coeval giant landslides in the canary islands implications for global regional and local triggers of giant flank collapses on oceanic volcanoes abstract giant landslides are an important part of the evolution of most intra plate volcanic islands they often proceed in catastrophic events likely to generate voluminous debris avalanches and eventually trigger destructive tsunamis although knowledge of the timing of their recurrence is a key factor regarding the hazard assessment in coastal environments only a few of them have been well dated in this contribution we focus on the la orotava event on tenerife which we date with the unspiked k ar technique between 534 and 523 ka such narrow temporal interval is compatible within uncertainties with the age of the cumbre nueva collapse on the neighboring island of la palma we thus examine here the possible common triggering mechanisms at the global regional and local scales both events occurred shortly after the climax of the oxygen isotopic stage 14 during the rapid transition towards the interglacial stage 13 reinforcing the hypothesis of a control from global paleoclimatic changes on the destabilization of oceanic islands intense volcanic pulses at the regional scale also lead to the synchronous overgrowth of several volcanic islands in the archipelago but coeval destabilization on tenerife and la palma appears significantly controlled by the intrinsic morphology of the edifices with contrasted instability thresholds for shield volcanoes and volcanic ridges respectively finally we propose that the two events may be genetically linked dynamic transfer of voluminous debris avalanches during a giant landslide episode can induce isostatic readjustments generate significant ground acceleration and finally produce a large tsunami three processes which can concur to trigger large scale flank collapse on a neighboring mature unstable volcanic island

tectonic framework of the azores triple junction the lack of accurate and detailed magnetic information has in the past limited the development of well constrained models for the plate tectonic evolution of the azores triple junction an aeromagnetic survey made possible by the existing airport facilities has long been desired as it can provide high quality magnetic data whose homogeneity and coherency is far better than those provided by classic marine surveys the results presented in this paper concern only a part of the aeromagnetic survey conducted by the portuguese instituto nacional de meteorologia e geofisica and already allow an improved definition of the basic tectonic boundaries at the central part of the azores plateau

the insular shelves of the faial pico ridge azores archipelago a morphological record of its evolution shelves surrounding reefless volcanic ocean islands are formed by surf erosion of their slopes during changing sea levels posterosional lava flows if abundant can cross the coastal cliffs and fill partially or completely the accommodation space left by erosion in this study multibeam bathymetry high resolution seismic reflection profiles and sediment samples are used to characterize the morphology of the insular shelves adjacent to pico island the data show offshore fresh lava flow morphologies as well as an irregular basement beneath shelf sedimentary bodies and reduced shelf width adjacent to older volcanic edifices in pico these observations suggest that these shelves have been significantly filled by volcanic progradation and can thus be classified as rejuvenated despite the general volcanic infilling of the shelves around pico most of their edges are below the depth of the last glacial maximum revealing that at least parts of the island have subsided after the shelves formed by surf erosion prograding lava deltas reached the shelf edge in some areas triggering small slope failures locally decreasing the shelf width and depth of their edges these areas can represent a significant risk for the local population hence their identification can be useful for hazard assessment and contribute to wiser land use planning shelf and subaerial geomorphology magnetic anomalies and crustal structure data of the two islands were also interpreted to reconstruct the long term combined onshore and offshore evolution of the faial pico ridge the subaerial emergence of this ridge is apparently older than previously thought i e before 850 ka

reconstructing the architectural evolution of volcanic islands from combined k ar morphologic tectonic and magnetic data the faial island example azores the morpho structural evolution of oceanic islands results from competition between volcano growth and partial destruction by mass wasting processes we present here a multi disciplinary study of the successive stages of development of faial azores during the last 1 myr using high resolution digital elevation model dem and new k ar tectonic and magnetic data we reconstruct the rapidly evolving topography at successive stages in response to complex interactions between volcanic construction and mass wasting including the development of a graben we show that 1 sub aerial evolution of the island first involved the rapid growth of a large elongated volcano at ca 0 85 ma followed by its partial destruction over half a million years 2 beginning about 360 ka a new small edifice grew on the ne of the island and was subsequently cut by normal faults responsible for initiation of the graben 3 after an apparent pause of ca 250 kyr the large central volcano cv developed on the western side of the island at ca 120 ka accumulating a thick pile of lava flows in less than 20 kyr which were partly channelized within the graben 4 the period between 120 ka and 40 ka is marked by widespread deformation at the island scale including westward propagation of faulting and associated erosion of the graben walls which produced sedimentary deposits subsequent growth of the cv at 40 ka was then constrained within the graben with lava flowing onto the sediments up to the eastern shore 5 the island evolution during the holocene involves basaltic volcanic activity along the main southern faults and pyroclastic eruptions associated with the formation of a caldera volcano tectonic depression we conclude that the whole evolution of faial island has been characterized by successive short volcanic pulses probably controlled by brief episodes of regional deformation each pulse has been separated by considerable periods of volcanic inactivity during which the faial graben gradually developed we propose that the volume loss associated with sudden magma extraction from a shallow reservoir in different episodes triggered incremental downward graben movement as observed historically when immediate vertical collapse of up to 2 m was observed along the western segments of the graben at the end of the capelinhos eruptive crises 1957 58

