 20 km nmf2 could also be increased at night by realistically increasing the tigcm nighttime downward fluxes of o at the upper boundary

simultaneous mesosphere lower thermosphere and thermospheric f region observations during geomagnetic storms 1 simultaneous mesosphere lower thermosphere mlt and thermospheric f region observations made during geomagnetic storms are presented using the mu radar 35 n 136 e in alternate meteor and incoherent scatter is modes mf radar 45 n 136 e optical mesosphere thermosphere imagers omti 35 n 136 e and over 1000 gps receivers in japan the observations were made during one of the mtec s mesosphere thermosphere experiments for coupling studies campaigns conducted during 23 march to 2 april 2001 when a major storm with dst reaching 358 nt and a moderate storm with dst reaching 112 nt occurred and solar activity varied from high to very high f10 7 220 to 270 the campaign has provided zonal and meridional wind velocities at mlt altitudes 80 95 km over the mu and mf radars meridional wind velocity in the upper thermosphere 220 450 km and ionospheric electron density 150 600 km peak height and plasma drift velocity over the mu radar all sky airglow intensities at 557 7 nm 630 0 nm and 777 4 nm wavelengths over the mu radar location and vertical gps tec all over japan study of the data indicates that following the major storm the meridional wind in the upper thermosphere over the mu radar 35 n becomes weak less poleward during daytime and its diurnal amplitude reduces the winds and tides at mlt altitudes show changes during both nonstorm times and storm times but this study is not able to confirm any statistically significant changes related to the storms in the ionosphere following the onset of the major morning storm the electron density increases at altitudes near and above the ionospheric peak which after about 5 hours is followed by large increase in density at all altitudes above about 200 km on the following night though the density is generally low there is a large increase in density in the bottomside for about 3 hours centered at 0230 lt during this time a rare intense optical activity has occurred at all wavelengths 557 7 nm 630 nm and 777 4 nm over the low midlatitude location 35 n and an associated large scale traveling ionospheric disturbance lstid has propagated from north to south at f region altitudes

absolute ages aren t exactly the time scales of important events and processes in geology and archaeology are ascertained through measurements of radioisotopes the accuracy of the dating depends critically on how well known the radioactive decay constants are in their perspective renne karner and ludwig discuss the role that discrepancies in decay constants play in the accuracy of radioisotope dating as dating measurements become increasingly precise geochronologists will have to confront these kinds of systematic errors

northeastward motion of nighttime medium scale traveling ionospheric disturbances at middle latitudes observed by an airglow imager 1 nighttime medium scale traveling ionospheric disturbances mstids observed in 630 nm airglow images at middle latitudes are known to have a predominantly northwest southeast phase surface and to move southwestward in the northern hemisphere of earth however the mechanisms of mstid generation and their systematic southwestward motion have not been clarified in this paper we report the northeastward motion of the mstids observed at paratunka far east russia 52 97 n 158 25 e using an all sky 630 nm airglow imager at 2000 2300 lt on 19 august 2007 the mstids moved first southwestward but then back northeastward in the northern part of the images the northeastward motion of the mstids took place coincident with a f layer height decrease observed by an ionosonde at paratunka the f layer height decrease was also confirmed by an enhancement of the 630 nm airglow intensity which seemed to propagate from northeast to southwest this fact suggests that the f layer height decrease was caused by poleward wind enhancement rather than westward electric field these observations imply that the f layer height decrease or the poleward thermospheric wind has some role in the northeastward turning of the mstid propagation direction

zircon crystallization and recycling in the magma chamber of the rhyolitic kos plateau tuff aegean arc in contrast to most large volume silicic magmas in continental arcs which are thought to evolve as open systems with significant assimilation of preexisting crust the kos plateau tuff magma formed dominantly by crystal fractionation of mafic parents deposits from this 60 km3 pyroclastic eruption the largest known in the aegean arc lack xenocrystic zircons secondary ion mass spectrometry sims u pb ages on zircon cores never older than 500 ka and display sr nd whole rock isotopic ratios within the range of european mantle in an area with exposed paleozoic and tertiary continental crust this evidence implies a nearly closed system chemical differentiation consequently the age range provided by zircon sims u th pb dating is a reliable indicator of the duration of assembly and longevity of the silicic magma body above its solidus the age distribution from 160 ka age of eruption by sanidine 40ar 39ar dating smith et al 1996 1 to ca 500 ka combined with textural characteristics high crystal content corrosion of most anhydrous phenocrysts but stability of hydrous phases suggest 1 a protracted residence in the crust as a crystal mush and 2 rejuvenation reduced crystallization and even partial resorption of minerals prior to eruption probably induced by new influx of heat and volatiles this extended evolution chemically isolated from the surrounding crust is a likely consequence of the regional geodynamics because the thinned aegean microplate acts as a refractory container for magmas in the dying aegean subduction zone continent continent subduction 1 ref 32

age and timing of the permian mass extinctions u pb dating of closed system zircons the age and timing of the permian triassic mass extinction have been difficult to determine because zircon populations from the type sections are typically affected by pervasive lead loss and contamination by indistinguishable older xenocrysts zircons from nine ash beds within the shangsi and meishan sections china pretreated by annealing followed by partial attack with hydrofluoric acid result in suites of consistent and concordant uranium lead u pb ages eliminating the effects of lead loss the u pb age of the main pulse of the extinction is 252 6 0 2 million years synchronous with the siberian flood volcanism and it occurred within the quoted uncertainty

