late quaternary terraced marine deposits as tools for wide scale correlation of unconformity bounded units in the volcanic aeolian archipelago southern italy abstract late quaternary raised terraced marine deposits are commonly interlayered with volcanic deposits along the coasts of the aeolian archipelago they mostly reflect the interplay between long term crustal vertical movements and glacio eustatic sea level changes during marine isotope stages mis 5 and 9 key discontinuity surfaces are represented by those bounding terraced marine deposits formed in correspondence of recurrent individual interglacial sea level peaks they are the basal ravinement surface formed during gradual sea level rise at the onset of a sea level peak and the upper surface of subaerial erosion developed during ensuing sea level fall and lowstand the discontinuity surfaces are classified according to their sequence stratigraphic significance field documentation and areal extent mis 5 marine deposits are bounded by the first order ui and uii unconformities the ui unconformity is the ravinement surface formed during mis 5e sea level rise age between 130 and 124 ka the uii unconformity is the surface of subaerial erosion and non deposition developed during sea level lowering after mis 5a age 70 ka unconformities ui and uii are correlated throughout the entire aeolian archipelago thus assuming a regional stratigraphic significance by linking to the global sea level curve they are assigned a relative age and assume a substantial chronostratigraphic significance and potential for dating of volcanic rocks further correlation on most of the aeolian archipelago is provided by the l3 unconformity that is the ravinement surface formed during sea level rise of mis 5c 100 ka moreover the f1 unconformity bounds at the base marine deposits older than the last interglacial i e mis 9 and is ascribed of an inter island stratigraphic outcome these allogenic unconformities driven by sea level fluctuations allow definition of a regional unconformity bounded framework for the aeolian archipelago into which local volcanic successions subdivided by autogenic unconformities of volcanic origin may be arranged

modelled atmospheric temperatures and global sea levels over the past million years the climate has passed through a series of glacials and interglacials over the past million years but the nature of this cyclicity in terms of temperature ice volume and sea level and the underlying causes are not well known bintanja et al use a new method to deduce a one million year time series of these variables the reconstructed records are much longer than other methods have provided for any of these variables individually the most intense glacial stages were 17 c colder than today and most of the continental ice was present in north america strong cooling in the beginning of glacials was found to precede ice sheet build up these findings may shed light on the causes of ice age cycles marine records of sediment oxygen isotope compositions show that the earth s climate has gone through a succession of glacial and interglacial periods during the past million years but the interpretation of the oxygen isotope records is complicated because both isotope storage in ice sheets and deep water temperature affect the recorded isotopic composition1 2 3 4 5 separating these two effects would require long records of either sea level or deep ocean temperature which are currently not available here we use a coupled model of the northern hemisphere ice sheets6 and ocean temperatures forced to match an oxygen isotope record for the past million years compiled from 57 globally distributed sediment cores to quantify both contributions simultaneously we find that the ice sheet contribution to the variability in oxygen isotope composition varied from ten per cent in the beginning of glacial periods to sixty per cent at glacial maxima suggesting that strong ocean cooling preceded slow ice sheet build up the model yields mutually consistent time series of continental mean surface temperatures between 40 and 80 n ice volume and global sea level we find that during extreme glacial stages air temperatures were 17 1 8 c lower than present with a 120 10 m sea level equivalent of continental ice present