corrigendum to gps and tectonic evidence for a diffuse plate boundary at the azores triple junction earth planet sci lett 381 2013 177 187

geomorphic evolution of the piton des neiges volcano reunion island indian ocean competition between volcanic construction and erosion since 1 4 ma abstract reunion island indian ocean is a volcanic complex whose eruptive history was dominated by the activity of two main edifices piton des neiges pn and piton de la fournaise pf volcanoes the tropical climate induces erosion processes that permanently compete with volcanic constructional processes exposed to the trade winds and associated heavy rainfalls the northeastern part of the island exhibits the most complex morphological evolution geomorphological analysis performed on a 50 m dem and associated to new k ar ages has clarified the overall history of pn volcano each massif is assigned to one of the main building stages of the edifice in addition the arrangement of these different massifs reveals that the eruptive phases have led to successive relief inversions and successive excavations of large central depressions in the proximal area as a result the younger massifs are always located in more proximal parts of the volcano the youngest being close to the edifice center in distal areas early lava flows were channeled into valleys incised along the massif boundaries leading to a more complex geochronological organization quantitative study of the dissection of pn volcano allows us to propose a minimum eroded volume of 101 44 and 105 41 km3 for the mafate and cilaos cirques depressions respectively during the last 180 kyr and a minimum average long term erosion rate of 1 2 0 4 km3 ka this leads us to estimate the removed volume during the whole history of pn volcano 1000 km3 as equivalent to the volume of the deposits identified on the submarine flanks of piton des neiges volcano therefore as regressive erosion appears to be the prevailing geomorphic process during the whole pn history it questions the presence of major flank collapses younger than 1 4 ma on this volcano erosion processes have largely been neglected in recent models but our study emphasizes them as a key component of landscape development and a major process in the morphological evolution of reunion island that has to be fully integrated in future studies

reply to the comment by quartau and mitchell on reconstructing the architectural evolution of volcanic islands from combined k ar morphologic tectonic and magnetic data the faial island example azores j volcanol geotherm res 241 242 39 48 by hildenbrand et al 2012

volcano tectonic and geochemical evolution of an oceanic intra plate volcano tahiti nui french polynesia abstract geological mapping accurate k ar dating and geochemical analyses of lavas allow a detailed reconstruction of the geological history of tahiti nui island french polynesia the exposed volcanic activity is first characterized by the construction of a main shield from 1 4 ma to 870 ka with a maximum aerial eruptive rate around 2 km3 kyr lavas from this early building stage are alkaline slightly silica undersaturated with 87sr 86sr and 143nd 144nd compositions rather constant and close to the enriched mantle ii type vent locations were first concentrated along a main e w rift zone which was responsible for the lateral collapse of the northern and southern flanks of the main shield around 0 87 ma ago the subsequent activity was first restricted to the northern depression corresponding to an eruptive rate of about 5 km3 kyr in the period 850 760 ka significant variations in la sm 87sr 86sr and 143nd 144nd occur in lavas erupted immediately after the main northern landslide indicating a sudden increase in the extent of partial melting likely caused by the decompression subsequent to collapse however the later activity declined and the lavas exhibit a gradual change toward strongly silica undersaturated basanites likely indicating a decreasing extent of partial melting of the upper mantle the evolution of radiogenic isotope ratios over time indicates a change in the source toward more depleted compositions until around 500 ka post erosion volcanic activity following an apparent hiatus of 240 kyr exhibits similar major and trace element and isotope compositions the volcano structural and geochemical evolution of tahiti nui and the overall alkaline character of the lavas from other eruptive complexes of the society alignment suggest a relative weakness low temperature and low eruptive rate of the society plume compared to the hawaiian hot spot

eruptive response of oceanic islands to giant landslides new insights from the geomorphologic evolution of the teide pico viejo volcanic complex tenerife canary large sector collapses are a major component of oceanic islands evolution here we show that voluminous events such as the icod landslide on tenerife canary islands cause dramatic changes on the magma feeding system and control the subsequent volcanic and geomorphologic evolution of the eruptive complex over a period of more than 150 kyr instantaneous unloading by the icod landslide is marked by the development of a large phonolitic explosive eruption dated at 175 3 ka and interpreted as reflecting the immediate emptying of a shallow pre existing magma chamber geochronological geomorphological and geochemical analyses carried out on the post landslide volcanic succession sampled in a 4 4 km long underground water recovery gallery provide further evidence for an enhanced extrusion of primitive lavas starting in the 10 kyr time interval following the failure rapid construction 40 kyr of a thick basaltic volcano in the landslide scar at high eruptive rates up to 8 km3 kyr 1 increased the lithostatic pressure which then favored the intermittent storage of basic magma under the edifice this resulted in more episodic construction evidenced by a significant decrease in output rates and the increasing occurrence of lavas with intermediate composition from 117 7 to 52 7 ka an apparent volcanic gap is observed between 52 7 and 18 1 ka after which highly differentiated lavas have been dominantly erupted we propose that part of the gap can be explained by the individualization of a shallow magma reservoir a few kilometers below the base of the teide volcano during recent periods vertical and lateral extrusions of trachytic and phonolitic viscous bodies from this storage area contributed to increase the slope of the main edifice up to 35 overall favoring its present day instability

