geochemical and mineralogical control of different genetic types of deep sea nodules from the pacific ocean deep sea nodules from the northeast pacific nodule belt and the southeast pacific sonne basin being formed in areas bordering the equatorial zone of high biological productivity accumulate by two basically different growth processes a early diagenetic growth by supply from pore water and b hydrogenetic growth by supply from near bottom sea water these growth processes lead to different genetic types of nodules early diagenetic type a hydrogenetic type b and mixed type ab a further type ac very rich in mn is being formed by increasing influence of early diagenesis these types can clearly be distinguished by their shapes surface textures mineral constituents of oxide fraction internal microstructures and geochemistry a genetical classification is being proposed on the basis of statistically computed interelement relationships todorokite very poor in fe is the main mn phase in the early diagenetic substance mno2 intimately intergrown with feooh xh2o is the main phase in the hydrogenetic substance consequently an important difference can be pointed out the metal supply for the growth of the early diagenetic nodules is based on an ionic solution of me2 e g mn2 ni2 cu2 zn2 whereas the supply for the hydrogenetic nodules is caused by transport of colloidal particles mobilization of mn2 and fractionation from fe is controlled by the amount of decomposing organic matter in the peneliquid layer of the sediments the main factor controlling the intensity of early diagenesis is the biological productivity in surface waters the crucial point of reversal at a mn fe ratio of about 5 obtained by hyperbolical regression of the analyses of nodules from the southeast pacific represents best concentrations in ni and cu mn fe quotients greater than 5 cause a decrease of ni and cu content nodules from the northeast pacific nodule belt generally contain higher concentrations in cu than nodules from the southeast pacific this can be explained by an additional supply of cu transported below ccd by siliceous plankton

failure of volcano slopes magmatic intrusions can initiate and sustain massive and catastrophic volcano collapse their role is twofold involving both driving and resisting forces first flank stability is diminished by magmastatic and magma overpressures and steepened slopes that accompany intrusion second excess pore pressures in potential failure zones can be generated as a result of intrusion related mechanical or thermal straining of the rock fluid medium pressurized retrograde boiling in high level magma chambers or hydrothermal fluid circulation also earthquakes may aid collapse through inertial forces and shaking induced pore pressure generation these excess pore pressures reduce the sliding resistance as shown for wedge shaped slide blocks for selected cases the destabilizing influence of mechanically induced pore pressures is maximized as the intruded width or corresponding overpressure of the intrusion is increased the destabilizing influence of thermally induced pore pressures is conditioned by the seve

growth rate variations of manganese nodules and crusts induced by paleoceanographic events time markers at about 3 ma 6 5 ma and 14 ma are common to 16 manganese nodules and crusts from different localities in the world oceans these time markers correspond to variations in the growth rates in the inner structure and in the chemistry of the samples the observed time markers could be related to 1 changes of the bottom water velocity and 2 variations in the manganese and iron contents in the deep ocean the time markers were determined by high resolution 10be dating applying the accelerator mass spectrometry facility at the eidgenossische technische hochschule zurich

estimating exposure around san miguel volcano el salvador abstract san miguel one of the most active volcanoes in el salvador is surrounded by several villages and cantons which could be seriously affected in case of a new eruption this study presents an exposure analysis of the san miguel volcano area by considering population distribution land use private houses official buildings hospitals schools etc and communication infrastructure we use spatial analysis geographic information system tools to estimate exposure for different volcanic hazards air fallout lava flows pyroclastic density currents lahars moreover in the particular case of private houses and official buildings we estimate a vulnerability index for the hazardous areas applying the physical vulnerability methodology based on the characterization of the type of construction materials of walls and roofs we construct different exposure maps for 1 population 2 land use 3 road networks 4 schools and 5 health centers this approach identifies the elements at risk according to each potential hazard thus providing the authorities with a comprehensive tool to better understand the problem and to define emergency plans to minimize risk

a new volcanic management risk database design verdi application to el hierro island canary islands abstract one of the most important issues in modern volcanology is the assessment of volcanic risk which will depend among other factors on both the quantity and quality of the available data and an optimum storage mechanism this will require the design of purpose built databases that take into account data format and availability and afford easy data storage and sharing and will provide for a more complete risk assessment that combines different analyses but avoids any duplication of information data contained in any such database should facilitate spatial and temporal analysis that will 1 produce probabilistic hazard models for future vent opening 2 simulate volcanic hazards and 3 assess their socio economic impact we describe the design of a new spatial database structure verdi volcanic management risk database design which allows different types of data including geological volcanological meteorological monitoring and socio economic information to be manipulated organized and managed the root of the question is to ensure that verdi will serve as a tool for connecting different kinds of data sources gis platforms and modeling applications we present an overview of the database design its components and the attributes that play an important role in the database model the potential of the verdi structure and the possibilities it offers in regard to data organization are here shown through its application on el hierro canary islands the verdi database will provide scientists and decision makers with a useful tool that will assist to conduct volcanic risk assessment and management

nucleation and growth of todorokite from birnessite implications for trace metal cycling in marine sediments the phyllomanganate birnessite is the main mn bearing phase in oxic marine sediments and through coupled sorption and redox exerts a strong control on the oceanic concentration of micronutrient trace metals however under diagenesis and mild hydrothermal conditions birnessite undergoes transformation to the tectomanganate todorokite the mechanistic details of this transformation are important for the speciation and mobility of metals sequestered by birnessite and are necessary in order to quantify the role of marine sediments in global trace element cycles here we transform a synthetic poorly crystalline hexagonal birnessite analogous to marine birnessite into todorokite under a mild reflux procedure developed to mimic marine diagenesis and mild hydrothermal conditions we characterize our birnessite and reflux products as a time series employing x ray diffraction xrd fourier transform infrared spectroscopy ftir bet surface area analysis scanning electron microscopy sem high resolution transmission electron microscopy hr tem and extended x ray absorption fine structure spectroscopy exafs we provide new insight into the crystallization pathway and mechanism of todorokite formation from birnessite under conditions analogous to those found in marine diagenetic and hydrothermal settings specifically we propose a new four stage process for the transformation of birnessite to todorokite beginning with todorokite nucleation then crystal growth from solution to form todorokite primary particles followed by their self assembly and oriented growth via oriented attachment to form crystalline todorokite laths culminating in traditional crystal ripening we suggest that contrary to current understanding trace metals like ni might retard the transformation of birnessite to todorokite and be released to marine sedimentary pore waters during this diagenetic process thus potentially providing a benthic flux of these micronutrients to seawater

vertical and lateral collapses on tenerife canary islands and other volcanic ocean islands recent studies demonstrate that tenerife has undergone large lateral collapses this has led to the suggestion that the las canadas caldera one of the best exposed calderas in the world is the result of lateral collapse we have tested this idea using the available structural stratigraphic volcanological and geochronological data we conclude that the las canadas caldera is the result of a complex sequence of vertical collapse events associated with a long history of phonolitic explosive activity in the central part of tenerife our results indicate however that vertical collapses may have played a major role in triggering lateral collapses we propose that the association of vertical and lateral collapse events such as inferred for tenerife can also explain similar sequences of events interpreted to have affected other large volcanic ocean islands

variations in the fine scale composition of a central pacific ferromanganese crust paleoceanographic implications a 47 to 60 mm thick fe mn crust from horizon guyot water depth 1800 1780 m central pacific was used to evaluate the potential of crusts as recorders of neogene paleoceanographic and paleoclimatic conditions the chemical composition was determined by microprobe for 16 elements from a polished thin section three analyses were made per millimeter and averaged to give the composition of each millimeter the age of the crust was determined by measuring the strontium isotope composition of the crust and comparing it with the tertiary seawater curve the crust represents 18 5 m y of growth of fe and mn oxyhydroxides the crust is composed of alternating botryoidal and laminated layers the botryoidal layers formed during the same time intervals that widespread neogene deep sea hiatuses were forming in bottom sediments the botryoidal layers represent growth during times of intensified deepwater flow whereas the laminated intervals represent more quiescent conditions the correspondence between the botryoidal layers and the neogene hiatuses is so strong that we were able to choose a variable growth rate model over a constant growth rate model for the crust chemical changes in the crust take two forms the first is represented by broad changes in the composition defined chiefly by fourth order polynomial fits to the chemical profiles of each element with depth in the crust the second is high frequency changes in composition the broader changes occurred primarily at about 15 11 5 7 4 6 4 5 2 and 4 6 ma which may correlate with major changes in paleoceanographic circulation and development of ice caps at the poles the periods of the high frequency changes may reflect climatic changes that resulted from orbital forcing these high frequency changes may correspond to the high order eccentricity periods of 3 47 2 04 and 1 31 m y

