magnetic fabrics of the miocene ignimbrites from west cameroon implications for pyroclastic flow source and sedimentation abstract the miocene ignimbrites of mounts bambouto and bamenda located in the central part of cameroon volcanic line are generally made of welded and non welded massive lapilli tuff and lithic breccias these discontinuous deposits cover a total area of 180 km 2 with thickness ranging from 25 to 200 m the different facies contain several lithic fragments of mainly trachytic nature the devitrified matrix of the welded ignimbrites is constituted by sanidine anorthoclase quartz plagioclase clinopyroxene biotite fe ti oxides and devitrified fiammes anisotropy of magnetic susceptibility ams is used to characterize magnetic fabrics and to provide an estimate of flow direction of each ignimbrite sheet magnetic mineralogy results from different flow units show that titanomagnetite titanohematite maghemite and goethite with grain size ranging from coarse md to very fine sp are the main magnetic carriers of these ignimbrites inferred transport directions based on the ams data and field indicators show that bambouto caldera is the source of main pyroclastic deposits of mount bambouto in southwestern mount bamenda santa mbu caldera or bambouto caldera constituted the probable emission center of mbengwi bamenda and mbu ignimbrite sheets whereas magnetic fabrics of bambili sabga and big babanki ignimbrites demonstrate that these deposits were emitted from a northeastern source namely oku vent in mount oku a small number of subvertical ams fabrics correspond to rocks possibly modified by an elutriation process

eruptive processes and caldera formation in a nested downsagcollapse caldera cerro panizos central andes mountains abstract the cerro panizos ignimbrite center in the central andes mountains produced two ignimbrite sheets and many lava flows the ignimbrite of quebrada cienago was erupted at 7 9 ma and effusive eruptions continued until the two cooling units of the crystal rich dacitic cerro panizos ignimbrite were emplaced at 6 7 ma the lower unit has no laterally continuous flow breaks and was erupted from a single vent or small cluster of vents with limited fluctuation in discharge lithic fragments reach significant concentrations 5 only in the uppermost two meters of this cooling unit where they document vent wall collapse or the opening of a new vent the upper cooling unit contains many flow units with variations in welding thicknesses and lithic fragment concentrations implying an unsteady eruption column the opening of many vents and probable caldera collapse triangulation of anisotropy of magnetic susceptibility flow direction measurements locate a single vent for the lower cooling unit whereas the upper cooling unit had many vents within the present dome cluster a 15 km diameter topographic depression marked by inward dips of 4 8 at the cooling unit contact is centered on the vent area of the lower cooling unit the depression is interpreted as a downsag caldera formed during emplacement of the lower cooling unit collapse began late in the eruption of the lower cooling unit and continued through the emplacement of the upper cooling unit resurgent magmatism occurred as lava flows that mundated the caldera area a ring of dacite domes erupted until at least 6 1 ma in the northern half of the downsag caldera traces the margin of a collapse caldera associated with the upper cooling unit maximum caldera subsidence 353 km 3 is not enough to account for the erupted volume 652 km 3 dre minimum the ash poor crystal rich nature up to 50 crystals in the pumice 75 in the matrix of the cerro panizos pyroclastic flows resulted in poor retention of gases and there is little evidence of fluidization the high crystal content however favored modified grain flow processes in which several particle support mechanisms combine with grain dispersive forces it is postulated that the flows were initially partially fluidized but rapidly lost their gases and grain flow processes grew in relative importance grain flow processes destroyed evidence of fluidization before deposition

a comparison of high resolution seismic methods for determining seabed velocities in shallow water the ability to resolve both the seismic velocity of the seabed in shallow water and the lateral variability of these measured velocities using four conventional seismic methods is compared the four methods described here differ in the ease and efficiency in which the field data are collected and interpreted and in the resolution of the velocity of the seabed they provide narrow aperture refraction studies provide limited constraints due to the frequent absence of first arriving sediment refractions in the narrow portion of the wave field that is sampled wide aperture refraction experiments using ocean bottom seismometers provide high resolution of both the compressional and shear wave velocities of the seabed but are time consuming to perform and to interpret narrow aperture multichannel reflection data are easily collected and are ideal for areal mapping of sedimentary sequences but resolution of seismic velocities is low unless the aperture of the multichannel streamer is several water depths in

turbulent transport and deposition of the ito pyroclastic flow determinations using anisotropy of magnetic susceptibility the ito pyroclastic flow erupted about 22 000 years ago from aira caldera in southern kyushu japan flow directions were determined by anisotropy of magnetic susceptibility ams which measured the preferential alignment of magnetite microphenocrysts usually 0 25 mm in diameter the microphenocrysts are aligned with the long axis of the clasts during strain and fracture in the vent the grains are then deposited parallel to the flow direction with an imbrication there is no evidence of rolling of clasts or nonflow parallel lineations and thus ams can be used to determine flow directions that occurred immediately before deposition beyond 30 km from the center of the caldera flow directions were predominantly down paleogradient indicating expanded flow and that the depositional system was gravity driven and largely decoupled from the transport system within 30 km measured flow directions are random indicating that sedimentation occurred from a depositional system that was closely coupled to the turbulent transport system individual flow directions at all sites except one varied more than the analytical error demonstrating that a variety of flow directions existed even within a small area of the flow this implies that the depositional system was turbulent

the anisotropy of magnetic susceptibility in biotite muscovite and chlorite single crystals the anisotropy of magnetic susceptibility ams of single crystals of biotite muscovite and chlorite has been measured in order to provide accurate values of the magnetic anisotropy properties for these common rock forming minerals the low field ams and the high field paramagnetic susceptibility are defined for the high field values it is necessary to combine the paramagnetic deviatoric tensor obtained from the high field torque magnetometer with the paramagnetic bulk susceptibility measured from magnetization curves of the crystals this leads to the full paramagnetic susceptibility ellipsoid due to the anisotropic distribution of iron cations in the silicate lattice the ellipsoid of paramagnetic susceptibility which was obtained for the three phyllosilicates is highly oblate in shape and the minimum susceptibility direction is subparallel to the crystallographic c axes the anisotropy of the susceptibility within the basal plane of the biotite has been evaluated and found to be isotropic within the accuracy of the instrumental measurements the degree of anisotropy of biotite and chlorite is compatible with previously reported values while for muscovite is smaller than previously published values the shape of the chlorite ams ellipsoid for all the samples is near perfect oblate in contrast with a wide distribution of oblate and prolate values reported in earlier studies reliable values are important for deriving models of the magnetic anisotropy where it reflects mineral fabrics and deformation of rocks d 2003 elsevier science b v all rights reserved

the holocene secche di lazzaro phreatomagmatic succession stromboli italy evidence of pyroclastic density current origin deduced by facies analysis and ams flow directions the edifice of stromboli volcano gravitationally collapsed several times during its volcanic history 100 ka present the largest holocene event occurred during the final stage of the neostromboli activity 13 5 ka and was accompanied by the emplacement of phreatomagmatic and lahar deposits known as the secche di lazzaro succession a stratigraphic and paleomagnetic study of the secche di lazzaro deposits allows the interpretation of the emplacement and the eruptive processes we identify three main units within the succession that correspond to changing eruption conditions the lower unit ua consists of accretionary lapilli rich thinly bedded parallel to cross stratified ash deposits interpreted to indicate the early stages of the eruption and emplacement of dilute pyroclastic density currents upward the second unit ub of the deposit is more massive and the beds thicker indicating an increase in the sedimentation rate from pyroclastic density currents the upper unit uc caps the succession with thick immediately post eruptive lahars which reworked ash deposited on the volcano s slope flow directions obtained by anisotropy of magnetic susceptibility ams analysis of the basal bed of ua at the type locality suggest a provenance of pyroclastic currents from the sea this is interpreted to be related to the initial base surges associated with water magma interaction that occurred immediately after the lateral collapse which wrapped around the shoulder of the sector collapse scar upward in the stratigraphy upper beds of ua and ub paleoflow directions change and show a provenance from the summit vent probably related to the multiple collapses of a vertical pulsatory eruptive column

mineralogical control on the magnetic anisotropy of lavas and ignimbrites a case study in the caviahue copahue field argentina

paleoflow directions of a subaqueous lahar deposit around the miocene keserűs hill lava dome complex north hungary as constrained by photo statistics and anisotropy of magnetic susceptibility ams abstract a twofold fabric analysis by using photo statistics on rock surfaces and low field anisotropy of magnetic susceptibility ams is presented making it possible to infer paleoflow directions which in turn helps to constrain the primary volcanic geomorphology of a deeply eroded mid miocene field keser s hill lava dome group visegrad mountains north hungary the analyses were carried out on the ram hill pumiceous sandstone rhps that based on its petrographic features is considered as a subaqueously emplaced laharic deposit the observed anisotropic frequencies of clast a axis azimuths the good agreement of fabric directions obtained for all and most elongated samples elongation 2 5 the good clustering of the declinations of the k1 susceptibilities largely corresponding with the result of image analysis allow to infer reliable flow directions the obtained large scale paleoflow paths show a quasi radial pattern around the central part of the visegrad mountains which quantitatively confirms the previous hypothesis on the volcanic structure namely a central edifice topped syn eruptive topography the rhps is characterized by a clast fabric revealed by photostatistics on cutted rock surfaces considering the lapilli sized fraction as strong as in subaerial pdc deposits but by a significantly weaker magnetic fabric the weak magnetic fabric is supposed to be the result of rock heterogeneity thus the weakening effect of abundant lithic clasts with strong internal magnetic susceptibility anisotropy different from the shape anisotropy of the clasts and the flow related magnetic fabric of the fine grained matrix

a comparison of broadband and narrow band modal inversions for bottom geoacoustic properties at a site near corpus christi texas detailed comparison between narrow band and broadband techniques used in a series of acoustic experiments are presented with emphasis on a comparisons of the pressure field versus range predicted b comparisons of the bottom compressional wave speed model generated c the variance of the bottom model estimated and d the resolution of the bottom model generated the range dependence of the bottom medium and the seasonal dependence of the near surface sediment sound speed profile are observed and discussed

