vertical sheets of dense plasma in the topside martian ionosphere 1 the low frequency radar mars advanced radar for subsurface and ionosphere sounding marsis on board the mars express spacecraft is used to sound electron densities in the topside martian ionosphere the radar records the delay times to echoes of reflected radio waves as a function of frequency yielding spectrograms with traces of radar echoes at times two traces are present in spectrograms of the martian ionosphere one of these traces corresponds to reflections from the direction to nadir the other trace originates in a localized reflector in the ionosphere the local reflectors can be associated with the cusplike regions of near vertical crustal magnetic fields the apparent nadir angle of reflection can occasionally increase to 90 this suggests that steep gradients of the altitude of the electron isodensity exist in the martian ionosphere and indicates rapid horizontal spatial variations of vertical diffusion of martian plasma such gradients may arise owing to preferential access of solar wind to the cusplike regions or to precipitation of energetic electrons from acceleration regions located on cusp magnetic field lines high above the ionosphere

the december 2002 july 2003 effusive event at stromboli volcano italy insights into the shallow plumbing system by petrochemical studies abstract on 28 december 2002 the persistent strombolian activity at stromboli was interrupted by the sudden onset of lava emission onto the sciara del fuoco slope a horseshoe shaped depression on the nw flank of the volcano the effusive episode went on until 22 july 2003 and produced a cumulative volume of lavas of 11 106 m3 ranking the event as the largest occurred in the past 30 years the eruptive vents were mainly located in the ne sector of the sciara del fuoco depression at an elevation of 550 600 m a s l on 30 december the eastern portion of the sciara del fuoco collapsed producing a tsunamigenic landslide on 5 april 2003 a paroxysmal eruption occurred at the summit craters during which crystal poor pumiceous products were emitted the paroxysm did not interrupt the lava emission the strombolian activity at the summit craters gradually resumed starting from march 2003 and fully recovered by the end of july periodic sampling of the lava at the active vents was carried out during the entire effusive event all the analysed samples are shoshonitic basalts sio2 48 5 50 4 wt k2o 2 1 2 4 wt in the range of composition observed in the products erupted during the past 20 years they bear about 50 vol zoned crystals of plagioclase an90 60 diopside augite and olivine fo70 73 in a compositionally homogeneous shoshonitic groundmass bulk rock major and trace element contents measured with different methodologies at different laboratories show only minor variations sr and nd isotope ratios are close to those of the crystal rich scoriae erupted in the previous years despite of small compositional variations related to the emptying of the zoned topmost portion of the conduit the data show that the switch from strombolian explosive to effusive activity is not associated with changes of the textures and composition of the erupted products slight but somehow systematic variation of trace elements and isotope ratios between products erupted before and after the 5 april eruption are likely accounted by limited mixing between the fresh volatile rich crystal poor magma erupted as pumice during the paroxysm and the volatile poor crystal rich magma feeding the lava flow the uniform composition of the erupted lava indicates the presence of a large volume of well mixed crystal rich homogeneous magma residing in the shallow plumbing system of the volcano two possible trigger mechanism of the effusive event are here proposed i a discrete input of fresh magma into the lower part of the shallow magmatic system occurred some months before the eruption and was followed by crystallisation degassing and mixing with the crystal rich shallow magma which re homogenised the system these processes eventually led to the rise of the magma at a higher level and failure of the conduit walls ii the onset of the effusion may represent the consequence of a gradual rise of the magma level in the conduits occurred in the past two decades the process of progressive refilling initiated after the 1985 effusive eruption ultimately culminated on 28 december 2002 with the failure of the conduit wall and the opening of vents 100 150 m below the summit craters

combined discrete and continuous gravity observations at mount etna systematic investigation of discrete gravity measurements has continued at mount etna since 1986 the network now covers an area of 400 km2 with about 70 stations 0 5 3 km apart mass redistributions occurring at depths ranging between about 8 km below sea level and a few hundred metres below the surface magma level changes within the shallower parts of the feeding conduits have been identified from these data conventional discrete microgravity monitoring on a network of stations furnishes only instantaneous states of the mass distribution at continuously active systems in order to obtain information on the rate at which the volcanic processes and thus mass transfers occur three stations for continuously recording gravity where installed on mount etna in 1998 a 16 month long sequence from one of the continuously running stations pdn located 2 km from the active northeast crater at the summit of etna volcano is presented after removing the effects of earth tide and tilt the correlation of the residual gravity sequence with simultaneous recordings of meteorological parameters acquired at the same station was analysed once the meteorological effects have also been removed continuous gravity changes are within 10 gal of gravity changes measured using conventional microgravity observations at sites very close to the continuous station this example shows how discrete and continuous gravity observations can be used together at active volcanoes to get a fuller and more accurate picture of the spatial and temporal characteristics of volcanic processes

multi method dating comparison for mid pleistocene rangitawa tephra new zealand abstract the rangitawa tephra a widespread mid pleistocene marker in the new zealand region is dated by fission track thermoluminescence tl infrared stimulated luminescence irsl k ar and single crystal laser fusion sclf 40 ar 39 ar methods as well as by matching to the astronomical timescale via oxygen isotope stratigraphy in deep sea cores fifty one independent numerical age estimates for rangitawa tephra range from 173 to 456 ka however only 15 of these results are considered to be reliable five zircon fission track results four isothermal plateau fission track itpft age estimates on glass shards four sclf 40 ar 39 ar results and two astronomically calibrated age estimates from deep sea cores the weighted mean of the nine reliable fission track age determinations is 345 12 ka in excellent agreement with the weighted mean of 340 7 ka for the two reliable astronomically calibrated age estimates the weighted mean of the four reliable 40 ar 39 ar results 302 8 ka is significantly younger and further ar ar dating is recommended to investigate this difference since the tl and irsl dating methods are experimental for sediments beyond 200 ka we have excluded these from the group of reliable age results tl and irsl results on dunesand appear to be systematically younger than tl results on loess and loess results depend upon analytical procedures

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

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

direct marine terrestrial correlations wanganui basin new zealand the last 1 million years abstract wanganui basin a back arc basin in north island new zealand contains a detailed sequence of interfingering terrestrial and shallow marine sediments spanning the entire quaternary rhyolite tephras erupted from the taupo volcanic zone together with magnetostratigraphy and biostratigraphy facilitate correlations between wanganui basin and the astronomically calibrated oxygen isotope chronology of deep sea cores particularly over the last 1 ma eustatic changes are interpreted from both marine shelf sediments and marine terraces within the basin non marine sediments including loess dunesand and alluvial deposits coupled with pollen analyses are used to interpret climatic changes they can also be directly related to the marine record through stratigraphic relations between marine and non marine deposits in the basin

mgs radio science electron density profiles interannual variability and implications for the martian neutral atmosphere density of 7 3 8 5 10 4 cm 3 is also measured during solar moderate conditions at mars strong wave number 2 3 oscillations in peak heights are consistently observed as a function of longitude over the 2 martian years these observed ionospheric features are remarkably similar during aphelion conditions 1 martian year apart this year to year repeatability in the thermosphere ionosphere structure is consistent with that observed in multiyear aphelion temperature data of the mars lower atmosphere clancy et al 2000 smith 2004 coupled mars general circulation model mgcm and mars thermospheric general circulation model mtgcm codes are run for mars aphelion conditions yielding mean and longitude variable ionospheric peak heights that reasonably match rs observations a tidal decomposition of mtgcm thermospheric densities shows that observed ionospheric wave number 3 features are linked to a nonmigrating tidal mode with semidiurnal period s 2 and zonal wave number 1 s 1 characteristics the height of this photochemically determined ionospheric peak should be monitored regularly index terms 5435 planetology solid surface planets ionospheres 2459 5409 planetology solid surface planets atmospheres structure and dynamics 6225 planetology solar system objects mars keywords ionosphere mars thermosphere

the effect of inertial accelerations on the higher frequency components of the signal from spring gravimeters summary experimental and theoretical studies have shown that due to the magma gas dynamics in the upper part of a volcano s plumbing system gravity changes can develop over periods between a few tens of seconds and several hours the mass transport implied by certain fast evolving volcanic processes also constitute the source mechanism of seismic waves with frequencies over the lower limit of the seismic band these seismic waves could affect the measuring system of spring gravimeters that are increasingly used as continuously running devices to monitor and study active volcanoes as a consequence under some circumstances the signal from a continuously running spring gravimeter will be the combination of the gravity field component and the inertial acceleration component the latter due to the ground motion in such cases the inertial acceleration must be separated from the gravity signal to assess the amount of mass redistributed during the studied process to achieve this separation the frequency response curve of the spring gravimeter to inertial accelerations must be calculated since it is not supplied by manufacturers in this paper we present a method to retrieve the above curve using simultaneous recordings during the transit of teleseismic waves of a lacoste romberg d gravimeter and a nanometrics trillium 40 broad band seismometer whose frequency response curve to ground acceleration is known ap riori the use of teleseismic waves is particularly useful for our purpose since teleseisms are not associated with a local mass redistribution the gravimeter will thus be affected only by the ground motion making the above calculation possible our results show that because of the instrumental damping the effect of the inertial acceleration is reduced in the output signal from the gravimeter to 0 5 and 0 1 of its original value at frequencies between 0 02 and 0 07 hz respectively the robustness of the calculated frequency response curve is proven using independent simultaneous signals from gravimeter and broad band seismometer

infrasonic waves and volcanic tremor at stromboli the origin of the volcanic tremor is still under debate many theories have been proposed in the last years but none has yet been completely accepted in 1993 highly sensitive pressure sensors 2 175 pa volt used to monitor the explosive activity at stromboli have revealed unexpected correlation between small spike shaped pressure signals 1 2 pa and volcanic tremor these pressure pulses repeat regularly in time with a recurrent period of ca 1 s video camera images allowed us to correlate the pressure pulses with small gas bursts occurring at one of the active vents the striking correlation 0 971 between infrasonic and seismic energy fluctuations is particularly meaningful in the frequency domain infrasonic and seismic signal share the same spectral content 3 hz for every station within a range of 700 m around the craters correlations in time and frequency domain remained unaltered during the 1994 field experiments moreover during 1994 the increased degassing activity has been followed by an increase in pressure release 7 8 pa and by a shift towards higher frequencies 8 hz both in the infrasonic and seismic records infrasonic waves and volcanic tremor show similar energy fluctuations and frequency contents appearing therefore to be produced by the same dynamical process on this basis we claim that volcanic tremor at stromboli originates by continuous outbursting of small gas bubbles in the upper part of the magmatic column