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

volcanic tremors good indicators of change in plumbing systems during volcanic eruptions abstract geophysical and geochemical signals recorded during episodes of unrest preceding volcanic eruptions provide information on movements of magma inside the lithosphere and on how magma prepares to reach the surface when the eruption ensues continuous volcanic monitoring can reveal the nature of changes occurring in the volcano s plumbing system which may be correlated with changes in both eruption behaviour and products during the 2011 2012 submarine eruption of el hierro canary islands the seismic signal surface deformation a broad stain on the sea surface of the eruption site and the occasional appearance of floating lava balloons and pyroclastic fragments were the main observable signs a strong continuous tremor in the vent accompanied the eruption and varied significantly in amplitude frequency and dynamical parameters we analysed these variations and correlated them with changes in the distribution of earthquakes and in the petrology of the erupting magma this enabled us to relate variations in tremors to changes in the i stress conditions of the plumbing system ii dimensions of the conduit and vent iii intensity of the explosive episodes and iv rheological changes in the erupting magma the results obtained show how the tremor signal was strongly influenced by stress changes in the host rock and in the rheological variations in the erupting magma we conclude that the tracking of real time syn eruptive tremor signals via the observation of variations in plumbing systems and magma physics is a potentially effective tool for interpreting eruption dynamics and suggest that similar variations observed in pre eruptive tremors will have a similar origin

in situ u pb ages of zircons from the bishop tuff no evidence for long crystal residence times ion microprobe u pb isotope analyses of zircons from fallout and intercalated ash flow deposits of the early most chemically evolved bishop tuff east central california yield a weighted mean age of 823 11 ka mean square of weighted deviates mswd 0 8 n 22 a similar mean age of 839 36 ka mswd 0 6 n 15 obtained on unpolished zircon rims suggests that the difference between these ages and that of 760 ka for the bishop tuff obtained by recent ar isotope determinations may be largely analytical in origin considerations based only on the effect of 230 th 234 u disequilibria on the u pb ages yield an apparent maximum mean crystal residence time for zircon of 100 k y the zircon residence times are significantly shorter than those inferred from previous estimates for the timing of phenocryst growth and suggest that once evolved the early bishop tuff rhyolite was not stored for long before erupting

shrimp u pb dating of the preeruption growth history of zircons from the 340 ka whakamaru ignimbrite new zealand evidence for 250 k y magma residence times the whakamaru group ignimbrites are products of one of the largest caldera forming eruptions from the central taupo volcanic zone new zealand ca 340 ka imaging of zircons separated from low silica rhyolite pumice from whakamaru group ignimbrite reveals a complex magmatic crystallization history some grains contain resorbed cores cores and rims of individual zircons were dated using the sensitive high resolution ion microprobe due to the high u contents of the zircons 206 pb count rates were sufficiently high to obtain 206 pb 238 u ages with precisions of 5 10 1 s using longer than usual 206 pb count times and this has allowed zircon core and rim ages to be distinguished zircon rim and outer growth zone ages range from within 1 s error of the eruption age to 449 20 ka whereas zircon cores produced ages to 608 20 ka indicating magmatic residence times exceeding 250 k y for some zircons the data are consistent with a prolonged evolution of the magma system over hundreds of thousands of years involving magma replenishment and mixing with residual phases of older silicic magma chambers in addition to crystal fractionation processes prior to eruption the study has shown that 206 pb 238 u dating using high resolution ion microprobe can be used to determine zircon preeruptive growth histories in quaternary lavas and pyroclastic rocks

second reply to comment of r s j sparks h e huppert and c j n wilson on evidence for long residence times of rhyolitic magma in the long valley magmatic system the isotopic record in the precaldera lavas of glass mountain

observations and simulations of quasiperiodic ionospheric oscillations and large scale traveling ionospheric disturbances during the december 2006 geomagnetic storm 1 a numerical simulation was performed to investigate quasiperiodic ionospheric oscillations that were observed with periods of 4 5 h by the ionosonde network okinawa yamagawa kokubunji and wakkanai in japan during the 15 december 2006 magnetic storm this simulation used the coupled magnetosphere ionosphere thermosphere cmit 2 0 model the cmit model reproduced the main characteristics of the observed ionospheric oscillations although it remains a challenging task to simulate the observations in a quantitative sense term analysis of the ion continuity equation demonstrated that the ionospheric oscillations in this event were mainly induced by the disturbed neutral winds which were associated with the large scale thermospheric circulation and traveling atmospheric disturbances tads during the storm the tads simulated from the model were then compared with those observed by the gps earth observation network geonet in japan to validate the simulation results a prominent northward propagating large scale traveling ionospheric disturbance lstid during daytime seen by the geonet total electron content tec data was captured by the cmit model two southward lstids observed by geonet gps network were also reproduced by the cmit model however the model gave faster phase speeds for the southward propagating lstid occurred during 0620 0800 ut and the northward propagating lstid furthermore the model missed the lstid seen in the tec perturbation data during 0140 0220 ut finally both observations and simulations showed a strong hemispheric asymmetry for the tad propagation that occurred during 0000 0400 ut which may be associated with the hemispheric asymmetry of the change of joule heating at high latitude

spatial and temporal variations of diffuse co2 degassing at el hierro volcanic system relation to the 2011 2012 submarine eruption we report herein the results of extensive diffuse co2 emission surveys performed on el hierro island in the period 1998 2012 more than 17 000 measurements of the diffuse co2 efflux were carried out most of them during the volcanic unrest period that started in july 2011 two significant precursory signals based on geochemical and geodetical studies suggest that a magma intrusion processes might have started before 2011 in el hierro island during the preeruptive and eruptive periods the time series of the diffuse co2 emission released by the whole island experienced two significant increases the first started almost 2 weeks before the onset of the submarine eruption reflecting a clear geochemical anomaly in co2 emission most likely due to increasing release of deep seated magmatic gases to the surface the second one between 24 october and 27 november 2011 started before the most energetic seismic events of the volcanic seismic unrest the data presented here demonstrate that combined continuous monitoring studies and discrete surveys of diffuse co2 emission provide important information to optimize the early warning system in volcano monitoring programs and to monitor the evolution of an ongoing volcanic eruption even though it is a submarine eruption

