the taupo eruption new zealand i general aspects the ca a d 186 taupo eruption was the latest eruption at the taupo volcanic centre occurring from a vent at horomatangi reefs now submerged beneath lake taupo in the central north island of new zealand minor initial phreatomagmatic activity was followed by the dry vent 6 km 3 hatepe plinian outburst large amounts of water then entered the vent during the 2 5 km 3 hatepe phreatoplinian ash phase eventually stopping the eruption though large amounts of water continued to be ejected from the vent area causing gullying of the ash deposits after a break of several hours to weeks phreatoplinian activity resumed generating the 1 3 km 3 rotongaio ash notable for its fine grainsize and for containing significant quantities of non or poorly vesicular juvenile material the vent area then became dry again and eruption rates and power markedly increased into the 23 km 3 taupo ultraplinian phase which is the most powerful plinian outburst yet documented synchronous with this ultraplinian activity lesser volumes of non to partially welded ignimbrite were generated by diversion of ejecta from or partial collapse of the eruption column the rapid rate of magma withdraw al during this phase removed support from the vent area to trigger local vent collapse and initiate the catastrophic eruption of the ca 30 km 3 taupo ignimbrite finally after some years lava was extruded on to the floor of the reformed lake taupo and floating fragments derived from the lava carapace were driven ashore the known eruption volume is more than 65 km 3 while additional volumes are represented by primary material now beneath lake taupo and layer 3 to the ignim brite phases a total volume of more than 105 km 3 is likely equivalent to more than 35 km 3 of magma plus more than 3 km 3 of lithic debris airfall deposits more than 10 cm thick blanketed 30000 km 2 of land east of the vent while ignimbrite covers a near circular area of 20000 km 2 widespread and locally severe ground shaking occurred during but mostly after the eruption associated with subsidence in the lake taupo basin secondary deposits are abundant above and extending beyond the taupo ignimbrite consisting of the products of surface water interacting with the still hot ignimbrite and subsequent water reworking of the light pumiceous materials the complexity and size of this eruption preclude accurate forecasting of the size nature and return period of the inevitable next eruption from the taupo volcanic centre

wind generated eddy characteristics in the lee of the island of hawaii 1 weekly satellite sea surface height ssh anomaly data are used to clarify the mesoscale eddy characteristics in the lee of the island of hawaii the largest island in the hawaiian island chain the lee eddy variability can be separated into two geographical regions in the immediate lee southwest of hawaii region e eddy signals have a predominant 60 day period and a short life span whereas in the region along 19 n west of 160 w region w the eddy variability is dominated by 100 day signals and extends over a broad region by applying a linear ekman pumping model forced by the weekly quikscat wind data we find that the observed 60 day eddy signals originate in the southwest corner of hawaii and are induced by the local 60 day wind stress curl variability associated with the blocking of the trade wind by the island of hawaii the relationship between the wind forcing and the observed ssh signals demonstrates the role of the ocean as an integrator that responds more effectively to the low frequency synoptic atmospheric forcing 60 days than to the higher frequency forcing 30 days since the large amplitude 60 day ssh anomalies take 1 2 weeks to fully develop it is possible that real time observed wind stress data can be used for the prediction of these anomalies in contrast to the wind induced 60 day eddy signals in the lee of the island of hawaii the 100 day eddy signals in region w are likely generated by the instability of the sheared north equatorial current and hawaii lee countercurrent

offshore wind forcing in the gulf of tehuantepec mexico the asymmetric circulation since the early surveys carried out by the eastern tropical pacific eastropic and scripps tuna oceanographic research stor projects in the tropical pacific off mexico the northerly winds which blow over the gulf of tehuantepec were described as an important factor controlling the dynamics of this coastal ocean in january february 1989 an international team carried out the experiment tehuano designed to study the response of the gulf to these wind pulses the complete evolution of the coastal ocean after an event of moderate intensity was observed the forcing is characterized by a mostly symmetric fan shaped offshore wind jet which in turn produces a remarkably asymmetric upper ocean response while analytical results based on ekman theory forced by a symmetric offshore wind predict the formation of a symmetric dipolar circulation the observed flow consists mainly of a large 200 km in diameter anticyclonic warm core eddy in the western gulf with only a weak cyclonic counterpart in the eastern gulf intense surface cooling under the wind jet is caused by entrainment of subsurface water into the upper layer the thermocline in the west deepens with the development of the eddy which is formed initially by the advection of warm surface waters from west of the gulf east of the axis of the wind the mixed layer deepens due to wind induced entrainment while at the same time shoaling and compression of the deeper isotherms by curl induced upwelling ekman pumping strengthen the thermocline

a transbasin mode of interannual variability of the central american gap winds seasonality and large scale forcing abstracta transbasin mode tbm is identified as the leading mode of interannual surface wind variability over the intra americas seas across central america based on empirical orthogonal function analysis the tbm is associated with variability in central american gap winds most closely with the papagayo jet but with considerable signals over the gulfs of tehuantepec and panama although el nino southern oscillation enso is the main large scale forcing the tbm features a distinct seasonality due to sea level pressure slp adjustments across the pacific and atlantic during july september enso causes meridional slp gradient anomalies across central america intensifying anomalous geostrophic winds funneling through papagayo to form the tbm during wintertime enso peaks but imparts little anomalous slp gradient across central america with a weak projection on the tbm because of the competing effects of the pacific north american teleconnection and tropospheric kelvin waves besides enso tropical at

mass partition during collapsing and transitional columns by using numerical simulations pyroclast dispersal and mass partition between convective and collapsing transport systems represent a major issue in the understanding of the dynamics of quasi steady explosive eruptions and the interpretation of their deposits the spatial and temporal dispersal of pyroclasts during the initial 15 min of collapsing and transitional columns was investigated by using a transient two dimensional and three phase one gas phase and two solid phases representative of pyroclasts of varying size and density flow model the different behaviors of the column were simulated by using different water contents of the eruptive mixture and assuming both pressure balanced and overpressured conditions at the vent for each simulation results allowed the quantification of the mass of pyroclasts of different size forming the pyroclastic density current the co ignimbrite column and the convective plumes rising from the proximal area and above the fountain for collapsing columns the total mass transported in the convective system composed of the plume above the fountain and the co ignimbrite column ranges from about 10 to 30 wt of the total erupted mass according to the specific water content of the mixture at the vent fine particles are dominant in this convective system with the increase of the water content the character of the column shows a collapsing buoyant transitional behavior such a regime is characterized by greater collapse height generation of more dilute density currents shorter flow runout less steady behavior of the column and intermittent feeding of the flows for these columns the total mass forming the convective portions reaches values of up to 50 wt of the erupted pyroclasts with a significant amount of coarse particles entrained in the convective plume above the fountain at higher water contents the column becomes fully buoyant with the whole mass feeding the convective column simulations assuming overpressured conditions at the vent are characterized by more unsteady dynamics of the dispersal process with significant variations in the collapse height of the column mass flow rate of the flow and amount of mass elutriated in the convective system simulation results suggest that plinian columns that undergo a transition from convective to collapsing regimes as a consequence in our case of a water content decrease in the magma but not necessarily limited to this case would be characterized by a gradual decrease of the carrying capacity of the convective column above the fountain and by the emplacement of pyroclastic density currents which evolve from dilute to dense gradually increasing their runout

isthmus of tehuantepec wind climatology and enso signal abstract the statistical characteristics of the winds at the isthmus of tehuantepec and their seasonal and interannual variability are studied through the analysis of several datasets and a reconstruction of the winds for a 31 yr period observations show that the long term monthly mean wind speeds and frequency of occurrence of northerly winds have a strong seasonal signal with maximum values during december january minimum during may june and a relative maximum in july the frequency distribution of wind speed is bimodal a feature that is closely related to the wind direction with northerly winds being stronger based on these results and the close relationship between the across isthmus pressure differences and the local winds a statistical model is developed to get a reconstruction of 12 hourly winds through the isthmus of tehuantepec for 1964 95 the model reproduces fairly well the main characteristics of the observed winds the bimodal distribution of the wind speed and the seasonal signal in

