space weathering of asteroid surfaces abstract visible and near infrared spectra of reflected sunlight from asteroid surfaces exhibit features that hold the promise for identifying surface mineralogy however the very surfaces that are observed by remote sensing are also subject to impingement by micrometeoroids and solar wind particles which are believed to play the dominant role in space weathering which is the time dependent modification of an asteroid s reflectance spectrum such space weathering has confused the interpretations of telescopic spectra of asteroids especially concerning the possible association of common ordinary chondritic meteorites with so called s type asteroids recent spacecraft studies of asteroids especially of eros by near shoemaker have documented aspects of space weathering processes but we still do not understand the physics of space weathering well enough to confidently assay mineralogy of diverse asteroids by remote sensing a review of the intellectual history of this topic reveals the complexity of

optical properties in waters around the mendeleev ridge related to the physical features of water masses abstract irradiance profiles were measured during the korean 2012 summer arctic ocean cruise and optical properties were studied the optical attenuation coefficient in all surface waters was low as the nutrients in the surface layers became exhausted and phytoplankton growth was only possible at the subsurface where optimal conditions of nutrients and sufficient illumination existed this high attenuation zone was at about 40 60 m the attenuation properties were categorized to three types type 1 waters had weaker maximum attenuation coefficients and were located at the chukchi plateau and the north margin of the study region type 2 water had an intense maximum of attenuation coefficient up to 0 56 m located on west flank of mendeleev ridge and continental slope of east siberian sea two integral parameters attenuation depth and optical thickness were mapped by spatial distribution the attenuation depth was basically shallower 40 m to the west and deeper to the east 100 m the averaged optical thickness at the level of 30 60 m was the main zone of high attenuation both the optical attenuation property and the physical features of the water indicated two subsurface water masses one is the cold shelf water well mixed with river water and transported to the east by a subsurface current along the east siberian slope the other is the warmer water from the pacific with lower nutrients and transported to the northwest along the north margin of the observed region a cyclonically re circulated branch of shelf water passing over the chukchi abyssal plain was described in this study

aznalcollar dam failure part 1 field observations and material properties the paper describes the failure of aznalcollar dam in southern spain in april 1998 the rockfill dam slid forward and released a flow of acid saturated tailings the geology and geomorphology of the site are described the results of a detailed laboratory testing programme on the tailings material and on the overconsolidated high plasticity foundation clay are given special attention is paid to the identification of cementation of the tailings and to the strength and consolidation properties of the foundation clay failure features are interpreted on the basis of the field evidence taking into account the measured geotechnical properties of the materials involved

impact excavation on asteroid 4 vesta hubble space telescope results hubble space telescope images of asteroid 4 vesta obtained during the favorable 1996 apparition show an impact crater 460 kilometers in diameter near the south pole color measurements within the 13 kilometer deep crater are consistent with excavation deep into a high calcium pyroxene rich crust or olivine upper mantle about 1 percent of vesta was excavated by the crater formation event a volume sufficient to account for the family of small vesta like asteroids that extends to dynamical source regions for meteorites this crater may be the site of origin for the howardite eucrite and diogenite classes of basaltic achondrite meteorites

atmospheric controls on sea ice motion in the southern beaufort sea 1 the beaufort sea ice gyre is characterized in winter months by an anticyclonic regime associated with sea level pressure slp highs previous studies have shown instances of a reversal in this regime in summer months with the arrival of slp lows over the beaufort sea while also demonstrating a link to variations in lower stratospheric potential vorticity in this study we examine the role of relative vorticity in describing dynamic variability on weekly timescales from the surface to the middle stratosphere results from this analysis show that the beaufort gyre is characterized predominantly by anticyclonic activity throughout the year for the time interval considered from 1979 to 2000 with a summer reversal to cyclonic activity whose strength and duration varies between years these reversals coincide with reversals in slp based on a correlation analysis comparison of ice and atmospheric relative vorticity fields in the beaufort sea region bsr for all weeks from 1979 to 2000 indicates that sea ice and lower tropospheric processes are anticorrelated at zero time lag this is in contrast to relative vorticity fields at 10 mbar which exhibit maximum correlation between stratospheric and sea ice responses when 10 mbar leads ice relative vorticity by 2 6 weeks

photographic observations of neuschwanstein a second meteorite from the orbit of the přibram chondrite photographic observations of meteoroids passing through the atmosphere provide information about the population of interplanetary bodies in the earth s vicinity in the size range from 0 1 m to several metres it is extremely rare that any of these meteoroids survives atmospheric entry to be recovered as a meteorite on the ground p ibram was the first meteorite an ordinary chondrite with a photographically determined orbit it fell on 7 april 1959 ref 1 here we report the fourth meteorite fall to be captured by camera networks we determined the atmospheric trajectory and pre atmospheric orbit of the object from the photographic records one 1 75 kg meteorite named neuschwanstein and classified as an enstatite chondrite2 was recovered within the predicted impact area the bolide s heliocentric orbit is exceptional as it is almost identical to the orbit of p ibram suggesting that we have discovered a stream of meteoritic objects in an earth crossing orbit the chemical classifications and cosmic ray exposure ages of the two meteorites are quite different however which implies a heterogeneous stream