sequential inversion of modal data for sound attenuation in sediment at the new jersey shelf this paper presents a method for estimating bottom geoacoustic properties especially the sediment attenuation from information contained in normal modes of a broadband signal propagating modes are resolved using the time warping technique applied to signals from light bulb sound sources deployed at ranges of 5 and 7 km in the shallow water 06 experiment a sequential inversion approach is designed that uses specific features of the acoustic data that are highly sensitive to specific geoacoustic model parameters the first feature is the modal group speed which is inverted for seabed sound speed density and sediment thickness the second feature is the modal depth function for inverting receiver depths the third feature is related to the modal coefficient spectra and this is inverted for source depth and sediment attenuation in each subsequent stage estimates from the previous stage s are used as known values the sequential inversion is stable and generates estimates for the geoacoustic model parameters that agree very well with results from other experiments carried out in the same region notably the inversion obtains an estimated attenuation of 0 078 db in the band 120 180 hz for the de watered marine sediment characteristic of the continental shelf at the site

geoacoustic inversion using combustive sound source signals in the summer of 2006 combustive sound sources css were deployed in shallow waters off new jersey during the shallow water experiment sw 06 the depth of these sources were 26 m in water depths of the order of 100 m css are low frequency broadband sound sources and suitable for modal dispersion based inversion css data collected on various receivers single hydrophone receiving units shru vertical line array etc will be used for the inversions the inversions are based on an iterative scheme using a new time frequency analysis technique dispersion based short time fourier transform in which each time frequency tiling is adaptively rotated in the time frequency plane depending on the local wave dispersion data from various receivers will be used to investigate the spatial variation in compressional wave speed compressional wave attenuation will also be estimated using modal amplitude ratios inversion results will be validated by comparing the data with model predictions work supported by the office of naval research

tomographic inversion for sediment parameters in shallow water this article discusses inversions for bottom geoacoustic properties using broadband acoustic signals obtained from explosive sources the experimental data used for the inversions are sus charge explosions acquired on a vertical hydrophone array during the shelf break primer experiment conducted south of new england in the middle atlantic bight in august 1996 the sus signals were analyzed for their time frequency behavior using wavelets the group speed dispersion curves were obtained from the wavelet scalogram of the sus signals a genetic algorithm ga was used for the inversion of sound speeds in the water column and compressional wave speeds in the sediment layers the variations in the sound speeds in the water column were represented using empirical orthogonal functions eofs a range independent normal mode routine was used to construct the replica fields corresponding to the parameters comparison of group speeds for modes 1 to 9 and for a range of frequencies 8 to 200 hz was used to arrive at the best parameter fit an efficient hybrid optimization scheme using the ga and a levenberg marquardt algorithm is presented linear perturbation methods were also used to fine tune the inversions and to obtain resolution and variance estimates analysis was also done to compute the degree of convergence of each of the parameters by explicitly calculating the hessian matrices numerically a posteriori estimation of mean and covariance was also done to obtain error estimates group speeds for the inverted sound speed fields provide an excellent match to the experimental data the inverted sediment compressional speed profile compares well with in situ measurements

low frequency sound speed and attenuation in sandy seabottom from long range broadband acoustic measurements a joint china u s underwater acoustics experiment was conducted in the yellow sea with a very flat bottom and a strong and sharp thermocline broadband explosive sources were deployed both above and below the thermocline along two radial lines up to 57 2 km and a quarter circle with a radius of 34 km two inversion schemes are used to obtain the seabottom sound speed one is based on extracting normal mode depth functions from the cross spectral density matrix the other is based on the best match between the calculated and measured modal arrival times for different frequencies the inverted seabottom sound speed is used as a constraint condition to extract the seabottom sound attenuation by three methods the first method involves measuring the attenuation coefficients of normal modes in the second method the seabottom sound attenuation is estimated by minimizing the difference between the theoretical and measured modal amplitude ratios the third method is based on finding the best match between the

magnetic versus crystallographic fabrics in a basaltic lava flow combined anisotropy of magnetic susceptibility ams and crystallographic studies were performed within a quaternary lava flow for which we have a thorough knowledge of the flow direction microscope examinations microprobe analyses and studies of rock magnetic properties show that ams is carried by homogeneous multidomain ti rich titanomagnetite xc0 6 this mineral forming either subhedral isolate individuals or grouped in various elongated aggregates represents a late crystallized interstitial phase ams determined from samples collected in the lower the middle and the upper part of the flow is characterized by a well defined magnetic foliation whereas magnetic lineation is generally poorly grouped and therefore meaningless the foliation plane of the lower and upper part of the flow show an obliquity which is interpreted as an opposite imbrication indicating a westward flow in agreements with the known flow direction in the lower part of the lava flow the tight correlation between ams and plagioclase lattice preferred orientation suggests that a silicate framework control the titanomagnetite crystallization and thus the orientation of the ams ellipsoid d 2005 elsevier b v all rights reserved

rock magnetism and compositional investigation of brown tuffs deposits at lipari and vulcano aeolian islands italy abstract a rock magnetic investigation was carried out on the nonwelded ash deposits of the brown tuffs aeolian islands southern tyrrhenian sea to improve the stratigraphic correlation between the deposits cropping out on lipari and vulcano islands and locate their source area the study was supplemented by petrographical and geochemical analyses on selected strata with the intent to compare the brown tuffs to other rocks emplaced at vulcano in the same time span more than 30 levels were sampled in the intermediate 56 4 ka ibt 21 22 ka and upper 21 22 ka ubt parts of the brown tuffs sequences on the two islands their characteristic remanent magnetization chrm directions were derived from stepwise thermal demagnetization and the magnetic fabric from measurements of the anisotropy of magnetic susceptibility the levels with indistinguishable chrm directions were regarded as coeval and to form an individual stratigraphic unit the units were referred to the brown tuffs sequence of lucchi et al 2008 on the grounds of their emplacement age provided by comparison of their mean paleomagnetic direction with the paleosecular variation curves of the southern tyrrhenian region as well as the field constraints the closer correlation between the sequences of lipari and vulcano contributes to a better understanding of the volcanic activity that produced the brown tuffs and shows that most of the ibt and the oldest ubt levels were emplaced in a short time span between 24 and 20 17 ka the magnetic fabric is typically well developed but at most sites the magnetic foliation is very close to horizontal and no imbrication is defined the source area of the brown tuffs parent pyroclastic flows as constrained from the intersection of the magnetic lineations falls in the northeastern part of la fossa caldera structure although limited to major elements compositional data provide further indication about the parent plumbing system and its behaviour magma batch es involved in the ibt eruptions have homogeneous features and underwent frequent refilling and tapping processes conversely those involved in the early ubt eruptions are compositionally more variable this suggests more complex evolution and plumbing system activity the ubt eruptions represent either residual mafic magmas from the previous eruptions or the arrival of new fresh shoshonitic magma in the system

glacier runoff and its impact in a highly glacierized catchment in the southeastern tibetan plateau past and future trends we investigate past and future trends in glacier runoff and the associated hydrological impacts on river runoff in the hailuogou catchment a highly glacierized catchment with extensive debris cover in the southeastern tibetan plateau using a catchment scale glacio hydrological model past trends in various runoff components of the catchment indicate that glacier runoff has been a large component of total runoff contributing similar to 53 4 of total runoff during the period 1952 2013 future changes in runoff calculated using the outputs of ten global climate models for representative concentration pathway rcp 4 5 and rcp8 5 reveal that glacier runoff plays different roles in the water supply of the catchment for the two rcps and the discrepancies between the two rcps increase in the second half of this century leading to a considerable difference in the hydrological regime of the catchment in particular changes are more remarkable under rcp8 5 under which all glaciers are projected to retreat dramatically and total runoff to decrease slightly by the end of this century an experimental analysis in which no debris cover is assumed on glacier ablation zones indicates that excess meltwater from the debris covered area provides an 8 1 increase in total runoff relative to the no debris assumption case

magnetic fabrics of the bloodgood canyon and shelley peak tuffs southwestern new mexico implications for emplacement and alteration processes anisotropy of magnetic susceptibility ams of the middle tertiary bloodgood canyon and shelley peak tuffs of the mogollon datil volcanic field has been used to 1 evaluate the ability of ams to constrain flow lineations in low susceptibility ash flow tuffs 2 establish a correlation between magnetic fabric magnetic mineralogy tuff facies and characteristics of the depositional setting and 3 constrain source locations of the tuffs the tuffs are associated with the overlapping bursum caldera and gila cliff dwellings basin the high silica bloodgood canyon tuff fills the gila cliff dwellings basin and occurs as thin outcrops outside of the basin the older shelley peak tuff occurs as thin outcrops both along the boundary between the two structures and outside of the complex ams data were collected from 16 sites of bloodgood canyon tuff basin fill 19 sites of bloodgood canyon tuff outflow and 11 sites of shelley peak tuff sites were classified on the basis of within site clustering of orientations of principal susceptibility axes based on the categories of knight et al 1986 most microscopically visible oxide minerals in the bloodgood canyon tuff outflow and basin fill and in the shelley peak tuff are members of the hematite ilmenite solid solution series however irm acquisition data indicate that bloodgood canyon tuff basin fill and shelley peak tuff have magnetic mineralogy dominated by single or pseudo single domain magnetite and that the magnetic mineralogy of the bloodgood canyon tuff outflow is dominated by hematite hematite in bloodgood canyon tuff outflow is likely to be the result of deuteric and or low temperature alteration of magnetite and iron silicate minerals bulk magnetic susceptibility is higher in magnetite dominated ash flow tuff bloodgood canyon tuff basin fill and shelley peak tuff than it is in hematite dominated ash flow tuff bloodgood canyon tuff outflow bloodgood canyon tuff outflow has the highest total anisotropy h of the three units followed by shelley peak tuff and bloodgood canyon tuff basin fill all three ash flow tuffs are genearlly characterized by oblate susceptibility ellipsoids with those of the bloodgood canyon tuff basin fill nearest to spherical at high values of total anisotropy shelley peak tuff susceptibility ellipsoids attain a prolate shape those of bloodgood canyon tuff outflow attain an increasingly oblate shape three factors may influence differences in total anisotropy and susceptibility ellipsoid shape 1 ash which travelled the greatest distance before deposition may show the best development of magnetic fabric particularly of magnetic lineation 2 deposition of ash in a closed basin may inhibit laminar flow throughout the sheet and the resulting development of flow textures and 3 replacement of magnetite and iron silicates preferentially oriented within the foliation plane by hematite with strong crystalline anisotropy may enhance the magnetic susceptibility within that plane scatter in ams axis orientation within sites may result from 1 greater orientation inaccuracy in block sampled than in fielddrilled samples 2 rheomorphism and 3 low accuracy of ams measurement in low susceptibility ashflow tuffs evaluation of flow lineation based on ams of sites with well clustered k1 axes indicates that 1 bloodgood canyon tuff basin fill flowed along a generally northwest southeast azimuth 2 shelley peak tuff located on the boundary of the bursum caldera and the gila cliff dwellings basin flowed along a nearly east west azimuth and 3 bloodgood canyon tuff outflow sites have k1 susceptibility axes generally radial to the bursum gila cliff dwellings complex but within site scatter of k1 orientations is generally too large to draw conclusions about flow lineation orientation limited petrographic work on pilot thin sections adds flow direction information to ams derived flow lineation information

