sedimentological characteristics and depositional processes of sediment gravity flows in rift basins the palaeogene dongying and shahejie formations bohai bay basin china abstract sediment gravity flow deposits are common particularly in sandy formations but their origin has been a matter of debate and there is no consensus about the classification of such deposits however sediment gravity flow sandstones are economically important and have the potential to meet a growing demand in oil and gas exploration so there is a drive to better understand them this study focuses on sediment gravity flow deposits identified from well cores in palaeogene deposits from the liaodong bay depression in bohai bay basin china we classify the sediment gravity flow deposits into eight lithofacies using lithological characteristics grain size and sedimentary structures and interpret the associated depositional processes based on the scale spatial distribution and contact relationships of sediment gravity flow deposits we defined six types of lithofacies associations las that reflect transformation processes and depositional morphology la1 unconfined proximal breccia deposits la2 confined channel deposits la3 braided channel lobe deposits la4 unconfined lobe deposits la5 distal sheet deposits and la6 non channelized sheet deposits finally we established three depositional models that reflect the sedimentological characteristics and depositional processes of sediment gravity flow deposits 1 slope apron gravel rich depositional model which involves cohesive debris flows deposited as la1 and dilute turbidity currents deposited as la5 2 non channelized surge like turbidity current depositional model which mainly comprises sandy slumping suspended load dominated turbidity currents and dilute turbidity currents deposited as la5 and la6 and 3 channelized subaqueous fan depositional model which consists of non cohesive bedload dominated turbidity currents suspended load dominated turbidity currents and dilute turbidity currents deposited as la2 la5 originating from sustained extrabasinal turbidity currents hyperpycnal flow the depositional models may be applicable to oil and gas exploration and production from sediment gravity flow systems in similar lacustrine depositional environments elsewhere

altered atmospheric responses to eastern pacific and central pacific el ninos over the north atlantic region due to stratospheric interference the two types of el nino that have been identified namely the eastern pacific ep and central pacific cp el ninos are known to exert different climatic impacts on the north atlantic region during winter here we investigate the characteristics of the teleconnection of the two el nino types with a focus on the stratosphere troposphere coupling during the ep el nino polar stratospheric warming and polar vortex weakening frequently occur with a strong tendency for downward propagation near the tropopause consequently the atmospheric pattern within the troposphere over the north atlantic sector during midwinter closely resembles the negative north atlantic oscillation pattern in contrast during cp el nino events stratospheric warming events exhibit a much weaker downward propagation tendency this difference in the stratospheric circulation response arises from the different seasonal evolution of the tropospheric wave response to the two el nino types for the ep el nino the aleutian low begins growing during december and is sustained throughout the entire winter december to february which provides favorable conditions for the continuous downward propagation of the stratospheric warming we also discuss the origin of the difference in the teleconnections from the two types of el nino associated with the distinct longitudinal position of the warm sst anomaly that determines troposphere stratosphere coupling

the role of linear wave refraction in the transient eddy mean flow response to tropical pacific sst anomalies the midlatitude response to tropical pacific sst anomalies involves changes in transient eddy propagation but the processes leading to the transient eddy changes are still not clear in a recent study we used a series of controlled general circulation model gcm experiments in which an imposed tropical pacific sea surface temperature sst anomaly is turned on abruptly and the response is analyzed in terms of its high and low frequency parts to show that the changes in transient eddies induced by el nino southern oscillation enso arise from changes in wave refraction on the altered mean flow in this work we use a quasi geostrophic linear model and a linear stationary wave model to interpret the gcm experiments and obtain the sequence of events that lead from a tropical sst anomaly to the quasi equilibrium change in the mean and transient atmospheric circulation the initial direct response of the mean flow is confined to the tropical and subtropical pacific similar to what is obtained from a stationary wave model this tropical subtropical mean flow change initiates a transient eddy response which induces a midlatitude mean flow anomaly the wave mean flow system evolves towards a state in which the eddy anomalies maintain the mean flow anomalies allowing them to persist it is further shown that while eddy momentum fluxes persistently accelerate and decelerate the subtropical and midlatitude mean flow the eddy heat flux effect on the zonal mean flow is much more variable and only marginally significant the linear quasi geostrophic model calculations capture the evolution of eddy momentum flux anomalies equatorwards of 60 n quite well suggesting linear wave refraction can explain the midlatitude enso anomalies however other processes like stationary waves or changes in the nonlinear stage of eddy life cycles are needed to explain the enso related anomalies at high latitudes polewards of around 60 n copyright 2010 royal meteorological society

the annular response to tropical pacific sst forcing abstract the leading pattern of northern hemisphere winter height variability exhibits an annular structure one related to tropical west pacific heating to explore whether this pattern can be excited by tropical pacific sst variations an atmospheric general circulation model coupled to a slab mixed layer ocean is employed ensemble experiments with an idealized sst anomaly centered at different longitudes on the equator are conducted the results reveal two different response patterns a hemispheric pattern projecting on the annular mode and a meridionally arched pattern confined to the pacific north american sector induced by the sst anomaly in the west and the east pacific respectively extratropical air sea coupling enhances the annular component of response to the tropical west pacific sst anomalies a diagnosis based on linear dynamical models suggests that the two responses are primarily maintained by transient eddy forcing in both cases the model transient eddy forcing response has a maximum

