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

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

solar semidiurnal tide in the dusty atmosphere of mars abstract vertical coupling due to the solar semidiurnal tide in mars s atmosphere and effects on zonal mean temperature and wind structures are investigated using a numerical model the model provides self consistent solutions to the coupled zonal mean and tidal equations from the surface to 250 km breaking convective instability of the semidiurnal tide is parameterized using a linear saturation scheme with associated eddy diffusivities thermal forcing in the model gives rise to surface pressure perturbations and middle atmosphere zonal mean winds and temperatures that are consistent with available measurements and general circulation models results presented here primarily focus on globally elevated dust levels during southern hemisphere summer conditions similar to those experienced by the viking 1 and viking 2 landers during the 1977 global dust storms semidiurnal temperature and wind amplitudes maximize in the winter hemisphere and exceed 50 k and 100 m s 1 above 150 km and are typically 10 2

factors governing the flow lineation of a large scale pyroclastic flow an example in the ata pyroclastic flow deposit japan schmincke andswanson 1967 explained laminar flowage structures as indicators for flow direction of pyroclastic flows that show a radial flow pattern away from the source several other authors have reported similar examples but the influence of pre flow topographic relief has not been analyzed flow lineations were measured for the ata pyroclastic flow deposit southwestern japan this deposit has covered an undulating basement topography preferred orientation of crystals and lithic fragments were measured on thin sections cut parallel to sedimentary layering the following three factors which control the flow lineation have been recognized 1 flow lineations oriented radially away from the source as described by previous authors were obtained only for samples collected from the surface of the pyroclastic flow plateau where the basement valleys were nearly filled by earlier flow units 2 lineations near the floor of narrow valleys were parallel to the strike of the valley 3 flow lineations near the wall of valleys tend to be parallel to the dip of the valley walls these data suggest that the initial radial movement of pyroclastic flows from the source gradually changes direction to parallel the strike of deep valleys due to confining effect of valley wall flows which are trapped within a valley tends to move towards the bottom of the valley just prior to the final settlement after the basement topographic relief has been filled up with earlier flow units the later flows maintain their original radial movement until final settlement

thermal tides in the dusty martian atmosphere a verification of theory major features of the daily surface pressure oscillations observed by the viking landers during the two great dust storms on mars in 1977 can be explained in terms of the classical atmospheric tidal theory developed for the earth s atmosphere the most dramatic exception is the virtual disappearance of only the diurnal tide at viking lander 1 just before the second storm this disappearance is attributed to destructive interference between the usually westward traveling tide and an eastward traveling diurnal kelvin mode generated by orographically induced differential heating the continuing viking lander 1 pressure measurements can be used with the model to monitor future great dust storms

radio occultation measurements of forced atmospheric waves on mars mars global surveyor performed a series of radio occultation experiments in december 1998 resulting in 36 profiles of the neutral atmosphere in late northern spring ls 74 1 77 3 the measurements are confined in latitude 64 6 67 2 n and local time 0321 0418 but their distribution in longitude is fairly uniform we used least squares spectral analysis to characterize the zonal structure of the atmosphere and constructed longitude height cross sections of both temperature and geopotential zonal variations of temperature exceed 12 k near the surface but are much smaller 2 3 k at higher altitudes zonal variations of geopotential are 200 m throughout the vertical range of the measurements these patterns of temperature and geopotential appear to be stationary relative to the surface with little day to day variation within the 7 sol span of the measurements we relied heavily on mars general circulation models gcms for guidance in understanding these data stationary planetary waves are responsible for some aspects of the temperature and geopotential fields particularly at pressures exceeding 100 200 pa on the basis of strong similarities between a gcm simulation and the observations we conclude that the disturbance takes the form of a planetary wave train excited by alba patera the data also include the signature of non sun synchronous thermal tides which produce a pattern that appears to be stationary when sampled at fixed local time comparison between a gcm simulation and the measured geopotential field provides evidence for the presence of the resonantly enhanced diurnal wave 1 kelvin mode

observations of planetary waves and nonmigrating tides by the mars climate sounder 1 temperature profiles from the mars reconnaissance orbiter s mro mars climate sounder mcs indicate the presence of several types of stationary planetary waves and nonmigrating thermal tides in the martian atmosphere we analyze 35 months of mcs data to identify the dominant waves with the contribution of the zonal mean and migrating tides removed the temperature perturbations remaining are due to planetary waves nonmigrating tides and topographic and surface albedo thermal inertia effects we characterize waves with satellite relative wave numbers 1 through 4 in the martian middle atmosphere 40 80 km in tropical latitudes eastward propagating diurnal kelvin waves are the dominant component observed in the satellite relative wave number 2 through 4 fields we identify these as diurnal kelvin waves 1 through 3 respectively the kelvin waves have very long vertical wavelengths and amplitudes of 1 3 k this is the first unambiguous detection of diurnal kelvin wave 3 we also identify the zonally symmetric diurnal tide and an eastward propagating semidiurnal wave 1 tide possibly the semidiurnal kelvin wave 1 stationary planetary waves with wave numbers 1 and 2 produce 5 10 k amplitudes in the middle and high latitudes of both hemispheres

influences of urban fabric on pyroclastic density currents at pompeii italy 1 flow direction and deposition 1 to assess ways in which the products of explosive eruptions interact with human settlements we performed volcanological and rock magnetic analyses on the deposits of the a d 79 eruption at the pompeii excavations italy during this eruption the roman town of pompeii was covered by 2 5 m of fallout pumice and then partially destroyed by pyroclastic density currents pdcs anisotropy of magnetic susceptibility measurements performed on the fine matrix of the deposits allowed the quantification of the variations in flow direction and emplacement mechanisms of the parental pdcs that entered the town these results integrated with volcanological field investigations revealed that the presence of buildings still protruding through the fallout deposits strongly affected the distribution and accumulation of the erupted products all of the pdcs that entered the town even the most dilute ones were density stratified currents in which interaction with the urban fabric occurred in the lower part of the current the degree of interaction varied mainly as a function of obstacle height and density stratification within the current for examples the lower part of the eu4pf current left deposits up to 3 m thick and was able to interact with 2 to 4 m high obstacles however a decrease in thickness and grain size of the deposits across the town indicates that even though the upper portion of the current was able to decouple from the lower portion enabling it to flow over the town it was not able to fully restore the sediment supply to the lower portion in order to maintain the deposition observed upon entry into the town