wind velocity and wind curl variability over the black sea from quikscat and ascat satellite measurements abstract measurements of quikscat for 2000 2009 and ascat scatterometers for 2009 2016 are used to describe the variability of the black sea wind velocity and wind curl high resolution 12 5 km scatterometry data provide a possibility to investigate several small scale features hot points of the wind field in the basin related to the topographic effects they include the gap winds near the bosphorus the kerch strait and tuapse tip jets at the south and west of the crimean peninsula several capes of the anatolian coast the kolkheti valley winds wind shadow zones at the eastern turkey coast and the western crimean coast driving factors and directional variability of wind in these hot points is discussed quikscat and ascat data are used to describe seasonal and interannual variability of wind characteristics in 2000 2016 comparison with in situ data shows that quikscat noticeably overestimates wind magnitude during low winds conditions wind curl has a different sign and a completely different interannual variability in the western and eastern parts of the sea near the eastern coast of the basin high resolution satellite measurements reveal three powerful small scales maximums of cyclonic vorticity these maximums are related to the wind jets flowing around topographic obstacles in the vicinity of the kerch strait in the mountain gap near tuapse and from the kolkheti valley they are observed throughout the whole year but are largest in winter the contribution of these maximums to the overall cyclonic vorticity is essential 30 in the quikscat data and 50 in the ascat data in the western part of the basin the wind curl is negative anticyclonic on average with the highest anticyclonic curl observed in summer winds are decreasing in 2000 2016 in agreement with the data on the 20 century at the same time the basin average wind curl rises due to its increase in the eastern black sea we speculate that these trends are associated with the displacement of the siberian anticyclone to the west the related rise of pressure over the eastern europe correlates significantly with the wind curl variability on interannual time scales

surface generated mesoscale eddies transport deep sea products from hydrothermal vents atmospheric forcing which is known to have a strong influence on surface ocean dynamics and production is typically not considered in studies of the deep sea our observations and models demonstrate an unexpected influence of surface generated mesoscale eddies in the transport of hydrothermal vent efflux and of vent larvae away from the northern east pacific rise transport by these deep reaching eddies provides a mechanism for spreading the hydrothermal chemical and heat flux into the deep ocean interior and for dispersing propagules hundreds of kilometers between isolated and ephemeral communities because the eddies interacting with the east pacific rise are formed seasonally and are sensitive to phenomena such as el nino they have the potential to introduce seasonal to interannual atmospheric variations into the deep sea

anatomy and evolution of a cyclonic mesoscale eddy observed in the northeastern pacific tropical subtropical transition zone a cyclonic eddy in the ne pacific

growth of a young frequently active composite cone ngauruhoe volcano new zealand ngauruhoe cone in southern taupo volcanic zone new zealand has grown rapidly over the last 2 500 years in an alternation of effusive strombolian vulcanian and sub plinian eruptions of andesitic magma at times growth has been staccato in fashion as evidenced in the historical record each historical eruption typically lasted days to months alternating with repose periods of years to decades major historic eruptions occurred in 1870 1949 1954 1955 and 1973 1975 encompassing wide variations in eruptive style over short timescales the early period of cone building appears to have been dominated by a more continuous form of activity characterised by a series of numerous frequent explosive eruptions with associated lava flows the 2 2 km3 cone has grown in a piecemeal sectorial manner reflecting constant modification to the morphology of the summit which has funnelled eruption products to specific sectors of the cone eruption rates can be calculated on several different timescales discharge rates averaged over individual eruptive pulses vary by two orders of magnitude 2 7 280 m3 s 1 reflecting variations in high level magma ascent rates and processes such as degassing which are in turn reflected in contrasting eruptive styles lower rates e g 0 65 m3 s 1 are obtained by averaging the discharge over an entire eruption lasting several months and may correspond to the ascent rate of magma batch es feeding the eruption the long term growth rate of ngauruhoe is 0 9 km3 ky 1 this is an average rate reflecting the long term deep supply rate of magma to crustal reservoirs by looking at eruption rates on these different timescales we are better able to constrain processes occurring at various depths within the plumbing system there are few detailed studies of the growth patterns of young volcanic cones but such data are essential in understanding the dynamics of andesitic systems more than 60 lavas and pyroclastic units mapped on different sectors of ngauruhoe cone have been correlated by flow chronology and their distinctive compositions into five groups although the cone has grown rapidly ngauruhoe shows little evidence for the existence of large crustal magma reservoirs and long lived magma batches instead abrupt and non systematic changes in magma chemistry and isotopic composition between and within the five groups indicate that the volcano has an open system multi process multi directional character and erupts small 0 1 km3 and short lived 100 103 years magma batches with no simple time composition relationships between successive batches

midsummer gap winds and low level circulation over the eastern tropical pacific abstract the low level seasonal and intraseasonal wind variability over the northeastern tropical pacific netp its relationship with other variables and the connection with large and middle scale atmospheric patterns are analyzed using a suite of datasets quick scatterometer quikscat wind data show that the low level circulation over the netp is mainly affected by the northerly trades the southerly trades and the wind jets crossing through the tehuantepec papagayo and panama mountain gaps the seasonal and intraseasonal evolution of these wind systems determines the circulation patterns over the netp showing predominant easterly winds in winter and early spring and wind direction reversals in summer over the central region of the netp during summer when southerly trades are the strongest and reach their maximum northward penetration weak westerlies are observed in june easterlies in july august despite that strong southerlies tend to turn eastward and again westerlies in september octob

enso s impact on the gap wind regions of the eastern tropical pacific ocean abstractthe recently released ncep climate forecast system reanalysis cfsr is used to examine the response to enso in the northeast tropical pacific ocean netp during 1979 2009 the normally cool pacific sea surface temperatures ssts associated with wind jets through the gaps in the central american mountains at tehuantepec papagayo and panama are substantially warmer colder than the surrounding ocean during el nino la nina events ocean dynamics generate the enso related sst anomalies in the gap wind regions as the surface fluxes damp the ssts anomalies while the ekman heat transport is generally in quadrature with the anomalies the enso driven warming is associated with large scale deepening of the thermocline with the cold thermocline water at greater depths during el nino in the netp it is less likely to be vertically mixed to the surface particularly in the gap wind regions where the thermocline is normally very close to the surface the thermocline deepening is enhanced to the south

satellite observations of the wind jets off the pacific coast of central america part i case studies and statistical characteristics measurements of near surface winds by the nasa scatterometer nscat from october 1996 through june 1997 are analyzed to investigate the three major wind jets along the pacific coast of central america that blow over the gulfs of tehuantepec papagayo and panama each jet is easily identifiable as locally intense offshore winds in the lee of low elevation gaps through the sierra madre mountain range the jets have relatively narrow cross stream width but often extend several hundred kilometers or more into the pacific the tehuantepec and papagayo jets sometimes merge with the northeast trade winds of the pacific the tehuantepec jet was highly energetic with characteristic timescales of about 2 days events were triggered by high pressures associated with cold surges into the gulf of mexico that originated over the great plains of north america the papagayo and panama jets were much more persistent than the tehuantepec jets the winds at both of these lower latitude locations exhibited a strong seasonal variation with almost exclusively offshore flow from late november 1996 through late may 1997 and periods of onshore flow in october and november during the late stages of the 1996 central american monsoon season superimposed on this low frequency seasonal variation were events with characteristic timescales of a few days based on nscat data the spatial and temporal evolution of major wind events is described in detail for three representative case studies in december 1996 the jets developed sequentially from north to south consistent with the notion that wind events in the two lower latitude jets are associated with cold air outbreaks that trigger the tehuantepec jet a day or so earlier in november 1996 and march 1997 the papagayo and panama jets were strongly influenced by tropical phenomena that had little apparent association with the tehuantepec jet these latter two case studies together with the distinction between the statistical characteristics of the three jets suggest that the papagayo and panama jets are predominantly controlled by a mechanism that is very different from the across gap pressure gradients associated with high pressure systems of midlatitude origin that control the tehuantepec jet

patterns of ca sr and 87sr 86sr variation before and after a whole watershed casio3 addition at the hubbard brook experimental forest usa abstract forty one metric tons of the mineral wollastonite casio3 was applied to an 11 8 hectare watershed at the hubbard brook experimental forest hbef white mountains new hampshire usa with the goal of restoring the ca estimated to have been depleted from the soil exchange complex by acid deposition this experiment provided an opportunity to gain qualitative information on whole watershed hydrologic flow paths by studying the response of stream water chemistry to the addition of ca because the ca sr and 87sr 86sr ratios of wollastonite strongly contrast that of other ca sources in the watershed the wollastonite derived ca can be identified and its amount estimated in various ecosystem components stream water chemistry at the hbef varies seasonally due to shifts in the proportion of base flow and interflow prior to the wollastonite application seasonal variations in 87sr 86sr ratios indicated that 87sr 86sr was higher during base flow than interflow due largely to greater amounts of biotite weathering along deeper flow paths after the application ca sr and 87sr 86sr changed markedly as the high ca sr and low 87sr 86sr wollastonite dissolved and mixed with stream water the ca addition provided information on the response times of various flow paths and ion exchange processes to ca addition in this small upland watershed during the first year after the addition wollastonite applied to the near stream zone dissolved and was partially immobilized by cation exchange sites in the hyporheic zone in the second and third years after the addition we infer that much of this ca and sr was subsequently desorbed from the hyporheic zone and was exported from the watershed in stream flow in the fourth through ninth years after the addition ca and sr from wollastonite that had dissolved in upland soils was transported to the stream by interflow during wet periods when the ground water table was elevated between years three and nine the minimum annual ca sr ratio in late summer base flow increased providing evidence that ca and sr had increasingly infiltrated to the deepest flow paths strong seasonal variations in ca sr and 87sr 86sr ratios of stream water resulted from the wollastonite addition to upland forest soils and these ratios have become sensitive to changing flow paths during the annual cycle most notably high flow events now produce large excursions in stream geochemistry toward the high ca sr and low 87sr 86sr ratios of wollastonite nine years after the application we estimate that 360 kg of ca from wollastonite has been exported from the watershed in stream flow the rate of export of ca from wollastonite dissolution has stabilized at about 11 kg of ca per year which accounts for 30 of the dissolved ca in the stream water given that 19 metric tons of ca were applied to the watershed and assuming this current rate of loss it should take over 1000 years for this added ca to be transported from the watershed

