a comparative study of equatorial daytime vertical e b drift in the indian and indonesian sectors based on 150 km echoes 1 in this paper we study for the first time the daytime vertical e bdrift velocities from gadanki and kototabang using the doppler shifts of the 150 km echoes observed during 2008 2010 a period of low solar activity drift velocities are mostly positive and confined to 35 m s 1 at both the locations except for gadanki where on a few occasions negative drift velocities have been observed in the afternoon hours drift velocities generally show a decreasing trend with local time and the largest drift is generally observed in the forenoon hours consistent with extensively reported observations and models of e bdrift drift velocities from gadanki and kototabang compared exceeding well on some days and differed remarkably on many days despite the fact that they are longitudinally separated by only 20 the day to day variation in the drift velocity could be as high as 15 m s 1 at gadanki and 7 m s 1at kototabang seasonal mean drifts over gadanki are found to be generally larger than those of kototabang the observations have been compared in detail with those reported earlier based on ground and satellite based observations and also with the scherliess fejer model the observed differences in the drifts at the two locations including the downward drifts have been discussed in the light of current understanding of the longitudinal variability ofe b drift

the trow point bed a deposit of upper permian marine oncoids peloids and columnar stromatolites in the zechstein of ne england

geostrophic versus friction dominated storm flow palaeocurrent evidence from the late permian brotherton formation england the late permian brotherton formation of northeastern england is a 0 75 m thick carbonate sequence which exhibits abundant erosively amalgamated hummocky cross stratification gutter casts and shallow scour fills suggesting deposition in a storm dominated platformal shelf setting the outcrop ca 15 m thick is divisible into three facies associations a basal transgressive interval 4 5 m thick facies association a which passes upwards into a thinly bedded argillaceous condensed section 1 m thick facies association b which in turn rapidly grades upwards into a 8 10 m thick regressive highstand succession of hummocky cross stratified amalgamated scour fills facies association c the dominance of hummocky cross stratification in all facies associations would suggest that post storm deposition and fairweather reworking was largely under oscillatory currents however the erosional palaeocurrent data indicate that facies associations a and b were deposited following combined oscillatory and geostrophically balanced shore parallel flows in contrast facies association c was deposited by infilling the scours of friction dominated offshore directed and downwelling jet like flows combined with oscillatory wave currents the dominance of geostrophic or friction dominated flows in the study area is interpreted to be controlled by relative sea level changes during transgressive conditions increasing accommodation permitted rotation of the downwelling pressure driven currents in the regressive phase particularly in the accommodation limited late highstand bottom friction was important in inhibiting flow rotation it is suggested that the paucity of evidence for geostrophic flows in the ancient record may in part be attributed to the palaeocurrent indicators in sand grade substrates being restricted to thin transgressive intervals or surfaces whilst in the volumetrically more important regressive deposits palaeocurrent data are largely contained within facies from the friction dominated zone

estimating daytime vertical exb drift velocities in the equatorial f region using ground based magnetometer observations 1 the daytime equatorial electrojet is a narrow band of enhanced eastward current flowing in the 100 to 120 km altitude region within 2 latitude of the dip equator a unique way of determining the daytime strength of the electrojet is to observe the difference in the magnitudes of the horizontal h component between a magnetometer placed directly on the magnetic equator and one displaced 6 to 9 degrees away the difference between these measured h values provides a direct measure of the daytime electrojet current and in turn the magnitude of the vertical exb drift velocity in the f region ionosphere this paper discusses a recent study that has established the quantitative relationship between the vertical exb drift velocity in the ionospheric f region and the daytime strength of the equatorial electrojet in the south american west coast longitude sector

fingerprints and age models for widespread new zealand tephra marker beds erupted since 30 000 years ago a framework for nz intimate abstract the role of tephras in the nz intimate project is a critical one because most high resolution palaeoclimatic records are linked and dated by one or more tephra layers in this review first we document eruptive distributional and compositional fingerprinting data both mineralogical and geochemical for 22 key marker tephras erupted since 30 000 years ago to facilitate their identification and correlation we include new glass compositional data the selected marker tephras comprise 10 from taupo and nine from okataina volcanoes rhyolitic one from tuhua volcano peralkaline rhyolitic and one each from tongariro and egmont volcanoes andesitic second we use four approaches to develop 2 age models for the tephras youngest to oldest 1 calendar ages for kaharoa and taupo y were obtained by wiggle matching log derived tree ring sequences dated by 14c 2 whakaipo v was dated using an age depth model from peat 3 14 tephras in the montane kaipo peat sequence waimihia s unit k whakatane tuhua mamaku rotoma opepe e poronui c karapiti b okupata konini waiohau rotorua rerewhakaaitu were dated by simultaneously wiggle matching stratigraphic position and 51 independent 14c age points against intcal04 using bayesian probability methods via both oxcal and bpeat and 4 the five oldest tephras erupted before ca 18 000 cal yr bp were dated by calibrating limited numbers of 14c ages using intcal04 okareka or comparison curves of the expanded cariaco basin sequence te rere kawakawa oruanui poihipi okaia kawakawa oruanui tephra the most widely distributed marker tephra was erupted probably ca 27 097 957 cal yr bp potential dating approaches for the older tephras include their identification in antarctic ice cores if present or annually laminated sediments for which robust calendar age models have been constructed high precision ams 14c dating on appropriate material from environmentally stable sites systematic luminescence dating or new radiometric techniques e g u th he if suitable minerals are available and errors markedly reduced further application of bayesian age modelling to stratigraphic sequences of 14c ages possibly augmented with luminescence ages may help refine age models for pre holocene tephras with the largest errors finally we discuss the critical role these marker tephras play in the ongoing construction of an event stratigraphy for the new zealand region which is a key objective of australasian and southern hemisphere intimate projects

the 0 57 ma plinian eruption of the granadilla member tenerife canary islands an example of complexity in eruption dynamics and evolution the granadilla member is one of the most widely dispersed and largest volume pyroclastic units at tenerife canary islands and represents the culminating eruption to a second cycle of explosive volcanism of the las canadas edifice the member dared at 0 57 ma comprises a plinian fall deposit the granadilla pumice which is overlain by ignimbrite up to 30 m thick the granadilla pumice is up to 9 m thick approximately 10 km from sourer pyle b t value is 5 35 km and is subdivided into four fail units unit 1 is up to 1 2 m thick and is further divisible into another four pumice fall subunits based on bedding and grainsize differences unit 2 is a thin but distinctive ash layer similar to2 cm thick and its wide dispersal 550 km 2 constant thickness planar laminations and ash aggregate textures collectively indicate a phreatoplinian fall origin the lithic rich nature and abundance of unaltered lithic fragments reflect magma interaction with aquifer derived water at depth unit 3 less than or equal to1 8 m thick records a reversal to dry plinian eruptive activity unit 4 the thickest of the fall units up to 6 3 m thick records the maximum dispersal and intensity of the eruption pyle b t and b c values are 5 7 and 6 3 km respectively best illustrated by the presence of large pumice bombs up to 30 cm diameter at distances up to 20 km from vent and reverse grading of lithic and pumice clasts the widespread 500 km 2 nonwelded and pumice rich granadilla ignimbrite unit 5 records the collapse of the plinian eruption column the ignimbrite has a simple sheet like geometry but exhibits a complex internal stratigraphy the base of the ignimbrite locally cuts down through the underlying granadilla pumice removing it entirely indicating up to 9 m of erosion by the pyroclastic flows a coarse vent derived lithic breccia horizon towards the top of the ignimbrite is interpreted to record the onset of caldera collapse late in the eruption minimum volume estimates for the granadilla pumice and ignimbrite are 5 2 and 5 km 3 respectively the dispersal area deposit characteristics and exponential thickness and clast size decay relationships with isopach area 1 2 are consistent with dispersal and fallout from the umbrella region of a moderately high similar to 17 to greater than or equal to 25 km plinian column we propose that the eruption involved two vents probably aligned along a ne sw fissure within the las canadas caldera c 2000 elsevier science b v all rights reserved

the 1963 1964 eruption of agung volcano bali indonesia the february 1963 to january 1964 eruption of gunung agung indonesia s largest and most devastating eruption of the twentieth century was a multi phase explosive and effusive event that produced both basaltic andesite tephra and andesite lava a rather unusual eruption sequence with an early lava flow followed by two explosive phases and the presence of two related but distinctly different magma types is best explained by successive magma injections and mixing in the conduit or high level magma chamber the 7 5 km long blocky surfaced andesite lava flow of 0 1 km3 volume was emplaced in the first 26 days of activity beginning on 19 february on 17 march 1963 a major moderate intensity 4 107 kg s 1 explosive phase occurred with an 3 5 h long climax this phase produced an eruption column estimated to have reached heights of 19 to 26 km above sea level and deposited a scoria lapilli to fine ash fall unit up to 0 2 km3 dense rock equivalent dre in volume with plinian dispersal characteristics and small but devastating scoria and ash flow deposits on 16 may a second intense 4 h long explosive phase 2 3 107 kg s 1 occurred that produced an 20 km high eruption column and deposited up to 0 1 km3 dre volume of similar ash fall and pyroclastic flow deposits the latter of which were more widespread than in the march phase the two magma types porphyritic basaltic andesite and andesite are found as distinct juvenile scoria populations this indicates magma mixing prior to the onset of the 1963 eruption and successive injections of the more mafic magma may have modulated the pulsatory style of the eruption sequence even though a total of only 0 4 km3 dre volume of lava scoria and ash fall and scoria and ash pyroclastic flow deposits were produced by the 1963 eruption there was considerable local damage caused mainly by a combination of pyroclastic flows and lahars that formed from the flow deposits in the saturated drainages around agung minor explosive activity and lahar generation by rainfall persisted into early 1964 the climactic events of 17 march and 16 may 1963 managed to inject ash and sulfur rich gases into the tropical stratosphere

