trace element transport rates in subduction zones evidence from th sr and pb isotope data for tonga kermadec arc lavas abstract trace element and th sr and pb isotope data for young lavas from the tonga kermadec arc in the southwest pacific suggest that geochemical variations in the lavas along the arc are linked to differences in the material being subducted beneath the arc lavas from the southern kermadec segment of the arc have relatively radiogenic pb isotope compositions which reflects a contribution from subducted sediment in contrast much of the pb in tonga lavas is derived from the altered oceanic crust in the subducting pacific plate and lavas from the northernmost tonga islands of tafahi and niuatoputapu contain pb and sr derived from the subducted part of the louisville seamount chain the origin of the pb in the lavas from these two islands can thus be traced to a point on the subducting slab and this observation is used to estimate the rate at which trace elements are transported beneath the arc our calculations suggest that fluid soluble elements such as u sr and pb are transported from the subducted slab across the mantle wedge and back to the surface in lavas over a period of approximately 2 3 ma and that magmas are erupted at the surface less than 350 ka after the melts are generated in the mantle wedge

observation and modeling of gravity wave propagation through reflection and critical layers above andes lidar observatory at cerro pachon chile a complex gravity wave event was observed from 04 30 to 08 10 utc on 16 january 2015 by a narrow band sodium lidar and an all sky airglow imager located at andes lidar observatory alo in cerro pachon 30 25 s 70 73 w chile the gravity wave packet had a period of 18 35 min and a horizontal wavelength of about 40 50 km strong enhancements of the vertical wind perturbation exceeding 10 m s 1 were found at 90 km and 103 km consistent with nearly evanescent wave behavior near a reflection layer a reduction in vertical wavelength was found as the phase speed approached the background wind speed near 93 km a distinct three layered structure was observed in the lidar data due to refraction of the wave packet a fully nonlinear model was used to simulate this event which successfully reproduced the amplitudes and layered structure seen in observations the model results provide dynamical insight suggesting that a double reflection occurring at two separate heights caused the large vertical wind amplitudes while the three layered structure in the temperature perturbation was a result of relatively stable regions at those altitudes the event provides a clear perspective on the filtering processes to which short period small scale gravity waves are subject in mesosphere and lower thermosphere

gravity waves around the subtropical jet of the southern winter in an atmospheric general circulation model 1 gravity wave gw activities around the subtropical jet of the southern winter june are analyzed using atmospheric general circulation model outputs of t106l60 in order to clarify roles of gws in maintaining the zonal mean zonal wind dominant gws are characterized with periods of 10 24 hours relative to the ground and with horizontal and vertical wavelengths of about 600 700 km and 2 2 4 4 km respectively these gws propagate both upward and downward from the jet and westward relative to the mean zonal wind most of the upward propagating waves do not reach the upper stratosphere due to negative vertical wind shear of the zonal wind in the lower stratosphere dominant upward fluxes of easterly momentum due to the non stationary gws extend zonally along 30 s above the jet remarkable ep flux convergence due mostly to these gws is seen around 100 hpa at 30 s and explains up to 30 of the total ep flux convergence

gravity wave generation around the polar vortex in the stratosphere revealed by 3 hourly radiosonde observations at syowa station intensive radiosonde observations were performed at syowa station 69 0 s 39 6 e over about 10 days in each of march june october and december 2002 to examine inertia gravity wave characteristics in the antarctic lower stratosphere based on the 3 hourly observation data two dimensional i e vertical wavenumber versus frequency spectra of wind fluctuations were examined utilizing a double fourier transform method clear signals of gravity waves whose phases propagate upward suggesting downward energy propagation are detected in june and october when the polar night jet pnj was present on the other hand downward phase propagation i e upward energy propagation components are dominant in all months there is a spectral peak around the inertial frequency in a wide range of vertical wavenumbers in december when the background wind was weak whereas large spectral densities are distributed over lower frequency regions in june and october these spectral characteristics are consistent with the results obtained using a gravity wave resolving global circulation model gcm by sato et al dynamical characteristics are examined separately for upward and downward propagating gravity waves in june using a hodograph analysis method as a result it is found that upward and downward propagating wave packets observed simultaneously in the same height regions have similar horizontal wavelengths and phase velocities this fact suggests that these gravity waves are generated from the same source with a similar mechanism when the wave packets were observed both the local rossby number and the residual in the nonlinear balance equation estimated using ncep ncar reanalysis data are large around the pnj situated slightly to the lower latitudes of syowa station therefore it is likely that the observed inertia gravity waves are generated by a spontaneous adjustment around the geostrophically unbalanced pnj and propagate toward syowa station the possibility of spontaneous gravity wave generation around the pnj is confirmed by comparison with the gcm simulation by sato et al

mesospheric momentum flux studies at adelaide australia observations and a gravity wave tidal interaction model abstract we present here the results of an analysis of gravity wave momentum fluxes in the mesosphere and lower thermosphere inferred using a dual beam doppler radar near adelaide australia during june 1984 our analysis reveals that over 70 of the momentum flux and of the inferred zonal drag was due to gravity waves with observed periods less than one hour this suggests that it is the gravity waves with high intrinsic frequencies and small horizontal scales that are most effective at transporting momentum into the middle atmosphere the temporal variations in the momentum flux and flux divergence due to high frequency motions were also examined in detail in addition to daily variability a strong diurnal modulation was observed to occur this was found to be correlated with the phase of large amplitude diurnal tidal motions as a result of these observations a gravity wave tidal interaction model was proposed which accounts for all of the major features of the observed data including a reduction i

long term variability in the equatorial middle atmosphere zonal wind the high resolution doppler imager hrdi on the upper atmosphere research satellite uars has provided measurements of the horizontal wind field in the stratosphere mesosphere and lower thermosphere since november 1991 this data set which spans a period of more than 3 years has facilitated an investigation of the long term behavior of the background circulation on a nearly global basis at middle and high latitudes the zonal circulation is characterized by an annual oscillation at low latitudes 30 the most prominent long term variation above the stratopause is the mesosphere semiannual oscillation msao which maximizes near the equator at an altitude of between 80 and 85 km further analysis of the time series reveals an additional strong variation with an amplitude near 30 ms 1 and a period of about 2 years this feature shows the same altitude and latitude structure as the msao and exhibits a phase relationship with the stratospheric quasi biennial oscillation qbo observations from the christmas island mf radar 2 n 130 w confirm the presence of this mesospheric qbo mqbo these observations support recent findings from a modeling study which generates an mqbo via the selective filtering of small scale gravity waves by the underlying winds they traverse