geochemical and petrological evidence of the subduction of delaminated adriatic continental lithosphere in the genesis of the neogene quaternary magmatism of central italy abstract serri g innocenti f and manetti p 1993 geochemical and petrological evidence of the subduction of delaminated adriatic continental lithosphere in the genesis of the neogene quaternary magmatism of central italy in m j r wortel u hansen and r sabadini editors relationships between mantle processes and geological processes at or near the earth s surface tectonophysics 223 117 147 the neogene quaternary magmatism of the northern apenninic arc took place in four phases separated in space and time which become progressively younger from west to east phase i 14 ma phase ii 7 3 6 0 ma phase iii 5 1 2 2 ma phase iv 1 3 0 1 ma this magmatism is the result of the activation of three physically separate sources 1 the adriatic continental crust extracted from the mantle in the late proterozoic 2 a strongly refractory recently k enriched harzburgitic mantle located in the mechanical boundary layer mbl of the lithosphere and 3 a recently metasomatized cpx rich mantle compositionally variable from iherzolite to wehrlite clinopyroxenite interpreted as an ephemerally k enriched asthenosphere the adriatic continental crust is the dominant source of the acid plutonic and volcanic rocks of the tuscan region the acid magmatism is mostly found inside an ellipsoidal area about 150 300 km centred on giglio island here defined as the tuscan crustal dome within this area mantle derived magmas unaffected by important crustal contamination processes and mixing with crustal anatectic melts have so far not been found pure crustal magmas are rare but are represented for example by some of the san vincenzo and roccastrada rhyolites virtually all the tuscan acid centres show evidence of mixing with potassic mantle derived magmas major and trace elements as well as 87 sr 86 sr and 143 nd 144 nd data on primitive rocks mg 65 reveal two groups of mantle derived magmas these define two distinct mantle enrichment trends both essentially due to the additions of k rich components which metasomatized separate compositionally diverse upper mantle sectors in both cases the most remarkable mineralogical effect of these enrichment processes is the production of variable amount of phlogopite through reaction between fluids and or melts with the mantle the rocks of group i ol hy and q normative lamproites ultrapotassic high mg latites ultrapotassic shoshonites and shoshonites saturated trend are considered to be derived by partial melting at low pressure 87 sr 86 sr 0 717 ce sr 0 3 and k 2 o na 2 o 6 7 and low ratios of 143 nd 144 nd 0 5121 0 5120 and ba la 87 sr 86 sr 0 712 and k 2 o na 2 o 8 9 values and low 143 nd 144 nd ba la 0 10 ratios these constraints do not allow to exclude a complete identity between the k rich components which metasomatized the mantle sources of the saturated and undersaturated trend magmas the geochemical and isotopic features of the components that metasomatized the mantle sources of the northern apenninic arc magmatism can be explained by a geodynamic process which causes a large amount of crustal materials to be incorporated within the upper mantle we propose that the delamination and subduction of the adriatic continental lithosphere related to the still ongoing northern apennine continental collision provide a viable mechanism to explain the genesis and eastward discontinuous migration of the magmatism in central italy the subduction of delaminated lithospheric mantle with lower crustal slivers would have exposed uppermost mantle adriatic mbl and crustal units previously imbricated in the apennine chain to the heating advected by the upwelling of a recently and ephemerally k enriched asthenospheric mantle wedge and by the underplating of magmas derived from it we consider that the diapiric uprising of a hot crustally contaminated asthenosphere occurs in the wake left above the sinking of the adriatic delaminated subducting continental lithosphere the delamination subduction process of the adriatic lithosphere has probably started in the early middle miocene but earlier than 15 14 ma ago as indicated by the age and petrologic characteristics of the first magmatic episode sisco lamproite of the northern apennine orogenesis

structural evolution of the pleistocene cimini trachytic volcanic complex central italy structural geomorphological geophysical and volcanological data have been processed for the implementation of a dedicated gis through which the structural evolution of the pleistocene trachytic cimini volcano central italy has been reconstructed the evolution of the cimini complex includes three main close in time phases 1 intrusion of a shallow laccolith rising along nw and ne trending faults and stagnating at the contact between the mesozoic cenozoic and the pliocene pleistocene sedimentary units constituting the bedrock of the volcano 2 emplacement of lava domes along radial and tangential fractures formed by the swelling induced by the laccolith growth 3 ignimbrite eruptions and final effusion of olivine latitic lavas domes are both of pelean and low lava dome type and their morphology was controlled by the location on the inclined surface of the swelled area some domes show to have uplifted upper pliocene thermally metamorphosed clay sediments suggesting a cryptodome like growth comparison of the top of the mesozoic cenozoic units with the top of the upper pliocene pleistocene sedimentary complex suggests that the laccolith emplaced in a graben of the mesozoic cenozoic sedimentary complex filled by the pliocene pleistocene sediments uplifted by the shallow intrusion stress patterns acting on the cimini area have been deduced analysing the drainage network and the morphotectonic lineaments rose diagrams show a large dispersion of the lineaments reflecting the local presence of radial and tangential fractures the most frequent extensional nw and ne trending lineaments have regional significance and controlled the magma uprise leading to the laccolith emplacement

orientation of logs in the taupo ignimbrite as an indicator of flow direction and vent position the taupo ignimbrite is an unwelded rhyolitic ignimbrite that originated about 1 820 yr ago from an eruptive vent within lake taupo in the taupo volcanic zone new zealand this ignimbrite is rich in carbonized plant matter including many logs the logs lie subhorizontally throughout all levels of the ignimbrite but are especially common in the lower half regionally the logs show a strong radial orientation indicating flow directions and position of the source vent log orientation is thus a reliable indicator of vent position

anisotropy of magnetic susceptibility in relation to source vents of ignimbrites empirical observations the anisotropy of magnetic susceptibility ams of young undeformed ashflow deposits e g bishop tuff california bandlier tuff new mexico show alignment of the maximum axis of magnetic susceptibility kmax with inferred flow lines the sense of flow is deduced from the predominant plunge bias of kmax axes these principles are discussed in relation to four deformed settings of ashflow deposits in the great basin of the western united states the magnetic susceptibility data provide valuable but not always unambiguous insight into probable source areas various complications arise in interpreting the ams data in terms of flow directions but these can be reduced by integration with geologic observations

anisotropy of magnetic susceptibility studies of depositional processes in the campanian ignimbrite italy the late pleistocene trachytic campanian ignimbrite underlies much of the campanian plain near naples italy and occurs in valleys in the mountainous area surrounding the plain out to about 80 km from its source the campi flegrei caldera at sites within 15 km of the campi flegrei anisotropy of magnetic susceptibility ams principal directions indicate that in the absence of significant topography deposition came from a flow moving in a roughly radial direction ams studies of the more distal ignimbrite reveal downhill and or downvalley flow directions prior to deposition even where these directions are at high angles to a generally radial transport direction from the vent on the flanks of roccamonfina volcano flow was directly downhill as if the source of the ignimbrite was the summit of the volcano in most localities the ignimbrite consists of a single massive deposit in a few localities in the apennine mountains however the confluence of multiple drainage systems off mountains resulted in multiple local flow units that cannot be correlated between valleys a detailed study of the ignimbrite in the flat titerno river valley near massa shows that the ams fabrics are not due to late stage creeping during deposition or compaction well defined but non parallel ams fabrics from vertical and lateral sections in the massa area are best explained by the merging of gravity currents flowing down the valley and steep valley sides to form a single aggradational deposit clast compositions and ams axes at mondragone indicate that the pyroclastic flow encountered the monte massico massif and was partially blocked so that flow during deposition was toward the campi flegrei similar ams data from sites along the edge of the campanian plain indicate back flow off the first ridge of the apennine mountains reached at least 5 km from their base the campanian ignimbrite was deposited from a density stratified pyroclastic flow the depositional system consisted of the lower denser portion of the current and was controlled by topography the grouping of the ams axes is interpreted to indicate that deposition occurred under laminar flow conditions

syn depositional substrate deformation produced by the shear force of a pyroclastic density current an example from the pleistocene ignimbrite at monte cimino northern lazio italy substrate deformation by pyroclastic density currents is very sparsely described in the literature the rare occurrence of syn depositional substrate deformation suggests that special circumstances are required to transmit shear from the base of a pyroclastic density current into the deposited ignimbrite and the substrate one example of a substrate deformed by a pyroclastic density current is found at the base of the pleistocene ignimbrite at monte cimino central italy a series of reverse faults that offsets the basal contact were produced by the shear force of the pyroclastic current during deposition of the ignimbrite the faults formed on the vent facing side of a palaeo slope that strikes sub parallel to the flow direction of the pyroclastic current fault offsets suggest motion was parallel to the flow direction of the pyroclastic current rather than down slope we propose that these faults resulted from fluctuations in the shear force of the pyroclastic density current as it was channelled down a palaeovalley the lower flow boundary which separated the deposited ignimbrite and the substrate from the moving pyroclastic density current momentarily stepped down into the substrate so that the upper 0 5 m of the substrate and about 1 5 m of the deposited ignimbrite became incorporated into the current this momentary coupling of the current and the substrate induced reverse faulting in the substrate and the deposited portion of the ignimbrite deposition appears to have been ongoing during the formation of these faults as well as afterward following the formation of the faults the lower flow boundary seems to have been quickly re established above the faults approximately 1 5 m above the base of the ignimbrite allowing deposition to continue without further deformation of the substrate