eruptive and structural history of teide volcano and rift zones of tenerife canary islands the teide and pico viejo stratocones and the northwest and northeast rifts are products of the latest eruptive phase of the island of tenerife initiated with the lateral collapse of its northern flank that formed the las canadas caldera and the icod la guancha valley ca 200 ka the eruptive and structural evolution of this volcanic complex has been reconstructed after detailed geological mapping and radioisotopic dating of the significant eruptive events a set of 54 new 14 c and k ar ages provides precise age control of the recent eruptive history of tenerife particularly teide volcano the third highest volcanic feature on earth 3718 m above sea level 7 km high and unique in terms of its intraplate setting the development of the teide pico viejo volcanoes may be related to the activity of the northwest and northeast rifts volcanic and intrusive activity along both rift zones may have played an important role in activating the gravitational landslide and in the subsequent growth nested within the collapse embayment of an increasingly higher central volcano with progressively differentiated magmas the coeval growth of the central volcano with sustained activity along the rifts led to a clear bimodal distribution in composition of eruptive products with the basaltic eruptions in the distal part of the rifts and phonolitic and more explosive eruptions in the central area where the differentiated stratocones developed current volcanic hazard in tenerife is considered to be moderate because eruptive frequency is low explosivity is modest and the eruptive activity of the teide stratocone seems to have declined over the past 30 k y with only one eruption in this period 1150 yr b p

volcanic evolution of the island of tenerife canary islands in the light of new k ar data new age determinations from tenerife together with those previously published 93 in all provide a fairly comprehensive picture of the volcanic evolution of the island the oldest volcanic series with ages starting in the late miocene are formed mainly by basalts with some trachytes and phonolites which appear in anaga teno and roque del conde massifs in anaga ne three volcanic cycles occurred one older than 6 5 ma a second one between 6 5 and 4 5 ma with a possible gap between 5 4 and 4 8 ma and a late cycle around 3 6 ma in teno nw after some undated units the activity took place between 6 7 and 4 5 ma with two main series separated by a possible pause between 6 2 and 5 6 ma in the zone of roque del conde s the ages are scattered between 11 6 and 3 5 ma between 3 3 and 1 9 ma the whole island underwent a period of volcanic quiescence and erosion the large canadas volcano made up of basalts trachytes and phonolites was built essentially between 1 9 and 0 2 ma to the ne of this central volcano linking it with anaga is a chain of basaltic emission centers with a peak of activity around 0 8 ma the canadas caldera had several collapse phases associated with large ignimbrite emissions there were at least an older phase more than 1 ma old on the western part of the volcano and a younger one less than 0 6 ma old in the eastern side the two large valleys of guimar and la orotava were formed by large landslides less than 0 8 ma ago and probably before 0 6 ma ago the present canadas caldera was formed by another landslide less than 0 2 ma ago this caldera was later filled by the huge teide volcano which has been active even in historic times during the same period a series of small volcanoes erupted at scattered locations throughout the island the average eruptive rate in tenerife was 0 3 km3 ka with relatively small variations for the different eruptive periods this island and la gomera represent a model of growth by discontinuous pulses of volcanic activity separated by gaps often coinciding with episodes of destruction of the edifices and sometimes extended for several million years the neighbouring gran canaria on the other hand had an initial rapid shield building phase during which more than 90 of the island was built and a series of smaller pulses at a much later period a comparison between these three central islands indicates that the previously postulated westward displacement in time of a gap in the volcanic activity is valid only as a first approximation several gaps are present on each island overlapping in time and not clearly supporting either of the models proposed to explain the evolution of the canaries

role of olivine cumulates in destabilizing the flanks of hawaiian volcanoes the south flank of kilauea volcano is unstable and has the structure of a huge landslide it is one of at least 17 enormous catastrophic landslides shed from the hawaiian islands mechanisms previously proposed for movement of the south flank invoke slip of the volcanic pile over seafloor sediments slip on a low friction decollement alone cannot explain why the thickest and widest sector of the flank moves more rapidly than the rest or why this section contains a 300 km3 aseismic volume above the seismically defined decollement it is proposed that this aseismic volume adjacent to the caldera in the direction of flank slip consists of olivine cumulates that creep outward pushing the south flank seawards average primary kilauea tholeiitic magma contains about 16 5 wt mgo compared with an average 10 wt mgo for erupted subaerial and submarine basalts this difference requires fractionation of 17 wt 14 vol olivine phenocrysts that accumulate near the base of the magma reservoir where they form cumulates submarine erupted kilauea lavas contain abundant deformed olivine xenocrysts derived from these cumulates deformed dunite formed during the tholeiitic shield stage is also erupted as xenoliths in subsequent alkalic lavas the deformation structures in olivine xenocrysts suggest that the cumulus olivine was densely packed probably with as little as 5 10 vol intercumulus liquid before entrainment of the xenocrysts the olivine cumulates were at magmatic temperatures 1100 c when the xenocrysts were entrained olivine at 1100 c has a rheology similar to ice and the olivine cumulates should flow down and away from the summit of the volcano flow of the olivine cumulates places constant pressure on the unbuttressed seaward flank leading to an extensional region that localizes deep intrusions behind the flank these intrusions add to the seaward push this mechanism ties the source of gravitational instability to the caldera complex and deep rift systems and therefore limits catastrophic sector failure of hawaiian volcanoes to their active growth phase when the core of olivine cumulates is still hot enough to flow

discriminating between different genetic types of marine ferro manganese crusts and nodules based on rare earth elements and yttrium marine ferro manganese fe mn crusts and nodules are metal rich chemical sediments that are archives of paleoceanographic proxies and potential metal resources and targets of deep sea mining traditionally crusts and nodules are subdivided into hydrogenetic diagenetic and hydrothermal types because these are characterized by different compositions and hence economic resource potential a useable genetic classification is not only a tool for geochemical studies but may also help to characterize potential exploration targets we propose two easy to use yet robust discrimination diagrams based on geochemical relationships controlling the rare earths and yttrium rey inventory of marine fe mn oxyhydr oxide deposits the rey are a set of trace elements that show coherent behavior are routinely determined in geochemical studies and for which the analytical quality can easily be evaluated graphs of ce anomaly vs nd concentration and ce anomaly vs y anomaly effectively discriminate between the different types of precipitates regardless of their diverse mineralogical composition both hydrogenetic crusts and nodules show positive ce anomalies negative y anomalies and high nd concentrations of 100 mg kg 1 although nodules tend to have slightly lower nd concentrations than crusts in marked contrast hydrothermal deposits generally yield negative ce anomalies positive y anomalies and low nd concentrations of 10 mg kg 1 in spite of their large geochemical mineralogical and sedimentological diversity diagenetic nodules show negative ce anomalies negative y anomalies and intermediate nd concentrations between 10 and 100 mg kg 1 we discuss the geochemical background of these diagrams the respective sources of rey in the different precipitates and address the processes that control their rey inventory besides the three end members we also use rey systematics to define mixed type diagenetic hydrogenetic nodules and classify well studied international reference standards