magnetic properties and emplacement of the bishop tuff california anisotropy of magnetic susceptibility ams and characteristic remanence were measured for 45 sites in the 0 76 ma bishop tuff eastern california thirty three sites were sampled in three stratigraphic sections two in owens gorge south of long valley caldera and the third in the adobe lobe north of long valley the remaining 12 sites are widely distributed but of limited stratigraphic extent weakly indurated highly porous to dense welded ash flow tuffs were sampled saturation magnetization vs temperature experiments indicate two principal iron oxide phases low ti magnetites with 525 570 c curie temperatures and maghemite with 610 640 c curie temperatures af demagnetization spectra of isothermal remanent magnetizations are indicative of magnetite maghemite predominantly in the multidomain to pseudo single domain size ranges remeasurement of ams after application of saturating direct fields indicates that randomly oriented single domain grains are also present the degree of anisotropy is only a few percent typical of tuffs the ams ellipsoids are oblate with kmin axes normal to subhorizontal foliation and kmax axes regionally aligned with published source vents for 12 of 16 locality means kmax axes plunge sourceward confirming previous observations regarding flow sense topographic control on flow emplacement is indicated by the distribution of tuff deposits and by flow directions inferred from kmax axes deposition east of the benton range occurred by flow around the south end of the range and through two gaps benton notch and chidago gap flow down mammoth pass of the sierra nevada is also evident at least some of the adobe lobe in the northeast flowed around the west end of glass mountain eastward flow directions in the upper owens gorge and southeast directions in the lower owens gorge are parallel to the present canyon suggesting that the present drainage has been established along the pre bishop paleodrainage characteristic remanence directions from 45 sites 267 samples yield an overall mean of d 348 i 53 for the bishop tuff a correlation is found in two of the three profiles between density and remanence inclination a mean remanence direction based on 13 localities together with data from uncompacted xenoliths and data from the ash fall tuff at lake tecopa is d 353 i 54 k 172 95 2 9 n 15

radio occultation measurements and mgcm simulations of kelvin waves on mars we have derived new results concerning thermal tides on mars from a combination of radio occultation measurements and numerical simulations by a mars general circulation model mgcm this investigation exploits a set of concurrent observations by mars express mex and mars global surveyor mgs in mid 2004 when the season on mars was midspring in the northern hemisphere the mex occultations sampled the atmosphere near the evening terminator at latitudes ranging from 54 n to 15 s the mgs occultations provided complementary coverage near the morning terminator at latitudes of 35 n and 71 s the geopotential field derived from these measurements contains distinctive modulation caused by solar asynchronous thermal tides through careful analysis of the combined observations we characterized two prominent wave modes obtaining direct solutions for some properties such as the amplitude and phase as well as constraints on others such as the period zonal wave number and meridional structure we supplemented these observations with mgcm simulations after evaluating the performance of the mgcm against the measurements we used the validated simulation to deduce the identity of the two tidal modes and to explore their behavior one mode is a semidiurnal kelvin wave with a zonal wave number of 2 sk2 while the other is a diurnal kelvin wave with a zonal wave number of 1 dk1 both modes are known to be close to resonance in the martian atmosphere our observations of the sk2 are more complete and less ambiguous than any previous measurement the well known dk1 is the dominant solar asynchronous tide in the martian atmosphere and our results confirm and extend previous observations by diverse instruments

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

mars mesosphere and thermosphere coupling semidiurnal tides the national center for atmospheric research thermosphere ionosphere general circulation model for earth has been modified to examine the three dimensional structure and circulation of the upper atmosphere of mars mtgcm bougher et al 1988b 1990 recent examination of mariner 9 uvs airglow measurements taken during a global dust storm provide evidence of large temperature variations and atomic oxygen distributions uncorrelated with solar activity and the corresponding mtgcm in situ driven winds we suspect significant forcing of the thermosphere from below as a result of upward propagating gravity waves or tides generated by solar heating of airborne dust stewart et al 1992 the effects of upward propagating tides are introduced into the mtgcm by appropriately specifying its lower boundary condition according to classical tidal theory we initially adapt the terrestrial scheme used by fesen et al 1986 to a mars model appropriate to mariner 9 near solar minimum conditions estimates of the amplitude and phase of the likely dominant semidiurnal 2 2 mode at the mesopause 100 km are specified for a range of possible lower atmosphere dust conditions mtgcm simulations contrasting tidally driven fields with solar only forced ones show a dramatic change in the horizontal and vertical wind patterns whereby the global temperature and oxygen distributions are also modified significantly this semidiurnal component predominates below 135 km while the in situ solar driven diurnal component is largely dominant above constructive interference serves to enhance midafternoon exospheric temperatures toward mariner 9 observed values the thermospheric response and the altitude of penetration of these semidiurnal tides is found to be much greater during solar minimum periods when dissipation due to viscosity and thermal conductivity is diminished from that at solar maximum finally the martian response during dusty periods is predicted to be much larger than that typically observed for earth martian dust driven tides especially during solar minimum time periods cannot be ignored when addressing the mars thermospheric structure and dynamics