the north pacific a global scale estuary abstract the atmospheric net flow of water from the atlantic to the pacific ocean is supposed to maintain the salinity difference between the two oceans assuming the existence of a subsurface level of no horizontal pressure gradient in the ocean the mean sea level in the northern pacific must be higher than in the arctic ocean this mean sea level difference is supposed to drive the observed mean flow through the bering strait the estimated flow of freshwater through the bering strait is approximately equal to the estimated atmospheric net flow of water from the north atlantic to the north pacific this justifies the formulation of a simple estuary model for the north pacific in which the brackish water exits through the bering strait the salinity difference between the two oceans is shown to be controlled by the topography of the bering strait the estuary model gives residence times for water in the upper layer 1000 m thick of approximately 1000 years and in the lower layer of approximately 400

pacific ventilation of the arctic ocean s lower halocline by upwelling and diapycnal mixing over the continental margin 1 pacific winter waters a major source of nutrients and buoyancy to the arctic ocean are thought to ventilate the arctic s lower halocline either by injection isopycnal or penetrative of cold saline shelf waters or by cooling and freshening atlantic waters upwelled onto the shelf although ventilation at salinity s 34 psu has previously been attributed to hypersaline polynya waters temperature salinity nutrient and tracer data suggest instead that much of the western arctic s lower halocline is in fact influenced by a diapycnal mixing of pacific winter waters with s 33 1 psu and denser eastern arctic halocline atlantic waters the mixing taking place possibly over the northern chukchi shelf slope estimates from observational data confirm that sufficient quantities of atlantic water may be upwelled to mix with the inflowing pacific waters with volumes implying the halocline over the chukchi borderland region may be renewed on timescales of order a year

east west differences in water mass nutrient and chlorophyll a distributions in the sea ice reduction region of the western arctic ocean 1 the r v mirai conducted hydrographic surveys in the western arctic ocean during summer 2004 across a front between cold arctic water and warm water from the pacific ocean where sea ice cover has been largely reduced in recent summers the hydrographic data indicate a new type of vertical temperature minimum water west of the front along isohaline surfaces with approximate salinity s of 32 which is fresher than the typical temperature minimum s 33 caused by spreading of pacific winter water pww mainly to the east of the front both of the temperature minimum waters are characterized by low potential vorticity with near freezing temperature suggesting that they are formed by winter convection with sea ice formation a difference between the waters results from a large contribution of sea ice meltwater to the fresh temperature minimum frtmin water of s 32 the distributions of the sea ice meltwater contribution and nitrogen deficit suggest that summer shelf water largely influenced by the sea ice melt in the chukchi sea is modified by winter convection on its way to the chukchi abyssal plain to form the frtmin water this water supplies nutrients through the water distribution to the west of the front at depths shallower than the nutrient maximum layer caused by the pww spreading the shallower nutrient supply by the frtmin water combined with light penetration without sea ice cover could produce a prominent chlorophyll a maximum layer west of the front

mineralogical petrological characterization of near earth asteroids studies of near earth asteroids are aimed at determining their dynamical and structural history the mineralogy and petrology of 17 near earth asteroids are characterized using reflectance spectroscopy with ground based telescopes as one method to address their major issues implications for the origin and evolution are discussed in a separate paper assuming the surfaces are composed of cosmically abundant materials the presence of certain mineralogical species can be determined from diagnostic absorption features and spectral characteristics which have been studied under known laboratory conditions and understood in terms of crystal field theory with one possible exception the surface composition of near earth asteroids consists of common rock forming minerals such as olivine pyroxene and phyllosilicates opaque components are present but cannot be mineralogically identified with existing experimental data the spectrum of 2201 oljato cannot be interpreted in terms of common rock forming minerals this spectrum was examined for cometary features because its high orbital eccentricity suggests a possible relation to comets no common cometary features are identified in its spectrum the predominance of mafic silicate absorption features in spectra of near earth asteroids compared to the majority of main belt asteroids may be a primary compositional feature or may be the signature of relatively fresher asteroid material

decrease of river runoff in the upper waters of the eurasian basin arctic ocean between 1991 and 1996 evidence from δ18o data 1 measurements of the h218o h216o ratio of water from two sections crossing the eurasian basin in 1991 and 1996 show that the observed decrease in the freshwater contained in the upper waters of the eurasian basin during the 1990s is due to decrease in meteoric water mainly river runoff the decrease in meteoric water inventories between 1991 and 1996 calculated from balances of mass salinity 18o and po4 is about 3 meters and accounts for basically the entire freshwater change inferred from salinity budgets climatological data are used to ensure that the two sections can be considered to belong to the same hydrographic regime the data also suggest that in 96 the formation of sea ice from the upper waters in the amundsen basin was lower by about 1 meter 3 m in 1996 compared to 4 m in 1991