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

pb diffusion in zircon abstract chemical diffusion of ti under anhydrous conditions at 1 atm and under fluid present elevated pressure 1 1 1 2 gpa conditions has been measured in natural zircon the source of diffusant for 1 atm experiments was a zro2 tio2 zircon mixture with experiments run in crimped pt capsules diffusion experiments done in the presence of h2o co2 fluid were run in a piston cylinder apparatus using a source of ground tio2 zrsio4 and sio2 with oxalic acid added to produce h2o co2 vapor and partially melt the solid source material yielding an assemblage of rutile zircon melt vapor nuclear reaction analysis nra with the resonant nuclear reaction 48ti p 49v was used to measure diffusion profiles for both sets of experiments the following arrhenius parameters were obtained for ti diffusion normal to cover the temperature range 1350 1550 c at 1 atm d ti 3 33 10 2 exp 754 56 kj mol 1 r t m 2 s 1 ti diffusivities were found to be similar for experiments run under fluid present conditions a fit to all of the data yields the arrhenius relation d 1 34 102 exp 741 46 kj mol 1 rt m2 s 1 these data suggest that zircon should be extremely retentive of ti chemical signatures indicating that the recently developed ti in zircon crystallization geothermometer watson e b harrison t m 2005 zircon thermometer reveals minimum melting conditions on earliest earth science 308 841 844 will be quite robust in preserving temperatures of zircon crystallization titanium diffuses somewhat faster in zircon than larger tetravalent cations u th and hf but considerably more slowly than pb the ree and oxygen hence ti crystallization temperatures may be retained under circumstances when radiometric ages or other types of geochemical information are lost

evidence from acoustic imaging for submarine volcanic activity in 2012 off the west coast of el hierro canary islands spain we report precursory geophysical geodetic and geochemical signatures of a new submarine volcanic activity observed off the western coast of el hierro canary islands submarine manifestation of this activity has been revealed through acoustic imaging of submarine plumes detected on the 20 khz chirp parasound subbottom profiler topas ps18 mounted aboard the spanish rv hesperides on june 28 2012 five distinct filament shaped acoustic plumes emanating from the flanks of mounds have been recognized at water depth between 64 and 88 m on a submarine platform located nw el hierro these plumes were well imaged on topas profiles as flares of high acoustic contrast of impedance within the water column moreover visible plumes composed of white rafts floating on the sea surface and sourcing from the location of the submarine plumes were reported by aerial photographs on july 3 2012 5 days after acoustic plumes were recorded in addition several geophysical and geochemical data support the fact that these submarine vents were preceded by several precursory signatures i a sharp increase of the seismic energy release and the number of daily earthquakes of magnitude 2 5 on june 25 2012 ii significant vertical and horizontal displacements observed at the canary islands gps network nagoya university iter grafcan with uplifts up to 3 cm from june 25 to 26 2012 iii an anomalous increase of the soil gas radon activity from the end of april until the beginning of june reaching peak values of 2 7 kbq m3 on june 3 2012 and iv observed positive peak in the air corrected value of 3he 4he ratio monitored in ground waters 8 5 atmospheric 3he 4he ratio ra at the northwestern el hierro on june 16 2012 combining these submarine and subaerial information we suggest these plumes are the consequence of submarine vents exhaling volcanic gas mixed with fine ash as consequence of an event of rapid rise of volatile rich magma beneath the nw submarine ridge of el hierro these precursory signals have revealed important to improve and optimize the detection of early warning signals of volcanic unrest episodes at el hierro

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

on the relation between ground surface deformation and seismicity during the 2012 2014 successive magmatic intrusions at el hierro island abstract six different magmatic intrusions were detected around el hierro island in the two years that followed the end of the 2011 2012 submarine eruption each intrusion lasted between few days to three weeks and produced intense seismic swarms and rapid ground deformation we performed a hypodd relocation of 6000 earthquakes and inverted the gps data in order to obtain the location of the magma source of each intrusion each episode presents a spatial gap between seismicity and magma source of 3 8 km with the earthquakes located always deeper than the deformation sources we propose a magma plumbing system consisting on a deep structure injecting magma to a more ductile shallower location beneath el hierro crust while the seismicity is associated with the deeper structure the ascent and accumulation of magma at shallower level deforms the crust aseismically the mechanism of most of these episodes consists of an initial injection of magma producing most of the ground deformation and high b values of the seismicity indicating fluid fractures during the first days and finishes with high magnitude earthquakes and low b values indicating an overpressure of the injection process there is a correlation between the seismic and geodetic moment ratio and the direction of propagation of each intrusion towards one of the volcanic rifts of the island suggesting the possible existence of a deep structure beneath the island related with to the triaxial origin of the island this work presents important advances in the knowledge of monogenetic magmatic intrusions and specifically in those occurred in el hierro island between 2011 and 2014 with important implications for future volcano monitoring in the canary islands

monazite th pb age depth profiling the significant capabilities of the ion microprobe for thermochronometric investigations of geologic materials remain largely unexploited whereas sup 208 pb sup 232 th spot analysis allows approximately 10 mm scale imaging of pb loss profiles or overgrowths in sectioned monazite grains the spatial resolution offered by depth profiling into the surface region of natural crystals is more than two orders of magnitude higher the authors document here the ability of the high resolution ion microprobe to detect sup 208 pb sup 232 th age differences of 1 m y with better than 0 05 micro m depth resolution in the outer micron of tertiary monazites from the hanging wall of the himalayan main central thrust age gradients on this scale are inaccessible to ion microprobe spot analysis or conventional thermal ionization mass spectrometry interpretation of the near surface sup 208 pb distributions with available monazite pb diffusion data illustrates the potential of the approach for recovering continuous high temperature thermal history information not previously available

