deposit from a giant wave on the island of lanai hawaii limestone bearing gravel the newly named hulopoe gravel blankets the coastal slopes on lanai the deposit which reaches a maximum altitude of 326 meters formerly was believed to have been deposited along several different ancient marine strandlines but dated submerged coral reefs and tide gauge measurements indicate that the southeastern hawaiian islands sink so fast that former worldwide high stands of the sea now lie beneath local sea level evidence indicates that the hulopoe gravel and similar deposits on nearby islands were deposited during the pleistocene by a giant wave generated by a submarine landslide on a sea scarp south of lanai

return of the coral reef hypothesis basin to shelf partitioning of caco3 and its effect on atmospheric co2 differences in the rate of coral reef carbonate deposition from the pleistocene to the holocene may account for the quaternary variation of atmospheric co sub 2 volumes of carbonate associated with holocene reefs require an average deposition rate of 2 0 times 10 sup 13 mol yr for the past 5 ka in light of combined riverine mid ocean ridge and ground water fluxes of calcium to the oceans of 2 3 times 10 sub 13 mol yr the current flux of calcium carbonate to pelagic sediments must be far below the pleistocene average of 1 2 times 10 sub 13 mol yr the authors suggest that sea level change shifts the locus of carbonate deposition from the deep sea to the shelves as the normal glacial interglacial pattern of deposition of quaternary global carbonates to assess the impact of these changes on atmospheric co sub 2 a simple numerical simulation of the global carbon cycle was developed atmospheric co sub 2 as well as calcite saturation depth and sediment responses to these carbonate deposition changes are examined atmospheric co sub 2 changes close to those observed in the vostok ice core approximately 80 ppm co sub 2 for the quaternary are observed as well as the approximate depth changes in percent carbonate of sediments measured in themore pacific ocean over the same time interval less

oxygen and carbon isotope record of east pacific core v19 30 implications for the formation of deep water in the late pleistocene north atlantic abstract a detailed oxygen and carbon isotope record has been obtained from benthic foraminifera in core v19 30 from the carnegie ridge on the south side of the panama basin expressing these records and the oxygen and carbon isotope records previously published for atlantic core m 12392 on a common timescale it is apparent that the oxygen isotope records are very similar but that the carbon isotope records are quite different by obtaining the carbon isotope gradient between the two sites as a function of time we show that the production of north atlantic deep water has varied over a wide range during the late pleistocene and that the pattern of variation is not simply related to the well known oxygen isotope record although the two oxygen isotope records are very similar changes in the interoceanic gradient are detectable and support the hypothesis that in the glacial mode the north atlantic was colder and less oxygenated than it is today shackleton s 1 1977 interpretation whereby the carbon isotope record from the atlantic core reflects changes in the terrestrial biomass is an over simplification however the record from the pacific core v19 30 probably can be explained in these terms since it probably approximates the carbon isotope record of global mean oceanic dissolved co 2

interpreting and modelling late quaternary dune accumulation in the southern arabian peninsula abstract one of the fundamental questions in the reconstruction of quaternary dryland environmental conditions is what do dune osl ages mean in terms of palaeoenvironmental change this paper investigates the relationship between dune chronological records and external environmental forcing in the southern arabian peninsula during the last 30 ka aeolian records from the region are reviewed with reference to other regional palaeoenvironmental proxies and these findings are related to a modelled assessment of dune response to the aeolian system state of the northeastern rub al khali the model replicates a range of features of the regional dune chronology when forced by three external parameters sediment supply sediment availability and transport capacity including extensive regional dune accumulation during the late pleistocene holocene transition and reduced activity during the early holocene humid period dune chronologies incorporate the influence of both external forcing parameters and localised short term factors included as stochastic processes thick sedimentary units most likely represent external forcing conditions conducive to aeolian sediment transport and deposition but at the same time these factors may be represented by periods of erosion of sediment at different sites confident interpretation of past environmental conditions is therefore not possible based on results from individual stratigraphic records sampling at multiple locations is needed in order to distinguish dune accumulation and preservation due to external forcing from stochastic processes of dune development

coda q distribution in the canary islands abstract the canary archipelago near the african plate between 27 and 30 n and 13 and 19 w is included in the oldest region 135 m y of the eastern atlantic ocean the tectonic seismicity is moderate with low magnitudes and it is almost totally related to an active fault located between the islands of tenerife and gran canaria the purpose of this paper is to provide a clear idea of the anelasticity of coda waves in the region in order to compute master dispersion curves as a function of the quality factor q we have applied inversion methods to obtain analytical magnification curves for all the seismographic stations used fp t data corresponding to the coda wave dispersion of 52 local and regional seismic events recorded at 6 seismographic stations have been obtained the fit of the data to the master curves determined yields estimates of coda q values and their frequency dependence most of the q0 values determined at 1 hz vary between 100 and 300 showing a strong frequency dependence in the range 0 2 2 hz the characteristic v value degree of frequency dependence of q in the region given by the law q q0 fv is v 0 9 by applying regionalization techniques an iso q0 map for a reference frequency of 1 hz has been obtained for the canary archipelago this map shows important lateral variations in q0 reflecting the tectonics and the volcanism of the region the lowest q0 values are found along the trend of the fault and beneath the islands

comparison and cross checking of historical archaeological and geological evidence for the location and type of historical and sub historical eruptions of multiple vent oceanic island volcanoes

thorium 230 profiling in deep sea sediments high resolution records of flux and dissolution of carbonate in the equatorial atlantic during the last 24 000 years variations in carbonate flux and dissolution which occurred in the equatorial atlantic during the last 24 000 years have been estimated by a new approach that allows the point by point determination of paleofluxes to the seafloor an unprecedented time resolution can thus be obtained which allows sequencing of the relatively rapid events occurring during deglaciation the method is based on observations that the flux of unsupported 230th into deep sea sediments is nearly independent of the total mass flux and is close to the production rate thus excess 230th activity in sediments can be used as a reference against which fluxes of other sedimentary components can be estimated the study was conducted at two sites ceara rise western equatorial atlantic and sierra leone rise eastern equatorial atlantic in cores raised from three different depths at each site from measurements of 230th and caco3 changes in carbonate flux with time and depth were obtained a rapid increase in carbonate production starting at the onset of deglaciation was found in both areas this event may have important implications for the postglacial increase in atmospheric co2 by increasing the global carbonate carbon to organic carbon rain ratio and decreasing the alkalinity of surface waters and possibly the north atlantic deep water increased carbonate dissolution occurred in the two regions during deglaciation followed by a minimum during mid holocene and renewed intensification of dissolution in late holocene during the last 16 000 years carbonate dissolution was consistently more pronounced in the western than in the eastern basin reflecting the influence of antarctic bottom water in the west this trend was reversed during stage 2 possibly due to the accumulation of metabolic co2 below the level of the romanche fracture zone in the eastern basin

a 300 kyr high resolution aridity record of the north african continent new oxygen isotope data and a high resolution carbonate record of a core from the northwest african margin are presented in combination with geochemical zr rb ratio al ba organic carbon and biogenic opal fluxes and sedimentological median grain size parameters to show variations in african continental aridity wind strength and upwelling productivity the carbonate record is diluted by the supply of aeolian dust from the arid saharan region of north africa and is seen to vary with a characteristic sawtooth pattern indicating rapid increases in dust flux followed by gradual declines spectral analysis of the carbonate profile and comparison with specmap stacked oxygen isotope and etp solar radiation profiles shows that the precessional 23 kyr insolation induced african climate system is decoupled from global ice volume climate changes operating on a 100 kyr frequency detailed studies of glacial terminations i ii and iii confirm the presence of rapid short timescale climatic variations in aridity