simulation of the eastward 4 day wave in the antarctic winter mesosphere using a gravity wave resolving general circulation model 1 the eastward moving 4 day wave in the antarctic winter mesosphere is investigated using a high resolution middle atmosphere general circulation model that directly simulates the spontaneous generation propagation and dissipation of gravity waves the results are also compared with the simulated seasonal march of the meridional structures of the westerly jet streams in the southern hemisphere upper stratosphere and mesosphere in order to investigate baroclinic barotropic instability as a possible excitation mechanism for the 4 day wave the model successfully reproduces the dynamically unstable double jet structure of the mesospheric westerly winds the simulated 4 day wave develops in association with the baroclinic and barotropic instability of the mesospheric mean flows and has similar characteristics to those observed at 50 60 s near the stratopause the 4 day wave has strong equatorward heat flux associated with strong baroclinicity in the antarctic winter mesosphere mainly attributable to poleward overturning circulation driven by gravity wave forcing eastward forcing due to the 4 day wave occurs within the double jet structure and offsets part of the westward forcing due to gravity waves such an effect partially acts to stabilize the unstable mean flow structure in the antarctic winter mesosphere

general aspects of a t213l256 middle atmosphere general circulation model 1 a high resolution middle atmosphere general circulation model gcm developed for studying small scale atmospheric processes is presented and the general features of the model are discussed the gcm has t213 spectral horizontal resolution and 256 vertical levels extending from the surface to a height of 85 km with a uniform vertical spacing of 300 m gravity waves gws are spontaneously generated by convection topography instability and adjustment processes in the model and the gcm reproduces realistic general circulation in the extratropical stratosphere and mesosphere the oscillations similar to the stratopause semiannual oscillation and the quasi biennial oscillation qbo in the equatorial lower stratosphere are also spontaneously generated in the gcm although the period of the qbo like oscillation is short 15 months the relative roles of planetary waves large scale gws and small scale gws in maintenance of the meridional structures of the zonal wind jets in the middle atmosphere are evaluated by calculating eliassen palm diagnostics separately for each of these three groups of waves small scale gws are found to cause deceleration of the wintertime polar night jet and the summertime easterly jet in the mesosphere while extratropical planetary waves primarily cause deceleration of the polar night jet below a height of approximately 60 km the meridional distribution and propagation of small scale gws are shown to affect the shape of the upper part of mesospheric jets the phase structures of orographic gws over the south andes and gws emitted from the tropospheric jet stream are discussed as examples of realistic gws reproduced by the t213l256 gcm

first observations of mesospheric dynamics with a partial reflection radar in hawaii 22 n 160 w we present here an overview of the wind measurements made during the first year of operation of a partial reflection radar system in hawaii the system operates at 1 98 mhz and provides wind estimates between 60 and 100 km at 2 km intervals our wind observations reveal a zonal mean motion that has several features in common with the mesopause semiannual oscillation msao seen at more equatorial latitudes but which is influenced as well by the seasonal variations of the mesospheric jet structure at higher latitudes major features of the zonal mean wind structure include a downward progression of strong eastward and westward phases of the msao from january to july coinciding with the period during which the msao and the annual cycle of the zonal mean wind at higher latitudes are in phase this results in an eastward maximum of 60 ms 1 near 80 km during january and february which descends rapidly and a westward maximum of 50 ms near 85 km during march and april which descends much more slowly the second msao cycle is greatly suppressed relative to the first due to the reversal of the correlation between this and the annual cycle at higher latitudes from july to december mean eastward motions occur primarily above 85 km early in this cycle and throughout the height range at later times planetary wave activity is seen to contribute substantial variability during times of eastward mean flow and to have a smaller role when zonal mean motions are westward tidal and 2 day motions are found to be large and variable with the maximum 2 day amplitudes occurring during february and august the largest diurnal tides were observed during october and november march and april and july and august while the semi diurnal amplitudes exhibited a minimum from april to june

multiple sources for sea rafted loisels pumice new zealand sea rafted loisels pumice is one of the few stratigraphic markers used to correlate late holocene coastal deposits in new zealand along with underlying sea rafted products of the local taupo eruption of ca 1800 yr b p these events have been used to bracket the first arrival of humans at new zealand loisels pumice is dacitic to rhyolitic sio263 78 wt in composition but individual clasts are homogeneous sio2range 1 wt characteristics include very low k2o 0 5 1 75 wt and rb 25 ppm and a mineralogy dominated by calcic and mafic xenocrysts similar features are shared by pumices of the tonga kermadec arc suggesting a common tholeiitic oceanic source interclast diversity of loisels pumice suggests that it is the product of several eruptive events from different volcanoes the differences in glass and mineral compositions found at various sites can be explained if the deposits are from different events a multisource origin can also partially explain the discrepancy in reported14c ages ca 1500 600 yr b p from different localities therefore the value of loisels pumice as a stratigraphic marker is questionable and it does not constrain the arrival of humans the predominant westward drift of historic tonga kermadec arc pumices and prevailing ocean currents suggest a long anticlockwise semicircular transport route into the tasman sea before sea rafted pumice arrival in new zealand the diversity of the pumices indicates that silicic eruptions frequently occur from the predominantly basic oceanic volcanoes

mean motions and tidal and two day structure and variability in the mesosphere and lower thermosphere over hawaii abstract an overview of the motion field and an analysis of the tidal and 2 day wave motions observed in the mesosphere and lower thermosphere over the central pacific from 1 october 1990 through 19 august 1992 is presented characteristics and interactions of motions at lower and higher frequencies will be addressed elsewhere wind measurements were obtained with an mf radar operating on kauai hawaii 22 n 160 w using the partial reflection drift technique results presented in this paper reveal a zonal mean motion reflecting the mesopause semiannual oscillation msao observed at more equatorial latitudes from january to july coinciding with the period during which the msao and the annual cycle of the zonal mean wind at higher latitudes are in phase eastward and westward maxima are 55 m s 1 below 80 km and 45 m s 1 near 85 km during the first year with maxima of 57 and 53 m s 1 during the second year and evidence of substantial interannual variability the second msao cycle is greatly suppresse