on the use of unconformities in volcanic stratigraphy and mapping insights from the aeolian islands southern italy abstract the approach to volcanic stratigraphy and mapping in the aeolian islands has found the concept of unconformity bounded units ubus extremely useful for purposes of stratigraphic classification and correlation volcanic unconformities erosive and collapse unconformities relative to processes of internal modification of a volcano are classified separately from sea level driven unconformities the erosive unconformities formed during periods of volcanic quiescence are generally characterized by angular relationships and lithological change between the products below and above an unconformity and may be associated with paleosols or epiclastic horizons the collapse unconformities related to calderas and lateral collapses represent surfaces of structural truncation along the collapse borders passing outside of the collapse to erosive unconformities developed during the corresponding repose periods instead the sea level driven unconformities are marine and subaerial erosive surfaces bounding in pairs the depositional cycles relative to sea level highstands which are recorded in raised marine terraces most unconformities can be correlated on a variable scale from local volcanic island to regional inter island by means of careful stratigraphic analysis targeted to identify the corresponding stratigraphic hiatus in the volcanic successions in different points of observation this helps to solve the problems arising from the difficult recognition of the unconformities in the field moving away from the type locality due to their variable features a practical nomenclature scheme for a hierarchy of ubus to be applied in volcanic areas can be established on the basis of the areal magnitude of the bounding unconformities and their importance in the volcano history passing through a slight modification of the international stratigraphic guide s rules combined with lithostratigraphic units mapped rock bodies and lithosomes eruptive centres the ubus provide a useful stratigraphic synthesis of a volcanic area by means of a framework of time stratigraphic unconformable surfaces moreover ubus can be directly interpreted in terms of volcanic activity units with a time stratigraphic significance thus providing the key elements for the eruptive history of a volcano and the definition of its event stratigraphy

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

insular erosion isostasy and subsidence organic reefs and shore erosion record the intersection of sea level with islands from this record it is possible to reconstruct the history of vertical movement of the islands and the adjacent deep sea floor including midplate swells as judged by coral thickness islands with barrier reefs sink as though they were on thermally youthful crust regardless of the actual age reefless islands do not sink until truncated by erosion apparently thermal subsidence is balanced by isostatic uplift in response to erosion barrier reefs prevent wave erosion of encircled volcanoes and capture products of stream erosion so that isostatic uplift is eliminated insular shelves widen initially at rates of 0 6 to 1 7 kilometers per million years the rates decrease with time thus the subsidence of islands depends on the size of the is land and the presence of reefs and it may not always be the same as that of the surrounding oceanic crust

post eruptive morphological evolution of island volcanoes surtsey as a modern case study abstract surtsey is a small volcanic island in the vestmannaeyjar archipelago off the south coast of iceland the eruption leading to the island s emersion lasted for 3 5 yr 1963 1967 while destructive forces have been active for over 50 yr 1963 present day during which surtsey has suffered rapid subaerial and submarine erosion and undergone major morphological changes surtsey is a well documented modern example of the post eruptive degradational stage of island volcanoes and has provided the unique opportunity to continuously observe and quantify the effects of intense geomorphic processes in this paper we focus on coastal and marine processes re shaping the shoreline and shallow water portions of the surtsey complex since its formation and on the related geomorphological record analogies with the post eruptive morphological evolution of recently active island volcanoes at the emerging stage encompassing different climatic conditions wave regimes and geological contexts are discussed

bedforms on the submarine flanks of insular volcanoes new insights gained from high resolution seafloor surveys a comparative analysis of bedform fields along the submarine flanks of insular volcanoes characterized by different morpho structural settings volcanic and meteo marine regimes vanuatu kermadec bismark madeira and aeolian archipelagos is presented here to provide insights on the size distribution morpho dynamic and genesis of such bedforms two main types of bedforms are recognized according to their size location and preconditioning triggering processes small scale bedforms have wavelengths of tens to hundreds of metres and wave heights of metres because of their small size they are typically not recognizable at water depths greater than 400 m from vessel mounted bathymetric surveys however few examples of small scale bedforms are reported from upper volcanic flanks where steep gradients commonly hinder their formation their recognition is mostly limited to the thalweg of shallow and flat bottomed channels that carve the insular shelf on slope gradients 15 small scale bedforms are mostly related to erosional depositional processes due to sedimentary gravity flows that are often the result of a cascading effect between volcanic and non volcanic processes for example flood discharges and retrogressive landslides large scale bedforms occur at all water depths having wavelengths of hundreds thousands of metres and wave heights up to few hundreds of metres the origin of large bedforms is more difficult to ascertain especially if only bathymetric data are available some diagnostic criteria are presented to distinguish between bedforms associated with landslide deposits and those associated with density currents in this latter case relevant sediment sources and slope gradients 8 are key factors for bedform development erosional depositional bedforms are typically related to eruption fed density flows formed during large caldera collapses or to large turbidity flows bedforms generated by turbidity flows are often observed in the lower volcanic flanks where an abrupt decrease of gradients is present often matching a change from confined to unconfined settings in summary this study provides insights to interpret bedforms in modern and ancient marine volcaniclastic settings elsewhere