giant quaternary landslides in the evolution of la palma and el hierro canary islands in the past large morphological escarpments in the canaries have been generally related to explosive and or erosive processes recent onshore and offshore investigations drastically changed this interpretation by providing evidence of the importance of giant lateral collapses in the evolution of the islands especially in their earlier stages of growth giant landslide scars and deposits are readily observed both onshore and offshore in the younger western canaries and seem to be a common feature of the development of the entire archipelago at least one catastrophic collapse is apparent on la palma the cumbre nueva giant landslide which occurred about 560 ka ago this collapse removed some 200 km3 of central western la palma forming a large embayment three successive giant landslides and evidence of an aborted attempt at another are seen in the island of el hierro the combined volume of those collapses estimated at about 400 500 km3 considerably exceeds the present subaerial volume of the island about 140 km3 giant landslides and erosion during the past million years have removed more than half of the total subaerial volume of la palma and el hierro

global chemical erosion during the last glacial maximum and the present sensitivity to changes in lithology and hydrology geographically based calculations for 18 000 years ago 18 ka and today were made to examine the potential effects on terrestrial chemical erosion of changes in lithology and hydrology on glacial interglacial timescales runoff fields were derived from general circulation model predictions of precipitation minus evaporation then global lithologic maps were prepared so that empirical relationships for runoff versus bicarbonate flux for different rock types could be used to calculate global chemical erosion rates assuming that significant chemical erosion does not occur beneath ice sheets we find that chemical erosion in ice free areas at 18 ka was only slightly greater than today this result arises because the amount of land covered by ice sheets is roughly compensated for by exposed shelf areas and because there is little difference in global runoff the small 20 increase in the global chemical erosion rate during glacial conditions is due to exposure on the shelves of a relatively high proportion of carbonates which weather faster than average data on glacial interglacial movements of the calcite compensation depth ccd are inconclusive but seem to indicate little change whereas even a 20 increase in the riverine bicarbonate flux should cause an observable deepening if the ccd did not indeed change then our predicted increase in the bicarbonate flux from land during glaciations would have to be accommodated by other means such as increased carbonate productivity about half of the observed decrease in atmospheric pco2 at 18 ka could be explained if increased silicate chemical erosion accompanied increased total chemical erosion in ice free areas consideration of the maximum possible effect of meltwater at ice margins leads to an 80 increase in the global chemical erosion rate at 18 ka such an increase would lead to a larger and faster drop in atmospheric pco2 but also to an excessive deepening of the global ccd this scenario seems unrealistic our results are contrary to interpretations of a much higher silicate chemical erosion rate during glaciations based on recently published records of quaternary marine sr isotopic ratios therefore if these records are indeed globally representative and entirely due to increased silicate chemical erosion as opposed to changes in source areas or hydrothermal inputs then other factors such as a shift in the global weathering regime which we do not explicitly consider here may be involved sensitivity tests show that considering spatial heterogeneities in lithology and runoff leads to lower predictions of global chemical erosion rates than what one would obtain by considering only global averages in a non spatially resolved calculation

experiments on rift zone evolution in unstable volcanic edifices large ocean island volcanoes frequently develop productive rift zones located close to unstable flanks and sites of older major sector collapses flank deformation is often caused by slip along a decollement within or underneath the volcanic edifice we studied how such a stressed volcanic flank may bias the rift zone development the influence of basal lubrication and lateral flank creep on rift development and rift migration is still poorly constrained by field evidence here our analog experiments provide new insights we injected colored water into gelatin cones and found systematic orientations of hydro fractures dikes propagating through the cones at the base of the cone diverse friction conditions were simulated by variation of the basal creep conditions we modeled radial dike swarms collinear rift zones and three armed rift systems it is illustrated that a single outward creeping flank is sufficient to modify the entire rift architecture of a volcano the experiments highlight the general unsteadiness of dike swarms and that the distribution and alteration of weak substratum may become a major player in shaping a volcano s architecture

deepwater source variations during the last climatic cycle and their impact on the global deepwater circulation the degree of similarity of the 13c records of the planktonic foraminiferal species n pachyderma and of the benthic foraminiferal genus cibicides in the high latitude basins of the world ocean is used as an indicator of the presence of deepwater sources during the last climatic cycle whereas continuous formation of deep water is recognized in the southern ocean the norwegian sea stopped acting as a sink for surface water during isotope stage 4 and the remainder of the last glaciation however deep water formed in the north atlantic south of the norwegian sea during the last climatic cycle as early as isotope substage 5d and this area was also the only active northern source during stages 4 2 a detailed reconstruction of the geographic distribution of 13c in benthic foraminifera in the atlantic ocean during the last glacial maximum shows that the most important deepwater mass originated from the southern ocean whereas the glacial north atlantic deep water cannot be traced south of 40 n at shallower depth an oxygenated 13c rich intermediate water mass extended from 45 n to 15 s in the pacific ocean a ventilation higher than the modern one was also found in open ocean in the depth range 700 2600 m and is best explained by stronger formation of intermediate water in high northern latitudes

glacial to interglacial changes in carbonate and clay sedimentation in the atlantic ocean estimated from 230th measurements abstract the cause of the climatically controlled fluctuations in the carbonate content of deep sea sediments remains the subject of uncertainty and debate three variables are involved supply of biogenic carbonate loss by dissolution and dilution by non carbonate phases it is suggested that 230 th which is produced in the ocean at a constant rate provides a reliable reference for measuring variations in rate of sedimentation on a regional scale results of a preliminary analysis based on published data indicate that for depths at and above the lysocline the carbonate fluctuations observed in cores from the north atlantic ocean are due primarily to variations in the terrigenous clay input which was 2 5 times higher during glacials than during interglacials carbonate deposition appears to have been somewhat reduced during glacials but probably not by more than a factor of 2 from published 230 th 232 th profiles it appears that the south atlantic ocean also received increased inputs of terrigenous clay during glacial periods

a physical model for the origin of volcanism of the tyrrhenian margin the case of neapolitan area abstract the onset of volcanism in the neapolitan area and the tensile tectonics of the tyrrhenian margin of the apennine chain have been related to the opening of the tyrrhenian basin which may have resulted in horizontal asthenosphere flows giving rise in turn to crustal distension local mantle upwellings and ensuing volcanism geological and structural data were taken into consideration the existence of a shallow crust mantle discontinuity in the neapolitan area the onset of volcanism in a graben type structure the distribution of volcanism along three main directions these facts are all consistent with processes of crustal deformation associated with hot masses as well as fracture systems along three branches often separated by a 120 angle such fracture mechanism was therefore analyzed in physical terms on the assumption of an elasto plastic behaviour of the crust and with reference to the limit analysis theorems

a search for an early holocene caco3 preservation event the co2 record for air bubbles from the byrd station ice core suggest a drawdown in the ocean atmosphere carbon reservoir during the early holocene such a drawdown would require a corresponding increase in the co3 ion concentration in the deep sea we report here the results of a search in atlantic sediments for evidence that the lysocline showed a corresponding deepening while both the pteropod and the calcite preservation records we have obtained are consistent with expectation they are not conclusive

