the san venanzo maar and tuff ring umbria italy eruptive behaviour of a carbonatite melilitite volcano the late pleistocene san venanzo maar and nearby pian di celle tuff ring in the san venanzo area of umbria central italy appear to represent different aspects of an eruptive cycle accompanied by diatreme formation approximately 6x106 m3 of mostly lapillisized juvenile ejecta with lesser amounts of lithics and 1x106 m3 of lava were erupted the stratigraphy indicates intense explosive activity followed by lava flows and subvolcanic intrusions the pyroclastic material includes lithic breccia derived from vent and diatreme wall erosion roughly stratified lapilli tuff deposited by concentrated pyroclastic surge chaotic scoriaceous pyroclastic flow and inverse graded grain flow deposits the key feature of the pyroclastics is the presence of concentric shelled lapilli generated by accretion around the lithics during magma ascent in the diatreme conduits the rock types range from kalsilite leucite olivine melilitite lavas and subvolcanic intrusions to carbonatite phonolite and calcitic melilitite pyroclasts juvenile ejecta contain essential calcite whose composition and texture indicate a magmatic origin pyroclastic carbonatite activity is also indicated by the presence of carbonatite ash beds the san venanzo maar forming event is believed to have been trigered by fluid rich carbonatite phonolite magma the eruptive centre the moved to the pian di celle tuff ring where the eruption of degassed olivine melilititic magma and late intrusions ended magmatic activity in the area in both volcanoes the absence of phreatomagmatic features together with the presence of large amounts of primary calcite suggests carbonatite segregation and violent exsolution of co2 which flowing through the diatremes produced the peculiar intrusive pyroclastic facies and triggered explosions

significant depletions of the ionospheric plasma density at middle latitudes a possible signature of equatorial spread f bubbles near the plasmapause 1 plasma density irregularities in the equatorial f region ionosphere are generally called equatorial spread f esf large scale plasma bubbles associated with esf processes are generated in the bottomside f region and penetrate the f peak to the topside f region it is still not fully understood how high esf bubbles can reach in this paper we present the measurements of deep depletions of the ionospheric plasma density at 840 km altitude with the defense meteorological satellite program dmsp satellites in the evening sector on 29 october 2003 the plasma depletions occurred after an interval of strong southward interplanetary magnetic field imf a prominent feature of the observations is that the plasma depletions occurred at very high magnetic latitudes mlat as well as at equatorial latitudes the equatorial depletions were identified as plasma bubbles the depletions at middle latitudes 20 46 mlat were separated from the conventional ionospheric midlatitude trough and identified as the extension of esf flux tubes into these latitudes it implies that the plasma bubble which caused the emptied flux tube at 46 mlat reached the altitude of 6800 km over the magnetic equator the observations may represent the highest altitude latitude of plasma bubbles that has ever been reported in the literature for the plasma depletions at even higher latitudes 47 49 mlat near the subauroral polarization stream saps midlatitude trough there are two candidate generation mechanisms one is the extension of esf flux tubes into these latitudes implying that the plasma bubbles reached the altitude of 8400 km over the magnetic equator because the saps midlatitude trough corresponds to the plasmapause at the plasmaspheric heights the observations suggest that esf plasma bubbles may have reached the plasmapause another mechanism is a field aligned low density structure between the plasmasphere and ionosphere and the plasma structure is generated through the strong electric field in the subauroral polarization stream region

the architecture eruptive history and evolution of the table rock complex oregon from a surtseyan to an energetic maar eruption abstract the table rock complex trc pliocene pleistocene first documented and described by heiken heiken g h 1971 tuff rings examples from the fort rock christmas lake valley basin south central oregon j geophy res 76 5615 5626 is a large and well exposed mafic phreatomagmatic complex in the fort rock christmas lake valley basin south central oregon it spans an area of approximately 40 km2 and consists of a large tuff cone in the south trc1 and a large tuff ring in the northeast trc2 at least seven additional smaller explosion craters were formed along the flanks of the complex in the time between the two main eruptions the first period of activity trc1 initiated with a surtseyan style eruption through a 60 70 m deep lake the trc1 deposits are dominated by multiple 1 2 m thick fining upward sequences of massive to diffusely stratified lapilli tuff with intermittent zones of reverse grading followed by a finely laminated cap of fine grained sediment the massive deposits are interpreted as the result of eruption fed subaqueous turbidity current deposits whereas the finely laminated cap likely resulted from fallout of suspended fine grained material through a water column other common features are erosive channel scour and fill deposits massive tuff breccias and abundant soft sediment deformation due to rapid sediment loading subaerial trc1 deposits are exposed only proximal to the edifice and consist of cross stratified base surge deposits the eruption built a large tuff cone above the lake surface ending with an effusive stage which produced a lava lake in the crater 365 m above the lake floor a significant repose period occurred between the trc1 and trc2 eruptions evidenced by up to 50 cm of diatomitic lake sediments at the contact between the two tuff sequences the trc2 eruption was the last and most energetic in the complex general edifice morphology and a high percentage of accidental material suggest eruption through saturated trc1 deposits and or playa lake sediments trc2 deposits are dominated by three dimensional dune features with wavelengths 200 500 m perpendicular to the flow and 20 200 m parallel to the direction of flow depending on distance from source large u shaped channels 10 32 m deep run up features over obstacles tens of meters high and a large 13 m chute and pool feature are also identified the trc2 deposits are interpreted as the products of multiple erosive highly inflated pyroclastic surges resulting from collapse of an unusually high eruption column relative to previously documented mafic phreatomagmatic eruptions

foreword to special section on remote sensing of the low and middle latitude thermosphere and ionosphere from the ground and from space the low and midlatitude thermosphere and ionosphere constitute a tightly coupled dynamic region of the near earth environment this region exhibits strong and complex coupling between charged and neutral species between different altitudes and between equatorial and nonequatorial latitudes the ion and neutral composition and temperature are affected by dynamics electric and magnetic fields photochemistry and geomagnetic and solar forcing this special section focuses on this region and the remote sensing techniques that are providing the measurements needed to better understand this complex region of the near earth space environment

generation of volcanic ash by basaltic volcanism 1 the recent eruptions of eyjafjallajokull and grimsvotn volcanoes in iceland demonstrate the importance of a better understanding of processes leading to the formation of volcanic ash specifically of fine volcanic ash that poses a threat to air traffic continuous deformation and brittle type experiments were carried out to better constrain these processes the studies on short time continuous deformation behavior of basaltic melt showed viscoelastic properties deviating from hydrodynamic newtonian models by more than 5 orders of magnitude high temperature deformation experiments on basaltic rock samples revealed an increase of elastic strengths as approaching the melting regime also pointing to a very complex behavior at the solid ductile boundary understanding magma fragmentation from the liquid side is a challenge but meanwhile we propose a pragmatic solution a thermodynamic model based on fracture mechanics this model is in agreement with experiments and observations that show that fine volcanic ash is produced by brittle type fragmentation of magma a critical material property was defined characterizing the conditions for brittle fragmentation the fracture surface energy density which represents the critical fragmentation energy short term fracture experiments using silicate glass have been performed to investigate the formation of ash sized particles by brittle failure and to extract this critical physical property which was found to range between 40 and 130 j m2 this value is in good agreement to fragmentation energies determined from experiments using remelted volcanic rocks now there is a tool to define critical conditions for the production of volcanic ash of a specific magma type