the relations between the linear and bilinear atmospheric tidal fields in geometric height and in log pressure coordinates the relationships between the linearized meteorological variables as expressed in geometric height and in log pressure coordinates are derived from the assumptions of classical atmospheric tidal theory while the horizontal velocity components are the same to first order in the two coordinate systems a linearized vertical velocity differencew h0 occurs because of the periodic vertical displacement of the constant pressure surfaces due to time dependent hydrostatic density perturbations a linearized temperature differencet also results when these displacements occur in the presence of a zero order vertical gradient of temperature both of these differences can be expressed in terms of the tidal geopotential field for a given tidal mode both differences are generally proportional to the square root of the ratio of the tidal mode s equivalent depth and the atmospheric scale height the temperature difference is also proportional to the background temperature lapse rate it is further shown that the two classical tidal vertical structure equations commonly derived in their respective geometric height and log pressure coordinate systems are in fact identical to first orderas long as the same thermotidal forcing function is used expressions for the zonal mean components of the tidal bilinear fluxes formed by zonally averaging the product of two longitudinally varying linearized tidal fields are also derived for the two coordinate systems for the bilinear fields the largest relative differences a few tens of percent are for the tidal zonal mean forcing per unit mass of the zonal wind for earth and mars differences between the tidal vertical velocity fields are generally less than 25 but may be significantly larger in the martian atmosphere during one of its episodic planetary scale dust storms tidal temperature differences are generally smaller

travel of pyroclastic flows as transient waves implications for the energy line concept and particle concentration assessment abstract we here consider the precept that pyroclastic flows travel as transient waves or pulses we provide simple geometric models to estimate the wave height that may form under specified conditions and how it may vary with progression away from the vent a main uncertainty is the length of the wave relative to the total travel distance but the simple sequence of segregation layers observed in many ignimbrites may enable crude constraints to be placed on the wavelength application of these models to actual ignimbrites suggests wave heights of tens to hundreds of meters a corollary is that a wave is able to surmount obstacles less high than itself irrespective of its velocity the wave may also possess momentum which confers an additional landscape surmounting capability thus a part of the obstacle crossing ability of a pyroclastic flow is due to the height of the wave and a part is due to the velocity of the wave another corollary is that the deposit will normally be much thinner than the wave height estimates of the degree of expansion of pyroclastic flows or surges based on the relationships of the height of a trimline to the depth of a deposit may therefore be invalid this is important as at el chichon when diagnosing whether a deposit was laid down by a pyroclastic flow or surge care must also be taken not to confuse a trimline or upper limit of a veneer which exists and is a wave height level with an energy line which is a theoretical concept application of the wave concept helps explain many observed features of pyroclastic flows and their deposits for example drainage of a wave off topographic highs to generate the secondary valley ponds such as were observed in the mount st helens 1980 blast flow deposit

paleomagnetic constraints on the geometry and timing of deformation at yucca mountain nevada paleomagnetic data from miocene ash flow sheets indicate that southern yucca mountain has undergone about 30 of clockwise vertical axis rotation since emplacement of the tiva canyon member of the paintbrush tuff at about 13 ma declinations of remanent magnetization from 32 sites in the reversely magnetized tiva canyon member display a systematic southward increase over the 25 km north south extent of yucca mountain probable errors in estimating structural attitudes are a major source of uncertainty in determining the amount of rotation between any two sites analysis of tilt corrected directions of remanent magnetization from the tiva canyon sites indicates that structural attitudes determined from outcrop patterns on geologic maps are generally more accurate than field measurements of attitudes of compaction foliation or contacts attitudes determined from map patterns apparently minimize effects of 1 initial dips 2 poorly defined compaction foliation and 3 tilting that occurred after compaction but before blocking of remanence however such attitudes cannot accurately represent tilting related to unmapped local structures rotations implied by data from three older ash flow sheets the topopah spring member of the paintbrush tuff seven sites and the prow pass four sites and bullfrog three sites members of the crater flat tuff are generally consistent with the amount and sense of rotation documented by data from the tiva canyon member uncertainties in the declinations of tilt corrected site mean directions from these older units preclude evaluating whether older units have undergone more rotation than the tiva canyon member

convective vortices and dust devils at the msl landing site annual variability two hundred fifty two transient drops in atmospheric pressure likely caused by passing convective vortices were detected by the rover environmental monitoring station instrument during the first martian year of the mars science laboratory msl landed mission these events resembled the vortex signatures detected by the previous mars landers pathfinder and phoenix however the msl observations contained fewer pressure drops greater than 1 5 pa and none greater than 3 0 pa apparently these vortices were generally not lifting dust as only one probable dust devil has been observed visually by msl the obvious explanation for this is the smaller number of strong vortices with large central pressure drops since according to arvidson et al 2014 ample dust seems to be present on the surface the annual variation in the number of detected convective vortices followed approximately the variation in dust devil activity dda predicted by the marswrf numerical climate model this result does not prove however that the amount of dust lifted by dust devils would depend linearly on dda as is assumed in several numerical models of the martian atmosphere since dust devils are only the most intense fraction of all convective vortices on mars and the amount of dust that can be lifted by a dust devil depends on its central pressure drop sol to sol variations in the number of vortices were usually small however on 1 martian solar day a sudden increase in vortex activity related to a dust storm front was detected

particle velocity fields and depositional processes in laboratory ash flows with implications for the sedimentation of dense pyroclastic flows we conducted laboratory experiments on dam break flows of sub 250 m volcanic ash generated by the release of gas fluidized and variably non expanded to expanded up to 35 beds in order to gain insights into the internal kinematics of pyroclastic flows the flows were typically several cm thick and had frontal speeds of up to 2 m s 1 high speed videos taken through the transparent sidewall of the 3 m long channel were analyzed with a particle tracking algorithm providing a spatial and temporal description of transport and sedimentation the flows deposited progressively as they traveled down the flume being consumed by sedimentation until they ran out of volume deposition commenced 5 20 cm rearward of the flow front and for a given expansion proceeded at a rate independent of distance from the lock gate deposit aggradation velocities were equal to those inferred beneath quasi static bed collapse tests of the same ash at the same initial expansions implying that shear rates of up to 300 s 1 have no measurable effect on aggradation rate the initially non expanded and just fluidized flow deposited progressively at a rate indicative of an expansion of a few percent perhaps due to shear induced reynolds dilation during initial slumping the fronts of the flows slid across the flume floor on very thin basal shear layers but once deposition commenced a no slip condition was established at the depositional interface within the flows the trajectory of the constituent particles was linear and sub horizontal the velocities of the particles increased with height above the depositional interface reached a maximum then declined slightly towards the flow surface perhaps due to air drag at a given location the velocity profiles were translated upwards as the deposit aggraded the results show that even cm thin poorly expanded flows of ash deposit progressively as inferred for many pyroclastic flows the change from frontal slip to rearward no slip conditions at the bases of the laboratory flows are qualitatively consistent with some textural features of pyroclastic flow deposits