equatorial kelvin waves generated in the western tropical pacific ocean trigger mass and heat transport within the middle america trench off costa rica sequences of correlated seafloor temperature current velocity and acoustic backscatter events recorded at ocean drilling program odp sites at 4300 m depth in the middle america trench have been inferred to result from tidally induced turbidity currents generated in the vicinity of the 3300 m deep sill at the southern end of the trench new data from the borehole observatories extend the temperature records to 11 years november 2002 to december 2013 and confirm the highly episodic nature of the events we present satellite altimetry data and ocean circulation model results to show that event timing is correlated with intraseasonal kelvin wave motions in the equatorial pacific the observed temperature events had a mean 1 standard deviation occurrence interval of 61 24 days which spans the periods of the first two baroclinic modes lag times between peak bottom water temperatures at the odp sites and the passage of eastward propagating kelvin wave crests at locations in the eastern equatorial pacific are consistent with the time for mode 1 waves to propagate to the southern end of the trench at a mean phase speed of 2 0 m s 1 findings indicate that kelvin wave currents augment tidal motions in the vicinity of the sill triggering turbidity currents that travel northwestward along the trench axis at mean speeds of 0 1 m s 1 we conclude that mode 1 or possibly mixed mode 1 and mode 2 baroclinic kelvin waves generated by large scale atmospheric processes in the western tropical pacific lead to heat and mass transport deep within middle america trench in the eastern tropical pacific

intraseasonal oscillations in sea level along the west coast of the americas abstract hourly observations of coastal sea level at stations from peru to british columbia are analyzed for low frequency content a space time contour plot of sea level from four years of data during the 1971 75 period shows the meridional structure of the seasonal cycle and interannual variability associated with the 1972 73 el nino oscillations with intraseasonal periods of 36 73 days are also evident coherent over alongshore distances of several thousand kilometers further investigation using spectral methods and empirical orthogonal function analysis in the frequency domain reveals in particular that intraseasonal sea level variability has a peak in spectral density along the coasts of south america central america and mexico with high coherence from near the equator tumaco 2 n north to central california 34 n and south to at least callao 12 s phase propagation north of the equator is poleward at 150 200 kilometers day atmospheric pressure alongshore wind stress and wind stress cu

large scale phreatomagmatic silicic volcanism a case study from new zealand abstract pyroclastic deposits of the 20 000 year old wairakei formation occur in the region surrounding lake taupo in the central north island of new zealand recent advances in the correlation of both proximal and distal equivalents of the wairakei deposits show that they were the result of one large eruption the ash layers once covered most of new zealand they are also present in deep sea cores from the sw pacific and on the chatham islands the dispersal and grain size parameters of the ash fall members indicate that their vent area was within the taupo volcano tectonic depression which for a long period has contained a large lake the wairakei eruption is interpreted to have been phreatomagmatic throughout each phase of the eruption sequence generated its own characteristic deposits the sequence of events can be summarized as follows 1 eruption and deposition of a white fine grained bedded fall deposit 2 eruption and deposition of a medium grained pumice fall deposit 3 generation of ultra fine wet ash clouds with a fall deposit accumulating largely as aggregates and accretionary lapilli accompanied by base surges 4 formation of water cooled pyroclastic flows and deposition of an extensive ignimbrite 5 return to a dominantly vertical eruption column and deposition of a medium grained bedded ash fall immediately followed by another wet ultra fine fall deposit charged with accretionary lapilli finally 6 an ignimbrite less widespread than that of phase 4 was produced co ignimbrite fall deposits of fine vitric dust and medium grained pumice were laid down over a huge area there may have been a short hiatus in activity between phases 4 and 5

inertial wind path and sea surface temperature patterns near the gulf of tehuantepec and gulf of papagayo during the northern hemisphere winter the surface atmospheric pressure on the gulf of mexico side of central america is often higher than that on the pacific side the resultant southward pressure gradient drives strong southward winds through a gap in the sierra madre mountain range at the isthmus of tehuantepec the atmospheric jet is narrow in comparison with the relevant radius of deformation so when it leaves the coast and flows out over the gulf of tehuantepec it is an inertial jet therefore the jet is expected to be deflected into a clockwise inertial circle by the coriolis force a similar process should also occur for central american atmospheric jets through mountain range gaps near the gulf of papagayo satellite measurements of sea surface temperature together with coastal wind data for the first 41 days of 1986 were examined to see if the expected wind path influenced sea surface temperature sst near the gulf of tehuantepec and the gulf of papagayo consecutive daily satellite images when the coastal southward tehuantepec wind increased suggest that the initial development of cold surface water in a clockwise loop is due to the wind mixing the shallow thermocline surface water along its inertial path a simple 1 layer analytical ocean model suggests in agreement with observations that the wind can drive surface quasi geostrophic currents of 1 m s 1 since the wind path is circular the wind actually generates a clockwise rotating ocean eddy with the approximate scale of the wind inertial circle the satellite sea surface temperature measurements also suggest that the wind driven surface ocean current is unstable in addition stronger gradients in sst to the right of the expected wind flow are consistent with advection of sea surface temperature by ocean surface ekman flow

surface morphology of caldera forming eruption deposits revealed by lidar mapping of crater lake national park oregon implications for deposition and surface modification abstract large explosive eruptions of silicic magma can produce widespread pumice fall extensive ignimbrite sheets and collapse calderas the surfaces of voluminous ignimbrites are rarely preserved or documented because most terrestrial examples are heavily vegetated or severely modified by post depositional processes much research addresses the internal sedimentary characteristics flow processes and depositional mechanisms of ignimbrites however surface features of ignimbrites are less well documented and understood except for comparatively small volume deposits of historical eruptions the 7700 calendar year b p climactic eruption of mount manama usa vented 50 km 3 of magma deposited first as rhyodacite pumice fall and then as a zoned rhyodacite to andesite ignimbrite as crater lake caldera collapsed lidar collected during summer 2010 reveals the remarkably well preserved surface of the manama ignimbrite and related deposits surrounding crater lake caldera in unprecedented detail despite forest cover the 1 m lateral and 4 cm vertical resolution lidar allows surface morphologies to be classified surface morphologies are created by internal depositional processes and can point to the processes at work when pyroclastic flows come to rest we describe nine surface features including furrow ridge sets and wedge shaped mounds in pumice fall eroded by high energy pyroclastic surges flow parallel ridges that record the passage of multiple pyroclastic flows perched benches of marginal deposits stranded by more mobile pyroclastic flow cores hummocks of dense clasts interpreted as lag deposit transverse ridges that mark the compression and imbrication of flows as they came to rest scarps indicating ignimbrite remobilization fields of closely spaced pits caused by phreatic explosions fractures and cracks due to extensional processes resulting from ignimbrite volume loss and stream channels eroded in the newly formed surface the nine morphologies presented here illustrate a dynamic depositional environment that varied spatially and with time during the eruption and show that multiple processes modified the ignimbrite after deposition both during and after the eruption

the intraseasonal oscillation in eastern pacific sea levels how is it forced abstract daily sea level and surface winds at eastern pacific shore locations and equatorial islands together with gridded five day averages of 850 mb winds have been analyzed for the 1979 84 period to determine how the 40 60 day intraseasonal oscillation of eastern pacific sea levels is forced as described by spillane et al for 1971 75 the oscillation was also present in 1980 84 from callao peru to san francisco with maximum energy near 52 57 days and band limits of 43 and 65 days during 1980 84 there was no evidence for forcing of the large scale oscillation in the eastern pacific although a local contribution of forcing was superimposed on the remote signal at the california stations interannual fluctuations in amplitude were evident in the sea level time series consistent with those of the corresponding wind oscillation in the western equatorial pacific the oscillation was best developed in both variables in 1980 82 and became weak or nonexistent during the recovery phase of the 1982 83 e