crustal subsidence rate off hawaii determined from 234u 238u ages of drowned coral reefs a series of submerged coral reefs off northwestern hawaii was formed during largely glacial intervals when the rate of local sea level rise was less than the maximum upward growth rate of the reefs mass spectrometric sup 234 u sup 238 u ages for samples from six such reefs range from 17 to 475 ka and indicate that this part of the hawaiian ridge has been subsiding at a roughly uniform rate of 2 6 mm yr for the past 475 ka the sup 234 u sup 238 u ages are in general agreement with model ages of reef drowning based on estimates of paleo sea level stands derived from oxygen isotope ratios of deep sea sediments but there are disagreements in detail the high attainable precision plus minus 10 ka or better on samples younger than approximately 800 ka large applicable age range relative robustness against open system behavior and ease of analysis for this technique hold great promise for future applications of dating of 50 1 000 ka coral

large scale catastrophic flank collapses in a steep volcanic ridge the pico faial ridge azores triple junction abstract large scale flank collapses are common in the geological evolution of volcanic ocean islands in the atlantic to date catastrophic lateral collapses in the azores islands have been difficult to identify leading to suggestions that a lack of events may relate to the relatively small size of the islands here we show evidence for two major collapses on the northern flank of pico island pico faial volcanic ridge central azores suggesting that this island had a collapse incidence similar to that of other atlantic volcanic islands the study is based on the analysis of 1 offshore and onshore high resolution digital elevation models 2 field data focused on the n flank and 3 new k ar ages on selected lava flow samples pico sub aerial northern flank is marked by two conspicuous arcuate shaped depressions concave towards the sea here interpreted as landslide scars a main debris field is observed offshore the largest depression this deposit has 20 km of maximum length covers ca 150 km2 is composed of meter to hectometer blocks and has an exposed volume here estimated between 4 and 10 km3 though the actual volume probably exceeds 10 km3 debris flow towards the ese was apparently determined by the slope of the narrow wnw ese s jorge channel young lava flows cascade over the interpreted scars thus concealing the older volcanic sequence s affected by the landslide s new k ar ages measured on these lava flows provide a minimum age of ca 70 ka for the large scale collapse s in pico s northern flank

offshore evidence for a huge landslide of the northern flank of tahiti nui french polynesia a bathymetric analysis of the flanks of tahiti nui french polynesia reveals the existence of a major catastrophic north directed landslide during its eruptive history the related debris avalanche da deposits extend north 70 km from the island shore and have a total volume of about 800 km3 two contrasted facies of the debris are recognized 1 relatively small sized material including a few blocks with well developed flow structures elongate downslope directed ridges and transversal pressure ridges and 2 a scattering of large kilometer sized individual blocks that form in part a prominent bathymetric hummock in the proximal central part of the landslide deposits bathymetric analyses suggest that the tahitian failure evolved through two main successive shots the da debris were rapidly overlain by subsequent volcanic material producing a smooth surface down to 1500 m below sea level the on land and offshore structures indicate a listric fault geometry for the landslide scar the volume removed by the landslide is thus estimated between 400 km3 and 450 km3 discrepancy in the volume of the scar and the debris derived from it is due in part to expansion of the debris to fragmentation of the avalanche and to incorporation of sediments comparison with a recently recognized southern tahitian landslide clouard et al 2001 and with landslides recognized around the hawaiian islands and the canary islands shows that the huge northern tahitian landslide described here has a reduced mobility in its central part perhaps the older tetiaroa eruptive complex to the north acted as a buttress to inhibit movement of the da products the northern and southern tahiti nui landslides moved in opposite directions away from the main central e w directed rift zone that served as the main magma feeding structure then the huge northern landslide strongly controlled the later volcano structural evolution by capturing subsequent volcanic activity to the north despite the northwestward displacement of the pacific plate over the society hot spot

changes in the trophic state of lake erie discordance between molecular δ13c and bulk δ13c sedimentary records abstract prior to 1980 anthropogenic phosporus p loadings resulted in increased algal productivity and the deterioration of water quality within lake erie we measured c and n elemental compositions geolipid concentrations and 13 c values for bulk organic material and individual alkanes in samples taken from a 40 cm sediment core from the eastern basin of lake erie to infer recent trends in primary productivity and diagenesis the predominance of autochthonous algal derived c throughout the core is evidenced by low c n values 9 10 and the persistent abundance of n c 15 to n c 17 alkanes throughout the core the 13 c values of bulk organic c from lake erie vary between 25 9 and 24 9 with a maximum corresponding to the period of elevated historical p loading within lake erie 13 c values of short chained algal derived alkanes n c 18 are lower approximately 1 0 than their terrestrial derived homologs n c 25 down core variations in the 13 c composition of algal derived short chained alkanes do not exhibit the same trend as that observed for bulk organic c down core variation in 13 c values of individual alkanes likely reflect multiple diagenetic effects including kinetic fractionation effects variations in the relative contributions of isotopically unique n alkanes to the sediments and or temporal changes in 13 c enrichments of n alkanes associated with a single source high sedimentation rates characteristic of this core emphasize temporal variations in molecular 13 c values that might not otherwise be observed whereas 13 c data for bulk sedimentary organic c appear to reflect variation in trophic state the isotopic record for algal derived n alkanes e g n c 17 and pristane from lake erie must be considered from the perspective of molecular transformations