character genesis and tectonic setting of igneous rocks in the sistan suture zone eastern iran abstract igneous rocks in the sistan suture zone have characteristics that can be correlated with important tectonic events a late cretaceous ocean basin is recorded by ophiolites now exposed in numerous melange zones subduction beneath the afghan block is indicated by late cretaceous paleocene calc alkaline volcanics collision of the lut block with the subduction complex in the middle eocene produced widespread deformation and was followed by the emplacement of late eocene early oligocene calc alkaline granitic batholiths that probably formed by widespread anatexis of marine sediments a dominantly oligocene magmatic event is represented by widespread alkaline volcanics and minor intrusions that appear to be related to major transcurrent faults miocene calc alkaline activity was limited to sporadic volcanism in the north and minor intermediate intrusions farther south these units are largely underformed and not related to any major faults the youngest magmatic event is recorded by late miocene pliocene mafic flows that are weakly alkaline clearly related to right lateral faults and probably were derived from a deep crustal or upper mantle source

westward plasma drift in the midlatitude ionospheric f region in the midnight dawn sector in this paper we report the observations of a sharp ionospheric plasma velocity reversal boundary at subauroral latitudes during magnetic storms in the midnight dawn sector the zonal plasma drift was eastward poleward of the velocity boundary and became westward equatorward of the boundary the latitudinal extent of the westward drifts was 20 a local maximum of the drift occurred only 2 5 below the boundary the magnitude of the maximum velocity was 200 400 m s 1 between 2100 and 0300 local time lt and as high as 780 m s 1 near midnight the large westward plasma drift immediately equatorward of the velocity boundary first occurred at 2100 lt and continuously extended across midnight to the dawn sector the location of the maximum velocity coincided with the minimum density within the midlatitude ionospheric trough the latitude of the velocity boundary decreased from geographic latitude 53 to 43 corresponding to geomagnetic latitude 65 to 55 between 2100 and 0800 lt we propose that the large westward drift at subauroral latitudes is driven by the polarization jet electric fields in the ring current and that the lower latitude westward drift with moderate magnitude is caused by the disturbance wind dynamo

descriptive nomenclature and classification of pyroclastic deposits and fragments the iugs subcommission on the systematics of igneous rocks herein presents its recommendations on the nomenclature and classification of pyroclastic and mixed pyroclastic epiclastic deposits using descriptive mainly granulometric criteria the recommendations are the result of an international inquiry by means of questionnaires during the last four years

thermal expansion on volcanic tuff rocks used as building stones examples from mexico three cities in the center of mexico declared as cultural heritage were erected mainly of volcanic tuffs as main construction element many of the historic buildings of these cities show significant damage and deterioration one of the causes of these damages can be attributed to a phenomenon poorly studied in volcanic tuffs the thermal expansion to understand the response of volcanic tuffs to thermal expansion as well as to know their thermal expansion coefficient thermal expansion test was performed on 12 representative tuffs of these localities in the same way and to know which of their petrographic petrophysical mineralogical and geochemical properties influence this phenomenon several laboratory studies were carried out to determine which of these plays an important role in the expansion the results of our tests showed that volcanic tuffs rocks have very varied thermal expansion values ranging from 0 7 mm m at their maximum expansion to even contraction in the order of 0 5 mm m equally varied were the thermal expansion coefficient values ranging from 10 1 to 7 2 10 6 k the most dominant behavior type is the anisotropic no residual strain behavior in general the behavior of the tuffs in practically all the tests carried out showed a very important heterogeneity in the rocks however in spite of the non homogeneous behavior of the tuffs three main factors could be identified that play an important role in the thermal expansion of the studied rocks the chemical composition e g acid volcanic tuff rocks rhyolitic composition had greater expansions while the more basic rocks basaltic composition expanded less the textural and fabrics homogeneity e g the most homogeneous rocks texturally have higher expansion values and the degree of crystallinity and e g the tuff rocks with the largest amount of glass showed smaller thermal expansions than the tuffs composed of microcrystals

lithofacies association and stratigraphy of the paredao volcano trindade island brazil abstract a stratigraphic framework can be constructed through lithofacies description and interpretation the application of this method in volcanic systems is a fundamental tool for understanding their evolution and eruptive dynamics and for establishing hazard assessments in active volcanic areas this work presents and discusses a detailed stratigraphy of the paredao volcano allowing the understanding of the lateral and vertical distribution of volcanic facies and the 3d geometry of the deposits generating a model for the volcanism and discussing the erupting mechanisms the paredao volcano is a scoria cone located in the southeast of trindade island and represents the youngest subaerial volcanic episode pleistocene recorded in brazil its stratigraphic organization indicates nephelinitic flows alternate with lapillistones and lapilli tuffs of same composition at the base and a pyroclastic cone with nearly 200 m high above the sea level through lithofacies description and association 4 stratigraphic columns were constructed in scale 1 50 three of them at the tartarugas beach trv 01 trv 02 trv 03 and the other one at the pyroclastic cone trv 04 the petrographic characterization of facies was carried through conventional optical microscopy the stratigraphic analysis resulted in the distinction of seven lithofacies divided into two coherent and five volcaniclastic one autoclastic and four pyroclastic the coherent lithofacies are of massive npm and vesicular porphyritic nephelinite npv texturally the lavas are holocrystalline and vesicular composed by olivine phenocrysts in a very fine matrix of clinopyroxene nepheline zeolite and titanomagnetite at times with phlogopite the autoclastic lithofacies of nephelinitic breccia nb is composed of fragments 2 mm 15 cm of vesicular nephelinite and the pyroclastic ones are composed mainly of lapillitic scoria fragments with subordinate bombs and volcanic ash the pyroclastic lithofacies are of massive lapillistone lm and lapilli breccia lbm planar stratified lapilli tuff ltp and reverse grading lapillistone lrg the lithofacies associations characterize a a rubbly pahoehoe and pahoehoe flow types distal and proximal pyroclastic deposits the interpretation of the vertical and lateral facies distribution leads to the conclusion that the volcanism occurred with an initial phreatomagmatic stage succeeded by a strombolian stage pyroclastic with primary fragments domain and a final hawaiian stage lava flows domain

structured subauroral polarization streams and related auroral undulations occurring on the storm day of 21 january 2005 we investigate structured subauroral polarization streams saps and their impacts on the midlatitude trough and auroral regions during the 21 22 january 2005 geomagnetic storm this was a storm with two sudden commencements occurring under varying interplanetary magnetic field imf conditions and three main phases two of them unfolding during northward imf its onset at 1700 ut allowed us to investigate saps wave structures ws and their impacts during the local evening hours under both southward and northward imf conditions in the american sector results suggest that during southward imf saps ws might be related with standing toroidal alfven waves and structured most intensively the stagnation trough during northward imf the trough was created by saps electric e field effects only and became less structured by saps ws that were of alfvenic origin auroral wave structures and undulations occurred in the structured and unstructured oval regions respectively and triggered the subauroral region s response to produce saps ws spectrogram images only one shown confirmed ring current injections implying magnetotail reconnections during the four saps ws events investigated periodic tail connections are also evidenced by the periodic increases seen in both the solar wind magnetosphere coupling function e and the energy input efficiency finally we conclude for the time period investigated that 1 the nature of saps ws was informative of imf orientation 2 plasma stagnation enhanced saps e field and saps ws development and 3 more efficient energy input into the magnetosphere contributed to the better development of auroral undulations and saps ws