multi decadal ice velocity and elevation changes of a monsoonal maritime glacier hailuogou glacier china digital elevation models dems of the ablation area of hailuogou glacier china produced from advanced spaceborne thermal emission and reflection radiometer aster data obtained in 2009 differential gps dgps data surveyed in 2008 and aerial photographs acquired in 1966 and 1989 are differenced to estimate long and short term glacier surface elevation change dh dt the mean dh dt of the ablation area over 43 years 1966 2009 is 1 1 0 4 m a 1 since 1989 the thinning has accelerated significantly ice velocities measured by dgps at 28 fixed stakes implanted in the ablation area increase with distance from the glacier terminus ranging from 41 0 m a 1 approaching the glacier terminus to a maximum of 205 0 m a 1 at the base of an icefall our results reveal that the overall average ice velocity in the ablation area has undergone significant temporal variability over the past several decades changes in glacier surface elevation in the ablation area result from the combined effects of climate change and glacier dynamics which are driven by different factors for different regions and periods

the origin of tectonic lineation in extensional basins combined neutron texture and magnetic analyses on undeformed clays abstract in extensional sedimentary basins fine grained sediments that appear undeformed at the outcrop scale can carry a magnetic fabric consistent with the regional deformation pattern the origin of the magnetic lineation which is often found in extensional basins is not yet well understood in clays from extensional basins in southern italy the magnetic lineation is tectonically controlled and oriented perpendicular to the main normal faults a combined analysis of magnetic and mineral fabrics was made to gain insight into the processes that lead to a lineation in extensional settings low field high field and low temperature susceptibility measurements were used to distinguish the ferrimagnetic and paramagnetic contributions to the magnetic susceptibility and its anisotropy the magnetic anisotropy of the sediments is predominantly carried by paramagnetic phyllosilicates neutron texture analysis was used to evaluate the spatial distribution of chlorite basal planes results demonstrate that the orientation of the magnetic lineation is related to the spatial distribution of chlorite lying parallel to the common axis of differently oriented basal planes a quantitative correlation between the magnetic and rock fabric was made comparing the low and high field magnetic anisotropy ams hfa to the theoretical anisotropy calculated from the chlorite preferred orientation a good linear correlation is found between the degree of theoretical anisotropy and the ams and hfa results show that the integrated approach of magnetic and mineral fabric investigations represents a valid alternative tool for detecting grain scale and regional deformation patterns in weakly deformed extensional basins where macroscopic evidence of deformation is often not visible

magnetic fabric and implications for pyroclastic flow and lahar emplacement albano maar italy 1 the albano polygenetic maar is the youngest eruptive center of the quiescent colli albani volcano located near the city of rome the most recent activity of the albano maar extends from 23 ka into the holocene and produced the small volume basic phreatomagmatic peperino albano pa ignimbrite and more recently phreatomagmatic surge and lahar deposits related to the overspill of the albano maar lake we have performed an anisotropy of magnetic susceptibility ams study in order to define the relationships between the magnetic fabric and the flow mechanisms of the pa and of the phreatomagmatic deposits and lahars ams results indicate different transport and or depositional systems for the veneer and valley pond facies in the pa ignimbrite and for the lahar deposits ams also demonstrates that flow directions are mainly controlled by the paleotopography the paleotopographic control has been interpreted in terms of talweg sedimentation even at proximal locations where deposition occurs from dilute pyroclastic flows furthermore ams results clearly evidence a southward provenance for holocene post pa ignimbrite units cropping out in the ciampino plain and confirm their origin from albano maar lake overspill we demonstrate that ams is a reliable marker to determine paleoflow directions also in small volume phreatomagmatic ignimbrites and in syneruptive lahar deposits and can be successfully used to define their depositional systems

pulsating flow dynamics of sustained forced pyroclastic density currents insights from a facies analysis of the campo de la piedra pomez ignimbrite southern puna argentina the quaternary campo de la piedra pomez ignimbrite cppi is a superbly exposed partially indurated rhyolitic ignimbrite emplaced on the southern puna of argentina it is characterized by a variety of facies that record in unprecedented detail the flow dynamics of the parent pyroclastic density currents pdcs detailed facies analysis and internal architecture defined using a sequential stratigraphy approach reveal that cppi was formed by sustained pdcs generated from a low fountain eruptive style boiling over the pdcs had overall flow conditions characterized by high particle concentration and limited capability to surmount topographic obstacles the mobility of the pdcs was largely controlled by high pore pressure and the continuous supply at the source sustained forced convection dominated pdcs the successive forestepping backstepping stacking patterns identified in the cppi reflect a marked unsteadiness of its parent pdcs due to a pulsating discharge rate at the source the lateral facies variations in the cppi record the non uniform character of its parent pdcs as they flowed outward from the base of the collapsing fountain proximal medial areas characterized by steady aggradation rates pass through to distal braided thalwegs with highly variable aggradation rates to frontal edges characterized by the step aggradations of secondary decoupled pumice rich lobes collectively the facies variations in the cppi record the complex dynamics of sustained pdcs that include pulsating discharge rate at the source progressive modification of the original topography and lateral flow transformations

correlation of deposits and vent locations of the proximal campanian ignimbrite deposits campi flegrei italy based on natural remanent magnetization and anisotropy of magnetic susceptibility characteristics abstract correlation of the distal deposits of the campanian ignimbrite with their proximal equivalents in the campi flegrei caldera is complicated by a lack of medial exposures complex and limited proximal stratigraphic sections and large lateral facies changes paleomagnetic data from 10 sites in and near the campi flegrei yield natural remanent magnetizations nrm that are statistically indistinguishable from the distal campanian ignimbrite in addition their virtual geomagnetic pole vgp yields a possible correlation with lac du bouchet france secular variation data that indicate an age of approximately 32 850 14 c years the secular variation curve at this age was only briefly at this vgp and did not return to it for 10 000 years so the paleomagnetic correlation of proximal and distal deposits is unique and robust the date is consistent with 14 c dates from the campanian ignimbrite but younger than 39 ar 40 ar dates for the same rocks this suggests that a better correction factor for cosmic flux for this time period is needed to calibrate older 14 c dates anisotropy of magnetic susceptibility ams data show that the proximal deposits have an oblate disk shaped poorly lineated magnetic fabric the distal deposits are much better lineated the difference may be due to chaotic depositional currents in the proximal areas in which particles were not well aligned with greater distance of travel and loss of energy particles within the flow became aligned and developed stronger ams lineations early eruptions of the piperno tuff were from a central vent north of pozzuoli whereas later tuffs that underlie the breccia museo may have been emplaced by flows associated with ring vents located on the northern and southern caldera margins

stratigraphy paleomagnetism and magnetic fabric of the toba tuffs constraints on the sources and eruptive styles the toba depression in north central sumatra is a complex of several overlapping calderas resulting from three major ignimbrite forming eruptions within the depression the upland masses of samosir and northern uluan consist of welded ignimbrite capped by coarse breccia and lacustrine sediment hitherto interpreted to be two parts of a single resurgent dome this study has demonstrated that the welded tuffs of samosir and uluan have different magnetic polarities and therefore at least two different ignimbrites are present the samosir uluan massif may consist of parts of two resurgent domes the first ignimbrite eruption occurred at 0 84 ma and produced a very thick 400 m densely welded unit having a reversed polarity anisotropy of magnetic susceptibility ams flow direction and lithic size data indicate that the source lies in the southern part of the toba depression and the thick deposit of uluan is thought to have ponded in a 40 km wide caldera the second ignimbrite is normally magnetized ams flow direction data indicate two separate source vents one to the north in the haranggaol caldera and another to the south the thick deposit at samosir is thought to have ponded in the southern caldera coarse sediments then accumulated over samosir and northern uluan and were capped by lacustrine deposits a renewed episode of resurgence then uplifted samosir island and possibly the northern part of uluan at approximately 0 075 ma the last and apparently largest ignimbrite eruption occurred from calderas in the north and south parts of the toba depression this ignimbrite is mostly nonwelded and normally magnetized part of the uluan dome was destroyed by collapse of the sibandung caldera and latung graben and concomitant with renewed subsidence of the haranggaol and porsea calderas

high resolution magnetic susceptibility imaging of geological thin sections pilot study of a pyroclastic sample from the bishop tuff california u s a high resolution magnetic susceptibility imaging is a new technique for studying the magnetic properties of geological thin sections the two dimensional distribution of both remanent and induced magnetization can be determined with a spatial resolution 1 0 mm that is similar to the size of phenocrysts in the sample amongst many problems in rock magnetism to which it could be applied the technique holds great potential for understanding the origin of the anisotropy of magnetic susceptibility in pyroclastic flows preliminary tests on a single sample of ignimbrite indicate that secondary iron titanium oxide particles deposited within vesicle walls prior to their collapse are responsible for the bulk susceptibility

magnetic fabric investigations of pyroclastic deposits from phlegrean fields southern italy magnetic fabric investigations of pyroclastic deposits from phlegrean fields southern italy

mobility of a large volume pyroclastic flow emplacement of the campanian ignimbrite italy abstract the trachytic campanian ignimbrite originally exposed over a 30 000 km 2 area around naples italy is the product of a highly energetic gas rich eruption the deposit lies in valleys and isolated watersheds and in its medial and distal extent to the south north and east of naples the campanian pyroclastic current encountered mountains exceeding 1000 meters anisotropy of magnetic susceptibility ams measurements indicate that the campanian pyroclastic current the transport system traveled radially outward from the phlegrean fields area but the ignimbrite forming flow the deposition system that developed from the base of the transport system moved downslope from mountainsides to valleys including slopes facing the eruption source and flowed down drainage systems from intermontane basins the campanian pyroclastic current flowed 35 km over the water of the bay of naples to deposit 43 m of ignimbrite on the south shore and also overtopped a 685 1000 m high ridge of the sorrento peninsula to deposit more on the other side the distribution of the ignimbrite and the measured flow directions suggest that the campanian pyroclastic current moved across the landscape as an expanded and therefore turbulent decompressing flow rather than as a high density nonturbulent sheet like current moving over mountains by momentum acquired by eruption column collapse strong expansion is corroborated by shard morphology that indicates derivation from highly inflated pumice and suggests vesicles must have been at least 80 by volume of the original magma