emplacement of the 18 may 1980 lateral blast deposit ene of mount st helens washington facies variations east northeast of mount st helens preserve a record of depositional processes in the 18 may 1980 lateral blast cloud this paper reports new field grain size and component data from the ene sector of the timber blowdown zone and presents a model for blast flow and sedimentation the first erupted ejecta was rich in juvenile components and extends to the distal blowdown limit the last erupted ejecta was rich in accidental lithics and reached no further than a few kilometres from the mountain due to waning discharge the blast cloud was a turbulent stratified flow which transported and deposited sediment in the manner of a high density turbidity current the possibility that the blast was emplaced as a giant shearing fluidised bed is not favoured by compositional zoning patterns depositional conditions were strongly influenced by the rate of suspended load fallout from the blast within about 8 km from vent rapid sedimentation caused deposition under moderate to high concentration conditions and formation of a basal hindered settling zone able to detach gravitationally and drain into local depressions the resulting proximal facies resembles a low aspect ratio ignimbrite fines depletion in the proximal facies is attributed to a combination of residual turbulence and rapid gas escape during particle settling and compaction through the hindered settling zone component data suggest that the blast head played no significant role in the generation of fines depletion in the blast deposit as suggested by previous workers with increasing distance from vent the rate of particle fallout declined and sedimentation took place under increasingly dilute and tractional conditions building up antidune like bedforms wavelengths of these bedforms range from 20 to 1 m and decrease away from vent there is a systematic relationship between antidune migration direction and depositional slope the transition from proximal ignimbrite like to distal surge like facies suggests a possible gradation in transport and deposition processes between conventional pyroclastic surges and high velocity pyroclastic flows

mount st helens 1980 and mount pelee 1902 flow or surge the far reaching directed blast of mount st helens and the devastating nuees ardentes of mount pelee produced deposits that in many places consist of three main layers a basal gravelly or sandy layer 1 a massive or bedded ash layer 2 and a capping ash cloud layer 3 these thin and in part landscape mantling deposits are generally ascribed to pyroclastic surges and the dune bedding seen in parts of layer 2 has reinforced this interpretation there are several reasons however for preferring a pyroclastic flow origin 1 much of layer 2 is unequivocal pyroclastic flow 2 the tripartite subdivision and landscape mantling habit is similar to that displayed by ignimbrites of the low aspect ratio type 3 the deflation of a pyroclastic surge and the subsequent deposition of particulate material will tend not to conserve the fine ash and dust that are abundant in valley ponded parts of layer 2 and cannot explain the observed tendency for layer 2 to show stronger fines depletion on ridges than in valley bottoms and 4 the coarseness and the variance of grain size found within dune bedded bed sets in mount st helens layer 2 are like those of very weak pyroclastic surges and the dune bedding most likely resulted from local minor turbulence as could have been caused by surface roughness in a mountainous terrain littered with tree stumps and fallen trees in a thin depositing pyroclastic flow the directed blast and nuees ardentes at mount st helens and mount pelee are interpreted to have been violently emplaced pyroclastic flows producing deposits of low aspect ratio type the characteristics of which stem from an exceptionally high flow velocity

formation of high grade ignimbrites part ii a pyroclastic suspension current model with implications also for low grade ignimbrites analogue experiments in part i led to the conclusion that pyroclastic flows depositing very high grade ignimbrite move as dilute suspension currents in the thermo fluid dynamical model developed the degree of cooling of expanded turbulent pyroclastic flows dynamically evolves in response to entrainment of air and mass loss to sedimentation initial conditions of the currents are derived from column collapse modeling for magmas with an initial h2o content of 1 3 wt erupting through circular vents and caldera ring fissures the flows spread either longitudinally or radially from source up to a runout distance that increases with higher mass flux but decreases with higher gas content temperature bottom slope and coarser initial grain size progressive dilution by entrainment and sedimentation causes pyroclastic currents to transform into buoyant ash plumes at the runout distance the ash plumes reach stratospheric heights and distribute 30 80 of the erupted material as widespread co ignimbrite ash pyroclastic suspension currents with initial mass fluxes of 107 1012 kg s can spread for tens of kilometers with only limited cooling although they move as supercritical strongly entraining currents for the eruption conditions considered here with increasing eruption mass flux cooling during passage through the fountain diminishes while cooling during flow transport increases the net effect is that eruption temperature exerts the prime control on emplacement temperature pyroclastic suspension currents can form welded ignimbrite across their entire extent if eruption temperature is to 1 3 tmw the minimum welding temperature high eruption rates a large fraction of fine ash and a ring fissure vent favor the formation of extensive high grade ignimbrite for very hot eruptions producing sticky partially molten pyroclasts analysis of particle aggregation systematics shows that factors favoring longer runout also favor more efficient aggregation which reduces runout as a result very high grade ignimbrites cannot spread more than a few tens of kilometers from their source in cooler pyroclastic currents particles do not aggregate and the sedimentation process may involve re entrainment of particles which potentially leads to more extensive cooling and longer runout such effects however are only significant when net erosion of substrate occurs model results can be employed to estimate mass flux and duration of ignimbrite eruptions from measured ignimbrite masses and aspect ratios the model also provides an alternative explanation of the observed decrease in h lratios with ignimbrite mass