environmental influence on the biohopanoid composition of recent sediments abstract bacteriohopanepolyols are the biological precursors of extended hopane biomarkers which are ubiquitous in the geosphere the abundance and composition of these biohopanoids were determined for modern sediments from eight depositional environments by gc ms analysis of hopanols derived from a side chain cleavage reaction periodic acid and sodium borohydride of the bacteriohopanepolyols we report quantitative data for bacteriohopanetetrol bht composite tetrafunctionalised biohopanoids pentafunctionalised biohopanoids and hexafunctionalised biohopanoids bht was found in concentrations higher than previously reported up to ca 1500 g g toc but comprised only a relatively small proportion 0 26 of the total biohopanoids in all except one sample composite tetrafunctionalised biohopanoids were the dominant group of bacteriohopanepolyols in all other sediments and are likely to be a major source of the geologically occurring extended hopanes hexafunctionalised biohopanoids were most abundant in lake sediments particularly two small highly productive stratified lakes where they comprised 20 40 of total biohopanoids this feature is interpreted to be due to greater contribution to the organic matter of these sediments from type i methanotrophic bacteria which produce dominantly hexafunctionalised biohopanoids consistent with the environmental settings in the marine environments where sulphate reduction is dominant hexafunctionalised biohopanoids are relatively minor constituents 2 6 of total biohopanoids these data comprise the first clear demonstration that bacteriohopanepolyols vary in composition between depositional environments and have the potential to preserve specific bacterial source information in sedimentary organic matter

diploptene an indicator of terrigenous organic carbon in washington coastal sediments the pentacyclic triterpene 17 beta h 21 beta h hop 22 29 ene diploptene occurs in sediments throughout the columbia river drainage basin and off the southern coast of washington state in concentrations comparable to long chain plantwax n alkanes the same relationship is evident for diploptene and long chain n alkanes in soils from the willamette valley microorganisms indigenous to soils and soil erosion are indicated as the biological source and physical process respectively for diploptene in coastal sediments similarity between the stable carbon isotopic composition delta 13cpdb of diploptene isolated from soil in the willamette valley 31 2 0 3 and from sediments deposited throughout the washington coastal environment 31 2 0 5 supports this argument values of delta for diploptene in river sediments are variable and 8 17 lighter indicating that an additional biological source such as methane oxidizing bacteria makes a significant contribution to the diploptene record in river sediments selective biodegradation resulting from a difference in the physicochemical association within eroded particles can explain the absence of the more 13c depleted form of diploptene in washington coastal sediments but this mechanism remains unproven

palaeomagnetic study of a subaerial volcanic ridge sao jorge island azores for the past 1 3 myr evidence for the cobb mountain subchron volcano flank instability and tectonomagmatic implications we present a palaeomagnetic study on 38 lava flows and 20 dykes encompassing the past 1 3 myr on s jorge island azores archipelagonorth atlantic ocean the sections sampled in the southeastern and central western parts of the island record reversed and normal polarities respectively they indicate a mean palaeomagnetic pole 81 3 degrees n 160 7 degrees e k 33 and a95 3 4 degrees with a latitude shallower than that expected from geocentric axial dipole assumption suggesting an effect of non dipolar components of the earth magnetic field virtual geomagnetic poles of eight flows and two dykes closely follow the contemporaneous records of the cobb mountain subchron odp dsdp programs and constrain the age transition from reversed to normal polarity at ca 1 207 0 017 ma volcano flank instabilities probably related to dyke emplacement along an nnwsse direction led to southwestward tilting of the lava pile towards the sea two spatially and temporally distinct dyke systems have been recognized on the island the eastern is dominated by nnwsse trending dykes emplaced before the end of the matuyama chron whereas in the central western parts the eruptive fissures oriented wnwese controlled the westward growth of the s jorge island during the brunhes chron both directions are consistent with the present day regional stress conditions deduced from plate kinematics and tectonomorphology and suggest the emplacement of dykes along pre existing fractures the distinct timing and location of each dyke system likely results from a slight shift of the magmatic source