biogenic sedimentation beneath the california current system for the past 30 kyr and its paleoceanographic significance a north south transect of 17 cores was constructed along the eastern boundary of the california current system from 33 to 42 n to investigate the changes in biogenic sedimentation over the past 30 kyr percentages and mass accumulation rates of caco3 corg and biogenic opal were assembled at 500 to 1000 years sample to provide relatively high resolution time space maps reveal a complex pattern of changes that do not follow a simple glacial interglacial two mode model biogenic sedimentation shows responses that are sometimes time transgressive and sometimes coeval and most of the responses show more consistency within a limited geographic area than any temporal consistency reconstructed conditions during late oxygen isotope stage 3 were more like early holocene conditions than any other time during the last 30 kyr coastal upwelling and productivity during oxygen isotope stage 3 were relatively strong along the central california margin but were weak along the northern california margin precipitation increased during the last glacial interval in the central california region and the waters of the southern california margin had relatively low productivity productivity on the southern oregon margin was relatively low at the beginning of the last glacial interval but by about 20 ka productivity in this area significantly increased this change suggests that the center of the divergence of the west wind drift shifted south at this time the end of the last glacial interval was characterized by increased productivity in the southern california margin and increased upwelling along the central california margin but upwelling remained weak along the northern california margin a sudden 300 years decrease in caco3 corg and biogenic opal occurred at 13 ka the changes suggest a major reorientation of the atmospheric circulation in the north pacific and western north america and the establishment of a strong seasonality in the central california region a carbonate preservation event occurred at 10 ka that appears to reflect the uptake of co2 by the terrestrial biosphere as the northern latitudes were reforested following retreat of the glaciers the holocene has been a period of relatively high productivity in the southern california margin relatively strong coastal upwelling along the central california margin relatively weak upwelling along the northern california margin and the northward migration of the divergence zone of the west wind drift

hotspot volcanism close to a passive continental margin the canary islands the canarian archipelago is a group of volcanic islands on a slow moving oceanic plate close to a continental margin the origins of the archipelago are controversial a hotspot or mantle plume a zone of lithospheric deformation a region of compressional block faulting or a rupture propagating westwards from the active atlas mountains fold belt have been proposed by different authors however comparison of the canarian archipelago with the prototypical hotspot related island group the hawaiian archipelago reveals that the differences between the two are not as great as had previously been supposed on the basis of older data quaternary igneous activity in the canaries is concentrated at the western end of the archipelago close to the present day location of the inferred hotspot this is the same relationship as seen in the hawaiian and cape verde islands the latter archipelago associated with a well defined but slow moving mantle plume shows anomalies in a plot of island age against distance which are comparable to those seen in the canary islands these anomalies cannot therefore be used to argue against a hotspot origin for the canaries individual islands in both archipelagoes are characterized by initial rapid growth the shield building stages of activity followed by a period of quiescence and deep erosion erosion gap which in turn is followed by a post erosional stage of activity the absence of post shield stage subsidence in the canaries is in marked contrast with the major subsidence experienced by the hawaiian islands but is comparable with the lack of subsidence evident in other island groups at slow moving hotspots such as the cape verdes comparison of the structure and structural evolution of the canary islands with other oceanic islands such as hawaii and reunion reveals many similarities these include the development of triple mercedes star rift zones and the occurrence of giant lateral collapses on the flanks of these rift zones the apparent absence of these features in the post erosional islands may in part be a result of their greater age and deeper erosion which has removed much of the evidence for their early volcanic architecture we conclude that the many similarities between the canary islands and island groups whose hotspot origins are undisputed show that the canaries have been produced in the same way

the 2011 2012 submarine eruption off el hierro canary islands new lessons in oceanic island growth and volcanic crisis management forty years after the eruption of the teneguia volcano on la palma 1971 the last volcanic event in the canary islands a submarine eruption took place in 2011 off shore el hierro the smallest an

gravitational spreading controls rift zones and flank instability on el hierro canary islands ocean island volcanoes frequently develop local rift zones associated with flank movement and flank collapses the ocean island el hierro grew by coalescence and collapse of three volcanic edifices which are an elongated topographic ridge the southern ridge and two semi circular volcanic cones tinor volcano el golfo volcano during edifice growth and volcano coalescence eruption fissures nucleated into rift zones that developed a complex triangle pattern in scaled analogue experiments we could successfully reproduce the geometry of rift zones and unstable flanks as observed on el hierro the experimental results suggest that the rift configuration on el hierro is the result of gravitational volcano spreading over deformable basal substrata rather than of deep seated magma updoming as thought previously this paper elucidates the importance of the basal substratum and gravitational spreading and the relationship to rifting and flank instability on el hierro island and may help in understanding similar volcano architectures elsewhere

dynamics of diffuse carbon dioxide emissions from cumbre vieja volcano la palma canary islands we report herein the results of 13 soil co2 efflux surveys at cumbre vieja volcano la palma island the most active basaltic volcano in the canary islands the co2 efflux measurements were undertaken using the accumulation chamber method between 2001 and 2013 to constrain the total co2 output from the studied area and to evaluate occasional co2 efflux surveys as a volcanic surveillance tool for cumbre vieja soil co2 efflux values ranged from non detectable up to 2442 g m 2 days 1 with the highest values observed in the south where the last volcanic eruption took place teneguia 1971 isotopic analyses of soil gas carbon dioxide suggest an organic origin as the main contribution to the co2 efflux with a very small magmatic gas component observed at the southern part of the volcano total biogenic and magmatic combined co2 emission rates showed a high temporal variability ranging between 320 and 1544 t days 1 and averaging 1147 t days 1 over the 220 km2 region two significant increases in the co2 emission observed in 2011 and 2013 were likely caused by an enhanced magmatic endogenous contribution revealed by significant changes in the 3he 4he ratio in a co2 rich cold spring the relatively stable emission rate presented in this work defines the background co2 emission range for cumbre vieja during a volcanic quiescence period

slope failures on the flanks of the western canary islands abstract landslides have been a key process in the evolution of the western canary islands the younger and more volcanically active canary islands el hierro la palma and tenerife show the clearest evidence of recent landslide activity the evidence includes landslide scars on the island flanks debris deposits on the lower island slopes and volcaniclastic turbidites on the floor of the adjacent ocean basins at least 14 large landslides have occurred on the flanks of the el hierro la palma and tenerife the majority of these in the last 1 million years with the youngest on the northwest flank of el hierro as recent as 15 thousand years in age older landslides undoubtedly occurred but are difficult to quantify because the evidence is buried beneath younger volcanic rocks and sediments landslides on the canary island flanks can be categorised as debris avalanches slumps or debris flows debris avalanches are long runout catastrophic failures which typically affect only the superficial part of the island volcanic sequence up to a maximum thickness of 1 to 2 km they are the commonest type of landslide mapped in contrast slumps move short distances and are deep rooted landslides which may affect the entire thickness of the volcanic edifice debris flows are defined as landslides which primarily affect the sedimentary cover of the submarine island flanks some landslides are complex events involving more than one of the above end member processes individual debris avalanches have volumes in the range of 50 500 km3 cover several thousand km2 of seafloor and have runout distances of up to 130 km from source overall debris avalanche deposits account for about 10 of the total volcanic edifices of the small relatively young islands of el hierro and la palma some parameters such as deposit volumes and landslide ages are difficult to quantify the key characteristics of debris avalanches include a relatively narrow headwall and chute above 3000 m water depth on the island flanks broadening into a depositional lobe below 3000 m debris avalanche deposits have a typically blocky morphology with individual blocks up to a kilometre or more in diameter however considerable variation exists between different avalanche deposits at one extreme the el golfo debris avalanche on el hierro has few large blocks scattered randomly across the avalanche surface at the other icod on the north flank of tenerife has much more numerous but smaller blocks over most of its surface with a few very large blocks confined to the margins of the deposit icod also exhibits flow structures longitudinal shears and pressure ridges that are absent in el golfo the primary controls on the block structure and distribution are inferred to be related to the nature of the landslide material and to flow processes observations in experimental debris flows show that the differences between the el golfo and icod landslide deposits are probably controlled by the greater proportion of fine grained material in the icod landslide this in turn relates to the nature of the failed volcanic rocks which are almost entirely basalt on el hierro but include a much greater proportion of pyroclastic deposits on tenerife landslide occurrence appears to be primarily controlled by the locations of volcanic rift zones on the islands with landslides propagating perpendicular to the rift orientation however this does not explain the uneven distribution of landslides on some islands which seems to indicate that unstable flanks are a weakness that can be carried forward during island development this may occur because certain island flanks are steeper extend to greater water depths or are less buttressed by the surrounding topography and because volcanic production following a landslide my be concentrated in the landslide scar thus focussing subsequent landslide potential in this area landslides are primarily a result of volcanic construction to a point where the mass of volcanic products fails under its own weight although the actual triggering factors are poorly understood they may include or be influenced by dyke intrusion pore pressure changes related to intrusion seismicity or sealevel climate changes a possible relationship between caldera collapse and landsliding on tenerife is not in our interpretation supported by the available evidence