continent derived vitric mud and mafic arc rocks in deep kermadec trench diamictons abstract bimodal volcanogenic sediments dredged from depths greater than 7 km on the kermadec trench inner slope at latitude 31 s comprise diamictons of mudstone basalt and dolerite clasts enclosed in noncalcareous mud the mud and mudstones are medium to high k rhyolitic vitric mud of continental arc derivation that has been transported 900 km from new zealand all contain minor shards of kermadec arc low k rhyolitic glass all mudstones appear to be quaternary but one basalt clast gave a latest miocene k ar age 7 84 0 64 ma there have been at least three periods of deposition of mud and two or three episodes of emplacement of diamict the present trench slope is 10 24 and diamicts are interpreted to be deposits of debris flows of varying fluidity graded mafic volcanic sand beds are interpreted to be deposits of turbidity currents or sandy debris flows the degree of consolidation of mudstone clasts along with the presence of compaction faults suggests burial followed by re exhumation implying that redeposition processes may be deep reaching shallow water fossils and calcareous mudstone clasts originating above the carbonate compensation depth c 4 5 km plus clasts of basalt and dolerite sourced locally on the crest of the kermadec arc reached the lower trench slope in gravity flows that bypassed the mid slope terrace there was extensive mixing of products from various eruptions and sources during multiple episodes of transportation and during deposition and redeposition on the lower trench slope a range of agencies and routes is available to carry new zealand taupo volcanic zone derived vitric mud to the kermadec trench both low level and high level winds plus the north flowing deep western boundary current dwbc of antarctic bottom water the latter washes the raukumara plain forearc basin and the western trench slope to depths as shallow as 2 3 km we infer that ashfall tephra carried over the raukumara plain by the prevailing low level southwesterly wind is the principal source of the muds found in the trench the relative purity of the vitric mud in the trench might be explained by the tendency of rhyolitic material to dominate sediment dispersal systems in the aftermath of very large caldera eruptions confinement of the mud to the lower trench slope is probably caused by the tendency of dwbc surges of 20 cm s to veer 10 30 clockwise of the trench axis the continent derived volcanic ash on the subducting slab may influence oceanic arc magma composition

inertia gravity waves spontaneously generated by jets and fronts part i different baroclinic life cycles abstract the spontaneous generation of inertia gravity waves in idealized life cycles of baroclinic instability is investigated using the weather research and forecasting model two substantially different life cycles of baroclinic instability are obtained by varying the initial zonal jet the wave generation depends strongly on the details of the baroclinic wave s development in the life cycle dominated by cyclonic behavior the most conspicuous gravity waves are excited by the upper level jet and are broadly consistent with previous simulations of o sullivan and dunkerton in the life cycle that is dominated by anticyclonic behavior the most conspicuous gravity waves even in the stratosphere are excited by the surface fronts although the fronts are no stronger than in the cyclonic life cycle the anticyclonic life cycle also reveals waves in the lower stratosphere above the upper level trough of the baroclinic wave these waves have not been previously identified in idealized simulations the sensiti

on the origins of mesospheric gravity waves 1 using hourly data from a three year simulation based on a gravity wave resolving general circulation model we have first inferred a global view of gravity wave sources and propagation affecting significantly the momentum balance in the mesosphere the meridional cross section of momentum fluxes suggests that there are a few dominant propagation paths originating from the subtropics in summer and the middle to high latitudes in winter these gravity waves are focused into the mesospheric jets in their respective seasons acting effectively to decelerate the jets the difference in the source latitudes likely contributes to the hemispheric asymmetries of the jets the horizontal distribution of the momentum fluxes indicates that the dominant sources are steep mountains and tropospheric westerly jets in winter and vigorous monsoon convection in summer the monsoon regions are the most important window to the middle atmosphere in summer because of the easterlies associated with the monsoon circulation

meteor radar observed mesospheric semi annual oscillation sao and quasi biennial oscillation qbo over maui hawaii 1 we observed the variations of the semi annual oscillation sao in the mesopause region of northern subtropics and we describe its origin and forcing implications using the measurements of horizontal wind profiles made by the university of illinois meteor radar in maui hawaii 20 7 n 156 3 w from may 2002 to june 2007 and the european centre for medium range weather forecasts ecmwf interim data set we find that the mesospheric sao with the winter westerly near 80 90 km clearly stronger than the summer westerly is out of phase with the stratospheric sao near 1 hpa 50 km the mesospheric sao easterly is strong during the easterly phase and weak during the westerly phase of the stratospheric quasi biennial oscillation qbo near 10 hpa 30 km suggesting the modulation of the mesospheric sao by the stratospheric qbo the mesospheric qbo has an amplitude of approximately 5 m s near 80 km it is in phase with the stratospheric qbo near 10 hpa and out of phase with the qbo like oscillation near 1 hpa the correlation of the gravity wave gw and the quasi two day wave qtdw activities with the mesospheric sao and qbo suggests that the gw drags and the qtdw eliassen palm flux divergences likely contribute to the qbo modulation of the mesospheric sao the winter easterly wind in the tropical upper stratosphere pushes further into the northern subtropics during the qbo westerly phase than during the easterly phase this may have impacts on the upward propagation of westward propagating gws originated from the middle latitudes and thus the westward gw forcing in the upper mesosphere of northern subtropics