the permian to jurassic stratigraphy and structural evolution of the central cheshire basin new seismic reflection data reveal details of the permo triassic basin fill in the central cheshire basin the seismic stratigraphy indicates that the permian and triassic succession is far thicker than previously estimated seismic data and backstripping of the preserved permian to early jurassic sedimentary succession suggest that at least two phases of fault controlled subsidence occurred in early permian and early triassic times an intra triassic unconformity is seen on the seismic data near the top of the sherwood sandstone group this may equate with the hardegsen unconformity it is possible that this unconformity was generated by syn extensional regional uplift accompanying lithospheric thinning the gross morphology and location of the faults on the eastern margin of the cheshire basin are interpreted to be at least locally controlled by extensional re activation of a westwards dipping reverse fault possibly an extension of the pontesford linley lineament

probabilistic modeling of tephra dispersal hazard assessment of a multiphase rhyolitic eruption at tarawera new zealand 1 the tarawera volcanic complex comprises 11 rhyolite domes formed during five major eruptions between 17 000 b c and a d 1886 the first four of which were predominantly rhyolitic the only historical event erupted about 2 km3 of basaltic tephra fall a d 1886 the youngest rhyolitic event erupted a tephra fall volume more than 2 times larger and covered a wider area northwest and southeast of the volcano a d 1315 kaharoa eruption we have used the kaharoa scenario to assess the tephra fall hazard from a future rhyolitic eruption at tarawera of a similar scale the plinian phase of this eruption consisted of 11 discrete episodes of vei 4 we have developed an advection diffusion model tephra that allows for grain size dependent diffusion and particle density a stratified atmosphere particle diffusion time within the rising plume and settling velocities that include reynolds number variations along the particle fall simulations are run in parallel on multiple processors to allow a significant implementation of the physical model and a fully probabilistic analysis of inputs and outputs tephra is an example of a class of numerical models that take advantage of new computational tools to forecast hazards as conditional probabilities far in advance of future eruptions three different scenarios were investigated for a comprehensive tephra fall hazard assessment upper limit scenario eruption range scenario and multiple eruption scenario hazard curves and probability maps show that the area east and northeast of tarawera would be the most affected by a kaharoa type eruption

displaced carbonates in the zechstein of the uk north sea abstract the cored zechstein 2 interval of amoco well 38 24 1 drilled on the southern margin of the mid north sea high contains deformed conglomeratic and brecciated dolostones which are interpreted as displaced distal shelf sediments redeposited in deeper water the displaced dolostones indicate disruption and sliding of consolidated rock down a slope accompanied by slumping of semi consolidated sediment minor collapse brecciation also occurred as a result of the partial removal of underlying evaporites such features have not hitherto been described from cored wells in the uk north sea nor have their petrophysical attributes been discussed the best reservoir properties occur in the slumped deposits showing plastic deformation brecciated beds have unpredictable and wide ranging porosity and permeability values which are attributable to variable anhydrite cementation and clasts with different textures and very variable fabric displaced zechstein carbonates on or at the foot of unstable palaeo slopes for example in the vicinity of the mid north sea high can develop moderately attractive reservoir characteristics and might in places be thick enough to be of economic importance

unconventional reservoir potential of the upper permian zechstein group a slope to basin sequence stratigraphic and sedimentological evaluation of carbonates and organic rich mudrocks northern germany the late permian zechstein group in northeastern germany is characterized by shelf and slope carbonates that rimmed a basin extending from eastern england through the netherlands and germany to poland conventional reservoirs are found in grainstones rimming islands created by pre existing paleohighs and platform rimming shoals that compose steep margins in the north and ramp deposits in the southern part the slope and basin deposits are characterized by debris flows and organic rich mudstones lagoonal and basinal evaporites formed the seal for these carbonate and underlying sandstone reservoirs the objective of this investigation is to evaluate potential unconventional reservoirs in organic rich fine grained and or tight mudrocks in slope and basin as well as platform carbonates occurring in this stratigraphic interval therefore a comprehensive study was conducted that included sedimentology sequence stratigraphy petrography and geochemistry sequence stratigraphic correlations from shelf to basin are crucial in establishing a framework that allows correlation of potential productive facies in fine grained organic rich basinal siliceous and calcareous mudstones or interfingering tight carbonates and siltstones ranging from the lagoon to slope to basin which might be candidates for forming an unconventional reservoir most organic rich shales worldwide are associated with eustatic transgressions the basal zechstein cycles z1 and z2 contain organic rich siliceous and calcareous mudstones and carbonates that form major transgressive deposits in the basin maturities range from over mature gas in the basin to oil generation on the slope with variable toc contents this sequence stratigraphic and sedimentologic evaluation of the transgressive facies in the z1 and z2 assesses the potential for shale gas oil and hybrid unconventional plays potential unconventional reservoirs might be explored in laminated organic rich mudstones within the oil window along the northern and southern slopes of the basin although the zechstein z1 and z2 cycles might have limited shale gas potential because of low thickness and deep burial depth to be economic at this point unconventional reservoir opportunities that include hybrid and shale oil potential are possible in the study area

a new and working petroleum source rock on the uk continental shelf upper permian offshore yorkshire we report on the discovery of oil from the boulby mine and its likely productive source rock from yorkshire in ne england located to the west 30 km of the newly licenced petroleum exploration areas in the vicinity of the mid north sea high oil samples from the mine have likely been generated from zechstein group kirkham abbey formation kaf sapropelic carbonate rock as indicated by aliphatic and aromatic hydrocarbon biomarkers other potential source rocks of carboniferous westphalian namurian visean coals and mudrocks and jurassic the jet rock bituminous shales kimmeridge clay formation age are ruled out on the basis of organic geochemical data boulby oil was generated in the peak to late oil window and it is characterised by the high abundance of c32 and c34 homohopanes slight even over odd predominance eop of c20 25 n alkanes indicating restricted carbonate evaporite depositional conditions and c29 ethyl diacholestane 20 s likely implying a clay rich source rock the structural framework and tectonic history of the permian strata reveal the presence of several fault systems which served as conduits for migrating petroleum similar zechstein sourced oil is known from poland and germany but the occurrence at boulby is the first positive identification of oil derived from zechstein source rock in the north sea area the boulby oil is reservoired in zechstein 3 z3 brotherton formation dolomite and sealed by z3 evaporite rocks the proven oil occurrence at boulby has significant implications in terms of reducing the risk of a lack of oil mature source rock for acreage offered in the neighbouring north sea during the uk s 30th and 31st licencing rounds

time gcm study of the ionospheric equatorial vertical drift changes during the 2006 stratospheric sudden warming this modeling study quantifies the daytime low latitude vertical e b drift changes in the longitudinal wave number 1 wn1 to wn4 during the major extended january 2006 stratospheric sudden warming ssw period as simulated by the national center for atmospheric research thermosphere ionosphere mesosphere electrodynamics general circulation model time gcm and attributes the drift changes to specific tides and planetary waves pws the largest drift amplitude change approximately 5 m s is seen in wn1 with a strong temporal correlation to the ssw the wn1 drift is primarily caused by the semidiurnal westward propagating tide with zonal wave number 1 sw1 and secondarily by a stationary planetary wave with zonal wave number 1 pw1 sw1 is generated by the nonlinear interaction of pw1 and the migrating semidiurnal tide sw2 at high latitude around 90 100 km the simulations suggest that the e region pw1 around 100 130 km at the different latitudes has different origins at high latitudes the pw1 is related to the original stratospheric pw1 at midlatitudes the model indicates pw1 is due to the nonlinear interaction of sw1 and sw2 around 95 105 km and at low latitudes the pw1 might be caused by the nonlinear interaction between de2 and de3 the time evolution of the simulated wn4 in the vertical e b drift amplitude shows no temporal correlation with the ssw the wn4 in the low latitude vertical drift is attributed to the diurnal eastward propagating tide with zonal wave number 3 de3 and the contributions from se2 te1 and pw4 are negligible

multiple rhyolite magmas and basalt injection in the 17 7 ka rerewhakaaitu eruption episode from tarawera volcanic complex new zealand abstract the 17 7 ka rerewhakaaitu eruption episode volume 5 km3 dre rhyolite magma was the second of five major episodes that have built the tarawera volcanic complex in the okataina volcanic centre over the past 22 kyr the rerewhakaaitu episode produced a widespread tephra fall deposit associated proximal pyroclastic flow deposits and voluminous rhyolite lava extrusions two different rhyolite magmas t1 and t2 were simultaneously erupted from the main vent area throughout much of the eruption episode t1 magma was a crystal poor orthopyroxene hornblende rhyolite that is highly evolved whole rock sio2 77 wt with a moderate temperature 760 c based on fe ti oxides t2 is a crystal rich biotite hornblende rhyolite that is less evolved sio2 75 wt with a fe ti oxide temperature of 700 c ejecta from the simultaneous and sequential eruption of these two magmas include some pumice clasts with mixed hybrid and mingled glass compositions and crystal populations a third rhyolite magma t3 was extruded from another vent 3 km distant to form an apparently contemporaneous lava dome t3 was the least evolved sio2 74 wt and hottest 820 c of the three magmas saturation pressures calculated using dissolved h2o and co2 contents of melt inclusions in quartz crystals indicate that t2 magma stagnated and crystallised at about 12 km depth while small quartz crystals in t1 magma grew during ascent through 8 km depths some t1 and t2 rhyolite clasts contain vesicular brown blebs with widely variable andesite to rhyolite glass compositions accompanied by olivine clinopyroxene and calcic plagioclase crystals that are interpreted as xenocrysts derived from injected basalt temperatures over 1000 c estimated from pyroxene phase equilibria in these clasts reflect intrusion of the more mafic magma which is now identified as the priming and triggering mechanism for three of the four post 22 ka tarawera rhyolite eruption episodes however the rhyolite magma bodies and conduits modelled for each episode have considerable differences in characteristics and geometry our preferred model for the rerewhakaaitu episode is that eruptions occurred from three laterally and vertically isolated rhyolite magma bodies that were initially primed and triggered by basalt intrusion during a regional rifting event the ascending hotter and less viscous t1 rhyolite magma intersected and further invigorated a stagnant pond of cooler denser and more viscous t2 magma and lubricated its transport to the surface