shishimuta caldera the buried source of the yabakei pyroclastic flow in the hohi volcanic zone japan drill hole geochronologic and gravity data identify the buried shishimuta caldera beneath post caldera lava domes and lacustrine deposits in the center of the hohi volcanic zone the caldera is the source of the yabakei pyroclastic flow which erupted 1 0 ma ago with a bulk volume of 110 km3 the caldera is a breccia filled funnel shaped depression 8 km wide and 3 km deep with a v shaped negative bouguer gravity anomaly up to 36 mgal neither ring vents nor resurgence was recognized instead post caldera monogenetic volcanism in an extensional setting dominated the area the andesitic breccia has a relatively low density and fills the caldera it possibly formed by fragmentation of disrupted roof rock during the violent yabakei eruption and related collapse fewer normal faults and shallow microearthquakes occur inside the caldera than around it possibly because rocks beneath the caldera are structurally incoherent a profile of shishimuta caldera may be more elongated vertically and have a more intensely fractured zone than that of a valles type caldera

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

thermal tides during the 2001 martian global scale dust storm the 2001 mars year 25 global dust storm radically altered the dynamics of the martian atmosphere using observations from the thermal emission spectrometer onboard the mars global surveyor spacecraft and marswrf general circulation model simulations we examine the changes to thermal tides and planetary waves caused by the storm we find that the extratropical diurnal migrating tide is dramatically enhanced during the storm particularly in the southern hemisphere reaching amplitudes of more than 20 k the tropical diurnal migrating tide is weakened to almost undetectable levels the diurnal kelvin waves are also significantly weakened particularly during the period of global expansion at ls 200 210 in contrast the westward propagating diurnal wavenumber 2 tide strengthens to 4 8 k at altitudes above 30 km the wavenumber 1 stationary wave reaches amplitudes of 10 12 k at 50 70 n far larger than is typically seen during this time of year the phase of this stationary wave and the enhancement of the diurnal wavenumber 2 tide appear to be responses to the high altitude westward propagating equatorial wavenumber 1 structure in dust mixing ratio observed during the storm in previous works this work provides a global picture of dust storm wave dynamics that reveals the coupling between the tropics and high latitude wave responses we conclude that the zonal distribution of thermotidal forcing from atmospheric aerosol concentration is as important to understanding the atmospheric wave response as the total global mean aerosol optical depth

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

grain orientation and depositional ramps as flow direction indicators of a large scale pyroclastic flow deposit in japan flow lineation was measured using the orientation of the elongated crystals and lithic fragments in the large scale welded ata pyroclastic flow deposit in southwestern japan in order to analyze the effect of preflow topographic relief three different types of lineations were obtained flow lineations radially away from the source were obtained only for samples collected from the surface of the pyroclastic flow plateau samples collected along the floor of narrow valleys have lineations parallel to the axis of valley samples collected from valley walls tend to be parallel to the slope of the valley this evidence suggests the following process earlier flow material moves along the valley axis in the narrow valley bottom when the flow is trapped within a valley it moves toward the bottom of the valley just prior to the final settlement when the basement relief is filled up with the earlier flow units the flow maintains its original radial movement until final settlement asymmetrical depositional ramps on the original surface of the pyroclastic flow provide an independent indicator of the flow direction

seasonal variation of martian middle atmosphere tides observed by the mars climate sounder the increased local time coverage retrieved from the mars climate sounder on board the mars reconnaissance orbiter enables the direct extraction of thermal tides in the mars middle atmosphere using temperature profiles from mars years 30 to 32 we studied the latitudinal and seasonal variations in the tides and stationary planetary waves with zonal wave numbers s 1 3 the amplitude of the migrating diurnal tide exhibits strong semiannual variations in both the equatorial region and the middle latitudes of southern hemisphere the migrating semidiurnal tide sw2 shows clear semiannual variations in the equatorial region and the middle latitudes of northern hemisphere but an annual variation in the southern hemisphere the spatial and temporal correlations between the sw2 amplitude and the density scaled opacity of both the water ice and dust in the equatorial region may provide a possible explanation for the tidal forcing of sw2 three kelvin modes with zonal wave numbers 1 3 de1 de3 have significant seasonal variations in the equatorial region de1 appears to have a semiannual variation whereas de2 and de3 have clear annual variations herein for the first time we have extracted the westward propagating diurnal tide with s 2 and 3 and semidiurnal tide with s 1 in the mars middle atmosphere using observational data all three waves have asymmetric latitudinal distributions which should correspond to their possible excitation source i e nonlinear interactions between stationary planetary waves and migrating tides

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

decoding pyroclastic density current flow direction and shear conditions in the flow boundary zone via particle fabric analysis abstract one of the greatest challenges in volcanology is extracting information from volcanic deposits that inform the conditions at the time of emplacement here we explore particle shape fabric within samples from the column collapse pyroclastic density current pdc deposits generated by the 18 may 1980 eruption of mt saint helens msh particle shape fabric is the mutual alignment of particles within a sample which is dependent on shearing conditions at the time of deposition here particle shape fabric is used to address the following hypotheses 1 particle shape fabric will align with bulk flow direction estimates made by previous studies while resolving fine scale flow direction variations 2 samples extracted from pdc deposits immediately above a basal contact will show higher extents of fabric development i e clast alignment relative to samples extracted well above the contact and 3 samples extracted from cross stratified deposits will have higher extents of fabric development relative to samples extracted from the massive facies we find that fabric orientations approximate previous flow direction interpretations of general flow from south to north and channelization due to paleo topography furthermore shape fabric records flow interaction with the substrate created by debris avalanche deposits leading to fine scale variations in flow paths these variations are recorded in samples extracted near the substrate deposit contact moreover these samples do not show a higher measure of clast alignment relative to samples taken well above flow contacts but do exhibit bimodal clast alignment this suggests some degree of traction transport and thus higher shearing conditions relative to when the currents deposited massive lapilli tuffs samples extracted from the cross stratified deposits do not show higher extents of fabric development relative to the massive deposits supporting previous interpretations that these deposits formed from a rapidly sedimenting concentrated flow boundary zone that was thin enough to be frequently interrupted or influenced by the overriding turbulent portion of the flow finally observations of fine scale variability in measured fabric within a single outcrop indicates unsteady flow conditions and step wise aggradation during deposition this work demonstrates that particle shape fabric analyses can aid in decoding pdc flow conditions future complementary experimental work may allow for the extraction of quantitative information regarding the magnitudes of shear and subsequent particle alignments within the flow boundary zone providing further insight into pdc dynamics