a 1 d mechanistic model for the evolution of earthflow prone hillslopes 1 in mountainous terrain deep seated landslides transport large volumes of material on hillslopes exerting a dominant control on erosion rates and landscape form here we develop a mathematical landscape evolution model to explore interactions between deep seated earthflows soil creep and gully processes at the drainage basin scale over geomorphically relevant 10 3 year timescales in the model sediment flux or incision laws for these three geomorphic processes combine to determine the morphology of actively uplifting and eroding steady state topographic profiles we apply the model to three sites one in the gabilan mesa california with no earthflow activity and two along the eel river california with different lithologies and varying levels of historic earthflow activity representative topographic profiles from these sites are consistent with model predictions in which the magnitude of a dimensionless earthflow number based on a non newtonian flow rheology reflects the magnitude of recent earthflow activity on the different hillslopes the model accurately predicts the behavior of earthflow collection and transport zones observed in the field and estimates long term average sediment fluxes that are due to earthflows in agreement with historical rates at our field sites finally our model predicts that steady state hillslope relief in earthflow prone terrain increases nonlinearly with the tectonic uplift rate suggesting that the mean hillslope angle may record uplift rate in earthflow prone landscapes even at high uplift rates where threshold slope processes normally limit further topographic development

drought rain and movement of a recurrent earthflow complex in new zealand in 1978 a 20 10 6 m 3 landslide of 900 yr return period was reactivated near waipara river south island new zealand in lower tertiary marine muds marls sands and limestone a central block moved 155 m reaching 5 m s after 3 months before slowing exponentially over 4 yr movement began after a wet winter of 100 yr return period but a previous drought may have hastened the movement the sequence of dry summer and wet winter had a 1 in 1500 yr recurrence interval a favored hypothesis for the role of drought is desiccation cracking allowing greater or more thorough wetting of impermeable regolith acid leaching of calcite as pyrite weathered and dilation of overcompacted mudstone also occurred movement began as the water store peaked at the end of winter and rising shear stress exceeded diminishing strength a kinematic model showing viscosity friction and a linearly varying thrust explains most of the movement small spurts in movement perhaps from growth of the head region suggest that ultimate displacement was unpredictable the net driving force 10 2 to 10 3 n was so very small relative to gravity9s downslope pull 10 10 n that a deterministic model including slope and gravity would require impossible precision 1 10 12 to give useful predictions if the preconditioning role of drought is not refuted the antithesis of current palliatives spray irrigation to prevent desiccation may be needed to reduce the likelihood of recurrence

historic drought puts the brakes on earthflows in northern california california s ongoing unprecedented drought is having profound impacts on the state s resources here we assess its impact on 98 deep seated slow moving landslides in northern california we used aerial photograph analysis satellite interferometry and satellite pixel tracking to measure earthflow velocities spanning 1944 2015 and compared these trends with the palmer drought severity index a proxy for soil moisture and pore pressure that governs landslide motion we find that earthflow velocities reached a historical low in the 2012 2015 drought but that their deceleration began at the turn of the century in response to a longer term moisture deficit our analysis implies depth dependent sensitivity of earthflows to climate forcing with thicker earthflows reflecting longer term climate trends and thinner earthflows exhibiting less systematic velocity variations these findings have implications for mechanical hydrologic interactions that link landslide movement with climate change as well as sediment delivery in the region

distribution and origin of igneous rocks from the landward slopes of the mariana trench implications for its structure and evolution the landward slope of the mariana trench is composed largely of igneous rocks serpentinites and serpentinized ultramafic rocks occur at nearly all structural levels on the slope from depths of 8000 to 1200 m seamountlike features on the trench slope break are the surface expression of serpentinite diapirs cumulate and massive gabbros are found several varieties of volcanic rocks are common including boninites altered and metamorphosed basalts andesites and dacites the chemical characteristics of the volcanic rocks indicate that nearly all are products of island arc volcanism together with the gabbros these volcanic rocks represent what is probably a late eocene arc complex these rocks were probably the first volcanic products to result from the subduction of the pacific plate beneath the phillippine sea plate their exposure on the trench slope today implies a significant amount of tectonic erosion of the landward slope since eocene time most of this removal of material appears to have occurred during the early stages of subduction there are isolated occurrences on the landward slope of rock assemblages including alkalic basalts chert hyaloclastites upper cretaceous siliceous sediments and shallow water limestones these assemblages are very similar to rocks dredged from seamounts on the offshore flankmore of the trench and their presence on the landward slope suggests that since the cessation of vigorous tectonic erosion there has been episodic accretion of seamount fragments to the landward slope less

the bouma sequence and the turbidite mind set abstract conventionally the bouma sequence bouma a h 1962 sedimentology of some flysch deposits a graphic approach to facies interpretation elsevier amsterdam 168 pp composed of ta tb tc td and te divisions is interpreted to be the product of a turbidity current however recent core and outcrop studies show that the complete and partial bouma sequences can also be interpreted to be deposits formed by processes other than turbidity currents such as sandy debris flows and bottom current reworking many published examples of turbidites most of them hydrocarbon bearing sands in the north sea the norwegian sea offshore nigeria offshore gabon gulf of mexico and the ouachita mountains are being reinterpreted by the present author as dominantly deposits of sandy debris flows and bottom current reworking with only a minor percentage of true turbidites i e deposits of turbidity currents with fluidal or newtonian rheology in which sediment is suspended by fluid turbulence this reinterpretation is based on detailed description of 21 000 ft 6402 m of conventional cores and 1200 ft 365 m of outcrop sections the predominance of interpreted turbidites in these areas by other workers can be attributed to the following 1 loose applications of turbidity current concepts without regard for fluid rheology flow state and sediment support mechanism that result in a category of turbidity currents that includes debris flows and bottom currents 2 field description of deep water sands using the bouma sequence an interpretive model that invariably leads to a model driven turbidite interpretation 3 the prevailing turbidite mind set that subconsciously forces one to routinely interpret most deep water sands as some kind of turbidites 4 the use of our inability to interpret transport mechanism from the depositional record as an excuse for assuming deep water sands as deposits of turbidity currents 5 the flawed concept of high density turbidity currents that allows room for interpreting debris flow deposits as turbidites 6 the flawed comparison of subaerial river currents fluid gravity flows dominated by bed load transport with subaqueous turbidity currents sediment gravity flows dominated by suspended load transport that results in misinterpreting ungraded or parallel stratified deep sea deposits as turbidites and 7 the attraction to use obsolete submarine fan models with channels and lobes that require a turbidite interpretation although the turbidite paradigm is alive and well for now the turbidites themselves are becoming an endangered facies