source mechanisms of explosions at stromboli volcano italy determined from moment tensor inversions of very long period data 1 seismic data recorded in the 2 30 s band at stromboli volcano italy are analyzed to quantify the source mechanisms of strombolian explosions during september 1997 to determine the source centroid location and source mechanism we minimize the residual error between data and synthetics calculated by the finite difference method for a point source embedded in a homogeneous elastic medium that takes topography into account two source centroids are identified each representative of the distinct event types associated with explosive eruptions from two different vents the observed waveforms are well reproduced by our inversion and the two source centroids that best fit the data are offset 220 and 260 m beneath and 160 m northwest of the active vents the source mechanisms include both moment tensor and single force components the principal axes of the moment tensor have amplitude ratios 1 1 2 which can be interpreted as representative of a crack if one assumes the rock matrix at the source to have a poisson ratio n 1 3 a value appropriate for hot rock both imaged cracks dip 60 to the northwest and strike northeast southwest along a direction parallel to the elongation of the volcanic edifice and a prominent zone of structural weakness as expressed by lineaments dikes and brittle structures for our data set the volume changes estimated from the moments are 200 m 3 for the largest explosion from each vent together with the volumetric source is a dominantly vertical force with a magnitude of 10 8 n consistent with the inferred movement of the magma column perched above the source centroid in response to the piston like rise of a slug of gas in the conduit index terms 7215 seismology earthquake parameters 7280 seismology volcano seismology 8419 8414 volcanology eruption mechanisms keywords very long period seismicity moment tensor inversions eruption mehanics

flow to fracture transition in a volcanic mush plug may govern normal eruptions at stromboli stromboli is a model volcano for studying eruptions driven by degassing the current paradigm posits that strombolian eruptions represent the bursting of gas slugs ascending through melt filled conduits but petrological observations show that magma at shallow depth is crystalline enough to form a three phase plug consisting of crystals bubbles and melt we combine a 1d model of gas flushing a crystalline mush with a 3d stress model our results suggest that localized gas segregation establishes hot conduits of mobile magma within a stagnant plug the plug is prone to tensile failure controlled by gas over pressure and tectonic stress with failure most likely beneath the observed vent locations we hence argue that strombolian eruptions are related to plug failure rather than flow our proposed three phase model of the shallow plumbing system may provide a promising framework for integrating geophysical petrological and morphological observations at stromboli and in open system volcanism more generally

explosive volcanic eruptions triggered by cosmic rays volcano as a bubble chamber abstract volcanoes with silica rich and highly viscous magma tend to produce violent explosive eruptions that result in disasters in local communities and that strongly affect the global environment we examined the timing of 11 eruptive events that produced silica rich magma from four volcanoes in japan mt fuji mt usu myojin sho and satsuma iwo jima over the past 306 years from ad 1700 to ad 2005 nine of the 11 events occurred during inactive phases of solar magnetic activity solar minimum which is well indexed by the group sunspot number this strong association between eruption timing and the solar minimum is statistically significant to a confidence level of 96 7 this relationship is not observed for eruptions from volcanoes with relatively silica poor magma such as izu ohshima it is well known that the cosmic ray flux is negatively correlated with solar magnetic activity as the strong magnetic field in the solar wind repels charged particles such as galactic cosmic rays that originate from outside of the solar system the strong negative correlation observed between the timing of silica rich eruptions and solar activity can be explained by variations in cosmic ray flux arising from solar modulation because silica rich magma has relatively high surface tension 0 1 nm 1 the homogeneous nucleation rate is so low that such magma exists in a highly supersaturated state without considerable exsolution even when located relatively close to the surface within the penetration range of cosmic ray muons 1 10 gev these muons can contribute to nucleation in supersaturated magma as documented by many authors studying a bubble chamber via ionization loss this radiation induced nucleation can lead to the pre eruptive exsolution of h 2 o in the silica rich magma we note the possibility that the 1991 mt pinatubo eruption was triggered by the same mechanism an increase in cosmic ray flux triggered by typhoon yunya as a decrease in atmospheric pressure results in an increase in cosmic ray flux we also speculate that the snowball earth event was triggered by successive large scale volcanic eruptions triggered by increased cosmic ray flux due to nearby supernova explosions

a co2 rich gas trigger of explosive paroxysms at stromboli basaltic volcano italy in addition to rhythmic slug driven strombolian activity stromboli volcano occasionally produces discrete explosive paroxysms 2 per year on average for the most frequent ones that constitute a major hazard and whose origin remains poorly elucidated partial extrusion of the volatile rich feeding basalt as aphyric pumice during these events has led to consider their triggering by the fast ascent of primitive magma blobs from possibly great depth here i examine and discuss the alternative hypothesis that most of the paroxysms could be triggered and driven by the fast upraise of co2 rich gas pockets generated by bubble foam growth and collapse in the sub volcano plumbing system data for the so2 and co2 crater plume emissions are used to show that stromboli s feeding magma may originally contain as much as 2 wt of carbon dioxide and early coexists with an abundant co2 rich gas phase with high co2 so2 molar ratio 60 at 10 km depth below the vents compared to 7 in time averaged crater emissions pressure related modelling indicates that the time averaged crater gas composition and output are well accounted for by closed system decompression of the basalt gas mixture until the volcano crust interface 3 km depth followed by open degassing and crystallization in the volcano conduits however both the low viscosity and high vesicularity of the basaltic magma permit bubble segregation and bubble foam growth at deep sill like feeder discontinuities and at shallower physical boundaries such as the volcano crust interface where the gas rich aphyric basalt interacts with the unerupted crystal rich and viscous magma drained back from the volcano conduits gas pressure build up and bubble foam collapse at these boundaries will intermittently trigger the sudden upraise of co2 rich gas blobs that constitute the main driving force of the paroxysms deeper sourced gas blobs driving the most powerful explosions will be the richest in co2 and have highest co2 so2 ratios this mechanism is shown to account well for the dynamic seismic and petrologic features of stromboli s paroxysms and hence to provide a potential alternative interpretation for their genesis and their forecasting enhanced bubble foam leakage prior to a paroxysm or foam emptying in several steps should lead indeed to precursory upstream of co2 rich gas and increasing co2 so2 ratio in crater plume emissions the recent detection of such signals prior to two explosions in december 2006 and march 2007 strongly supports this expectation and the model proposed in this study

geophysical indications of magma uprising at mt etna during the december 2005 to january 2006 non eruptive period 1 during the december 2005 january 2006 non eruptive period the tremor amplitude at etna markedly increased and negatively correlated with the gravity signal from one of the two summit station over 2 3 hour periods no correlation was found with the signal from the other gravity station we locate the tremor source by inverting the spatial distribution of seismic amplitudes relying on the relative position of the two stations we define a volume within which the gravity source must lie during the period of marked anti correlation the tremor sources intersect this volume in a region located 1 km s se of the summit craters and about 2 km beneath the surface this finding suggests that the anti correlation marks the activation of a joint source process possibly related to the arrival of fresh magma and the consequent gas separation our study has implications for the early recognition of gas segregation processes at active volcanoes

paleomagnetic constraints on the initiation of uplift on the santa susana fault western transverse ranges california the plio pleistocene nonmarine saugus formation is widely exposed in the east ventura basin and the northern san fernando valley north and south of the santa susana fault in the east ventura basin the saugus is overlain by the pacoima formation magnetostratigraphy of the fine grained saugus and pacoima strata and the presence of the 0 76 ma bishop ash are used to calculate their average sedimentation rates 0 9 km m y in the east ventura basin and 1 1 km m y in the northern san fernando valley extrapolation of the saugus and pacoima sedimentation rates shows that they were deposited from about 2 3 to 0 5 ma both north and south of the santa susana fault the shift from remote to locally derived clasts marks the initiation of uplift of the santa susana mountains the extrapolated age of this boundary is about 0 7 0 6 ma

ground based insar reveals conduit pressurization pulses at stromboli volcano at stromboli volcano southern italy only few minor precursors gas output have been identified for major strombolian explosions we use ground based interferometric synthetic aperture radar gbinsar technology to monitor the displacement rate of the summit area of stromboli we analysed the 2009 2011 period the analysis of the displacement rate has been performed by dividing the summit zone monitored by the gbinsar into three regions corresponding to the edge of the crater area 1 and 2 and to the slope of the ne crater 3 pulses of rapid expansion of sector 3 of variable duration and amplitude appear in coincidence with periods of intense activity that include lava flows and major explosions we associate this expansion with the pressurization of the magma column that is recharged by deep derived gas promoting the onset of major explosion dominated activity

age and correlation of a paleomagnetic episode in the western united states by 40ar 39ar dating and tephrochronology the jamaica blake or a new polarity episode high resolution paleomagnetic records from two sites near pringle falls oregon are compared with similar records from summer lake oregon 170 km to the southeast paoha island in mono lake 660 km to the southeast and benton crossing in long valley approximately 700 km to the southeast in east central california the sequences at pringle falls contain a distinctive coarse pumice lapilli tephra layer which we have dated as 218 10 ka by 40ar 39ar step heating of plagioclase feldspar stratigraphically this tephra is closely associated with a suite of several other tephra layers that bracket the interval studied paleomagnetically each tephra layer is distinguished by the unique chemical composition of its volcanic glass shards the pumice layer dated at pringle falls is correlated with layers at three of the other localities using all the tephra layers we can correlate the lake stratigraphic sequences and associated paleomagnetic records among the four distant localities additional age control is obtained from a fifth locality at tulelake in northern california where the stratigraphic interval of interest is bracketed between 171 43 and approximately 140 ka characteristics of the paleomagnetic records indicate virtually identical paleofield variation particularly the geometry of a normal to normal n n geomagnetic polarity episode the observed paleofield behavior resembles the blake geomagnetic polarity episode but is significantly older than the generally accepted age of the blake episode either the age of the blake episode is significantly underestimated or the polarity episode documented here is older perhaps the jamaica episode or is an as yet unreported episode a corollary of the latter option is that paleomagnetic polarity episodes of different ages may have similar transition polar paths a conclusion implying that a common mechanism is involved