sequence stratigraphy and cyclic development of basal zechstein carbonate evaporite deposits with emphasis on zechstein 2 off platform carbonates upper permian northeast germany abstract although the basal zechstein is classically subdivided into two cycles z1 and z2 lower part it can alternatively be subdivided into three complete third order depositional sequences zs1 zs3 and the associated lowstand systems tract transgressive systems tract of a fourth sequence zs4 third and higher order sea level fluctuations influenced the depositional and diagenetic history of the carbonate evaporite alternations within the basal zechstein the main subject of the present study the zechstein 2 carbonate stassfurt carbonate or ca2 is interpreted to encompass both transgressive predominantly in slope and basinal settings and highstand systems tracts of zechstein sequence zs3 as well as part of the lowstand systems tract of the fourth zechstein sequence zs4 in northeastern germany hydrocarbon reservoirs of the ca2 developed along both northern and southern margins of the southern permian basin on top of the topography of the zechstein 1 cycle z1 this z1 topography resulted from deposition of the werra anhydrite a1 the highstand systems tract of the second zechstein sequence zs2 the northern ca2 carbonate platform is consistently narrow and fringed by coated grain and composite grain bars and shoals it is characterized by a steep fault controlled slope which precluded the formation of in situ shallow water grain dominated carbonates during relative sea level lowstands displaced shallow water coated grain and composite grain packstones wackestones may however occur as slope fan deposits turbidites in contrast the southern carbonate platform is wide tectonically dissected and fringed by grain dominated shallow water carbonates coated grain and composite grain bars and shoals zechstein 2 shallow water carbonates detectable by basal zechstein seismic anomalies also developed on pre existing topographical highs in off platform positions three depositional cycles ca2 cycles i ii and iii most probably reflecting high amplitude fourth order sea level fluctuations can be identified within the stassfurt carbonate our observations suggest that sea level variations possibly reflecting cyclicity in the milankovitch frequency band 0 1 0 4 ma and the pre zechstein topography pronounced during formation of the werra anhydrite were the most important factors in controlling the depositional as well as the diagenetic history of the zechstein 2 carbonate in off platform positions

ionospheric variability over indian low latitude linked with the 2009 sudden stratospheric warming in this paper we analyze radar observations of e b drift and plasma irregularities ionosonde observations of e and f layer parameters including spread f and magnetic field observations made from indian low latitudes linked with the 2009 sudden stratospheric warming ssw event e b drift variations presented here are the first of their kind from the indian sector as far as the effect of ssw is concerned difference of magnetic fields observed from the equator and low latitude h and e b drift show linear relation and both show remarkably large positive values in the morning and negative values in the afternoon exhibiting semidiurnal behavior remarkable changing patterns in the critical frequency of f2 layer fof2 and f3 layer fof3 were observed after the occurrence of ssw large variations with quasi 16 day periodicity were observed in h fof2 and fof3 both semidiurnal and quasi 16 day wave modulation observed after the 2009 ssw event are consistent with those reported earlier we also noted quasi 6 day variations in h and fof2 soon after the ssw commencement not much reported before during the counterelectrojet events linked with the ssw event while equatorial es esq disappeared as expected there were no blanketing es esb a finding not reported and discussed earlier esb was also not formed at the off equatorial location indicating the absence of required vertical wind shear but e region plasma irregularities were observed by the ionosonde and radar with a close relationship between the two weak f region irregularities were observed in the postmidnight hours and case studies suggest the possible role of ssw related background electric field in the manifestation of postmidnight f region irregularities

aura microwave limb sounder observations of dynamics and transport during the record breaking 2009 arctic stratospheric major warming a major stratospheric sudden warming ssw in january 2009 was the strongest and most prolonged on record aura microwave limb sounder mls observations are used to provide an overview of dynamics and transport during the 2009 ssw and to compare with the intense long lasting ssw in january 2006 the arctic polar vortex split during the 2009 ssw whereas the 2006 ssw was a vortex displacement event winds reversed to easterly more rapidly and reverted to westerly more slowly in 2009 than in 2006 more mixing of trace gases out of the vortex during the decay of the vortex fragments and less before the fulfillment of major ssw criteria was seen in 2009 than in 2006 persistent well defined fragments of vortex and anticyclone air were more prevalent in 2009 the 2009 ssw had a more profound impact on the lower stratosphere than any previously observed ssw with no significant recovery of the vortex in that region the stratopause breakdown and subsequent reformation at very high altitude accompanied by enhanced descent into a rapidly strengthening upper stratospheric vortex were similar in 2009 and 2006 many differences between 2006 and 2009 appear to be related to the different character of the ssws in the two years

ionospheric electron content within the equatorial f 2 layer anomaly belt this paper describes some new results on the day to day behavior of the location of the equatorial anomaly in the columnar electron content the measurements were made from a unique network of stations covering dip latitudes from 0 n to 25 n during the period in 1975 1976 near sunspot minimum when the ats 6 satellite was visible from india the latitudinal distribution of the total electron content on a particular day was found to depend only on the strength of the electrojet current as determined by the difference of the horizontal magnetic field at stations on the magnetic equator and another outside the equatorial electrojet rather than on the horizontal magnetic field measured only at the equatorial station during magnetically disturbed periods the presence or absence of the anomaly was also found to depend only upon the strength of the electrojet current the varying electrojet current that is the equatorial electric field is very effective in moving the ionization to the anomaly latitudes of 15 20 but the columnar electron content over the magnetic equator remains relatively constant

september 2019 antarctic sudden stratospheric warming quasi 6 day wave burst and ionospheric effects an exceptionally strong stationary planetary wave with zonal wavenumber 1 led to a sudden stratospheric warming ssw in the southern hemisphere in september 2019 ionospheric data from esa s swarm

lunar and solar tidal variabilities in mesospheric winds and eej strength over tirunelveli 8 7 n 77 8 e during the 2009 major stratospheric warming 1 mesospheric wind observations by the medium frequency radar and geomagnetic field observations at tirunelveli 8 7 n 77 8 e 1 75 n dip angle are used to study the relative importance of solar and lunar influences in the variabilities of mesospheric tides and equatorial electrojet eej strength during the unprecedented major stratospheric sudden warming ssw of 2009 it is observed that the afternoon reversal in the eej popularly known as counter electrojet occurs consecutively for several days during the ssw event when there is an enhancement of solar semidiurnal tide in both zonal wind at 90 km and eej strength over tirunelveli although the amplitude of lunar tides also shows enhancement it is much less than that of solar the diurnal tidal amplitude in zonal wind and eej strength also shows large enhancement just before the onset of ssw however solar semidiurnal tide dominates diurnal tide during the ssw the diurnal tidal phase in zonal wind shifts to a few hours earlier during the ssw the lunar semidiurnal tidal phase shifts to later hours in both zonal wind and eej strength the main observation of the present study is that the large semidiurnal tide observed during the ssw 2009 is mostly solar driven and only partly lunar driven although tidal planetary wave interaction also may play a vital role although a similar behavior is noticed during the ssw 2006 also the large lunar semidiurnal tide observed in the eej strength without having large lunar semidiurnal tide in the underlying mesospheric winds needs further investigation

the bishop tuff new insights from eruptive stratigraphy the 0 76 ma bishop tuff from long valley caldera in eastern california consists of a widespread fall deposit and voluminous partly welded ignimbrite the fall deposit f exposed over an easterly sector below and adjacent to the ignimbrite is divided into nine units f1 f9 with no significant time breaks except possibly between f8 and f9 maximum clast sizes are compared with other deposits where accumulation rates are known or inferred to estimate an accumulation time for f1 f8 as ca 90 hrs the ignimbrite ig is divided into chronologically and or geographically distinct packages of material earlier packages ig1 were emplaced mostly eastward are wholly intraplinian coeval with fall units f2 f8 lack phenocrystic pyroxenes and contain few or no glass mountain derived rhyolite lithic fragments earlier packages ig2 were erupted mostly to the north and east are at least partly intraplinian interbedded with fall unit f9 to the east contain pyroxenes and have lithic fractions rich in g

the ion microprobe as a tool for obtaining strontium isotopes in magmatic plagioclase a case study at okataina volcanic centre new zealand abstract we investigated the potential of multi collector secondary ion mass spectrometry mc sims as a tool for obtaining sr isotopic compositions in plagioclase a ubiquitous mineral in igneous rocks that serves as a recorder of crystallization history mc sims allows for high spatial resolution analysis 12 m in this study of isotopes and therefore improves the temporal scale at which fluctuations in crystallization conditions can be recognized ultimately improving our understanding of rates of magmatic processes plagioclase crystals from two young rhyolitic deposits from two major eruptive complexes tarawera and haroharo of the okataina volcanic centre in new zealand were analysed results were corrected for matrix effects using linear modelling of mc sims data versus an contents as well as 87sr 86sr ratios acquired via laser ablation inductively coupled plasma mass spectrometry la mc icp ms corrected mc sims sr isotopic ratios had an average 2 uncertainty of 0 0008 per spot and were homogeneous in okataina plagioclase at high spatial resolutions average la mc icp ms 87sr 86sr ratios of plagioclase from both intra caldera volcanic complexes tarawera 87sr 86sr 0 7056 and haroharo 87sr 86sr 0 7054 suggest similar magma sources and similar assimilation and fractional crystallization processes for the two complexes overall homogeneity of plagioclase excluding relict cores indicates no significant changes in contributions i e crustal assimilation mafic influx to the system during the majority of plagioclase crystal growth furthermore lack of 87sr 86sr ratio fluctuations in plagioclase rims suggest interaction between the resident silicic magma and the intruding mafic magma that triggered the eruptions was largely limited to volatile and heat transfer using appropriate standards and analysis this mc sims method can be used to detect short lived open system events in magma reservoirs where differences in 87sr 86sr isotopic ratios are significant