factors controlling 13c contents of sedimentary organic compounds principles and evidence the carbon isotopic composition of any naturally synthesized organic compound depends on 1 the carbon source utilized 2 isotope effects associated with assimilation of carbon by the producing organism 3 isotope effects associated with metabolism and biosynthesis and 4 cellular carbon budgets these factors are reviewed and quantitative considerations summarized particularly with regard to active and passive modes of carbon assimilation by phytoplankton and the existence of discernible regularities in isotope effects associated with lipid biosynthesis it is concluded that n alkyl lipids are in general depleted in 13c by about 1 5 relative to polyisoprenoid lipids produced by the same organism the effects of biological reworking on isotopic compositions of organic carbon are examined and it is suggested that enrichment of 13c in sedimentary organic carbon may result from loss of ch4 from zooplanktonic gut communities isotopic methods for estimation of ancient co2 levels are considered and a hyperbolic form favored for the relationship between concentrations of dissolved co2 and isotopic fractionation

development of volcanic insular shelves insights from observations and modelling of faial island in the azores archipelago a variety of geological processes contribute to the development of volcanic island shelves although their relative importance remains unclear we have mapped the morphology of faial island s shelf in the azores from geophysical multibeam sonar chirp and boomer seismic reflection and geological data sediment sampling a wave erosional model and a eustatic record of glacially induced oscillations of sea level which modulated the elevation at which the waves operated through time was used to determine the contribution of mechanical wave erosion to shelf development wave regimes varied according to the orientation of the coast the model was run for 10 to 800 ka depending on the age of the various coastal sectors based on published radiometric data the modelling replicated the shape of the island s shelf reasonably well supporting the contention that it developed primarily through mechanical wave erosion operating in an intertidal zone that migrated landwards and seawards with changes in the level of the sea disparities between modelled and actual shelf morphologies may reflect varied geological resistance to erosion errors in the radiometric dates more recent unrecognised volcanic deposits sediment deposition and tectonic vertical movements there were some variation in rates of shelf development over different time scales but over the long term the relationship between shelf age and width was essentially linear the depth of the shelf break in some areas suggests that there have been differential vertical movements of the land around the island probably related to local faults the poor development or absence of terraces on the shelf may be attributed either to recent volcanic progradation or to sediment infilling of the space created by earlier erosion however poorly developed terraces on the southern shelf of faial are similar to those predicted by the model given appropriate adjustments for vertical movements of the land

large scale active slump of the southeastern flank of pico island azores we report evidence for ongoing lateral slump of part of the southeastern flank of the pico volcanic ridge in the azores data from a high resolution digital elevation model field work gps and radar interferometry show that 1 the slumping sector is several cubic kilometers in size 2 the structure involves several curved scars with normal fault kinematics 3 the central part is undergoing little horizontal displacement toward the southeast 1 6 1 3 mm yr but significant downward movement 5 12 mm yr and 4 the outer part of the southeastern flank of pico is subsiding faster than the inner parts this likely reflects recent individualization of a steep seaward dipping fault in the moving mass the slump shares similarities with active slumps recognized elsewhere although the studied area may represent only the proximal part of a much larger complex potentially affecting the deep submarine base of the island displacement of the subaerial part of the southeastern flank of pico seems to be accommodated by the movement and rotation of large blocks along listric normal faults

the azores triple junction evolution since 10 ma from an aeromagnetic survey of the mid atlantic ridge abstract in the past two decades several models have been presented to describe the evolution and the present structure of the azores triple junction these models were mainly based on morphological analysis of sea bottom topography sparse magnetic profiling sidescan sonar surveying over the plateaus and global plate kinematic considerations for the north atlantic in this paper we follow a different approach from a detailed aeromagnetic survey covering both sides of the mid atlantic ridge between 37 n and 40 30 n the magnetic anomalies up to anomaly 5 are accurately identified allowing careful modelling of the kinematics of this region for the past 10 ma and thus establishing a coherent framework for the design of geophysical models for the azores triple junction the analysis of magnetic anomalies and the use of fourier domain inversion techniques show that the ridge is made up of six segments each one varying in length from 50 to 60 km the more continuous section of the ridge can be defined from the first four northern segments although the north azores fracture zone right offsets the ridge at 39 30 n 29 40 w the fifth and sixth segments are respectively right offset by the acor fracture zone at 38 23 n 30 15 w and by the princess alice fracture zone at 38 00 n 30 50 w anomaly identifications using a two dimensional model and plate tectonics reconstruction techniques allowed the calculation of rotation pole parameters the results thus obtained reveal that at least between anomalies 5 and 3 10 3 85 ma the azores displayed an independent motion relative to the neighbouring plates and after anomaly 2a 2 45 ma the azores moved attached to the eurasian plate the triple junction azores north america africa or eurasia north america africa moved northward from 38 00 n 30 50 w to 38 20 n 30 15 w between 4 and 3a and probably to 38 50 n 30 00 w at anomaly 2a time a detailed reconstruction model is presented