the 6 5 day wave and its seasonal variability in the middle and upper atmosphere 1 the zonal wave number 1 planetary wave of period near 6 5 days is a robust feature in the mesosphere and lower thermosphere mlt region with prominent seasonal variability as revealed by ground based and satellite observations this wave and its seasonal variability are well reproduced in a recent one model year run of the national center for atmospheric research thermosphere ionosphere mesosphere electrodynamics general circulation model time gcm with its lower boundary specified according to the national centers for environmental prediction analysis year 1993 wavelet analysis of the model output shows that in the mlt region the wave maximizes before and after the equinoxes and minimizes at solstices the wave amplitudes at the equinoxes are smaller than the peaks before and after but are still larger than the wave amplitudes at solstices however at the lower boundary near 30 km the wave peaks are predominantly between fall and the following spring by examining the episodes of maximum and minimum wave amplitude and by conducting additional control experiments using the time gcm the structure of this planetary wave and the factors determining the wave characteristics and seasonal variability are studied in detail it is found that the wave source mean wind structure instability and the critical layers of the wave can all affect the wave response in the mlt region and can have a strong seasonal dependence before and after equinox the wave follows the waveguide and propagates from the stratosphere to the summer mesosphere mesopause where it may amplify due to baroclinic barotropic instability such instability is usually absent from the equinoctial atmosphere so that there is no wave amplification at equinox at solstice the wave decays significantly when propagating away from its winter source due to the strong eastward winter stratospheric jet in the summer side the westward jet is also strong and the meridional and vertical extension of the critical layer of the wave is large enough to enclose the instability in the summer mesosphere mesopause at middle to high latitudes the wave is thus reflected away and prevented from reaching and amplifying at the unstable region the seasonal variation of the quasi two day wave which has zonal phase speed similar to the 6 5 day wave is also studied using similar diagnostics it is further shown that within certain seasonal window periods the variability in the mlt especially the summer mlt may closely track the lower atmospheric variability associated with these waves

sediment yield spatial characteristics and the long term evolution of active earthflows determined from airborne lidar and historical aerial photographs eel river california in mountainous landscapes with weak fine grained rocks earthflows can dominate erosion and landscape evolution by supplying sediment to channels and controlling hillslope morphology to estimate the contribution of earthflows to regional sediment budgets and identify patterns of landslide activity earthflow movement needs to be quantified over significant spatial and temporal scales presently there is a paucity of data that can be used to predict earthflow behavior beyond the seasonal scale or over spatially extensive study areas across 226 km 2 of rapidly eroding franciscan complex rocks of the eel river catchment northern california we used a combination of lidar light detection and ranging and orthorectified historical aerial photographs to objectively map earthflow movement between 1944 and 2006 by tracking the displacement of trees growing on earthflow surfaces we find that 7 3 of the study area experienced movement over this 62 yr interval preferentially in sheared argillaceous lithology this movement is distributed across 122 earthflow features that have intricate elongate planform shapes a preferred south southwesterly aspect and a mean longitudinal slope of 31 the distribution of mapped earthflow areas is well approximated by a lognormal distribution with a median size of 36 500 m 2 approximately 6 of the study area is composed of earthflows that connect to major channels these flows generated an average sediment yield of 19 000 t km 2 yr 1 rock erosion rate of 7 6 mm yr over the 62 yr study period equating to a regional yield of 1100 t km 2 yr 1 0 45 mm yr if distributed across the study area as such a small fraction of the landscape can account for half of the regional denudation rate estimated from suspended sediment records 2200 t km 2 yr 1 or 0 9 mm yr we propose a conceptual model for long term earthflow evolution wherein earthflows experience intermittent activity and long periods of dormancy when limited by the availability of readily mobilized sediment on upper slopes ultimately high order river channels and ephemeral gully networks may serve to destabilize hillslopes controlling the evolution of earthflow prone terrain

new geochemical evidence for the youngest toba tuff in india abstract new geochemical data on tephra samples from a layer present at several archeological sites in india support correlation of this layer to the youngest toba tuff erupted from northern sumatra about 74 000 yr ago the data show that the indian tephra layer is not a correlative of older tephra erupted from toba as has been suggested on the basis of artifact assemblages previously published geochemical data on the indian tephra beds was based on bulk ash samples containing mineral and clay contaminants and the resulting variability in analyses did not allow identification or discrimination of individual eruptive events our new data were collected on individual glass shards and small purified glass separates which have greater resolving power in fingerprinting acheulian and paleolithic artifacts found at some of the indian tephra sites do not reflect the antiquity of the tephra bed as they occur in fluvial sediments and may be reworked

gravity flows and rock recycling on the tonga landward trench slope relation to trench slope tectonic processes dredge samples collected from the flanks of the frontal arc platform from the mid slope forearc terrace and from the lower landward slope of the tonga trench are dominated by arc derived volcaniclastic sediment and calcareous ooze much of the sediment was delivered by sediment gravity flows recycling of older fossils and rocks is very widespread with evidence for several cycles of erosion and deposition in a single sample steep slopes and outcropping rock have prevailed around the frontal arc platform throughout the late neogene probably driven by movement on bounding normal faults the upper trench slope is dominated by coarse grained turbidites and debris flows the mid slope terrace receives mainly finer grained turbidites with fewer coarse turbidites and debris flows the lower trench slope is dominated by clast rich debris flows containing a majority of clasts of volcaniclastic deposits derived from the upper trench slope and mid slope terrace mixed with arc substrate and ocean plate rocks