submarine depositional terraces in the tyrrhenian sea as a proxy for paleo sea level reconstruction problems and perspective abstract in the last decade great effort was put in the study of relative sea level changes on mediterranean coastlines through the integration of geophysical modelling and proxy data of paleo shorelines in this paper we show potential and limitations of using additional marine geomorphic sedimentary markers for earlier and lower sea levels these markers are submarine depositional terraces sdts i e deposits formed by a set of small prograding sedimentary wedges having a terraced shape and found at variable shallow water depths mainly the first 150 m on continental and insular shelves in the tyrrhenian sea the shallowest terraces near shore have their edges at depths between 10 m and 30 m approximating the modern local storm wave base level their formation is thought to be associated with the modern sea level highstand and thus can be used as the modern analogue for deeper terraces formed in the past when the sea level was on the middle and outer shelf mid shelf terraces have their edges at variable depths between 40 m and 90 m and probably formed during the last sea level rise they show a patchy spatial distribution and a large variability in their internal structure so that they are not suitable for correlation on a regional scale shelf edge terraces have their edges at depths between 120 m and 170 m which is close or deeper than the last glacial maximum lgm sea level stand they show a remarkable lateral continuity and a prograding internal structure similar to those at shallower depth and thus represent a proxy for the sea level position at around 20 ka however the position of sdts edges is not a direct measure of paleo sea level positions because their depth depends on a complex interplay of several factors such as the base of the storm wave and its variation in response to coastal physiography as well as the occurrence of subsequent erosional or depositional processes depending on the geophysical and mapping methods used to determine their depth the associated error range can also differ based on the analysis of these complexities and a wide range of physiographic settings of the tyrrhenian sea we discuss these error ranges in order to assess potential and limitation of the sdt for analyses of vertical mobility of an area

aeromagnetic anomalies reveal hidden tectonic and volcanic structures in the central sector of the aeolian islands southern tyrrhenian sea italy 1 salina island italy in the central aeolian chain is the northernmost volcanic structure of an elongated ridge on a regional shear zone with nnw sse strike slip faults and second order n s and ne sw faults modeling of high resolution low altitude aeromagnetic data collected in 2003 and 2005 using volcanological data constraints reveals the inner structure of the salina volcanoes and surrounding marine regions regional negative anomalies overlie e w elongated sedimentary basins related to the early pliocene pleistocene opening of the southern tyrrhenian sea these negative anomalies flank positively magnetized crust of salina and seamounts off its eastern coast where the shorter wavelength anomalies map late pleistocene holocene volcanic conduits dikes and faults the magnetic and volcanological data indicate that the early circa 168 100 ka basaltic to andesitic salina volcanism developed along n s and ne sw tectonic faults whereas the more recent andesitic lavas and rhyolitic pyroclastics circa 100 13 ka were emitted by vents related to the main nw se faults the tectonic structures also controlled the location of the seamounts around the island and the geometry of the volcano tectonic collapses salina volcanism was emplaced on a nnw sse tear fault of the presently developing roll back slab in the southern tyrrhenian sea