geomorphic analysis of small rayed craters on mars examining primary versus secondary impacts 1 twenty confirmed impacts over a 7 year time period on mars were qualitatively and statistically compared to 287 secondary craters believed to originate from zunil an 500 ka 10 km diameter primary crater our goal was to establish criteria to distinguish secondaries from primaries in the general crater population on the basis of their horizontal planforms recent primary impacts have extensive air blast zones distal ray systems 100 crater radii r and ephemeral ejecta recent primaries formed clusters of craters from atmospheric fragmentation of the meteoroid body secondary craters have ejecta blankets with shorter rays that are consistent with emplacement by low impact velocities near 1 km s the mean extent of the continuous ejecta blankets was less distal for secondaries 5 38 1 57r versus primaries 18 07 7 01r though primary ejecta were less fractal fractal dimension index fdi 1 30 and more circular on average circularity ratio cr 0 55 0 25 versus 0 27 0 13 for secondaries crater rims were remarkably circular primaries cr 0 97 0 02 secondaries at 0 94 0 05 though secondaries have the lowest values cr 0 9 secondary crater rims were elongated toward or orthogonal to their primary of origin uprange source directions for most secondaries determined by ejecta planform and crater rim ellipticity point toward zunil although contamination from other primaries is considered in some areas ejecta blanket discrepancies between recent primaries and zunil secondaries are attributable to differences in impact velocity and retention age after removal of the ejecta blanket crater rims are generally not diagnostic for determining crater origin fragmentation of primaries may play some role in steepening the size frequency distribution of crater diameters in the 5 m d 30 m range

gps and tectonic evidence for a diffuse plate boundary at the azores triple junction abstract we use gps bathymetric structural and seismic data to define the pattern of present deformation along the northern half of the azores plateau where the nubia eurasia plate boundary terminates at the axis of the mid atlantic ridge mar new and existing campaign gps velocities from the azores islands reveal extension oblique to a series of en echelon volcanic ridges occupied by terceira s jorge pico and faial islands in a frame of reference defined by 69 continuous gps stations on the eurasia plate terceira island moves 2 1 mm yr away from eurasia consistent with the island s location within the terceira rift and plate boundary structure the volcanic ridges south of the terceira rift move toward wsw at progressively faster rates reaching a maximum of 3 5 0 5 mm yr 2 for the pico faial volcanic ridge the hypothesis that the terceira rift accommodates all nubia eurasia plate motion is rejected at high confidence level based on the motions of sites on s jorge island just west of terceira rift all of the islands move relative to the nubia plate with pico island exhibiting the slowest motion only 1 0 5 mm yr 2 detailed bathymetry from the interior of the hypothesized azores microplate reveals faults that crosscut young mar seafloor fabric these observations and the gps evidence for distributed deformation described above argue against the existence of a rigid or semi rigid azores microplate and instead suggest that nubia eurasia plate motion is accommodated by extension across a 140 km wide zone east of the mar axis most likely bounded to the north by the northern shoulder of the terceira rift the mar spreading rate along the western end of the azores deformation zone 38 5 n 39 5 n is intermediate between the eurasia north america rate measured at 39 5 n and the nubia north america rate measured at 38 5 n consistent with the joint conclusions that the nubia eurasia boundary is broad where it intersects the mar and the azores triple junction is diffuse rather than discrete

lipids of aquatic organisms as potential contributors to lacustrine sediments ii abstract the relationship between the lipid composition of organisms in the water column of an eutrophic lake and the lipid composition of underlying sediments previously examined for n alkanols and steroids is now reported for hydrocarbons ketones and carboxylic acids the n c7 alkane and alkenoic acids from two primary sources are rapidly metabolized in the water column and surficial sediment bacterial biomarkers including hopenes and i ai branched fatty acids were detected in the photosynthetic bacterial layer occurring just above the sediment water interface within the sediment the apparent conversion of free n alkanes alkan 2 ones and hydroxy acids to the corresponding bound form is noted microbiological oxidation of n alkanes to alkan 2 ones is supported by the detection of the intermediate alkan 2 ols with a distribution similar to that of the ketones the geochemistry of sediment deposited c 1900 prior to biological study of the site was interpreted from stable biomarkers and the diagenetic changes recognised in the study of contemporary deposition a qualitative difference in algal input to the older sediment is inferred from the low 7 sterol content and presence of 2 6 10 trimethyl 7 3 methylbutyl dodecane however there was still significant dinoflagellate input as indicated by the presence of 4 methylsterols a difference in higher plant input to the older sediment indicated from the n alkane alkene and triterpenoid ketone distributions is consistent with the recent development of tree cover