geochemical processes controlling the relationship between co mn and fe in early diagenetic deep sea nodules abstract early diagenetic manganese nodules from the northeast pacific nodule belt and from the southeast pacific peru basin show primary growth features of dendritic microtextures consisting of alternating laminae of crystalline 10 amanganate a1 substance and amorphous material which is composed of an intimate mixture of ferric hydroxide silicate and mno 2 a2 substance the formation of rhythmic sequences of a1 and a2 microlayers is explained by physico chemical changes in the peneliquid sediment layer and in the microenvironment of the accreting nodule surface a upward diffusion of mn 2 in the interstitial water as a result of decay of organic matter and mn mobilization b oxidation of mn 2 and formation of 10 amanganate in the upper part of the peneliquid sediment layer leading to ph depression in the microenvironment of the nodule surface which decreases the mobility of silicate resulting in formation of a2 layers c restoration of ph and renewed precipitation of 10 amanganate based on data of 171 bulk analyses and on electron microprobe investigations interelement relationships between co mn and fe are pointed out fe and co show a significant positive correlation r 0 84 while mn and co are poorly negatively correlated r 0 21 assuming linear regression the enrichment of co within the amorphous a2 phase is attributed to specific surface adsorption and subsequent oxidation of co 2 to co 3 in the strong electric field of si 4 robust complexes of co iii and feh 2 sio 4 prevent most of the co from being available for the 10 amanganate precipitation concerning the relation between mn and fe and co respectively the highest correlation coefficients are obtained using an inverse logarithmic regression under early diagenetic conditions the concentration and precipitation of mn 2 in the interstitial water depends on the redox gradient which is controlled by the amount of decomposing organic matter the nernst equation describes the relationship as a reciprocal logarithmic function however the quantities of colloidal ferric hydroxide and of dissolved silicate are not affected by variations of the redox potential these different characteristics in the precipitation of mn and the fe and si rich colloidal phase may cause the significantly negative logarithmic correlation of mn versus fe and co respectively

intermediate wavelength magnetic anomaly field of the north pacific and possible source distributions the objective of this study is to investigate the feasibility of extracting intermediate wavelength magnetic anomalies of wavelengths between 4000 and 400 km from total field data acquired in marine magnetic surveys the intention is to develop a second data set which may be used in conjunction with the satellite magnetic field to determine anomaly and source distributions we apply our technique to the recovery of intermediate wavelength total intensity anomalies over the north pacific from marine survey data the technique also provides a record of secular variation during the period 1960 to 1980 in areas of high track density the sea surface data can be used to refine the magsat data processing techniques and also provide further constraints on source models in areas of reduced sea surface track density the magsat field provides higher resolution the magsat data set also records vector field data as will be shown the filtered sea surface data set provides a higher resolution field than the magsat data due to proximity to lithospheric source bodies the sea surface data also provide an independent check of the magsat field since the two fields should be equivalent after upward continuation of the sea surface field we notice however that for the central pacific the upward continued sea surface field is approximately 2 times the amplitude of the magsat field the spatial correlation of the two anomaly fields is very strong

crustal evolution of the mid atlantic ridge near the fifteen twenty fracture zone in the last 5 ma author posting american geophysical union 2003 this article is posted here by permission of american geophysical union for personal use not for redistribution the definitive version was published in geochemistry geophysics geosystems 4 2003 1024 doi 10 1029 2002gc000364

age determinations and growth rates of pacific ferromanganese deposits using strontium isotopes abstract 87 sr 86 sr ratios trace element and ree compositions and textural characteristics were determined for three hydrogenetic fe mn crusts one hydrothermal deposit and two mixed hydrothermalhydrogenetic crusts from the pacific the sr isotope data are compared to the sr seawater curve for the cenozoic to determine the ages and growth rates of the crusts the 87 sr 86 sr in the crusts does not increase monotonically with depth as expected if the sr were solely derived from seawater and perfectly preserved since deposition this indicates post depositional exchange of sr or heterogeneous sources for the sr originally contained in the crusts textures of hydrogenetic crusts generally correlate with sr isotopic variations the highest porosity intervals commonly exhibit the highest 87 sr 86 sr ratios indicating exchange with younger seawater intervals with the lowest porosity commonly have lower 87 sr 86 sr and may preserve the original sr isotopic ratios minimum ages of crust growth inception were calculated from dense low porosity intervals growth of the hydrogenetic crusts began at or after 23 ma although their substrates are cretaceous estimated average growth rates of the three hydrogenetic crusts vary between 0 9 and 2 7 mm ma consistent with published rates determined by other techniques within the marshall islands crust growth rates for individual layers varied greatly between 1 0 and 5 4 mm ma for one crust very low 87 sr 86 sr ratios occurred in detrital rich intervals hydrothermal fe mn oxide from the active lau basin back arc spreading axis valu fa ridge has an 87 sr 86 sr ratio with a predominantly seawater signature 87 sr 86 sr 0 709196 indicating a maximum age of 0 9 ma one crust from an off axis seamount west of gorda ridge may have begun precipitating hydrogenetically at 0 5 ma 0 709211 and had increasing hydrothermal or volcanic input in the top half of the crust indicated by a significantly lower 87 sr 86 sr ratio 0 709052

the crustal structure across the transform continental margin off ghana eastern equatorial atlantic forward modeling of a suite of wide angle seismic lines across the transform continental margin at the eastern end of the romanche fracture zone off ghana has shown the transition from continental to oceanic crust to be confined to a narrow 6 to 11 km wide zone located at the foot of the steep continental slope the structure of the adjacent oceanic and continental crusts has also been resolved these results are confirmed and enhanced by gravity and magnetic models the crust of the ocean continent transition zone is characterized by high velocities 5 8 7 3 km s 1 a high density 3 10 mg m 3 and high magnetizations 1 1 1 25 a m 1 this rules out a purely continental origin for the zone and suggests that it may be formed of basic igneous rocks intruded when the hot oceanic spreading center migrated along the margin the oceanic crust within 70 km of the margin is abnormally thin compared to normal atlantic oceanic crust and shows an average thickness of just 4 4 km we suggest that the region of abnormally thin oceanic crust is the result of a reduced magma supply due to a combination of closely spaced fracture zones and the conductive loss of heat from the upwelling oceanic mantle in small basins surrounded on at least three sides by cold continental lithosphere the preferred seismic model also shows a new fracture zone 30 km southeast of the ocean continent transition which is characterized by low velocities in the upper crust a lens shaped layer with velocities of 7 2 7 4 km s 1 at the base of the crust and a crustal thickness of just 3 4 km the continental crust appears largely unaffected by the proximity of the adjacent oceanic crust there is no evidence for underplating of the continental crust adjacent to the ocean continent transition zone

fluxes of metals to a manganese nodule radiochemical chemical structural and mineralogical studies fluxes of metals to the top and bottom surfaces of a manganese nodule were determined by combining radiochemical 230th 231pa 232th 238u 234u and detailed chemical data the top of the nodule had been growing in its collected orientation at 4 7 mm myr 1 for at least 0 5 myr and accreting mn at 200 g cm 2 kyr 1 the bottom of the nodule had been growing in its collected orientation at about 12 mm myr 1 for at least 0 3 myr and accreting mn at about 700 g cm 2 yr 1 although the top of the nodule was enriched in iron relative to the bottom the nodule had been accreting fe 50 faster on the bottom 232th was also accumulating more rapidly in the bottom despite a 20 fold enrichment of230th on the top the distribution of alpha emitting nuclides calculated from detailed radiochemical measurements matched closely the pattern revealed by 109 day exposures of alpha sensitive film to the nodule however the shape and slope of the total alpha profile with depth into the nodule was affected strongly by226ra and222rn migrations making the alpha track technique alone an inadequate method of measuring nodule growth rates diffusion of radium in the nodule may have been affected by diagenetic reactions which produce barite phillipsite and todorokite within 1 mm of the nodule surface however our sampling interval was too broad to document the effect we have not been able to resolve the importance of nodule diagenesis on the gross chemistry of the nodule