mega tsunami conglomerates and flank collapses of ocean island volcanoes abstract marine conglomerates at high elevation on the flanks of ocean islands are usually interpreted as evidence of mega tsunamis generated by volcano flank collapses although their origin is sometimes debated elevated littorals vs tsunami in this review we introduce case studies of well documented examples of tsunami conglomerates in hawaii pacific ocean the canary and cape verde islands atlantic ocean and mauritius island indian ocean other less documented marine conglomerates are also presented as tsunami candidates then we build a comprehensive picture of the general characteristics of these conglomerates and the different methods that can be applied to date them different perspectives of research are proposed especially on the use of tsunami conglomerates as proxies for better constraining numerical models of ocean island flank collapses and associated tsunamis we also discuss the possible links between volcano growth flank instability and climate

late pleistocene flank collapse triggered by dome growth at tacana volcano mexico guatemala and its relationship to the regional stress regime during late pleistocene time the extrusion of an andesitic dome at the summit of tacana volcano caused the collapse of its northwestern flank the stratocone collapse was nearly parallel to the min stress direction suggesting that failure was controlled by the regional stress field the event produced a debris avalanche that was channelized in the san rafael river and moved 8 km downstream the deposit covered a minimum area of 4 km2 had a volume of 0 8 0 5 km3 with an h l vertical drop to horizontal transport distance ratio of 0 35 defining a degree of mobility that is atypical for volcanic debris avalanches the flank failure undermined the summit dome leading to its collapse and the generation of a series of block and ash flows that were emplaced in quick succession and covered the avalanche surface the collapse event left a 600 m wide summit amphitheatre with a 30 degree opening to the northwest and 200 m thick debris that blocked the san rafael river remobilization of this material produced debris flows that eroded the primary deposits and cascaded into the coatan river after the collapse the activity of tacana continued with the emission of the agua zarca lava flow dated at 10 6 ka 40ar 39ar and pyroclastic surges dated at 10 610 330 315 yr bp 14c which provide a minimum age for the collapse event during the holocene tacana has been very active producing explosive and effusive eruptions that ended with the extrusion of two summit domes that today occupy the amphitheatre the 1950 and 1986 phreatic outbursts occurred along the pleistocene collapse scar currently 300 000 inhabitants live within a 35 km radius of tacana and could conceivably be impacted by future events of similar magnitude

using a genetic algorithm for 3 d inversion of gravity data in fuerteventura canary islands the use of genetic algorithms in geophysical inverse problems is a relatively recent development and offers many advantages in dealing with the non linearity inherent in such applications we have implemented a genetic algorithm to efficiently invert a set of gravity data employing several fixed density contrasts this algorithm determines the geometry of the sources of the anomaly gravity field in a 3 d context the genetic algorithms based on darwin s theory of evolution seek the optimum solution from an initial population of models working with a set of parameters by means of modifications in successive iterations or generations this searching method traditionally consists of three operators selection crossover and mutation acting on each generation but we have added a further one which smoothes the obtained models in this way we have designed an efficient inversion gravity method confirmed by both a synthetic example and a real data set from the island of fuerteventura in the latter case we identify crustal structures related to the origin and evolution of the island the results show a clear correlation between the sources of gravity field in the model and the three volcanic complexes recognized in fuerteventura by other geological studies

sedimentary signatures of cyclic growth and destruction of stratovolcanoes a case study from mt taranaki new zealand abstract the long term behaviour of andesite stratovolcanoes is characterised by a repetition of edifice growth phases followed by collapse this cyclic pattern represents a natural frequency at varying timescales in the growth dynamics of stratovolcanoes worldwide around the 130 ka mt taranaki egmont volcano new zealand coastal cliff successions at 20 40 km distance comprise repeating packages of lithologically and sedimentologically distinctive mass flow deposits varying depositional mechanisms and source properties of these units record growth and collapse cycles of the central edifice these are used to construct a model for cyclic volcaniclastic sedimentation in the surrounds of stratovolcanoes during edifice construction phases thick packages of tabular predominantly monolithologic hyperconcentrated flow and debris flow deposits accumulate with intercalated tephra beds the mass flow units commonly contain large proportions of fresh pumice or juvenile lithic andesite intervals of quiescence separating eruptive periods are characterised by landscape re adjustment accompanied by deposition of fluvial and aeolian sediments along with steady accretion of medial ash in contrast brief episodes of destruction are marked by wide spread distinctively clay rich polylithologic debris avalanche deposits and related marginal debris flow units the growth stages can be terminated by an eruption triggered sector collapse or by external forces once the edifice exceeds a critical stable height or profile dependent on eruptive style and local geo tectonic conditions once the edifice becomes metastable regional tectonic earthquakes or shallow level intrusion events are likely triggers for collapse although the resulting debris avalanches represent the greatest individual hazard from such andesite stratovolcanoes their frequency is relatively low compared with other types of mass flows generated during edifice growth phases accurate forecasts of future hazard from mass flow events are therefore dependent on recognition of both the frequency of a stratovolcano s growth cycle and its current position in that cycle

terrigenous helium in deep sea sediments abstract we have measured the isotope ratios of helium contained in various terrigenous materials that contribute to deep sea sediments these materials include ice rafted debris from the north atlantic chinese loess and sediment collected at or near the mouths of three large rivers the amazon the ganges and the yangtze we observe terrigenous 3he 4he ratios that vary from 1 8 10 9 to 4 6 10 7 i e values that are higher than the theoretically derived range of 10 9 to 10 8 atlantic and pacific deep sea sediment 3he 4he ratios can be explained by mixing of helium from similar extraterrestrial but different terrigenous sources terrigenous sources for north atlantic and north pacific sediments are characterized by 3he and 4he contents that are higher and 3he 4he ratios that are lower than those for central and eastern equatorial pacific sediments this is consistent with the supply to the north atlantic and north pacific oceans of older cratonic continental material that contains high amounts of in situ produced nucleogenic and radiogenic helium terrigenous material transported to central and eastern equatorial pacific sediments contains lower amounts of 3he and 4he and higher 3he 4he ratios indicative of supply from a more juvenile andean source in the equatorial atlantic core v31 135 we have used previously published 230th data to determine an extraterrestrial 3he flux of 1 16 0 15 10 12 cm3stp cm 2 ka 1 within error of that previously determined in sediments from the equatorial pacific ocean 0 78 0 29 10 13 cm3stp cm 2 ka 1 marcantonio et al 1996