reply to the comment by quartau et al on construction and destruction of a volcanic island developed inside an oceanic rift graciosa island terceira rift azores j volcanol geotherm res 284 32 45 by sibrant et al 2014 abstract in sibrant et al 2014 we reconstructed the evolution of graciosa island azores we extensively discussed the nature and the meaning of the destruction episodes either tectonics or gravitational and concluded that the island has evolved through major landslides in their comment quartau et al 2015 conclude that 1 sibrant et al 2014 is based almost solely on subaerial observations which is false because we used the bathymetric data available to us figs 3 and 4 in sibrant et al 2014 2 the published multibeam sonar data around graciosa reveals that their proposed successive phases of destruction of the volcanic edifices composing the island by massive landslides is incompatible with the high resolution bathymetry first saying that the data were published is misleading because only two images are now provided in quartau et al 2015 most of the high resolution data used by quartau et al 2015 are not published and they still do not release the data for us to analyse and use in this reply second the high resolution bathymetric maps are not incompatible with our model for instance mounds on the eastern submarine slope may actually be landslide blocks and the platform developed to the s may correspond to flank collapses of the successive volcanoes blanketed more recently by the young basaltic cover 3 the interpretation of collapse structures appears to have originated partly from a misreading of the volcano stratigraphy and tectonic structures we certainly did not misread the volcanic stratigraphy and tectonic structures in graciosa in great contrast to quartau et al 2015 we a used major unconformities to establish the volcano stratigraphy b calibrated this stratigraphy with high precision k ar dating c made careful measurement of lava flow attitudes to infer the pre collapse position of the main edifices and d did not use hypothetical tectonic faults as quartau et al 2015 did to draw an evolutionary cartoon of graciosa the lava flows in the southern cliffs of graciosa dip inland as recognised by gaspar 1996 fig 3b in great contrast to the claims of quartau et al 2015 and therefore do not support successive volcanoes coinciding with the centre of the island 4 from unreleased high resolution bathymetric data quartau et al 2015 consider that no large landslide s occurred in graciosa and propose a new model first their geological model is not new as it reproduces a cartoon in gaspar 1996 fig 3a second quartau et al 2015 have not reported any major faults exposed at the surface as expected for an island scale graben but their summary cartoon of graciosa evolution is based on major faults third the new model of quartau et al their fig 8 and our fig 4 misrepresents the initial model of gaspar 1996 figs 4 1 and 4 2 as the whole sw flank of the island has been arbitrarily removed on their drawing see our fig 3 in contrast sibrant et al 2014 propose that the sw flank has been effectively removed but by landslides therefore their new model for the evolution of graciosa is based on misleading hypotheses rather than convincing arguments in conclusion there is no need to change our proposed new stratigraphy and evolution of the island based on quartau et al s claims because these are not supported by actual geological data well established and calibrated stratigraphy geometry of lava flows and geometry and kinematics of faults given the absence of sound geological data to support the evolutionary cartoon proposed by quartau et al 2015 we conclude that it is mostly flawed and therefore mere speculation

coastal erosion rates of lava deltas around oceanic islands abstract rates of coastal erosion are needed for planning purposes and to improve understanding of how the shelves of islands develop ultimately becoming submerged banks near shore submarine platforms created by erosion of lava deltas of known age provide an opportunity to quantify erosion rates and to investigate how those rates vary between different types and ages of lava flows as well as how they vary with wave climate we have compiled data on deltas formed during historical and holocene eruptions age 6 ka from both a and p hoehoe lava flows and from diverse localities azores and hawaiian islands and ascension island near shore platforms were interpreted from multibeam sonar bathymetric light detection and ranging lidar and historical sounding data from them we estimated time averaged shoreline retreat rates from the seaward distances between the modern coastlines and the submarine platform edges the 35 interpreted platforms have rugged dipping surfaces left behind by erosion with an average gradient of 5 range 2 10 eroded distance of 436 m 78 1119 m and depth of platform edge of 25 m 5 56 m to evaluate the latter depths we computed seabed orbital speeds due to surface waves at the platform edges depths of platform edges correlate only modestly with those speeds suggesting that platform surfaces have adjusted to wave conditions with a wide range of particle sizes and hence thresholds of motion the largest retreat distances 800 m are associated with platforms of the central azores islands which are exposed to higher waves however retreat rates are highly varied 0 08 12 5 m yr and weakly correlated with measures of wave power suggesting that waves are only a secondary influence given that lack of correlation we suspect that the main factor contributing to variability arises from varied cliff resistance to erosion blocks between joints in lava flows and hence resistance to erosion vary greatly in size from the thicker and less densely jointed a flows to the thinner and shell like layered lavas in p hoehoe flows

deformation in a hyperslow oceanic rift insights from the tectonics of the sao miguel island terceira rift azores the evolution of hyperslow oceanic rifts like the terceira rift tr in the azores is still poorly understood here we examine the distribution of strain and magmatism in the portion of the tr making up the nubia eurasia plate boundary we use sao miguel island because it stretches most of the tr width which allows to investigate the tr s architecture and shedding light on tr s age and mode of deformation from topography and structural analysis and new measurements of 380 faults and dikes we show that 1 sao miguel has two main structural directions n150 and n110 mostly concentrated in the eastern part of the island as an onshore continuation of the faults observed offshore in the ne n110 faults and sw n140 tr walls 2 a new n50 n80 fault system is identified in sao miguel 3 fault and dike geometries indicate that eastern sao miguel comprises the tr s northern boundary and the lack of major faults in central and western sao miguel indicates that rifting is mostly concentrated at master faults bounding the tr based on tr s geometry structural observations and plate kinematics we estimate that the tr initiated between 1 4 and 2 7 ma ago and that there is no appreciable seafloor spreading associated with rifting based on plate kinematics on the new structural data and on sao miguel s structural and volcanic trends we propose that the eastern two thirds of sao miguel lie along a main tr related transform fault striking n70 n80 which connects two widely separated n130 n150 tr trending segments