estimating building exposure and impact to volcanic hazards in icod de los vinos tenerife canary islands abstract principal and subsidiary building structure characteristics and their distribution have been inventoried in icod tenerife canary islands and used to evaluate the vulnerability of individual buildings to three volcanic hazards tephra fallout volcanogenic earthquakes and pyroclastic flows the procedures described in this paper represent a methodological framework for a comprehensive survey of all the buildings at risk in the area around the teide volcano in tenerife such a methodology would need to be implemented for the completion of a comprehensive risk assessment for the populations under threat of explosive eruptions in this area the information presented in the paper is a sample of the necessary data required for the impact estimation and risk assessment exercises that would need to be carried out by emergency managers local authorities and those responsible for recovery and repair in the event of a volcanic eruption the data shows there are micro variations in building stock characteristics that would influence the likely impact of an eruption in the area as an example of the use of this methodology for vulnerability assessment we have applied a deterministic simulation model of a volcanic eruption from teide volcano and its associated ash fallout which when combined with the vulnerability data collected allows us to obtain the vulnerability map of the studied area this map is obtained by performing spatial analysis with a geographical information system gis this vulnerability analysis is included in the framework of an automatic information system specifically developed for hazard assessment and risk management on tenerife but which can be also applied to other volcanic areas the work presented is part of the eu funded exploris project explosive eruption risk and decision support for eu populations threatened by volcanoes evr1 2001 00047

assessing the potential for future explosive activity from teide pico viejo stratovolcanoes tenerife canary islands abstract since the onset of their eruptive activity within the canadas caldera about 180 ka ago teide pico viejo stratovolcanoes have mainly produced lava flow eruptions of basaltic to phonoltic magmas the products from these eruptions partially fill the caldera and the adjacent icod and la orotava valleys to the north although less frequent explosive eruptions have also occurred at these composite volcanoes in order to assess the possible evolution teide pico viejo stratovolcanoes and their potential for future explosive activity we have analysed their recent volcanic history assuming that similar episodes have the highest probability of occurrence in the near future explosive activity during the last 35000 years has been associated with the eruption of both mafic basalts tephro phonolites and felsic phono tephrites and phonolites magmas and has included strombolian violent strombolian and sub plinian magmatic eruptions as well as phreatomagmatic eruptions of mafic magmas explosive eruptions have occurred both from central and flank vents ranging in size from 0 001 to 0 1 km3 for the mafic eruptions and from 0 01 to 20 km3 dre eruptions of phonolitic magmas while teide pico viejo is dominated by effusive eruptions these differences can be explained in terms of the different degree of evolution of teide pico viejo compared to the preceding cycles and consequently in the different pre eruptive conditions of the corresponding phonolitic magmas a clear interaction between the basaltic and phonolitic systems is observed from the products of phonolitic eruptions indicating that basaltic magmatism is the driving force of the phonolitic eruptive activity the magmatic evolution of teide pico viejo stratovolcanoes will continue in the future with a probably tendency to produce a major volume of phonolitic magmas with an increasing explosive potential therefore the explosive potential of teide pico viejo cannot be neglected and should be considered in hazard assessment on tenerife

morphological and geological aspects related to large slope failures on oceanic islands the huge la orotava landslides on tenerife canary islands huge volcanic landslides are one of the most hazardous geomorphological processes that can occur during the evolution of volcanic ocean islands the causes of these phenomena however are very complex and combine non volcanic and volcanic factors in the canary islands more than 20 events have been detected during the last decades a detailed analysis was carried out for la orotava amphitheatre on tenerife in order to understand the relationship between geomorphological and geological aspects and huge volcanic landslides the results indicated four major features that play a significant role in such mass movements deep erosive canyons high coastal cliffs widespread residual soils and structural axes high coastal cliffs and deep erosive canyons locally reduce the stability conditions and control both the seaward and the lateral boundary of the landslide weak residual soils formed above phonolitic pyroclastic deposits occur repeatedly in the stratigraphic column of la orotava and are characterised by their large extent thus one of these soils may have evolved into the slip surface of the failure part of the head scarp of the amphitheatre is defined by a volcanic rift zone as indicated by the measurement of dike orientation and a density map of eruptive vents the four features are not able to trigger a failure but to destabilise the volcano flank and determine the boundary of the slide therefore information on depth and orientation of canyons location and height of coastal cliffs stratigraphic repetition extension and thickness of residual soils and orientation and density of dikes and eruptive vents along structural axes should be incorporated into a hazard assessment on large landslides on volcanic islands

new sonar evidence for recent catastrophic collapses of the north flank of tenerife canary islands previous sonar surveys show that the north flank of tenerife has been subject to at least four major landslides during the past 1 ma the youngest icod affected the region to the north of the teide pico viejo complex the world s third highest oceanic volcano recently we obtained the first detailed acoustic images of icod using a deep tow side scan sonar the images suggest that tenerife s north flank has experienced at least two types of flow deposit in the recent past the older flow deposit icod i is characterised by a 15 to 20 km wide 65 km long chaotic debris avalanche deposit which includes several very large blocks we believe the deposit to be 170 ka and that it represents the mass wasting products of the canadas edifice remnants of which are now found in the las canadas caldera wall the younger flow deposit icod ii associated with a shute in its proximal part appears to have produced a less chaotic deposit in its distal part which clearly preserves flow structures such as latitudinal boulder ridges and longitudinal shear structures the sonar images cannot determine how much younger icod ii is than icod i although it is likely that they are a consequence of the same lateral collapse event there is evidence from the shute area for erosional scour and sediment deposition since the icod landslide if this is correct then it suggests that mass wasting is an ongoing process that has already started to modify the teide pico viejo complex itself

later stages of volcanic evolution of la palma canary islands rift evolution giant landslides and the genesis of the caldera de taburiente the islands of la palma and el hierro form the western end of the hotspot induced canary islands chain both islands are at present in the earliest and fastest shield building stage of growth and show many similarities with the hawaiian islands la palma shows two very distinct phases of volcanic construction 1 a pliocene submarine volcanic and intrusive series interpreted as an uplifted seamount at least 1500 m above present sea level and 2 a subaerial volcanic series erupted in the past 2 m y taburiente volcano initially formed the northern part of the island and then extended to the south forming a ridge cumbre nueva ridge that was partially destroyed about 560 ka by a giant lateral collapse the cumbre nueva collapse possibly involving 180 200 km 3 of subaerial volcanic material the northwest boundary of the cumbre nueva collapse formed a vertical scarp that enlarged by headward erosion formed the spectacular depression of caldera de taburiente cumbre vieja volcano a north south elongated rift forms the southern half of la palma and constitutes its last stage of growth including all eruptive activity in the past 125 k y detailed field observations mapping and high precision radiometric dating have allowed reconstruction of the growth and structural changes of the cumbre vieja volcano interactions between eruption rates coastal erosion and glacio eustatic sea level change allow stratigraphic subdivision of the edifice the structure of the volcano has been controlled for most of its history by a rift system with a clearly dominant north south and less distinct north east and north west volcanic rift zones the rift reorganization of the volcano to a single north south rift since 7 ka and the opening of faults during the 1949 eruption probably reflect increasing instability of the west flank of the volcano

petrogenesis of ferromanganese nodules from east of the chagos archipelago central indian basin indian ocean abstract deep sea ferromanganese nodules occur over a large area and on many different sediment types of the central indian basin indian ocean selected samples were studied to determine their chemical and mineralogical compositions and microstructural features repeated laminations of variable thickness alternately dominated by todorokite and vernadite are characteristic of these nodules these laminae show on electron microprobe line scans corresponding interlaminar partitioning of mn cu ni and fe co the bulk chemical compositions of these nodules plot in both the hydrogenetic and early diagenetic fields on the fe mn ni cu co 10 ternary diagram the binary diagram depicting the covariation of mn ni cu against fe co shows two distinct parallel regression lines one delineated by nodules from terrigenous siliceous ooze and siliceous ooze terrigenous sediments and the other by nodules from red clay siliceous ooze red clay and calcareous ooze red clay an increasing diagenetic influence in the nodules with the nature of the host sediment types was observed in the sequence terrigenous siliceous ooze and red clay siliceous calcareous ooze red clay a negative correlation between mn fe ratio and co and a positive correlation between mn fe ratio and ni cu was established the nodules show dendritic laminated and globular microstructures formed by primary growth of fe mn oxide laminae depositional hiatuses in the primary microstructures indicate that the growth of these nodules was episodic the oxide laminations show extremely complex growth patterns scattered biogenic remains and mineral grains acted as accessory seeds for growth of oxide layers in addition to the main nuclei none of the primary microstructures can be uniquely linked to a particular growth process or growth rate radial cracks cutting across primary microstructures are often filled by todorokite of a later generation post depositional modifications of the nodules were largely controlled by accreted biogenic remains as indicated by their progressive dissolution with increasing depth from nodule surfaces their pseudomorphic replacement by todorokite and the later growth of phillipsite and todorokite in the microfossil molds the growth patterns of the in filled oxides are often controlled entirely by the cavity walls and are discordant with the primary growth fabric primary todorokite was recrystallized to coarser grains of different chemical composition later generation veins of todorokite cut across and chaotically disrupted primary laminae