east west ion drifts at mid latitudes observed by dynamics explorer 2 zonal ion drifts measured from the polar orbiting de 2 spacecraft are examined to determine the effects of dynamo electric fields and penetration of high latitude electric fields at middle latitudes construction of a local time distribution from satellite data results in a mixture of local time and season as well as a range of magnetic activity encompassing kp le 2 and kp ge 3 thus some combination of magnetospheric effects expected to dominate during disturbed times are seen during both quiet and disturbed times and solar tidal influences are most easily observed during quiet times during quiet times at invariant latitudes near 25 degrees the solar diurnal tide dominates the local time distribution of the ion drift at latitudes above 50 degrees a diurnal component of comparable magnitude is also present but its magnetospheric origin produces a shift in phase of almost 180 degrees from the lower latitude diurnal tide in the intervening region between 20 degrees and 50 degrees invariant latitude semidurnal and terdiurnal components in the local time distribution of the drift velocity are also seen these components are generally larger than those seen by ground based radars during quiet times and may be attributable in part to a difference in solarmore activity and in part to a combination of the solar tides and magnetospheric penetration fields less

neogene and quaternary ignimbrites in the area of arequipa southern peru stratigraphical and petrological correlations abstract this study focuses on the correlation of four newly identified rhyolitic ignimbrites located around arequipa which were previously described as a single ignimbrite sheet 1 the rio chili ignimbrite ca 13 33 ma crops out in the rio chili canyon and consists of a cooling unit of non welded to partially welded massive crystal rich lapilli tuff this ignimbrite represents the base of the neogene ignimbrite succession in the arequipa area and may be stratigraphically equivalent to the 14 13 ma huaylillas ignimbrites in southern peru 2 the second voluminous 20 km3 and widespread la joya ignimbrite sheet ca 4 87 ma filled the arequipa depression its probable source is now buried underneath the chachani volcanic complex the la joya ignimbrite covers both the arequipa batholith toward the rio vitor piedmont and also part of the altiplano to the east and north of the chachani complex 3 the arequipa airport ignimbrite aai sheet ca 1 6 ma 18 km3 the third and latest infill of the arequipa basin consists of a lower white columnar jointed massive lapilli tuff indurated by vapor phase recrystallization and is overlain by an upper pink lithic rich non welded massive lapilli tuff the source of this ignimbrite is also buried underneath the chachani complex as indicated by anisotropy of magnetic susceptibility measurements and component lithology 4 the yura non welded pumice flow deposits ca 1 02 ma 1 5 km3 are restricted to the northern and western flanks of the chachani complex and may correlate with tuffs of the capillune formation on the altiplano all ignimbrites are high k calc alkaline to alkaline rhyolites which contain variable amounts of plagioclase biotite quartz sanidine and fe ti oxides the modal composition of mineral phases and chemistry of amphiboles and biotites are useful for distinguishing the ignimbrites specific geochemical fingerprints such as sr y rb ba cs ree and sr isotopes were effective discriminator elements magmatic differentiation crustal residence time and contamination and source melting processes are discussed in order to explain compositional variations the older la joya ignimbrite and rio chili ignimbrite reflect initial wetter crustal melts closer to granite composition whereas with time the younger arequipa airport ignimbrite and yura tuffs initial melts are slightly less evolved and dryer due to more extensive crustal melting the voluminous 40 km3 neogene ignimbrites of the arequipa area were produced by three major explosive volcanic pulses in the central volcanic zone of southern peru whose genetic relation with tectonic uplift and crustal thickening of the andean cordillera are still a matter of debate

coordinated stable auroral red arc observations relationship to plasma convection during the march 20 22 1990 magnetic storm millstone hill radar and dmsp satellite observations detailed the conditions surrounding the occurrence of a sar arc which was observed continuously through an 8 hour interval from dusk till past midnight in the north american sector all sky imaging with a 630 0 nm imager continually monitored the two dimensional position and magnitude of the sar arc emission while radar scans and satellite overflights measured magneto spheric inputs and ionospheric response the arc was colocated with a deep narrow plasma trough and a region of enhanced westward plasma convection of similar width simate3 immediately equa torward of the low latitude extent of plasma sheet particle precipitation a region of low energy ion precipitation was observed at the equatorward edge of the sar arc during a period of spatial tem poral coincident satellite radar observations near the millstone hill longitude the width of the sar arc and related phenomena was of the order of 2 o and the 200 r emission was associated with an electron temperature of 3500ok and a 10x reduction of plasma density at an altitude of 450 kin the best fit model for the emission intensities of both the sar arc and the background airglow suggests that either the electron temperature at the center of the sar arc was somewhat higher than observed by the radar 4000ok or the neutral densities 0 2 and o were increased by factors of 2 and 4 respectively with respect to the msis values the ionospheric trough and a colocated region of enhancext sunward convection 500 1700 m s 1 were observed in conjugate hemispheres through out the local time range 18 02 mlt the convection feature seen in association with the sar arc had many of the characteristics of a subauroral ion drifts said event we report here the first long duration observations of a colocated said sar arc event a narrow ionospheric trough developed during the interval when the said velocity was 1000 m s and was accompanied by a weak 100 r 630 0 nm emission as the velocity fell to 700 m s 1 the density in the trough recovered some what and the arc intensity rose to 300 r above background this brighter period of the sar arc occurred within a fossil trough said we conclude that there is a close spatial and temporal associ ation among these three types of subauroral low altitude phenomena the sar arc the said even and the fossil convection related trough and that this is indicative of the interrelationship of the

pyroclast tracking velocimetry a particle tracking velocimetry based tool for the study of strombolian explosive eruptions image based techniques enable high resolution observation of the pyroclasts ejected during strombolian explosions and drawing inferences on the dynamics of volcanic activity however data extraction from high resolution videos is time consuming and operator dependent while automatic analysis is often challenging due to the highly variable quality of images collected in the field here we present a new set of algorithms to automatically analyze image sequences of explosive eruptions the pyroclast tracking velocimetry pytv toolbox first a significant preprocessing is used to remove the image background and to detect the pyroclasts then pyroclast tracking is achieved with a new particle tracking velocimetry algorithm featuring an original predictor of velocity based on the optical flow equation finally postprocessing corrects the systematic errors of measurements four high speed videos of strombolian explosions from yasur and stromboli volcanoes representing various observation conditions have been used to test the efficiency of the pytv against manual analysis in all cases 106 pyroclasts have been successfully detected and tracked by pytv with a precision of 1 m s for the velocity and 20 for the size of the pyroclast on each video more than 1000 tracks are several meters long enabling us to study pyroclast properties and trajectories compared to manual tracking 3 to 100 times more pyroclasts are analyzed pytv by providing time constrained information links physical properties and motion of individual pyroclasts it is a powerful tool for the study of explosive volcanic activity as well as an ideal complement for other geological and geophysical volcano observation systems