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

a multi year survey of dynamics near the surface in the northern hemisphere of mars short period baroclinic waves and dust storms abstract baroclinic waves figure prominently in the dynamics of the northern hemisphere of mars and extensive observations by the viking landers and two atmospheric sounders on mars global surveyor have revealed many of their basic properties however previous investigations considered these data sets individually so that their cumulative value is not fully appreciated we have re examined these data to extract new information about the dynamics near the surface at mid to high northern latitudes by applying the same method of spectral analysis to each type of observation we derive a uniform multi year characterization of basic elements of martian weather this survey documents the time evolution of baroclinic waves among modes with different periods and zonal wave numbers we devote particular attention to a recurring wave 3 mode which is distinguished by its capacity to initiate regional dust storms in the topographic basins of the northern hemisphere our results include a detailed case study that shows how the intermittence of this mode and the strong zonal modulation of its amplitude influence the timing and location of these distinctive flushing dust storms more generally we find that the properties of the wave 3 mode are largely the same whenever it appears and that its intermittence plays an important role in the annual dust cycle

image analysis and circular statistics for shape fabric analysis applications to lithified ignimbrites computer assisted image analysis can be successfully used to derive quantitative textural data on pyroclastic rock samples this method provides a large number of different measurements such as grain size particle shape and 2d orientation of particle main axes directional or shape fabric automatically and in a relatively short time orientation data reduction requires specific statistical tests mainly devoted to defining the kind of particle distribution pattern the possible occurrence of preferred particle orientation the confidence interval of the mean direction and the degree of randomness with respect to pre assigned theoretical frequency distributions data obtained from image analysis of seven lithified ignimbrite samples from the vulsini volcanic district central italy are used to test different statistics and to provide insight about directional fabrics first the possible occurrence of a significant deviation from a theoretical circular uniform distribution was evaluated by using the rayleigh and tukey 2 tests then the kuiper test was performed to evaluate whether or not the observation fits with a unimodal von mises like theoretical frequency distribution finally the confidence interval of mean direction was calculated with the exception of one sample fpd10 which showed a well developed bimodality all the analysed samples display significant anisotropic and unimodal distributions the minimum number of measurements necessary to obtain reasonable variabilities of the calculated statistics and mean directions was evaluated by repeating random collections of the measured particles at increments of 100 particles for each sample although the observed variabilities depend largely on the pattern of distribution and an absolute minimum number cannot be stated approximately 1500 2000 measurements are required in order to get meaningful mean directions for the analysed samples

observations of the initiation and evolution of the 2001 mars global dust storm 1 a global dust storm occurred on mars between june and october 2001 the storm began near hellas just before southern spring equinox ls 177 local storms likely forced by a combination of slope flow and ice cap thermal contrasts were observed to propagate along the northwestern rim of hellas apparently triggering the global storm cap edge storm activity for much of late southern winter was similar in 2001 to one mars year earlier however a very large storm propagated into the basin just after ls 177 subsequently the total area of storm activity in 2001 was roughly double that of the previous year for about 10 days dust lifting was limited to the hellas region as additional storms propagated into hellas activity built and extended northward into syrtis and eastward into hesperia it is not clear whether transport or spreading of lifting were of greatest importance for expansion at ls 185 the storm began to spread rapidly to the east along a line from the southern pole to the northern tropics essentially no storm propagation to the west occurred yielding strong zonal asymmetry of expansion as the dust storm reached the western edge of tharsis secondary dust lifting centers developed in daedalia and solis southeastern tharsis subsequently the storm rapidly encompassed the planet by ls 193 once fully global the syria solis daedalia lifting center appeared to dominate on the basis of cloud top morphology with hellas quiescent by ls 212 lifting could no longer be discerned thereafter dust haze appeared uniform and diffuse and decay appeared to have set in

particle fabric in a small type 2 ignimbrite flow unit laacher see germany and implications for emplacement dynamics ignimbrites of the 13 ka upper laacher see tephra were deposited from small highly concentrated moderately fluidized pyroclastic flows their unconsolidated nature and the prominence of accidental devonian slate fragments make these ignimbrites ideal for clast fabric studies the upper flow unit of ignimbrite m14 has characteristics typical of a type 2 ignimbrite layer 2a and the lower part of layer 2b of the flow unit have strong upstream inclined a p fabrics a p means long particle axes parallel to flow direction only clasts with a b axial ratios of 2 5 or greater preserve good a p fabrics whereas the a b planes of flat fragments dip upstream irrespective of axial ratio the a axis fabric becomes weaker flatter and more girdle like in the upper half of layer 2b at one locality the a axis fabric appears to rotate 40 up through the flow unit suggesting either shear decoupling of different levels in the moving flow or unsteadiness effects in a flow depositing progressively at its base the existence of similarly strong a p fabrics in layer 2a and the lower half of layer 2b appears inconsistent with the common interpretation that ignimbrite flow units are emplaced as a plug of essentially non shearing material layer 2b on a thin shear layer layer 2a and that the entire flow freezes en masse to form the deposit the data suggest that if the flow froze en masse it was shearing pervasively through at least half its thickness another possibility is that the flow unit aggraded progressively from the base up and that the fabrics record the integrated history of shear directions and intensities immediately above the bed throughout the duration of deposition