varieties of shallow temperature maximum waters in the western canadian basin of the arctic ocean the properties and spreading pathways of shallow temperature maximum waters stms in the western canadian basin are investigated using ctd and mooring data obtained in 1997 98 as part of the sheba surface heat budget of the arctic ocean drift experiment and available historical data three distinct varieties of stm are recognized on the basis of salinity range 1 surface mixed layer water smlw with s 32 psu these stms carry sufficient heat within the upper layers of the ocean to significantly affect the rates of ice cover and decay for example during the winter of 1997 98 anomalously warm stm 0 c originating from ecsw was observed to spread northwards along the northwind ridge and chukchi plateau where the maximum reduction of the ice covers was subsequently observed in late summer 1998 maslanik et al 1999 regional climate variability and ice cover in the western canadian basin are thus affected not only by anomalous atmospheric circulation patterns but also by the circulation of upper ocean water masses

suspended particulate matter on the laptev sea shelf siberian arctic during ice free conditions optical turbidity surveys combined with pigment plankton and current measurements were used to investigate the vertical and horizontal dynamics of suspended particulate matter spm in the laptev sea one of the largest siberian shelf seas during the ice free period optical measuring devices prove to be an excellent tool to measure spm distribution in real time spm concentrations were quantified owing to the high correlation of water samples and optical backscatter thus the formation and distribution of the bottom nepheloid layer a layer of increased spm concentration and its significance for the sediment transport on the laptev sea shelf can be described two nepheloid layers exist in the eastern and central laptev sea formation and concentration of the surface layer are mainly related to the amount of phytoplankton and zooplankton occurrence however in the vicinity of the lena delta the concentration is strongly dependent on riverine discharge the bottom nepheloid layer is suggested to develop during and briefly after the spring breakup when about 60 of the mean annual sediment input is discharged onto the shelf spm spreads over the shelf and is kept in suspension within the bottom layer especially during the ice free period almost no sedimentation takes place however bottom material is resuspended due to wind induced increased bottom currents mainly in paleo river valleys and on shoals valleys act as transport conduits during the ice free period and spm is shifted within them an intermediate layer near stolbovoy bank is probably caused by the displacement of the bottom layer from the topographic highs into the valleys the combined turbidity and current measurements indicate that most of the sediment transport on the laptev sea shelf takes place in the bottom nepheloid layer

distribution of atlantic and pacific waters in the upper arctic ocean implications for circulation the atlantic and pacific oceans provide source waters for the arctic ocean that can be distinguished by their differing nitrate and phosphate concentration relationships using these relationships we estimate the amount of atlantic and pacific waters in the surface layer top 30 m of the arctic ocean atlantic source water is dominant in most of the eurasian basin and is present in significant amounts in the makarov basin north of the east siberian sea pacific source water is dominant in most of the canadian basin and is present in significant amounts in the amundsen basin north of greenland we deduce circulation patterns from the distributions of atlantic and pacific source waters in the surface layer of the arctic ocean and conclude that the flow within the surface layer differs from ice drift along the north american and european boundaries of the polar basin

portales valley petrology of a metallic melt meteorite breccia portales valley pv is an unusual metal veined meteorite that has been classified as an h6 chondrite it has been regarded either as an annealed impact melt breccia as a primitive achondrite or as a meteorite with affinities to silicated iron meteorites we studied the petrology of pv using a variety of geochemical mineralogical techniques our results suggest that pv is the first well documented metallic melt meteorite breccia mineral chemical and other data suggest that the protolith to pv was an h chondrite the composition of feni metal in pv is somewhat fractionated compared to h chondrites and varies between coarse vein and silicate rich portions it is best modeled as having formed by partial melting at temperatures of 940 1150 c with incomplete separation of solid from liquid metal solid metal concentrated in the coarse vein areas and s bearing liquid metal concentrated in the silicate rich areas possibly as a result of a surface energy effect both carbon and phosphorus must have been scavenged from large volumes and concentrated in metallic liquid graphite nodules formed by crystallization from this liquid whereas phosphate formed by reaction between p bearing metal and clinopyroxene components depleting clinopyroxene throughout much of the meteorite and growing coarse phosphate at metal silicate interfaces some phosphate probably crystallized from p bearing liquids but most probably formed by solid state reaction at 975 725 c phosphate forming and feo reduction reactions were widespread in pv and entailed a change in the mineralogy of the stony portion on a large scale portales valley experienced protracted annealing from supersolidus to subsolidus temperatures probably by cooling at depth within its parent body but the main differences between pv and h chondrites arose because maximum temperatures were higher in pv a combination of a relatively weak shock event and elevated pre shock temperatures probably produced the vein and breccia texture with endogenic heating being the main heat source for melting and with stress waves from an impact event being an essential trigger for mobilizing metal portales valley is best classified as an h7 metallic melt breccia of shock stage s1 the meteorite is transitional between more primitive chondritic and evolved achondrite iron meteorite types and offers clues as to how differentiation could have occurred in some asteroidal bodies