stable carbon isotopic correlation of individual biolipids in aquatic organisms and a lake bottom sediment abstract isotope ratio monitoring gc ms irm gcms analyses of individual hydrocarbons isolated from the surface sediment of a small eutrophic lake priest pot u k and a phytoplankton tow sample from the upper water column have been undertaken in order to assign sources of sedimentary lipids the 13c values for the sedimentary n alkanes showed no clear distinction between lower molecular weight components c17 c19 of presumed algal origin and higher members c23 c33 of presumed higher plant origin thus indicating a limitation to the use of compound specific isotope analysis in the freshwater system studied in contrast the 13c values of sedimentary hopenes were markedly depleted by over 20 compared with those in the phytoplankton sample from the upper water column hop 22 29 ene in the surficial sediment had a 13c value of 55 2 which contrasts witht he value of the phytoplankton component 32 7 attributed to cyanobacteria these values indicate that a highly 13c depleted source provides a major contribution to the sedimentary component it is proposed that the sedimentary hopenes originate in part from methanotrophic bacteria demonstrating the presence of a bacterial methane cycle in this environment

evidence for a persistent uplifting of la palma canary islands inferred from morphological and radiometric data abstract the morpho structural evolution of la palma canary islands is characterized by vertical movements responsible for or favoring large landslides in its northern part conglomerate terraces nowadays topographically hanged and re incised by the present day barranco de las angustias reveal a recent ongoing uplift process lava flows covered by this geological unit have been sampled and dated by the k ar cassignol technique at a mean age of 507 11 ka the minimum rate of uplift inferred of about 0 4 mm yr is similar to the one deduced from the abnormal elevation of the early submarine series staudigel and schmincke j geophys res 89 1984 11195 11215 this indicates that the northern shield may have experienced a global rise fairly constant throughout most of its geological history it probably results from the combination of regional atlas tectonic processes and the existence of a swell at the island scale this global rise together with the existence of a north south fault in the basement may have controlled triggering of the sw flank collapse of the northern shield and the subsequent concentration of magma along a southern still active topographic ridge the cumbre vieja cv morphological asymmetry of this structure may result from the destabilization of its distal western part favored by strong injections at the axis tilting processes along lateral listric faults can then explain the existence of slope break ups especially on the western side of the ridge such tectonic processes are likely responsible for local superimposed uplifting contributing to the genesis and development of huge western coastal cliffs even in sub historic and historic times we show that unlike many oceanic islands la palma island has experienced important positive vertical movements rather than subsidence

merging gps and atmospherically corrected insar data to map 3 d terrain displacement velocity a method to derive accurate spatially dense maps of 3 d terrain displacement velocity is presented it is based on the merging of terrain displacement velocities estimated by time series of interferometric synthetic aperture radar insar data acquired along ascending and descending orbits and repeated gps measurements the method uses selected persistent scatterers pss and gps measurements of the horizontal velocity an important step of the proposed method is the mitigation of the impact of atmospheric phase delay in insar data it is shown that accurate vertical velocities at ps locations can be retrieved if smooth horizontal velocity variations can be assumed furthermore the mitigation of atmospheric effects reduces the spatial dispersion of vertical velocity estimates resulting in a more spatially regular 3 d velocity map the proposed methodology is applied to the case study of azores islands characterized by important tectonic phenomena

the 1980 1997 and 1998 azores earthquakes and some seismo tectonic implications abstract we have studied the focal mechanisms of the 1980 1997 and 1998 earthquakes in the azores region from body wave inversion of digital gdsn global digital seismograph network and broadband data for the 1980 and 1998 shocks we have obtained strike slip faulting with the rupture process made up of two sub events in both shocks with total scalar seismic moments of 1 9 1019 nm mw 6 8 and 1 4 1018 nm mw 6 0 respectively for the 1997 shock we have obtained a normal faulting mechanism with the rupture process made up of three sub events with a total scalar seismic moment of 7 7 1017 nm mw 5 9 a common characteristic of these three earthquakes was the shallow focal depth less than 10 km in agreement with the oceanic type crust from the directivity function of rayleigh lr waves we have identified the nw se plane as the rupture plane for the 1980 and 1998 earthquakes with the rupture propagating to the se slow rupture velocity about of 1 5 km s has been estimated from directivity function for the 1980 and 1998 earthquakes from spectral analysis and body wave inversion fault dimensions stress drop and average slip have been estimated focal mechanisms of the three earthquakes we have studied together with focal mechanisms obtained by other authors have been used in order to obtain a seismotectonic model for the azores region we have found different types of behaviour present along the region it can be divided into two zones zone i from 30 w to 27 w zone ii from 27 w to 23 w with a change in the seismicity and stress direction from zone i in zone i the total seismic moment tensor obtained corresponded to left lateral strike slip faulting with horizontal pressure and tension axes in the e w and n s directions respectively in zone ii the total seismic moment tensor corresponded to normal faulting with a horizontal tension axis trending ne sw normal to the terceira ridge the stress pattern for the whole region corresponds to horizontal extension with an average seismic slip rate of 4 4 mm yr