center to center analysis and flow fabric characterization in ash flow tuffs the center to center method of strain analysis can be used to estimate flow lineation in high silica ash flow tuffs it can be used as an alternative or supplement to other techniques for flow lineation identification such as the examination of flow textures in thin sections and the measurement of anisotropy of magnetic susceptibility the center to center method is a modification of a technique described by fry 1979 and by ramsay and huber 1983 for determination of finite strain based on the spacing of particles within a deformed rock in the present study application of the method to an anticlustered array of phenocrysts in the flattening plane of an ash flow tuff produces an ellipse with center to edge distances representative of the minimum distance between centers of phenocrysts in all directions within the flattening plane the long axis of the ellipse corresponds to the maximum axis of finite strain this direction is suggested to correspond to the flow lineation the orientation of the stretching lineation was chosen both by eye and by least squares analysis from center to center plots the calculated orientation of the long ellipse axis can be varied by choice of a maximum distance between digitized objects which are included in the calculation comparison is made between late stage flow lineations identified using the center to center method and the ams anisotropy of magnetic susceptibility method on samples of the high silica oligocene bloodgood canyon tuff from the mogollon datil volcanic field of southwestern new mexico flow lineations based on center to center analyses of flattening plane parallel rock slabs and thin sections agree well with ams derived flow lineations on most samples from which high quality ams lineations were obtained center to center analuses from flattening plane perpendicular lineation parallel planes of ash flow tuff produce ellipses inclined from 15 to 85 to the flattening plane despite compaction of the ash which should cause angles of inclination to be very low the inclined ellipses may result from heterogeneities in grain size and distribution of phenocrysts in vertical sections of tuff or from fragmentation of phenocrysts which occurred during the final stages of emplacement and compression center to center analyses on rock slabs rather than thin sections helps to avoid the effects of either textural heterogeneity and fragmentation of phenocrysts with flow lineation identified by center to center analysis petrographic examination of thin sections cut perpendicular to the flattening plane and parallel to the flow lineation allow for the identification of flow direction

pebble orientation on large experimental debris flow deposits abstract replicable pronounced orientation of discoid pebbles 8 mm embedded on surfaces of large 10 m3 experimental debris flow deposits reveals that strongly aligned imbricate fabric can develop rapidly over short distances in mass flows pebble long axes aligned subparallel to deposit margins as well as subparallel to margins of surge waves arrested within the deposits pebble alignment exhibited modes both parallel to a p the primary flow direction intermediate axes dipped preferentially inward from surge wave margins b i orientation repetitive development of margin parallel imbricate fabric distributed across deposit surfaces provides compelling evidence that deposits formed dominantly through progressive incremental accretion rather than through simple en masse emplacement pronounced fabric along deposit and arrested surge wave margins reflects significant grain interaction along flow margins this sedimentological evidence for significant marginal grain interaction complements theoretical analyses iverson 1997 and other experimental data major 1996 iverson 1997 that indicate that resistance along flow margins is an important factor affecting debris flow deposition the fabric on the experimental deposits demonstrates that debris flows can develop strongly imbricate particle orientation that mimics fabric developed during fluvial deposition particle shape and local stress fields appear to have more control over fabric development than does general depositional process other criteria in addition to particle orientation are needed to discriminate mass flow from fluvial gravel deposits and to unravel depositional history

nonmigrating tides inferred from the mars odyssey and mars global surveyor aerobraking data 1 we analyzed mars odyssey ody and mars global surveyor mgs accelerometer density retrievals in narrow local time lt bands during their respective aerobraking phases to study the large scale longitudinal density variations in the martian upper atmosphere the ody data and three seasons of mgs data fall winter and spring all displayed large zonal variations in density especially wave 2 and 3 with little vertical phase variation consistent with previous studies using mgs aerobraking data the large scale density structures were most likely nonmigrating tides sampled at specific lts the wave 2 modes observed in the ody and mgs data were approximately out of phase and their respective lt samplings were approximately 12 hours apart this reinforces the conclusion from previous studies that this mode is most likely an eastward propagating diurnal kelvin wave of zonal wave 1 which is produced by the interaction of the diurnal thermal forcing and the wave 2 component of the martian topography we also note a close association of enhanced gravity wave variances with the strong longitudinal variations in the large scale densities suggesting the possibility of tidal filtering of the gravity wave gw field

observations of martian tides over two annual cycles abstract the first four diurnal surface pressure harmonics have been analysed over major portions of two martian annual cycles mars years at the two viking lander sites the diurnal harmonies of surface wind have also been analysed at one of the sites since the atmospheric tides have previously been shown to provide a good indication of martian global dust storms these results provide a basis for comparing dust storm activity in the two years two global dust storms occurred during the first year during the second year there was only one major storm and it closely followed the pattern of the first storm of the first year a significant feature of the results is the brief but nearly complete vanishing of the diurnal pressure tide at the onset of one of the global dust storms it is proposed that this may have been due to interference between the normal westward propagating diurnal tide and a topographically forced eastward propagating tide and that the latter may have helped initiate the global s

mars global atmospheric oscillations annually synchronized transient normal mode oscillations and the triggering of global dust storms observation and analyses of the atmospheric pressure at the surface on mars for several martian years has led to the discovery of transient events in the daily pressure variations of an unusual nature these events last only a few sols mars days appear to repeat on an annual basis to within a few sols appear to cover a large portion of the hemisphere on the same sol or at least within a few sols occur in pairs with separations of 20 sols in some instances are coincident with the annual pressure minimum i e the maximum concentration of carbon dioxide in the southern hemisphere and consist of spectral components near to and sometimes identical in frequency to the diurnal and semidiurnal harmonics it is suggested that these events are kelvin normal mode transient global oscillations examination of the initiation of the 1977a 1977b and 1982a global dust storms indicate that pseudo diurnal and some times pseudo semidiurnal oscillations exist during the initiation phase and might be involved in triggering the global dust storms possibly in conjunction with winds due to longer period circulations the diurnal harmonic disappears prior to the 1977b global dust storm and is replaced by an oscillation at 1 1 cycles sol if the lack of a classical diurnal tide indicates the suppression of convection this might partially explain the slow growth of the 1977b storm the daily average pressure during the transient season which precedes the global dust storm season by almost one fourth of a year exhibits a different behavior during the global dust storm years than during the nonglobal dust storm years this implies that the global circulation must differ significantly in these cases and may be related to the presence or absence of global dust storms later in a given year these analyses suggest that an almost diurnal and an almost semidiurnal high frequency global oscillation different from the classical solar driven tides may be quite common on mars