crustal structure gravity anomalies and flexure of the lithosphere in the vicinity of the canary islands summary simple elastic plate models have been used to calculate the flexure of the lithosphere caused by volcanic loading at the canary islands and sediment loading at the moroccan continental margin by comparing the calculated flexure to observations based on seismic refraction and free air gravity anomaly data constraints have been placed on the long term 106 years elastic thickness of the lithosphere te the best fit between the calculated and observed flexure in the vicinity of the canary islands is for te 20 km this value of te also explains seismic reflection data in regions that flank the island provided that the lithosphere underlying the moroccan margin is sufficiently weak te 5 km for sediment loading to contribute little to the island flexure a backstripping study in which gravity data are used to constrain the value of te supports the suggestion that the lithosphere underlying the moroccan margin like its conjugate at the baltimore canyon trough is weak although sediment loading at the moroccan margin appears therefore to have exerted little influence on the structure of the canary islands there is evidence that island flexure may have influenced the stratigraphic development of the moroccan margin especially in the region of the slope anticline a te of 20 km is about 15 km lower than would be expected on the basis of the thermal age of the oceanic lithosphere that underlies the canary islands similar low values have been reported from oceanic islands in the pacific superswell region of french polynesia where they have been attributed to re heating of the lithosphere by one or more hotspots a general e w age progression of the volcanic rocks suggests that the canary islands were also generated by a hotspot they lack however the topographic swell and gravity geoid high which usually accompanies these features one possibility is that the low te values are the result of a pre existing weakness in the oceanic crust a te of 20 km is large enough however for a significant part of the mantle to still be involved in the support of the island loads a more likely explanation is thermal weakening by a hotspot which has been localized enough to reduce te but not to produce a swell or gravity geoid high irrespective of its cause the low te suggests that oceanic lithosphere does not necessarily progressively increase its strength with age so that even 140 ma old lithosphere is vulnerable and can in some regions be significantly weakened by later thermal and mechanical processes

hotspot tracks and the early rifting of the atlantic abstract many hotspot tracks appear to become the locus of later rifting as though the heat of the hotspot weakens the lithosphere and tens of millions of years later the continents are split along these weakened lines examples are the west coast of greenland east coast of labrador madeira hotspot the south coast of mexico north coast of honduras guyana hotspot and the south coast of west africa north coast of brazil st helena hotspot a modern day analog of a possible future rift is the snake river plain where the north american continent is being pre weakened by the yellowstone hotspot track this conclusion is based on reconstructions of the motions of the continents over hotspots for the past 200 million years the relative motions of the plates are determined from magnetic anomaly isochrons in the oceans and the motion of one plate is chosen ad hoc to best fit the motions of the plates over the hotspots however once the motion of this one plate is chosen the motions of all the other plates are prescribed by the relative motion constraints in addition to the correlation between the predicted tracks and sites of later continental breakup exposed continental shields correlate with the tracks their exposure may be the result of hotspot induced uplift which has led to erosion of their former platform sediment cover

hyaloclastites and the slope stability of hawaiian volcanoes insights from the hawaiian scientific drilling project s 3 km drill core abstract core samples recovered during the hawaiian scientific drilling project hsdp drilling project reveal that the upper 1 km of the submarine flank of mauna kea is comprised mainly of hyaloclastites progressive very low temperature alteration of these hyaloclastites has been accompanied by systematic transformations in physical properties of these deposits hyaloclastite deposits which directly underlie ca 1 km of subaerially emplaced lavas are very poorly consolidated but over a depth interval of ca 500 m compaction and especially precipitation of zeolitic pore filling cements associated with palagonitization of sideromelane have eliminated porosity as well as promoted the consolidation of these hyaloclastites the latter is reflected in unconfined compressive strengths which increase from mean values respectively of 2 5 and 4 6 mpa in weakly consolidated smectite rich hyaloclastites from the incipient 1080 to 1335 mbsl and smectitic 1405 1573 mbsl alteration zones to a mean value of 10 0 mpa in the more highly consolidated hyaloclastites of the palagonitic zone of alteration from 1573 mbsl to the bottom of the drill hole conversely overlying intercalated and underlying lava flows are generally much less altered and have mean compressive strengths which are 1 to 2 orders of magnitude greater then hyaloclastites at equivalent depths the shear strengths of the hyaloclastites also increase with depth and grade of alteration but are uniformly and substantially lower in the lavas those hyaloclastites exhibiting the highest grade of alteration i e palagonitic also exhibit the highest measured strengths and thus the alteration of hyaloclastites appears to strengthen as opposed to weaken the flanks of the edifice however the contrast in strength between hyaloclastites and lavas may be a primary factor in localizing destabilization and the zones of weak and poorly consolidated hyaloclastites may facilitate slumping by servings as hosts for shallow detachment surfaces on the unsupported flanks of these volcanoes

the δ13c of equatorial atlantic surface waters implications for ice age pco2 levels carbon isotopic records of nutrient depleted surface water place constraints on the past fertility of the oceans and on past atmospheric pco2 levels the best records of nutrient depleted 13c are obtained from planktonic foraminifera living in the thick mixed layers of the western equatorial and tropical atlantic ocean we have produced a composite stacked globigerinoides sacculifer 13c record from the equatorial atlantic which exhibits significant spectral power at the 100 000 and 41 000 year milankovitch periods but no power at the 23 000 year period similar to the record presented by shackleton and pisias 1985 surface deep ocean 13c produced with the g sacculifer record leads the 18o ice volume record however the glacial interglacial amplitudes of 13c differ between our record and shackleton and pisias 1985 record although large changes in 13c occur in the equatorial atlantic during early stages of the last three glacial cycles surface deep 13c at glacial maxima 18o stage 2 late stage 6 and late stage 8 was only about 0 2 greater than during the subsequent interglacial our results imply that nutrient driven pco2 changes account for about one third of the pco2 decrease observed in ice cores and consequently 13c should not be used as a proxy pco2 index enough variance in the ice core pco2 records remains to be explained that conclusions about pco2 and ice volume phase relationships should also be reexamined as much as 40 ppm pco2 change still has not been accounted for by models of past physics and chemistry of the ocean

ventilation changes in the northeast pacific during the last deglaciation under present climate conditions convection at high latitudes of the north pacific is restricted to shallower depths than in the north atlantic to what extent this asymmetry between the two ocean basins was maintained over the past 20 kyr is poorly known because there are few unambiguous proxy records of ventilation from the north pacific we present new data for two sediment cores from the california margin at 800 and 1600 m depth to argue that the depth of ventilation shifted repeatedly in the northeast pacific over the course of deglaciation the evidence includes benthic foraminiferal cd ca 18o 16o and 13c 12c data as well as radiocarbon age differences between benthic and planktonic foraminifera a number of features in the shallower of the two cores including an interval of laminated sediments are consistent with changes in ventilation over the past 20 kyr suggested by alternations between laminated and bioturbated sediments in the santa barbara basin and the gulf of california keigwin and jones 1990 kennett and ingram 1995 behl and kennett 1996 data from the deeper of the two california margin cores suggest that during times of reduced ventilation at 800 m ventilation was enhanced at 1600 m depth and vice versa this pronounced depth dependence of ventilation needs to be taken into account when exploring potential teleconnections between the north pacific and the north atlantic