two dimensional kinematic and rheological modeling of the 1912 pyroclastic flow katmai alaska pyroclastic flow emplacement is strongly influenced by eruption column height a surface along which kinetic energy is zero theoretically connects the loci of eruption column collapse with all coeval ignimbrite termini this surface is reconstructed as a two dimensional energy line for the 1912 katmai pyroclastic flow in the valley of ten thousand smokes from mapped flow termini and the runup of the ignimbrite onto obstructions and through passes extrapolation of the energy line to the vicinity of the source vent at novarupta suggests the eruption column which generated the ignimbrite eruption was approximately 425 m high the 1912 pyroclastic flow travelled about 25 km downvalley empirical velocity data calculated from runup elevations and surveyed centrifugal superelevations indicate initial velocities near novarupta were greater than 79 88 m s 1 the flow progressively decelerated and was travelling only 2 8 m s 1 when it crossed a moraine 16 km downvalley the constant slope of the energy line away from novarupta suggests the flow was systematically slowed by internal and basal friction using a simple physical model to calculate flow velocities and a constant kinetic friction coefficient heim coefficient of 0 04 derived from the reconstructed energy line the flow is estimated to have decelerated at an average rate of 0 16 m s 2 and to have taken approximately 9 5 minutes to travel 25 km down the valley of ten thousand smokes the shear strength of the flowing ignimbrite at the moraine was approximately 0 5 kpa and its bingham viscosity when it crossed the moraine was 3 5 103p if the flow was newtonian its viscosity was 4 2 103p reynolds and froude numbers at the moraine were only 41 62 and 0 84 1 04 respectively indicating laminar subcritical flow

interrelations among pyroclastic surge pyroclastic flow and lahars in smith creek valley during first minutes of 18 may 1980 eruption of mount st helens usa a devastating pyroclastic surge and resultant lahars at mount st helens on 18 may 1980 produced several catastrophic flowages into tributaries on the northeast volcano flank the tributaries channeled the flows to smith creek valley which lies within the area devastated by the surge but was unaffected by the great debris avalanche on the north flank stratigraphy shows that the pyroclastic surge preceded the lahars there is no notable wet character to the surge deposits therefore the lahars must have originated as snowmelt not as ejected water saturated debris that segregated from the pyroclastic surge as has been inferred for other flanks of the volcano in stratigraphic order the smith creek valley floor materials comprise 1 a complex valley bottom facies of the pyroclastic surge and a related pyroclastic flow 2 an unusual hummocky diamict caused by complex mixing of lahars with the dry pyroclastic debris and 3 deposits of secondary pyroclastic flows these units are capped by silt containing accretionary lapilli which began falling from a rapidly expanding mushroom shaped cloud 20 minutes after the eruption s onset the smith creek valley bottom pyroclastic facies consists of a a weakly graded basal bed of fines poor granular sand the deposit of a low concentration lithic pyroclastic surge and b a bed of very poorly sorted pebble to cobble gravel inversely graded near its base the deposit of a high concentration lithic pyroclastic flow the surge apparently segregated while crossing the steep headwater tributaries of smith creek large fragments that settled from the turbulent surge formed a dense pyroclastic flow along the valley floor that lagged behind the front of the overland surge the unusual hummocky diamict as thick as 15 m contains large lithic clasts supported by a tough brown muddy sand matrix like that of lahar deposits upvalley this unit contains irregular friable lenses and pods meters in diameter blocks incorporated from the underlying dry and hot pyroclastic material that had been deposited only moments earlier the hummocky unit is the deposit of a high viscosity debris flow which formed when lahars mingled with the pyroclastic materials on smith creek valley floor overlying the debris flow are voluminous pyroclastic deposits of pebbly sand cut by fines poor gas escape pipes and containing charred wood the deposits are thickest in topographic lows along margins of the hummocky diamict emplaced several minutes after the hot surge had passed this is the deposit of numerous secondary pyroclastic flows derived from surge material deposited unstably on steep valley sides

the nonlinear northern hemisphere winter atmospheric response to enso 1 a nonlinear projection of the tropical pacific sea surface temperature anomalies ssta onto the northern hemisphere winter 500 mbar geopotential height z500 by a neural network reveals asymmetric atmospheric patterns associated with el nino and la nina while the linear response of z500 to tropical pacific ssta is largely confined over north pacific and north america the nonlinear response mainly a quadratic response to the ssta reveals that regardless of the sign of the ssta positive z500 anomalies are found over the central eastern north america north atlantic and western europe and negative z500 anomalies over the west coast of north america scandinavia and eastern europe consistent with the positive pacific north america pna teleconnection pattern and the positive north atlantic oscillation nao pattern being excited

el nino as a mediator of the solar influence on climate 1 using a climate model of intermediate complexity we simulate the response of the el nino southern oscillation enso system to solar and orbital forcing over the holocene solar forcing is reconstructed from radiocarbon production rate data using various scaling factors to account for the conflicting estimates of solar irradiance variability as estimates of the difference since the maunder minimum range from 0 05 to 0 5 of the solar constant we consider these two extreme scenarios along with the intermediate case of 0 2 we show that for large or moderate forcings the low pass filtered east west sea surface temperature gradient along the equator responds almost linearly to irradiance forcing with a short phase lag about a decade wavelet analysis shows a statistically significant enhancement of the century to millennial scale enso variability for even a moderate irradiance forcing in contrast the 0 05 case displays no such enhancement orbitally driven insolation forcing is found to produce a long term increase of enso variability from the early holocene onward in accordance with previous findings when both forcings are combined the superposition is approximately linear in the strong scaling case overall the sea surface temperature response is of the magnitude required and is persistent enough to induce important climatic perturbations worldwide the results suggest that enso may plausibly have acted as a mediator between the sun and the earth s climate a comparison to key holocene climate records from the northern hemisphere subtropics and midlatitudes shows support for this hypothesis