analysis of progressive failure and cracking in old british dams three sections representative of existing old puddle core embankments were analysed using non linear finite element techniques they had shoulders of granular fill puddle clay cores and strong foundations the analyses showed that progressive failure was negligible during drained construction operation and undrained draw down the cores were vulnerable to cracking if they were subjected to full reservoir pressure on their upstream boundary however very slow drained impounding caused mean total stresses to rise so that fracture was not indicated hydraulic fracture was predicted in a deep cut off trench filled with puddle clay cyclic drawdown and impounding increased stresses in the upstream side of the core so increasing the resistance to cracking total stresses increased and decreased with reservoir level as has been observed in the field les auteurs ont utilise des techniques des elements finis non lineaires pour analyser trois sections types de vieux barrages en enrochements a noyau en argi

evidence for rapid thinning of sea ice in the western arctic ocean at the end of the 1980s examination of springtime ice drafts obtained from submarine profiles in a narrow band of the western arctic ocean from offshore alaska to 89 n indicates that the mean ice draft decreased 1 5 m between the mid 1980s and early 1990s no similar trend was evident in ice drafts near the north pole the 1980s drafts were composed largely of ice exceeding 3 5 m while the early 1990s drafts contained more ice in thinner categories the differences in drafts between the two periods appear to be related largely to ice dynamics effects associated with the presence and strength of the beaufort gyre which weakened considerably in the early 1990s

near infrared spectral reflectance of mineral mixtures systematic combinations of pyroxenes olivine and iron oxides near infrared spectral reflectance data are presented for systematic variations in weight percent of two component mixtures of ferromagnesian and iron oxide minerals mixtures were chosen for application to the study of the dark materials on mars but the results are equally applicable to mafic and ultramafic assemblages elsewhere in the solar system olivine spectral features are greatly reduced in contrast by admixture of other phases but remain distinctive even for low olivine contents clinopyroxene and orthopyroxene mixtures show resolved pyroxene absorptions near 2 m the addition of limonite greatly modifies pyroxene and olivine reflectance but does not fully eliminate distinctive spectral characteristics using only spectral data in the 1 m region it is difficult to differentiate orthopyroxene and limonite goethite in a mixture additional spectral coverage or other evidence may be required for a unique interpretation all composite mineral absorptions observed in this study are either weaker than or intermediate in strength to the end member absorptions and have bandwidths greater than or equal to those for the end members in general spectral properties in an intimate mixture combine in a complex nonadditive manner with features demonstrating a regular but usually nonlinear variation as a function of end member phase proportions

relation of the spectroscopic reflectance of olivine to mineral chemistry and some remote sensing implications using high resolution visible and near infrared diffuse spectral reflectance we have systematically investigated apparent wavelength shifts as a function of mineral chemistry in the fe mg olivine series from fo11 to fo91 the study also shows that trace amounts of nickel can be spectrally detected in the olivine structure we show that significant compositional information can only be extracted at relatively high resolution because the overall spectral characteristics of the olivines change only subtly as a function of the fe mg ratio significant spectral variation as a function of grain size is also demonstrated adding a further complication to the interpretation of remotely sensed data from olivine rich surfaces this laboratory study is expected to aid in the interpretation of remotely sensed data from both terrestrial and extraterrestrial bodies terrestrial applications may include the recognition of ultramafic ultrabasic and basaltic terrains which in themselves may have mineral potential among extraterrestrial applications the asteroids are obvious candidates for further examination if instrumentation can provide the necessary wavelength coverage resolution and signal to noise ratio so that spectra can be compared to those laboratory data discussed here some permutations of fe mg ni relations in olivines are discussed as they apply to the interpretation of asteroid surfaces and other extraterrestrial bodies