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

using paleoseismology and tephrochronology to reconstruct fault rupturing and hydrothermal activity since c 40 ka in taupo rift new zealand abstract the taupo volcanic zone tvz in north island new zealand is the on land continuation of the tonga kermadec arc formed in the quaternary at the obliquely convergent boundary of the pacific and australian tectonic plates the central tvz is a region of intense silicic volcanism and active rifting with a very high heat flux within this zone is a dynamic landscape affected by a dense active fault network the taupo rift in this rift the ngakuru graben hosts fossil hydrothermal systems in an area parallel to numerous active faults including the east strand of whirinaki fault that forms a major structure using various geoscientific techniques including mapping stratigraphy paleoseismic trenching and tephrostratigraphy in conjunction with lidar derived dems we reconstruct and date the fault s rupture history along with hydrothermal activity including silica sinter development since c 40 000 calendar years ago 40 cal ka at a site near hossack road called meade ages for kawakawa c 25 4 cal ka okareka c 21 8 cal ka rotorua c 15 6 cal ka rotoma c 9 4 cal ka and taupo c 1 7 cal ka tephras enabled us to date five identified fault rupture events using the meade trench excavation slip rates of 2 66 0 77 mm yr pre kawakawa tephra 0 28 0 04 mm yr between c 25 4 ka and taupo and 0 51 0 19 mm yr post taupo and the recurrence interval of 5500 cal yr during the last c 25 4 cal kyr all correlate with events of similar ages determined from studies on other trenches on whirinaki fault intercalated with tahuna tephra c 39 3 cal ka and additionally dated at c 38 9 cal ka using radiocarbon the hydrothermal sinter began developing at the meade site at c 39 cal ka and ceased by c 21 8 cal ka marked by okareka tephra we examine the causative relationship between fault activity and the development of sinter by comparing the chronology of volcanic eruptions and fault rupturing events with that of sinter formation as recorded in three neighbouring sites mangatete matthews and fitzpatrick the findings improve understanding of the complex rupture behaviour of faulting and provide evidence for relationships between tectonic and hydrothermal activities which were additionally influenced by the impacts of climatic change and geomorphic processes on landscape evolution within the late quaternary period the study also exemplifies the unique value of tephrochronology in helping to disentangle complex geological deposits and events in an extremely dynamic part of the earth s surface the taupo rift

winter eddy genesis in the eastern south china sea due to orographic wind jets abstract generation of mesoscale eddies in the eastern south china sea scs in winters during august 1999 to july 2002 is studied with a reduced gravity model it is found that the orographic wind jets associated with the northeast winter monsoon and the gaps in the mountainous island chain along the eastern boundary of the scs can spin up cyclonic and anticyclonic eddies over the scs results suggest that direct wind forcing could be an important generation mechanism for the rich eddy activity in the scs and that to simulate this mechanism the resolution of the wind forcing has to be high enough to resolve the local wind jets induced by orographic effects

particle transport in subaqueous eruptions an experimental investigation abstract subaqueous volcanic eruptions are natural events common under the world s oceans here we report results from bench scale underwater explosions that entrain and eject particles into a water tank our aim was to examine how particles are transferred to the water column and begin to sediment from it and to visualize and interpret evolution of the eruption cloud understanding particle transfer to water is a key requirement for using deposit characteristics to infer behaviour and evolution of an underwater eruption for the experiments here we used compressed argon to force different types of particles under known driving pressures into water within a container and recorded the results at 1 mpx frame and 1000 fps three types of runs were completed 1 particles within water were driven into a water filled container 2 dry particles were driven into water 3 dry particles were driven into air at atmospheric pressure across the range of particles used for all subaqueous runs we observed a initial doming b a main expansion of decompressing gas and c a phase of necking when a forced plume separated from the driving jet phase c did not take place for the subaerial runs a key observation is that none of the subaqueous explosions produced a single simple open cavity in all cases multiphase mixtures of gas bubbles particles and water were formed explosions in which the expanding argon ejects particles in air analogous to delivery of particles created in an explosion produce jets and forced plumes that release particles into the tank more readily than do those in which particles in water are driven into the tank the latter runs mimic propulsion of an existing vent slurry by an explosion explosions with different particle types also yielded differences in behaviour controlled primarily by particle mass particle density and particle population homogeneity particles were quickly delivered into the water column during plume rise following necking with minor transfer along initial jet margins and for breaching explosions additional delivery from splashdown of tephra jets plume rise after necking also draws upward and re entrains some groups of particles most delivered particles participate in initiating vertical sediment gravity flows some of which reached the tank floor and began lateral flow within the short duration of our experiments particles transferred from plume margins locally were sufficiently well separated to settle independently from suspension

east pacific ocean eddies and their relationship to subseasonal variability in central american wind jets subseasonal variability in sea surface height ssh over the east pacific warm pool off central america is investigated using satellite observations and an eddy resolving ocean general circulation model ssh variability is organized into two southwest tilted bands on the northwest flank of the tehuantepec and papagayo wind jets and collocated with the thermocline troughs eddy like features of wavelength similar to 600 km propagate southwestward along the high variance bands at a speed of 9 13 cm s wind fluctuations are important for eddy formation in the gulf of tehuantepec with a recurring interval of 40 90 days when forced by satellite wind observations the model reproduces the two high variance bands and the phase propagation of the tehuantepec eddies our observational analysis and model simulation suggest the following evolution of the tehuantepec eddies on the subseasonal timescale in response to the gap wind intensification a coastal anticyclonic eddy forms on the northwest flank of the wind jet and strengthens as it propagates offshore in the following two to three weeks an energetics analysis based on the model simulation indicates that besides wind work barotropic and baroclinic instabilities of the mean flow are important for the eddy growth both observational and model results suggest a re intensification of the anticyclonic eddy in response to the subsequent wind jet event off papagayo ocean eddy formation is not well correlated with local wind jet variability in both the gulfs of tehuantepec and papagayo subseasonal ssh variability is preferentially excited on the northwest flank of the wind jet factors for this asymmetry about the wind jet axis as well as the origins of wind jet variability are discussed

on the evolution of coastally trapped waves generated by hurricane juliette along the mexican west coast 1 an operational real time eddy resolving 1 16 global ocean nowcast forecast system is used to study the evolution of two coastally trapped waves generated by hurricane juliette along the mexican west coast results indicate that the first wave was generated along mainland mexico and it propagated poleward as a free coastally trapped wave it also generated anticyclonic eddies near cabo corrientes and the maria islands upon entering the gulf of california the wave weakened cyclonic eddies and after reaching the shelf break north of guaymas it reversed direction and propagated southward along the east coast of the baja california peninsula bcp next the wave generated an anticyclonic eddy at cabo san lucas finally the wave weakened while exiting the gulf and propagated northward along the bcp west coast the second coastally trapped wave was generated by juliette s poleward winds along the bcp west coast but was subsequently greatly weakened by juliette s equatorward winds

the 1993 superstorm cold surge frontal structure gap flow and tropical impact in the wake of the eastern united states cyclone of 12 14 march 1993 a cold surge originating over alaska and western canada brought northerlies exceeding 20 m s21 and temperature decreases up to 158c over 24 h into mexico and central america this paper addresses the multiscale aspects of the surge from the planetary scale to the mesoscale focusing on 1 the structure and evolution of the leading edge of the cold surge 2 the reasons for its extraordinary intensity and equatorward extent and 3 the impact of the surge on the tropics specifically on the strength of the trade winds and on the sea surface temperature in the eastern pacific the cold surge was initiated as a developing cyclone over the gulf of mexico and an upstream anticyclone east of the rockies caused an along barrier pressure gradient to form forcing topographically channeled northerlies along the rocky and sierra madre mountains to transport cold air equatorward on the mesoscale the leading edge of the cold surge possessed nonclassical frontal structure for example as the cold surge entered mexico the coldest air and the strongest wind arrived at about 900 hpa before affecting the surface suggestive of a tipped forward leading edge to the surge also satellite imagery and surface observations indicate that the leading edge appeared to be successively regenerated in the warm presurge air the cold surge had characteristics reminiscent of a kelvin wave a tipped forward cold front a pressure jump line a bore and a gravity current but none of these conceptual dynamical models was fully applicable associated with the cold surge gap winds up to 25 m s21 were observed in the gulfs of tehuantepec a tehuantepecer fonseca papagayo and panama owing to the strong cross mountain pressure gradient in the case of the tehuantepecer a rope cloud emanated from the isthmus of tehuantepec and turned anticyclonically consistent with an inertial oscillation on the synoptic and planetary scales the extraordinary equatorward extent of the cold surge was aided by topographic channeling similar to cold air damming by a low latitude upper tropospheric trough and by the lower branch of the secondary circulation associated with a confluent jet entrance region aloft the cold surge also impacted the tropical atmosphere and ocean by contributing to the strengthening of the northeast trade winds over the eastern pacific ocean and by inducing local cooling of the sea surface temperature in the gulfs of tehuantepec and papagayo by about 48 88c