carbon and noble gases in archean chert abstract in order to study the origin and evolution of volatiles trapped in archean and early proterozoic cherts we have measured contents and isotopic compositions of carbon and noble gases using step heating and mass spectrometry the observed negative correlation between the 13c value and nitrogen carbon ratio in the samples suggests that trapped carbon in archean cherts is a mixture of carbonate sedimentary organic matter and an atmospheric component elemental abundance patterns of noble gases show a slight depletion of 20ne and excess of 132xe relative to air which is explained by atmospheric noble gases dissolved in water at relatively low temperature the 3 he 4 he ratios indicate an apparent crustal value of 1 3 10 3 consistent with the in situ radiogenic production ratio significant excess 21ne 131xe and 132 136xe as well as slight enrichment of 38ar and 86kr relative to atmosphere are found in the onverwacht chert at the 800 and 1200 c steps similar but small isotope anomalies are detected in the frere formation chert at the 1800 c step excess 21ne shows positive correlations with 38ar 86kr and 132xe 136xe enrichments while excess 131xe has no relation with the other isotope anomalies the 21ne anomaly can be attributable to the nuclear reaction 18o n 21ne the enrichments of 86kr and 132xe 136xe are derived from spontaneous fission of 238u in the cherts the slight excess 38ar may be due to the 35cl p 38ar reaction based on the positive correlation between 21 ne 22 ne and 38 ar 36 ar ratios but should be verified in future work

an examination of observed southern oscillation effects in the northern hemisphere stratosphere abstract the effects of the southern oscillation on the december february mean circulation in the northern hemisphere stratosphere were investigated using 34 years of data no evidence for a significant relation between the southern oscillation so and the zonally averaged flow is found for any region poleward of 20 n the effects of the tropical quasi biennial oscillation qbo on the zonal mean flow are much stronger and this complicates the detection of 50 effects some more suggestive results are evident when hemispheric maps of height anomalies at 50 or 30 mb are composited for the warm extremes of the 50 the present findings are broadly consistent with earlier suggestions that on average the aleutian high is intensified during the warm extremes of the southern oscillation even using the 34 years of data now available however the statistical significance of this relationship cannot be demonstrated unequivocally once again the separation of so effects from qbo influences in the limited data a

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

propagation of enso temperature signals into the middle atmosphere a comparison of two general circulation models and era 40 reanalysis data the vertical propagation of the el nino southern oscillation enso temperature signal has been analyzed in two general circulation models the whole atmosphere community climate model and the middle atmosphere european center hamburg model and in the era 40 reanalysis data set monthly mean data have been used and composite differences el nino la nina have been computed our results show that the enso signal propagates into the middle atmosphere by means of planetary rossby waves significant wave like anomalies are observed up to around 40 km this propagation is strongly influenced by the zonal mean zonal winds being most effective in midlatitudes of the northern hemisphere because enso events tend to peak in northern winter when stratospheric winds are westerly in the northern hemisphere and allow vertical propagation of rossby waves in addition zonal mean temperature anomalies are observed in the middle atmosphere in the tropics and at polar latitudes of the northern hemisphere these anomalies are the result of changes in the residual mean meridional circulation our analysis reveals that during an el nino event vertical wave propagation and divergence of eliassen palm flux are enhanced forcing a stronger residual circulation in the stratosphere which cools the tropics and warms the higher latitudes this pattern is highly significant in the models during certain months but much less in the era 40 data where other sources of variability in particular the quasi biennial oscillation also influence the residual circulation

the plinian eruptions of 1912 at novarupta katmai national park alaska the three day eruption at novarupta in 1912 consisted of three discrete episodes episode i began with plinian dispersal of rhyolitic fallout layer a and contemporaneous emplacement of rhyolitic ignimbrites and associated proximal veneers the plinian column was sustained throughout most of the interval of ash flow generation in spite of progressive increases in the proportions of dacitic and andesitic ejecta at the expense of rhyolite accordingly plinian layer b which fell in unbroken continuity with purely rhyolitic layer a is zoned from 99 to 15 rhyolite and accumulated synchronously with emplacement of the correspondingly zoned ash flow sequence in mageik creek and the valley of ten thousand smokes vtts only the andesiterichest flow units that cap the flow sequence lack a widespread fallout equivalent indicating that ignimbrite emplacement barely outlasted the plinian phase on near vent ridges the passing ash flows left proximal ignimbrite veneers that share the compositional zonation of their valley filling equivalents but exhibit evidence for turbulent deposition and recurrent scour episode ii began after a break of a few hours and was dominated by plinian dispersal of dacitic layers c and d punctuated by minor proximal intraplinian flows and surges after another break dacitic layers f and g resulted from a third plinian episode iii intercalated with these proximally are thin intraplinian ignimbrites and several andesite rich fall flow layers both cd and fg were ejected from an inner vent 400 m wide nested within that of episode i into which the rhyolitic lava dome novarupta was still later extruded two finer grained ash layers settled from composite regional dust clouds layer e which accumulated during the d f hiatus includes a contribution from small contemporaneous ash flows and layer h settled after the main eruption was over both are distinct layers in and near the vtts but distally they merge with cd and fg respectively they are largely dacitic but include rhyolitic shards that erupted during episode i and were kept aloft by atmospheric turbulence published models yield column heights of 23 26 km for a 22 25 km for cd and 17 23 km for fg and peak mass eruption rates of 0 7 1x108 0 6 2x108 and 0 2 0 4x108 kg s 1 respectively fallout volumes adjusted to reflect calculated redistribution of rhyolitic glass shards are 8 8 km3 4 8 km3 and 3 4 km3 for episodes i ii and iii microprobe analyses of glass show that as much as 0 4 km3 of rhyolitic glass shards from eruptive episode i fell with cde and 1 1 km3 with fgh most of the rhyolitic ash in the dacitic fallout layers fell far downwind se of the vent near the rhyolite dominated ignimbrite however nearly all of layers e and h are dacitic showing that the downwind rhyolitic ash is of co plinian rather than co ignimbrite origin