insight into vent opening probability in volcanic calderas in the light of a sill intrusion model the aim of this paper is to discuss a novel approach to provide insights on the probability of vent opening in calderas using a dynamic model of sill intrusion the evolution of the stress field is the main factor that controls the vent opening processes in volcanic calderas on the basis of previous studies we think that the intrusion of sills is one of the most common mechanism governing caldera unrest therefore we have investigated the spatial and temporal evolution of the stress field due to the emplacement of a sill at shallow depth to provide insight on vent opening probability we carried out several numerical experiments by using a physical model to assess the role of the magma properties viscosity host rock characteristics young s modulus and thickness and dynamics of the intrusion process mass flow rate in controlling the stress field our experiments highlight that high magma viscosity produces larger stress values while low magma viscosity leads to lower stresses and favors the radial spreading of the sill also high rock young s modulus gives high stress intensity whereas low values of young s modulus produce a dramatic reduction of the stress associated with the intrusive process the maximum intensity of tensile stress is concentrated at the front of the sill and propagates radially with it over time in our simulations we find that maximum values of tensile stress occur in ring shaped areas with radius ranging between 350 m and 2500 m from the injection point depending on the model parameters the probability of vent opening is higher in these areas

the las canadas caldera tenerife canary islands an overlapping collapse caldera generated by magma chamber migration abstract the las canadas caldera is one of the most important geological structures of tenerife stratigraphic structural volcanological petrological geochronological and geophysical data suggest that the las canadas caldera resulted from multiple vertical collapse episodes that occurred during the construction of the las canadas edifice upper group three long term 200 ka cycles of phonolitic explosive activity each culminating with a caldera collapse have been identified in the upper group during the construction of the upper group the focus of felsic volcanism migrated from west to east using the results of field observations experimental analogue models and numerical studies we propose that the formation of the overlapping las canadas collapse caldera is related to the migration of the associated magma chamber our model implies that each collapse of this overlapping caldera partly or completely destroyed the feeding magma chamber this destruction led to changes in the local stress field that favoured the formation of a new chamber at one side of the previous one resulting in magma chamber migration the proposed model accounts for the formation of the las canadas caldera in particular it explains the geometrical relationships stratigraphy and chronology of the caldera wall deposits comparison with other overlapping collapse calderas suggests that our model may apply to other overlapping calderas

potential impacts of tephra fallout from a large scale explosive eruption at sakurajima volcano japan we present an exposure analysis of infrastructure and lifeline to tephra fallout for a future large scale explosive eruption of sakurajima volcano an eruption scenario is identified based on the field characterization of the last subplinian eruption at sakurajima and a review of reports of the eruptions that occurred in the past six centuries a scenario based probabilistic hazard assessment is performed using the tephra2 model considering various eruption durations to reflect complex eruptive sequences of all considered reference eruptions a quantitative exposure analysis of infrastructures and lifelines is presented primarily using open access data the post event impact assessment of magill et al earth planets space 65 677 698 2013 after the 2011 vei 2 eruption of shinmoedake is used to discuss the vulnerability and the resilience of infrastructures during a future large eruption of sakurajima results indicate a main eastward dispersal with longer eruption durations increasing the probability of tephra accumulation in proximal areas and reducing it in distal areas the exposure analysis reveals that 2300 km of road network 18 km2 of urban area and 306 km2 of agricultural land have a 50 probability of being affected by an accumulation of tephra of 1 kg m2 a simple qualitative exposure analysis suggests that the municipalities of kagoshima kanoya and tarumizu are the most likely to suffer impacts finally the 2011 vei 2 eruption of shinmoedake demonstrated that the already implemented mitigation strategies have increased resilience and improved recovery of affected infrastructures nevertheless the extent to which these mitigation actions will perform during the vei 4 eruption presented here is unclear and our hazard assessment points to possible damages on the sakurajima peninsula and the neighboring municipality of tarumizu

marine magnetic data processing in equatorial regions off ghana summary total field magnetic values recorded during a survey by rrs charles darwin off ghana yielded large track crossover errors of up to 120 nt rms value of 58 7 nt which masked the weak magnetic anomalies in this equatorial region the heading effect of the ship s magnetic field and strong diurnal variation in the earth s field are likely causes of the errors a heading effect experiment shows differences of up to 30 nt for charles darwin on different headings which have been corrected for the diurnal variation has been calculated by using the magnetic field observations themselves because observatories are either too distant or were inoperative at the time of the survey a method that uses the anomalies corrected for heading effect and differences at track crossovers was found to produce an acceptable curve with an amplitude of 120nt and a shape similar to that of equatorial observatories fully corrected anomalies have crossover errors of up to only 40 nt with an rms value of 17 5 nt these anomalies reveal a linear magnetic anomaly low along the continental slope off ghana

sector collapse forming at casita volcano nicaragua catastrophic sector collapse occurs when a volcano becomes structurally unable to support its own load one process particularly capable of weakening the edifice is hydrothermal activity it can produce high pore pressures and alter strong rock to clays alteration can extend progressively over long periods 100 yr allowing deformation to develop slowly before collapse an important finding is that structures produced by such deformation are recognizable and could permit collapse prediction we present the case of casita nicaragua where hydrothermal activity has been weakening the edifice core causing flank spreading altering original constructional shape and steepening flank slopes one side is slumping outward producing a crescentic scar with a basal bulge we identify this feature as the site of a potential sector collapse with conditions ripe for failure

manganese nodules in the miocene bahia inglesa formation north central chile petrography geochemistry genesis and palaeoceanographic significance abstract manganese nodules recovered from two stratigraphic horizons of tortonian messinian late miocene age in the bahia inglesa formation of north central chile were studied using xrd sem and geochemical analysis the dominant mineral in the nodules is todorokite which suggests a diagenetic marine environment this is supported by field observations of nodules replacing ophiomorpha burrows preliminary traditional statistical analysis of the nodule geochemistry including single element binary and ternary ratios suggests that the nodules are of the supergene deep marine type as also indicated by the presence of foraminifers typical of the upper continental slope as well as debris flow and turbidity current deposits in an associated submarine palaeocanyon however abnormally low cu concentrations seem to contradict this interpretation so that additional analyses were carried out this included multiple discriminant analysis mda as well as a new technique applied for the first time to manganese nodules namely artificial neural network analysis ann in both methods central log ratio clr normalization was applied to the raw data the results in particular those of the ann analysis suggest that the bahia inglesa nodules present a chemical signature distinct from that of nodules described to date a new class is therefore proposed namely supergene intermediate marine partially restricted basin