erosion of the submarine flanks of the canary islands surveying with multibeam echo sounders around old 1 ma volcanic ocean islands reveals that their submarine flanks contain a strong downslope oriented ridge and valley corrugation which modifies the original volcanic morphology of lava terraces and cones by analogy with canyons in other settings this corrugation was probably caused by channel incision by erosive sedimentary mass flows such as turbidity currents and debris flows we adapt a method first used in subaerial geomorphology to isolate the erosion depth exhumation and apply it to the eroded flanks of the 6 8 ma anaga massif of tenerife the channels formed around this massif divert around local topographic highs these highs which are probably original volcanic cones are therefore preferentially preserved during erosion so that their elevations can be used to construct an artificial reference surface terrain depth was calculated by subtracting this reference surface from measured bathymetry comparison of the terrain depth of the old eroded submarine flank of anaga with that of the young mostly unaltered submarine flank of el hierro allows us to infer the mean depth of anaga s submarine erosion which is 100 m volcanic terrains can be dated by radiometric methods so they also provide a way of quantifying long term denudation rates we infer that submarine denudation of anaga has occurred at comparable rates to that of subaerial lowlands and much slower than denudation of highlands illustrated locally by the more extensive erosion of the subaerial anaga edifice

imprints of volcanic erosional depositional tectonic and mass wasting processes in the morphology of santa maria insular shelf azores abstract the present day morphology of volcanic island shelves is the result of several factors namely the original shape and structure of the volcanic edifice the nature and age of the materials that compose its flanks and the erosional volcanic tectonic and sedimentary processes that acted to form these shelves by combining detailed seafloor mapping with onshore studies it is possible to gain a unique insight onto the evolution of volcanic island edifices and the processes that helped to shape their shelves here we look at santa maria island in the azores archipelago which is a 6 ma old ocean island volcano surrounded by a 135 km2 shelf characterized by an history of subsidence since its formation c 6 ma ago followed by uplift from 3 5 ma onwards by analyzing the geomorphic parameters of the insular shelf such as the shelf width and the erosive edge depth the island s history of vertical movements and by relating the morphology of the outcrops found on the shelf with those onshore we contribute to a better knowledge of the evolutionary history of santa maria with particular focus on its earlier stages of growth we infer that the outer part of the northern shelf is carved on units older than the oldest volcanic sequences exposed on land the western and southern shelves are almost entirely carved in the products of the oldest shield volcano anjos volcanic complex whilst the eastern shelf is the youngest in formation being related to units of the pico alto volcanic complex we also discuss the distribution of sediments on the shelf high wave energy concomitant with sea level drops contributed to the erosion and transport of older sequences offshore which were ultimately lost to the slopes of the island resulting in a shelf that is sediment stripped for the most part presently wide shelves further contribute to wave energy dissipation resulting in a significantly diminished sediment production the shelf edges around santa maria exhibit several erosive scars interpreted as the head of a submarine drainage network carved on the slopes of the island on the western southern and eastern shelves these mass wasting features are mostly controlled by tectonics since the extension of faults can be followed from onshore to the shelf edge on the northern shelf mass wasting appears to be mostly correlated with presence of unstable sediments on the shelf edge that triggered landsliding overall this work shows how detailed mapping of the shelves surrounding old volcanic islands can still provide important complementary information about the evolution of these islands which could not be acquired solely by the study of their subaerial and deeper submarine parts

depths of modern coastal sand clinoforms abstract clinoforms are classical geological features examples in the rock record or in seismic reflection data that originally formed in shallow water can potentially help to locate paleo sea level but their precise links with sea level need to be established using modern examples before such inferences can be made accurately some near shore areas of high wave energy and steep coasts host sand bodies with upwards convex surfaces these clinoforms have been suggested to have been created from sand exported from the upper shoreface during stormy conditions and deposited at depths where wave action diminishes below the threshold of motion field and roy 1984 hernandez molina et al 2000 we have compiled the shapes of these bodies in a variety of wave environments in order to test this idea the interpreted depths at which the sand surface steepens i e the clinoform rollover vary from 21 m off southern california to deeper than 50 m off se australia to assess the link with wave action rollover depths were compared with adjacent deep water wave properties over the period 1992 2001 in the era 40 reanalysis dataset rollover bed shear stresses were computed from properties representing average wave conditions and from properties associated with upper percentile conditions stresses were found to reach 0 1 0 5 pa during upper 5 percentile wave conditions exceeding the sediment threshold of motion estimated from reported grain size data sediment to below the rollover is therefore mobile during extreme wave conditions