a new 14 c age for the oruanui wairakei eruption new zealand the oruanui eruption was the largest known outburst of taupo volcano new zealand and is among the larger quaternary eruptions documented the eruption deposits are variously known as the oruanui wairakei kawakawa tephra or aokautere ash formations and represent a bulk volume probably exceeding 500 km 3 four new 14 c age determinations on carbonized vegetation in the non welded oruanui ignimbrite are combined to give a conventional age of 22590 230 yr b p compared with the previously accepted figure of 20000 yr b p this new age resolves the anomaly of apparently older 14 c ages being obtained from a demonstrably younger new zealand deposit and strengthens correlation of this eruption with an antarctic ice core acid anomaly the trace of this eruption has great potential as a time plane marker in the antarctic just prior to the last glacial maximum the close similarity in ages between the oruanui and a comparable sized eruption ito aira tn in japan suggests that this period of activity may represent the best chance of resolving any linkages between large scale explosive silicic volcanism and climate changes

volcanic signatures in time gravity variations during the volcanic unrest on el hierro canary islands gravity changes occurring during the initial stage of the 2011 2012 el hierro submarine eruption are interpreted in terms of the preeruptive signatures during the episode of unrest continuous gravity measurements were made at two sites on the island using the relative spring gravimeter lacoste and romberg gphone 054 on 15 september 2011 an observed gravity decrease of 45 mu gal associated with the southward migration of seismic epicenters is consistent with a lateral magma migration that occurred beneath the volcanic edifice an apparently clear precursor of the eruption that took place 25 days later on 10 october 2011 high frequency gravity signals also appeared on 6 11 october 2011 pointing to an occurring interaction between a magmatic intrusion and the ocean floor these important gravity changes with amplitudes varying from 10 to 90 mu gal during the first 3 days following the onset of the eruption are consistent with the northward migration of the eruptive focus along an active eruptive fissure an apparent correlation of gravity variations with body tide vertical strain was also noted which could indicate that concurrent tidal triggering occurred during the initial stage of the eruption

magma emission rates from shallow submarine eruptions using airborne thermal imaging abstract the effusion rate is the most important parameter to gather when a volcanic eruption occurs because it controls the way in which a lava body grows extends and expands influencing its dimensional properties calculation of lava flow volume from thermal images collected by helicopter surveys has been largely used during the last decade for monitoring subaerial effusive eruptions however due to the depths where volcanic activity occurs monitoring submarine volcanic eruptions is a very difficult task the 2011 2012 submarine volcanic eruption at el hierro canary islands has provided a unique and excellent opportunity to monitor eruptive processes occurring on the seabed the use of a hand held thermal camera during daily helicopter flights allowed us to estimate for the first time the daily and total erupted magma volumes from a submarine eruption the volume of magma emitted during this eruption has been estimated at 300 mm3 giving an average effusion rate of 25 m3 s 1 thermal imagery by helicopter proved to be a fast inexpensive safe and reliable technique of monitoring volcanic eruptions when they occur on the shallow seabed

k ar ages and magnetic stratigraphy of a hotspot induced fast grown oceanic island el hierro canary islands abstract the combined use of accurate radiometric dating and magnetic stratigraphy can be applied to define the main stages of the building of oceanic volcanic islands this method has been successfully applied on the island of el hierro the westernmost island of the canaries archipelago for the emerged part of this island built in the last 1 2 ma magnetic stratigraphy and mapping show the presence of four consecutive subchrons k ar dating of eighteen samples in stratigraphic sequences using an unspiked technique produced ages consistent with the general volcanic stratigraphy the ages show that the magnetic polarity zones correlate to the upper part of the matuyama and to the brunhes chrons the jaramillo normal polarity subchron of the upper part of the matuyama reverse polarity chron is recorded in one of the lava sequences the lower limit of this event is constrained by two ages of 1 04 0 02 ma and one of 1 05 0 02 ma close to the value deduced from the astronomically tuned magnetic polarity time scale apts the volcanic history can be summarised by two consecutive main basaltic volcanic edifices the el tinor active during the upper part of the matuyama chron and the el golfo edifice constructed during the brunhes chron

landslides and the evolution of el hierro in the canary islands seismic and sonar data have been used to evaluate the extent and characteristics of giant landslides on the flanks of el hierro in the canary islands as the youngest and most southwesterly of the canary islands el hierro has experienced rapid growth and destructive events in its 1 12 million year history at least four giant landslides el golfo el julan san andres and las playas have modified 450 km3 of el hierro during the last 200 300 thousand years with each landslide event removing around 3 of the total edifice volume the extent of landsliding indicates that it is the main process of decay we characterise flank morphology around el hierro and distinguish between rugged unfailed flank failed flank and steep gullied ridge flanks affected by landsliding have downslope long profiles with distinctive b coefficients and exponential forms the el golfo landslide is the most recent 15 ka best described and clearly defined landslide in the canary islands the el julan landslide sw flank has an estimated volume of 130 km3 an age of 200 ka and is characterised by gravitational slumping on the se flank two new landslide events are reported the younger landslide las playas occurred 145 176 ka has a narrow steep sided embayment and a corresponding blocky debris avalanche deposit the older landslide san andres is recognised on the basis of a highly chaotic seismic facies offshore and reduced upper flank gradients its lack of an upper flank embayment and offshore blocky debris avalanche lead us to interpret that the landslide involved gravitational slumping possibly a series of events which reduced upper flank gradients but did not catastrophically collapse to produce a debris avalanche