three dimensional propagation effects near the mid atlantic bight shelf break l significant three dimensional 3 d environmental variability exists in the vicinity of the shelf break along the mid atlantic bight this study examines the influence of azimuthal coupling due to this variability on acoustic propagation in this region numerical studies employing a 3 d ray code a hybrid ray mode code and a 3 d parabolic equation model are used to study the significance of azimuthal coupling on various propagation paths these paths include up slope slant slope and cross slope propagation the numerical analysis suggests that for the propagation ranges less than 60 km examined the influence of azimuthal coupling is negligible compared to the inherent uncertainty in the environment itself

magnetic fabric flow directions and source area of the lower miocene peach springs tuff in arizona california and nevada we have used anisotropy of magnetic susceptibility ams to define the flow fabric and possible source area of the peach springs tuff a widespread rhyolitic ash flow tuff in the mojave desert and great basin of california arizona and nevada the tuff is an important stratigraphic marker from the colorado plateau to barstow california a distance of 350 km however the location of its source caldera is unknown dated at 18 5 ma by 40ar 39 ar the tuff erupted during the early stages of miocene extension along the lower colorado river the thicker accumulations 100 m occur at kingman arizona and in the piute mountains california on opposite sides of the colorado river extensional corridor our ams studies produced well defined magnetic lineations in 30 of 42 sites distributed throughout the tuff typical ratios of the principal ams axes are 1 01 for the magnetic lineation kmax kint and 1 02 for the foliation kint kmin the bulk magnetic susceptibility of the peach springs tuff averages 2 0 10 3 in the si unit system the subhorizontal lineations which presumably parallel the flow directions form a pattern radiating outward from the approximate center of the outcrop area magnetic foliations define an imbrication that generally dips away from the distal margins and toward the center of the outcrop of the tuff the lineation and imbrication indicate a source region near the southern tip of nevada defining the best intersection of the ams lineations required restoration of major extension strike slip faulting and associated tectonic rotation in the disrupted tuff the optimum intersection of magnetic lineations lies in the southern black mountains of arizona on the eastern side of the colorado river extensional corridor no caldera structures are known from that area but the area contains thick sections of the peach springs tuff above a silicic volcanic center the caldera may be buried under younger deposits in the mohave valley of arizona tertiary granite in the newberry mountains may represent a deeper level of the peach springs tuff vent that has been exhumed by detachment faulting

paleocurrent direction measurements in a volcanic setting by means of anisotropy of magnetic susceptibility a case study from the lower miocene tepoztlan formation transmexican volcanic belt central mexico sources of ancient volcanic rocks are often unknown if they are either eroded and or covered by younger deposits this problem as well as the provenance of reworked volcaniclastic fluvial and mass flow deposits can be partially solved by the application of anisotropy of the magnetic susceptibility ams for massive and poorly sorted volcaniclastic rocks in particular this may be the only way of finding reliable transport directions and therefore allowing for paleogeographic reconstructions here we present a data set of 428 ams measurements and 249 measurements of sedimentary paleocurrent indicators from the miocene tepoztlan formation at the southern edge of the transmexican volcanic belt central mexico the highest degree of reliability of ams measurements is gained for data from lava samples and the lowest from mass flows sedimentary structures in sandstones and conglomerates such as trough cross stratification asymmetric ripple marks and the shape of scours and channels could be used to calibrate the results from ams data and to prove their reliability ams data on fluvial deposits point to a drainage system with a w e flow direction indicating an outflow of the river system into the ancient gulf of mexico

summary of marine sedimentary shear modulus and acoustic speed profile results using a gravity wave inversion technique experimental techniques and inverse methods have been established to extract marine sediment shear modulus with depth profiles from measurements of wave induced seabed motion on the shallow continental shelf seabed sediments are modeled as a quasistatic incompressible layered elastic medium in response to wave induced pressures an iterative eigenvalue expansion technique is used to extract the inverse under typical continental shelf conditions this inversion method is found to have a depth resolution limit of approximately 3 m with a maximum penetration of 200 m using semiempirical sediment models it is possible to deduce sediment porosity bulk density and shear and compressional wave speeds from the shear modulus profile one representative result from the new jersey shelf is examined in detail and favorably compared with independent sediment profiling methods a summary of experimentally determined sediment profiles from four other sites on the eastern u s continental shelf is given

flow directions in ash flow tuffs a comparison of geological and magnetic susceptibility measurements tshirege member upper bandelier tuff valles caldera new mexico usa this study concludes that the elongation axis k 1 of the ellipsoid of anisotropic magnetic susceptibility ams is a suitable proxy for flow axis in ashflow tuffs 153 oriented samples 176 specimens were studied from 18 sites in the 1 1 ma tshirege member of the bandelier tuff these sites are distributed around the valles caldera at distances of 5 25 km outside of the rim k 1 axes correlate well with postulated radial flow axes at 13 sites k 1 also agrees with measured geological flow indicators mainly imbricated larger clasts at 7 sites at 2 of the 5 sites where significant disagreement is seen between theoretical radial flow directions and measuredk 1 axes thek 1 axes correspond well with geological flow indicators indicating that the divergence of flow from the predicted radial flow pattern is real two major topographic buttresses are suggested as the cause of flow divergence for the tshirege ash flows the san pedro buttress northwest of the caldera and the san miguel buttress in the southeast in situk 1 axes plunge about 7 toward the source at two thirds of the sites therefore the plunge ofk 1 is a plausible in situ indicator for thedirection of flow multiple flow zones in sections of several meters thickness indicate changes of flow direction that are both rapid and large during ash flow emplacement these observations raisre the question of how best to represent mean flow directions in ash flow sheets by eigenvector methods by vector sum methods or by modes a method for measuring imbrication of larger clasts using apparent dips in vertical joints is outlined imbrication determined in this way at one third of the sites dips toward the source i e up flow the minimum k 3 axis of the ams ellipsoid correlates with the flow foliation rather than with the larger clast imbrication the flow axes of ash flows correspond with thek 1 axes not with the declination ofk 3 axes as suggested by some authors initial dip of the sampled ash flows is not large and does not affect the paleomagnetic remanence direction which is reversed with a mean ofd 173 5 i 38 4 95 3 4 n 18 this mean is not different at the 95 confidence level from that of earlier workers the mean pole at 098 0 e 74 8 n a 95 3 3 n 18 is about 15 far sided relative to the expected time averaged geomagnetic pole suggesting a history of emplacement too short to adequately average secular variation

instantaneous record of the geomagnetic field direction of various facies from pyroclastic flow deposits tests for consistency in paleomagnetic directions abstract a comparative study of the paleomagnetism of various lithofacies of pyroclastic flow deposits has been undertaken to examine the accuracy of their remanent magnetization direction at the time of deposition the aso 2 pyroclastic flow deposit which erupted at 141 ka from aso caldera japan was chosen as the site of our investigation because the deposit formed over a short time period and the paleomagnetic directions of the deposit are expected to record substantial contemporaneous volcanism paleomagnetic samples of densely welded lava like rheomorphic and non welded pyroclastic deposits were collected at nine sites from the aso 2 pyroclastic flow deposit remanence directions from densely welded pyroclastic deposits display good within and between site consistency and are considered to accurately record the ambient geomagnetic field direction at the time of emplacement rheomorphic pyroclastic deposits had directions that show good within site consistency and it is considered that this material obtains its remanence direction parallel to the ambient field corresponding to the time of its emplacement remanence directions from non welded pyroclastic deposits show large confidence limits or deviations from their expected directions such deposits would likely be prone to modification of remanence direction introduced from random rotations of remanence carrying material during syn or post depositional stages in conclusion we suggest that among various lithofacies of pyroclastic flow deposits remanence directions observed from non welded pyroclastic deposits may need to be interpreted cautiously

bayesian environmental inversion of airgun modal dispersion using a single hydrophone in the chukchi sea this paper presents estimated water column and seabed parameters and uncertainties for a shallow water site in the chukchi sea alaska from trans dimensional bayesian inversion of the dispersion of water column acoustic modes pulse waveforms were recorded at a single ocean bottom hydrophone from a small ship towed airgun array during a seismic survey a warping dispersion time frequency analysis is used to extract relative mode arrival times as a function of frequency for source receiver ranges of 3 and 4 km which are inverted for the water sound speed profile ssp and subbottom geoacoustic properties the ssp is modeled using an unknown number of sound speed depth nodes the subbottom is modeled using an unknown number of homogeneous layers with unknown thickness sound speed and density overlying a halfspace a reversible jump markov chain monte carlo algorithm samples the model parameterization in terms of the number of water column nodes and subbottom interfaces that can be resolved by the data the estimated ssp agrees well with a measured profile and seafloor sound speed is consistent with an independent headwave arrival time analysis environmental properties are required to model sound propagation in the chukchi sea for estimating sound exposure levels and environmental research associated with marine mammal localization

quaternary glaciations of the rongbuk valley tibet randomisation tests on boulder weathering data distinguish moraines of four different ages in the rongbuk valley all deposited by valley glaciers flowing northward into tibet from the himalaya lichenometry utilising subgenus rhizocarpon distinguishes two groups of moraines those 100 yr old and those older than several thousand years the degree of soil development has a similar limited utility in relative age dating these moraines the radiocarbon ages of calcium carbonate coatings in the lower horizons of moraine soils provide minimum limiting ages of 1900 yr bp for the penultimate advance of the rongbuk glacier samdopo moraine and 9500 yr bp for the rongbuk moraine the moraine suggested by previous workers to represent the last glacial maximum equilibrium line depression associated with the rongbuk moraine probably was slight 200 m the small magnitude of this depression relative to glaciers in other mountain ranges could relate to a weakening of the monsoon in full glacial times recent tectonic uplift and or to the insensitivity of these high altitude glaciers to lowering temperatures in the rain shadow of mount everest