millennial timescale resolution of rhyolite magma recharge at tarawera volcano insights from quartz chemistry and melt inclusions most rhyolite eruption episodes of tarawera volcano have emitted several physiochemically distinct magma batches 1 10 km3 these episodes were separated on a millennial timescale the magma batches were relatively homogeneous in temperature and composition at pumice scale 4 cm but experienced isolated crystallisation histories at the sub cm scale matrix glasses have trace element compositions sr ba rb that vary by factors up to 2 5 indicating incomplete mixing of separate melts some quartz hosted melt inclusions are depleted in compatible trace elements sr ti ba compared to enclosing matrix glasses this could reflect re melting of felsic crystals deeper in the crystal pile individual quartz crystals display a variety of cathodoluminescence brightness and ti zoning patterns including rapid changes in melt chemistry and or temperature 50 100 c and point to multi cycle crystallisation histories the tarawera magma system consisted of a crystal rich mass containing waxing and waning melt pockets that were periodically recharged by silicic melts driven by basaltic intrusion

dilute gravity current and rain flushed ash deposits in the 1 8 ka hatepe plinian deposit taupo new zealand two groups of poorly sorted ash rich beds previously interpreted as rain flushed ashes occur in the ca ad 180 hatepe plinian pumice fall deposit at taupo volcano new zealand two ash beds with similar dispersal patterns and an aggregate thickness of up to 13 cm make up the lowermost group a group a beds extend 45 km north east of the vent and cover 290 km2 in the southern part of the group a distribution area a coarse ash to lapilli size plinian pumice bed deposit b separates the two group a beds the scarcity of lapilli material seen elsewhere from the still depositing pumice fall in group a beds indicates that they were rapidly transported and deposited however this rapid transportation and deposition did not produce cross bedding nor did it erode the underlying deposits it is proposed that thick 600 m but dilute gravity currents generated from the collapsing outer margin of the otherwise buoyant hatepe plinian eruption column deposited the group a beds the upper ash beds group c consist of one to seven layers attain an aggregate thickness of 35 cm and vary considerably in thickness and number of beds with respect to distance from vent group c beds contain variable amounts of ash mixed with angular plinian pumices and are genuine rain flushed ashes several recent eruptions at other volcanoes ukinrek maars vulcan rabaul la soufrere de guadeloupe and soufriere st vincent have produced gravity currents similar in style but much smaller than those envisaged for group a deposits the overloaded margins of otherwise buoyant eruption plumes generated these gravity currents laboratory studies have produced experimental gravity current analogues hazards from dilute gravity currents are considerable but often overlooked thus the recognition of gravity current deposits will contribute to more thorough volcanic hazard assessment of prehistoric eruption sequences

complex bombs of phreatomagmatic eruptions role of agglomeration and welding in vents of the 1886 rotomahana eruption tarawera new zealand 1 basaltic bombs ejected from a rotomahana crater during the 1886 tarawera eruption in new zealand are of two fundamental types cored bombs which have single large fragments generally of rhyolite wall rock material as their cores and loaded bombs which contain abundant small fragments dispersed through the bombs similar lithic bearing bombs are common products of other phreatomagmatic eruptions worldwide cored bombs originate when a large wall rock fragment is entrained in basaltic melt and then ejected with an adhering skin of basalt in contrast loaded bombs are constructed by agglomeration of multiple fragments of basalt among which smaller rhyolitic wall rock fragments are dispersed different styles and rates of bomb loading are reflected in the bombs textures and compositions these textures provide insight into the nature of fragmentation during the eruption the processes of recycling that produce multiply ejected clasts versus recapitulated ones those where early formed clasts were reingested in magma and then formed the cores of new bombs the degree and timescale of interaction of magma with vent walls and the timescales over which lithic material from the vent walls is incorporated into complex bombs prior to their ejection because fragments of rhyolitic pumice are readily refused their condition constrains estimates of the timing of fragmentation and agglomeration the presence of nonfused rhyolite pumice within many loaded bombs implies that the processes forming and quenching the bombs cannot have exceeded several seconds in contrast other bombs contain patches of compositionally modified basalt with isolated rhyolite derived feldspar xenocrysts that indicate complete fusing melting and assimilation of entrained rhyolitic debris the bomb population overall indicates that conditions within this rotomahana vent were thermally and physically heterogeneous and that recycling of debris was ubiquitous both as recycling of large individual clasts and by fallback and aggregation of material which was reingested in magma before being reejected as new bombs

the 31 ka rhyolitic plinian to sub plinian eruption of tlaloc volcano sierra nevada central mexico abstract tlaloc is a late pleistocene stratovolcano located ne of mexico city it is the northernmost volcano of the n s sierra nevada volcanic range which consists from north to south of tlaloc telapon iztaccihuatl and popocatepetl volcanoes tlaloc has always been considered the oldest and extinct volcano of the sierra nevada volcanic range recent field data revealed that tlaloc was very active during late pleistocene through a series of explosive eruptions one of these eruptions produced the multilayered white pumice mwp a rhyolitic pyroclastic sequence the eruption began with a 24 km high plinian column mwp f1 that was dispersed to the ne by prevailing winds it was interrupted by fountaining of the column with the generation of a pyroclastic density current that emplaced mwp s1 layer then followed five unstable sub plinian columns mwp f2 to f6 that reached altitudes between 16 and 19 km fall deposits as a whole are 1 m thick at 12 km from the vent cover a minimum area of 577 km2 for a total volume of 4 68 km3 dre 1 58 km3 the eruption ejected a total mass of 3 45 1012 kg at different mass discharges the last sub plinian column mwp f6 collapsed and produced dense pyroclastic density currents that deposited pumiceous pyroclastic flows mwp pf following main ravines to the north and east of the vent these density currents filled gullies with 23 m thick deposits at a distance of 12 km from the vent totaling a minimum dre volume of 0 2 km3 pyroclastic flow deposits charred tree trunks that yielded an age of 31 490 1995 1595 yr b p that closely date the age of the eruption rain during this phase of the eruption generated syn eruptive lahars mwp df post eruptive lahars mwp ed finally swept the volcano flanks the mwp deposits consist of abundant white pumice up to 96 vol rare gray pumice cognate lithics accidental altered lithics xenocrysts white and gray pumice clasts contain phenocrysts of quartz plagioclase sanidine biotite rare fe ti oxides monazite zircon and apatite xenocrysts are represented by plagioclase microcline orthoclase and quartz likely coming from a deeper plutonic body both pumices have a rhyolitic composition 74 98 1 wt sio2 in water free basis representing one of the most acidic products of tlaloc and the entire sierra nevada volcanic range the rhyolitic liquid was likely extracted from a mush like plutonic body reaching the minimum predicted vesicularity values for plinian fragmentation for which the triggering mechanism of the mwp eruption is attributed to the high viscosity of the magma that provoked overpressure of the magmatic system the parameters studied suggest that eruption behavior evolved from plinian to sub plinian eruptive columns over time due to conduit dynamics rather than variations in magma properties of the mwp products

lunar tide in the equatorial electrojet in relation to stratospheric warmings 1 the relationship between sudden stratospheric warmings ssws and large amplitude lunar tides in the equatorial electrojet eej is studied analysis of ground magnetometer data shows that the lunar tide in the eej is maximum during the northern winter season except in the pacific ocean region since ssws are also a northern winter phenomenon it is suggested that the relation between the large lunar tide in the eej and the ssw may possibly be coincidental the lunar tide in the geomagnetic variations at huancayo is anomalously large compared with other eej stations an examination of geomagnetic variations at eej stations during ssw events shows that afternoon counter electrojets are frequently present at new moon and full moon though the relationship is sometimes broken the observation of large lunar eejs when no ssw is present and of various different delay times suggests that other atmospheric processes are likely to be in play

dolomite calcitization and cement zonation related to uplift of the raisby formation zechstein carbonate northeast england abstract the raisby formation is the basal zechstein carbonate of northeast england it has undergone a complex diagenetic history during burial including multiphase dolomitization and replacement by sulphates upon uplift meteoric derived fluids have dissolved this replacive sulphate and precipitated calcite cements in the resultant porosity study of these cements by cathodoluminescence and trace element geochemistry shows that they are zoned and different cathodoluminescence zones correlate well with iron and manganese geochemical changes demonstrating a gradual increase in oxygenation of the precipitating fluids through time major diagenetic processes during cement growth include precipitation of anhydrite fluorite and barite calcitization of dolomite and internal sedimentation relating these processes to cement zonation allows this complex diagenesis to be explained in terms of uplift under the influence of meteoric derived groundwaters of constantly changing geochemical and electrochemical characteristics

quiet variability of equatorial e b drifts during a sudden stratospheric warming event 1 we present strong evidence that during the january 2008 minor sudden stratospheric warming ssw event the equatorial vertical e b drifts exhibit a unique and distinctive daytime pattern we do not think one event causes the other however both events might be related through the global effects of planetary waves the drifts were measured by the jicamarca incoherent scatter radar located under the magnetic equator we have observed an anomalous temporal variation of the vertical e b drifts during the minor ssw event showing a semidiurnal variation with very large amplitudes lasting for several days large differences in the e b drifts were observed during a period of large increase of temperature and a large decrease of mean zonal wind in the high latitude stratosphere 60 90 n this high correlation is an unexpected finding which might shed new light on sources and mechanisms of quiet time ionospheric variability

an improved approach to characterize potash bearing evaporite deposits evidenced in north yorkshire united kingdom traditionally potash mineral deposits have been characterized using downhole geophysical logging in tandem with geochemical analysis of core samples to establish the critical potassium k2o content these techniques have been employed in a recent exploration study of the permian evaporite succession of north yorkshire united kingdom but the characterization of these complex deposits has been led by mineralogical analysis using quantitative x ray diffraction qxrd the novel qxrd approach provides data on k content with the level of confidence needed for reliable reporting of resources and also identifies and quantifies more precisely the nature of the k bearing minerals errors have also been identified when employing traditional geochemical approaches for this deposit which would have resulted in underestimated potash grades qxrd analysis has consistently identified polyhalite k2ca2mg so4 4 2 h2o in the fordon evaporite formation and sylvite kcl in the boulby potash and sneaton potash members as the principal k bearing host minerals in north yorkshire however other k hosts including kalistrontite k2sr so4 2 a first recorded occurrence in the uk and a range of boron bearing minerals have also been detected application of the qxrd led characterization program across the evaporitic basin has helped to produce a descriptive empirical model for the deposits including the polyhalite bearing shelf and basin seams and two newly discovered sylvite bearing bittern salt horizons the pasture beck and gough seams the characterization program has enabled a polyhalite mineral inventory in excess of 2 5 billion metric tons bt to be identified suggesting that this region possesses the world s largest known resource of polyhalite this is an open access article distributed under the terms of the creative commons attribution license http creativecommons org licenses by 3 0 which permits unrestricted use distribution and reproduction in any medium provided that the original work is properly attributed