fluvial sediment flux to the arctic ocean the paper presents an overview of recent publications on the fluvial suspended sediment flux to the arctic ocean the total suspended matter exported from the russian territory is 102 10 6 t year and from the canadian arctic is 125 10 6 t year the total suspended matter tsm flux to the arctic 227 10 6 t year is very low only about 1 of the global flux mean concentrations of suspended matter and specific sediment discharge are approximately one order of magnitude lower than the global concentration an analysis of the trends in the sediment loads based on records of up to 62 years in length shows decreases yenisey increases kolyma and stability ob among the reasons for the very low concentrations and fluxes of suspended sediment in the arctic rivers are thin weathering crusts on the arctic watersheds low precipitation extensive permafrost low temperatures for most of the year large areas of swamps and lakes and a low level of human activity a stochastic sediment transport model by morehead et al morehead m d syvitski j p hutton e w peckham s d 2003 modeling the temporal variability in the flux of sediment from ungauged river basins glob planet change 39 95 110 is applied to the arctic rivers to estimate the sediment load increase should the surface temperature of the drainage basin increase for every 2 c of warming a 30 increase in the sediment flux could result and for each 20 increase in water discharge a 10 increase in sediment load could follow based on this model an increase of the sediment flux of six largest arctic rivers yenisey lena ob pechora kolyma and severnaya dvina is predicted to range from 30 to 122 by 2100

spatial patterns of primary production on the shelf slope and basin of the western arctic in 2002 in the spring and summer of 2002 primary production in the chukchi sea was measured using 14 c uptake experiments our cruise track encompassed the shelf and continental slope area of the chukchi and beaufort seas progressing into deep water over the canada basin the study area experienced upwards of 90 ice cover during the spring with ice retreating into the basin during the summer production in the spring was light limited due to ice cover with average euphotic zone production rates of o0 3 g c m 2 d 1 values of 8 g c m 2 d 1 were observed in association with surface bloom conditions during the initial ice breakup considerable nutrient reduction in the surface waters took place between the spring and summer cruise and although not observed this was attributed to a spring bloom decreased ice cover and increased clarity of surface waters in the summer allowed greater light penetration the highest rates of production during the second cruise were found at 25 30 m coincident with the top of the nutricline daily euphotic zone productivity in the summer averaged 0 78 g c m 2 d 1 on the shelf and 0 32 g c m 2 d 1 on the edge of the canada basin these data provide an estimated annual production of 90 g c m 2 yr 1 in the study area

asteroid 6 hebe the probable parent body of the h type ordinary chondrites and the iie iron meteorites the s iv type asteroid 6 hebe is identified as the probable parent body of the h type ordinary chondrites and of the iie iron meteorites the ordinary chondrites are the most common type of meteorites falling to earth but prior to the present study no large mainbelt source bodies have been confirmed hebe is located adjacent to both the v6 and 3 1 resonances and has been previously suggested as a major potential source of the terrestrial meteorite flux hebe exhibits subtle rotational spectral variations indicating the presence of some compositional variations across its surface the silicate portion of the surface assemblage of hebe is consistent both in overall average and in its range of variation with the silicate components in the suite of h type chondrites the high albedo of hebe rules out a lunar style space weathering process to produce the weakened absorption features and reddish spectral slope in the s type spectrum of hebe linear unmixing models show that a typical ni fe metal spectrum is consistent with the component that modifies an h chondrite spectrum to produce the s type spectrum of hebe on the basis of the association between the h chondrites and the he iron meteorites our model suggests that large impacts onto the relatively metal rich h chondrite target produced melt bodies sheets or pods that differentiated to form thin laterally extensive near surface layers of ni fe metal fragments of the upper silicate portions of these melt bodies are apparently represented by some of the igneous inclusions in h chondrite breccias alternately masses of metal could have been deposited on the surface of hebe by the impact of a core or core fragment from a differentiated parent body of h chondrite composition subsequent impacts preferentially eroded and depleted the overlying silicate and regolith components exposing and maintaining large masses of metal at the optical surface of hebe in this interpretation the nonmagmatic iie iron meteorites are samples of the ni fe metal masses on the surface of hebe whereas the h chondrites are samples from between and or beneath the metal masses

circulation of summer pacific halocline water in the arctic ocean 1 we present an analysis of arctic ocean hydrographic and sea ice observations from the 1990s with a focus on the circulation of water that originates in the north pacific ocean previous studies have shown the presence of two varieties of relatively warm summer halocline water in the vicinity of the chukchi sea i e the relatively fresh alaskan coastal water acw and the relatively saltier summer bering sea water sbsw here we extend these studies by tracing the circulation of these waters downstream into the arctic ocean we find that acw is generally most evident in the southern beaufort gyre while sbsw is strongest in the northern portion of the beaufort gyre and along the transpolar drift stream we find that this separation is most extreme during the early mid 1990s when the arctic oscillation was at historically high index values this leads us to speculate that the outflow to the north atlantic ocean through the canadian archipelago and fram strait may be similarly separated as arctic oscillation index values fell during the later 1990s acw and sbsw began to overlap in their regions of influence these changes are evident in the area north of ellesmere island where the influence of sbsw is highly correlated with a 3 year lag with the arctic oscillation index we also note the presence of winter bering sea water wbsw which underlies the summer varieties all together this brings the number of distinct pacific water types in our arctic ocean inventory to three acw sbsw and wbsw