finding eruptive mechanisms through pyroclasts from the current eruption 1984 present at nevado del ruiz volcanic complex colombia abstract the dominant fragmentation mechanisms in the magma involved in a volcanic eruption can be understood from the compositional and textural analysis of the fragments emitted as pyroclasts individual pyroclasts can be juvenile accessory and accidental and detailed analyses of their relative proportions as well as the juvenile clast features can shed light into the fragmentation processes involved in the eruption despite the multiple hundreds eruptive pulses since the nevado del ruiz re activation in 1984 following a quiescence of nearly 100 years such analyses have not been carried out for the ash emissions preceding the recently emplaced plug here four deposits related to the recent emissions were analysed from their pyroclasts the samples correspond to eruptive pulses from the years 1985 1986 1988 and 2012 their characterisation allowed proposing differences between likely juvenile fragments i e representative of involved magma and accessory fragments i e pre existing co magmatic the results indicate that alteration can be used as a criterion to distinguish them although this could not account for syn eruptive hydrothermal alteration of juvenile glass or for the preservation of accessory glass emplaced in glacial conditions this criterion could serve as a foundation to direct fresh glass fragment analyses following this criterion the fresh glass fragments which are assumed to be juvenile fragments are highly vesicular they exhibit spongy and fibrous textures that are related to the predominant vesicle shape their predominance suggests a magmatic fragmentation mechanism while blocky shaped poorly vesicular cracked glass shards suggest a phreato magmatic origin specifically november of 1985 and january of 1986 glassy ashes are primarily highly vesicular suggesting magmatic explosive events by contrast samples from the march of 1988 and may of 2012 events are primarily characterised by low fresh glass content they also exhibit quenched surfaces indicating that the magma water interaction acted as an important factor for triggering the eruptive pulses real time componentry petrography and glass characterisation in fine ash could significantly complement traditional geophysical monitoring and importantly improve the hazard assessments on the civil aviation during the ongoing nevado del ruiz activity

antique stone quarries in turkey a case study on tuffs in the temple of apollon smintheus all types of stones have been used as building stones depending on their durability visual harmony with the intended construction and availability in the hellenistic period as in other periods tuff was preferred as a building stone due to its convenience it was easy to extract transport and use for building in the present study three ancient quarries that were the possible tuff sources for the apollon smintheus temple in canakkale are investigated by comparing the durability properties of stones in the temple and in the quarries these properties are determined using physical and physico mechanical tests comparing fresh and artificially weathered samples microstructural and elemental correlations were found using optical microscopy stereomicroscopy x ray diffraction scanning electron microscopy methylene blue adsorption and x ray fluorescence analyses the results indicate that temple tuffs and two of three quarries have similar geological engineering and microstructural properties with the strong claim that those two quarries could have been the source of building stone for the temple gold open access this article is published under the terms of the cc by 3 0 license historically only high status stone blocks were transported for longer distances whereas local quarries were used for larger constructions gomezheras fort gonzalez 2004 torok p ikryl 2010 since local stones do not entail high transportation costs they can be extracted whenever is suitable bell 1990 what matters most is that the rock must not include closely spaced joints cracks or other planes of weakness in large blocks extracted by stone quarrying rapp 2002 in hellenistic architecture all types of stones marble gneiss limestone sandstone granite andesite tuff breccias serpentinite porphyry and trachyte were used among all other stones tuffs were easy to get carry and process and were therefore relatively cheap and could be used in any part of a building on condition that it was sheltered from the weather tucci 2015 in turkey tuffs that have low unit weight high to very high porosity and poor to good durability properties topal doyuran 1997 1998 topal 2002 topal sozmen 2003 yavuz 2012 celik et al 2014 are seen in antique structures as well as in historic monuments of the seljuk ottoman period that have survived to the present day unremarkably antique quarries can be found with the masons marks and shear ledges of dimension stones however it is not possible today to observe the tuff quarries as they appeared in ancient times because tuffs deteriorate over time when exposed to weathering and or because of the urban construction mass p ikryl 2006 p ikryl torok 2010 in the case of lack of knowledge of the original quarry the most contiguous geological resources are examined through mineralogical chemical and physical analyses and in situ observation and testing to find replacement stones that are compatible in terms of characteristics and appearance this approach may yield misapplication of stones the purpose of this study is to determine the provenance of the tuffs used in the temple of apollon smintheus architecture dating from the hellenistic period by comparison of physical mechanical chemical and mineralogical features to that end samples taken from the temple and samples taken from three potential quarry regions were compared using several analytical techniques to from p ikryl r torok a gomez heras m miskovsky k theodoridou m eds sustainable use of traditional geomaterials in construction practice geological society london special publications 416 http doi org 10 1144 sp416 17 2015 the author s published by the geological society of london publishing disclaimer www geolsoc org uk pub ethics determine the source quarry for the temple tuffs the results of the analyses may serve for surface deterioration studies and durability assessment as well site description the apollon smintheus temple is situated on the southwest corner of the biga peninsula troas fig 1 location map of the study area fig 2 temple of apollon smintheus d ergenc et al

seasonal and magnetic activity variations of ionospheric electric fields over millstone hill incoherent scatter observations of e and f region drifts over millstone hill 42 6 n were made routinely from may 1976 to november 1977 at monthly intervals some 667 hours of data gathered over this 19 month period have been analyzed to yield the ionospheric polarization electric field in the magnetic south and magnetic east directions for three seasons during quiet magnetic conditions as well as the annual average during magnetically disturbed conditions kp 3o the results for the quiet days are compared with earlier results obtained at millstone hill kirchhoff and carpenter 1976 and with those reported from st santin 44 6 n by blanc and amayenc 1979 we find that there is best agreement between millstone and st santin for the east west component of the field which exhibits a roughly 12 hour period variation during the daytime in all seasons the north south field exhibits a predominantly diurnal variation that in winter and equinox is almost identically opposite at the two stations this component shows substantial changes in summer at both stations and at millstone appears to exhibit a significant 1mv m average northward component not seen at st santin we attribute the differences in the quiet time behavior observed at millstone and st santin to the very large difference in the latitude of their conjugate points where presumably the tides and hence the dynamo effects are dissimilar there are marked differences in the electric field patterns between disturbed and quiet times which mainly are evident in the nighttime period commencing after noon there is a gradual enhancement of both the northward and eastward fields on disturbed days the eastward field reverses near midnight and becomes westward until dawn while the other component remains northward for most of the night these changes are thought to result from the penetration of auroral electric fields inside the plasmasphere

average characteristics and activity dependence of the subauroral polarization stream 1 data from the millstone hill incoherent scatter radar taken over two solar cycles 1979 2000 are examined to determine the average characteristics of the disturbance convection electric field in the midlatitude ionosphere radar azimuth scans provide a regular database of ionospheric plasma convection observations spanning auroral and subauroral latitudes and these scans have been examined for all local times and activity conditions we examine the occurrence and characteristics of a persistent secondary westward convection peak which lies equatorward of the auroral two cell convection individual scans and average patterns of plasma flow identify and characterize this latitudinally broad and persistent subauroral polarization stream saps which spans the nightside from dusk to the early morning sector for all kp greater than 4 premidnight the saps westward convection lies equatorward of l 4 60 invariant latitude spans 3 5 of latitude and has an average peak amplitude of 900 m s in the predawn sector saps is seen as a region of antisunward convection equatorward of l 3 55 spanning 3 of latitude with an average peak amplitude of 400 m s

permian to recent volcanism in northern sumatra indonesia a preliminary study of its distribution chemistry and peculiarities sumatra has been a volcanic arc above an ne dipping subduction zone since at least the late permian the principal volcanic episodes in sumatra n of the equator have been in the late permian late mesozoic palaeogene miocene and quaternary late permian volcanic rocks of limited extent are altered porphyritic basic lavas interstratified with limestones and phyllites late mesozoic volcanic rocks widely distributed along and w of the major transcurrent sumatra fault system sfs which axially bisects sumatra include ophiolite related spilites andesites and basalts possiblepalaeogene volcanic rocks include an altered basalt pile with associated dyke swarm in the extreme nw intruded by an early miocene 19 my dioritic stock and variable pyroxene rich basic lavas and agglomerates ranging from alkali basaltic to absarokitic in the extreme sw miocene volcanic rocks widely distributed especially w of the sfs and cropping out extensively along the w coast include calc alkaline to high k calc alkaline basalts andesites and dacites quaternary volcanoes 3 active 14 dormant or extinct are irregularly distributed both along and across the arc thus they lie fore arc of the sfs near the equator but well back arc farther north the largest concentration of centres around lake toba includes the 2000 km3 pleistocene rhyolitic toba tuffs quaternary volcanics are mainly calc alkaline andesites dacites and rhyolites with few basalts they seem less variable but on the whole more acid than the tertiary