vertical and lateral splitting of a hydrothermal plume at steinaholl reykjanes ridge iceland abstract the generation of multiple neutrally buoyant intrusions by a single bubble rich plume asaeda and imberger j fluid mech 249 1993 35 57 and plume bifurcation ernst et al bull volcanol 56 1994 159 169 lavelle j geophys res 102 1997 3405 3420 are predicted from theory and experiments but have yet to be documented for hydrothermal plumes in contrast bifurcation of volcanic plumes which are dynamically analogous to hydrothermal plumes is very common ernst et al bull volcanol 56 1994 159 169 and thus bifurcation of hydrothermal plumes should be expected lavelle j geophys res 102 1997 3405 3420 ernst et al bridge newslett 10 1996 76 77 recent 38 khz echo sounder and water column chemical tracer studies near the steinaholl vent site reykjanes ridge iceland identified a bubble rich hydrothermal plume intruding at three levels two main ones and a subsidiary one before reaching the sea surface and spreading there ernst et al bridge newslett 10 1996 76 77 olafsson et al ridge events 2 1991 35 38 german et al earth planet sci lett 121 1994 647 654 the two main intrusions ca 100 and 200 m above the vent show lateral development of two lobes away from the vent and are consistent with the 350 m rise of a bubble plume yielding seafloor and surface gas fluxes of 2 5 10 3 and 0 75 10 1 m3 s respectively the bubble rich core of the hydrothermal plume also penetrates the 150 m deep thermocline and generates an intrusion visible at the sea surface although bifurcation of the bent over plume could have been initiated by crossflow alone ernst et al bull volcanol 56 1994 159 169 several other processes may also have enhanced plume bifurcation including interaction with the thermocline and entrainment of the plume lobes by horseshoe eddies in the lee of a 150 m high hill on the seafloor

upper permian zechstein supergroup carbonate evaporite platform palaeomorphology in the uk southern north sea abstract seismic interpretation geological mapping and depth conversion of the zechstein supergroup z2 cycle using high quality well calibrated three dimensional 3 d seismic has revealed the complex palaeomorphology of a deeply buried ancient carbonate shelf margin on the southwestern margin of the southern permian basin the new mapping shows that the margin comprises a series of corrugated embayments and promontories which extend up to 5 km 3 mi into the basin and locally have a palaeobathymetric relief of 200 m 650 ft well calibration across the margin demonstrates a strongly bipartite lateral thickness distribution between a high velocity anhydrite dominated shelf and a lower velocity halite dominated basin strong lateral and vertical velocity variations in the upper permian zechstein supergroup are known to have major impacts upon seismic imaging and depth conversion in the spb the resulting uncertainty remains one of the major challenges when interpreting and assessing the prospectivity of the underlying upper permian rotliegend group leman sandstone formation reservoirs in the uk southern north sea an understanding of the zechstein shelf edge s 3 d physiography and its velocity variation has implications for the delineation of traps containing the prospective reservoirs that lie below recognition of the complexity and effects of this shelf margin contributed to the recent juliet discovery whose position outside of the presently defined rotliegend group play fairway suggests that prospectivity is more extensive along the basin margin than previously thought as such the work provides a means by which to identify and delineate new structures and extend the life of this mature yet prolific gas province

the ad1315 tarawera and waiotapu eruptions new zealand contemporaneous rhyolite and hydrothermal eruptions driven by an arrested basalt dike system a series of large hydrothermal eruptions occurred across the waiotapu geothermal field at about the same prehistoric time as the ad1315 kaharoa rhyolite magmatic eruptions from tarawera volcano vents 10 20 km distant triggering of the waiotapu hydrothermal eruptions was previously attributed to displacement of the adjacent ngapouri fault the kaharoa rhyolite eruptions are now recognised as primed and triggered by multiple basalt intrusions beneath the tarawera volcano a 1000 t day pulse of co2 gas is recorded by alteration mineralogy and fluid inclusions in drill core samples from waiotapu geothermal wells this co2 pulse is most readily sourced from basalt intruded at depth and although not precisely dated it appears to be associated with the waiotapu hydrothermal eruptions we infer that the hydrothermal eruptions at waiotapu were primed by intrusion of the same arrested basalt dike system that drove the rhyolite eruptions at tarawera this dike system was likely similar at depth to the dike that generated basalt eruptions from a 17 km long fissure that formed across the tarawera region in ad1886 fault ruptures that occurred in the waiotapu area in association with both the ad1886 and ad1315 eruptions are considered to be a result rather than a cause of the dike intrusion processes

c nofs observations of the equatorial ionospheric electric field response to the 2009 major sudden stratospheric warming event 1 we present new observations made by the coupled ion neutral dynamics investigation cindi ion velocity meter ivm instrument onboard the communication navigation outage forecasting system c nofs satellite that show the effects of the january 2009 sudden stratospheric warming ssw event on equatorial electric fields we have used ivm observations to construct composite curves of mean equatorial vertical plasma drifts as a function of local time and longitude sector these curves show large upward vertical drifts during morning hours and downward drifts during afternoon our analysis indicates that this pattern could be observed over the range of longitudes where adequate ivm measurements were available from approximately 165 e to about 315 e longitude a clear day to day quasi deterministic variability in the drifts is also observed with the transition from upward to downward drifts occurring at increasing local times from 25 to 30 january 2009 the analysis also suggests some level of longitudinal variability in the magnitude of the drifts these in situ observations are in good agreement with previous ground based measurements of the response of equatorial electric fields to ssw events in particular we found that ivm drift measurements centered around 285 e depart significantly from climatological values but agree exceptionally well with ground based measurements of vertical drifts made by the jicamarca incoherent backscatter radar overall the results agree well with previous studies of ssw events demonstrate the usefulness of the ivm observations and motivate further studies of the variability of the equatorial ionosphere using c nofs

investigation on the variability of the geomagnetic daily current during sudden stratospheric warmings the magnetic field records of the magnetometer networks in the american east asian australian and european african sectors were employed in this present work we used them to investigate equatorial electrojet eej counter electrojet cej tidal variability in eej strength and ionospheric current during the 2005 2006 and 2008 2009 sudden stratospheric warming ssw events in addition to the well investigated tidal variability in eej strength over the american and east asian sectors we investigated that of the african sector for the first time interestingly the tidal components in eej strength during both ssw events clearly exhibit marked longitudinal differences with high moderate and low amplitudes in the american east asian and african sectors respectively an exception found around day 71 in the african sector after the 2008 2009 ssw event had higher solar diurnal tidal component as compared to that of the asian sector over the american sector solar and lunar semidiurnal tides were strongly associated with cej current during both ssw events whereas at the african and east asian sectors such variabilities are not evident a solar diurnal tidal component was strongly related to a reduction in the eej strength over the east asian sector in addition a prolonged period of cej occurrence that begins during the ssw precondition and ends when the ssw was evolving characterized the african sector during both ssw events there is a steady shift in phase at later hours when both ssw events are evolving

basalt triggering of the c ad 1305 kaharoa rhyolite eruption tarawera volcanic complex new zealand abstract the ad 1305 kaharoa eruption episode of tarawera volcanic complex was the largest 4 km3 magma eruption in new zealand in the last 1000 years high silica 76 sio2 rhyolite was erupted from seven vents along an 8 km linear zone to form pumiceous pyroclastic deposits and lava domes initial vent clearing explosions were followed by a series of plinian pumice eruptions that spread tephra downwind and pyroclastic density current deposits over the volcano slopes the early pyroclastic eruptions were followed by extrusion of a dome in the summit vent and the migration of further plinian activity to adjacent vents the episode finished with the extrusion of three summit lava domes accompanied by block and ash flows two main types of rhyolite were erupted 1 a low zr low sr high rb type comprising the early plinian pyroclastics and 2 a high zr high sr low rb type comprising the late eruptives including the summit domes basaltic material basalt and basaltic andesite is commonly present as free clasts within the kaharoa pyroclastic deposits along with rare clasts of granodiorite diorite gabbro and olivine clinopyroxenite the basaltic clasts are often veneered by kaharoa rhyolite basaltic material is also common as inclusions within rhyolite pumices along with olivine and augite xenocrysts derived from the basalt the basaltic clasts and inclusions contain complexly zoned plagioclase and corroded olivine commonly with a reaction rim consistent with disequilibrium caused by magma mixing some basaltic clasts and inclusions are hornblende free others contain groundmass hornblende plumes of brown glass often extend from hornblende bearing basaltic inclusions into the surrounding rhyolite these plumes demonstrate magma mixing as does the presence of rhyolitic glass and quartz xenocrysts in some basaltic inclusions most basaltic inclusions have crenulate boundaries suggesting they were fluidal when coming into contact with the rhyolite magma diorite gabbro and olivine clinopyroxenite clasts have mineralogy similar to the basalts commonly contain patches of fine grained basaltic material and are considered co magmatic with the basalts intrusion of basalt magma into the base of the rhyolite magma chamber appears to have occurred for some time before the kaharoa eruptions began allowing considerable mixing with the rhyolite magma transfer of water to some basalt inclusions and formation of hornblende in their groundmass conversely the hornblende free basalt inclusions did not have time to react with the rhyolite magma and must have been intruded shortly before the start of the eruption intrusion of this hornblende free basalt appears to have triggered the kaharoa eruption after the magma chamber had been primed by the earlier intrusions