40ar 39ar dating of the brunhes matuyama geomagnetic field reversal magnetostratigraphic studies are widely used in conjunction with the geomagnetic polarity time scale gpts to date events in the range 0 to 5 million years ago a critical tie point on the gpts is the potassium argon age of the most recent brunhes matuyama geomagnetic field reversal astronomical values for the forcing frequencies observed in the oxygen isotope record in ocean drilling project site 677 suggest that the age of this last reversal is 780 ka thousand years ago whereas the potassium argon based estimate is 730 ka results from 4039 ar incremental heating studies on a series of lavas from maui that straddle the brunhes matuyama reversal give an age of 783 11 ka in agreement with the astronomically derived value the astronomically based technique appears to be a viable tool for dating young sedimentary sequences

the 2007 stromboli eruption event chronology and effusion rates using thermal infrared data accepted for publication in journal of geophysical research copyright 2009 american geophysical union further reproduction or electronic distribution is not permitted

analysis of simultaneous gravity and tremor anomalies observed during the 2002 2003 etna eruption abstract in this paper we discuss the data collected by a large aperture array of broadband seismometers and a continuously recording gravity station during the 2002 2003 eruption of etna volcano italy seismic signals recorded during the eruption are dominated by volcanic tremor whose energy spans the 0 5 5 hz frequency band on three different occasions 12 november 19 20 november and 8 9 december 2002 we observed marked increases of the tremor amplitude up to a factor of 4 which occurred simultaneously with gravity decreases up to 30 gal the three concurrent gravity tremor anomalies last 6 to 12 hours and terminate with rapid up to 2 hours changes after which the signals return back to their original levels based on volcanological observations encompassing the simultaneous anomalies we infer that the accumulation of a gas cloud at some level in the conduit plexus feeding a new eruptive vent could have acted as a joint source this study highlights the potential of joint gravity seismological analyses to both investigate the internal dynamic of a volcano and to improve the confidence of volcanic hazard assessment

hook structure in marsis ionogram and its interpretation 1 marsis mex is a low frequency radar used to sound the ionosphere of mars in general the echo trace associated with reflections in nadir indicates an ionosphere with a main maximum electron density at typically about 130 km altitude and a monotonously decreasing density with increasing altitude another maximum is sometimes detected at higher altitudes indicating a double layer in the upper ionosphere sometimes a special structure here called a hook is observed at the low frequency end of the trace as the sounding frequency decreases the delay time of sounding signal increases rapidly it is here proposed that this signature indicates a secondary maximum with density which is so low that it can be only partly resolved by the radar an analytical inversion approach coping with the hook case is then proposed it is further suggested that the hook is caused by vertical wavelike structures in the martian topside ionosphere

active faulting and block rotations in the western transverse ranges california the geometry of faulting slip vectors of major earthquakes and results of very long baseline interferometry vbli are consistent with active clockwise rotation of crustal blocks in the western transverse ranges about vertical axes oblique left lateral thrust faults trending roughly east west across the western transverse ranges apparently separate long east west blocks of upper crust and the large components of lea lateral shear on east striking planes suggest that the blocks rotate with respect to the san andreas fault in the mojave region between the western transverse ranges and the mojave desert paleomagnetic declinations indicate some 35 and possibly 60 of clockwise rotation since about 10 ma and more importantly the relative velocity between the only two frequently measured vbli sites in the western transverse ranges is consistent with a rotation rate of 6 ma 3 ma during a 5 year period in the 1980s azimuths of slip vectors of major earthquakes are essentially orthogonal to the segment of the san andreas fault across the western mojave desert indicating that crustal shortening across the region is absorbed by crustal thickening and not by lateral translation extension of material parallel to that segment of the fault plate motions late quaternary offsets on the san andreas and san jacinto faults and geodetic measurements in the mojave region yield a calculated direction of relative motion between the san gabriel mountains and the pacific plate across the western transverse ranges that also is perpendicular to the san andreas fault in the mojave region rotation rates associated with simple mechanisms for applying essentially normal tractions to the lateral margins of blocks are not consistent with the observed geometry of faulting and with average rotation rates the rotation rate of 2 8 5 3 ma calculated assuming that the long east west blocks rotate in response to a uniform compression of a viscous substratum to the western transverse ranges however overlaps the range of observed average rotation rates thus the hypothesis that blocks of continental crust move as if carried passively by a substratum undergoing continuous deformation passes one test that can be made of it

a test on a neuro fuzzy algorithm used to reduce continuous gravity records for the effect of meteorological parameters abstract gravity measurements are utilized at active volcanoes to detect mass changes linked to magma transfer processes and thus to recognize forerunners to paroxysmal volcanic events continuous gravity measurements are now increasingly performed at sites very close to active craters where there is the greatest chance to detect meaningful gravity changes unfortunately especially when used against the adverse environmental conditions usually encountered at such places gravimeters have been proved to be affected by meteorological parameters mainly by changes in the atmospheric temperature the pseudo signal generated by these perturbations is often stronger than the signal generated by actual changes in the gravity field thus the implementation of well performing algorithms for reducing the gravity signal for the effect of meteorological parameters is vital to obtain sequences useful from the volcano surveillance standpoint in the present paper a neuro fuzzy algorithm which was already proved to accomplish the required task satisfactorily is tested over a data set from three gravimeters which worked continuously for about 50 days at a site far away from active zones where changes due to actual fluctuation of the gravity field are expected to be within a few microgal after accomplishing the reduction of the gravity series residuals are within about 15 gal peak to peak thus confirming the capabilities of the neuro fuzzy algorithm under test of performing the required task satisfactorily

ionospheric characteristics above martian crustal magnetic anomalies 1 we studied several thousand electron density profiles from the mars global surveyor radio science experiment electron densities in some of these profiles change significantly over vertical distances as short as 1 2 km often causing localized bite outs these anomalous profiles are preferentially located above crustal magnetic anomalies anomalous features and their association with strong magnetic fields are also seen in profiles from mariner 9 the probability of a profile being anomalous depends on the orientation of the magnetic field suggesting localized electrodynamic effects upon otherwise global photochemical ionospheric processes on mars unlike most other planets the magnetic field has a short characteristic lengthscale so its effects on the ionosphere will vary over short horizontal distances we discuss possible ionospheric dynamo processes and encourage additional ionospheric observations over regions of strong crustal magnetic field

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

u pb dating of zircon in subsurface hydrothermally altered pyroclastic deposits and implications for subsidence in a magmatically active rift taupo volcanic zone new zealand abstract recognising and correlating hydrothermally altered rock units within buried volcanic sequences in the taupo volcanic zone tvz in new zealand is difficult this is because of broad similarities in the lithologies of many major ignimbrite units and the destruction by hydrothermal alteration of distinctive chemical and mineralogical characteristics however magmatic zircons are commonly present are highly resistant to hydrothermal alteration and yield crystallisation ages in intensely altered rocks crystallisation age spectra have been obtained by sims techniques shrimp rg on zircons extracted from cores from altered ignimbrites penetrated by drillholes at the waiotapu te kopia and orakei korako geothermal fields in the central tvz at waiotapu the thick up to 350 m densely welded waiotapu ignimbrite returned a zircon age spectrum with a probability density function pdf peak of 0 79 ma consistent with an eruption age from 40ar 39ar techniques of 0 71 0 06 1 s d ma three older ignimbrite sheets yielded age spectra that were consistent stratigraphically the shallowest of the three yielded sparse zircons that gave a pdf peak of 1 24 ma and it may correlate with the 1 18 0 02 ma ahuroa ignimbrite the middle sheet although 220 m thick yielded an age spectrum identical to that obtained from pumice in the widespread 1 21 0 04 ma ongatiti ignimbrite extending earlier estimates of the likely volume of this large deposit the deepest sheet has a spectrum consistent with an eruption age of 1 45 0 05 ma it has no surficial correlative but its likely coeruptive ash forms part of a concentrated group of primary or secondary tephra in sediments on the ocean floor east of new zealand and in sedimentary basins across the north island these three ignimbrites were previously correlated with either major ignimbrites exposed on the paeroa fault scarp 10 km to the west or the akatarewa ignimbrite that occurs in drillholes at te kopia and orakei korako but these correlations are disproved from our age data drillholes at te kopia tk and orakei korako ok reach but do not penetrate the base of one or more deposits collectively termed the akatarewa ignimbrite samples from 62 tk and 165 m ok below the top contact of this unit yielded closely similar age spectra and pdf maxima of 1 00 tk and 1 02 ma ok implying that the same deposit was penetrated at both fields this ignimbrite is not correlated with a specific surface equivalent several candidate deposits exist but all are areally restricted the akatarewa ignimbrite at tk and ok is however not the same deposit as those earlier correlated with it at waiotapu the age data are consistent with there being two zones of subsidence on both sides of a horst aligned with the three geothermal fields sampled the eastern zone is the reporoa basin which has high heat flow but little surface faulting and the western one is the axis of the taupo rift currently with low heat flow but abundant surface faulting overall subsidence rates at the three geothermal fields studied vary between 2 and

magma budgets and steady state activity of vulcano and stromboli we present three models for magma budget during steady state volcanic activity by which non erupted magma is emplaced as dykes or cumulates or crystallises in place using gas and thermal data we apply our models at vulcano to calculate degassing cooling and crystallisation of magma at a rate of 40 375 kg s 1 within a magma body with an upper surface at a 2 km depth at stromboli we calculate a steady magma supply of 300 1300 kg s 1 to shallow 1 km depths

revised chronostratigraphy of the kenai group from 40ar 39ar dating of low potassium bearing minerals cook inlet basin alaska thirty seven tephra beds primarily from coal partings in the sterling and beluga formations were successfully dated by the 40ar 39ar method providing a new and revised understanding of the chronostratigraphy of late tertiary strata within cook inlet basin meticulous sample preparation multiple analyses and statistical evaluation of the data were required for these low k plagioclase and hornblende bearing tephras dating of subsurface core material provides the first subsurface to outcrop tie in cook inlet between well 212 24 in the beluga river unit and deposits in the clam gulch diamond creek and fox creek areas the new 40ar 39ar chronostratigraphic framework place the age of upper part of the kenai group strata between 4 6 and 9 4 ma and support the 8 ma interpretation of the boundary between the homerian and clamgulchian paleobotanical stages the 49 ma age from core data in pioneer unit suggests the tyonek formation is older than previously thought or that these units belong to an older form

dynamics of magma mixing and degassing recorded in plagioclase at stromboli aeolian archipelago italy crystal rich materials scoriae and lava flows emitted during the 1985 2000 activity of stromboli were taken into consideration for systematic study of bulk rock matrix glass chemistry and in particular for the study of chemical and textural zoning of plagioclase the most abundant mineral phase over the considered time period bulk rock composition remained fairly constant in both major sio2 49 2 50 9 wt and k2o 1 96 2 18 wt and trace elements the quite constant chemistry of matrix glasses also indicates that the degree of crystallization of magma was maintained at around 50 vol plagioclase ranges in composition between an62 and an88 and is characterized by alternating 10 100 m thick bytownitic and labradoritic concentric layers although the dominant and representative plagioclase of scoriae is an68 the labradoritic layers an62 70 show small scale 1 5 m oscillatory zoning are free of inclusions and appear to record episodes of slow crystal growth in equilibrium with a degassed liquid having the composition of the matrix glass in contrast the bytownitic layers an70 an88 are patchy zoned show sieve structure with abundant micrometric glass inclusions and voids and are attributed to rapid crystal growth