a study of the correlation between electrical resistivity and matric suction for unsaturated ash fall pyroclastic soils in the campania region southern italy in the territory of the campania region southern italy critical rainfall events periodically trigger dangerous fast slope movements involving ashy and pyroclastic soils originated by the explosive phases of the mt somma vesuvius volcano and deposited along the surrounding mountain ranges in this paper an integration of engineering geological and geophysical measurements is presented to characterize unsaturated pyroclastic samples collected in a test area on the sarno mountains salerno and avellino provinces campania region the laboratory analyses were aimed at defining both soil water retention and electrical resistivity curves versus water content from the matching of the experimental data a direct relationship between electrical resistivity and matric suction is retrieved for the investigated soil horizons typical of an ash fall pyroclastic succession the obtained relation turns out to be helpful in characterizing soils up to close saturation which is a critical condition for the trigger of slope failure in such a regime the water content and the matric suction have small variations while electrical resistivity variations can be appreciated in a larger range of values for this reason besides suction measurements on very small soil volumes through classical tensiometers our analyses suggest the direct monitoring of in situ electrical resistivity values as an effective tool to recognise the hydrological state of larger and more representative soil volumes and to improve early warning of dangerous slope movements

electrodynamic coupling of high and low latitudes observations on may 27 1993 the penetration of disturbance electric fields from the polar region to the magnetic equator on the dayside of the earth is examined with geomagnetic data on may 27 1993 first we examine a dayside equatorial disturbance that followed the rapid recovery of magnetic activity from a storm and that has the characteristics of overshielding caused by persistent region 2 field aligned currents it lasted 0 3 hours second we analyze a series of fluctuations with periods of 25 75 min to determine the variations of amplitude and phase with magnetic latitude and magnetic local time the fluctuations were highly coherent at all latitudes between the magnetic equator and the auroral zone but the coherency decreasedin the polar cap a northward fluctuation at the equator during midday hours accompanied auroral zone fluctuations that were southward before noon eastward around noon and northward after noon the amplitudes decreased away from the auroral zone toward midlatitudes but were amplified under the equatorial electrojet no detectablep hased ifferencesa re found indicating that any temporal lags which might be inducedb y persistencein the region 2f ield alignedc urrentsa re less than i min for fluctuations having periods like those examined here a synoptic inversion analysis of the high latitude magnetic data to estimate the time varying high latitude electric potential patterns shows that fluctuations of the high latitude east west potential gradient tended to be concentrated around midday where they were in phase with fluctuations in the midday east west potential gradient at the magnetic equator

mechanism of formation of volcanic bombs insights from a pilot study of anisotropy of magnetic susceptibility and preliminary assessment of analytical models volcanic bombs and achneliths are a special type of pyroclastic fragments formed by mildly explosive volcanic eruptions models explaining the general shapes of those particles can be divided in two broad categories the most popular envisages the acquisition of shapes of volcanic bombs as the result of the rush of air acting on a fluid clot during flight and it includes many variants the less commonly quoted model envisages their shapes as the result of forces acting at the moment of ejection of liquid from the magma pool in the conduit experiencing an almost negligible modification through its travel through air quantitative evidence supporting either of those two models is limited in this work i explore the extent to which the anisotropy of magnetic susceptibility ams might be useful in the study of mechanisms of formation of volcanic bombs by comparing measurements made on two spindle and two bread crusted bombs the results of this pilot study reveal that the degree of anisotropy of spindle bombs is larger and their principal susceptibility axes are better clustered than on bread crusted bombs also the orientation of the principal susceptibility axes is consistent with two specific models one of the in flight variants and the general ejection model consequently the reported ams measurements albeit limited in number indicate that it is reasonable to focus attention on only two specific models to explain the acquisition of the shapes of volcanic bombs based on a parallel theoretical assessment of analytical models a third alternative is outlined envisaging volcanic bomb formation as a two stage process that involves the bursting of large m gas bubbles on the surface of a magma pond the new model advanced here is also consistent with the reported ams results and constitutes a working hypothesis that should be tested by future studies richer in data fortunately since this work also establishes that ams can be used to determine magnetic fabric in small size samples the possibility to expand this study to a larger collection of bombs is granted

permafrost evidence for severe winter cooling during the younger dryas in northern alaska 1 the younger dryas cold event a rapid reversion to glacial climate conditions at the pleistocene holocene transition has generally been attributed to the release of meltwater from the laurentide ice sheet to the north atlantic or arctic oceans the reaction of the north pacific region to this shutdown of the thermohaline circulation in the north atlantic during younger dryas is little understood in this paper we present the first radiocarbon dated centennial scale stable water isotope record from permafrost in northern alaska this late glacial winter climate reconstruction from barrow ice wedges demonstrates the existence of a younger dryas cold event formerly believed to be reduced or absent in this area our stable isotope data display a gradual change of the atmospheric moisture source conditions during the younger dryas likely associated with the successive opening of the bering strait

hawaiian and strombolian style monogenetic volcanism in the extra andean domain of central west argentina abstract in the provinces of mendoza and la pampa central western argentina retroarc volcanism was active from the miocene through historic times there are approximately 40 basaltic eruptive centers between 36 s and 37 30 s to the east of 68 40 w these centers were studied in order to define their volcanological evolution the vents are constituted of seven lithofacies i e a 1 weakly welded lapilli and bomb beds a 2 agglutinated spatter and bomb beds a 3 agglutinated spatter beds b ash beds c lava flows d conduit fill and e dikes three eruptive episodes phases were identified the first one generated agglutinated spatter and bomb beds lithofacies a 2 which constitute the internal part of the edifices these are followed by weakly welded lapilli and bomb beds lithofacies a 1 and agglutinated spatter beds lithofacies a 3 the final episode includes lava flows lithofacies c minor agglutinated spatter deposits lithofacies a 3 and isolated lapilli and bomb clasts we postulate hawaiian style fountaining activity as responsible for the generation of agglutinated spatter and bombs beds and variations between strombolian and hawaiian activity for the formation of successions of weakly welded lapilli and bomb beds and agglutinated spatter beds the vent features and the homogeneity of the erupted magma suggest that the studied volcanoes were monogenetic

correlation of the subauroral polarization streams saps with the dst index during severe magnetic storms 1 the subauroral polarization stream saps is the enhanced poleward electric field westward plasma flow in the region equatorward of the auroral electron precipitation boundary in the dusk midnight sector an important characteristic of saps is its great intensification during magnetic storms however the relationship of saps characteristics to the strength of magnetic storms is not well known using defense meteorological satellite program dmsp satellite measurements we have examined the location magnetic latitude of the saps channel during four severe magnetic storms with minimum dst values between 271 and 422 nt we find that the latitude of the saps channel varies directly with the magnitude of dst for example in one storm case saps moved from 60 magnetic latitude at the storm sudden commencement with dst of near zero to 38 at the end of the storm main phase with dst of 422 nt we have identified more than 300 locations of saps and corresponding dst values during the four storms the most important finding is that the saps latitude is linearly correlated with dst and an empirical formula is derived if the saps channel is mapped along the magnetic field lines to the magnetospheric equatorial plane the mapped saps location corresponds to the inner edge of the ion plasma sheet and is close to the peak of the ring current the result of this paper suggests a promising method of using ionospheric satellite and radar measurements of saps to monitor the evolution of the plasma sheet inner boundary and ring current during magnetic storms