deep submarine pyroclastic eruptions theory and predicted landforms and deposits submarine pyroclastic eruptions at depths greater than a few hundred meters are generally considered to be rare or absent because the pressure of the overlying water column is sufficient to suppress juvenile gas exsolution so that magmatic disruption and pyroclastic activity do not occur consideration of detailed models of the ascent and eruption of magma in a range of sea floor environments shows however that significant pyroclastic activity can occur even at depths in excess of 3000 m in order to document and illustrate the full range of submarine eruption styles we model several possible scenarios for the ascent and eruption of magma feeding submarine eruptions 1 no gas exsolution 2 gas exsolution but no magma disruption 3 gas exsolution magma disruption and hawaiian style fountaining 4 volatile content builds up in the magma reservoir leading to hawaiian eruptions resulting from foam collapse 5 magma volatile content insufficient to cause fragmentation normally but low rise speed results in strombolian activity and 6 volatile content builds up in the top of a dike leading to vulcanian eruptions we also examine the role of bulk interaction steam explosivity and contact surface steam explosivity as processes contributing to volcaniclastic formation in these environments we concur with most earlier workers that for magma compositions typical of spreading centers and their vicinities the most likely circumstance is the quiet effusion of magma with minor gas exsolution and the production of somewhat vesicular pillow lavas or sheet flows depending on effusion rate the amounts by which magma would overshoot the vent in these types of eruptions would be insufficient to cause any magma disruption the most likely mechanism of production of pyroclastic deposits in this environment is strombolian activity due to the localized concentration of volatiles in magma that has a low rise rate magmatic gas collects by bubble coalescence and ascends in large isolated bubbles which disrupt the magma surface in the vent producing localized blocks bombs and pyroclastic deposits another possible mode of occurrence of pyroclastic deposits results from vulcanian eruptions these deposits being characterized by the dominance of angular blocks of country rocks deposited in the vicinity of a crater should be easily distinguishable from strombolian and hawaiian eruptions however we stress that a special case of the hawaiian eruption style is likely to occur in the submarine environment if magmatic gas buildup occurs in a magma reservoir by the upward drift of gas bubbles in this case a layer of foam will build up at the top of the reservoir in a sufficient concentration to exceed the volatile content necessary for disruption and hawaiian style activity the deposits and landforms are predicted to be somewhat different from those of a typical primary magmatic volatile induced hawaiian eruption specifically typical pyroclast sizes might be smaller fountain heights may exceed those expected for the purely magmatic hawaiian case cooling of descending pyroclasts would be more efficient leading to different types of proximal deposits and runout distances for density flows would be greater potentially leading to submarine pyroclastic deposits surrounding vents out to distances of tens of meters to a kilometer in addition flows emerging after the evacuation of the foam layer would tend to be very depleted in volatiles and thus extremely poor in vesicles relative to typical flows associated with hawaiian style eruptions in the primary magmatic gas case we examine several cases of reported submarine volcaniclastic deposits found at depths as great as 3000 m and conclude that submarine hawaiian and strombolian eruptions are much more common than previously suspected at mid ocean ridges furthermore the latter stages of development of volcanic edifices seamounts formed in submarine environments are excellent candidates for a wide range of submarine pyroclastic activity due not just to the effects of decreasing water depth but also to 1 the presence of a summit magma reservoir which favors the buildup of magmatic foams enhancing hawaiian style activity and episodic dike emplacement which favors strombolian style eruptions and 2 the common occurrence of alkalic basalts the co2 contents of which favor submarine explosive eruptions at depths greater than tholeiitic basalts these models and predictions can be tested with future sampling and analysis programs and we provide a checklist of key observations to help distinguish among the eruption styles

a large scale traveling ionospheric disturbance during the magnetic storm of 15 september 1999 enhancement of gps total electron content 1 0 10 16 m 2 multipoint and imaging observations of these parameters show that the lstid moved equatorward over japan with a velocity of 400 450 m s from a comparison with the sheffield university plasmasphere ionosphere model supim we conclude that an enhancement 250 300 m s of poleward neutral wind that is propagating equatorward caused these observational features of the lstid at midlatitudes to investigate generation of the lstid by auroral energy input we have used auroral images obtained by the polar uvi instrument magnetic field variations obtained at multipoint ground stations and the empirical joule heating rate calculated by the assimilative mapping of ionospheric electrodynamics amie technique intense auroral energy input was observed at 0800 1100 ut 4 6 hours before the lstid probably causing equatorward neutral wind at lower latitudes it is likely that the poleward wind pulse that caused the observed lstid was generated associated with the cessation of this equatorward wind the effect of lorentz force is also discussed index terms 0310 atmospheric composition and structure airglow and aurora 2427 ionosphere ionosphere atmosphere interactions 0335 2435 ionosphere ionospheric disturbances 2437 ionosphere ionospheric dynamics 2788 magnetospheric physics storms and substorms keywords large scale traveling ionospheric disturbance thermosphere ionosphere coupling magnetic storm airglow imaging gps network ionosonde

submarine eruption fed and resedimented pumice rich facies the dogashima formation izu peninsula japan in the izu peninsula japan the pliocene pumice rich dogashima formation 4 55 0 87 ma displays exceptional preservation of volcaniclastic facies that were erupted and deposited in a below wave base marine setting it includes high concentration density current deposits that contain clasts that were emplaced hot indicating an eruption fed origin the lower part of the dogashima 2 unit consists of a very thick sequence 1 m pumice and ash rich bed overlying the breccias may be derived from delayed settling of pyroclasts from suspension in dogashima 1 and 2 thick cross and planar bedded facies composed of sub rounded pumice clasts are intercalated with eruption fed facies implying inter eruptive mass wasting on the flank of a submarine volcano and reworking and resedimentation by high energy tractional currents in a below wave base environment

reply to comment from blanco et al 2015 on evidence from acoustic imaging for submarine volcanic activity in 2012 off the west coast of el hierro canary islands spain by perez et al bull volcanol 2014 76 882 896

repeated magmatic intrusions at el hierro island following the 2011 2012 submarine eruption abstract after more than 200 years of quiescence in july 2011 an intense seismic swarm was detected beneath the center of el hierro island canary islands culminating on 10 october 2011 in a submarine eruption 2 km off the southern coast although the eruption officially ended on 5 march 2012 magmatic activity continued in the area from june 2012 to march 2014 six earthquake swarms indicative of magmatic intrusions were detected underneath the island we have studied these post eruption intrusive events using gps and insar techniques to characterize the ground surface deformation produced by each of these intrusions and to determine the optimal source parameters geometry location depth volume change source inversions provide insight into the depth of the intrusions 11 16 km and the volume change associated with each of them between 0 02 and 0 13 km 3 during this period 20 cm of uplift was detected in the central western part of the island corresponding to approximately 0 32 0 38 km 3 of magma intruded beneath the volcano we suggest that these intrusions result from deep magma migrating from the mantle trapped at the mantle lower crust discontinuity in the form of sill like bodies this study using joint inversion of gps and insar data in a post eruption period provides important insight into the characteristics of the magmatic plumbing system of el hierro an oceanic intraplate volcanic island