the complex behavior of el nino winter 2015 2016 this paper examines the outstanding characteristics of the strong 2015 2016 el nino en winter and its impact over the european region through the stratosphere despite being classified as a strong eastern pacific ep en event our analysis reveals an anomalous behavior with some signatures that are more typical of central pacific cp en events instead they include i a record breaking value of the cp index ii a stronger polar vortex in early and midwinter due to reduced upward wave activity and a weakened aleutian low and iii the occurrence of one of the earliest stratospheric final warmings sfws on record which are more prone to occur during cp en following the sfw a stratospheric influence on the euro atlantic sector is reported in spring with persistent greenland blocking resulting in extreme precipitation over some southern european regions results highlight the importance of considering early sfws as mediators of el nino teleconnections

multi model assessment of the late winter extra tropical response to el nino and la nina el nino southern oscillation enso is known to affect the northern hemisphere tropospheric circulation in late winter january march but whether el nino and la nina lead to symmetric impacts and with the same underlying dynamics remains unclear particularly in the north atlantic three state of the art atmospheric models forced by symmetric anomalous sea surface temperature sst patterns mimicking strong enso events are used to robustly diagnose symmetries and asymmetries in the extra tropical enso response asymmetries arise in the sea level pressure slp response over the north pacific and north atlantic as the response to la nina tends to be weaker and shifted westward with respect to that of el nino the difference in amplitude can be traced back to the distinct energy available for the two enso phases associated with the non linear diabatic heating response to the total sst field the longitudinal shift is embedded into the large scale rossby wave train triggered from the tropical pacific as its anomalies in the upper troposphere show a similar westward displacement in la nina compared to el nino to fully explain this shift the response in tropical convection and the related anomalous upper level divergence have to be considered together with the climatological vorticity gradient of the subtropical jet i e diagnosing the tropical rossby wave source in the north atlantic the enso forced slp signal is a well known dipole between middle and high latitudes different from the north atlantic oscillation whose asymmetry is not indicative of distinct mechanisms driving the teleconnection for el nino and la nina

the 1982 eruptions of el chichon volcano mexico stratigraphy of pyroclastic deposits abstract following a repose period of 500 to 600 years el chichon volcano in se mexico erupted explosively during the months of march and april 1982 three major eruptions involving trachyandesite magma injected ash into the stratosphere on 29 march at 0515 gmt and on 4 april at 0139 and 1110 gmt the first major eruption generated only tephra fall which was dispersed ene in the troposphere over the yucatan peninsula and wsw in the stratosphere towards the pacific ocean the second eruption produced tephra fall and pyroelastic surges and pyroclastic flows by repeated collapse of a lithicrich eruption column the surge and flow activity devastated a roughly circular area 153 km 2 around el chichon to a distance of about 6 km from the vent nine villages within the zone were either partially or completely destroyed and loss of human life was perhaps as high as 2000 pyroclastic flows and surges were also generated during the third eruption although ash fall was the primary activity as a result of both the second and third eruptions tephra was transported ene in the troposphere and wsw in the stratosphere the total volume of material ejected during the three major eruptions 0 50 km 3 d r e is represented by tephra fall 0 37 km 3 pyroclastic surges 0 09 km 3 and pyroclastic flows and debris flows 0 04 km 3 as a result of the eruptions a new 1 km wide and 300 m deep crater was formed by the disruption and excavation of a pre existing summit dome

atmospheric conditions associated with labrador sea deep convection new insights from a case study of the 2006 07 and 2007 08 winters abstractdeep convection in the labrador sea ls resumed in the winter of 2007 08 under a moderately positive north atlantic oscillation nao state this is in sharp contrast with the previous winter with weak convection despite a similar positive nao state this disparity is explored here by analyzing reanalysis data and forced ocean simulations it is found that the difference in deep convection is primarily due to differences in large scale atmospheric conditions that are not accounted for by the conventional nao definition specifically the 2007 08 winter was characterized by an atmospheric circulation anomaly centered in the western north atlantic rather than the eastern north atlantic that the conventional nao emphasizes this anomalous circulation was also accompanied by anomalously cold conditions over northern north america the controlling influence of these atmospheric conditions on ls deep convection in the 2008 winter is confirmed by sensitivity experiments where surface forcing and or in

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

the tropospheric pathway of the enso north atlantic teleconnection abstractel nino southern oscillation enso exerts an influence on the north atlantic european nae region however this teleconnection is nonlinear and nonstationary owing to the superposition a

ignimbrite depositional facies the anatomy of a pyroclastic flow a model is presented for the depositional regimes in a pyroclastic flow to explain the origin of facies in the taupo ignimbrite and to compare these with other published examples in this model a pyroclastic flow consists of a head a body and a tail the head which is where fluidization caused by air ingestion occurs generates layer 1 deposits on lithological grounds these are divided into layers 1 p which is fines depleted and rich in pumice and 1 h which is fines depleted and rich in lithics and crystals layer 1 p represents material thrown forwards from the flow head and is termed the jetted deposits layer 1 h represents material sedimented from within the flow head and is termed the ground layer the body represents the bulk of the flow and the tail is its trailing part which is slowed by ground friction these parts generate the layer 2 deposits which include the valley pond ignimbrite and its associated ignimbrite veneer deposit localized depositional modes within the body and tail generate distinctive coarse pumice concentration zones and pumiceous lee side lenses behind obstacles at its outer limits all of the flow on interfluves is affected by air ingestion fluidization producing the distant facies which combines features of both layer 1 and 2 deposits one important conclusion of this work is that the thicknesses and compositions of the various facies are not related in any simple way to the thickness and composition of the parent flow