equatorially forced intraseasonal propagations along the peru chile coast and their relation with the nearshore eddy activity in 1992 2000 a modeling study 1 a regional eddy resolving oceanic model spanning the 1992 2000 period is used to study the influence of 50 to 80 day intraseasonal equatorial kelvin waves iekw on mesoscale eddy activity off the west coast of peru and northern and central chile the model is shown to realistically simulate nearshore intraseasonal sea level variability poleward propagation of equatorially forced coastal trapped waves along the coastal waveguide and offshore variability related to mesoscale eddies and rossby waves rw in agreement with linear theory rw are confined equatorward of 12 s in the 50 80 days period range south of that critical latitude westward propagation is dominated by energetic mesoscale signals resulting mainly from coastal flow instability sensitivity experiments to the open boundary conditions are then used to estimate to what extent eddy activity is impacted by the remote equatorial forcing a coastal increase in eddy kinetic energy related to the energetic 60 day iekw activity present in the open boundary forcing is evidenced and is largest off northern peru whereas no major changes are observed offshore additional regional simulations with different open boundary conditions corroborate our findings and suggest that this limited effect of iekw on the offshore eddy kinetic energy may be a robust feature citation belmadani a v echevin b dewitte and f colas 2012 equatorially forced intraseasonal propagations along the peru chile coast and their relation with the nearshore eddy activity in 1992 2000 a modeling study j geophys res 117 c04025 doi 10 1029 2011jc007848

sea level variability in the eastern tropical pacific as observed by topex and tropical ocean global atmosphere tropical atmosphere ocean experiment sea surface height measurements from the topex altimeter and dynamic height from tropical ocean global atmosphere tropical atmosphere ocean toga tao moorings are used to explore sea level variability in the northeastern tropical pacific ocean after the annual harmonic is removed there are two distinct bands of variability one band is centered at 5 n to 7 n and extends from 165 w to 110 w and the other band is centered at 10 n to 12 n and extends from 120 w to the coast of central america the correspondence between the two independent observation data sets at 5 n is excellent with correlations of about 90 the variability at 5 7 n is identified as instability waves formed just south of the north equatorial countercurrent during the months of july through march wave amplitudes are largest in the range of longitudes 160 140 w where they can exceed 10 cm the waves disappear when the equatorial current system weakens during the months of march through may the variability at 11 n in 1993 has the form of anticyclonic eddies these eddies propagate westward at a speed of about 17 cm s 1 consistent with the dispersion characteristics of free rossby waves the eddies are shown to have their origin near the coast of central america during northern fall and winter their formation seems to result from intense wind bursts across the gulfs of tehuantepec and papagayo which generate strong anticyclonic ocean eddies the disappearance of the eddies in the summer of 1993 coincides with the seasonal intensification of equatorial currents thus the variability at 11 n has very little overlap in time with the variability at 5 n

critical frequencies at ocean boundaries past theoretical work has shown that for low frequency flow at a given ocean boundary location a critical frequency c exists such that for c unforced motion is trapped to the coast while for c energy leaves the coast alternatively for motion of a given frequency on the boundary there exists a critical latitude such that the motion is trapped to the coast poleward of that latitude but equatorward it is not this theory is discussed physically for both meridional and nonmeridional boundaries the simple formula for critical frequency along a nonmeridional boundary is used to document critical periods for the eastern and western atlantic pacific and indian ocean boundaries the theory occasionally breaks down when boundary curvature is too large

environmental impact of the 1 8 ka taupo eruption new zealand landscape responses to a large scale explosive rhyolite eruption abstract large scale ignimbrite eruptions from rhyolitic caldera volcanoes can trigger geologically instantaneous changes in sedimentary systems over huge areas by either burying existing environments or overloading them with vast quantities of unconsolidated particulate material the post eruption readjustment of the landscape to such perturbations is one of the most dramatic processes in physical sedimentology exemplified here by the 1 8 ka taupo eruption in the central north island of new zealand this eruption generated voluminous fall deposits then climaxed with emplacement of a c 30 km 3 non welded ignimbrite over a near circular area of c 20 000 km 2 approximately 90 of the area but the headwaters of many of the north island s largest rivers were impacted by both the primary pyroclastic fall and flow material large scale post eruption remobilisation of this material coupled with the re establishment of fluvial systems occurred in a distinct sequence as recorded by the evolution of sedimentary facies in different sub environments following an initial period dominated by mass flows re establishment of fluvial systems began with the headward erosion of box canyons through the ponded ignimbrite deposits a process often associated with the break out of temporary lakes aggradational streams developed in these channels rapidly evolved from shallow ephemeral sediment laden outbursts associated with flash flood events to deeper permanent braided rivers before declining sediment yields led to retrenchment of single thread rivers and a return to pre eruption gradients and bedloads years to decades later typically the modern profile of many streams and rivers follow closely their pre eruption profiles and incision and erosion is overwhelmingly confined to the deposits of the eruption itself although the general remobilisation pattern is similar for all impacted river systems detailed studies of the waikato rangitaiki mohaka ngaruroro and whanganui catchments show that the relative timing and scale of each eruption response phase differs between each catchment these reflect differences in catchment physiography and hydrology and the volume and type of pyroclastic material deposited in each ultimately the landscape response reflects the relative spatial distributions of and the volumetric ratios between the volumes of pyroclastic debris water and accommodation space in the basin cf kataoka and manville this volume

pyroclastic flows and surges over water an example from the 1883 krakatau eruption pyroclastic deposits from the 1883 eruption of krakatau are described from areas northeast of the volcano on the islands of sebesi sebuku and lagoendi and the southeast coast of sumatra massive and poorly stratified units formed predominantly from pyroclastic flows and surges that traveled over the sea for distances up to 80 km granulometric and lithologic characteristics of the deposits indicate that they represent the complement of proximal subaerial and submarine pyroclastic flow deposits laid down on and close to the krakatau islands the distal deposits exhibit a decrease in sorting coefficient median grain size and thickness with increasing distance from krakatau crystal fractionation is consistent with the distal facies being derived from the upper part of gravitationally segregated pyroclastic flows in which the relative amount of crystal enrichment and abundance of dense lithic clasts diminished upwards the deposits are correlated to a major pyroclastic flow phase that occurred on the morning of 27 august at approximately 10 a m energetic flows spread out away from the volcano at speeds in excess of 100 km h and traveled up to 80 km from source the flows retained temperatures high enough to burn victims on the sw coast of sumatra historical accounts from ships in the sunda straits constrain the area affected by the flows to a minimum of 4x103 km2 at the distal edge of this area the flows were relatively dilute and turbulent yet carried enough material to deposit several tens of centimeters of tephra the great mobility of the krakatau flows from the 10 a m activity may be the result of enhanced runout over the sea it is proposed that the generation of steam at the flow seawater interface may have led to a reduction in the sedimentation of particles and consequently a delay in the time before the flows ceased lateral motion and became buoyantly convective the buoyant distal edge of these ash and steam laden clouds lifted off into the atmosphere leading to cooling condensation and mud rain

rossby wave radiation in the cape verde frontal zone abstract radiating baroclinic rossby waves excited through instability of the cape verde frontal zone are proposed as a mechanism for the generation of mesoscale variability at middepth 1000 m in the southeastern north atlantic basin linear quasigeostrophic theory is applied to an idealized front representative of the cape verde frontal zone to demonstrate that the front is unstable to modes that may radiate away from the frontal region as baroclinic rossby waves evidence for the existence of these waves is obtained from an eddy resolving basin scale general circulation primitive equation model in addition the model fields are used to identify characteristic signature of the waves in terms of quantities that may be directly observed in the ocean lagrangian trajectories reynolds stress eddy kinetic energy and frequency spectra taken from sofar float and current meter records are all in good agreement with the amplitude and distribution implied by the wave radiation in both the linear theory and