40ar 39ar ages from the rhyolite of alder creek california age of the cobb mountain normal polarity subchron revisited new 40 ar 39 ar age determinations on sanidine from the rhyolite of alder creek california indicate a 1 186 0 006 ma age for the cobb mountain normal polarity subchron the new age is statistically older 0 05 than the previously reported k ar age 1 12 0 02 ma and agrees with the age suggested by the astronomical polarity time scale incomplete extraction of radiogenic 40 ar 40 ar from the sanidine is the most likely reason for the disparity between the 40 ar 39 ar and k ar ages because the cobb mountain subchron is a worldwide short duration event and because no widely used interlaboratory 40 ar 39 ar standard younger than 27 ma exists we propose that sanidine from the rhyolite of alder creek be considered for use as a new quaternary 40 ar 39 ar mineral standard

extreme u th disequilibrium in rift related basalts rhyolites and granophyric granite and the timescale of rhyolite generation intrusion and crystallization at alid volcanic center eritrea received september 20 2005 accepted june 14 2006 advance access publication july 14 2006rhyolite pumices and co erupted granophyric granite xenolithsyield evidence for rapid magma generation and crystallization priorto their eruption at 15 2 2 9 ka at the alid volcanic center inthe danikil depression eritrea whole rock u and th isotopicanalyses show

40ar 39ar laser probe ages of bishop tuff quartz phenocrysts substantiate long lived silicic magma chamber at long valley united states laser probe ar 40 ar 39 dating of quartz phenocrysts with rhyolite glass inclusions from the bishop tuff air fall and ignimbrite deposits reveals that the long valley magma system existed as a long lived silicic magma chamber throughout most of the pleistocene sanidine phenocryst and matrix glass analyses show that the bishop tuff eruption occurred at 759 1 to 761 1 ha initial and radiogenic ar isotope ratios indicate isotopic equilibrium between the sanidine phenocrysts and their host melt at the time of eruption the quartz phenocrysts in contrast the most abundant phenocryst phase of the bishop rhyolite crystallized trapped their glass inclusions and became a closed system with respect to ar at 1 89 0 03 to 2 3 0 3 ma consequently the bishop rhyolite magma already resided in the long valley basement and had formed most of its quartz phenocrysts similar to 1 1 m y before its principal eruption providing important constraints on the longevity of large silicic magma chambers

revised ages for tuffs of the yellowstone plateau volcanic field assignment of the huckleberry ridge tuff to a new geomagnetic polarity event 40 ar 39 ar ages were determined on the three major ash flow tuffs of the yellowstone plateau volcanic field in the region of yellowstone national park in order to improve the precision of previously determined ages total fusion and incremental heating ages of sanidine yielded the following mean ages huckleberry ridge tuff 2 059 0 004 ma mesa falls tuff 1 285 0 004 ma and lava creek tuff 0 639 0 002 ma the huckleberry ridge tuff has a transitional magnetic direction and has previously been related to the reunion normal polarity subchron dating of the reunion event has been reviewed and its ages have been normalized to a common value for mineral standards the age of the huckleberry ridge tuff is significantly younger than lava flows of the reunion event on re union island supporting other evidence for a normal polarity event younger than the reunion event

catastrophic collapse of the volcanic island of hierro 15 ka ago and the history of landslides in the canary islands landslides play an important role in the evolution of many volcanic islands producing huge fields of blocky volcanic debris on their submarine slopes sidescan sonar images presented in this paper provide evidence for a large debris avalanche el golfo on the northern flank of hierro island in the canary islands angular blocks as much as 1 2 km across and 200 m high cover the debris avalanche surface el golfo avalanche is related to both the canary debris flow and a volcaniclastic turbidite found in the madeira abyssal plain 600 km west of the canaries dating of the turbidite and the failure scarp onshore indicates that the failure probably occurred between 13 and 17 ka there appears to be a general correlation between volcaniclastic turbidites in the abyssal plain sequence and landslides in the canaries during the past 750 ka tentatively this correlation suggests that seven major landslides have affected the canaries in that time

tsunamis of volcanic origin summary of causes with particular reference to krakatoa 1883 known tsunamis of volcanic origin are reviewed and classified according to their causes earthquakes accompanying eruptions excluding tectonic events which apparently triggered eruptions pyroclastic flows and submarine explosions have each accounted for about 20 of cases ten causes of volcanic tsunamis are discussed from the risk point of view those due to landslides are particularly dangerous eruptions at calderas are more likely to generate tsunamis than eruptions elsewhere of those killed directly by volcanic eruptions nearly a quarter have died as a result of tsunamis by transfer of energy to sea waves a violent eruption which would be comparatively harmless on land extends greatly the radius over which destruction occurs