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

a coupled model for dispersal of tephra during sustained explosive eruptions abstract we present a model for fallout of tephra based on approximate analytical solutions of the advection diffusion transport equation as usual the model requires the distribution of mass throughout the eruptive column as a boundary condition an input which is normally imposed ad hoc by means of analytical expressions we propose an alternative way to assess this input based on coupling the model of fallout with already existing simple models for volcanic plumes flow along the volcanic conduit and magma chamber withdrawal the final outcome is a one way coupled model that involves all the spatial domains simultaneously and has a good compromise between physical accuracy and computational efficiency the coupled model outputs not only maps of isopachs but also several relevant eruptive parameters such as column height mass eruption rate or duration of the eruption time dependency is introduced via a quasi steady approach that is considering a succession of steady states we apply the model to simulate the 2 ka subplinian eruption of montana blanca tenerife island

stratigraphy structure and volcanic evolution of the pico teide pico viejo formation tenerife canary islands abstract the structure and volcanic stratigraphy of the pico teide pico viejo pt pv formation deriving from the basanite phonolite stratovolcanoes pt and pv and numerous flank vent systems are documented in detail based on new field and photogeologic mapping geomorphologic analysis borehole data and petrological and geochemical findings results provide insight into the structure and evolution of the pt pv magma system and the long term cyclic evolution of tenerife s post shield volcanic complex the pt pv formation comprises products of central volcanism mainly emplaced into the las canadas caldera lcc and contemporaneous products from adjacent rifts pt pv central volcanic products become more differentiated up section with felsic lavas dominating the recent output of the system this is attributed to the evolution of a shallow magma reservoir beneath pt that was emplaced early in the pt pv cycle on the intra caldera segment of tenerife s post shield rift system the rift axis has been the focus of pt pv intrusive and eruptive activity and has controlled the location of the stratocones the current geometry of the rifts reflects a major structural reorganisation defining the start of the pt pv cycle at 0 18 ma namely the truncation of the north side of the lcc lce by the giant icod landslide the internal stratigraphy of the pt pv formation suggests that pt developed early with pv developing as a satellite vent activity has since alternated between pt and pv due to episodes of vent blockage or chamber sealing these processes have allowed significant volumes of phonolitic magmas to develop and accumulate within the pt chamber which have vented through radial dike systems during tumescence episodes and from the rift system which has permitted lateral magma transport the pt pv magma system is a potentially hazardous source of future felsic eruptive activity on tenerife

10 be dating of a manganese crust from central north pacific and implications for ocean palaeocirculation one of the most promising applications of the new 10be detection technique using accelerator mass spectrometry is the determination of growth rates of mn nodules and crusts1 5 because the half life of cosmogenic 10be 1 5 myr is of the same order as the time needed for a few millimetres of nodule material to grow 10be is a useful tool for unravelling such evolution during the late tertiary when most nodules are assumed to have started their growth6 mass spectrometric measurement of a 10be profile across the manganese crust va 13 2 from the central pacific using a tandem van de gr a ff accelerator yields growth rates of 2 7 and 4 8 mm myr 1 for the layers of the crust accumulated between recent and 6 myr bp and between 6 and 11 myr respectively using these measurements as well as 230th dating we have been able to distinguish boundaries between zones in the crust with different structures and chemical compositions and to assign ages to them these ages are 0 12 2 9 3 4 5 7 6 7 7 9 10 12 and 13 16 myr bp all of these boundaries apparently coincide with the times reported for quaternary and late tertiary palaeoclimatic events suggesting that the crust growth has been strongly influenced by palaeoclimate

atypical ferromanganese nodules from pelagic areas of the central indian basin equatorial indian ocean abstract two box core samples one each from red clay and siliceous ooze sediment provinces from the central indian basin indian ocean were studied both cores contained ferromanganese nodules at their tops the red clay sediment also hosts buried nodules at a depth of 82 cm chemical characterization of the sediments indicates that early diagenetic remobilization of transitional metals is pronounced in the siliceous ooze sediment while in the red clay no such effect is discernible this is further corroborated by the abundance and dissolution patterns of microorganisms and ferromanganese micronodules occurring in the two sediment columns bulk chemical analyses indicate that all the nodules are of the hydrogenetic b type vernadite and todorokite are the major minerals both of which constitute laminated nondirectional colloform and cuspate microstructures petrographic studies yield evidence of recrystallization of todorokite and partial transformation of vernadite to todorokite the former process being more advanced in buried nodules microprobe analyses revealed that primary todorokite has a lower mn fe ratio and higher ni content than recrystallized todorokite in the same sample the mineralogical reconstitution in the nodules is attributed to postdepositional intranodule diagenesis the present study does not reveal the correlation between mineralogy and microstructure in the nodules which has been suggested for the nodules from the pacific neither can any mineral or microstructure be considered specific for any particular genetic model the studied nodules are therefore atypical the mineralogical and chemical reordering in these ferromanganese nodules raises the question of the viability of radiometric methods in determining growth rates of such nodules

evolution of a deep water ferromanganese nodule in the south china sea in response to pacific deep water circulation and continental weathering during the plio pleistocene abstract the south china sea scs is connected to the west pacific through a deep channel in the luzon strait thus the scs deep water is sensitive to the evolution of pacific ocean circulation which significantly influences the global climate system geochemical data pb isotope and redox sensitive elements data and magnetic data were determined for a fe mn nodule obtained from jiaolong seamount in the central scs these records reflect interactions between changes in ice sheets deep pacific circulation and weathering inputs to the deep scs during the pliocene and quaternary our results show that the scs deep water environment can be divided into three major stages stages 1 3 stage 1 4 8 1 4 ma was characterized by a well oxygenated pacific deep water pdw and lower dust inputs then moderate stable deep water ventilation and greater inputs of asian dust occurred during stage 2 1 4 0 9 ma during stage 3

late miocene pliocene coastal acid sulphate system in southeastern australia and implications for genetic mechanisms of iron oxide induration abstract ferricrete sediment cemented by iron oxides and hydroxides is common in subaerial weathering environments around the world formed under alternating oxidising and reducing conditions ferricretes record pedogenetic processes of translocation and concentration of iron and trace elements in the soil given their stability and high preservation potential ferricretes can provide insights to ancient soil forming and weathering processes in this study the key processes controlling ferricrete geochemistry in a neogene strandplain are identified and interpreted in the context of a coastal acid sulphate weathering system textural and geochemical variations in sediment indurated by hematite and goethite represent a record of in situ induration erosion and reworking this development took place within an environment of fluctuating ph and eh and subaerial wetting and drying cycles we distinguished depositional and post depositional processes based on the results of whole rock geochemistry hyperspectral mineralogy and major and trace element maps of petrographic thin sections the ferricretes have three morphological types flat lying indurations concentric pisoliths and rounded nodules with fragmented internal textures successive laminae of fe oxides and hydroxides in all morphological types of ferricrete have variable fe al and si abundances reflecting cyclic precipitation and groundwater chemistry changes episodic wetting and drying of near coastal sediments was superimposed on a long term trend of marine regression and local tectonic uplift from 7 ma to present this resulted in the diachronous exposure of relatively reduced shoreline sediments and concomitant acid production due to ferrolysis and the oxidation of biogenic sulphide local landform variations contributed to a wide variety of pedogenic processes and subsequent ferricrete formation acid sulphate weathering recorded by these indurated sediments is similar to conditions that are observed at present in the shallow water estuary of the lower lakes near the mouth of the murray river

seismic hazard of volcanic activity abstract seismic activity is a common feature of volcanic eruptions the majority of volcanic earthquakes are small their magnitudes do not exceed 2 or 3 at the same time significant moderate size and large volcanic earthquakes may also occur the study of 28 significant m w 4 5 earthquakes associated with volcanic eruptions of 20th century allowed us to formulate the following results about seismic hazard of volcanic activity 1 during the 20th century only three large m w 7 0 earthquakes directly associated with volcanic eruptions in the world were recorded 2 the maximum magnitude m w was estimated to be 5 4 for earthquakes related to central eruptions 7 0 for caldera collapse 5 9 for central eruptions accompanied by flank and or fissure eruptions 7 1 for flank and or fissure eruptions without central eruptions and 5 9 for submarine eruptions for seismicity just before the eruption the maximum magnitude of earthquakes was estimated to be m w 7 1 for seismicity at the initial stage of eruption m w 7 0 for paroxysmal stage of eruption m w 5 6 and for final stage of eruption m w 6 1 3 it was shown that the recurrence time of eruptions of the same type of volcano associated with significant m w 4 5 earthquakes was more than 100 years for 86 of events studied