catchment scale reconstruction of glacier mass balance using observations and global climate data case study of the hailuogou catchment south eastern tibetan plateau summary debris covered glaciers are common in the tibetan plateau where ablation zones are mantled in a supraglacial debris cover that influences glacier mass balance runoff and response to climate change by affecting the melt rate of the underlying ice the impact of debris cover has not yet been taken into account in regional or global scale assessments of glacier mass balances and freshwater resources by using physically based numerical models here a surface energy mass balance model that accounts for the significance of debris cover and its effect on the ice melt rate is applied to reconstruct the glacier mass balance of hailuogou catchment which is located in the south eastern tibetan plateau and contains three debris covered and four debris free monsoonal maritime glaciers according to our calculations the glaciers in hailuogou catchment show a mean annual balance of 0 42 m water equivalent w e per year for a total mass loss of 24 3 m w e over the period 1952 2009 a comparison of summer temperature and precipitation mass balance equilibrium line altitude ela relations indicates that the glaciers in the catchment are much more sensitive to temperature change than to precipitation change in the last 20 yrs increasing summer temperature is the main cause of rapid wasting of the glacier mass in the catchment meanwhile the presence of supraglacial debris markedly accelerates glacier mass loss resulting in the unstable termini of debris covered glaciers in hailuogou catchment this highlights the importance of debris cover for understanding glacier mass balance and hydrology in the tibetan plateau

meandering flow of a pyroclastic density current documented by the anisotropy of magnetic susceptibility ams in the quartz latite ignimbrite of the pleistocene monte cimino volcanic centre central italy abstract a pattern of shifting current direction is revealed by the anisotropy of magnetic susceptibility ams in the quartz latite ignimbrite associated with the pleistocene cimini dome complex in central italy high field ams documents that both paramagnetic and ferrimagnetic minerals contribute to the magnetic fabric of the ignimbrite the results of low field ams studies suggest that the pyroclastic density current changed both direction and character during deposition of each flow unit that makes up the ignimbrite the meandering behaviour of the currents can be observed on the scale of 15 cm increments in the fine grained basal layer 2a of one flow unit in an area lacking significant palaeotopography ams data from 1 2 and 4 metre increments through the flow units also show complex changes in flow direction throughout the deposition of each unit studied the most closely aligned ams fabrics occur near the bases of flow units and dispersion increases upward this trend may represent decreased shear between the flow and the substrate or increased turbulence in the upper depositional zone of the pyroclastic density current or both suggesting a progressively waning current in terms of capacity or particle concentration the phenomena observed in this study have broad implications for the general methodology of ams studies detailed vertical profiles made up of several individual sample sites within 1 metre thickness intervals can reveal small scale current flow variations that may not be evident if sampling is done more sparsely

distribution of debris thickness and its effect on ice melt at hailuogou glacier southeastern tibetan plateau using in situ surveys and aster imagery debris cover is widely present in glacier ablation areas of the tibetan plateau and its spatial distribution greatly affects glacier melt rates high resolution in situ measurements of debris thickness on hailuogou glacier mount gongga southeastern tibetan plateau show pronounced inhomogeneous debris distribution an analysis of transverse and longitudinal profiles indicates that the ground surveyed debris thicknesses and advanced spaceborne thermal emission and reflection radiometer aster derived thermal resistances of debris layers correlate strongly over the entire ablation area across and along glacier patterns of aster derived thermal resistance correspond well with spatial patterns of debris thickness which may reflect large scale variations in the extent and thickness of the debris cover the ice melt rate variability over the ablation area simulated by a surface energy balance model that considered thermal resistance of the debris layer indicates clearly the crucial role of debris and its spatial continuity in modifying the spatial characteristics of melt rates because of the inhomogeneous distribution of debris thickness about 67 of the ablation area on hailuogou glacier has undergone accelerated melting whereas about 19 of the ablation area has experienced inhibited melting and the sub debris melt rate equals the bare ice melt rate in only 14 of the ablation area

an ams study of different silicic units from the southern parana etendeka magmatic province in brazil implications for the identification of flow directions and local sources abstract in the southern portion of the parana etendeka magmatic province in brazil extensive silicic dacite rhyolite deposits occur at the top of a sequence of low ti pahoehoe to rubbly basalts the internal architecture of the silicic deposits and their eruptive style as well as the location of their sources are still unsatisfactorily known in an attempt to provide independent evidence for flow directions in deposits previously characterized as effusive and test the hypothesis of local sources we carried out anisotropy of magnetic susceptibility ams studies on the two main silicic units caxias do sul dacites and santa maria rhyolites with the best exposures in an area previously mapped in detail magnetic anisotropies were determined on oriented cylindrical specimens from a total of 28 sites rock magnetism properties indicate that pseudo single domain magnetite carries the fabrics and the remanence magnetic fabrics were determined by applying anisotropy of low field magnetic susceptibility ams and anisotropy of anhysteretic remanent magnetization aarm both ams and aarm tensors are coaxial indicating that the ams fabric is not affected by the effect of magnetite single domain grains magnetic data from several dacitic coulees caxias do sul unit indicate flows from se to nw the location and spatial distribution of these lavas support the hypothesis of local sources aligned along a ne sw trend these data are in agreement with the alignments of structures dome shaped hills observed in field work and dem images on the other hand magnetic data obtained in santa maria rhyolites indicate that flow directions in two different areas are distinct towards nw ne and w suggesting that they derived from different emission centers so regarding the silicic volcanism in the studied region our data do not support the model which classifies the entire silicic volcanism of the province as extensive rheomorphic pyroclastic deposits released from a central conduit in contrast we propose the occurrence of local volcanic events implying in the existence of different sources possibly characterized by local emission centers

the reliability of anisotropy of magnetic susceptibility ams data as flow direction indicators in friable base surge and ignimbrite deposits italian examples abstract the base surge deposits in linosa and procida islands italy show minimum axes k3 of the anisotropy of magnetic susceptibility ams that are mostly parallel to the flow directions inferred from field evidence but sometimes perpendicular to them samples from different heights above the base of an ignimbrite bed vulsini area italy showing a coarse tail reverse grading and a fine grained basal layer have different magnetic fabrics at 10 and 40 cm from the base the declinations of maximum axes k1 of the ams are approximately 90 from the theoretical flow direction whereas at 60 and 75 cm from the base the k1 axes are approximately parallel to the flow direction this bed also shows a decrease upward of the magnetic foliation lineation and degree of anisotropy suggesting that the ams data could be used to obtain information about flow mechanisms the airm data in the case of the ignimbrite bed show that the long shape axes of the ferromagnetic grains are probably aligned with the maximum axes of the ams for this reason the change in the magnetic fabric at different distances from the base is probably due to differences in the flow behaviour rather than the domain state of magnetite grains this study shows that the ams lineations can indicate the flow direction in base surge and ignimbrite deposits but other geological and magnetic information is necessary to assess if these lineations are flow perpendicular or flow parallel

structural rotation and volcanic source implications of magnetic data from eocene volcanic rocks sw idaho eocene crystal rich ash flow tuffs in the southwest part of the challis volcanic field in idaho yield a biotite kar isochron data near 45 38 0 19 ma this age determination is in good agreement with a previous result 1 from this locality near poison creek which corrected for modern decay constants is near 44 7 0 8 ma af and thermal demagnetization experiments on 113 oriented cores from sixteen sites in these challis ash flow tuffs provide a tilt corrected mean paleomagnetic direction with i 63 6 d 019 4 95 6 2 n 15 k 39 4 the corresponding paleomagnetic pole 74 9 n 313 3 e a95 8 9 lies clockwise 34 0 9 8 relative to a synthetic 40 ma reference pole for north america 2 the observed inclination 63 6 is close to that expected 61 8 for this locality and age therefore a clockwise tectonic rotation of about 34 is inferred to have affected these rocks in the interval 40 to 15 ma approximately accompanying basin and range regional extension ams analyses of these ash flow tuffs yield a predominant e w trend for the maximum susceptibility axis assuming that this axis reflects the primary flow fabric of the rock and that this direction was also rotated by the amount indicated in the paleomagnetic results a flow source along a trend n55 e s55 w is calculated a source region northeast of the study area in the main region of development of the challis volcanic field is consistent with these results

magnetic petrofabric of igneous rocks lessons from pyroclastic density current deposits and obsidians abstract measurement of the anisotropy of magnetic susceptibility ams of igneous rocks can provide clues concerning their mechanism of formation and in particular are very helpful as flow direction indicators unlike other igneous rocks however pyroclastic density current deposits pdcds present a challenge in the interpretation of ams measurements due to the complexity of their mechanism of emplacement in this paper we review the most common assumptions made in the interpretation of the ams of pdcd taking advantage of key lessons obtained from obsidians despite the complexities on the mechanism of formation of pdcds it is shown that a key element for the fruitful interpretation of ams is to give proper attention to the various components likely to be involved in controlling their general petrofabric the anisotropies of ferromagnetic crystals whether as free phases or embedded within clasts or shards and those of paramagnetic minerals mainly ferrosilicates need to be taken into consideration when interpreting the ams measurements of pdcds variations of the deposition regime both as a function of position and of time also need to be considered on the interpretations nevertheless if a suitable sampling strategy is adopted the potential of the ams method as a petrofabric indicator is maximized

measurements of three dimensional propagation in a continental shelf environment although a significant amount of theoretical and numerical modeling effort has been put into the study of three dimensional 3d acoustic propagation on a coastal wedge including the development of the asa 3d benchmark problem set there have been few observations of the predicted 3d propagation effects significant horizontal multipath arrivals were observed in a pair of acoustic transmission tests on the continental shelf off the east coast of florida in september 2007 and february 2008 for many transmissions arrivals were received coming from nearly the global positioning system gps bearing of the ship as well as up to 30 deg inshore of the true bearing the inshore path was up to 25 db stronger than the direct path in some cases the experimental waveforms transmitted included continuous wave transmissions ranging in frequency from 24 to 415 hz as well as wideband linear frequency modulation pulses 20 420 hz horizontal multipath arrivals were observed for source ranges from 10 to 80 km sourc