the 2011 expedition to the el gygytgyn impact structure northeast russia toward a new geological map for the crater area el gygytgyn is a 3 6 ma 18 km diameter impact crater formed in an approximately 88 ma old volcanic target in northeast siberia the structure has been the subject of a recent icdp drilling project in parallel to those efforts a russian german expedition was undertaken in summer 2011 to investigate the permafrost soil lake terraces and the volcanic rocks of the southern and eastern crater rim this provided the unique opportunity for mapping and sampling of the volcanic target rocks around a large part of this complex impact structure samples from 43 outcrops were collected and analyzed petrographically and geochemically the results were combined with earlier mapping outcomes to create a new geological map of this impact structure and its immediate environs at the scale of 1 50 000 compositions of our rock suites are compared with the lithologies of the 2009 icdp drill core the ignimbrite described as lower bedrock in the icdp drill core shows petrographically and chemically strong similarities to the rhyolitic and rhyodacitic ignimbrites observed on surface the suevite sequence exposed in the icdp drill core is a mixture of all observed target rocks at their respective proportions in the area in contrast to previous studies the calculated average target composition of el gygytgyn takes the contribution of the basic target rocks into consideration mafic and intermediate rocks approximately 7 5 and felsic rocks approximately 92 5

late quaternary paleoceanography and paleo sea ice conditions in the mackenzie trough and canyon beaufort seathis article is one of a series of papers published in this special issue on the theme polar climate stability network the mackenzie trough provides a high resolution signal for paleoceanography as a result of high sedimentation rates at the mouth of the mackenzie river three cores were collected along a transect covering a depth range of 58 671 m and the time period of the last 11 500 cal bp prior to the last 10 000 cal bp the distal core is characterized by laminated sediment and a foraminiferal fauna of arctic bottom water calcareous species and abundant planktic foraminifera suggesting little freshwater runoff and or perennial sea ice cover this occurs at a similar time as laminated sediments from the west of this site which have been suggested to be part of the lake agassiz flood outburst and or cold period if this outburst occurred the very positive oxygen isotope values from our core pc3 3 0 ppm indicate that it did not flow through the mackenzie trough after 9000 cal bp the faunas in the three cores differ because of timing and different water depths however it is possible to see a progression

midlatitude ionospheric disturbances during magnetic storms and substorms 1 we present periodic 2 hour magnetospheric and ionospheric oscillations observed with multiple space based and ground based instruments during the severe magnetic storm of 25 september 1998 periodic particle injections were observed at geosynchronous orbit ground magnetometers registered very large as high as 3000 nt magnetic deviations in the nightside auroral zone the millstone hill incoherent scatter radar at magnetic latitude 55 measured periodic enhancements of ionospheric eastward ion velocity from midnight to 1000 mlt the periodic variations in the magnetometers and millstone hill radar were well correlated with the magnetospheric particle injections the observations are consistent with the occurrence of periodic magnetospheric substorms during a magnetic storm during each substorm cycle the ionospheric auroral zone expanded to the latitude of the millstone hill radar so the radar was periodically within the auroral zone and detected the auroral plasma return flows after substorm activity stopped the millstone hill radar measured near noon in phase periodic oscillations of the ionospheric f region electron density and temperature which may be due to particle precipitation from the ring current and or plasmasphere into the midlatitude ionosphere we suggest that magnetospheric substorms during magnetic storms have a cycle time of 2 hours the magnetosphere can sustain similar oscillations for several cycles even though the substorm activity has stopped all the observed periodic variations in the geosynchronous particle injections in the auroral magnetic deviations and in the ionospheric ion velocity are related to the periodic magnetospheric substorms and oscillations

eastern beringia and beyond late wisconsinan and holocene landscape dynamics along the yukon coastal plain canada terrestrial permafrost archives along the yukon coastal plain northwest canada have recorded landscape development and environmental change since the late wisconsinan at the interface of unglaciated beringia i e komakuk beach and the northwestern limit of the laurentide ice sheet i e herschel island the objective of this paper is to compare the late glacial and holocene landscape development on both sides of the former ice margin based on permafrost sequences and ground ice analyses at these sites involved a multi proxy approach including sedimentology cryostratigraphy palaeoecology of ostracods stable water isotopes in ground ice hydrochemistry and ams radiocarbon and infrared stimulated luminescence irsl dating ams and irsl age determinations yielded full glacial ages at komakuk beach that is the northeastern limit of ice free beringia herschel island to the east marks the late wisconsinan limit of the northwest laurentide ice sheet and is composed of ice thrust sediments containing plant detritus as young as 16 2 cal ka bp that might provide a maximum age on ice arrival late wisconsinan ice wedges with sediment rich fillings on herschel island are depleted in heavy oxygen isotopes mean delta o 18 of 29 1 parts per thousand this together with low d excess values indicates colder than modern winter temperatures and probably reduced snow depths grain size distribution and fossil ostracod assemblages indicate that deglaciation of the herschel island ice thrust moraine was accompanied by alluvial proluvial and eolian sedimentation on the adjacent unglaciated yukon coastal plain until similar to 11 cal ka bp during a period of low glacio eustatic sea level the late glacial holocene transition was marked by higher than modern summer temperatures leading to permafrost degradation that began no later than 11 2 cal ka bp and caused a regional thaw unconformity cryostructures and ice wedges were truncated while organic matter was incorporated and soluble ions were leached in the thaw zone thermokarst activity led to the formation of ice wedge casts and deposition of thermokarst lake sediments these were subsequently covered by rapidly accumulating peat during the early holocene thermal maximum a rising permafrost table reduced peat accumulation and extensive ice wedge growth resulted from climate cooling starting in the middle holocene until the late 20th century the reconstruction of palaeolandscape dynamics on the yukon coastal plain and the eastern beringian edge contributes to unraveling the linkages between ice sheet ocean and permafrost that have existed since the late wisconsinan

magma and sediment ii problems of interpreting palaeovolcanics buried in the stratigraphic column president9s anniversary address 1982 the preservation of volcanoes never more than partial involves a complex interaction of processes and these operate over periods of time which are often undervalued from a review of the relative rates of these processes it seems that short lived structures such as surtseyan ash rings may be preserved albeit in modified form around their whole circumference for larger composite volcanoes however growth and remoulding by activity is balanced by penecontemporaneous and later erosion in such a way that the central and most of the proximal zones are likely to be removed before they can be buried either by transported volcaniclastic or regional epiclastic sediments even the preservation of distal zones may be asymmetrical a one sided hinge line subsidence sedimentation model is therefore suggested to explain the elongate lens shaped aspects of the many extrusive piles known to lie approximately concordantly within stratigraphic sequences formed in both continental and littoral environments