depositional ramps asymmetrical distribution structure in the ata pyroclastic flow deposit japan the asymmetrical distribution of the welded ata large scale pyroclastic flow deposit in southern kyushu japan was identified this distribution pattern was defined as depositional ramps depositional ramps can be identified in valleys wider than 1 km and become smaller scale with increasing distance from the source upslope directions of depositional ramps are generally radially away from the source caldera suggesting that the structure was formed by the flow of pyroclastic material radially away from the source the original depositional surface was reconstructed based on field mapping and density measurements of the pyroclastic flow deposit depositional ramps having a dip angle of more than 9 were reconstructed on the vent facing slopes of the topography underlying the valley filling deposits in the area within 10 km of the caldera rim such a dip angle is much larger than previously described dip angles the size and gradient of the depositional ramps decreases with increasing distance from the source depositional ramps are recognized commonly in densely welded pyroclastic flow deposits a high emplacement temperature is required to form the depositional ramps this suggests that the pyroclastic flow was transported as a dense fluidized layer to minimize heat loss

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

paleomagnetic and ams studies of the el castillo ignimbrite central east mexico source and rock magnetic nature abstract lithological petromagnetic paleomagnetic and magnetic fabric studies are employed to determine the flow direction and the location of the source of the 2 44 to 2 21 ma el castillo ignimbrite in the central east mexico based on the increasing matrix to pumice ratio and decreasing pumice size the ignimbrite field is divided into the northwestern central and south southeastern sectors lithological comparisons among the three sectors reveal that the ignimbrite had flowed from nw to se and the source is in the nw part of the study area thermomagnetic results concur with the increasing matrix proportions from the proximal to the distal sector the coercivity and magnetization ratios of the hysteresis parameters are lower in the se sector than in the nw and central sectors the dominant flow direction inferred through magnetic fabrics at most sites is nw to se which coincides with the direction inferred from lithological comparisons however at some sites magnetic fabrics demonstrate flow towards ene or other various directions the paleomagnetic analysis and field observations reveal that these anomalous directions are a consequence of anticlockwise block rotation and tilting due to normal and lateral faulting in the region

mars surface pressure tides and their behavior during global dust storms simulations of mars atmospheric tides with the nasa ames mars general circulation model are presented and analyzed in an annual simulation diurnal and semidiurnal tides in the model s surface pressure field are shown to compare well with tides observed by the viking landers throughout the mars year focused simulations of global dust storms during the northern winter season show a semidiurnal tide that responds very strongly to the increased dust load during the storms again matching well with observations analysis of the structure and behavior of this tide during global storms verifies that it is dominated by the gravest symmetric hough mode h22 as has been noted previously however it is shown here that additional symmetric and asymmetric modes play an important role in accounting for the structure of the tide and its variation during the dust storms the phase advance observed between the viking lander sites earlier semidiurnal phase at the higher latitude site is explained by the presence of these higher order modes finally decomposition of the semidiurnal tide during a global dust storm into its component hough modes shows that the amplitude of the h22 mode mirrors changes in the observed overhead visible dust opacity while variations in higher order modes are indicative of the zonal and possibly longitudinal distribution of airborne dust

vent area and depositional mechanisms of the upper member of the neapolitan yellow tuff campi flegrei italy new insights from directional fabric through image analysis in order to provide new information about the source area and depositional mechanisms of the upper member of the neapolitan yellow tuff nyt a prominent pyroclastic deposit of the campi flegrei volcanic district southern italy statistics on directional fabric by means of computer assisted image analysis on 32 rock samples were compiled seventeen samples were collected along vertical direction on two selected exposures and fifteen were taken from outcrops widely distributed all around the campi flegrei volcanic district fabric measurements within the investigated successions reveal a vertically homogeneous direction of the mean particle iso orientation with considerable variability in the strength of particle iso orientation even at cm scale the existence of particle iso orientation can be related to continuous sedimentation from a concentrated bedload region beneath suspension currents producing massive or inversely graded beds by traction carpet sedimentation the considerable vertical variability in the strength of iso orientation is the result of very unstable flow regimes up to the extreme condition of discrete depositional events with a variable combination of traction carpet and or direct suspension sedimentation the vertical homogeneity in the mean orientation values found in the investigated sections may derive from the sequential deposition of laminae to thin beds whose relatively flat upper surfaces were unable to significantly deflect the depositional system of the following currents according to the observed homogeneous mean particle orientation values along the investigated vertical profiles samples collected through areal distribution are considered representative of the local paleo flow directions of the whole deposit the mean directions of the samples collected areally show two different coherent patterns which point to the existence of two different source areas the first which includes all samples from the northern outcrops appears to converge in a narrow area about 2 km ne of the town of pozzuoli largely in coincidence with the inferred area on the basis of the pumice fall distribution the second which includes samples from capo miseno and posillipo areas points to the central part of the pozzuoli bay about 4 km offshore the town of pozzuoli

flow behavior of large scale pyroclastic flows evidence obtained from petrofabric analysis the grain orientations within the matrix of two large scale welded two small scale nonwelded and two nonwelded low aspect ratio pyroclastic flow deposits are measured to analyze flow behavior preferred grain alignments are especially apparent in the middle part of layer 2 of each deposit preferred grain alignments do not vary laterally within a 10 m interval the grain alignments obtained are radial from the source caldera especially in proximal to medial and plateau forming facies of pyroclastic flow deposits grain alignments are controlled by valley channel directions for the valley ponded facies of pyroclastic flow deposits especially at medial to distal locations such local topographic factors strongly affect the data for high aspect ratio and smallscale deposits and weakly affect the data for widespread low aspect ratio pyroclastic flow deposits this work suggests that grain alignment analysis should be used with care when attempting to determine the location of an unknown source