incorporation of be isotopes and other trace metals into marine ferromanganese deposits abstract two to threefold inward increase of 10be 9be cu and ni have been found in surface layers of marine ferromanganese deposits we interpret this phenomenon as reflecting the manner in which the be isotopes and probably other trace metals e g cu and ni are incorporated on reaching the sea floor exchangeable be is released from its carrier phase to the pore water of the ferromanganese deposits diffuses inward and gets fixed into the deposits the fixation process may be related to the mineralogical reorganizations suggested by previous studies we have modeled this concept and applied it to a mn crust on which detailed analyses of cu ni and natural decay series nuclides as well as be isotopes are made post depositional fixation of th isotopes may also occur the redistributions of be and th isotopes are confined to regions very close to the surface of the deposits for all practical purposes they will not affect growth rate determinations conventionally done using these isotopes the linearly extrapolated 10 be 9 be ratio to the surface from deep layers of a mn deposit does not necessarily represent that ratio in sea water

international geomagnetic reference field the fourth generation abstract in august 1985 the international association of geomagnetism and aeronomy revised the international geomagnetism reference field igrf this is the third revision since the first igrf was produced in 1968 the revised igrf now consists of 10 spherical harmonic models of the main geomagnetic field and its secular variation and covers the interval 1945 1990 for the interval 1965 1980 the constituent models are definitive dgrfs in the sense that it is not intended to revise them in the future a brief description of the derivation of the revised igrf is given together with a brief review of basic formulae and a set of world contour maps of the geomagnetic elements for 1985

estimation of site effects in bucharest caused by the may 30 31 1990 vrancea seismic events the vrancea region seismicity characterized by focal depths larger than 60 km and major events with magnitudes m w 6 9 is responsible for the most destructive effects experienced in the romanian territory and may seriously affect high risk construction located on a wide area from central to eastern europe this seismogenic volume must be taken into account both for seismic hazard analysis at the regional level southeastern europe and national level romania and bulgaria as well as for microzonation studies of the highly populated cities located in the range of influence of this source since about four destructive earthquakes occur every century in vrancea the microzonation of bucharest the main city exposed to the potential damages due to these strong intermediate depth shocks represents an essential step towards the mitigation of the local seismic risk two main approaches can be considered for the evaluation of the local seismic hazard a collection and extended use for engineering purposes of the recorded strong motion data and b advanced modelling techniques that allow us the computation of a realistic seismic input which can compensate for the lack of strong motion records actually available only for a few events that occurred in the last 20 30 years

analysis of risk assessment factors of individuals in volcanic hazards review of the last decade abstract there are many methods and scientific research approaches where modeling and understanding on how individuals evaluate natural origin risks despite the proficiency and depth of such studies we evidenced a lack for a holistic approach where the most influencing factors in the individual decision making process were covered this research seeks to understand what those factors are how they relate to each other and how the behave with respect to individual perception and acceptance of risk for this we performed a thorough literature review covering the last decade in relation with the understanding of how these incidence factors affected the perception and acceptance of risk in the communities exposed to volcanic events under the decision making process our research was able to detect how the identified variables influenced each other in this process we analyzed different study cases found in the literature and additionally we propose as a further research a new theoretical approach related to decision making modeling process under dynamic system that would be valuable as a contribution to risk management

iron mineral structure reactivity and isotopic composition in a south pacific gyre ferromanganese nodule over 4ma abstract deep sea ferromanganese nodules accumulate trace elements from seawater and underlying sediment porewaters during the growth of concentric mineral layers over millions of years these trace elements have the potential to record past ocean geochemical conditions the goal of this study was to determine whether fe mineral alteration occurs and how the speciation of trace elements responds to alteration over 3 7 ma of marine ferromanganese nodule mfn formation a timeline constrained by estimates from 9be 10be concentrations in the nodule material we determined fe bearing phases and fe isotope composition in a south pacific gyre spg nodule specifically the distribution patterns and speciation of trace element uptake by these fe phases were investigated the time interval covered by the growth of our sample of the nodule was derived from 9be 10be accelerator mass spectrometry ams the composition and distribution of major and trace elements were mapped at various spatial scales using micro x ray fluorescence xrf electron microprobe analysis empa and inductively coupled plasma mass spectrometry icp ms fe phases were characterized by micro extended x ray absorption fine structure exafs spectroscopy and micro x ray diffraction xrd speciation of ti and v associated with fe was measured using micro x ray absorption near edge structure xanes spectroscopy iron isotope composition 56 54fe in subsamples of 1 3 mm increments along the radius of the nodule was determined with multiple collector icp ms mc icp ms the spg nodule formed through primarily hydrogeneous inputs at a rate of 4 0 0 4 mm ma the nodule exhibited a high diversity of fe mineral phases feroxyhite feooh goethite feooh lepidocrocite feooh and poorly ordered ferrihydrite like phases these findings provide evidence that fe oxyhydroxides within the nodule undergo alteration to more stable phases over millions of years trace ti and v were spatially correlated with fe and found to be adsorbed to fe bearing minerals ti fe and v fe ratios and ti and v speciation did not vary along the nodule radius the 56 54fe values when averaged over sample increments representing 0 25 0 75 ma were homogeneous within uncertainty along the nodule radius at 0 12 0 07 2sd n 10 our results indicate that the fe isotope composition of the nodule remained constant during nodule growth and that mineral alteration did not affect the primary fe isotope composition of the nodule furthermore the average 56 54fe value of 0 12 we find is consistent with fe sourced from continental eolian particles dust despite mineral alteration the trace element partitioning of ti and v and fe isotope composition do not appear to change within the sensitivity of our measurements these findings suggest that fe oxyhydroxides within hydrogenetic ferromanganese nodules are out of geochemical contact with seawater once they are covered by subsequent concentric mineral layers even though fe bearing minerals are altered trace element ratios speciation and fe isotope composition are preserved within the nodule

10be and th isotopes in manganese nodules and adjacent sediments nodule growth histories and nuclide behavior abstract the concentration profiles of 9 be 10 be 230 th 232 th 231 pa via 227 th and 238 u have been measured in three manganese nodules one each from the north pacific a47 16 4 the south pacific tf 5 and the indian ocean r v vitiaz in addition the 10 be concentration in deep water from the geosecs reoccupation station 500 of the north pacific and in cores raised from the manganese nodule field in the north pacific have been measured the 10 be concentration in nodule and seawater samples was measured by the accelerator masss spectrometric technique employing the yale tandem van de graaff accelerator the concentrations of 10 be 230 th exc and 231 pa exc and ratios of 10 be 9 be and 230 th exc 232 th all decrease with depth in the nodules this decrease interpreted in terms of nodule growth yields average growth rates of a few millimeters per million years for the nodules the growth rates of the nodules exhibit temporal variations both on short time 50 000 years and long time several million years scales of the three nodules studied only in tf 5 is the short term average growth rate based on 230 th exc in the top 0 0 5 mm the same as the long term average rate based on be isotope data for the 0 5 17 mm interval for the other two nodules the recent average growth rates based on 230 th exc data differ significantly from the long term average growth rates based on be isotopes in a47 16 4 the 10 be based rate is less than the 230 th exc rate and in r v vitiaz the 10 be based rate is greater than the 230 th exc rate this observation coupled with measurable changes in growth rates even during the past few hundred thousand years suggests but does not prove that the discordant growth rates deduced from 230 th exc and 10 be profiles document changes in nodule growth rate with time rather than mixing effects on 230 th exc profiles the 10 be concentration in the geosecs north pacific deep water is 6100 1200 atoms g this value coupled with the average surface 10 be 9 be ratio of north pacific nodules predicts a 9 be concentration within the limits of measured values the inventory of 10 be and 230 th exc in the nodules is only 10 of the total the remaining being in sediments the 10 be concentrations in the upper portions of two adjacent cores studied are nearly the same but the deposition fluxes of both 10 be and 230 th based on 230 th dating vary by a factor of two this difference is attributable to local redistribution of sediment at the time of deposition prior to accumulation