intrinsic and scattering seismic wave attenuation in the canary islands the canary islands volcanic complex is studied in terms of coda wave attenuation a multiple lapse time window method based on the hypothesis of multiple isotropic scattering with uniform distribution of scatterers is applied to the available seismic data in order to obtain the intrinsic absorption qi 1 and the scattering attenuation qs 1 in the canarian lithosphere the analysis is performed for two hypocentral distance ranges from 0 to 80 km and from 0 to 140 km results show that in both cases and for all the studied frequency bands 1 2 2 4 6 8 and 8 10 hz intrinsic absorption dominates the low albedos found in the region indicate the low degree of heterogeneity in the canarian lithosphere at the scale length of the studied frequencies on the other hand the coda attenuation qc 1 calculated on the basis of the single scattering theory gives values near qi 1 for low frequencies and near the total attenuation qt 1 for high frequencies the degree of frequency dependence of the attenuation parameters is strong in all cases a correlation of the observed attenuation parameters with the geological evidence for a hotspot type archipelago and with other geophysical studies is suggested

volcanic geomorphology an overview abstract the review examines the role of geomorphology in analyzing the volcanoes on earth five objectives are stressed first classifications of volcanic landforms should be improved to take care of the complexity in volcanic landform generation as magmatic systems style of eruption and the erupted material all influence the morphology second geomorphology should contribute to the science of volcanology through its capability in reconstructing growth stages in complex volcanoes and also in analyzing the structural factors which contribute to the catastrophic collapse of volcanoes third geomorphology can contribute to physical volcanology by assessing the effects of topography on transport erosion and deposition of volcanogenic flows and identifying the sources and climatic tectonic conditions which govern the emplacement of volcaniclastic deposits fourth volcanic geomorphology a identifies sedimentary facies associations b constructs facies models for dynamic volcano delivery systems and c analyzes the characteristics of sediment gravity flows in order to determine relevant parameters for modelling their behaviour fifth process oriented geomorphology is critical in developing accurate methods for measuring rates of geomorphic processes that shape ephemeral volcanic constructs and for evaluating and comparing geomorphic impacts on disturbed catchments and the related hydrologic response before during and after eruptions this should help to refine parameters for the exponential decay model finally volcanic geomorphology is essential for risk assessment through geomorphic hazard zonation and composite risk zonation such treatments are necessary in order to face the enhanced challenge posed by the combination of natural hazards and the increasing number of people who are at risk around volcanoes

rift zone volcanism and associated cinder cone field in utopia planitia mars 1 we analyzed a small cone field in sw utopia planitia that shows striking similarities to volcanic rift zones on earth this is of particular interest as the study area lies off any of the volcanic centers of mars in the northern hemisphere lowlands and is surrounded by material of the amazonian aged vastitas borealis formation vbf we believe that the study area could be the first direct evidence for volcanic activity in utopia planitia prior to the resurfacing by vbf material the most striking characteristics that we observed are 1 a set of broad eruptive fissures showing signs of ongoing extension during cone formation 2 parallel dike swarms 3 magmatic intrusions and 4 a number of lava flows that have erupted from the fissures and pitted cones that surround a larger cone in the center of the study area and that are often associated with or aligned along the fissures and dikes cratering model ages indicate that the study area is of late noachian to early hesperian age and is thus distinctly older than the surrounding vbf falling into the time frame of the main phases of activity in the volcanic centers of syrtis major elysium planitia and the southern highlands

giant miocene landslides and the evolution of fuerteventura canary islands abstract fuerteventura is the oldest island in the canaries archipelago following the growth of a pre miocene seamount its shield stage began 20 6 ma ago and ended in the mid miocene there followed a very extended period of quiescence then very minor quaternary post erosional volcanism the shield stage produced volcanoes up to 3000 m above sea level which were rapidly eroded by 17 5 ma both fuerteventura and lanzarote the older eastern most islands are in a post erosional stage and have subdued topography with elevations rarely rising above 400 m the western islands la palma and el hierro together with tenerife are the youngest in the archipelago and are still in their shield stage which began at most 7 5 ma ago they have a rugged topography with peaks rising to several thousand metres volcanic activity persists in these islands and in lanzarote the shield stage construction of the volcanically active western islands demonstrates that recent eruptive activity has concentrated in volcanic centres aligned in well defined rift zones in which major dyke emplacement has taken place and that volcano flank collapse has occurred with giant landslides initiated on the rifts in fuerteventura most of the shield stage volcanic rocks have been removed however evidence has now been advanced to show that major dyke swarms were emplaced in the oligocene and miocene these belonged to a line of intrusive complexes above which by the early to mid miocene volcanic peaks had been constructed three volcanic centres have been identified and in the central one a peak as high as the present mount teide on tenerife was rapidly denuded in less than 2 ma in the west of the island this erosion has exposed a window of more than 300 km 2 of submarine volcanics and sediments belonging to the pre shield phase seamount the principal mechanism of erosion seems to have been the generation of giant landslides analogous to those seen in the younger islands these appear to have removed some 3500 km 3 of lavas and volcaniclastics stripping the western sectors of the miocene volcanoes down to the pre shield phase basal complex and transporting the mass of volcanic material into the atlantic ocean as debris flows remnants of the shield volcanoes still exist in the eastern part of the island present day topographic variation indicates that the miocene base level of erosion is still visible in a central depression which runs through the axis of the island the eastern hills are composed of the miocene shield stage volcanics which still preserve a drainage pattern initiated on these peaks and the basal complex in the west has a juvenile landscape suggesting incision on a post miocene domal uplift of the volcano core structural links between intra island volcano tectonic events and the south atlas fault zone are not thought to be likely

effects of canary hotspot volcanism on structure of oceanic crust off morocco analysis of over 6400 km of multichannel seismics mcs and 50 sonobuoy reflection and refraction experiments reduced both in the domain of x t and tau p shows that a region within the jurassic quiet zone off morocco underwent dramatic changes as a result of the passage of the lithosphere over the canary hotspot commencing approximately 60 ma a seismic unit ucf interpreted as volcanic in origin is observed within the sediments in a region characterized by a broad bathymetric swell it shows diffractions from its upper surface and an internally chaotic seismic facies and pinches out between sedimentary units of continuous subparallel facies a velocity inversion is noted between the ucf 4 7km s and the underlying sediment 3 1 km s the ucf is time transgressive it lies near the cretaceous s tertiary boundary in the northern portion of the study area and is younger to the south kinematic studies of the movement of the canary hotspot relative to africa show that the hotspot first appeared off nw africa about 60 ma and was located beneath oceanic crust in the region where the ucf is observed depth to basement measurements in areas not effected by the hotspot show a consistent linear trend of increased depth with age in areas effected by the hotspot the thermal rejuvenation is evident as basement depths shoal with increased proximity to the present hotspot the reheating of the crust resets the thermal age of the lithosphere with many of the properties of crust of a younger age subsidence curves of the reheated crust off morocco show good correlation to subsidence curves of other reheated crust on a global basis a zone characterized by high crustal velocities 7 1 7 4 km s and greater crustal thicknesses by 1 2 km is observed in an area that corresponds to the bathymetric swell the region of the ucf and the reelevated basement the high velocities and increased crustal thickness are interpreted to be the result of underplating and assimilation of existing oceanic crust caused by the canary thermal anomaly the presence of high crustal velocities coupled with a thickened crustal section has been noted on various passive margins of the world they have generally been attributed to the thermal processes associated with continental rifting off morocco we believe that similar thermally induced phenomena have occurred but that here the heat anomaly was the midplate volcanism associated with the canary hotspot