statistical patterns of high latitude convection obtained from goose bay hf radar observations we have derived patterns that describe the statistical interplanetary magnetic field imf dependencies of ionospheric convection in the high latitude region of the northern hemisphere the observations of plasma motion were made with the hf coherent backscatter radar located at goose bay labrador over the period september 1987 to june 1993 the area covered by the measurements extended poleward of 65 to a working limit of about 85 distributions of electrostatic potential have been derived and expressed as series expansions in spherical harmonics the patterns are the first derived from direct ground based observations of ionospheric convection that approach in completeness and level of detail the patterns derived in recent satellite studies rich and hairston 1994 weimer 1995 we show the dependence of the convection on imf angle in the gsm y z plane for three intervals of imf magnitude in this plane except for predominantly northward imf the convection is primarily two cell the dusk cell is larger in terms of both spatial extent and potential variation the effect of imf by is apparent in the global shaping of the cells and the orientation of the overall pattern in mlt for by by the dusk dawn cell is more round crescent shaped and the pattern more rotated toward earlier mlts the by effect on the nightside convection is pronounced and is hemispherically antisymmetric like the well known day side by effect for imf increasingly northward the convection trajectories on the dayside become increasingly distorted evolving through a three cell to a four cell circulation the additional cells appear on either side of the noon meridian and result in sunward flow the overall agreement with the results of the satellite studies is good and extends to quite fine detail in the case of the comparison with weimer 1995 there are significant differences with the statistical patterns derived from magnetometer measurements which tend to show domination by the dawn rather than the dusk cell

observations of ionospheric convection from the wallops superdarn radar at middle latitudes 1 during geomagnetic storms the ability of the super dual auroral radar network superdarn to measure ionospheric convection becomes limited when the radars suffer from absorption and the auroral disturbance expands equatorward of the radar sites to overcome these shortcomings it was decided to construct a superdarn radar at middle latitudes on the grounds of the nasa wallops flight facility this paper presents the first comprehensive analysis of doppler measurements from the wallops radar which commenced operations in may 2005 wallops measurements are compared with the goose bay radar during the onset of a geomagnetic storm on 31 august 2005 goose bay measured the onset of geomagnetic activity at high latitude while wallops monitored the expansion of convection to middle latitudes average convection patterns binned by the kp geomagnetic index are also presented during weak moderate geomagnetic activity kp 3 the wallops radar observes ionospheric irregularities between 50 and 60 magnetic latitude drifting westward across much of the nightside when these measurements are incorporated into the calculation of an average superdarn convection pattern the streamlines of polar cap outflow on the nightside become kinked in a manner reminiscent of the harang discontinuity this morphology arises quite naturally when the two cell convection at high latitudes merges with the prevailing westward convection at middle latitudes during increased geomagnetic activity kp 3 wallops is able to measure the expansion of auroral electric fields to middle latitudes and the average superdarn cross polar cap potential is increased by 25

on the latitudinal variations of the ionospheric electric field during magnetospheric disturbances a joint alert campaign was organized during the month of october 1980 by the incoherent scatter radars in the american sector namely jicamarca arecibo millstone hill and chatanika the campaign which met with success was designed to study the behavior of the ionospheric electric field as a function of latitude during magnetically active conditions the arecibo data in this campaign support present and previous observations at jicamarca that suggest that when the convection e field suddenly decreases the alfven layer shielding field becomes unbalanced and penetrates the plasmasphere while this type of observation is reasonably convincing others are more difficult to categorize we suggest that beside the high latitude electric fields time varying auroral conductivity models will have to be considered in order to understand the morphology of the low latitude e field disturbances we present the first correlation analysis and determination of the amplitude ratio of the disturbed zonal electric field at 30 geometric latitude arecibo to the field at 0 jicamarca other highlights of the paper are a discussion of dp2 which may help clarify the controversy surrounding it and a discussion of the sensitivity of low and mid latitude radars to disturbances of magnetospheric origin we show that this sensitivity maximizes at the magnetic equator

prompt midlatitude electric field effects during severe geomagnetic storms meridian plane elevation scans with the millstone hill incoherent scatter radar provide evidence of a strong perturbation of the coupled mid latitude magnetosphere ionosphere system during the early phases of the november 4 1993 magnetic storm a narrow ionospheric trough formed at l 3 5 in the pre midnight sector immediately poleward of the millstone hill site the most pronounced radar signature of the developing activity was a brief 20 min uplifting of the f region plasma equatorward of the trough such that the peak altitude increased with distance away from the trough a similar signature had been observed during storm onset on march 20 1990 and in that event a pronounced topside ionospheric depletion developed in the region far equatorward of the mid latitude trough and was observed by the radar and the dmsp f9 satellite during the november 4 1993 event the dmsp f10 satellite observed narrow magnetically conjugate regions of plasma density depletion and strong horizontal and upward plasma velocity 1500 m s at l 1 5 at the time of the uplifting of the mid latitude f region observed by the radar these observations were confined to longitudes near the south atlantic magnetic anomaly and in the nov 1993 case the perturbation was coincident with the peak of the precipitating particle fluxes associated with innerbelt losses at the anomaly both the uplifting of the ionospheric f layer and the triggering of topside density perturbations can be explained in terms of an eastward electric field imposed on the mid and low latitude ionosphere during the initial stages of the geomagnetic storm the low latitude ionospheric perturbations in these events were similar to supersonic equatorial bubbles triggered by the destabilizing effects of the upward e b drift associated with the eastward electric field

penetration of magnetospheric electric fields to the equator during a geomagnetic storm 1 penetration of the magnetospheric electric field to the equatorial ionosphere was examined for the geomagnetic storm on 6 november 2001 by analyzing the difference in magnitude of the geomagnetic storm recorded at the dayside geomagnetic equator yap 0 3 gml and low latitude okinawa 14 47 gml the penetrated electric field caused the dp2 currents at the equator i e eastward currents during the main phase of the storm while the overshielding currents i e westward currents dominated during the recovery phase it is shown that the ring current started to develop simultaneously with the onset of the equatorial dp2 within the temporal resolution of a few minutes these results imply prompt transmission of the dawn to dusk convection electric field to the inner magnetosphere as well as to the equatorial ionosphere it is found that the equatorial dp2 started to decrease one hour after the onset of the ring current development indicating shielding effects becoming effective at the equator during the latter half of the storm main phase the dp2 was then overwhelmed by the overshielding which resulted in the counter electrojet cej in the beginning of the storm recovery phase the image magnetometer chain data indicate that the westward auroral electrojet aej in the dawn sector was driven over midlatitude centered at 57 corrected geomagnetic latitude cgml during the main phase while the aej shifted rapidly poleward to the auroral latitude centered at 67 cgml in the beginning of the recovery phase the overshielding must be caused by the abrupt poleward shift of the rl facs as inferred from the poleward shift of the aej in addition to the decrease in their magnitude due to the decrease in magnitude of the southward imf the geomagnetic storm at the dayside geomagnetic equator was enhanced in amplitude with the ratio of 2 7 as compared with the geomagnetic storm at low latitude this amplification is a result of both effects of the dp2 currents and the cej associated with the main and recovery phases respectively it is suggested that the electric field associated with the dp2 currents contributed to the development of the ring current during the main phase while the overshielding electric field may contribute to cease developing the ring current during the recovery phase