fault zone controls on the spatial distribution of slow moving landslides slow moving landslides earthflows can dominate hillslope sediment flux and landscape erosion in hilly terrain with mechanically weak fine grained rock controls on the occurrence of slow moving landslides are poorly constrained and need to be understood for landscape evolution models sediment budgets and infrastructure and hazards planning here we use airborne interferometric synthetic aperture radar insar and aerial photographs to document 150 previously unidentified active earthflows along the central creeping portion of the san andreas fault california the earthflows move seasonally in response to winter rainfall occur on hillslopes at 20 40 gradients less than typically associated with rapid catastrophic landslides and have similar morphological characteristics to earthflows in different climatic and tectonic settings although our data extend up to 10 km from the fault trace 75 of detected landslides occur within 2 km of the active fault topographic precipitation and rock type metrics alone are not enough to explain the observed spatial distribution of earthflows instead we hypothesize that earthflows cluster near the creeping san andreas fault because of a fault induced zone of reduced bulk rock strength that increases hillslope susceptibility to failure in addition similar lithology topography and climate exist north of the creeping section of the fault yet earthflows there are rare this may be due to large magnitude earthquakes episodically triggering coseismic rapid landslides which preferentially remove weak rock from the fault damage zone our analysis suggests that the necessary conditions for earthflow formation in central california include some combination of reduced rock strength fine grained sedimentary rock threshold precipitation and relief and possibly the absence of large magnitude earthquakes these conditions likely hold for earthflow development in other areas and our work suggests that local variations in rock strength and seismicity such as those associated with fault zones need to be taken into account in order to accurately predict earthflow occurrence

provenance of the detrital component of deep sea sediments from the sw pacific ocean based on mineralogy geochemistry and sr isotopic composition abstract clay mineralogy and chemical and strontium isotope compositions have been used to determine the detrital components of deep sea sediments from the sw pacific ocean continental detritus derived mainly from the new zealand landmass is characterised by high illite and chlorite contents and 87 sr 86 sr ratios close to 0 7110 this material eroded from the eastern margin of both islands is transported into deeper water by turbidity currents and hemipelagic processes and is carried northwards by the strong western boundary current as far north as the samoan basin due to the great distance from source and unfavourable prevailing winds the contribution of aeolian dust from the australian deserts to the sediment appears to be relatively small particularly in the northernmost part of the region in the vicinity of the oceanic volcanic islands of tonga samoa and the cook islands volcaniclastic material including heavy minerals pyroxene and magnetite pumice glass shards proximally and smectite clays distally is dispersed into the sediments by turbidity currents and airfall in areas of very low sedimentation distant from landmasses the sediments contain significant amounts of authigenic material rsos characterised by high concentrations of transition metals and rare earth elements strontium isotopes together with trace element compositions have proved particularly useful in determining the relative proportions of the detrital types the contrasting 87 sr 86 sr ratios and sr contents of the various source rocks permit the use of binary mixing relationships whch indicate that sediments less than 35 km from the cook islands contain 80 volcanic detritus and those more than 1200 km away contain up to 20 volcanic detritus

comparison of meteor radar and na doppler lidar measurements of winds in the mesopause region above maui hawaii 1 simultaneous sodium na doppler lidar and meteor radar measurements of horizontal winds in the mesopause region over maui hawaii were collected in july 2002 and october november 2003 the coincident measurements span 96 hours and altitudes between 80 and 100 km statistical comparisons are carried out on radar lidar winds with 1 hour and 4 km time and height resolution respectively the rms radar lidar wind component differences observed in this study are in the range 12 17 m s at altitudes below 96 km this is smaller than the rms differences observed in a previous na lidar and meteor radar comparison lidar wind component variances exceed radar variances and radar lidar covariance is nearly equal to the radar variance excess variance observed by the lidar is consistent with the fact that the meteor radar cannot resolve wind perturbations with horizontal scales smaller than 200 km whereas the lidar will respond to all horizontal scales close correspondence between the radar wind variance and radar lidar covariance suggests that measurement errors associated with the radar winds are swamped by geophysical variation furthermore the excess lidar variance exceeds lidar estimation errors by a large factor indicating that the lidar measurement errors are also insignificant relative to geophysical variations together these observations suggest that the observed radar lidar differences are a consequence of the different horizontal wave number filters associated with the techniques and hence the differences are determined by the strength and shape of the horizontal wave number spectrum for wind perturbations at scales smaller than 200 km

development of sediment drifts approaching an active plate margin under the sw pacific deep western boundary current the abyssal pacific ocean is fed by a 1000 km wide deep western boundary current dwbc that flows northward along the continental margin east of new zealand between the passive margin of chatham rise and the subduction zone of kermadec trench a distance of 1200 km the dwbc has formed a suite of sediment drifts over a depth range of 2200 5700 m airgun and 3 5 khz profiles record a variety of drift types that reflect regional variations in bathymetry sediment supply and the tectonic volcanic framework on chatham rise the dwbc has deposited a sinuous linear body along the south flank 3000 m an extensive apronlike drift on the north flank 2200 4500 m and a ridgelike drift about the rise base 4500 5200 m the flow has also deposited a body of sediment over 400 km long within a moat at the base of the nearby louisville seamount chain further downcurrent the 250 km long rekohu drift 3600 4190 m has developed northward to 39 s south of this latitude drifts comprise mainly reworked pelagic hemipelagic material and sediment transported from distant southerly sources in contrast drifts north of 39 s have received a major injection of terrigenous sediment from hikurangi channel which runs 1400 km from new zealand eastward across the hikurangi plateau to disgorge on to the abyssal floor at the plateau edge en route turbidity current overspill from the channel has moved north under the influence of the shallow dwbc to contribute to a series of small ridge and patch drifts among the numerous seamounts on the plateau at 3500 4200 m off hikurangi channel mouth a large fan has accumulated the dwbc has extended the fan into a drift running over 250 km along the base of hikurangi plateau 5150 5770 m toward kermadec trench here drift sediment becomes increasingly disrupted by mass wasting associated with the active subduction in this area the seismic stratigraphy reveals the drifts to rest mainly on a widespread erosional surface that is interpreted to mark the inception of the dwbc in the region with the late oligocene opening of the australian antarctic seaway drift construction commenced during the miocene but was punctuated in the late miocene by another period of erosion that coincided with increased bottom water production in antarctica deposition resumed in plio pleistocene times when large quantities of sediment from the rapidly rising landmass of new zealand were injected into the boundary current the modern flow continues to affect drift deposition as manifest by an active boundary channel along the foot of hikurangi plateau and widespread scour zones and sediment wave fields