3 d density structure and geological evolution of stromboli volcano aeolian islands italy inferred from land based and sea surface gravity data we present the first density model of stromboli volcano aeolian islands italy obtained by simultaneously inverting land based 543 and sea surface 327 relative gravity data modern positioning technology a 1 1 m digital elevation model and a 15 15 m bathymetric model made it possible to obtain a detailed 3 d density model through an iteratively reweighted smoothness constrained least squares inversion that explained the land based gravity data to 0 09 mgal and the sea surface data to 5 mgal our inverse formulation avoids introducing any assumptions about density magnitudes at 125 m depth from the land surface the inferred mean density of the island is 2380 kg m 3 with corresponding 2 5 and 97 5 percentiles of 2200 and 2530 kg m 3 this density range covers the rock densities of new and previously published samples of paleostromboli i vancori neostromboli and san bartolo lava flows high density anomalies in the central and southern part of the island can be related to two main degassing faults crossing the island n41 and n64 that are interpreted as preferential regions of dyke intrusions in addition two low density anomalies are found in the northeastern part and in the summit area of the island these anomalies seem to be geographically related with past paroxysmal explosive phreato magmatic events that have played important roles in the evolution of stromboli island by forming the scari caldera and the neostromboli crater respectively

40ar 39ar age constraints for the jaramillo normal subchron and the matuyama brunhes geomagnetic boundary our mid pleistocene 4oar 39ar age recalibration of the geomagnetic polarity timescale is nearly in accord with the oxygen isotope climate record calibration of the astronomical timescale proposed by johnson 1982 and shackleton et al 1990 4oar 39ar ages of a normally magnetized rhyolite dome in the valles caldera northern mexico yielded a weighted mean age of 1 004 0 019 ma a k ar age of 0 909 0 019 ma for this rock by doell and dalrymple 1966 was the linchpin for the recognition and calibration of the jaramillo normal subchron jns other 4oar 39ar ages from the vailes caldera and 4oar 39ar ages of ivory coast tektites indicate that the jns began at about 1 11 ma and ended before 0 92 ma probably near 0 97 ma the matuyama brunhes boundary occurred between 0 79 ma and 0 76 ma on the basis of 4oar 39ar sanidine ages from 1 three reversely magnetized rhyolite domes of the valles caldera 0 793 0 018 ma 0 794 0 007 ma and 0 812 0 023 ma and pumice 0 789 0 006 ma from the reversely magnetized oldest toba tuff of sumatra and 2 pumice 0 764 0 005 ma and 0 757 0 009 ma from the lower and upper units of the normally magnetized bishop tuff the age of the boundary may be close to 0 77 ma as deduced from rates of sedimentation in ancient lake bonneville utah increasingly aware that the polarity of earth s magnetic field has changed repeatedly through geologic time and isotopic dating of these polarity reversals resulted in a geomagnetic polarity time scale gpts for the late cenozoic this combined paleomagnetic and isotopic research played a pivotal role in confirming plate tectonic theory glen 19821 which revolutionized the earth sciences continual refinement of isotopic ages which define the gpts has increased the usefulness of geomagnetic polarity reversals as marker hori zons in many types of geologic studies we present 4oar 39ar data and ages for some key volcanic units that support changes in the isotopic age chronology of the gpts using volcanic rocks erupted near the time of the geologically youngest two geomagnetic polarity reversals figure 1 the older of the two reversals originally called by doell and dalrymple 1966 the jaramillo event is now named the jaramillo normal subchron jns it is recorded in middle pleistocene rocks as a brief episode of normal polar ity within the late matuyama chron the younger of the two called the matuyama brunhes boundary mbb is regis tered in middle pleistocene rocks worldwide and consists of

topside of the martian ionosphere near the terminator variations with season and solar zenith angle and implications for the origin of the transient layers abstract in this paper the morphological variations of the m2 layer of the martian ionosphere with the martian seasons and solar zenith angle sza at the terminator are investigated the data used are the marsis mars advanced radar for subsurface and ionosphere sounding measurements approximately 5000 ionograms that were acquired from 2005 to 2012 which have a sza 85 and detect the topside transient layers a simple effective data inversion method is developed for the situation in which the upper portion of the height profile is non monotonic and the observed data are insufficient for adequate reduction the inverted parameters are subsequently explored using a statistical approach the results reveal that the main body of the m2 layer approximately 10 km below the first topside layer can be well characterized as a chapman layer near the terminator sza 85 98 notwithstanding the high sza and the presence of the topside layers the height of the first topside layer tends to be concentrated approximately 60 km with a standard deviation of 20 km above the main density peak the peak density and height of the first topside layer are positively correlated to the density and height of the main peak respectively the density and height of the first topside layer appear to be independent of the sza but possess seasonal variations that are similar to those of the main layer the height of the topside layer is greater by 10 km on average in the southern spring and summer than in the southern autumn and winter coinciding with the observation that in the southern spring and summer the underlying atmosphere is warmer due to dust heating e g smith m d 2004 icarus 167 148 165 the statistical regularities of the parameters suggest a possibility that the formation of the topside layers are closely related to the processes of photoionization and diffusion that occur on the topside of the m2 layer we propose that development of beam plasma instabilities in the transitional region between the lower chapman region and the upper transport dominating region is possibly a mechanism that is responsible for the occurrences of the topside layers

seismic monitoring and modeling of an active volcano for prediction we describe seismic monitoring and modeling of an active volcano for the purpose of predicting the magma transport process in real time we selected the piton de la fournaise which has been monitored by an observatory since the early 1980s and is active with 28 eruptions from 1980 until august 1992 it erupted on march 9 1998 after an unusually long quiet period the eruption lasted until september 21 1998 before the march eruption we completed the initial construction of a model of a magma system based primarily on long period lp events and coda localization we found that lp events are associated with the lateral movement of magma to the rift zone and not with the vertical movement to the summit we also found that the source of 2 hz lp events is located below that of 1 hz lp events the coda localization is a newly discovered phenomenon that helped to locate a magma body this model was used for interpreting the incoming information from the precursory seismic crisis and the eruption tremor during the 6 months of the eruption the simultaneous monitoring and modeling of an active volcano led us to a quantitative simulation of the eruption process computing excess pressure and flow rate in a system of reservoirs connected by channels

dynamics of the 5 april 2003 explosive paroxysm observed at stromboli by a near vent thermal seismic and infrasonic array 1 on 5 april 2003 an array of thermal infrasonic and seismic sensors tracked the dynamics of a major explosive paroxysmal event at stromboli the thermal signal recorded a decline 1 hour before the paroxysm which itself lasted 6 5 minutes and opened with a 14 s low thermal amplitude phase this was followed by three main explosive phases with gas and ejecta velocities of 324 and 185 m s being calculated for the first phase the delay time between thermal and infrasonic signals indicates a very shallow 150 m source for fragmentation a strong tilt component in the seismic signals shows that the conduit began to expand at least 90 s before the explosion large seismic amplitudes were recorded during the emission onset the seismic signal can thus be related to stress build up followed by release during the ejection of the gas particles mixture we calculate that the cloud of hot gas and ash emitted during the explosion had an overpressure of 3 8 mpa and involved 5 7 105 m3 2 9 106 kg of gas

a case history of paroxysmal explosion at stromboli timing and dynamics of the april 5 2003 event abstract on april 5 2003 stromboli volcano italy produced the most violent explosion of the past 50 years the event was exceptionally well documented thanks to the presence on the island of several scientists and a large number of instruments deployed over the preceding months to monitor the effusive eruption that began in december 2002 integration of visual documentation deposit features and geophysical data allowed an accurate reconstruction of the explosive event and its dynamics the eruption consisted of a 8 min long explosive event which evolved through four phases whose timing was precisely recorded by an infrared thermometer located about 450 m from the summit crater phases 2 and 3 lasted 39 and 42 s respectively both had an impulsive character were responsible for ejecting almost the entire mass of the pyroclastic products phases 1 and 4 represented respectively a short lived precursory event and a waning tale during phase 2 meter sized ballistic blocks were launched with velocities of 170 m s to altitudes of up to 1400 m above the craters these fell on the volcano flanks and on the village of ginostra about 2 km distant from the vent a vertical jet rose above the craters which developed to feed a convective plume that reached a height of up to 4 km the calculated mass of the phase 2 fallout deposit and mass discharge rate were 1 1 1 4 108 kg and 2 8 3 6 106 kg s respectively during phase 3 a scoria flow deposit with an estimated volume of 0 9 1 1 104 m3 was erupted from the same vent that fed the ongoing sustained lava flow the average mass discharge rate for this phase was 2 5 3 1 105 kg s products emitted during phases 2 and 3 consisted of lithic and fresh magmatic material in similar proportions the juvenile fraction consisted of a deep originated almost aphyric highly vesicular pumice mingled with a shallow derived crystal rich moderately vesicular scoria similarities with the eruption dynamics of other historical paroxysms at stromboli makes the april 5 2003 explosion representative of these highly energetic events that constitute the most hazardous volcanic phenomena at stromboli volcano

extension of the astronomically calibrated polarity time scale to the miocene pliocene boundary the early pleistocene to late pliocene astronomically calibrated time scale of shackleton et al 1 and hilgen 2 is extended to the miocene pliocene boundary this is done by correlating the detailed record of caco3 cycles in the trubi and the lower part of the overlying narbone formation rossello composite section sicily to the astronomical record using 1 inferred phase relations between these caco3 cycles and the corresponding orbital cycles of precession and eccentricity and 2 calibration points provided by the previously established astronomical calibration of sapropelitic layers which occur in the topmost part of the caco3 record 2 this correlation allows all small scale caco3 cycles in the rossello composite section to be coded after the correlative precession peak and to be dated astronomically with an accuracy of 1 ky in combination with the available high resolution magnetostratigraphy it further allows the construction of an astronomically calibrated geomagnetic polarity time scale for the major part of the gilbert and gauss chrons this new time scale gives ages for the reversal boundaries of the kaena 3 04 3 11 ma and mammoth 3 22 3 33 ma the gilbert gauss chron boundary 3 58 ma and the reversal boundaries of the cochiti 4 18 4 29 ma nunivak 4 48 4 62 ma sidufjall 4 80 4 89 ma and thvera 4 98 5 23 ma these ages are significantly older than the ages given by conventional time scales age discrepancies gradually increase with increasing age the age of 5 32 ma for the miocene pliocene boundary as defined by the base of the trubi on sicily is almost 0 5 m y 9 5 older than the presently accepted age of 4 86 ma 3 these considerable discrepancies with the conventional time scale can either be explained by an consistent error in the decay constants used in k ar radiometric dating or more likely by diffusional loss of radiogenic argon