total grain size distribution and volume of tephra fall deposits on 17 june 1996 ruapehu volcano new zealand produced a sustained andesitic sub plinian eruption which generated a narrow tephra fall deposit extending more than 200 km from the volcano the extremely detailed data set from this eruption allowed methods for the determination of total grain size distribution and volume of tephra fall deposits to be critically investigated calculated total grain size distributions of tephra fall deposits depend strongly on the method used and on the availability of data across the entire dispersal area the voronoi tessellation method was tested for the ruapehu deposit and gave the best results when applied to a data set extending out to isomass values of 1 g m 2 the total grain size distribution of a deposit is also strongly influenced by the very proximal samples and this can be shown by artificially constructing subsets from the ruapehu database unless the available data set is large all existing techniques for calculations of total grain size distribution give only apparent distributions the tephra fall deposit from ruapehu does not show a simple exponential thinning but can be approximated well by at least three straight line segments or by a power law fit on semi log plots of thickness vs area 1 2 integrations of both fits give similar volumes of about 4 106 m3 integration of at least three exponential segments and of a power law fit with at least ten isopach contours available can be considered as a good estimate of the actual volume of tephra fall integrations of smaller data sets are more problematic

the physical volcanology of the 1600 eruption of huaynaputina southern peru volcan huaynaputina is a group of four vents located at 16 36 s 70 51 w in southern peru that produced one of the largest eruptions of historical times when 11 km3 of magma was erupted during the period 19 february to 6 march 1600 the main eruptive vents are located at 4200 m within an erosion modified amphitheater of a significantly older stratovolcano the eruption proceeded in three stages stage i was an 20 h sustained plinian eruption on 19 20 february that produced an extensive dacite pumice fall deposit magma volume 2 6 km3 throughout medial distal and distal parts of the dispersal area a fine grained plinian ashfall unit overlies the pumice fall deposit this very widespread ash magma volume 6 2 km3 has been recognized in antarctic ice cores a short period of quiescence allowed local erosion of the uppermost stage i deposits and was followed by renewed but intermittent explosive activity between 22 and 26 february stage ii this activity resulted in intercalated pyroclastic flow and pumice fall deposits 1 km3 the flow deposits are valley confined whereas associated co ignimbrite ash fall is found overlying the plinian ash deposit following another period of quiescence vulcanian type explosions of stage iii commenced on 28 february and produced crudely bedded ash lapilli and bombs of dense dacite 1 km3 activity ceased on 6 march compositions erupted are predominantly high k dacites with a phenocryst assemblage of plagioclase hornblende biotite fe ti oxides apatite major elements are broadly similar in all three stages but there are a few important differences stage i pumice has less evolved glass compositions 73 sio2 lower crystal contents 17 20 lower density 1 0 1 3 g cm3 and phase equilibria suggest higher temperature and volatile contents stage ii and stage iii juvenile clasts have more evolved glass 76 sio2 compositions higher crystal contents 25 35 higher densities up to 2 2 g cm3 and lower temperature and volatile contents all juvenile clasts show mineralogical evidence for thermal disequilibrium inflections on a plot of log thickness vs area1 2 for the fall deposits suggest that the pumice fall and the plinian ash fall were dispersed under different conditions and may have been derived from different parts of the eruption column system the ash appears to have been dispersed mainly from the uppermost parts of the umbrella cloud by upper level winds whereas the pumice fall may have been derived from the lower parts of the umbrella cloud and vertical part of the eruption column and transported by a lower altitude wind field thickness half distances and clast half distances for the pumice fall deposit suggests a column neutral buoyancy height of 24 32 km and a total column height of 34 46 km the estimated mass discharge rate for the 20 h long stage i eruption is 2 4 108 kg s and the volumetric discharge rate is 3 6 105 m3 s the pumice fall deposit has a dispersal index hildreth and drake 1992 of 4 4 and its index of fragmentation is at least 89 reflecting the dominant volume of fines produced of the 11 km3 total volume of dacite magma erupted in 1600 approximately 85 was evacuated during stage 1 the three main vents range in size from 70 to 400 m alignment of these vents and a late stage dyke parallel to the nnw sse trend defined by older volcanics suggest that the eruption initiated along a fissure that developed along pre existing weaknesses during stage i this fissure evolved into a large flared vent vent 2 with a diameter of approximately 400 m this vent was active throughout stage ii at the end of which a dome was emplaced within it during stage iii this dome was eviscerated forming the youngest vent in the group vent 3 a minor extra amphitheater vent was produced during the final event of the eruptive sequence recharge may have induced magma to rise away from a deep zone of magma generation and storage subsequently vesiculation in the rising magma batch possibly enhanced by interaction with an ancient hydrothermal system triggered and fueled the sustained plinian eruption of stage i a lower volatile content in the stage ii and stage iii magma led to transitional column behavior and pyroclastic flow generation in stage ii continued magma uprise led to emplacement of a dome which was subsequently destroyed during stage iii no caldera collapse occurred because no shallow magma chamber developed beneath this volcano

complex proximal sedimentation from plinian plumes the example of tarawera 1886 the 1886 eruption of tarawera new zealand was unusual for a plinian eruption because it involved entirely basaltic magma originated in a 17 km long fissure and produced extremely overthickened proximal deposits with a complex geometry this study focuses on an 8 km long segment cutting across mount tarawera where over 50 point source vents were active during the 5 5 h eruption a detailed characterization of the proximal deposits is developed and used to interpret the range of styles and intensities of the vents including changes with time we identify the four vents that contributed most heavily to the plinian fall and evaluate the extent to which current volcanic plume models are compatible with the depositional patterns at tarawera three proximal units are mapped that have phreatomagmatic magmatic and phreatomagmatic characteristics respectively within the magmatic proximal unit beds of like character are grouped into packages and delineated on scaled cross sections package dispersal is quantified by measuring the linear thickness half distance t1 2 in the planes of the fissure walls most packages have localized dispersals low t1 2 indicating that strombolian style activity dominated most vents the more widely dispersed packages high t1 2 reflect contributions from additional transport regimes that were more vigorous but still contributed considerable material to the proximal region we conclude that the geometry of the observed proximal deposits requires three modes of fall transport 1 fallout from the upper portions of the plinian plumes produced principally by vents in four craters 2 sedimentation from the margins of the lower portions of the plinian plumes including the jets and possibly the lower convective regions and 3 ejection by weak strombolian style explosions from vents that did not contribute significant volumes of particles to the high plume we suggest that the curvature of the velocity profile across the jet region of each plume 1 4 km height was important and that the lower velocity at the margins allowed proximal deposition of a large volume of material with a wide grain size range

quiet time variability of the gps tec and eej strength over indian region associated with major sudden stratospheric warming events during 2005 2006 1 this paper describes the quiet time variabilities of the ionospheric total electron content tec derived from the signals from global positioning satellite system gps recorded at several stations in india along with simultaneous observations of equatorial electrojet eej strength obtained from geomagnetic field variations during january march 2006 when sudden stratospheric warming ssw events occurred analysis of the observations presented here confirms that strong correlation exists among the variabilities in eej strength and gps tec observations investigations suggest that there exist large scale wave like structures with periodicity of quasi 16 day wave in the tec observations near the equatorial ionization anomaly eia crest quite similar to that of eej strength our observations also indicate the existence of morning enhancement and evening reduction of tec and eej strength and vice versa during ssw events similar to that reported elsewhere using these observations it is suggested that the quiet time variabilities seen in the gps tec over eia could be caused due to the nonlinear interaction of upward propagating planetary waves pws with atmospheric tides presence of similar periods in the eej strength and tec observations near the eia crest region supports the view that the large scale wave like structures seen in tec near the eia crest are associated with pws that are modifying the primary eastward electric field in the equatorial e region and hence the eej strength through non linear interactions with atmospheric tides

upper atmosphere wind systems during reverse equatorial electrojet events days of reversed equatorial electrojet were identified at trivandrum india and in order to seek a global wind change in the dynamo region responsible for these events upper atmosphere winds at a height of 99 km at saskatoon canada were examined during northern winter and also in april and september the reversed electrojets were accompanied by reversals of the eastward wind at saskatoon the winter events generally occurred during a stratwarm no changes in the winds were detected during summer reversed electrojets

deposition and generation of multiple widespread fall units from the c ad 1314 kaharoa rhyolitic eruption tarawera new zealand the c ad 1314 kaharoa eruption from tarawera volcano north island new zealand was a complex long duration multi episode rhyolitic event up to 13 discrete sub plinian to plinian style phases occurred in two stages from at least two different vents along an 8 km long fissure the early explosive stage produced seven pumice lapilli fall units dispersed solely to the southeast of the volcano while a later stage produced six fall units dispersed almost entirely to the north and northwest the duration of fallout for these 13 lapilli units is estimated to have totaled about 1 5 days the presence of massive textured ash layers between many of the lapilli fall units suggests that longer duration pyroclastic density current producing phases and more quiescent fallout intervals occurred between the intense explosive phases of the eruption total duration of ash fallout 7 5 days the ash deposition extended the minimum duration of the explosive episodes to at least 9 days based on settling rates of the ash possibly the explosive phase of eruptive activity lasted for 2 weeks including some brief hiatuses and pyroclastic density current deposition and was followed by 4 years of mainly lava dome forming activity at least 15 km3 7 3 km3 dense rock equivalent dre of tephra was erupted during the main explosive episodes and at least 9 1 km3 dre during the whole eruption more than doubling the previous estimate this may be an underestimate by up to 50 of the fallout volume eruption column heights for the two most widely dispersed fall units are estimated to have ranged from 25 28 km above the vents and durations of individual lapilli fall unit forming phases ranged from 1 5 to 4 h but the ash producing phases lasted much longer individually up to 30 h and represent a longer lived shut down to each eruptive episode time averaged mass discharge rates are estimated to have varied by more than one order of magnitude during the main plinian style phases from 107 to 108 kg s however the explosive phases were unsteady as indicated by fluctuating grain size with stratigraphic height in the lapilli fall units and common capping ash beds the north northwesterly dispersal of the later stage fall units and the possible duration of 4 days for these episodes indicate an unusual period of southerly to southeasterly winds therefore the main explosive part of the kaharoa eruption is most likely to have occurred during the austral winter to spring months the kaharoa eruption style is also shared by the three previous rhyolite dominated eruptions that have built tarawera volcano over the past 22 000 years knowledge of the widespread pumice and ash fallout from the kaharoa eruption is important in quantifying the hazard from this type of extended duration explosive activity and has implications for future similar rhyolitic activity in new zealand