mid bathyal current scours and sediment drifts adjacent to the hikurangi deep sea turbidite channel eastern new zealand evidence from echo character mapping abstract late quaternary sedimentary processes on the northwest chatham rise continental slope and southern hikurangi trough eastern new zealand have been examined using 3 5 khz seismic reflection profiles together with piston cores high frequency echo character mapping of the region shows that the slope has been dominated by current controlled sedimentary processes whereas turbidite processes characterise the adjacent part of the southern hikurangi trough on the slope north of mernoo saddle a 580 m deep bathymetric passage between the eastern south island continental shelf and the chatham rise a 160 km alongslope by 30 km wide region of current crosion occurs between 700 m and 2300 m depths within this region are several northeast trending channels 5 20 km wide and up to 105 km long scoured obliquely down slope these scours are inferred to have been formed mainly during glacial periods by a northward flowing current of subantarctic water passing through the mernoo saddle then braiding as it cascaded down and acoss the mid slope before merging again further east into a contour current on the unstable lower slope of the north chatham rise the lower slope in between and below the scours comprises a complex of coalescing sediment drifts the adjacent part of the southern hikurangi trough is characterised by a canyon leveed channel system receiving turbidites from the eastern south island continental margin and cook strait mapping reveals a meandering channel up to 10 km wide on the floor of the trough with a left bank dominated levee east of cook strait where the trough widens

generation of mesoscale gravity waves in upper tropospheric jet front systems abstract multiply nested mesoscale numerical simulations with horizontal resolution up to 3 3 km are performed to study the generation of mesoscale gravity waves during the life cycle of idealized baroclinic jet front systems long lived vertically propagating mesoscale gravity waves with horizontal wavelengths 100 200 km are simulated originating from the exit region of the upper tropospheric jet streak in a manner consistent with past observational studies the residual of the nonlinear balance equation is found to be a useful index in diagnosing flow imbalance and predicting wave generation the imbalance diagnosis and model simulations suggest that balance adjustment as a generalization of geostrophic adjustment is likely responsible for generating these mesoscale gravity waves it is hypothesized that through balance adjustment the continuous generation of flow imbalance from the developing baroclinic wave will lead to the continuous radiation of gravity waves

tectonic controls on sedimentation and diagenesis in the tonga trench and forearc southwest pacific sedimentation in the tonga forearc is dominated by the redeposition of volcaniclastic sediment from the arc volcanic front by mass flows and turbidity currents onto the adjacent tonga platform the shallowest flattest part of the forearc region the greatest sediment thicknesses accumulate in debris aprons close to the volcanic front collision of seamounts notably the capricorn seamount and the louisville ridge with the forearc radically shortens and steepens the adjacent modern trench slope allowing sediment to be redeposited deep into the trench rotation usually arcward of existing basins on the midslope during collision generates angular unconformities while synchronous uplift of the outer forearc high results in canyon development and downcutting along the eastern edge of the tonga platform collision also reactivated major across strike fault zones on the forearc the zones are subsequently exploited by canyons depositing sediment into the trench collapse and renewed extension of the forearc in the wake of collision result in the development of small perched basins measuring approximately 5 km by 15 km in the midslope area this morphology is especially developed at 18 30 s to 20 s implying a 2 3 m y interval for their formation following louisville ridge collision trenchward of these depocenters sedimentation is slow resulting in manganese crust formation and localized mass wasting along fault scarps over longer periods of time 5 m y tectonic erosion reestablishes a wide gently sloping forearc into which canyons incise the shallow tonga platform by headwall erosion and collapse

observational investigations of gravity wave momentum flux with spectroscopic imaging 1 we apply a newly developed gravity wave momentum flux estimation method to the mesospheric measurements obtained with colocated airglow imager and meteor radar at maui hawaii 20 7 n 156 3 w during the maui mesosphere and lower thermosphere maui malt campaign the method identifies individual quasi monochromatic gravity waves with periods between 6 and 40 min estimates the intrinsic wave parameters and calculates the momentum fluxes carried by vertically propagating waves data taken on 28 october 2003 are analyzed in detail to reveal the relationship between momentum flux and wave parameters the january april july and october 2003 data are divided into summer and winter categories and nightly average momentum fluxes are calculated for comparison of the seasonal wave propagation directions average wave momentum flux is directed to the northeast during most of the summer nights while a southwest preference exists for the winter nights the results extracted from maui hawaii combined with the earlier results from starfire optical range new mexico 35 n 107 w and other observations support the notion that the seasonal trend in meridional flux is a global phenomenon

observations of eastward currents in the tropical south atlantic ocean 1978 1980 data from four cruises to the tropical south atlantic ocean are used to describe the current distribution at 25 w and 27 5 28 w two distinct eastward flowing countercurrents separated by a branch of the westward flowing south equatorial current sec were observed during all the cruises the south equatorial undercurrent located between 3 s and 5 s has a subsurface velocity core with maximum speeds of about 0 4 m s geostrophic volume transports of the seuc from the surface to 1000 m range from 5 to 23 sv surface flow above the core of the seuc can be to the east or west the south equatorial countercurrent secc is located typically between 7 s and 9 s although weaker than the seuc with transports ranging from 3 to 7 sv the secc also has a subsurface velocity core maximum speeds of 0 1 m s are observed at about 275 m surface flow above the core of the secc is typically to the east upper layer waters of the secc are saltier and warmer than waters within similar density layers to the north

discriminant function analysis of glass chemistry of new zealand and north american tephra deposits major trace and rare earth element analyses of volcanic glass are used separately or in combination for correlating quaternary tephras often by graphical or simple comparative methods we have taken a statistical approach using discriminant function analysis dfa to assess the relative discriminating power of the different elements in volcanic glasses from several tectonovolcanic provinces we found that major oxides are powerful discriminating variables for widespread tephras from the taupo volcanic zone in new zealand and here they can be more discriminating than trace elements a wide selection of tephras from the western united states can also be distinguished on major oxides alone particularly those from cascade range volcanoes for tephras from large intracontinental calderas such as long valley or yellowstone ree and trace elements are more effective at discriminating than major oxides however tephras erupted from the long valley area can be distinguished on major oxide composition by dfa despite their similar chemistry the selection and relative significance of different elements for discriminating tephras depends on the total data set being compared as well as the source volcano and the individual eruptive events caution must be exercised in the nonstatistical selection of compositional data for characterizing tephras dfa is a more powerful and objective tool for the comparison of tephra chemistry