potassium argon dating of fine grained basalts with massive ar loss application of the 40ar39ar technique to plagioclase and glass from the kirkpatrick basalt antarctica 40ar39ar incremental heating measurements are reported for separated plagioclase and matrix fractions and a glass sample of the kirkpatrick basalt from victoria land antarctica these results are used to address the limitations of whole rock analyses of glassy or very fine grained basalts the use of plagioclase for determining ages of such rocks the ar behavior of matrix glass and feldspar components the use of k cl ratios in interpretation of step heating results and the age of the kirkpatrick basalt the precise age of the kirkpatrick basalt has been a long standing problem the wide range of reported k ar dates has been attributed to loss of ar despite massive ar loss from the matrix plagioclase is shown to yield good 40ar39ar plateaus plateaus are observed for increments above 700 c and are defined not only by consistent apparent ages but also appropriately low k ca and high k cl ratios cl relations help identify ar released from small amounts of matrix which can seriously contaminate a plagioclase separate an age of 176 8 1 8 ma defines the time of formation of the youngest lava at mt frustum in north victoria land a glass sample from south victoria land gives the same age indicating that terrestrial basaltic glasses as old as jurassic do not inherently lose ar the step heating profile of glass with very fine crystals shows discordance which is an artifact of ar recoil during irradiation

wavelike structures in the martian topside ionosphere observed by mars global surveyor 1 seven hundred and forty three martian ionospheric electron density altitude profiles obtained by the radio occultation experiment onboard mars global surveyor have been analyzed for the purpose of determining possible spatial density fluctuations in about 80 of these profiles the high altitude region above 145 km displays significant wavelike structures with spatial scales of tens kilometers these structures appear as spatial wave activity superposed on background electron density distributions that decrease exponentially with altitude the amplitudes of the density variations are mostly limited to be less than 50 of the background densities spectrum analysis is applied to the ionospheric profiles above 145 km and it is found that a spatial wavelength of 40 km is prevailing in the observations it is demonstrated that the observed fluctuations are consistent with the occurrence of local density fluctuations the prevailing scale of the wavelike structure agrees very well with the wavelength of hydrodynamic waves predicted by wang and nielsen 2002a 2002b 2003b if hydrodynamic waves is indeed the cause of these electron density fluctuations then the 145 km altitude should be considered the lowest altitude at which the effects of external dynamic disturbances of the martian ionosphere can reach and should therefore be considered the lower boundary of the topside ionosphere

revisions to the age of the brunhes matuyama boundary and the pleistocene geomagnetic polarity timescale the currently referenced age of 730 ka for the brunhes matuyama b m geomagnetic polarity boundary mankinen and dalrymple 1979 is based largely on k ar and paleomagnetic data from postcollapse rhyolites in the valles caldera new mexico doell and dalrymple 1966 doell et al 1968 dating of sanidine from valles rhyolites by the 40a 39ar laser fusion technique indicates that samples critical to defining the b m boundary are up to 90 ka older than previously thought the new data combined with earlier results yield an age for the b m boundary of 780 10 ka 40ar 39ar ages from other samples suggest the jaramillo normal polarity subchron extended from 1010 to 915 ka

relationship of dayside main layer ionosphere height to local solar time on mars and implications for solar wind interaction influence to understand the influence of solar wind on the daytime main layer ionosphere of mars we investigated the local solar time lst variations of three characteristic heights of the ionosphere namely the heights of the 1 mhz and 1 5 mhz reflection points i e 1 24 1010 m 3 and 2 79 1010 m 3 isodensity contours respectively and the density peak we used a total of 19 996 mars advanced radar for subsurface and ionosphere sounding observations distributed on the northern hemisphere with solar zenith angle 80 acquired from june 2005 to october 2013 we exploited the kernel partial least squares regression method to extract the nonlinear relationships of the heights to lst and a few other variables the average height of the 1 mhz reflection point decreased from 218 km at 10 00 a m to 206 km at 16 00 p m local time the height of the 1 5 mhz reflection point decreased simultaneously from 190 km to 181 km these decreasing trends are in contrast to the lst variation of the density peak height which increased from 128 km to 137 km over the same lst interval based on these findings and previous results we suggest that the solar wind may penetrate the martian ionosphere down to altitudes of about 50 km above the main density peak and may in conjunction with the asymmetric draping of the interplanetary magnetic field compress the upper part of the main ionosphere layer on the p m side 10 km more than on the a m side

radar soundings of the ionosphere of mars we report the first radar soundings of the ionosphere of mars with the marsis mars advanced radar for subsurface and ionosphere sounding instrument on board the orbiting mars express spacecraft several types of ionospheric echoes are observed ranging from vertical echoes caused by specular reflection from the horizontally stratified ionosphere to a wide variety of oblique and diffuse echoes the oblique echoes are believed to arise mainly from ionospheric structures associated with the complex crustal magnetic fields of mars echoes at the electron plasma frequency and the cyclotron period also provide measurements of the local electron density and magnetic field strength

early pleistocene 40ar 39ar ages for bapang formation hominins central jawa indonesia the sangiran dome is the primary stratigraphic window for the plio pleistocene deposits of the solo basin of central jawa the dome has yielded nearly 80 homo erectus fossils around 50 of which have known findspots with a hornblende 40 ar 39 ar plateau age of 1 66 0 04 mega annum ma reportedly associated with two fossils swisher c c iii curtis g h jacob t getty a g suprijo a widiasmoro 1994 science 263 1118 1121 the dome offers evidence that early homo dispersed to east asia during the earliest pleistocene unfortunately the hornblende pumice was sampled at jokotingkir hill a central locality with complex lithostratigraphic deformation and dubious specimen provenance to address the antiquity of sangiran h erectus more systematically we investigate the sedimentary framework and hornblende 40 ar 39 ar age for volcanic deposits in the southeast quadrant of the dome in this sector bapang kabuh sediments have their largest exposure least deformation and most complete tephrostratigraphy at five locations we identify a sequence of sedimentary cycles in which h erectus fossils are associated with epiclastic pumice from sampled pumice eight hornblende separates produced 40 ar 39 ar plateau ages ranging from 1 51 0 08 ma at the bapang sangiran formation contact to 1 02 0 06 ma at a point above the hominin bearing sequence the chronological sequence of 40 ar 39 ar ages follows stratigraphic order across the southeast quadrant an intermediate level yielding four nearly complete crania has an age of about 1 25 ma

nightside ionosphere of mars radar soundings by the mars express spacecraft 1 we present results of a survey of the nightside ionosphere of mars as observed by mars advanced radar for subsurface and ionospheric sounding marsis on board the mars express spacecraft the occurrence rate of the nightside ionosphere is studied as a function of solar zenith angle sza magnetic field magnitude and magnetic field inclination it is shown that at locations with weak crustal magnetic fields the occurrence rate of the nightside ionosphere decreases with increasing sza up to about 125 suggesting that plasma transport from the dayside plays a crucial role in its formation however at locations with strong crustal magnetic fields the dependence on sza is no longer apparent and the inclination of magnetic field becomes a crucial parameter the occurrence rate of the nightside ionosphere is more than 4 times larger at locations with nearly vertical magnetic fields as compared to the locations with nearly horizontal magnetic fields this indicates that impact ionization by precipitating electrons is the main ionization source at these locations observed peak electron densities are less than 2 104 cm 3 in the vast majority of cases lower estimates of altitudes of peak electron densities are mostly between 100 and 150 km

the shallow plumbing system of stromboli island as imaged from 1 hz instantaneous gps positions 1 the stromboli volcano aeolian islands italy erupted suddenly on 28 december 2002 after a 17 year period of typically persistent but moderate eruptive activity followed two days later by a tsunamigenic landslide on its nw flank sciara del fuoco felt in the coastal areas of southern italy three continuous gps stations were quickly deployed near the volcano s rim sampling at 1 hz with instantaneous positions computed relative to a fourth station on its flank we report on two deformation episodes a vent migration on 16 17 february 2003 caused significant displacements at only one site and contributed to the decision not to issue a warning of an impending tsunamigenic landslide the second episode on 5 april 2003 a paroxystic explosion from the summit crater allowed us to model for the first time with geodetic data the shallow magma chambers that give rise to strombolian explosive activity

probabilistic source location of explosion quakes at stromboli volcano estimated with double array data data from two dense arrays of short period seismometers are used to retrieve source locations of the explosion quakes at stromboli volcano slowness vectors estimated at both arrays with the zero lag cross correlation technique constitute the experimental data set a probabilistic approach based on a grid search spanning the volcano interior is used to calculate the probability of the source location results depict a shallow source located beneath the crater area at depths not greater than 500 m below the surface results are slightly different from but comparable to those obtained in a companion experiment carried out in the same time period using a broad band seismometer network which show a source shifted some hundreds of meters northwest of the crater area the method is revealed to be effective and useful for future studies having the purpose of real time tracking of the explosion quakes and tremor

characterizing high energy explosive eruptions at stromboli volcano using multidisciplinary data an example from the 9 january 2005 explosion abstract stromboli is well known for its persistent normal explosive activity consisting of intermittent mild to moderate strombolian explosions that typically occur every 10 20 min all tephras erupted during this activity usually fall back into the crater terrace and consist of volatile poor scoriae fed by highly porphyritic hp magma more occasionally large explosions or paroxysms eject a greater quantity of tephra mainly consisting of hp scoriae and pumice clasts of low porphyritic lp magma but also including large lithic blocks in addition to this activity between 2004 and 2006 high energy explosions displaying an intermediate eruptive style between that of normal and paroxysmal explosions in terms of column height duration and tephra dispersal were observed to occur at a frequency of one to eight events per year while many volcanological geochemical and geophysical studies have focused in the last few years on the two end members of activity i e normal or paroxysmal a detailed investigation on these intermediate types of events has not been carried out yet here we report of a study on the 9 january 2005 explosion one of the high energy explosions during which the main fountaining phase lasted nearly a minute causing ejection of coarse bombs up to a height of 120 m and of ash and lapilli to 200 m an accompanying ash plume rose up to 500 m at the end of the explosion we present a multidisciplinary approach that integrates the results from analysis of live camera images with compositional and textural characterization of the erupted products major element composition of glassy groundmass and 3d views of textures in the erupted scoriae support the hypothesis based on volcanological observations that this explosion falls between normal and paroxysmal activity for which we use the term intermediate by comparing the video camera images of the 9 january 2005 explosion with volcanological features of other high energy explosions that occurred at stromboli between june 2004 and october 2006 we find that three additional events can be considered intermediate explosions suggesting that this type of activity may be fairly common on this volcano the results of this study although preliminary given our limited dataset clearly indicate that the methodology used here can be successfully applied to better define the range of eruptive styles typifying the normal explosive activity potentially improving our capability of eruption forecasting and assessing volcanic hazard at stromboli