rapid rates of growth and collapse of monowai submarine volcano in the kermadec arc most of earth s volcanoes are under water as a result of their relative inaccessibility little is known of the structure and evolution of submarine volcanoes advances in navigation and sonar imaging techniques have made it possible to map submarine volcanoes in detail and repeat surveys allow the identification of regions where the depth of the sea floor is actively changing here we report the results of a bathymetric survey of monowai submarine volcano in the tonga kermadec arc which we mapped twice within 14 days we found marked differences in bathymetry between the two surveys including an increase in seafloor depth up to 18 8 m and a decrease in depth up to 71 9 m we attribute the depth increase to collapse of the volcano summit region and the decrease to growth of new lava cones and debris flows hydroacoustic t wave data reveal a 5 day long swarm of seismic events with unusually high amplitude between the surveys which directly link the depth changes to explosive activity at the volcano the collapse and growth rates implied by our data are extremely high compared with measured long term growth rates of the volcano demonstrating the pulsating nature of submarine volcanism and highlighting the dynamic nature of the sea floor

ground observation and amie tiegcm modeling of a storm time traveling ionospheric disturbance 1 this paper reports the first comparison between comprehensive observations of equatorward moving traveling ionospheric disturbance at midlatitudes and thermospheric general circulation model with high latitude energy input based on data assimilation a prominent traveling ionospheric disturbance tid was observed during the major magnetic storm of 31 march 2001 the tid propagated from north to south over japan with phase speeds of 370 640 m s the assimilative mapping of ionospheric electrodynamics amie technique was used as input to the thermosphere ionosphere electrodynamics general circulation model tiegcm to investigate generation and propagation of the observed tid in the model two joule heating enhancements in the high latitude dayside sector produced two distinct traveling atmospheric waves tads which propagated to japan in the midnight sector as enhancements in thermospheric temperature and southward wind speed the phase speed of the tads was much faster 1100 m s in the model probably due to the overestimation of joule heating in the model the second tad corresponds to the observed prominent tid while signatures of the first tad were also seen in the observed ionosonde data the observed tid was characterized by a decrease in southward wind speed causing a significant f layer height decrease and a temporal enhancement of f layer peak density these characteristics were reproduced by the model as a rarefaction of the second tad the temporal enhancement of f layer peak density was because of the vertical shear of meridional wind the absolute value of f layer electron density in the model was several factors smaller than that observed probably because of the underestimation of the supply of o ions from the plasmasphere

causes and mechanisms of the 2011 2012 el hierro canary islands submarine eruption 1 el hierro eruption started on 10 october 2011 after an unrest episode that initiated on 17 july 2011 this is the first eruption in the canary islands that has been tracked in real time although being submarine and not directly observable the data recorded allowed its reconstruction and to identify its causes and mechanisms seismicity surface deformation and petrological data indicate that a batch of basanitic magma coming from a reservoir located at a depth of about 25 km below the el hierro island was emplaced at shallower depth creating a new reservoir about 10 12 km above where magma evolved until the initiation of the eruption the characteristics of seismicity and surface deformation suggest that the necessary space to accumulate magma at this shallower position which coincides with the crust mantle boundary beneath el hierro was created in about 2 months by elastic deformation and magma driven fracturing of the crust after this first intrusion episode part of the magma started to migrate laterally toward the se for nearly 20 km always keeping the same depth and following a path apparently controlled by stress barriers created by tectonic and rheological contrasts in the upper lithosphere this lateral migration of magma ended with a submarine eruption at about 5 km offshore from the southern corner of el hierro island the total seismic energy released during the unrest episode was of 8 1 1011 j and the total uplift previous to the onset of the eruption was of 40 mm combining geological geophysical and petrological data and numerical modeling we propose a volcanological model of the causes and mechanisms of el hierro eruption that shows how the stress distribution in the crust beneath el hierro which was influenced by rheological contrasts tectonic stresses and gravitational loading controlled the movement and eruption of magma we also discuss the implications of this model in terms of eruption forecast in the canary islands

damping of large scale traveling ionospheric disturbances detected with gps networks during the geomagnetic storm 1 large scale traveling ionospheric disturbances lstids during the geomagnetic storm on 22 september 1999 were studied using total electron content tec data from the gps earth observation network geonet in japan international gps service igs and continuously operating reference stations cors in the united states the damping rates of the lstids were precisely derived in several local time sectors and were found to depend on values of the background tec this indicates that the dominant physical mechanism of the lstids damping is the ion drag effect by the background ionosphere the high resolution tec data from geonet revealed that two successive lstids were damped significantly as they traveled equatorward in the dawn sector the ratio of the perturbation component of tec to the background component i i0 decreased exponentially with the damping rate of 0 89 1000 km and 0 77 1000 km we studied also the amplitude of i i0 at high latitudes using igs data and found that the damping rates of lstids at high latitudes tended to be smaller than those at midlatitudes global tec observations during this geomagnetic storm by the igs and cors networks detected that several lstids propagated also equatorward in the afternoon sector and in the night sector the lstids in the afternoon sector were most damped with the damping rate of 1 04 1000 km which corresponds to the e folding length of 961 km the damping rate of lstids in the night sector was found to be small the lstids had a tendency to be damped rapidly in the regions where background tec was large this dependence of the damping rate on latitude and local time indicates that this intense damping of lstids was caused mainly by the ion drag effect that is proportional to the ion collision frequency the relation between the damping rates and the background tec derived from the observation are consistent with those estimated with a theoretical calculation of the gravity wave damping by the ion drag effect the worldwide distribution of gps receivers enabled us to estimate the longitudinal extent of these lstids the zonal width of lstids in the dawn sector was narrower than 45 in longitude 2 900 km around 55 n and wider than 20 in longitude 1 800 km around 40 n these widths were narrower than those reported in previous studies