the influence of enso on winter north atlantic climate 1 although the influence of the el nino southern oscillation on the extra tropical climate is well established for the pacific basin and north american regions there is no clear consensus as to whether there are reproducible effects from enso on the north atlantic and west european regions in this study we present a revised analysis of past el nino teleconnections by stratifying el nino events according to amplitude we find a highly non linear yet robust response to enso that changes sign over the eastern north atlantic as the amplitude of the el nino anomaly increases results from a series of experiments with a general circulation model indicate that the response to strong enso events is reproducible given the sea surface temperature anomalies in the tropical pacific the response to moderate el nino events resembles the negative phase of the north atlantic oscillation as found in previous studies

rotational atmospheric circulation during north atlantic european winter the influence of enso the dominant variability modes of the north atlantic european rotational flow are examined by applying a principal component analysis pca eof to the 200 hpa streamfunction mid winter anomalies jan feb monthly means the results reveal that when this norm is used the leading mode eof1 does not correspond to the traditional north atlantic oscillation nao which appears in our analysis as the second leading mode eof2 but is the local manifestation of the leading hemispheric streamfunction eof the regression of this regional mode onto the global sst field exhibits a clear el nino signature with no signal over the atlantic while the associated upper height anomalies resemble the tropical northern hemisphere tnh pattern east of north america this tnh like wavetrain produces a meridional dipole like pattern at lower levels although in some ways this pattern resembles the nao eof2 the dynamics of these two modes are very different in that only eof2 is associated with a latitudinal shift of the north atlantic stormtrack thus the choice of the streamfunction norm in the eof analysis allows the separation of two different phenomena that can produce similar dipolar surface pressure anomalies over the north atlantic but that have different impact on european climate these two modes also differ on their contribution to variability at lower levels while nao eof2 is mostly confined to the north atlantic tnh eof1 has a more annular global character at upper levels nao eof2 also produces a global pattern but with no annular structure reminiscent of the circumglobal teleconnection

explosive rhyolitic volcanism in the jemez mountains vent locations caldera development and relation to regional structure the jemez volcanic field straddles the western margin of the rio grande rift where the rift is intersected by the jemez lineament in north central new mexico the field has a record of volcanism extending back to before 13 ma initial basaltic activity was related to active rifting with minor rhyolitic eruptions occurring along n s rift bounding faults between 10 and 7 ma voluminous andesitic volcanism took place in the central jemez mountains area overwhelming contemporaneous basaltic and rhyolitic magmatism an apparent tectonic lull took place from 7 to 4 ma accompanied by lower eruption rates during this interval dacitic magmas were erupted to form the tschicoma volcanic center but mafic and rhyolitic volcanism virtually ceased since 4 ma accompanying resumption of rifting a growing silicic magma system has been present under the central part of the jemez mountains ultimately evolving to the magma body that produced the voluminous rhyolitic bandelier tuffs explosive rhyolitic eruptions from this large magma body have occurred many times since 3 to 4 ma early eruptions 3 6 2 8 ma produced high silica rhyolite ignimbrites restricted to the southwest part of the jemez mountains formation of these units may have been accompanied by caldera collapse these events were followed by the two caldera forming bandelier tuff ignimbrite eruptions 1 45 and 1 12 ma post caldera explosive and effusive rhyolite eruptions have also tapped the magma body from vents generally located along ring fractures after both bandelier events vent and caldera locations for the rhyolitic eruptions during 3 4 ma have been inferred from grain size characteristics dispersal patterns and facies variations in the plinian deposits and ignimbrites lithic breccia zones of the pre bandelier ignimbrites indicate possible caldera sources in the southwest part of the present valles caldera during the eruption of both bandelier tuffs initial plinian falls and early pyroclastic flows emanated from vents centrally located in the jemez mountains in the lower bandelier tuff eruption a transition to ring fracture vents occurred before the emission of later pyroclastic flows but there is no strong evidence to suggest such a transition occurred during the upper bandelier eruption calderas associated with the lower and upper bandelier tuffs toledo and valles respectively are almost identical in location as are the plinian vent sites for these two large eruptions the toledo embayment northeast of the valles caldera contains lava domes from up to 3 6 ma and may be a caldera or crater associated with early explosive dacitic volcanism in the tschicoma volcanic center post 1 4 ma lava domes also fill this depression the main volcanic features of the jemez mountains field including the valles caldera complex eruption vents and the apical graben of the post valles redondo resurgent block appear to be aligned along the ne sw trending jemez fault zone this zone the local expression of a precambrian basement feature the jemez lineament has exerted strong control on the location and style of eruptions from the bandelier rhyolitic magma system

impact of enso on the atmospheric variability over the north atlantic in late winter role of transient eddies abstractthe dynamical mechanism for the late winter teleconnection between el nino southern oscillation enso and the north atlantic oscillation nao is examined using the output from a 2000 yr integration of a coupled general circulation model gcm the coupled model captures many salient features of the observed behavior of both enso and nao as well as their impact on the surface climate in late winter both the observational and model data indicate more occurrences of negative phase of nao in late winter during el nino events and positive nao in la nina episodes the potential role of high frequency transient eddies in the above teleconnection is diagnosed during el nino winters the intensified transient disturbances along the equatorward shifted north pacific storm track extend their influences farther downstream the eddy induced negative height tendencies are found to be more coherent and stronger over north atlantic than that over north pacific these negative height tendencies over the north