brunhes matuyama magnetic reversal dated at 790 000 yr b p by marine astronomical correlations abstract the presence of the brunhes matuyama magnetic reversal in deep sea core sediments makes possible an alternative to the usual k ar radioistope method of dating the reversal as found in rocks the alternative method uses correlations of northern hemisphere summer insolation with oxygen isotope ratios from tropical cores the latitude dependent insolation variations are calculated from planetary mechanics and thus provide a highly accurate astronomical time scale the insolation variations strongly influence glacial ice volume fluctuations that dominate the oxygenisotope ratio changes recorded in core sediments the summer half year insolation variations are identified with corresponding isotope ratio changes in cores from the present through glacial stage 20 misleading effects of discontinuities or major nonuniformities of sediment deposition are avoided by an analysis of the uniformity of v28 238 and v28 239 the principal cores studied and by comparisons with other cores the top section stages 1 to 10 of v28 238 is uniformly deposited and for this section an isotope ratio time scale is chosen that agrees with the thorium uranium date for the high sea stand of the last interglacial extreme over this interval major glacial extremes strong isotope ratio minima coincide consistently with major insolation minima at times of low orbital eccentricity in addition interstadials are directly associated with precessional insolation peaks and the envelope of isotope ratio peaks resembles the envelope of precessionally dominated insolation peaks the assumption that the glacial extremes depended similarly on insolation minima during stages 10 to 20 permits minor age shifts of strong isotope ratio minima in the two cores relative to ages based on uniform overal deposition to match the ages of low eccentricity insolation minima the age shifts reflect residual nonuniformities of deposition the validity of this matching procedure is supported by a resulting consistent identification of principal isotope ratio peaks with high and low latitude coincident insolation maxima the brunhes matuyama reversal is found intinterglacial stage 19 and is dated on the astronomical time scale at 790 000 5000 yr b p

magnetically controlled density structures in the topside layer of the martian ionosphere magnetically controlled density structures in the main layer of the martian ionosphere are regularly detected by the mars advance radar for subsurface and ionospheric sounder marsis on board the mars express spacecraft when it passes over the regions of strong crustal magnetic fields these structures appear as oblique echoes in an ionogram and as hyperbola shaped feature in a radargram for the first time we observed such oblique echoes from the topside layer of the martian ionosphere comparison with a crustal magnetic field model suggests that these echoes mostly occur in regions close to magnetic field anomalies the marsis ionograms that show these oblique echoes are limited in number one reason for such limited occurrence is the fact that these echoes occur at the low frequency end of an ionogram where local plasma frequency lines and electron cyclotron lines make it difficult to discern these echoes in one case however we observed the topside layer with oblique echoes on several continuous ionograms and a hyperbola shaped feature on a radargram the apex of the hyperbola falls in the region of vertical magnetic fields unlike the main layer the recurrent occurrence of the topside layer at the same location is not common more importantly the oblique echoes from the topside layer are always associated with those from the main layer of the ionosphere but not vice versa the simultaneous observation of oblique echoes from the main and topside layers are explained by considering the formation of ionization bulges at the respective layer altitudes

excess argon in melt inclusions in zero age anorthoclase feldspar from mt erebus antarctica as revealed by the method abstract historically erupted 1984 anorthoclase phenocrysts from mt erebus yield k ar and 40 ar 40 ar apparent ages as old as 700 ka indicating the presence of excess argon 40 ar 39 ar furnace step heating results from anorthoclase reveal a positive correlation between the cl k ratio and apparent age because chlorine up to 1700 ppm is present in melt inclusions but not in the anorthoclase crystal lattice this correlation suggests that the excess argon is associated with melt inclusions trapped within the anorthoclase during rapid crystal growth confirmation of the source of excess argon comes from step heating experiments on multiple anorthoclase aliquots separated from two phenocrysts and one glass aliquot prepared from the matrix of a volcanic bomb the anorthoclase phenocrysts were crushed and hf etched to yield aliquots containing 30 10 and 1 melt inclusions the step heated anorthoclase with 30 and 10 melt inclusions yielded the highest cl k ratios and apparent integrated ages of 640 30 ka and 179 16 ka respectively the anorthoclase with i melt inclusions yielded significantly lower cl k ratios and apparent integrated ages of 48 8 ka and 50 30 ka the step heated volcanic glass yielded the least variable cl k ratios and a total gas age of 101 16 ka argon released from the anorthoclase and the trapped melt inclusions can be distinguished by differences in their degassing behavior allowing geologically more reasonable ages to be obtained melt inclusions exposed on the exterior of anorthoclase grains principally degas during furnace extraction at temperatures less than 1200 c inclusions entirely within anorthoclase grains principally degas at temperatures greater than 1200 c when incongruent melting of the anorthoclase allows melt inclusion hosted excess argon to escape anorthoclase aliquots prepared with less than 1 inclusions can be fitted with a plateau for heating steps below 1200 c to yield ages as young as 8 2 ka whereas steps above 1200 c yield ages in excess of 100 ka however anorthoclase aliquots containing 10 30 melt inclusions yield ages in excess of 200 ka for heating steps below 1200 c minimizing the effects of the excess argon from melt inclusions relies on sample preparation and step heating fine crushing and treatment with hydrofluoric acid removes many of the larger melt inclusions small melt inclusions which remain within the anorthoclase degas primarily at temperatures above 1200 c temperatures below 1200 c yield the most accurate ages attempts at post analytically correcting for the chlorine correlated excess argon are hindered by the variations in 40 ar e cl within and between samples elevated 40 ar e cl ratios in bubbles within the melt inclusions as deduced from in vacuo crushing experiments are the most likely cause for some or all of a sample s total 40 ar e cl variation in addition relative solubilities of argon and chlorine within phonolitic melts may be partly responsible for variations in 40 ar e cl

linking variable explosion style and magma textures during 2002 at stromboli volcano italy microtextural characteristics of fresh ejecta from stromboli volcano were examined from three periods of differing eruption style and intensity in 2002 activity shifted from relatively weak and infrequent ash charged explosions during january through may into two broad cycles of waxing activity in june through late september and late september through december followed by the onset on 28 december of the 2002 2003 effusive eruption analyzed sets of lapilli from may september october and 28 december show contrasts in the physical properties of magma resident in the shallow conduit during this range of activity three distinct textures are observed among the analyzed pyroclasts low density ld with an abundance of subspherical bubbles the presence of large irregularly shaped bubbles and a light to transparent glass matrix transitional texture tt with an intermediate number of subspherical bubbles a high frequency of large irregularly shaped bubbles and a honey colored glass matrix and high density hd with sparse relatively small bubbles conspicuous large irregular bubbles and a dark glass matrix observational and quantitative data density vesicle size indicate that these textures are linked through variable residence time in stromboli s shallow conduit with an ongoing evolution from ld to hd magma calculations suggest that residual ld magma will evolve to hd texture in a period of hours to days contrasting amounts of the ld tt and hd magmas are present in each sample with the most tt in may the most ld in september october and the most hd in december this implies that the shallow magma had a different rheology at each collection period the viscosity of ld and hd magmas are calculated to be in the range of 2 000 to 2 600 and 3 000 to 5 000 pa s respectively which with their changing proportions must have implications for rates of bubble slug ascent and processes of fragmentation this study suggests that an increasing maturity of magma in stromboli s shallow conduit with resultant increase in viscosity feeds back to reduce the intensity of explosions whereas a steady flux of ld magma favors more powerful explosions

a reappraisal of the geomagnetic polarity time scale to 4 ma using data from the turkana basin east africa recalibration of the pliocene and early pleistocene geomagnetic time scale using the k ar dated fluvial sequence of the turkana basin in east africa agrees with calibrations based on astronomical calculations ages estimated here are olduvai subchron 1 78 1 96 ma reunion subchrons 2 11 2 15 ma and 2 19 2 27 ma matuyama gauss boundary 2 60 ma kaena subchron 3 02 3 09 ma mammoth subchron 3 21 3 29 ma gauss gilbert boundary 3 57 ma

the 2007 eruption of stromboli volcano insights from real time measurement of the volcanic gas plume co2 so2 ratio abstract the recent eruption of stromboli in february april 2007 offered a unique chance to test our current understanding of processes driving the transition from ordinary persistent strombolian to effusive activity and the ability of instrumental geophysical and geochemical networks to interpret and predict these events here we report on the results of two years of in situ sensing of the co 2 so 2 ratio in stromboli s volcanic gas plume in the attempt to put constraints on the trigger mechanisms and dynamics of the eruption we show that large variations of the plume co 2 so 2 ratio range 0 9 26 preceded the onset of the eruption since december 2007 interrupting a period of relatively steady and low ratios time averaged ratio 4 3 lasting from at least may to november 2006 by contrasting our observations with numerical simulations of volcanic degassing at stromboli derived by use of an equilibrium saturation model we suggest that the pre eruptive increase of the ratio reflected an enhanced supply of deeply derived co 2 rich gas bubbles to the shallow plumbing system this larger than normal ascent of gas bubbles was likely sourced by a 1 3 km deep gas melt separation region probably a magma storage zone and caused faster convective overturning of magmas in the shallow conduit an increase in the explosive rate and in seismic tremor and finally the collapse of the la sciara del fuoco sector triggering the effusive phase the high co 2 so 2 ratios up to 21 observed during the effusive phase and particularly in the days and hours before a paroxysmal explosion on march 15 2007 indicate the persistence of the same gas source and suggest that de pressurization of the same 1 3 km deep magma storage zone could have been the trigger mechanism for the paroxysm itself