anatomy and evolution of a cyclonic mesoscale eddy observed in the northeastern pacific tropical subtropical transition zone 1 in november 2005 off cabo corrientes a cyclonic eddy was sampled from i remotely sensed data of sea level anomaly near surface wind chlorophyll a concentration and sea surface temperature and ii direct observations from a lowered acoustic doppler profiler and a conductivity temperature and depth sensor the sea level anomaly data set and an automated eddy detection method showed that this vortex formed near the mexican coast and traveled westward northwestward 1000 km into the open ocean for 8 months surface winds and currents indicated that the cyclone was generated during a coastal upwelling event that occurred simultaneously with an equatorward flow located close to the coast during its growing phase the eddy extended from the surface to 750 m depth and mixed the water column in the first 100 m showing an eastward shift of the eddy axis toward the sea surface of 1 5 of longitude that generated a southward meridional heat transport in the upper layers integrated in the vertical this heat transport accounted for a total of 105 1012 w within the region of the eddy the estimation of the available heat and salt anomaly contents revealed that the eddy transported relatively cold salty and anoxic waters associated with the subtropical subsurface water mass while traveling offshore the cyclonic eddy also exhibited relatively higher chlorophyll a concentrations at the sea surface than its surroundings comparison of some surface properties estimated from satellite and in situ data showed that satellite data tend to underestimate its amplitude and orbital geostrophic velocity

characteristics of wind generated rings in the eastern tropical pacific ocean eddies are generated in the eastern tropical pacific 3 s 23 n 75 105 w by winds blowing through central american mountain passes from the atlantic we used coastal zone color scanner czcs and advanced very high resolution radiometer avhrr satellite imagery complemented with monthly in situ sea surface temperature and wind series from the comprehensive ocean atmosphere data set coads to study these eddies and their effect on pigment concentrations in the region pigment values in the gulf of tehuantepec generally reach higher values in november march before those in the gulf of papagayo the eddies generated in the gulf of tehuantepec are associated with passages of cold fronts across the gulf of mexico from the north while the eddies off papagayo and panama are associated with increases in trade wind intensity czcs images showed larger numbers of eddies per season than have been previously reported on the basis of in situ and avhrr observations or numerical simulations we counted 13 eddies in 1979 1980 8 in 1984 1985 and 6 in 1985 1986 the eddies transfer both energy and biological constituents from the continental margin to the offshore tropical pacific the eddies frequently moved distances in excess of 1500 km from their point of origin both anticyclonic and cyclonic eddies are generated but in general there are more anticyclones anticyclonic eddies generally moved to the southwest some cyclonic eddies moved to the south and southeast along the central american coast and appeared to be trapped by the cyclonic costa rica thermal dome eddies traveled at speeds varying between 9 and 21 cm s 1 and had diameters of 100 500 km phytoplankton concentrations associated with the eddies varied from 2 to 10 mg m 3 within 70 km of the coast to 1 mg m 3 up to 600 km of the coast between late april and october fewer eddies were observed and phytoplankton concentrations were lower 0 25 mg m 3 and more uniform over the region

intraseasonal variability of sea surface height in the bay of bengal intraseasonal variability isv of sea surface height ssh over the bay of bengal bob is studied using altimetry data and an eddy resolving ocean model in both the model hindcast and satellite observations large ssh isv is found along the eastern and northern coasts of the bob in the western bob and in a zonal band across the bay centered near 5 degrees n the isv displays a clear seasonality in the western bob it reaches its annual maximum in spring whereas it does so in summer and autumn southeast of sri lanka driven by equatorial intraseasonal winds equatorial kelvin waves propagate eastward reach the western coast of sumatra and reflect there to propagate around the perimeter of the bob as coastally trapped waves two distinct bands of high eddy activity are detected in the western and central bob respectively in both bands isolated eddies propagate southwestward eddy formation in the eddy train in the central bay is linked to the coastal wave as it bends around the corner of the irrawaddy delta off myanmar eddy activity contributes to the high isv in the central bay to some extent an energetics analysis indicates that high total eddy energy in the western bob is due to barotropic baroclinic instability of the mean current citation cheng x s p xie j p mccreary y qi and y du 2013 intraseasonal variability of sea surface height in the bay of bengal j geophys res oceans 118 816 830 doi 10 1002 jgrc 20075

evidence of inertially generated coastal trapped waves in the eastern tropical pacific observations of coastal trapped waves ctw are limited by instrumentation technologies and temporal and spatial resolutions hence their complete description is still limited in the present work we used measurements from high frequency radio scatterometers hfr to analyze the subinertial dynamics of the gulf of tehuantepec in the mexican pacific a region strongly influenced by offshore gap winds the data showed subinertial oscillations that may be explained by poleward propagating ctws the oscillations showed higher coherence 95 confidence with gap winds in the gulfs of papagayo and panama than with local winds vertical thermocline oscillations measured with a moored thermistor chain also showed subinertial oscillations coherent with papagayo and panama winds the period of the observed oscillations was 4 days which corresponds to the inertial period of the gulf of panama this suggests that inertial oscillations generated by offshore wind outbursts over panama may have traveled northward along the coastal shelf and were detected as surface current pulses by the hfr installed approximately 2000 km further north in the gulf of tehuantepec to further explore the presence of ctws the 4 day band pass filtered currents measured by the hfr were analyzed using empirical orthogonal functions we found that the first mode behaved like a ctw confined to the shelf break additionally the observed oscillations were compared with baroclinic and barotropic ctw models the results support the notion that nearly inertial baroclinic ctws are generated in the gulfs of panama and papagayo and then propagate toward the gulf of tehuantepec

the basal ash deposit of the sovana eruption vulsini volcanoes central italy the product of a dilute pyroclastic density current a low aspect ratio decimeter thick ash deposit axisymmetrically distributed around the latera caldera western vulsini volcanoes central italy has been studied by means of field and laboratory investigations field studies comprise facies analysis at centimeter scale and maximum clast size and deposit thickness measurements grain size and component distribution chemical composition and particle morphoscopic features have been determined on selected samples we discuss the co ignimbrite ash fall vs pyroclastic surge origin of the deposit and the hydrovolcanic vs magmatic eruption nature complex facies association textural features and grain size data rule out an ash fall origin for the whole deposit the hydrovolcanic nature of the eruption has been discarded on the grounds of componentry and morphoscopic features of vitric fragments we propose that the main body of the ash deposit formed from a radially expanding dilute turbulent pyroclastic density current originated by a continuous collapse of a low altitude a few kilometers eruptive column with a possible radial jet component

sedimentology and allostratigraphy of post 240 ka to pre 26 5 ka lacustrine terraces at intracaldera lake rotorua taupo volcanic zone new zealand abstract lake rotorua partially occupies a nearly circular 20 km diameter volcano tectonic depression formed at c 240 ka by eruption of the voluminous mamaku ignimbrite three distinct lacustrine littoral terraces defined on the basis of contrasting geomorphology and field relations and separated by tephrostratigraphically dateable unconformities and basin floor disconformities fringe much of the lake basin they are here correlated with former high stands of the lake which resulted from the blockage and re establishment of a number of alternative outlets due to tectonic activity and volcanism at both the host and adjacent volcanic centres the unconformities allow division of the deposits into three allostratigraphic units each of which is then characterised by elevation and sediment provenance the

the flow dynamics of an extremely large volume pyroclastic flow the 2 08 ma cerro galan ignimbrite nw argentina and comparison with other flow types the 2 08 ma cerro galan ignimbrite cgi represents a 630 km3 dense rock equivalent vei 8 eruption from the long lived cerro galan magma system 6 ma it is a crystal rich 35 60 pumice 10 generally and lithic poor 5 generally rhyodacitic ignimbrite lacking a preceding plinian fallout deposit the cgi is preserved up to 80 km from the structural margins of the caldera but almost certainly was deposited up to 100 km from the caldera in some places only one emplacement unit is preserved in proximal to medial settings and in most distal settings suggesting constant flow conditions but where the pyroclastic flow moved into a palaeotopography of substantial valleys and ridges it interacted with valley walls resulting in flow instabilities that generated multiple depositional units often separated by pyroclastic surge deposits the cgi preserves a widespread sub horizontal fabric defined by aligned elongate pumice and lithic clasts and minerals e g biotite a sub horizontal anisotropy of magnetic susceptibility fabric is defined by minute magnetic minerals in all localities where it has been analysed the cgi is poor in both vent derived accessory lithics and locally derived lithics from the ground surface accidental lithics locally derived lithics are small 20 cm and were not transported far from source points all data suggest that the pyroclastic flow system producing the cgi was characterised throughout by high sedimentation rates resulting from high particle concentration and suppressed turbulence at the depositional boundary layer despite being a low aspect ratio ignimbrite based on these features we question whether high velocity and momentum are necessary to account for extensive flow mobility it is proposed that the cgi was deposited by a pyroclastic flow system that developed a substantial high particle concentration granular under flow which flowed with suppressed turbulence high particle concentration and fine ash content hindered gas loss and maintained flow mobility in order to explain the contemporaneous maintenance of high particle concentration high sedimentation rate at the depositional boundary layer and a high level of mobility it is also proposed that the flow s was continuously supplied at a high mass feeding rate it is also proposed that internal gas pressure within the flow directed downwards onto the substrate over which the flow was passing reduced the friction between the flow and the substrate and also enhanced its mobility the pervasive sub horizontal fabric of aligned pumice lithic and even biotite crystals indicates a consistent horizontal shear force existed during transport and deposition in the basal granular flow consistent with the existence of a laminar shearing granular flow regime during the final stages of transport and deposition