rotational spectral variations of asteroid 8 flora implications for the nature of the s type asteroids and for the parent bodies of the ordinary chondrites abstract the new interpretive calibrations olivine pyroxene abundance spectral signature of chondritic metal grains have been applied to visible and near infrared spectral reflectance data for the typical s type asteroid 8 flora chondritic metal grains do not exhibit the steeply reddened spectral signature previously associated with a nickel iron nife metal phase the conditions required to produce a s type spectral curve from a chondritic material are much more restrictive and improbable than previously supposed five mineralogic and patrologic parameters have been derived for the surface material of flora from the analysis of the spectral reflectance and rotational spectral variations of this object these include bulk mineralogy nife metal olivine pyroxene mafic mineral abundance ol py 2 8 metal nature abundant 50 and coarse grained in the substrate pyroxene composition orthopyroxene f s 50 and or abundant clinopyroxene and spatial mineralogic variations olivine pyroxene ratio and pyroxene composition do not covary in a chondritic manner all of the diagnostic mineralogic properties of the flora surface material indicate that this is a differentiated body none of the derived surface properties unambiguously support a chondritic type material and several contradict any type of undifferentiated assemblage flora is most probably the residual core of an intensely heated thermally evolved and magmatically differentiated planetesimal which was subsequently disrupted the present surface samples layers formed at and near the core mantle boundary in the parent body several lines of evidence suggest that the s type asteroids as a class are predominantly the core fragments of disrupted differentiated planetesimals a main belt source of the ordinary chondrites remains elusive

geologic mapping of vesta from 1994 hubble space telescope images we utilize the 56 images of asteroid 4 vesta obtained through four mineralogically diagnostic filters by the hubble space telescope zellneret al 1997 icarus to construct a geologic map vesta s surface is found to be geologically diverse and to be dichotomous at a hemispheric scale the eastern hemisphere longitude definition from thomaset al 1997 icarus is dominated by units interpreted to be impact excavated plutonic material composed of magnesium rich and calcium poor pyroxene the mineralogy of this region is most analogous to diogenite meteorites several eastern hemisphere units which have the deepest and broadest 1 m absorption bands may contain a substantial olivine component the locations of these units are consistent with a previous map based on rotationally resolved groundbased spectroscopy gaffey 1997 icarus the western hemisphere is dominated by units interpreted to consist of a single component of iron rich and relatively calcium rich pyroxene analogous to surface basalts such as eucrite meteorites we investigate the spectral properties of 20 representative surface regions and find a correlation between the 1 m absorption band depth and albedo the units with lower albedos have shallower band depths such a relation could arise from differences in lithologies differences in surface particle sizes or from a weathering effect which decreases albedo and band depth over time because of vesta s geologic diversity and hemispheric dichotomy it is apparent that any major impact events such as those possibly related to the formation of the vesta family binzel and xu 1993 science260 186 191 did not globally resurface the planet the spectral evidence for remnants of a basaltic crust implies that the oldest units on the surface date back to the time of their emplacement most likely 4 5 byr ago if a weathering process exists which alters the albedo then the lowest albedo units such as the feature with the proposed name olbers most likely represent remnants of vesta s ancient basaltic crust

failure mechanism of the aznalcollar dam seville spain in this paper an explanation is given of the geotechnical causes that induced the failure of the aznalcollar dam in seville spain on the day of the failure the dam was 28 m high with a crest length of approximately 3000 m it stored nearly 20 million m3 of mining waste the construction of the tailing pond started in 1979 on the night of 24 april 1998 a breach developed in the embankment of the dam to analyse the problem an extensive investigation of in situ and laboratory tests was carried out the data obtained have confirmed that the rupture was caused by a failure of the dam foundation at a depth of approximately 14 m below original ground level this gave rise to an almost flat slide with a horizontal movement of 60 m affecting a section of about 600 m along the dam the foundation consists of carbonated slightly expansive overconsolidated silty clays known locally as andalusian blue marls in spite of their low dry density they are hard and exhibit strain softening behaviour these phenomena

relationship of e type apollo asteroid 3103 1982 bb to the enstatite achondrite meteorites and the hungaria asteroids visible and near infrared observations confirm that apollo asteroid 3103 1982 bb has a reflectance spectrum consistent with its previous assignment to taxonomic type e it has been generally believed that the e type asteroids are analogous and perhaps even genetically related to the enstatite achondrite meteorites aubrites correlated variations of previously published visible and thermal infrared lightcurves and the lack of rotational color variations in the present data indicate that this is an elongated object with no substantial surface albedo variations apollo asteroid 3103 1982 bb is presently in an orbital resonance 3 5 with earth and appears to be a relatively long lived member of the earthapproaching population its orbit is consistent with both the fall dates and long cosmic ray exposure ages of the aubrites combined with the rarity of e type asteroids in the near earth asteroid population this indicates that 3103 1982 bb is probably either a major or the primary immediate source body of the aubrites the aphelion location and the mineralogy of 3103 1982 bb indicate that it was most probably derived from the hungaria region at the innermost edge 1 9 au of the asteroid belt although the exact dynamical mechanism for producing its present orbit is not clear these results represent the first plausible direct link of a set of meteorites aubrites or enstatite achondrites back to a particular source region in the asteroid belt this link allows the composition of the solar nebula to be constrained at that heliocentric distance during the time interval when the parent assemblage of the aubrites was isolated from contact with the nebular gas by accretion into its parent planetesimal 1992 academic press inc