magmatism and continental break up in the south atlantic high precision40ar 39ar geochronology abstract a detailed ar ar study of the parana etendeka continental flood basalts cfb has been undertaken using laser spot analysis data provide information not only on the age of the samples but also on the variability of the non radiogenic ar component and state of alteration the results indicate the parana etendeka cfb were erupted over 10 million years between 137 and 127 ma providing a minimum overall eruption rate of 0 1 km3 yr 1 this is an order of magnitude less than that previously proposed for this the deccan and siberian cfb provinces but it is similar to estimates for hawaii iceland and the columbia river cfb in detail the new ar ar analyses indicate that magmatism within the parana etendeka province migrated from nw to se prior to and during the opening of the south atlantic providing an explanation for the asymmetry of the cfb lavas about the south atlantic moreover chemically defined magma types were erupted at different times in different places and so within the paranathey may not be used as reliable chronostratigraphic units rather such magmatic units may reflect the extent of compositionally distinct source regions in the uppermost mantle and indicate that partial melting took place over a wide area under the paranabasin the nw se migration of the onset of magmatism might be interpreted as a plume trace but the inferred rate of movement is 3 times faster than that inferred from subsequent magmatism on the rio grande rise it is argued that the onset of magmatism reflected extensional tectonics normal to the ponta grossa dyke swarm given that magmatism preceded the main phase of rifting and that extension across the ponta grossa was moderate current plume models have difficulty in predicting sufficient melting within the asthenosphere

dayside ionosphere of mars empirical model based on data from the marsis instrument 1 we present results of a systematic study of electron densities in the dayside martian ionosphere measured by the mars advanced radar for subsurface and ionosphere sounding marsis instrument on board the mars express spacecraft there are two distinct regions controlled by different physical mechanisms the first region is located at altitudes up to about 5 neutral scale heights above the altitude of peak electron density electron densities in this region are well described by the basic chapman theory the observed small deviations can be most probably explained by the neutral scale height and electron temperature increasing with altitude rather than being constant the second region is located at altitudes higher than about 10 neutral scale heights above the altitude of peak electron density it is controlled primarily by diffusion and the observed electron densities decrease exponentially with increasing altitude the corresponding diffusion scale height increases with increasing solar zenith angle which can be probably explained by nearly horizontal magnetic fields in the ionosphere induced by interaction with the solar wind the obtained dependencies can be used as a simple empirical model of the dayside martian ionosphere

seismic attenuation and shallow velocity structures at stromboli volcano italy the surface wave field associated with the explosive activity at stromboli volcano is investigated using data recorded by two short period seismic arrays deployed on the north and west flanks of the volcano the group velocity dispersion curves for rayleigh waves are derived using the multiple filter technique the phase velocity dispersion curves are recovered using a phase match filter and compared with that inferred from zero lag cross correlation analysis applied to the array data these analyses indicate rayleigh wave group velocities ranging from 0 29 to 0 24 km sec in the 1 5 to 8 0 hz frequency band and phase velocities ranging from 1 km sec at 1 5 hz to about 0 3 km sec at frequencies above 5 hz in addition the dispersive properties of the attenuation coefficient for rayleigh waves are inferred from application of the multiple filter technique to seismograms recorded at different distances from the source these results are validated through examination of the spectral amplitude decay with distance for both body and rayleigh waves the values of the body wave quality factor thus obtained are q 20 and q 6 for the north and west side of the island respectively the velocity and attenuation dispersion curves are inverted for the shear wave velocity and q structures down to a depth of about 200 m shear wave velocities for the west flank range from about 0 3 km sec for the uppermost 17 m thick layer to 1 9 km sec at depths greater than 200 m comparison with previous studies indicates a similar velocity structure for the north and west flanks the attenuation structure for the west flank is described by a shallower 36 m thick layer with q 9 underlain by a half space with q 50 on the north flank q 40 for the shallower 30 m thick layer and q 44 for the underlying half space residuals from analysis of the spectral decay with distance are used to quantify site effects affecting the different array elements on the west flank local amplifications at that array are interpreted in terms of an edge effect associated with concave topography velocity similarities observed at the north and west flanks are compatible with surface geologic data discrepancies in attenuation properties at the two sites are interpreted in terms of different degrees of heterogeneity and crack density controlling the scattering quality factor q s manuscript received 15 april 2001

palaeomagnetism and chronology of the central taupo volcanic zone new zealand summary the central taupo volcanic zone tvz of new zealand is a region of intense quaternary silicic volcanism active since 1 6 ma we report palaeomagnetic measurements from 59 distinct volcanic units sampled at 98 sites in the tvz these are mainly rhyolitic ignimbrites and lava domes with a few basaltic andesitic and dacitic lavas most have new k ar or 4oar 39ar ages the remanent magnetizations are generally stable to both thermal and alternating field demagnetization and well determined mean palaeodirections were obtained for all sites our findings suggest that the taupo whakamaru maroa reporoa rotorua and okataina volcanic centres were magnetized during the brunhes normal chron kapenga is an older volcanic centre where activity commenced around 0 89 ma and extended into the brunhes mangakino volcanic centre is significantly older and was active from 1 6 to 0 95 ma transitional or intermediate palaeodirections were obtained from ahuroa ignimbrite 1 18 ko 02 ma and mamaku ignimbrite 0 22k0 01 ma the former almost certainly corresponds to the cobb mountain event the latter is significantly older than the blake event and probably corresponds to the recently reported pringle falls summer lake magnetic episode multiple sites from the whakamaru ignimbrite have indistinguishable 4oar 39ar ages 0 33 f 0 01 ma and glass composition but divergent palaeomagnetic directions this contrast suggests that either 1 the different sites were formed during a phase of extremely violent activity lasting up to a few hundred years during which geomagnetic secular variation was recorded or 2 that they were formed in a single eruption and rotation during subsequent extensional tectonism has caused divergence of the palaeodirections 40ar 39ar ages of 0 77 0 03 ma for the reversely magnetized rahopeka ignimbrite and 0 71 k 0 06 ma for the overlying normally magnetized waiotapu ignimbrite bracket and constrain the age of the matuyama brunhes transition

effect of crustal magnetic fields on the near terminator ionosphere at mars comparison of in situ magnetic field measurements with the data of radio science experiments on board mars global surveyor 1 electron density profiles of the ionosphere of mars derived from radio occultation data obtained by the radio science mars global surveyor mgs experiment have been compared with the crustal magnetic fields measured by the mgs magnetometer electron reflectometer mag er experiment in the northern hemisphere the crustal fields are rather weak and usually do not prevent direct interaction between the solar wind sw and the martian ionosphere atmosphere exceptions do occur in the isolated mini magnetospheres formed by the crustal anomalies much stronger crustal fields are located in limited regions in the southern hemisphere and lead to the formation of large scale mini magnetospheres a study of the electron density profiles obtained when the mini magnetosphere regions are near the terminator has been conducted using the magnetic field measurements at altitudes 170 180 km and 400 km the magnitude of the electron density peak and the effective scale height of the electron density for two altitude ranges 145 165 km and 165 185 km have been derived for each of the 326 selected profiles studied in each hemisphere the longitudinal variations of these derived parameters have been studied a significant difference between the large scale mini magnetospheres and regions outside of them has been found the neutral atmosphere is cooler inside the large scale mini magnetospheres the variations of the magnitude of the electron density peak indicate that the electrons are usually hotter inside a large scale mini magnetosphere than outside it appears that the mini magnetospheres formed by strong crustal magnetic fields prevent additional heating of the neutral atmosphere due to direct interaction of the sw and also confine the hotter electrons created by photo ionization

continuous gravity measurements reveal a low density lava lake at kīlauea volcano hawai i abstract on 5 march 2011 the lava lake within the summit eruptive vent at k lauea volcano hawai i began to drain as magma withdrew to feed a dike intrusion and fissure eruption on the volcano s east rift zone the draining was monitored by a variety of continuous geological and geophysical measurements including deformation thermal and visual imagery and gravity over the first 14 hours of the draining the ground near the eruptive vent subsided by about 0 15 m gravity dropped by more than 100 gal and the lava lake retreated by over 120 m we used gps data to correct the gravity signal for the effects of subsurface mass loss and vertical deformation in order to isolate the change in gravity due to draining of the lava lake alone using a model of the eruptive vent geometry based on visual observations and the lava level over time determined from thermal camera data we calculated the best fit lava density to the observed gravity decrease to our knowledge the first geophysical determination of the density of a lava lake anywhere in the world our result 950 300 kg m 3 suggests a lava density less than that of water and indicates that k lauea s lava lake is gas rich which can explain why rockfalls that impact the lake trigger small explosions knowledge of such a fundamental material property as density is also critical to investigations of lava lake convection and degassing and can inform calculations of pressure change in the subsurface magma plumbing system

review of ten years of volcano deformations recorded by the ground based insar monitoring system at stromboli volcano a tool to mitigate volcano flank dynamics and intense volcanic activity abstract stromboli volcano southern italy is one of the most monitored volcano in the world with a surveillance network that includes a permanently sited ground based sar interferometer gbinsar this work is the review of the gbinsar data gained from the last decade of monitoring activity the analysis of the entire dataset of gbinsar measurements allowed the assessment of the deformation field of the northern part of the summit crater area and the sciara del fuoco depression in detail the main displacements recognized can be related to different factors 1 the inflation deflation respectively immediately before and after each new effusive event 2 the bulging of localized sectors of the volcano involved in the vent opening 3 the gravitational sliding of the sciara del fuoco infill 4 the movement of lava flows accelerations in this sector are related to sheet intrusions while the possibility of vent opening associated with small sliding or catastrophic flank failure are related to highly overpressurized sheets able to produce high displacement rate in the sciara del fuoco in the summit crater area the increases in the displacement rate are related to the pressurization of the shallow conduit system as the consequence of the variation in the magma level magmastatic pressure or to the lateral magma migration lateral conduit expansion or dike intrusion in response to the increase of the overpressure component fluctuations in the displacement rate in the summit crater area can be related to the magma overturning within the conduit with the increases in displacement rate during the upwelling of less dense magma while displacement rate decreases as the degassed magma column is pushed out from the conduit lava flows or overflows instead the decrease in the displacement rate without coeval lava outpouring could be related to the sink of the degassed magma due to density contrast between the gas poor and the gas charged magmas using the displacement rate in the summit crater area as a proxy for the variation in the pressure condition in conduit both magmastatic and overpressure components thresholds for the crises characterized by the occurrence of overflows eventually associated with major explosions and flank effusions eventually associated with paroxysmal explosions are identified small conduit overpressure will produce overflows sometimes associated with crater rim collapses while large magma overpressure will laterally expand the conduit forming ne sw striking sheets feeding eruptive vents at the base of the summit crater area and within the sciara del fuoco generating conditions of instability that can evolve into catastrophic collapse of the instable flank