a review of eastern tropical pacific oceanography summary abstract the collection of articles in this volume reviewing eastern tropical pacific oceanography is briefly summarized and updated references are given the region is an unusual biological environment as a consequence of physical characteristics and patterns of forcing including a strong and shallow thermocline the itcz and coastal wind jets equatorial upwelling the costa rica dome eastern boundary and equatorial current systems low iron input inadequate ventilation of subthermocline waters and dominance of enso scale temporal variability remaining unanswered questions are presented

mesoscale variability in the northeastern tropical pacific forcing mechanisms and eddy properties 1 the generation mechanisms and properties of the mesoscale eddies in the northeastern tropical pacific netp are studied using a series of numerical solutions and satellite observations the spatial and temporal resolution of mountain wind jets over the gulfs of tehuantepec and papagayo are essential for an accurate modeling of the regional mesoscale variability three previously proposed eddy generation mechanisms are the local transient wind forcing the combined low frequency wind and boundary forcing and the remote equatorial kelvin wave forcing in our model the transient wind forcing was represented by wind fields with synoptic variability and the remote equatorial kelvin wave forcing by 5 day open boundary conditions with interannual variability solutions with and without high frequency forcings are contrasted to evaluate the contributions of the three mechanisms the combined low frequency wind and boundary forcing is the primary eddy forcing mechanism in the netp in the tehuantepec region the high frequency wind forcing contributes more to the mesoscale variability than the remote equatorial kelvin wave forcing while in the papagayo region their contributions are comparable eddies in the tehuantepec and papagayo regions are larger in both amplitude and size and are more likely to deflect equatorward than eddies in the rest of the netp the maximum temperature anomaly of eddies is at around 50 m depth eddies with lifetimes 6 weeks are more likely anticyclonic while eddies with lifetimes 6 weeks are more likely cyclonic the anticyclone dominance for large amplitude long lived eddies is the combined consequence of wind driven asymmetric dipole spin up and the evolutionary fragility of large amplitude cyclones

volatile contents of obsidian clasts in tephra from the taupo volcanic zone new zealand implications to eruptive processes obsidian clasts in 6500 20 000 year old rhyolitic tephra deposits from the taupo volcanic zone new zealand contain variable h2o 0 2 2 5 wt and ci 0 12 0 18 wt contents these are elevated compared to degassed obsidian from rhyolitic domes 0 1 wt h2o2 0 1 wt cl which quenched at the surface major and trace element compositions of obsidian from tephra deposits suggest that they are co genetic with associated pumice the clear glassy appearance of the obsidian their high h2o release temperatures and 18o of 7 show that the water is magmatic and was not absorbed into the obsidian after tephra deposition based on analysis of melt inclusions recent primary taupo volcanic zone rhyolitic magmas contain 4 3 wt h2o and 0 18 wt cl the obsidian in the tephra deposits therefore represents partially degassed quenched primary magma water and cl contents correlate in the obsidian suggesting that the magmatic cl partitioned into a h2o rich fluid phase during eruptive degassing the partitioning of cl between the water rich vapor phase and the residual magma can be modelled as open system rayleigh fractionation using a pre eruptive h2o content of 4 3 wt and burnham s 1979 water solubility model the pressure and depth of initial vesiculation of the taupo magma is calculated to occur at about 0 9 kbar or 3 5 km depth initial fragmentation assumed to occur at a vapor melt ratio of 3 1 began at 0 1 kbar or 500 m depth obsidian in most tephra deposits contains less than 1 wt h2o and are calculated to have formed at 0 1 kbar or 500 m depth therefore some obsidian in these tephra deposits may have formed from fragmented magma the variable water contents of obsidian fragments in a single deposit indicates that quenching occurred over a range of depths this and the strong alignment of microphenocrysts in obsidian suggests that fragmented magma was welded onto the conduit walls during eruption cooled to form obsidian then incorporated into the tephra the 2000 year old hatepe phreatoplinian tephra contains many obsidian fragments with 2 wt h2o the meteoric water which caused this eruption to be phreatomagmatic may have caused obsidian to quench at unusually great depths resulting in higher h2o contents

interannual variability of tehuantepec eddies 1 topex poseidon satellite altimeter observations and the naval research laboratory layered ocean model simulations show interannual variability in the number and intensity of tehuantepec eddies off the mexican southwest coast analysis of the results illustrates that downwelling coastally trapped waves which are generated in the equatorial pacific play a crucial role in the modulation and generation of tehuantepec eddies and a dominant role in tehuantepec eddy interannual variability this introduces a new paradigm in which the generation and modulation of tehuantepec eddies is not exclusively explained in terms of the strong and intermittent tehuantepec wind events in fact the results show anticyclonic eddy formation during periods of calm tehuantepec winds that is specifically exemplified by the formation of two anticyclonic tehuantepec eddies during a 5 month period of weak gulf of tehuantepec winds during summer of 1997 furthermore the satellite observed and nlom simulated proliferation of tehuantepec eddies during el nino years is explained by the corresponding increase in downwelling coastally trapped waves and a lack of increase in the number and strength of tehuantepec wind events during el nino years

dependence of the structure of the northern hemisphere annular mode on the polarity of enso 1 the structure of the northern hemisphere annular mode nam is shown to be significantly different during warm and cold winters of the enso cycle during warm winters the arctic center of action of the annular mode is more prominent and extends deeper into siberia its related surface air temperature signal is stronger and the compensating outer ring in the sea level pressure field is much broader encompassing the entire tropics during cold winters the nam signature is much more pronounced over the pacific sector the sea level pressure pattern exhibits a north pacific center of action positively correlated with the atlantic center and pronounced deflections of the storm track are also evident it is suggested that the former features are associated with the equatorward displacement of the jet stream and the storm tracks during warm winters of the enso cycle and the latter is related to the the more pronounced break in the subtropical jet stream over the pacific sector during cold winters

a subsurface warm eddy off northern baja california in july 2004 1 upper ocean eddies are commonly observed from remote sensing but submerged eddies are more difficult to detect during july 2004 a 21 day hydrographic survey in the southern region of the california current was carried out to investigate the mesoscale variability we observed for the first time a subsurface anticyclonic eddy off northern baja california with the same water mass characteristics as the california undercurrent the core of the eddy was quasi circular with radii of 35 km and thickness of 250 m the maximum swirl velocity was 3 cms 1 the water mass of the core of the eddy was characterized by potential temperature of 11 c salinity of 34 5 and dissolved oxygen of 1 4 mll 1 the eddy propagated westward the subsurface warm eddy could transport relatively saline water into the north pacific subtropical gyre

semidiurnal tidal currents in the deep ocean near the east pacific rise between 9 and 10 n spatial and temporal variations of the semidiurnal tidal currents especially the baroclinic components in the deep ocean near a segment of the east pacific rise epr are examined using observations from a set of current meter moorings over the ridge crest the baroclinic semidiurnal tidal current is dominated by the zonal component and is coherent along the observed ridge segment in the direction across the ridge crest the baroclinic semidiurnal tidal current is not coherent and its magnitude decreases away from the ridge crest vertically the baroclinic semidiurnal tidal current covaries in a few hundred meters near the seafloor both the semidiurnal kinetic energy ke and shear show significant subinertial temporal variations by comparing with background forcings the author found that the subinertial variation of the semidiurnal tides over the ridge crest is related to both the spring neap cycles and the eddy induced low frequency flows in the deep ocean particularly their cross ridge components the observation that the baroclinic tidal currents at the axial stations flowing perpendicularly to the ridge crest suggests that the baroclinic semidiurnal tides at the axial stations are generated locally it is therefore probable that the subinertial variation of the baroclinic semidiurnal tides near the epr is due to the eddy modulated internal tide generation since the mesoscale eddies in the eastern tropical pacific vary with the state of the climate the observed eddy modulated internal tide generation connects climate change and variability to the physical and biogeochemical dynamics in the deep ocean and implies an unexplored feedback mechanism potentially affecting the climate system