meteorite and asteroid reflectance spectroscopy clues to early solar system processes although earth has a magnetic shield that protects it from energetic ions and a cushioning atmosphere that catches the tons of small particles i mm that bombard it daily solid material from extraterrestrial sources nevertheless reaches the surface of earth many times a year dodd 1 98 1 when the largest of these bodies impact the surface with great velocity they release immense energy usually form a crater and often disrupt the terrestrial biosphere fortunately such events occur relatively infrequently although individual impacts are currently unpredictable beyond a statistical accounting shoemaker et al 1979 grieve 1 982 cosmic material between the size of small dust particles and the larger crater forming bodies is slowed by the terrestrial atmosphere upon entry the outermost portion of these objects is melted and ablated during passage forming a fusion crust which protects the interior and they land

finite element analysis of progressive failure of carsington embankment progressive failure occurs when brittle soils are loaded non uniformly the average shear stress at collapse is less than peak strength the effect cannot be examined by conventional limit equilibrium stability analysis the carsington embankment slipped in 1984 just before it reached full height the slide was 30 m deep and 500 m long and instrumentation had been installed and read up to the moment of collapse the strengths of the soils involved were carefully established as was the exact geometry of the slip limit equilibrium analysis showed that at collapse the average shear stress mobilized was less than peak strength with a safety factor based on peak strength of 1 2 since the soils involved were brittle progressive failure was a probable cause of the discrepancy finite element analyses were performed in which strain softening soil properties were assumed some of these analyses are reported here the pre failure displacements the collapse height and collapse mechanism were recovered by t

response of the equatorial pacific to chlorophyll pigment in a mixed layer isopycnal ocean general circulation model the influence of phytoplankton on the upper ocean dynamics and thermodynamics in the equatorial pacific is investigated using an isopycnal ocean general circulation model opyc coupled with a mixed layer model and remotely sensed chlorophyll pigment concentration from the coastal zone color scanner czcs in the equatorial pacific heat accumulation due to a higher abundance of chlorophyll pigments in the equatorial pacific leads to a decrease of the mixed layer thickness this generates anomalous westward geostrophic currents north and south of the equator in the western equatorial pacific these anomalous geostrophic currents merge into and strengthen the equatorial undercurrent euc supplying water mass from the 200 m depth to the eastern equatorial pacific this chlorophyll induced response of the undercurrent enhances upwelling around 110w resulting in a lower sea surface temperature sst than without chlorophyll thus thermal gradients due to absorption of solar radiation by phytoplankton may contribute remotely to equatorial upwelling in the eastern pacific

atlantic water circulation over the mendeleev ridge and chukchi borderland from thermohaline intrusions and water mass properties 1 hydrographic and tracer data from 2002 illustrate atlantic water pathways and variability in the mendeleev ridge and chukchi borderland cblmr region of the arctic ocean thermohaline double diffusive intrusions zigzags dominate both the fram strait fsbw and barents sea branch waters bsbw in the region we show that details of the zigzags temperature salinity structure partially describe the water masses forming the intrusions furthermore as confirmed by chemical tracers the zigzags peaks contain the least altered water allowing assessment of the temporal history of the atlantic waters whilst the fsbw shows the 1990s warming and then a slight cooling the bsbw has continuously cooled and freshened over a similar time period the newest boundary current waters are found west of the mendeleev ridge in 2002 additionally we show the zigzag structures can fingerprint various water masses including the boundary current using this tracer data and the advection of the 1990s warming we conclude the strongly topographically steered boundary current order 50 km wide and found between the 1500 m and 2500 m isobaths crosses the mendeleev ridge north of 80 n loops south around the chukchi abyssal plain and north around the chukchi rise with the 1990s warming having reached the northern but not the southern northwind ridge by 2002 pacific waters influence the atlantic layers near the shelf and over the chukchi rise the northwind abyssal plain is comparatively stagnant being ventilated only slowly from the north there is no evidence of significant boundary current flow through the chukchi gap