inversion for sediment geoacoustic properties at the new england bight this article discusses inversions for bottom geoacoustic properties using broadband acoustic signals obtained from explosive sources two different inversion schemes for estimating the compressional wave speeds and attenuation are presented in this paper in addition to these sediment parameters source receiver range is also estimated using the arrival time data the experimental data used for the inversions are sus charge explosions acquired on a vertical hydrophone array during the shelf break primer experiment conducted south of new england in the middle atlantic bight in august 1996 the modal arrival times are extracted using a wavelet analysis in the first inversion scheme arrival times corresponding to various modes and frequencies from 10 to 200 hz are used for the inversion of compressional wave speeds a hybrid inversion scheme based on a genetic algorithm ga is used for the inversion in an earlier study potty et al j acoust soc am 108 3 973 986 2000 have used this hybrid scheme in a range independent environment in the present study results of range dependent inversions are presented the sound speeds in the water column and bathymetry are assumed range dependent whereas the sediment compressional wave speeds are assumed range independent the variations in the sound speeds in the water column are represented using empirical orthogonal functions eofs the replica fields corresponding to the unknown parameters were constructed using adiabatic theory in the second inversion scheme modal attenuation coefficients are calculated using modal amplitude ratios the ratios of the modal amplitudes are also calculated using time frequency diagrams a ga based inversion scheme is used for this search finally as a cross check the computed compressional wave speeds along with the modal arrival times were used to estimate the source receiver range the inverted sediment properties and ranges are seen to compare well with in situ measurements and historical data

determination of acoustic attenuation in the hudson river estuary by means of ship noise observations analysis of sound propagation in a complex urban estuary has application to underwater threat detection systems underwater communication and acoustic tomography one of the most important acoustic parameters sound attenuation was analyzed in the hudson river near manhattan using measurements of acoustic noise generated by passing ships and recorded by a fixed hydrophone analysis of the ship noise level for varying distances allowed estimation of the sound attenuation in the frequency band of 10 80 khz the effective attenuation coefficient representing the attenuation loss above cylindrical spreading loss had only slight frequency dependence and can be estimated by the frequency independent value of 0 058 dbm

geologic volcanologic and tectonic setting of the vico cimino area italy abstract although the cimino and vico volcanic complexes are located close to each other in a structural low they belong to two different provinces cimino is connected to the tuscan roman anatectic magmatic province and vico to the roman campanian potassic alkaline province barberi et al 1971 marinelli 1975 the two volcanic centers lie on a basement formed by clays and sands of a miocene pliocene aged sedimentary cycle the mount cimino complex forms a central volcano composed of a series of rhyodacitic domes it was emplaced along a nw se trending fracture zone which can be followed for about 16 km cimino volcano was active from 1 4 m y to 0 95 m y ago eruption of rhyodacitic ignimbrites were preceded and followed by the emplacement of domes of the same composition fluid lavas of latitic and olivine latitic composition were emitted from the central volcano during the final phase of activity vico is a central volcano mainly composed of lava with a composite summit caldera it was emplaced along a ne sw trending fracture system the vico stratovolcano is formed by lavas of various compositions including phonolitic tephrites tephritic phonolites and slightly undersaturated trachytes the construction of the stratovolcano the most ancient exposed products of which have an age of 0 4 m y was followed by the eruption of four pyroclastic flows totalling several cubic kilometers which are dated at 0 3 0 15 m y the collapse of the caldera is most likely connected to the eruption of these pyroclastic flows the ring fractures of the caldera are associated with the emplacement of a pyroclastic unit most of which erupted along the inner northeast and north rim of the caldera post caldera activity is characterized by the emission of tephritic phonolitic and tephritic products that form the intra caldera stratovolcano named mount venere the vico cimino area northern latium located between the apennine chain and the tyrrhenian sea lies along the circum tyrrhenian belt that extends from northern tuscany to campania this zone has experienced post orogenic tensional movements since the middle miocene the teconic evolution of the tyrrhenian basin is closely associated with acid anatectic and potassic alkaline volcanism along the tyrrhenian margin of the apennines the age composition and geographic position of the volcanoes are controlled by different magnitudes of tensional tectonics and crustal thinning processes of the western margin of the apennine chain

computer assisted image analysis on clast shape fabric from the orvieto bagnoregio ignimbrite vulsini district central italy implications on the emplacement mechanisms abstract computer assisted image analysis can be succesfully used to derive quantitative information about grain size distribution particle shape and fabric on both consolidated and unconsolidated solid aggregates we have developed a new analytical method that provides a series of quantitative textural parameters from whatever particulate deposits by combining commercial image acquisition system with devoted c software after exhaustive tests of the method we applied it to a widespread quaternary ignimbrite formation in central italy the orvieto bagnoregio formation the results suggest some new aspects of emplacement mechanisms of ignimbrites 1 elongated particles shows variable degrees of flow related preferred orientation both on horizontal and vertical planes 2 vertical variations of flow related preferred particle orientations follow a zig zag pattern that we interpret to result from deposition by progressive aggradation during the passage of a particulate flow the filling up of paleovalleys by means of progressive aggradation proceeds flank to flank due to alternating flow directions induced by the already deposited material 3 the occurrence of vertically spaced peaks on the strength of clast orientation suggests the existence of discrete depositional units deposited by aggradation from an unsteady but persisting flow strong fabrics are inferred to result from the high amount of shear stress imparted to particles at the depositional boundary layer which at the same time can be responsible for the development of the basal inversely graded layer image analysis can also provide useful indications of paleoflow directions paleotopographic details and ignimbrite source areas

pilot experiment for the acquisition of marine sediment properties via small scale tomography system a 3 d high resolution crosswell acoustic tomography system was designed and tested in a shallow water environment this system makes use of a damped least squared inversion technique and is used to construct compressional wave velocity images from measured travel time data use of singular value decomposition allowed checks of the linear inversion confirming the validity of the modeled environment it is shown that when the ratio of width to depth of the cross section is about unity or smaller and the domain has not been overparametrized the inverted image model has sufficiently good figures of merit in resolution and variance to visualize small variations in the magnitude compressional velocity field

anisotropy of magnetic susceptibility in welded tuffs application to a welded tuff dyke in the tertiary trans pecos texas volcanic province usa consideration of published anisotropy of magnetic susceptibility ams studies on welded ignimbrites suggests that ams fabrics are controlled by groundmass microlites distributed within the existing tuff fabric the sum result of directional fabrics imposed by primary flow lineation welding and if relevant rheomorphism ams is a more sensitive indicator of fabric elements within welded tuffs than conventional methods and usually yields primary flow azimuth estimates detailed study of a single densely welded tuff sample demonstrates that the overall ams fabric is insensitive to the relative abundances of fiamme matrix and lithics within individual drilled cores ams determinations on a welded tuff dyke occurring in a choked vent in the trans pecos texas volcanic field reveals a consistent fabric with a prolate element imbricated with respect to one wall of the dyke while total magnetic susceptibility and density exhibit axially symmetric variations across the dyke width the dyke is interpreted to have formed as a result of agglutination of the erupting mixture on a portion of the conduit wall as it failed and slid into the conduit followed by residual squeezing between the failed block and in situ wallrock irrespective of the precise mechanism widespread occurrence of both welded tuff dykes and point welded aggregate pumices in pyroclastic deposits may imply that lining of conduit walls by agglutionation during explosive volcanic eruptions is a common process

magnetic fabric of ignimbrites a case study from the central anatolian volcanic province the magnetic fabric of the pliocene kizilkaya ignimbrite in the central anatolian volcanic province has been investigated by anisotropy of magnetic susceptibility ams and isothermal remanent magnetization airm seven sections were sampled at various stratigraphic heights within the devitrified portion of the ignimbrite the magnetic mineralogy is complex titanomagnetite occurs as magmatic grains and as inclusions in other phenocryst and glass shards an oxidized phase and hematite occur in deposit levels affected by alteration processes the disturbance produced by lithic and pumice clasts has been reduced by discarding the specimens that deviate more than 1 from the site mean value of the density the ams fabric varies along each individual section neither the ams magnetic lineation nor the magnetic foliation plunge clearly define a common area as the vent location the airm fabric of low coercivity minerals mainly represented by free titanomagnetite grains of magmatic origin is consistent between sites and the inferred flow directions converge on a region near derinkuyu in the nevsehir plateau previously reported as the kizilkaya ignimbrite source area this study shows that systematic use of the remanent fabric improves the results given by ams and aids the identification of the primary magnetic fabric related to the ignimbrite emplacement dynamics

interpretation of anisotropy of magnetic susceptibility fabric of ignimbrites in terms of kinematic and sedimentological mechanisms an anatolian case study abstract a study of the neogene low aspect ratio kizilkaya ignimbrite in the calc alkaline central anatolian volcanic province turkey has been carried out using the anisotropy of magnetic susceptibility ams technique on 46 sites irm hysteresis loops and curie temperature analysis indicate that magnetite is the main carrier of the magnetic signal in the ignimbrite the shape of the ams ellipsoids varies widely from site to site and the anisotropy is commonly low we review the data processing used in the literature on the ams of ignimbrites to calculate principal directions or to evaluate the quality of the results and we develop various simple techniques data filtering and contouring procedures in order to more accurately define the axis or symmetry of the ams fabric there is no simple relationship between the shape of the ams ellipsoids and the shape of the petrofabric ellipsoids similarly there is no direct relationship between magnetic and kinematic axes our results show that the source of the measured magnetic signal in these rocks is a complex result of various contributions including shape anisotropy of free and fixed magnetic crystals shape ams crystallization of magnetic grains on all surfaces and discontinuities during cooling of the ignimbrite distribution anisotropy and alteration by hydrothermal and meteoric water particular attention is paid to the interpretation of the ams stereoplots departing from the standard fabric of sedimentary rocks formed under unidirectional flow in order to explain these non standard ams fabrics we discuss their possible origin 1 in analytical and mineralogical terms instrumental artifact pollution by xenoclasts mineralogical inversion of the susceptibility axes secondary mimetic fabric and 2 in terms of sedimentological mechanisms rheology depositional processes in the present state of knowledge we conclude that due to the physico chemical complexity of the magnetic source the ams signal should be used and interpreted with care when attempting to decipher the sedimentological or rheological processes occurring in moving pyroclastic flows on the other hand ams has it greatest potential when used in conjunction with other techniques and when a large number of sampling sites and specimens is used