observations of martian surface winds at the viking lander 1 site partial failure of the wind instrumentation on the viking lander 1 vl1 in the martian sub tropics 22 5 n has limited previous analyses of meteorological data for this site we describe a method for reconstructing surface winds using data from the partially failed sensor and present and analyze a time series of wind pressure and temperature at the site covering 350 mars days sols at the beginning of the mission during early summer winds were controlled by regional topography but they soon underwent a transition to a regime controlled by the hadley circulation diurnal and semidiurnal wind oscillations and synoptic variations have been analyzed and compared with the corresponding variations at the viking lander 2 middle latitude site 48 n diurnal wind oscillations were controlled primarily by regional topography and boundary layer forcing although a global mode may have been influencing them during two brief episodes semidiurnal wind oscillations were controlled by the westward propagating semidiurnal tide from sol 210 onward comparison of the synoptic variations at the two sites suggests that the same eastward propagating wave trains were present at both sites at least following the first 1977 great dust storm but discordant inferred zonal wave numbers and phase speeds at the two sites cast doubt on the zonal wave numbers deduced from analyses of combined wind and pressure data particularly at the vl1 site where the signal to noise ratio of the dominant synoptic waves is relatively small

inference of dust opacities for the 1977 martian great dust storms from viking lander 1 pressure data abstract a eddington radiative transfer algorithm is used to compute the thermal tidal heating of a dusty martian atmosphere for a given set of dust optical depth effective single scattering albedo and phase function asymmetry parameter the resulting thermal tidal forcing is used in a classical atmospheric tidal model to compute the amplitudes of the surface pressure oscillations at the viking lander 1 site for the two 1977 martian great dust storms parametric studies show that the dust opacities and optical parameters derived from the viking lander imaging data are roughly representative of the global dust haze needed to reproduce the tidal surface pressure amplitudes also observed at lander 1 except that the model inferred asymmetry parameter is smaller during the onset of a great storm the observed preferential enhancement during dust storm onset of the semidiurnal tide at viking lander 1 relative to its diurnal counterpart is shown to be due primarily to the elevation of the tidal heating source in a very dusty atmosphere although resonant enhancement of the main semidiurnal tidal mode makes an important secondary contribution

observations of thermal tides in the middle atmosphere of mars by the spicam instrument 1 we use vertical profiles of martian atmospheric density pressure and temperature from the mars express spicam uv spectrometer to study thermal tides in the poorly studied middle atmosphere region at 70 120 km here we show that nonmigrating tides cause zonal pressure variations of tens of percent and zonal temperature variations on the order of 10 k in these observations wave 2 and wave 3 components are dominant consistent with previous work at lower and higher altitudes and with theoretical predictions normalized pressure amplitudes tend to increase with altitude for the cases and altitudes studied here phases of the pressure variations vary little with altitude indicating long vertical wavelengths for the underlying tidal modes we derive theoretical relationships between zonal variations in temperature and in pressure and find that they are generally satisfied failure of these relationships can be used to infer the presence of multiple tidal modes contributing to a single observed wave component the wave 2 component is dominated by the diurnal kelvin wave 1 dk1 above about 80 km but contains multiple tidal modes below this altitude in one unusual instance 40 s 30 s ls 150 180 and local time of 22 24 h the usually strong wave 2 component is extremely weak the wave 3 component is always dominated by a single tidal mode which for tropical and extratropical latitudes we identify as the diurnal kelvin wave 2 dk2

directional fabric measurements an investigative approach to transport and depositional mechanisms in pyroclastic flows abstract computer assisted image analysis data of rock fabrics from two quaternary ignimbrites in the vulsini and cimini volcanic districts of central italy are interpreted in terms of transport and depositional mechanisms samples were collected vertically at m spaces up two sections through each deposit the orvieto bagnoregio ignimbrite obi is a non welded ignimbrite that shows both fluctuations in the mean particle orientation values of up to approximately 60 and large variations in the strength of particle iso orientation with height the circular frequency distributions of particle orientations are almost always anisotropic and unimodal in line with a theoretical von mises distribution the circular equivalent of a unimodal log normal distribution in contrast the welded cimina ignimbrite ci shows vertical homogeneities in mean orientation values with height and generally lower degrees of anisotropy such differences are interpreted as being the results of different depositional mechanisms incremental deposition at the base of a density stratified partially turbulent flow for the obi deposition of a laminar mass flow for the ci in the former case during transport particles under solidus temperature are subjected to a frictional regime particles gliding and dispersive pressures which finally produce size inverse grading and variable fabric development depending on the residence time of particles at the basal shear conditions in the latter case elongated particles supported in a laminar flowing viscous matrix undergo periodic motions which tend to develop parallel to flow iso orientation fabric data in the deposit suggest vertical constancy in the rheological properties of the flow absence of rheological decoupling and shearing pervasively during transport a minor importance of plug horizons

further observations of regional dust storms and baroclinic eddies in the northern hemisphere of mars abstract we have investigated the near surface meteorology in the northern hemisphere of mars through detailed analysis of data obtained with mars global surveyor in january august 2005 the season in the northern hemisphere ranged from midsummer through winter solstice of mars year my 27 we examined composite wide angle images from the mars orbiter camera and compiled a catalog of the dust storms that occurred in this interval as in previous martian years activity in the northern hemisphere was dominated by regional flushing dust storms that sweep southward through the major topographic basins most frequently in acidalia planitia we also used atmospheric profiles retrieved from radio occultation experiments to characterize eddy activity near the surface at high northern latitudes there are strong correlations between the two sets of observations which allowed us to identify three factors that influence the timing and location of the regional dust storms 1 transitions among baroclinic wave modes which strongly modulate the intensity of meridional winds near the surface 2 storms zones which impose strong zonal variations on the amplitude of some baroclinic eddies and 3 stationary waves which further modulate the wind field near the surface the flushing dust storms ceased abruptly in midautumn possibly in response to source depletion co 2 condensation a shift in the period of the baroclinic eddies and changes in the tidal wind field near the surface our results extend the meteorological record of the northern hemisphere substantiate the findings of previous investigations and further illuminate the climatic impact of baroclinic eddies