variability of ash deposits at piton de la fournaise la reunion island insights into fragmentation processes at basaltic shield volcanoes 25 it is commonly accepted that effusive activity emplaces the main emitted magmatic volume in basaltic 26 shield volcanoes at piton de la fournaise la reunion island france eruptive activity occurs mostly within the 27 non populated enclos fouque caldera and generally does not pose any risk to the population however historical 28 observations recent monitoring data and field work on tephra deposits suggest that some eruptions have produced 29 unusual and unexpected explosive phases a comprehensive sampling of tephra from major historical and recent 30 eruptions on this volcano allowed us to perform systematic componentry grain size chemical and morphological 31 analyses in order to characterize the eruptive dynamics involved in these explosive basaltic eruptions this 32 integrative approach reveals highly variable characteristics of the studied tephra reflecting different fragmentation 33 efficiencies and multiple associated mechanisms primary ductile and partially brittle fragmentation of various 34 intensity of juvenile magma emitted during hawaiian fountaining or mild strombolian explosions were identified 35 as the most common fragmentation mechanisms in particular during the 2014 2018 dominantly effusive eruptive 36 sequence in parallel we distinguished more efficient short lived fragmentation events related to i plug 37 pressurization and brittle fragmentation enhanced by syn eruptive crystallization ii magma water interactions 38 iii rare phreatic explosions and iv secondary fragmentation producing fine ash during caldera collapse we 39 conclude that textural geochemical and morphological analysis make it possible to identify and characterize the 40 variability in eruptive processes with the grain size and the componentry of the ash particles being probably the 41 most important parameters to quantify both the efficiency and the nature of the fragmentation 42 43

timing of the last glacial maximum from observed sea level minima during the last glacial maximum ice sheets covered large areas in northern latitudes and global temperatures were significantly lower than today but few direct estimates exist of the volume of the ice sheets or the timing and rates of change during their advance and retreat here we analyze four distinct sediment facies in the shallow tectonically stable bonaparte gulf australia each of which is characteristic of a distinct range in sea level to estimate the maximum volume of land based ice during the last glaciation and the timing of the initial melting phase we use faunal assemblages and preservation status of the sediments to distinguish open marine shallow marine marginal marine and brackish conditions and estimate the timing and the mass of the ice sheets using radiocarbon dating and glacio hydroisostatic modelling our results indicate that from at least 22 000 to 19 000 calendar years before present land based ice volume was at its maximum exceeding today s grounded ice sheets by 52 5 x 10 exp 6 cu km a rapid decrease in ice volume by about 10 percent within a few hundred years terminated the last glacial maximum at 19 000 250 years

reconstructing eruption processes of a miocene monogenetic volcanic field from vent remnants waipiata volcanic field south island new zealand the miocene waipiata volcanic field new zealand is an eroded phreatomagmatic intracontinental volcanic field formed during a period of weak lithospheric extension the field includes remnants of at least 55 volcanoes in an area of 5000 km2 vent filling deposits comprising predominantly lava e g plugs necks lava flows or dykes often associated with thin basal phreatomagmatic pyroclastic deposits were classified as type 1 vents and are inferred to be the remnants of scoria cones vents represented by predominantly pyroclastic infill are classified as type 2 vents and are inferred to have been the substructures of phreatomagmatic tuff ring and or maar volcanoes type 3 vent complexes are groups of closely spaced or overlapping vents with voluminous preserved lava flows they are inferred to be the remnants of volcanoes comprising adjoining to coalescing maars and tuff rings with magmatic explosive and effusive products pyroclastic rocks of most of the waipiata vents record initial phreatomagmatic explosive activity fuelled by groundwater followed by strombolian style eruptions aligned and clustered vents are accommodated to structural features of the regional basement rock otago schist

dynamic variations of a convection flow reversal in the subauroral postmidnight sector as seen by the superdarn hokkaido hf radar 1 the superdarn hokkaido hf radar capable of measuring the subauroral ionospheric plasma convection especially during storms has been in continuous operation since the beginning of december 2006 we report the first two dimensional observation of a dynamic variation of convection flow reversal in subauroral postmidnight sector during the storm main phase on 29 january 2007 the flow reversal region is extended over 20 in longitude and 5 in latitude lasting for about 10 15 min and the maximum flow speed is about 0 5 1 0 km s the flow reversal structure is reasonably reproduced by the ring current simulation coupled with the ionosphere suggesting that it is produced by the region 2 field aligned current associated with the ring current enhancement during the storm main phase the dynamic variation of the flow reversal structure is interpreted as a transient eastward extension of the elongated dusk convection cell to the postmidnight and equatorward of the dawn cell associated with the variation of the ring current whose structure is controlled by the interplanetary magnetic field and solar wind dynamic pressure it is suggested that the ring current variation is highly coupled with the interplanetary parameters and is much more complicated than ever thought

time evolution of the subauroral electric fields a case study during a sequence of two substorms 1 the temporal evolution of the subauroral polarization stream saps is investigated using the doppler velocity observations by the unwin hf radar in conjunction with the simultaneously observed auroral luminosity and plasma convection reversal regions the event under study of 14 december 2004 1000 1600 ut occurred during geomagnetically quiet conditions when a sequence of two substorms separated by 2 hours was observed by the image satellite it is shown that the saps appeared shortly after the first substorm onset and continued to dominate the westward plasma convection at subauroral magnetic latitudes 59 63 s for 6 hours an unexpected exception occurred near the second substorm onset time when a narrow channel of weaker saps westward convection became embedded in the slow eastward drifting plasma for a short 25 min period which was attributed to the equatorward expansion of the dawn convection cell during the growth and expansion phases of the second substorm another remarkable plasma convection feature was observed in the same 25 min period 5 poleward of saps this was a narrow mirror channel of the eastward drifting plasma parallel to the main saps channel it is argued that the latter feature may also be caused by the equatorward expanding dawn convection cell whose streamlines become compressed by and aligned with the saps poleward edge a possible relationship between the saps intensity and its position relative to the auroral oval is also investigated the results suggest that the magnetosphere ionosphere feedback processes within saps become more effective as the equatorward edge of the eastward convection region retreats poleward with the saps position much less affected by the auroral dynamics

two new ordovician volcanic centres in the shelve inlier powys wales summary as a direct result of new work in the shelve ordovician inlier two new important extrusive andesitic members of a revised stapeley volcanic formation are described these members were originally regarded as extrusive however they have for over half a century been considered intrusive and a brief literature review attempts to account for this anomaly a palaeogeographic reconstruction suggests that the members represent the remains of two llanvirn volcanic islands which following subsidence were overlapped and buried by later llanvirn sedimentation this reinterpretation considerably increases the volume of andesitic material known to have been erupted in llanvirn times in this part of the welsh borderland

solar cycle and seasonal variations in f region electrodynamics at millstone hill incoherent scatter radar observations of ion drifts taken at millstone hill 42 6 degrees n 288 5 degrees e during 73 experiments in the period february 1984 to february 1992 are used to construct for the first time at this station average quiet time exb drift patterns for both solar cycle maximum and minimum for the summer winter and equinox seasons the daily variation of v sub perpendicular n shows a reversal from northward to southward drifts near noon and a return to northward drifts in the premidnight hours the weaker southward drift in the afternoon in summer noted by wand and evans is shown to occur only at sunspot minimum the daily variation of v sub perpendicular e shows daytime eastward drifts and nighttime westward drifts except in summer when the usual daytime eastward maximum near 1200 lt is suppressed the daily mean drift is westward for all seasons and is largest in summer the daytime eastward drift and nighttime westward drift tend to be stronger at solar maximum than at solar minimum average drift patterns are also constructed for equinox for both extremely quiet and geomagnetically disturbed periods v sub perpendicular n is appreciably more northward under extremely quiet than under disturbed conditions in the postmidnight and morning periods during extremelymore quiet periods v sub perpendicular e turns slightly eastward in the evening hours while it is strongly westward for disturbed conditions this result contrasts with the strong eastward drifts in the evening in summer reported for extremely quiet conditions at millstone hill by gonzalez et al a strong anticorrelation is seen at millstone hill between v sub perpendicular n and v sub parallel as is found at lower latitude stations the quiet time patterns are discussed in terms of the causative e and f region dynamo mechanisms 39 refs 6 figs 2 tabs less