underwater records of submarine volcanic activity el hierro canary islands 2011 2012 eruption abstract we present the monitoring of a submarine volcanic eruption that took place near the southernmost emerged land of el hierro island canary islands spain from october 2011 to february 2012 right after the onset of the eruption in mid october 2011 we deployed an offshore geophone array for the purpose of monitoring the submarine eruptive activity signals it acquired continuous data from october 2011 to may 2012 sometime after the end of the eruption the array consisted of 8 high frequency 3 component geophones assembled into a cable string with 6 m of separation the geophone string was installed in la restinga harbor at a distance of less than 2 km from the volcanic edifice the dataset acquired with the array is a unique continuous acoustic record of the activity associated with this eruption we analyzed the continuous signal of the eruptive activity with special interest in those events reflecting the eruption dynamics our results show that the geophone array was recording acoustic waves from a back azimuth source corresponding to the position of the submarine vent traveling at a speed of 1510 m s compatible with the speed of sound in water acoustic data shows a good correlation with the seismic data recorded on land for the case of earthquake occurrence in addition it provides relevant information towards the understanding of the eruptive surface activity therefore this methodology can be successfully used in cases of submarine eruptions

mixing in mantle magma reservoirs prior to and during the 2011 2012 eruption at el hierro canary islands understanding magmatic systems feeding volcanoes is critical for accurate interpretation of monitoring data and ultimately eruption forecasting following 3 months of precursory unrest the first historical eruption at el hierro canary islands took place 2 km offshore from october 2011 to march 2012 our detailed petrological analysis of lava samples reveals that at least two distinct magmas initially supplied from reservoirs in the mantle underwent hybridization at 15 25 km depth i e also largely within the upper mantle beneath el hierro diffusion chronometry applied to zoned olivine crystals indicates that magma mixing began during the period of preeruptive seismicity and continued for weeks after the eruption onset our data also capture a magma stagnation level at 10 15 km depth in the lower crust consistent with lateral propagation of an intrusion over substantial distances before rapid magma transit to the seafloor the remarkable spatial and temporal correlation of petrological and geophysical data at el hierro suggests that the observed seismicity records magma mixing and forceful intrusion as well as subsequent reservoir dynamics these results demonstrate that eruptions at el hierro are controlled principally by deep seated processes with little influence from shallow crustal levels and have important implications for monitoring of renewed unrest at long dormant volcanoes

age of the rockland tephra western usa abstract the age of the rockland tephra which includes an ash flow tuff south and west of lassen peak in northern california and a widespread ash fall deposit that produced a distinct stratigraphic marker in western north america is constrained to 565 000 to 610 000 yr by 40ar 39ar and u pb dating 40ar 39ar ages on plagioclase from pumice in the rockland have a weighted mean age of 609 000 7000 yr isotopic ages of spots on individual zircon crystals analyzed by the shrimp rg ion microprobe range from 500 000 to 800 000 yr a subpopulation representing crystal rims yielded a weighted mean age of 573 000 19 000 yr overall stratigraphic constraints on the age are provided by two volcanic units including the underlying tephra of the lava creek tuff erupted within yellowstone national park that has an age of 639 000 2000 yr the basaltic andesite of hootman ranch stratigraphically overlies the rockland in the lassen peak area and has 40ar 39ar ages of 565 000 29 000 and 565 000 12 000 yr for plagioclase and groundmass respectively identification of rockland tephra in odp core 1018 offshore of central california is an important stratigraphic age that also constrains the eruption age to between 580 000 and 600 000 yr

alder creek sanidine acs 2 a quaternary 40ar 39ar dating standard tied to the cobb mountain geomagnetic event accurate 40ar 39ar dating of quaternary and holocene samples requires a standard neutron fluence monitor of appropriate age this standard should be isotopically homogenous at the scale of analysis and should be well intercalibrated with other standards several such standards have been proposed including sanidine from the 1 19 ma alder creek rhyolite acs turrin et al 1994 turrin b d donnely nolan j m hearn b c jr 1994 40ar 39ar ages from the rhyolite of alder creek california age of the cobb mountain normal polarity subchron revisited geology 22 251 254 this sanidine is satisfactorily homogeneous well intercalibrated with fish canyon sanidine fcs renne et al 1998 renne p r swisher c c deino a l karner d b owens t l depaolo d j 1998 intercalibration of standards absolute ages and uncertainties in 40ar 39ar dating chem geol 145 117 152 and is linked to the astronomically calibrated magnetic polarity time scale since the alder creek rhyolite lava is the type occurrence of the cobb mountain event cm we collected 408 kg of this rock from which we anticipate being able to extract more than 8 kg of 425 m sanidine crystals analyses of sanidine phenocryts from the acs 2 from three separate irradiations and two distinct grain sizes yield ages ranging from 1 190 0 004 to 1 194 0 003 ma1 with a weighted mean age of 1 193 0 001 ma mswd 0 74 n 225 based on fcs 28 02 ma renne et al 1998 renne p r swisher c c deino a l karner d b owens t l depaolo d j 1998 intercalibration of standards absolute ages and uncertainties in 40ar 39ar dating chem geol 145 117 152 the value of the intercalibration factor renne et al 1998 renne p r swisher c c deino a l karner d b owens t l depaolo d j 1998 intercalibration of standards absolute ages and uncertainties in 40ar 39ar dating chem geol 145 117 152 is rfcsacs 2 0 04229 0 00012 n 8 identical with that of the original acs measurements 0 04229 0 00012 renne et al 1998 renne p r swisher c c deino a l karner d b owens t l depaolo d j 1998 intercalibration of standards absolute ages and uncertainties in 40ar 39ar dating chem geol 145 117 152 the age of acs 2 is in agreement with the recent astronomical calibration of the cm event 1 215 to 1 190 ma channell j e t mazaud a sullivan p turner s raymo m e 2002 geomagnetic excursions and paleointensities in the matuyama chron at ocean drilling program sites 983 and 984 iceland basin j geophys res 107 6 10 1029 2001jb000491 the apparent absence of xenocrysts and excess argon suggests that multigrain analyses are feasible and therefore the amount of material can be tailored to experimental requirements aliquots from various grain sizes will be available upon request zircon is also potentially available which may be of interest to u th he researchers