transport and deposition processes of the hydrothermal blast of the 6 august 2012 te maari eruption mt tongariro the 2012 eruption of tongariro volcano new zealand produced highly mobile low temperature blast derived pyroclastic density currents after partial collapse of the western flank of the upper te maari crater despite a low volume 340 000 m3 the flows traveled up to 2 5 km from source covering a total area of 6 1 km2 along one of the blast axes freshly exposed proximal to distal sedimentary structures and grain size data suggest emplacement of the fining upward tripartite depositional sequence massive stratified and laminated under a dilute and strongly longitudinally zoned turbulent density current while the zoning formed in the deposit in the first 1500 m of runout the current progressively waned to the extent where it transported a nearly homogenous grain size mixture at the liftoff position our data indicate that after the passage of an erosive flow front massive unit a was deposited under a rapid suspension sedimentation regime unit b was deposited under a traction dominated regime generated by a subsequent portion of the flow moving at lower velocities and with lower sediment transport capacity than the portion depositing unit a the final and slowest flow zone deposited the finest particles under weakly tractive conditions transport and emplacement dynamics inferred in this study show strong similarities between hydrothermal explosions magmatic blasts and high energy dilute pdcs the common occurrence of hydrothermal fields on volcanic flanks points to this hazard being an under appreciated one at stratovolcanoes worldwide

observational constraints on the tropospheric and near surface winter signature of the northern hemisphere stratospheric polar vortex a composite analysis of northern hemisphere s mid winter tropospheric anomalies under the conditions of strong and weak stratospheric polar vortex was performed on ncep ncar reanalysis data from 1948 to 2013 considering as additional grouping criteria the coincidental states of major seasonally relevant climate phenomena such as el nino southern oscillation enso quasi biennial oscillation and strong volcanic eruptions the analysis reveals that samples of strong polar vortex nearly exclusively occur during cold enso states while a weak polar vortex is observed for both cold and warm enso the strongest tropospheric and near surface anomalies are found for warm enso and weak polar vortex conditions suggesting that internal tropospheric circulation anomalies related to warm enso constructively superpose on dynamical effects from the stratosphere additionally substantial differences are found between the continental winter warming patterns under strong polar vortex conditions in volcanically disturbed and volcanically undisturbed winters however the small size samples obtained from the multi compositing prevent conclusive statements about typical patterns dominating effects and mechanisms of stratosphere troposphere interaction on the seasonal time scale based on observational reanalysis data alone hence our analysis demonstrates that patterns derived from observational reanalysis time series need to be taken with caution as they not always provide sufficiently robust constraints to the inferred mechanisms implicated with stratospheric polar vortex variability and its tropospheric and near surface signature notwithstanding this argument we propose a limited set of mechanisms that together may explain a relevant part of observed climate variability these may serve to define future numerical model experiments minimizing the sample biases and thus improving process understanding

enso influence on the north atlantic european climate a non linear and non stationary approach el nino southern oscillation enso impact on the north atlantic european sector nae is still under discussion recent studies have found a non stationary feature of this teleconnection suggesting an effective modulating role of the ocean mean state nevertheless physical explanations about the underlying mechanisms have been little studied in the available literature in addition enso events show different sst spatial patterns phases and amplitudes which can also influence on the related remote impacts in view of all this in the present study a set of partially coupled experiments have been performed with a global atmospheric general circulation model in which different sst enso patterns are superimposed over distinct pacific and atlantic sst mean states these sst background conditions are constructed according to the observational difference between periods with a distinct impact of enso on the leading euro mediterranean rainfall mode in late winter early spring our results point to two distinct mechanisms associated with enso that can be modulated by the sst mean state 1 the thermally driven direct circulation walker and hadley cells connecting the atlantic and pacific basins and 2 the rossby wave propagation from the tropical pacific to the north atlantic the former elucidates that the positive nao like pattern usually related to la nina events could be only valid for selected decades the latter explains a reinforced signature of eastern pacific ninos on the euro mediterranean rainfall when the tropical pacific is warmer than usual and the north atlantic is colder than usual this feature is consistent with the changing enso impact identified in previous studies and demonstrates how the enso teleconnection with the nae climate at interannual timecales could be modulated by multidecadal changes in the sst according to our results the assumption of stationarity which is still common to many studies of enso teleconnections clearly has to be questioned

the green tuff of pantelleria rheoignimbrite or rheomorphic fall detailed stratigraphic analysis of the green tuff of pantelleria shows that this formation can be divided into several members designateda throughh from base to top these members have a coherent pattern when traced from outcrop to outcrop throughout the island shedding light on their origin only memberg completely mantles the entire island the distribution of the other members is controlled by prevailing wind direction or by topography membera is entirely of fall origin membersc ande are of fall and or surge type membersb d andh have the characteristics of thin welded ash flow tuffs membersf andg are ash flow tuffs with textural characteristics of compound cooling units most of the ash flow tuffs exhibit characteristics of ignimbrites vertical fluidization pipes local concentrations of lithic lapilli imbrication of clasts and valley ponding memberg is unusual in that it is highly welded exhibits large scale rheomorphic structures contains huge lithic clasts and has near vertical foliation where it adheres to cliffs and caldera walls

an ignimbrite veneer deposit the trail marker of a pyroclastic flow abstract the term ignimbrite veneer deposit ivd is proposed for a new kind of pyroclastic deposit which is found associated with and passes laterally into taupo ignimbrite of valley pond type in new zealand it forms a thin layer mantling the landscape over 15 000 km 2 and is regarded as the deposit from the trailing tail of a pyroclastic flow where a relaxation of shear stress favoured the deposition of the basal part of the flow the ivd differs little in grain size from the associated ignimbrite but it shows a crude internal stratification attributed to the deposition of a succession of layers one after the passage of each pulse of the pyroclastic flow it locally contains laterally discontinuous lenses of coarse pumice lee side lenses on the far vent side of topographic obstacles in nearvent exposures the taupo ivd shows lensoid and cross stratified bed forms even where it stands on a planar surface attributed to deposition from a flow travelling at an exceedingly high velocity an ivd can be distinguished from a poorly sorted pyroclastic fall deposit because the beds in it show more rapid lateral variations in thickness it may show a low angle cross stratification and it contains carbonised wood from trees not in the position of growth from the deposit of a wet base surge because it lacks vesicles and strong antidune like structures and contains carbonised vegetation and from a hot and dry pyroclastic surge deposit because it possesses a high content of pumice and fines the significance of an ivd is that it records the passage of a pyroclastic flow where the flow itself has moved farther on