the kaharoa tephra as a critical datum for earliest human impact in northern new zealand the debate over the timing of arrival and earliest environmental impacts of the first new zealanders has intensified in recent years in part fuelled by new evidence or reinterpretation of old evidence from other points along prehistoric polynesian migratory routes an examination of two radiocarbon dated pollen records from northern new zealand shows how divergent interpretations could be drawn from the same evidence to support both early and late colonization models radiocarbon dated pollen records for deforestation at sites where the risk of contamination by older carbon may be high cannot be used to establish chronologies of settlement ombrogenous mires where peat accumulation proceeds independently of groundwater or surface runoff are likely to yield the most reliable records another solution applicable in northern new zealand is to base chronologies on tephra layers with reliable age estimates from multiple determinations analysis of 11 pollen records currently known to contain the 665 15 bp c 600 cal bp rhyolitic kaharoa tephra demonstrates the critical stratigraphic position that this isochronous surface occupies in new zealand prehistory the earliest inferred human impacts occurred at around the time of deposition of the tephra in eight of these sites 73 and well after it at the remainder these results are in agreement with a later colonization model and suggest that proximity to accessible food resources was more important than climate or latitude in determining early colonization sites these findings will be tested fully when the known range of kaharoa tephra is extended beyond its present limited range through the application of micro tephra analysis in line with anderson s 1995 128 premise that the later colonization model is eminently falsifiable we suggest that tephropalynological studies involving the kaharoa tephra may hold the key to resolving debates over the timing and spatial patterns of earliest human impact in northern new zealand in particular these records permit the investigator to avoid the ambiguities that emerge frequently when pollen profiles indicating deforestation are dated by radiocarbon alone

radiocarbon age of the kaharoa tephra a key marker for late holocene stratigraphy and archaeology in new zealand the kaharoa eruption the most recent rhyolitic volcanic event in new zealand resulted in the deposition of the compositionally distinctive kaharoa tephra over at least 30 000 km2 of northern and eastern north island the tephra forms an isochronous marker bed for various late holocene stratigraphic and palaeoen vironmental studies but is particularly important for evaluating the chronology of new zealand s notably short prehistory because it was erupted within the last millennium close to the time of first polynesian colonization we derive a definitive radiocarbon age previously ambiguous for the kaharoa tephra of 665615 bp using cluster analysis of 22 radiocarbon ages relevant to the kaharoa eruptive episode the error weighted mean age obtained on unscreened ages minus outliers is supported by statistically identical ages obtained from three sets of screened ages selected to minimize the effects of inbuilt age or contamination based on the intercepts method and 1 sigma range of northern hemisph

co ignimbrite ash fall deposits of the 1991 eruptions of fugen dake unzen volcano japan abstract fugen dake the main peak of unzen volcano began a new eruption sequence on november 17 1990 on may 20 1991 a new lava dome appeared near the eastern edge of the fugen dake summit small scale 10 4 10 6 m 3 in volume merapi type block and ash flows were frequently generated from the growing lava dome during may june 1991 these pyroclastic flows were accompanied by co ignimbrite ash plumes that deposited ash fall deposits downwind of the volcano three examples of co ignimbrite ash fall deposits from unzen pyroclastic flows are described the volume of fall deposits was estimated to be about 30 by volume of the collapsed portions of the dome that formed pyroclastic flows this proportion is smaller than that described for other larger co ignimbrite ash fall deposits from other volcanoes grain size distributions of the unzen co ignimbrite ash fall deposits are bi modal or tri modal most ashes are finer than 4 phi and two modes were observed at around 4 7 phi and 9 phi they are composed mainly of groundmass fragments fractions of another mode at around 2 phi are rich in crystals derived from dome lava some of the fine ash component fell as accretionary lapilli from the co ignimbrite ash cloud indicating either moisture or electrostatic aggregation we believe that the co ignimbrite ash of unzen block and ash flows were formed by the mechanical fracturing of the cooling lava blocks as they collapsed and moved down the slope these ashes were entrained into the convective plumes generated off the tops of the moving flows

contrasting grain size and componentry in complex proximal deposits of the 1886 tarawera basaltic plinian eruption the 1886 plinian eruption of tarawera new zealand is a unique basaltic fissure fed eruption with exceptionally well preserved fall deposits to within 200 meters of the source vents these proximal deposits form a series of spatter cinder half cones along the northeastern 8 km long segment of the 1886 fissure here we examine these deposits using grain size and clast componentry techniques we contrast the products of the phreatomagmatic phases i and iii and plinian phase ii stages of the eruption and examine deposit variability as a function of contrasting eruptive intensity within the climactic phase ii of the eruption the opening phreatomagmatic phase i of the eruption involved gas rich magma interacting with water and fragmenting at least 300 meters below the surface the deposits of the climactic phase that followed have relatively uniform grain size but marked contrasts in the relative abundance of juvenile and wall rock lithic clasts deposits linked to vents associated with the high plinian plume are more uniform than those characterized by a weaker cone forming eruption style during the third and closing phase of the eruption magma withdrawal accompanied the onset of decoupling of the exsolved gas phase leading to fragmentation at increasingly greater depths and significant wall rock collapse into the erupting vents variability in eruptive style during phase ii along the fissure appears to be a function of shallow seated controls in particular the variable extent of incorporation of lithic wall rock into the erupting jet as a consequence of vent wall collapse widely dispersed beds centralized around plinian sources along the fissure have very low lithic content cone forming beds at other craters that contain very high lithic contents this incorporation led to a significant reduction of the velocity and stability of the jet at these latter steep walled craters and induced episodicity in the form of vent clearing explosions the result is a large reduction of the physical and thermal ability of these vents to contribute to a stable high eruptive plume instead large volumes of ejecta were sedimented prematurely from shallow heights at rates an order of magnitude greater than for historical strombolian hawaiian and subplinian eruptions this study illustrates that sustained powerful plinian eruptions can be accompanied by heterogeneities and instabilities of the eruptive jet at tarawera the record of complex proximal transport and deposition processes in the eruptive jet cannot be inferred from the eruption products at distances greater than 400 m from the eruptive fissure we suggest that study of ultraproximal deposits as seen at mt tarawera provides the only opportunity to document the complex dynamic behavior of the jet region of plinian eruptions

planetary and gravity waves in the mesosphere and lower thermosphere region over tirunelveli 8 7 n 77 8 e during stratospheric warming events 1 an investigation of planetary wave pw activities in ukmo uk meteorological office winds during winter of the years 1998 99 and 2005 06 when major sudden stratospheric warming ssw events occurred shows that the amplitude of pw of zonal wave number 1 is considerably reduced in zonal winds when the warming event is onset and the reduced activity persists several days even after the end of the ssw event similar reduction of pw activity in zonal winds has been observed in the wavelet spectrum of mf radar zonal winds at altitudes 84 98 km over tirunelveli 8 7 n 77 8 e during this period of reduced pw activity enhancement in gravity wave activity is observed during 2005 06 and is not observed during 1998 99 and the mean meridional winds change to more equatorward during 2005 06 and remain poleward during 1998 99 in accordance with time gcm results our observations show that the wind reversal occurred in the stratosphere during major warming events allows more eastward gravity waves to propagate into the mesosphere and lower thermosphere mlt region which causes changes in the meridional circulation from poleward to equatorward

longitudinal variation of ionospheric vertical drifts during the 2009 sudden stratospheric warming 1 the whole atmospheric model wam initialized with a data assimilation scheme is capable of simulating real sudden stratospheric warming ssw events the electrodynamics in the coupled thermosphere ionosphere and plasmasphere with electrodynamics model ctipe was driven by the wam thermospheric winds in january 2009 to study the response of ionospheric drifts during the ssw simulation results are compared with observations of the vertical drift at jicamarca and the equatorial electrojet eej in the asian sectors early morning upward drift and afternoon downward drift are reproduced in all longitudes in the simulations and are consistent with the available observations results also show that the occurrence time of the early morning upward drift and afternoon downward drift have significant phase differences between different longitudes simulations suggest that during the ssw the longitude dependence of the amplitude and phase of the equatorial vertical plasma drift is caused by the changing magnitudes of the migrating tides modulated by the geometry of the geomagnetic field some additional day to day variability and modulation of the phase structures at different longitudes in ionospheric vertical drifts during the ssw are possibly produced by the short term changes in the non migrating tides and by planetary waves

first results on low latitude e and f region irregularities obtained using the gadanki ionospheric radar interferometer a 30 mhz radar has recently been established at gadanki 13 5 n 79 2 e 6 5 n magnetic latitude to make unattended observations of the ionospheric field aligned irregularities fai this radar called the gadanki ionospheric radar interferometer giri has been designed to have scanning capability of 100 in the east west plane perpendicular to earth s magnetic field and interferometry imaging system to study drifts and spatial distribution of plasma irregularities at both large and small scales in this paper we present the first results on the e and f region fai made using the scanning capability of the giri daytime observations of e region fai show type 2 echoes with velocities predominantly upward northward downward southward at altitudes 100 km 100 km and westward eastward in the forenoon afternoon with signature of tidal wind field f region irregularities show bottom type bottomside and plume structures with close resemblance to those observed over the magnetic equator observations made with the east west scanning capability have been used to study the origin evolution and drift of the fai for the first time from gadanki eastward drifts are estimated to be 90 210 m s 1 during 20 24 lt upward velocity as large as 500 m s 1 has been observed in the initial phase of the plume structures intriguingly downward velocity as large as 60 m s 1 has also been observed in the plumes displaying descending pattern observed in the early evening hours these results are presented and discussed in the light of current understanding of low latitude plasma irregularities and future prospects of giri are outlined