fabrics facies and flow through a large volume ignimbrite pampa de oxaya chile the miocene oxaya formation exposed along the western andean slope in northern chile represents one of the largest ignimbrite provinces on earth in this study magnetic fabric data were acquired from a 1 km long core drilled vertically through a single cooling unit of the oxaya formation the ca 22 ma cardones ignimbrite samples for magnetic analysis were obtained every 20 m from the fine grained matrix of the core detailed measurements of the variation in bulk magnetic properties including natural remanent magnetization nrm susceptibility and anisotropy of magnetic susceptibility ams were used to monitor changes in magnetic mineralogy as well as changes in the strength and orientation of the magnetic fabric throughout the flow ams ellipsoid orientation and shape reflect rapid deposition from a concentrated granular fluidized flow and constrain both the location of the source caldera for this catastrophic eruption and processes of transport and deposition in this large volume ignimbrite after utilizing the magnetic remanence to correct for rotation about the core axis well grouped and imbricated petrofabric orientations reveal a well defined sw 247 transport direction down a proto western andean slope indicating syn or post welding flow and confirming the deformed lauca caldera as the likely source of the eruption systematic variations in fabric shape t and intensity p with depth reveal a predominately oblate fabric toward the top and base of the flow and predominately prolate fabrics in the center these vertical changes in fabric reveal that this massive apparently homogeneous deposit has a systematic layering this layering reflects depth dependent temperature variations temporal changes in the flow boundary zone during deposition and post depositional processes

relatively rapid emplacement of dome forming magma inferred from strain analyses the case of the acid latian dome complexes central italy abstract we have analysed the relationship between the volcanic substratum and magma body emplacement for the acid dome complexes of latium central italy our study shows that the volcanic edifices which are mainly pleistocene cryptodomes and related explosive products were derived from mantle magmas contaminated by crustal materials the cimini tolfa and cerite manziate dome complexes of latium show the following characteristics a shallow laccolith origin emplacement in basins that have identical tectonic evolution and geological structure the same magmatic composition and density contrast between magma and host rock and geochronological data that are inconsistent with field evidence in the cimini and tolfa dome complexes the deformation induced by shallow intrusions was accompanied by 200 m uplift of the sedimentary cover the estimated pluton infilling time for the cimini and tolfa domes is 10 2 years while the strain rate required to uplift their pliocene overburden by 200 m is e m 10 9 s 1 the rapid evolution of the dome complexes is consistent with field data that show no relevant interruptions in the volcanic activity and no significant compositional changes in the volcanic products related to the extrusion of the domes for the cerite manziate dome complex the minimal input rate of magma favoured a monogenetic style of volcanism independent of the regional stress conditions

estimates of flow direction for calc alkaline welded tuffs and paleomagnetic data reliability from anisotropy of magnetic susceptibility measurements central san juan mountains southwest colorado abstract flow directions are estimated from the measurement of the magnetic fabric of 106 samples collected at 18 sites in four welded tuff units in the central san juan mountains of southern colorado the estimates assume that the tuffs generally flowed directly away from the extrusive vents and that the lineations of magnetic grains within the tuffs represent the flow direction at individual sites errors in the estimation may arise from topographic variation rheomorphism post emplacement mass flow within the tuff and other factors magnetic lineation is defined as the site mean anisotropy of magnetic susceptibility maximum azimuth a test on the flow directions for individual units is based on the projection of lineation azimuths and their intersection within or near the known source caldera for the tuff this test is positive for the four units examined paleomagnetic results for these tuffs are probably reliable indicators of the geomagnetic field direction in southwest colorado during the time 28 2 26 5 ma of emplacement

parameter estimation using multifrequency range dependent acoustic data in shallow water the estimation of all forward model parameters geometric geoacoustic and ocean sound speed by the inversion of acoustic field observations is considered the data was taken at a mildly range dependent shallow water site in the mediterranean sea the inversion is based on data from a vertical array and carried out using information at multiple frequencies global optimization using a directed monte carlo search based on genetic algorithms and the bartlett objective function is used all geometric parameters are well determined a range dependent geoacoustic model is determined and the ocean sound speed is estimated comparisons of the observed pressure field as a function of depth and the predicted field show good agreement the use of observations at multiple frequencies provides considerable stability for the estimated parameters optimization of only geometric and geoacoustic parameters in a range independent environment is found to be satisfactory at the lower frequencies 165 175 hz but for the h

the mesoproterozoic stac fada proximal ejecta blanket nw scotland constraints on crater location from field observations anisotropy of magnetic susceptibility petrography and geochemistry the stac fada member of the mesoproterozoic stoer group torridon supergroup in nw scotland is a proximal ejecta blanket surrounding an unidentified asteroid impact crater a combination of field observations of the ejecta deposit and underlying strata the geographical distribution of terrane identified basement clasts found embedded in the impactite and anisotropy of magnetic susceptibility of the impact melt rocks at different locations can constrain the crater location to be about 15 20 km wnw of enard bay and thus buried under mesozoic sediments in the minch syncompressional structures within the suevite at stattic point give a clear indication of a southeasterly direction of mass motion the signatures of two different terranes within the lewisian gneiss help identify the origin of clasts found in the impactite at three locations these clasts are unshocked and interpreted as having been swept up by the density current post impact their geographical distribution provides an important clue to ejecta emplacement pathways crossing the assynt and gruinard terranes anisotropy of magnetic susceptibility is used to measure flow direction in pyroclastic density current deposits and is applied here to derive a direction of motion for the impactoclastic density current it provides good agreement with the other independent methods

fe oxide microcrystals in welded tuff from southern nevada origin of remanence carriers by precipitation in volcanic glass although it is widely recognized that remanent magnetism in ash flow tuffs is carried by fine grained fe oxides the origin mineralogy and significance of such magnetic carriers are not well understood the authors have obtained transmission electron microscope images of distinctive fe oxide microcrystals in rhyolitic samples located 3 8 7 6 and 18 5 m above the base of a 110 m thick section of the miocene tiva canyon member of the paintbrush tuff the fe oxide microcrystals are lath shaped and increase in size from 20 x 140 nm in the lowermost sample near base of the member to 120 x 800 nm in the uppermost sample within the flow interior microcrystals in this size range are within or close to the range of single domain grain size for magnetite electron diffraction and analytical x ray data indicate that the microcrystals in the lower two samples are cubic fe oxides magnetite maghemite with less than 10 mol ti end member and that those in the uppermost sample are manganiferous hematite systematic variations in magnetic properties are consistent with the observed variations in size and mineralogy of the microcrystals these microcrystals are morphologically distinct from grains that the authors interpret to be fragments of phenocrysts the morphology and spatial distribution ofmore the microcrystals as well as their increase in grain size from the rapidly cooled base of the ash flow sheet into the flow interior are consistent with an origin by nucleation and growth from volcanic glass at elevated temperature subsequent to emplacement less

the origin of tectonic fabrics in undeformed clays the early stages of deformation in extensional sedimentary basins 1 an integrated approach was used to detect tectonic effects in apparently undeformed fine grained clay sediments filling extensional basins in southern italy results from low and high field anisotropy of magnetic susceptibility and mineral fabric deduced by neutron texture analysis show penetrative deformation on a grain scale the well defined tectonic magnetic lineation is parallel to the stretching direction and located at the intersection of the basal planes of phyllosilicates forming grain scale folds and crenulations this spatial configuration reflects basin scale deformation processes and suggests the existence of a nearly uniaxial stress field during the incipient extensional phases the integrated approach of magnetic and mineral fabric investigations is a valid tool to detect grain scale and regional deformation pattern in weakly deformed extensional basins where macroscopic evidence of deformation is not visible

from geology to geoacoustics evaluation of biot stoll sound speed and attenuation for shallow water acoustics a procedure for estimating acoustic wave velocity and attenuation in ocean sediment using a minimum amount of geological and geotechnical data is demonstrated first the biot stoll theory is presented next various asymptotic formulae for the attenuation coefficient are derived for high low and intermediate frequencies these expressions clearly isolate the effects of intergranular coulomb friction and fluid viscous dissipation on the attenuation of shear and compressional waves under the constraint of a minimum amount of geological and geotechnical information a sequence of empirical equations is compiled to convert basic data such as blow count number from a standard penetration test or shipboard density into sediment geoacoustic properties as a demonstration two well known field cases the atlantic generating station ags site and the atlantic margin coring amcor 6010 site are examined by incorporating the uncertainty involved in the data collection the estimated geoacoustical parameters are provided with a standard deviation

elevation changes measured during 1966 2010 on the monsoonal temperate glaciers ablation region gongga mountains china abstract temperate glaciers are more sensitive to climate change than are polar or continental glaciers and can drive remarkable runoff variation in local water catchments changes in the glacier area and surface elevation of the three monsoonal temperate glaciers in the gongga mountains china were analyzed using series of remote sensing images and digital elevation model dem data all possible sources of uncertainty were considered in detail the results showed that the total glacier area decreased by 4 3 km 2 6 7 between 1966 and 2010 a comparison of glacier surface elevations using dems derived from dual frequency differential gps dgps surveys in 2010 and from 1966 to 1989 from topographic maps the three glaciers underwent significant mass loss from 1966 to 2010 and the mean surface elevation changes were 0 90 0 45 m y 1 06 0 45 m y and 1 12 0 45 m y for hailuogou hlg dagongba dgb and yanzigou yzg glaciers respectively from 1966 to 2010 analysis of the meteorological data showed that the mean annual air temperature increase was the main reason for the thinning and volume loss thinning of the glacier tongue and volume loss was more intense in the period 1989 2010 than in 1966 89 debris thickness and other factors are also believed to play important roles in differential thinning among different areas and periods

geoacoustic inversion with two source receiver arrays in shallow water a geoacoustic inversion scheme based on a double beamforming algorithm in shallow water is proposed and tested double beamforming allows identification of multi reverberated eigenrays propagating between two vertical transducer arrays according to their emission and reception angles and arrival times analysis of eigenray intensities yields the bottom reflection coefficient as a function of angle of incidence by fitting the experimental reflection coefficient with a theoretical prediction values of the acoustic parameters of the waveguide bottom can be extracted the procedure was initially tested in a small scale tank experiment for a waveguide with a plexiglas bottom inversion results for the speed of shear waves in plexiglas are in good agreement with the table values a similar analysis was applied to data collected during an at sea experiment in shallow coastal waters of the mediterranean bottom reflection coefficient was fitted with the theory in which bottom sediments are modeled as a multi layered system retrieved bottom parameters are in quantitative agreement with those determined from a prior inversion scheme performed in the same area the present study confirms the interest in processing source receiver array data through the double beamforming algorithm and indicates the potential for application of eigenray intensity analysis to geoacoustic inversion problems