ferruginous vernadite in an indian ocean ferromanganese nodule select area electron diffraction and microanalysis of the optically dark component of a ferromanganese nodule from the south east indian ocean manganese field indicate that this is composed of a random stratification of crystallites of vernadite mno 2 r 2 o ro r 2 o 3 x y h 2 o where r represents elements such as k ba na ca mg and a disordered hydrated iron oxide possibly ferrihydrite 5fe 2 o 3 9h 2 o or feroxyhyte feooh whether the dark component is an irregular mixed layer hybrid mineral or a layered accumulation resulting from epitaxy of the above phases is uncertain

neogene oceanographic variations recorded in manganese nodules from the somali basin abstract a detailed study of a nodule from the somali basin dated by 230 th excess was correlated with the paleoceanographic events recorded in site 236 leg 24 deep sea drilling project dsdp cores tentative indications are that the phase of nodule accretion starting with the development of pillar structure at a depth of 20 mm in the nodule around 13 ma coincides with increased antarctic bottom water aabw flow and an elevated calciumcarbonate compensation depth ccd the late miocene lowering of the ccd is represented by the mottled zones between 8 and 18 mm in the nodule is characterised by an abundant silicate component 20 of aeolian origin the miocene pliocene boundary 5 ma occurs at a depth of about 8 mm and is represented by the development of pillar structure and a minimum of aeolian dust 10 3 the increased biological productivity of the somali surface water since the middle miocene is demonstrated by the increasing c org content of the nodule from 0 11 to 0 19 towards its surface

biogenic signature and ultra microfossils in ferromanganese nodules of the central indian ocean basin abstract theories related to the precipitation mechanism of the metallic elements in marine manganese nodules have remained controversial between two schools of thoughts 1 chemical oxidation abiotic origin and 2 deposition of the metals through microbial enzymatic processes biogenic origin one of the most important evidence in support of the biogenic origin is the occurrence of fossilized microbes however well documented literature in this regard is either lacking or very scanty in case of indian ocean nodules using high resolution feg sem we have recorded various biogenic signatures and ultra microfossils in the ferromanganese nodule samples from central indian ocean basin ciob that are presented in this paper the microfossils are mostly protozoans belonging to varieties of bacteria diatoms and foraminifera some of the features recorded in this study have perhaps never been reported before from any manganese nodules the chemical compositions of these ultra microfossils indicate a high level of manganese precipitation in and around them in comparison to the distant surrounding areas while clumpy microbes are enriched with nickel the rod shaped bacteria are rich in copper up to 4 70 wt nickel and 5 31 wt cu have been recorded in the fossilized microbe bodies the high abundance of biogenic features as well as microfossils in the ferromanganese nodules and their chemical compositions support arguments in favor of a dominant role of the microorganisms in the construction of the nodules of the ciob

volcanic risk assessment quantifying physical vulnerability in the built environment abstract this paper presents structured and cost effective methods for assessing the physical vulnerability of at risk communities to the range of volcanic hazards developed as part of the mia vita project 2009 2012 an initial assessment of building and infrastructure vulnerability has been carried out for a set of broadly defined building types and infrastructure categories with the likelihood of damage considered separately for projectile impact ash fall loading pyroclastic density current dynamic pressure and earthquake ground shaking intensities in refining these estimates for two case study areas kanlaon volcano in the philippines and fogo volcano in cape verde we have developed guidelines and methodologies for carrying out physical vulnerability assessments in the field these include identifying primary building characteristics such as construction material and method as well as subsidiary characteristics for example the size and prevalence of openings that may be important in assessing eruption impacts at risk buildings around kanlaon were found to be dominated by timber frame buildings that exhibit a high vulnerability to pyroclastic density currents but a low vulnerability to failure from seismic shaking around fogo the predominance of unreinforced masonry buildings with reinforced concrete slab roofs suggests a high vulnerability to volcanic earthquake but a low vulnerability to ash fall loading given the importance of agriculture for local livelihoods around kanlaon and fogo we discuss the potential impact of infrastructure vulnerability for local agricultural economies with implications for volcanic areas worldwide these methodologies and tools go some way towards offering a standardised approach to carrying out future vulnerability assessments for populated volcanic areas

bahia de banderas mexico morphology magnetic anomalies and shallow structure the bahia de banderas lies within a tectonically complex area at the northern end of the middle america trench the structure morphology subsurface geology and tectonic history of the bay are essential for unraveling the complex tectonic processes occurring in this area with this focus marine geophysical data multi beam bathymetry high resolution seismic reflection and total field magnetic data were collected within the bay and adjacent areas during four campaigns aboard the b o el puma conducted in 2006 and 2009 these data image the detailed morphology of and sedimentation patterns within the banderas canyon a prominent submarine canyon situated on the south side of the bay as well as the shallow subsurface structure of the northern part of the bay and the submarine marietas ridge which bounds the bay to the west we find that the marietas ridge is presently a transtensional feature the course of the banderas canyon is controlled by extensive turbidite fan sedimentation in its eastern extremity and by structural lineaments to the west the canyon floor is filled by sediments and exhibits almost no evidence for recent tectonic movements the southern canyon wall is quite steep and a few sediments are deposited as submarine fans at the base of the southern wall and extensive turbidite fans form the lower part of the northern canyon wall producing a gently sloping lower northern wall we find no evidence for a regional east west striking lineament between the bay and the middle america trench which casts doubts on the previous assertion that the banderas canyon is unequivocally related to the presence of a regional half graben finally a n71 e oriented normal fault offsets the seafloor reflector by 15 m within the central part of the bay suggesting that the bay is currently being subjected to nnw sse extension

volcanic hazard impacts to critical infrastructure a review abstract effective natural hazard risk assessment requires the characterisation of both hazards and vulnerabilities of exposed elements volcanic hazard assessment is at an advanced state and is a considerable focus of volcanic scientific inquiry whereas comprehensive vulnerability assessment is lacking cataloguing and analysing volcanic impacts provide insight on likely societal and physical vulnerabilities during future eruptions this paper reviews documented disruption and physical damage of critical infrastructure elements resulting from four volcanic hazards tephra fall pyroclastic density currents lava flows and lahars of eruptions in the last 100 years we define critical infrastructure as including energy sector infrastructure water supply and wastewater networks transportation routes communications and critical components common trends of impacts and vulnerabilities are summarised which can be used to assess and reduce volcanic risk for future eruptions in general tephra falls cause disruption to these infrastructure sectors reducing their functionality whilst flow hazards pyroclastic density currents lava flows and lahars are more destructive causing considerable permanent damage volcanic risk assessment should include quantification of vulnerabilities and we challenge the volcanology community to address this through the implementation of a standardised vulnerability assessment methodology and the development and use of fragility functions as has been successfully implemented in other natural hazard fields

erratum analysis of risk assessment factors of individuals in volcanic hazards review of the last decade journal of volcanology and geothermal research 2018 357 254 260 s0377027318300465 10 1016 j jvolgeores 2018 05 009

correlation between rate of sea level change and frequency of explosive volcanism in the mediterranean volcanic activity has frequently been linked to quaternary environmental change either by driving climate modification1 2 or in response to environmental changes3 although a link has been established between large explosive eruptions and small 0 5 c brief 1 2 years falls in global temperatures4 both the evidence and mechanisms responsible for longer episodes of eruption induced planetary cooling remain questionable1 2 5 6 in contrast recent research based on ice core data suggests that rapid climate changes during the past 110 000 years increased explosive volcanic activity7 here we present a statistical analysis relating the frequency of explosive activity of mediterranean volcanoes based on dated8 9 10 11 tephra layers in deep sea sediment cores to the rate of late quaternary sea level change the nonlinear correlation between the two is tentatively explained in terms of dynamic responses of the volcanoes to stress related influences on various spatial scales the correlation supports a mechanism or mechanisms by which the climate driven growth and decay of large ice sheets can influence the eruptive chronologies of distant volcanic edifices via changes in global sea level