presidential address presented 2000 august 28 chicago illinois usa the eucrite vesta story many lines of evidence indicate that meteorites are derived from the asteroid belt but in general identifying any meteorite class with a particular asteroid has been problematical one exception is asteroid 4 vesta where a strong case can be made that it is the ultimate source of the howardite eucrite diogenite hed family of basaltic achondrites visible and near infrared reflectance spectra first suggested a connection between vesta and the basaltic achondrites experimental petrology demonstrated that the eucrites the relatively unaltered and unmixed basaltic achondrites were the product of approximately a 10 melt studies of siderophile element partitioning suggested that this melt was the residue of an asteroidal scale magma ocean mass balance considerations point to a parent body that had its surface excavated but remains intact modern telescopic spectroscopy has identified kilometer scale vestoids between vesta and the 3 1 orbit orbit resonance with jupiter dynamical simulations of impact into vesta demonstrate the plausibility of ejecting relatively unshocked material at velocities consistent with these astronomical observations hubble space telescope images show a 460 km diameter impact basin at the south pole of vesta it seems that nature has provided multiple free sample return missions to a unique asteroid major challenges are to establish the geologic context of the hed meteorites on the surface of vesta and to connect the remaining meteorites to specific asteroids

the selborne cutting stability experiment the paper describes a field experiment in which a 9 m deep cut slope in gault clay was brought to failure by pore pressure recharge the geology of the site is described and the procedures used to

delayed collapse of cut slopes in stiff clay delayed failure of railway cutting slopes in stiff clays excavated in the nineteenth and early twentieth centuries has been studied for some forty years known failures have generally been deep seated more recently failures have been a problem in the slopes of motorway cuttings and embankments although generally these have been shallow the average operational strength at failure in these slides has been significantly less than the peak strength and progressive failure has been postulated as the probable cause of this progressive failure can now be analysed using advanced numerical techniques a series of coupled finite element analyses have been conducted assuming strain softening soil with properties based on the brown london clay and the results are reported they show that progressive failure is considerable and fully explain the observed field behaviour the delays experienced in the field are also recovered by the analyses progressive failure is generated primarily by the high lateral stresse

the failure of carsington dam the upstream slope of carsington dam failed just before its completion in 1984 the slip started on the right abutment and spread across the valley to a length of nearly 500m extensive investigations were conducted and further information was obtained when the dam was reconstructed the initial slip sheared through the core which contained shear surfaces due to rutting and along a layer of yellow clay which contained solifluction shears both materials were brittle with low residual strengths the factor of safety based on measured peak strengths was about 1 4 with reductions to allow for shears it was 1 2 it had been reduced to 1 0 by progressive failure finite element fe analyses in which strain softening was reproduced confirmed this it was concluded that the slide spread by lateral load transfer through sections of the dam with a safety factor greater than 1 in the vailey centre the slide passed through the base of the mudstone fill a combination of fe and limit equilibrium analysis ind

residual strength of clays in landslides folded strata and the laboratory the post peak drop in drained shear strength of an overconsolidated clay may be considered as taking place in two stages first at relatively small displacements the strength decreases to the fully softened or critical state value owing to an increase in water content dilatancy second after much larger displacements the strength falls to the residual value owing to reorientation of platy clay minerals parallel to the direction of shearing if the clay fraction is less than about 25 the second stage scarcely comes into operation the clay behaves much like a sand or silt with angles of residual shearing resistance typically greater than 20 degrees conversely when the clay fraction is about 50 residual strength is controlled almost entirely by sliding friction of the clay minerals and further increase in clay fraction has little effect the angles of residual shearing resistance of the three most commonly occurring clay minerals are approximately 15 degrees for kaolinite 10 degrees for illite or clay mica and 5 degrees for montmorillonite when the clay fraction lies between 25 and 50 there is a transitional type of behaviour residual strength being dependent on the percentage of clay particles as well as on their nature the post peak drop in strength of a normally consolidated clay is due only to particle reorientation measurements of strength on natural shear surfaces agree within practical limits of variation with values derived from back analysis of reactivated landslides this field residual strength can be recovered by multiple reversal shear box tests on cut plane samples but in high clay fraction materials it is typically somewhat higher than the strength measured in ring shear tests residual strength is little affected by variation in the slow rates of displacement encountered in reactivated landslides and in the usual laboratory tests but at rates faster than about 100 mm min qualitative changes take place in the pattern of behaviour a substantial gain in strength is followed with increasing displacement by a fall to a minimum value in clays and low clay fraction silts this minimum is not less than the slow or static residual but in clayey silts with clay fractions around 15 25 according to tests currently in progress the minimum can be as low as one half of the static value author trrl

contributions to geotechnique 1948 2008 slope stability and embankment dams the paper reviews the main contributions to geotechnical engineering in the allied fields of slope stability and embankment dams over the past sixty years of geotechnique skempton s rankine lecture is probably the most important single contribution to the science of slope stability engineering through the initial enunciation of the linked ideas of slip surfaces and residual strength embankment dam engineering papers do not have such a single identifiable seminal publication but the contribution of rankine lecturers to the science of embankment dams is equally evident