effect of el nino southern oscillation on the dynamical thermal and chemical structure of the middle atmosphere 1 a simulation of the middle atmosphere is presented using a general circulation model gcm forced with observed sea surface temperature for the period 1950 2000 the gcm extends to the lower thermosphere and reproduces realistic dynamical and temperature distributions the period contains several el nino and la nina events which are identified using the nino3 index composite anomalies of relevant meteorological fields are obtained by stratifying the northern winter season according to the nino3 index these anomalies have the structure of vertically propagating planetary waves extending from the troposphere to the mesosphere circulation anomalies in the middle atmosphere are accompanied by large temperature anomalies that are of opposite sign in the stratosphere and mesosphere the former being warmer and the latter colder during el nino events near the summer mesopause changes in momentum deposition by parameterized gravity waves results in warming during el nino detailed statistical analysis is used to determine the significance of these anomalies a chemical transport simulation is carried out using output from the gcm it shows that when the lower stratosphere is colder as during la nina events some ozone depletion takes place conversely when the lower stratosphere is warmer and more disturbed as is the case during el nino events heterogeneous chemical processes are inhibited

field observations and surface characteristics of pristine block and ash flow deposits from the 2006 eruption of merapi volcano java indonesia abstract a series of pristine block and ash flow deposits from the may june 2006 eruption of merapi represent an exceptional record of small volume pyroclastic flows generated by gravitational lava dome collapses over a period of about two months the deposits form nine overlapping lobes reaching 7 km from the summit in the gendol river valley on the volcano s southern flank which were produced by successive flows generated during and after the major dome collapse event on june 14 both single pulse post june 14 events and multiple pulse pyroclastic flows generated by sustained dome collapses on june 14 are recognised and three types of deposits spread over an area of 4 7 km are distinguished totalling 13 3 10 6 m 3 1 valley confined basal avalanche deposits 11 7 10 6 m 3 in the gendol river valley 2 overbank pyroclastic flow and associated surge deposits 1 4 10 6 m 3 where parts of the basal avalanche spread laterally onto interfluves and were subsequently channeled into the surrounding river valleys and 3 dilute ash cloud surge deposits 0 2 10 6 m 3 along valley margins variations in the distribution surface morphology and lithology of the deposits are related to the source materials involved in individual pyroclastic flow forming events and varying modes of transport and deposition of the different flows inferred flow velocities of the largest block and ash flows generated on june 14 vary from 43 8 13 5 m s for the basal avalanche and from 62 6 24 2 m s for the ash cloud surge the minimum temperatures range from 400 c for the basal avalanche to 165 c for the overlying ash cloud due to the potential of being re channeled into adjacent river valleys and flowing laterally away from the main river channel the overbank pyroclastic flows are considered the most hazardous part of the block and ash flow system the conditions that lead to their development during flow transport and deposition must be taken into account when assessing future pyroclastic flow hazards at merapi and similar volcanoes elsewhere

extratropical cyclogenesis changes in connection with tropospheric enso teleconnections to the north atlantic role of stationary and transient waves abstractthis study investigates mechanisms for changes in wintertime extratropical cyclogenesis over north america and the north atlantic during different phases of el nino southern oscillation en

lava flows as kinematic waves a recently proposed model for the emplacement of lava flows is reinterpreted as a kinematic wave theory for the depth of the flow with this interpretation the longitudinal profile of an advancing flow is considered to be a propagating waveform with its length limited continuously by the amount of lava extruded the application of kinematic wave formalism provides new insights into the effects of time dependent source behavior on the shape and extent of the wave eruption behavior with a period of increasing flow depth at the source is shown to produce so called breaking points in the depth profile where the kinematic wave model itself could be invalid two models of such eruption behavior are investigated and this is shown not to be the case specifically when the conservation of lava volume is imposed the breaking points always reside beyond the front of the wave in general it is found that source behavior propagates downstream faster than the flow advances thus only a fraction of the source time dependence is reflected in the shape of the kinematic wave the remainder of the time dependent source effects must be deposited in the flow front lateral margins or solidifying crust or be dissipated irretrievably by processes not included in the model the fraction of eruption history contained in the advancing waveform depends crucially on the nature of the flow rate flow depth relation for the lava distal surface waves budding at the nose of the flow distal levee collapse and other volcanological observations may be manifestations of time dependent source behavior that advanced beyond the kinematic wave front

the generation of global rotational flow by steady idealized tropical divergence abstract tropical convective heating is balanced on the large scale by the adiabatic cooling of ascent the horizontal divergence of the wind above this heating may be viewed as driving the upper tropospheric rotational wind field a vorticity equation model is used to diagnose this relationship it is shown that because of the advection of vorticity by the divergent component of the flow the rossby wave source can be very different from the simple fd source often used in particular an equatorial region of divergence situated in easterly winds can lead to a rossby wave source in the subtropical westerlies where it is extremely effective this part of the source can be relatively insensitive to the longitudinal position of the equatorial divergence a divergence field which is asymmetric about the equator can lead to a quite symmetric rossby wave source for a steady frictionless flow the rossby wave source averaged over regions within closed streamfunction or absolute vorticity contours is under cert