evolution of the nw margin of the north permian basin uk north sea mapping of depositional zones within the zechstein supergroup using semi regional 2d and 3dseismic data constrains the geological evolution of the northwestern margin of the north permian basinin uk offshore quadrants 14 15 19 20 and 21 four depositional zones are identified on the basis of mappable seismic facies which are assumed to vary with halite content well control characterizes the most reflective seismic facies as an interbedded carbonate and anhydrite shelf succession which grades laterally through clastic rich sequences to the least reflective a thick halite basinal equivalent the trendsof the depositional zones illustrate the geometry of the north permian basin and may have been locally controlled by basement lineaments within the north permian basin a n s trending axis devil s hole high characterized by thick reflective facies separates the central north sea from the forth approaches basin basement fault blocks control facies type and thickness along the northwest margin of the north permian basin in the moray firth area permian tilt of the zechstein shelf related to regional flexure played a role in precipitating gravity driven tectonics within the seismically reflective facies on the east flank of the devil s hole high this permian phase of salt tectonics resulted in numerous intra zechstein structures which can be interpreted as rafted and folded zones of interbedded halite carbonate sulphate and clastics the rafts initially slid downdip towards the main halite basin then their evolution became dominated by differential subsidence of the interbeds which forced salt layers into adjacent passive diapirs this episode predates deposition of the triassic smith bank shales which rest upon the zechstein with local angular unconformity the spatial distribution of zechstein facies influenced the tectonostratigraphy of the triassic jurassic and cretaceous systems boundaries between zechstein facies correspond to the limit of triassic halokinesis on the west central shelf and the limit of detachment of jurassic and lower cretaceous thin skinned tectonics in moray firth half graben

nature and origin of collapse breccias in the zechstein of ne england local observations with cross border petroleum exploration and production significance across the north sea

longevity of a small shield volcano revealed by crypto tephra studies rangitoto volcano new zealand change in eruptive behavior of a basaltic field abstract the life span of small volcanoes in terrestrial basaltic fields commonly considered monogenetic can be difficult to assess due to a paucity of datable materials capable of providing a 102 103 year age resolution we have used microscopic tephra layers crypto tephra in lake sediments to determine the longevity of rangitoto volcano a small shield that represents the most recent volcanism in the auckland volcanic field avf new zealand previous studies suggested construction in a relatively short interval at 550 500 cal yrs bp in contrast the tephra record shows evidence of intermittent activity from 1498 140 to at least 504 6 cal yrs bp a longevity of 1000 years rangitoto volcano is thought to represent about half the magma erupted in the 250 ka history of avf thus the avf has experienced a dramatic shift to prolonged and voluminous central vent volcanism in its most recent history this demonstrates the difficulty in determining time erupted volume relationships in such fields previous avf hazard risk modeling based on isolated short lived

tarawera 1886 new zealand a basaltic plinian fissure eruption abstract new zealand s biggest and most destructive volcanic eruption of historical times was that of tarawera in 1886 the resulting scoria fall has a dispersal very similar in extent to that of the vesuvius a d 79 pumice fall and is one of the few known examples of a basaltic deposit of plinian type a new estimate of the volume 2 km 3 is significantly greater than previous estimates the basalt came mainly from a 7 km length of fissure and emission and exit velocity were fairly uniform along at least 4 km of it this is one of the few documented examples of a plinian eruption from a fissure vent primary welding of the scoria fall resulted where the accumulation rate exceeded about 250 mm min 1 a model of the eruption dynamics is proposed which leads to an estimate of 28 km for the height of the eruption cloud and implies a magma volatile fraction of 1 5 3 violent phreatic explosions occurred in the southwestern extension of the fissure across the rotomahana geothermal field and it is thought that some of the water responsible for the power of the plinian eruption came from this source though its amount was not sufficient to turn the eruption into a phreatoplinian one

sudden stratospheric warming event signatures in daytime exb drift velocities in the peruvian and philippine longitude sectors for january 2003 and 2004 1 this paper first describes the technique that has been developed to obtain realistic daytime vertical exb drift velocities in the equatorial ionosphere using two ground based magnetometers one on the magnetic equator and the other located 6 9 away in latitude this technique is then employed to study the unique exb drift signatures associated with sudden stratospheric warming events ssw in both the peruvian and philippine longitude sectors occurring in january 2003 and january 2004 it is found that the semidiurnal shaped signature first appears in the peruvian sector and 3 days later appears in the philippine sector in both sectors the exb drift signature lasts for approximately 5 days

observations of 2 4 day inertia gravity waves from the equatorial troposphere to the f region during the sudden stratospheric warming event of 2009 1 we have observed strong 2 4 day wave activity in the f region peak critical frequency fof2 at 7 5 n obtained from gps radio occultation measurements of the constellation observing system for meteorology ionosphere and climate cosmic satellites and the horizontal component of geomagnetic field variations over tirunelveli 8 7 n 77 8 e 1 75 n dip angle during the sudden stratospheric warming ssw event of 2009 a similar wave is observed strongly in the meridional winds observed by the mf radar at tirunelveli the meridional winds at 9 n and the equator obtained from era interim which is the latest global atmospheric reanalysis produced by the european centre for medium range weather forecasts shows clearly the 2 4 day wave propagating eastward with zonal wave number 6 over the central and eastern pacific both before and during the ssw event and over the indian sector during the ssw event only the potential vorticity pv intrusion at 200 hpa to lower latitudes is near the central pacific before the onset of the ssw event however during the ssw event the pv intrusion is observed more strongly near the indian sector in addition to the weaker intrusion near the central pacific it clearly indicates the rossby wave propagation to equatorial latitudes in the form of pv intrusion and it selectively enhances the periodicities generated owing to equatorial convective heating these waves could propagate to upper heights and cause variations in the mesosphere thermosphere ionosphere system

contrasting plagioclase textures and geochemistry in response to magma dynamics in an intra caldera rhyolite system okataina volcano abstract the changing magmatic dynamics of the rhyolite caldera volcano okataina volcanic centre new zealand is revealed in plagioclase growth histories crystals from the 0 7 ka kaharoa eruption are characterized by resorbed cores displaying a cellular texture of high an 40 zones partially replaced by low an 50 20 elevated an fe mg sr and ti follow the resorption surface and display rimward depletion trends accompanied by ba and ree enrichment the zonation is consistent with fractional crystallization and cooling the cores display wide trace element diversity pointing to crystallization in a variety of melts before transport and mixing into a common magma where the rims grew plagioclase from the 36 ka hauparu eruption display several regrowth zones separated by resorption surfaces which surround small resorbed cores with a spongy cellular texture of variable an content an 40 50 the crystals display step wise regrowth of successively higher an fe mg and ti content consistent with progressive mafic recharge two crystal groups are distinguished by trace element chemistry indicating growth in separate melts and co occurrence via magma mingling for plagioclase in both eruption deposits partition coefficients d estimated from crystal rim groundmass glass analyses produce melt compositions similar to the array of rock and glass compositions erupted and are consistent with the processes of fractional crystallization and recharge however d values estimated from some published formulations based on an content and temperature produce unrealistic melts the contrasting zoning patterns in plagioclase correspond to the evolutionary history of magmatism at okataina emptying of the magma reservoir following caldera eruption at 46 ka reduced barriers to mafic magma ascent this is recorded by the frequent resorption and recharge episodes in hauparu crystals subsequent redevelopment of a more silicic reservoir zone post 26 ka dampened thermal and mass perturbations resulting in simpler growth histories of the kaharoa crystals the plagioclase lack features associated with rapid decompression events that are common in andesite systems this reflects the rapid ascent of the rhyolite magmas and lack of precursory eruptions that could decompressed the system

silicic recharge of multiple rhyolite magmas by basaltic intrusion during the 22 6 ka okareka eruption episode new zealand abstract deposits of the 22 6 ka okareka eruption episode from tarawera volcanic complex record the sequential and simultaneous eruption of three discrete rhyolite magmas following a silicic recharge event related to basaltic intrusion the episode started with basaltic eruption 0 01 km3 magma and rapidly changed to a plinian eruption involving a moderate temperature 750 c cummingtonite bearing rhyolite magma t1 with a volume of 0 3 km3 hybrid basalt rhyolite clasts demonstrate direct basaltic intrusion that helped trigger the eruption crystals shards and lapilli of two other rhyolite magmas then joined the eruption sequence they comprise a cooler 720 c crystal rich biotite hornblende rhyolite magma t2 0 3 km3 and a hotter 780 c crystal poor pyroxene hornblende rhyolite magma t3 4 5 km3 all mid to late stage ash units contain various mixtures of t1 t2 and t3 components with a general increase in abundance of t3 and rapid decline of t1 with time about 4 km3 of t3 magma was extruded as lavas at the end of the episode contrasts in melt composition crystal and volatile contents and temperatures influenced viscosity and miscibility and thus limited pre eruption mixing of the rhyolite magmas the eruption sequence and the restricted direct basaltic intrusion into only one magma t1 is consistent with the rhyolites occupying separate melt pods within a large crystal mush zone melt crystal equilibria and volatile contents in melt inclusions indicate temporary magma storage depths of

effect of sudden stratospheric warming on lunar tidal modulation of the equatorial electrojet 1 using the equatorial electrojet eej peak current intensity as deduced from champ magnetic observations from the years 2001 through 2009 we investigated the relationship between sudden stratospheric warming ssw and lunitidal signatures in the tropical ionosphere there is a practically one to one correspondence between midwinter ssw periods and the strongest 13 day modulation of the eej strength as observed by champ that is all the midwinter ssw periods from december 2001 to august 2009 were accompanied by an enhanced 13 day modulation of the eej strength no other geophysical phenomenon brought about as strong a 13 day modulation as those of the midwinter ssw periods during each midwinter ssw period the amplified 13 day modulation of the eej strengths starts roughly within 1 week around the first peak in stratospheric temperature difference an oscillation with a period of 13 26 days is predicted by the lunitidal equation when considering the precession of the champ orbit when fitting the lunitidal equation to the eej modulations during the midwinter ssw periods consistent phase delays of 4 4 0 3 days of the tidal signal emerge for all the cases the results suggest that the pronounced 13 day modulation of the eej strength is related to an enhancement of the lunar tide in the ionosphere by the ssw effect