landslides and the evolution of el hierro in the canary islands seismic and sonar data have been used to evaluate the extent and characteristics of giant landslides on the flanks of el hierro in the canary islands as the youngest and most southwesterly of the canary islands el hierro has experienced rapid growth and destructive events in its 1 12 million year history at least four giant landslides el golfo el julan san andres and las playas have modified 450 km3 of el hierro during the last 200 300 thousand years with each landslide event removing around 3 of the total edifice volume the extent of landsliding indicates that it is the main process of decay we characterise flank morphology around el hierro and distinguish between rugged unfailed flank failed flank and steep gullied ridge flanks affected by landsliding have downslope long profiles with distinctive b coefficients and exponential forms the el golfo landslide is the most recent 15 ka best described and clearly defined landslide in the canary islands the el julan landslide sw flank has an estimated volume of 130 km3 an age of 200 ka and is characterised by gravitational slumping on the se flank two new landslide events are reported the younger landslide las playas occurred 145 176 ka has a narrow steep sided embayment and a corresponding blocky debris avalanche deposit the older landslide san andres is recognised on the basis of a highly chaotic seismic facies offshore and reduced upper flank gradients its lack of an upper flank embayment and offshore blocky debris avalanche lead us to interpret that the landslide involved gravitational slumping possibly a series of events which reduced upper flank gradients but did not catastrophically collapse to produce a debris avalanche

k ar ages and magnetic stratigraphy of a hotspot induced fast grown oceanic island el hierro canary islands abstract the combined use of accurate radiometric dating and magnetic stratigraphy can be applied to define the main stages of the building of oceanic volcanic islands this method has been successfully applied on the island of el hierro the westernmost island of the canaries archipelago for the emerged part of this island built in the last 1 2 ma magnetic stratigraphy and mapping show the presence of four consecutive subchrons k ar dating of eighteen samples in stratigraphic sequences using an unspiked technique produced ages consistent with the general volcanic stratigraphy the ages show that the magnetic polarity zones correlate to the upper part of the matuyama and to the brunhes chrons the jaramillo normal polarity subchron of the upper part of the matuyama reverse polarity chron is recorded in one of the lava sequences the lower limit of this event is constrained by two ages of 1 04 0 02 ma and one of 1 05 0 02 ma close to the value deduced from the astronomically tuned magnetic polarity time scale apts the volcanic history can be summarised by two consecutive main basaltic volcanic edifices the el tinor active during the upper part of the matuyama chron and the el golfo edifice constructed during the brunhes chron

a past giant lateral collapse and present day flank instability of fogo cape verde islands fogo island is a large and extremely steepsided oceanic island volcano in the cape verde archipelago it has a large ca 9 km across east facing summit collapse structure the monte amarelo collapse with a probable volume of at least 150 200 km3 for most of its history the monte amarelo volcano had a small but productive central vent complex and radial rift zones fed by laterally propagating dykes shortly before the collapse the latter were replaced by north south trending arrays of en echelon vertically propagating dykes since the monte amarelo collapse the scar has partly filled with a new volcano the cha das caldeiras volcano the summit cone of this volcano the pico do fogo is a very young feature but has been abandoned in the most recent phase of activity from the 18th century onwards the same period has also seen the abandonment of earlier radial rift zones with laterally propagating dykes and their replacement with en echelon arrays of vents fed by vertically propagating dykes these form an n s trending array within the older collapse structure and are associated with seaward displacement of the eastern flank of the volcano within the old collapse structure the most recent eruptions those of 1951 and 1995 appear to be associated with episodes of flank instability manifested in n s surface fissuring and east facing normal faults these recent structural changes in the volcano parallel those which took place in the monte amarelo volcano prior to its collapse

offshore continuation of volcanic rift zones el hierro canary islands el hierro is the youngest and most southwesterly of the seven canary islands the established view based on subaerial geology is that el hierro is a classic example of an oceanic island with 120 spaced volcanic rift arms vrzs forming a mercedes star however new offshore data do not support this simple interpretation instead of the discrete ridges of vrzs we observe to the nw and ne broad areas of irregular morphology which suggest that rifting activity might not be confined to narrow zones furthermore our data suggest that the anomalously long and steep flanked southern ridge could be part of an older eroded volcanic edifice that predates much of the other submarine flanks of el hierro the southern ridge has a distinctive gullied morphology which strongly contrasts with adjacent flanks there is also a 400 m deep saddle in its longitudinal profile 15 km from the coastline which we interpret as evidence that the southern ridge did not form by continuous dyke intrusion from the el hierro volcanic centre south of the saddle mean flank slopes are 10 steeper 30 with a sharp slope break at 3700 m between the ridge and smoothly sedimented seafloor these steeper slopes and lack of landslide scars to the south of the saddle indicate that the southern ridge is a stable edifice relative to the rest of el hierro surrounding sediments to the southeast appear to onlap the southern ridge a large landslide deposit el julan estimated age 200 ka occurs to the west of the ridge this landslide appears to have been constrained from spreading southeastwards by the southern ridge resulting in an elevation difference of 300 m for the seafloor on either side of the ridge

deglacial co2 buildup constraints on the coral reef model abstract the coral reef hypothesis of degalcial co2 buildup in the atmosphere can account for about one half of the signal seen in ice cores assuming additional coral reef growth releases 2 atmospheric carbon masses acm the carbonate dissolution signal on the deep sea floor suggest titration of only 1 acm at least 4 acm of co2 must be made available to satisfy the requirements of pco2 increases growth of biosphere and of sedimentary carbon pool carbonate dissolution on the sea floor and saturation of newly introduced meltwater a drop in ocean fertility is called for to provide the missing co2 such a drop is evident in deep sea cores from the western equatorial pacific co2 buildup appears to occur as a step near 13 500 years b p dissolution on the deep sea floor begins near 11 000 years b p the difference of 2500 years may describe a mixing lag due to meltwater input the worthington effect

growth structure instability and collapse of canarian volcanoes and comparisons with hawaiian volcanoes recent onshore and offshore investigations in the canarian archipelago especially in the western islands of la palma and el hierro have greatly improved the understanding of the genesis and evolution of these islands and allow interesting comparisons with other hotspot induced oceanic island volcanoes especially the hawaiian archipelago genesis induced by hotspot activity and consequently shield and post erosional stages of growth allow the definition of similar main stratigraphic units the canarian and hawaiian volcanoes show common constructional and structural features such as rift zones progressive volcano instability and multiple gravitational collapses however the canaries present some important geological differences from the prototypical hotspot volcanoes of the hawaiian islands particularly the absence of significant subsidence the canarian volcanoes remain emergent until completely mass wasted by gravitational collapses and erosion volcanic formations over 20 million years are observable in outcrop in the canaries including the seamount stages of growth in several of the islands