late cretaceous pelagic sediments volcanic ash and biotas from near the louisville hotspot pacific plate paleolatitude 42 s abstract dredging on the deep inner slope of the tonga trench immediately north of the intersection between the louisville ridge hotspot chain and the trench recovered some late cretaceous maestrichtian slightly tuffaceous pelagic sediments they are inferred to have been scraped off a recently subducted late cretaceous guyot of the louisville chain in the vicinity of the louisville hotspot present location 50 26 s 139 09 w late cretaceous location 42 s longitude unknown late cretaceous rich diatom radiolarian silicoflagellate foraminiferal and coccolith biotas accumulated on the flanks of the guyot and are described in this paper rich sponge faunas are not described inoceramus prisms are present volcanic ash is of within plate alkalic character isotope ratios in bulk carbonate 18o 2 63 to 0 85 13c 2 98 to 3 83 are normal for pacific maestrichtian sediments the local ccd may have been shallower than the regional ccd because of high organic productivity in some samples late cretaceous materials have been mixed with neogene materials mixing may have taken place on the flanks of the guyot during transit across the western pacific or on the trench slope during or after subduction and offscraping about 0 5 ma

regional sediment recycling in the abyssal southwest pacific ocean an active plate boundary with a high sediment output three major submarine channels and the world9s largest deep western boundary current dwbc make up an extensive recycling system along the 4500 km continental margin east of new zealand seismic reflection sedimentary and oceanographic data demonstrate that detritus from the rising mountains of the new zealand plate boundary is transferred to the southwest pacific abyssal floor by turbidity currents flowing along solander 450 km long bounty 950 km and hikurangi 1400 km channels these conduits discharge directly into the dwbc which transports material north to form a series of sediment drifts the northernmost drift containing sediment from hikurangi channel and eroded drifts to the south is now subducting into kermadec trench geochemical data suggest that sediment is recycled through the mantle to re emerge in the arc volcanic rocks thus one cycle is completed and a new one begins

medium frequency radar studies of gravity wave seasonal variations over hawaii 22 n 160 w 1 using simple numerical filters estimates of wind variances with period bands of 0 1 to 1 hour and 1 to 5 hours have been derived from data taken with the medium frequency radar on the island of kauai hawaii 22 n 160 w the observations cover altitudes of 70 to 90 km and extend over the years 1990 2000 the results show seasonal and interannual variations of the wind variances which can be attributed to atmospheric gravity waves the mean zonal wind has mainly an annual variation below an altitude of 83 km and a semiannual variation above the gravity waves have maximum intensity at the solstices below 83 km but at higher altitudes the times of the maxima shift to the equinoxes numerical simulations suggest this behavior results from the dependence of gravity wave generation and propagation on the background wind and temperature

subduction of a late cretaceous seamount of the louisville ridge at the tonga trench a model of normal and accelerated tectonic erosion the hotspot generated louisville ridge is a 4000 km chain of seamounts typically 2 2 5 km high and 10 40 km in diameter and an underlying crustal swell 1 5 km high and 100 km wide trending nnw across the southwestern pacific the northwest end of the ridge collides with the north trending tonga trench 26 s which just north of that point is exceptionally deep 10 8 km and lacks both a turbidite wedge and a bordering accretionary complex the collision zone is moving rapidly southward multichannel seismic reflection data in the collision zone show a west dipping subsurface platform 2 3 km beneath the lower western trench slope which is interpreted as the flat summit of a subducted guyot motuku of the louisville chain projected eastward the summit plain passes 1 2 km above the trench floor dredging of the nearby inner trench wall recovered uppermost cretaceous maestrichtian oceanic pelagic sediments interpreted to be fragments of the sedimentary mantle of a subducted louisville seamount the principal effects of hotspot ridge collision with a sediment starved trench are 1 the impacting seamounts are subducted rather than accreted and 2 although some seamount rocks are temporarily accreted the inner trench wall is tectonically eroded arcward at rates possibly as high as 50 km m y accelerated tectonic erosion is related to 1 fracturing shearing and general weakening of arc substrate rocks as they are lifted by the swell penetrated by impacting seamounts and left to collapse as the ridge moves away 2 a more effective removal of weakened rock in underthrusting grabens which are larger in the crustal swell 3 a possible elevation of the subduction decollement to account for the removal of as much as 30 000 km of material from a 400 km sector of the trench in 1 million years and 4 a reduction in supply of arc derived debris resulting from the gap in arc volcanism accompanying subduction of the ridge normal tectonic erosion in the tonga trench is apparently minor and we conclude that the bulk of the 37 000 km of material which fills subducting grabens each million years is arc derived volcanic and pelagic sediment

morphology and history of the kermadec trench arc backarc basin remnant arc system at 30 to 32 s geophysical profile microfossil and k ar data abstract knowledge of the time span of arc activity essential for correct tectonic reconstructions has been lacking for the kermadec arc system but is supplied in this paper through study of microfossils contained in dredge samples and k ar ages on dredged basalt clasts the kermadec system at south latitudes 30 to 32 in the southwest pacific comprises from west to east the colville ridge remnant arc havre trough backarc basin kermadec ridge active arc and kermadec trench site of west dipping subduction of pacific plate lithosphere beneath the australian plate data are presented from two traverses dredge magnetic single channel seismic across the whole system an important transverse tectonic boundary the 32 s boundary lies between the two traverse lines and separates distinct northern 32 25 s and southern 32 36 s sectors the northern sector is shallower and well sedimented with broad ridges and a diffuse backarc basin the southern sector is deeper with narrow ridges and steep escarpments facing inwards to a little sedimented rifted backarc basin the kermadec ridge slopes smoothly trenchward to a mid slope terrace forearc basin with minor sediment fill at 5 6 km water depth a steeper 10 24 and more rugged lower trench slope is mantled with new zealand sourced rhyolitic vitric mud diamictons containing locally derived mafic volcanic clasts one clast is of late miocene age k ar age 7 84 ma the arc kermadec ridge is capped by active volcanoes very young k ar ages