correlation of fluvial terraces within the hikurangi margin new zealand implications for climate and baselevel controls abstract a correlation of fluvial terraces is presented for eight non glacial catchments of the eastern north island new zealand within the actively uplifting hikurangi margin using a combination of loess and tephra coverbed stratigraphy and radiocarbon and osl dating of fluvial deposits and loess coverbeds we demonstrate correlation of four fill terraces t1 t4 the available age constraints suggest t1 15 30 ka t2 31 50 ka t3 50 70 ka and t4 115 ka but the association and temporal link with loess deposits suggest correlation with cold periods and thus the refinement of t2 late mis 3 31 40 ka t3 mis 4 55 70 ka t4 mi substage 5b 90 ka 5d 110 ka or mis 6 140 160 ka the ability to correlate terraces between catchments plus the lack of independent evidence for tectonic triggering events indicates terraces have probably formed in response to either climate terrestrial or baselevel sea level control climate control is indicated by the temporal link of post glacial incision with re establishment of forest cover and of lgm aggradation with limited grass and shrub cover and periglacial processes aggradation due to increased sediment supply under reduced vegetation is dramatically demonstrated by formation of the taupo pumice alluvium terrace in response to inundation by volcanic deposits unwelded ignimbrite following the 1 8 ka taupo eruption and the response to post settlement

stratigraphy of the toba tuffs and the evolution of the toba caldera complex sumatra indonesia during the past 1 2 m y a magma chamber of batholithic proportions has developed under the 100 by 30 km toba caldera complex four separate eruptions have occurred from vents within the present collapse structure which formed from eruption of the 2800 km3 youngest toba tuff ytt at 74 ka eruption of the three older toba tuffs alternated from calderas situated in northern and southern portions of the present caldera the northern caldera apparently developed upon a large andesitic stratovolcano the calderas associated with the three older tuffs are obscured by caldera collapse and resurgence resulting from eruption of the ytt samosir island and the uluan block are two sides of a single resurgent dome that has resurged since eruption of the ytt samosir island is composed of thick ytt caldera fill whereas the uluan block consists mainly of the oldest toba tuff ott in the past 74000 years lava domes have been extruded on samosir island and along the caldera s western ring fracture this part of the ring fracture is the site of the only current activity at toba updoming and fumarolic activity the toba eruptions document the growth of the laterally continuous magma body which eventually erupted the ytt repose periods between the four toba tuffs range between 0 34 and 0 43 m y and give insights into pluton emplacement and magmatic evolution at toba

experimental studies of particle laden plumes experiments are described in which buoyant plumes of fresh water and solid particles are generated in a tank of salt water dependence of the behavior of the plumes on particle concentration and grain size was studied at low concentrations behavior was similar to single component plumes and the principal effect of the particles was to reduce the buoyancy flux measurements of particle concentration across the plumes demonstrated that there were substantial amounts of particle reentrainment from an outer sedimenting veil reentrainment caused the plume margins to become denser than the ambient fluid total particle flux in the plumes increased with height and can be several times greater than the flux at the plume source plumes with high particle concentration exhibit several kinds of convective instability which generated gravity currents and rapid sedimentation gravity currents were generated at the margins of concentrated plumes these flows are attributed to reentrainment causing the flow margins to have excess density when the plume density was close to but less than the density of the ambient fluid a fountain forms high in the plumes which collapsed asymmetrically to generate a gravity current on one side of the plume when the density of the particle laden flow was greater than the ambient fluid a symmetrical fountain formed and gravity currents moved across the tank floor depositing sediment at a well defined distance from the source buoyant fluid ascended from the flow fronts to form a ring of plumes around the central fountain these plumes coalesced to form a broad buoyant cloud the plumes are generated by the sedimentation from the gravity currents which resulted in the fresh water and some entrained particles being released all the experimental plumes ascended to the top of the tank and spread out as gravity currents beneath the upper surface particles often fall from this layer in discrete parcels of particle rich fluid with shapes similar to thermals the fall velocities were much greater than the terminal velocities of individual particles and the sedimenting region is inhomogeneous these observations indicate that sedimentation is enhanced by convective instabilities when particle rich fluid is emplaced above particle free fluid the experiments indicate that there may be several different mechanisms of generating pyroclastic flows and surges from the collapse of volcanic eruptions columns the experiments also demonstrate that the sedimentation of particles from a plume has an important influence on dynamical behavior

pre eruptive water content of rhyolitic magmas as determined by ion microprobe analyses of melt inclusions in phenocrysts abstract the ion microprobe was used to analyze trapped melt inclusions in phenocrysts from two rhyolitic eruptions for h2o f and incompatible trace elements eleven melt inclusions from phenocrysts in air fall tephra from obsidian dome near long valley usa gave an average of 4 1 1 2 wt h2o and showed large variations in f and incompatible trace elements reflecting a complex history reported to involve mixing of at least two magma types eight inclusions in phenocrysts from the taupo ultraplinian event new zealand gave 4 5 0 8 wt h2o with small variations in the other elements analyzed measured water contents are similar to earlier estimates of the pre eruptive water contents of these and similar rhyolites and major and trace element analyses of inclusions compare closely with bulk analyses suggesting that the analyses of inclusions represent the chemistry of the magma at the time of entrapment

charring of woods by volcanic processes an example from the taupo ignimbrite new zealand abstract one of the most violent and explosive eruptions in historic times was that of the taupo volcano in new zealand 1800 years ago this culminated in emplacement of the taupo ignimbrite laid down by a single vent generated pyroclastic density current that entombed and preserved abundant plant material the ignimbrite consists of two layers generated by processes within the concentrated part of the density current flow sensu stricto and where the current interacted with the atmosphere and the pre eruptive vegetative cover eighty four wood samples were collected from eight localities representing both layers at varying distances from the vent including the previously described pureora fossil forest samples were studied by light scanning electron and reflectance microscopy in order to determine their systematic affinity angiosperm or conifer degree of charring and reflectance values most samples 59 were conifer probably derived from podocarps that are known to have been common in the pre eruptive vegetation samples ranged from uncharred through incompletely charred to fully charred woods the variation in degrees of charring and reflectance values implies that the entrained charcoal did not equilibrate with the flow temperature minimum charring temperatures interpreted from the mean of the three highest maximum reflectance values showed no major differences between ignimbrite layers and were generally low ranging from 269 to 398 c both ignimbrite layers also show a trend of increasing deposit temperature away from the vent consistent with estimates from palaeomagnetic techniques

valley pond and ignimbrite veneer deposits in the small volume phreatomagmatic peperino albano basic ignimbrite lago albano maar colli albani volcano italy influence of topography abstract the ca 23 ka small volume basic phreatomagmatic peperino albano ignimbrite from the polygenetic albano maar colli albani volcano central italy shows valley pond facies as well as veneer deposits along the maar rim and along topographic ridges valley pond facies is characterised mainly by massive structure and chaotic texture and can be up to 30 m thick veneer deposit facies is characterised by parallel to low angle cross stratified bedforms alternating fines depleted lapilli sized layers and massive matrix supported beds occurrence of uncharred wood remains and accretionary lapilli suggests temperature of emplacement comprised between 246 and 100 c we have interpreted the lateral facies variations in terms of temporal and spatial variations of the sediment supply from the transport system to the depositional system of the pyroclastic flow ignimbrite veneer facies at the maar rim may reflect pulsatory eruption dynamics whereas valley pond facies may reflect the bulking of the pyroclastic flow inside the valleys and consequent high sedimentation rates ignimbrite veneer facies at topographic ridges has been interpreted to reflect detachment processes of more concentrated undercurrents draining within valleys from the more dilute upper part of the pyroclastic flow that climbs the ridges the present interpretation suggests that processes of pyroclastic flow transformation downcurrent and induced by topography are not necessarily peculiar of hot high mobility pyroclastic density currents the more likely source of water interacting with magma is interpreted to be groundwater contained within the karstic aquifer located at approximately 1 km below the ground level this is inferred by both the large amount of limestone xenoliths present in the peperino albano and the absence of vesicular juvenile clasts the latter implying that magma water interaction occurred before gas exolution processes were significant

satellite observations of the wind jets off the pacific coast of central america part ii regional relationships and dynamical considerations abstract satellite estimates of winds at 10 m above the sea surface by the nasa scatterometer nscat during the 9 month period october 1996 june 1997 are analyzed to investigate the correlations between the three major wind jets along the pacific coast of central america and their relationships to the wind and pressure fields in the inter american seas and eastern tropical pacific comparisons with sea level pressure confirm the conventional view that tehuantepec wind variations are driven by pressure variations in the gulf of mexico associated with north american cold air outbreaks the three jets sometimes developed sequentially from north to south statistically however the papagayo and panama jets were poorly correlated with variations of the tehuantepec jet over the nscat observational period the papagayo and panama jets were significantly correlated with each other and were coupled to coherent variations of the trade winds extending from the caribbean sea to the eastern tropical pacific the det