anomalously shallow palaeomagnetic inclinations and the question of the age of the canarian archipelago summary extensive geological geophysical and geochronological data available from the canary islands establish conclusively that formation of the oldest subaerial volcanic structure of the islands began during the miocene a mid cretaceous age for these volcanic formations has been postulated in previous works on the basis of palaeomagnetic determinations the results obtained in the present palaeomagnetic study of lanzarote include analysis of the record of variations of magnetic inclination in boreholes that penetrate the whole of the oldest volcanic series they show that the excessive age previously assigned to these formations is due to the utilization of volcanic units with abnormally low 15 magnetic inclinations lgis in lanzarote lavas exhibiting lgis appear interbedded in a volcanic series that overall shows a typical miocene inclination 45 the units stratigraphically beneath and above the lgi horizons give in fact directions consistent with the middle upper miocene field direction d 359 i 45 with k 29 a95 6 7 and a palaeopole of 87 n 178 e thereby confirming the miocene age of the oldest subaerial volcanics of lanzarote short excursions of the geomagnetic field seem likely to be the explanation for these lgis since other factors such as tectonic tilting post eruptive modification of the primary remanence or errors in sample orientation can be disregarded the detection in the canary archipelago of volcanic units with abnormally low magnetic inclinations seems to be related to the relatively continuous record of the geomagnetic field in rapidly growing volcanic edifices as seems to be indicated by the presence of a few usually one or two short polarity events in volcanic suites of several hundred metres thickness

variations in terrigenous input into the deep equatorial atlantic during the past 24 000 years estimates of terrigenous fluxes at three different water depths at two sites in the equatorial atlantic by normalization against excess 230 th flux indicate that the flux of terrigenous material to the seafloor was significantly higher during the last glacial period than it is today fluxes started to decrease during deglaciation and reached minimal values in the middle of the holocene from 15 000 to 5 000 years ago there was a substantial increase in flux with increasing water depth below 2 800 meters this increase may reflect resuspension and lateral transport of slope and rise sediment possibly because of intensification of deepwater circulation during that period

co 2 record in the byrd ice core 50 000 5 000 years bp the analysis of air in polar ice cores revealed 30 lower co2 values during glacial periods than during interglacial periods at present this is confirmed by results from six different ice cores two from greenland and four from antarctica1 5 in all cores the co2 change coincides with the change in the isotopic composition of the ice expressed as either the 18o or d ratio both are indicators for the mean annual surface temperature6 to investigate the relationship between atmospheric co2 concentration changes with changes in climate the atmospheric co2 concentration during and at the end of the last glaciation has to be known in detail to achieve this we have studied a great number of samples from the deep ice core from byrd station westantarctica drilled in 1968 these measurements allow us to reconstruct the atmospheric co02 concentration in the time period 50 000 15 000 yr bp in great detail

changes in the distribution of δ13c of deep water σco2 between the last glaciation and the holocene carbon isotopic measurements on the benthic foraminiferal genus cibicidoides document that mean deep ocean 13c values were 0 46 lower during the last glacial maximum than during the late holocene the geographic distribution of 13c was altered by changes in the production rate of nutrient depleted deep water in the north atlantic during the late holocene north atlantic deep water with high 13c values and low nutrient values can be found throughout the atlantic ocean and its effects can be traced into the southern ocean where it mixes with recirculated pacific deep water during the glaciation decreased production of north atlantic deep water allowed southern ocean deep water to penetrate farther into the north atlantic and across low latitude fracture zones into the eastern atlantic mean southern ocean 13c values during the glaciation are lower than both north atlantic and pacific 13c values suggesting that production of nutrient depleted water occurred in both oceans during the glaciation enriched 13c values in shallow cores within the atlantic ocean indicate the existence of a nutrient depleted water mass above 2000 m in this ocean

coherent intrusion complexes in large basaltic volcanoes a new structural model abstract highly concentrated coherent intrusion complexes consisting of thousands of small mafic intrusions occur in probably all major basaltic volcanoes and play an important role in volcano development magma excursions from the high level chamber travel laterally along a surface of neutral buoyancy at the margin of a complex and cause the complex to grow the limited distance however that narrow intrusions can propagate before becoming blocked causes complexes to be wedge like intrusive dike complexes underlie rift zones and asymmetric growth of the dike wedge causes rift zones of shield volcanoes to become non collinear and may initiate a third rift zone in the obtuse angle downbowing of stress trajectories across complexes causes dikes to be non vertical and results in axial subsidence intrusive sheet complexes form instead of dike complexes in volcanic systems that have a restricted ability to expand laterally and accommodate intrusions by expanding vertically instead downbowing of stress trajectories causes sheets to be non horizontal and this combined with subsidence increasing toward the thicker part of the sheet wedge produces the inward and inwardly increasing dip that characterizes cone sheet complexes this mechanism for cone sheets differs considerably from previously proposed mechanisms successive injections of sheets at the top of a sheet complex probably offers the most efficient means of powering a high intensity geothermal field such as the 5000 mw grimsvotn system in iceland it is inferred that similar mechanisms to those in major basaltic edifices operate in spreading ridges study of basaltic edifices has the potential to contribute significantly to the understanding of spreading ridges

is the magnitude of the carbonate ion decrease in the abyssal ocean over the last 8 kyr consistent with the 20 ppm rise in atmospheric co2 content 1 changes in the extent of shell fragmentation the wall thicknesses of foraminifera shells and the bulk caco3 content of deep pacific sediments demonstrate that the extent of dissolution has steadily increased during the past 8 kyr on the basis of measurements on sediment core top material from a range of water depths on the ontong java plateau these dissolution proxies have been calibrated allowing the extent of the decrease in carbonate ion concentration to be quantified the results suggest that the decrease was larger than that of 6 mol km expected to accompany the 20 atm rise in atmospheric co2 content that occurred during this time interval however the inconsistency between the magnitude of the change based on the decrease in shell weight on one hand and that based on the increase in fragmentation on the other hand is problematic if indeed the drop in carbonate ion concentration has been larger than expected then 8 kyr ago either a change in the pattern of thermohaline circulation or in the strength of the biological pump must have kicked in and become ever stronger as the millennia passed if thermohaline circulation is the villain then a possible explanation is that the strength of deepwater formation in the northern atlantic has weakened relative to that in the southern ocean

vertical axis rotation of the upper portions of the north east rift of tenerife island inferred from paleomagnetic data abstract paleomagnetic sampling sites were established in 82 dykes along an 8 km long section of the north east rift zone nerz of tenerife canary islands spain of the 70 interpretable sites 16 are of normal polarity and 54 of reversed polarity four normal polarity sites and fifteen reverse polarity sites were excluded from the grand mean calculation for statistical reasons after inverting the reverse polarity sites through the origin the in situ grand mean yields a declination d 023 8 an inclination i 42 3 95 3 2 39 0 n 51 that is discordant to the expected late miocene to pleistocene field direction d 357 6 i 38 8 95 4 7 this discordance can be explained as either a 26 clockwise vertical axis rotation or a 28 wnw side down tilt about an average 009 horizontal tilt axis the sampled section is composed of numerous semi vertical dykes cutting mainly lava flow units that are sub horizontal and cross cut by steeply dipping faults 70 90 field evidence is therefore more compatible with a vertical axis rotation rather than a horizontal axis tilt of the drilled units we argue that this clockwise vertical axis rotation is likely related to strike slip movements that occurred along the edges of the collapse scars and accommodate the emplacement and growth of the underlying intrusive core and associated dykes six new 40ar 39ar age determinations constrain the main interval of dyke emplacement within the nerz between 0 99 ma and 0 56 ma the intrusive activity in the sampled section of the rift appears to have been almost continuous with several intrusion pulses that are probably related to flank destabilisation event s during the mid pleistocene our study thus demonstrates a long lived multi faceted history that shaped the nerz