estimation of the total electron content of the martian ionosphere using radar sounder surface echoes 1 the martian ionosphere s local total electron content tec and the neutral atmosphere scale height can be derived from radar echoes reflected from the surface of the planet we report the global distribution of the tec by analyzing more than 750 000 echoes of the mars advanced radar for subsurface and ionospheric sounding marsis this is the first direct measurement of the tec of the martian ionosphere the technique used in this paper is a novel transmission mode sounding of the ionosphere of mars in contrast to the active ionospheric sounding experiment ais on marsis which generally operates in the reflection mode this technique yields a global map of the tec for the martian ionosphere the radar transmits a wideband chirp signal that travels through the ionosphere before and after being reflected from the surface the received waves are attenuated delayed and dispersed depending on the electron density in the column directly below the spacecraft in the process of correcting the radar signal we are able to estimate the tec and its global distribution with an unprecedented resolution of about 0 1 deg in latitude 5 km footprint the mapping of the relative geographical variations in the estimated nightside tec data reveals an intricate web of high electron density regions that correspond to regions where crustal magnetic field lines are connected to the solar wind our data demonstrates that these regions are generally but not exclusively associated with areas that have magnetic field lines perpendicular to the surface of mars as a result the global tec map provides a high resolution view of where the martian crustal magnetic field is connected to the solar wind we also provide an estimate of the neutral atmospheric scale height near the ionospheric peak and observe temporal fluctuations in peak electron density related to solar activity

counter current convection in a volcanic conduit abstract volcanoes of strombolian type are able to maintain their semi permanent eruptive states through the constant convective recycling of magma within the conduit leading from the magma chamber in this paper we study the form of this convection using an analytic model of degassing two phase flow in a vertical channel we provide solutions for the flow at small grashof and large prandtl numbers and we suggest that permanent steady state counter current convection is only possible if an initial bubbly counter current flow undergoes a regime transition to a churn turbulent flow we also suggest that the magma in the chamber must be under pressured in order for the flow to be maintained and that this compromises the assumed form of the flow

age and stratigraphic relationships of pre and syn rift volcanic deposits in the northern puertecitos volcanic province baja california mexico geologic mapping of volcanic strata of the northern puertecitos volcanic province pvp in northeastern baja california mexico performed in conjunction with 40 ar 39 ar analysis and petrochemical study documents the miocene geologic history of a well preserved volcanic succession within the northern sierra santa isabel and its relationship to the evolving pacific north america plate boundary subduction related volcanic deposits well exposed in profile along the northern margin of the pvp in the informally named santa isabel wash region span pre 17 to 15 ma minor rift related volcanism occurred at 12 5 and 9 ma prior to voluminous pvp forming volcanism at 6 6 5 ma isochron ages typically exhibit precision 1 for plagioclase of 2 7 and for anorthoclase and sanidine of 2 5 and replicate analysis of an internal anorthoclase standard indicate 1 2 reproducibility within a given irradiation and 2 5 for samples irradiated separately improved local correlations made possible by the rich stratigraphic section preserved in santa isabel wash help constrain the relationships of several widespread pyroclastic flow deposits in northeastern baja california these correlations are important for both paleomagnetic studies within the region and for establishing geologic ties across the gulf of california the combined mapping and age results imply that most extensional deformation in the study area is post 6 ma although some earlier faulting and the development of the pre 6 ma matomi accommodation zone are also documented results support a transitional plate boundary model which implies that much of the pacific north america relative plate motion north of delfin basin i e the northernmost gulf of california is accommodated on n to nnw striking faults developed during late miocene ene directed extension the model predicts a zone of divergence east of the pvp which provides a structural mechanism for the positions and jumps of nearby gulf of california spreading centers upper and lower tiburon and delfin basins since 6 ma and relates major pulses of pvp volcanism at 6 and 3 ma to these offshore spreading center adjustments results also imply that most extensional deformation in santa isabel wash is the result of incorporation of the pvp into the gulf extensional province 2 3 ma due to northwestward propagation of the guaymas fracture zone rotational deformation north of the pvp may have begun contemporaneously with this adjustment along the gulf extensional province rift margin

new geophysical insight into the dynamics of stromboli volcano italy abstract a 56 hour gravity sequence recorded in the crater area of stromboli volcano is presented data were acquired during a period of normal strombolian activity high frequency gravity anomalies up to 20 gal t tens of seconds are observed comparison with independent data reveals that these changes reflect the response of the gravimeter excited by seismic waves during strombolian explosions correlated changes in the energy distribution over time appear in the continuous wavelet transforms of gravity and rms tremor but over different scales corresponding to periods centered at about 50 and 25 min for gravity and tremor respectively we infer that the rate of fresh magma supply to the shallow feeding system controls the energy distribution over time of the coupled components in gravity and rms tremor signals in particular the gravity signal with an average amplitude of 1 2 gal could be induced by temporary accumulations at shallow depth of the volatiles discharged by quiescent degassing changes in the rate of explosions from the summit craters correlate with changes in the amplitude of the coupled gravity and volcanic tremor oscillations implying that even though the slug genesis process behind the explosions occurs at deeper levels it is also controlled by the rate of gas rich magma supply from below negative gravity anomalies of about 20 gal over intervals of some hours are also observed separated by intervals of about 24 h they could be induced by increases in magma vesicularity in the uppermost part of the conduit plexus a view supported by i changes in the time space distribution of tremor amplitudes and ii increases in spattering activity from a summit vent both occurring during the development of the negative gravity anomalies the processes behind mild strombolian explosions do not trigger measurable gravity changes nevertheless the slug ascent before a major explosion could induce a precursory gravity signal

stratigraphy and structure of the ngatamariki geothermal system from new zircon u pb geochronology implications for taupo volcanic zone evolution abstract recent drilling at the ngatamariki geothermal field taupo volcanic zone new zealand has provided new constraints on the stratigraphy and volcanic evolution of the region over 2800 m thickness of volcanic products are present at ngatamariki mainly comprised of rhyolitic ignimbrites linked to large caldera forming events at sources outside the field area but locally sourced andesite and rhyolite lavas and domes are also encountered most of the rocks are allocated to the pre 0 35 ma tahorakuri formation crystallisation age spectra and consequent best estimates of eruption age have been obtained by u pb dating on zircons from otherwise severely hydrothermally altered magmatic rocks by secondary ion mass spectrometry techniques using a shrimp rg instrument the oldest rock dated is an ignimbrite which yields an eruption age estimate of 1 85 0 06 ma this ignimbrite plus comparable aged units dated at the adjacent rotokawa and ohaaki geothermal fields are interpreted to represent the oldest silicic volcanic deposits in the area and onlap the basal andesite lava pile that is best developed at rotokawa to the south other pyroclastic units and associated volcaniclastic sediments with another intercalated andesite lava unit return age estimates between 1 85 0 06 and 0 701 0 039 ma between 0 7 and 0 35 ma contemporaneous surface lithologies in the ngatamariki area are dominated by sediments with subordinate lava domes between 0 716 0 017 and 0 655 0 016 ma at least three shallow to 5 km 3 the intrusions generated a large alteration halo 25 km 3 minimum and intense silicification of the wall rocks at 0 35 and 0 34 ma the area was buried by two ignimbrite packages of the whakamaru group erupted from sources just west and well north respectively of the field ignimbrites of the waiora formation and several rhyolite lava domes were then emplaced over a period bracketed by domes dated at 0 282 0 011 and 0 257 0 011 ma coeval with more extensive volcanic activity in the maroa dome complex west of the field sediments of the huka falls formation and deposits of the 25 4 0 2 ka oruanui eruption then cap and seal the system the new u pb data coupled with detailed petrographical studies allow us to build the history of the area encompassed by the ngatamariki geothermal field the field despite 2 8 km of subsidence does not lie in a caldera and is the only one known to date to have a plutonic intrusive complex of quaternary age two chemically and temporally distinct hydrothermal events are located at the ngatamariki field with no evidence of continuity between the two

transient layers in the topside ionosphere of mars 1 radar soundings from the marsis instrument on board the mars express spacecraft have shown that distinct layers can occur in the topside ionosphere of mars well above the main photo ionization layer these layers appear as cusps or sometimes steps in plots of the time delay as a function of frequency usually only one topside layer is observed typically at altitudes from 180 to 240 km however occasionally an additional layer occurs at even higher altitudes the layers are transient features and are present about 60 of the time near the subsolar point decreasing with increasing solar zenith angle to less than 5 at the terminator and the nightside the transient nature of the layers suggests that they are produced by a dynamical process most likely involving an interaction with the solar wind in the upper levels of the ionosphere

a multiple approach radiometric age estimate for the rotoiti and earthquake flat eruptions new zealand with implications for the mis 4 3 boundary abstract pyroclastic fall deposits of the paired rotoiti and earthquake flat eruptions from the taupo volcanic zone new zealand combine to form a widespread isochronous horizon over much of northern new zealand and the southwest pacific this horizon is important for correlating climatic and environmental changes during the last glacial period but has been the subject of numerous disparate age estimates between 35 1 2 8 and 71 6 ka all errors are 1 s d obtained by a variety of techniques a potassium argon k ar age of 64 4 ka was previously determined on bracketing lavas at mayor island volcano offshore from the taupo volcanic zone we present a new more precise 40ar 39ar age determination on a lava flow on mayor island that shortly post dates the rotoiti earthquake flat fall deposits of 58 5 1 1 ka this value coupled with existing ages from underlying lavas yield a new estimate for the age of the combined eruptions of 61 0 1 4 ka which is consistent with u th disequilibrium model age data for zircons from the rotoiti deposits direct 40ar 39ar age determinations of plagioclase and biotite from the rotoiti and earthquake flat eruption products yield variable values between 49 6 2 8 and 125 3 10 0 ka with the scatter attributed to low radiogenic ar yields and or alteration and or inheritance of xenocrystic material with inherited ar rotoiti earthquake flat fall deposits occur in new zealand in association with palynological indicators of mild climate attributed to marine isotope stage mis 3 and thus used to suggest an age that is post 59 ka the natures of the criteria used to define the mis 4 3 boundary in the northern and southern hemispheres however imply that the new 61 ka age for the rotoiti earthquake flat eruption deposits will provide the inverse namely a more accurate isochronous marker for correlating diverse changes across the mis 4 3 boundary in the southwest pacific