the morphology of insular shelves as a key for understanding the geological evolution of volcanic islands insights from terceira island azores shelves from volcanic ocean islands result from the competition between two main processes wave erosion that forms and enlarges them and volcanic progradation that reduces their dimension in places where erosion dominates over volcanism shelf width can be used as a proxy for the relative age of the subaerial volcanic edifices and reconstruction of their extents prior to erosion can be achieved in this study new multibeam bathymetry and high resolution seismic reflection profiles are exploited to characterize the morphology of the insular shelves adjacent to each volcanic edifice of terceira island in order to improve the understanding of its evolution subaerial morphological and geological stratigraphic data were also used to establish the connection between the onshore and offshore evolution shelf width contiguous to each main volcanic edifice is consistent with the known subaerial geological history of the island most of the older edifices have wider shelves than younger ones the shelf edge proved to be a very useful indicator in revealing the original extent of each volcanic edifice in plan view its depth was also used to reconstruct vertical movements showing that older edifices like serra do cume ribeirinha guilherme moniz and pico alto have subsided while more recent ones have not the morphology of the shelf namely the absence presence of fresh lava flow morphologies and several types of erosional depositional and tectonic features integrated with the analysis of the coastline morphology allowed us to better constrain previous geological interpretations of the island evolution

from basalt to dacite origin and evolution of the calc alkaline series of salina aeolian arc italy the island of salina comprises one of the most distinct calc alkaline series of the aeolian arc italy in which calc alkaline high k calc alkaline shoshonitic and leucite shoshonitic magma series are developed detailed petrological geochemical and isotopic sr nd pb o data are reported for a stratigraphically well established sequence of lavas and pyroclastic rocks from the middle pleistocene volcanic cycle 430 127 ka of salina which is characterized by an early period of basaltic volcanism corvo capo rivi fossa delle felci group 1 and a sequence of basaltic andesites and andesites and dacites in the final stages of activity fossa delle felci groups 2 8 major and trace element compositional trends rare earth element ree abundances and mineralogy reveal the importance of crystal fractionation of plagioclase clinopyroxene olivine orthopyroxene titanomagnetite amphibole apatite in generating the more evolved magma types from parental basaltic magmas and plagioclase accumulation in producing the high al2o3 contents of some of the more evolved basalts sr isotope ratios range from 0 70410 to 0 70463 throughout the suite and show a well defined negative correlation with 143nd 144nd 0 51275 0 51279 pb isotope compositions are distinctly radiogenic with relatively large variations in 206pb 204pb 19 30 19 66 fairly constant 207pb 204pb 15 68 15 76 and minor variations in 208pb 204pb ratios 39 15 39 51 whole rock 18o values range from 6 4 to 8 5 and correlate positively with sr isotope ratios overall the isotopic variations are correlated with the degree of differentiation of the rocks indicating that only small degrees of crustal assimilation are overprinting the dominant evolution by crystal liquid fractionation afc type processes the radiogenic and oxygen isotope composition of the salina basalts suggests derivation from primary magmas from a depleted mantle source contaminated by slab derived fluids and subducted sediments with an isotopic signature of typical upper continental crust these magmas then evolved further to andesitic and dacitic compositions through the prevailing process of low pressure fractional crystallization in a shallow magma reservoir accompanied by minor assimilation of crustal lithologies similar to those of the calabrian lower crust

late quaternary deformation history of the volcanic edifice of panarea aeolian arc italy a series of raised palaeoshorelines is documented along the emergent coastal slopes of panarea and surrounding islets at elevations of 115 palaeoshoreline ia and 100 m a s l ib 62 5 m ii 35 m iii 12 m iv 10 12 va and 5 m vb according to stratigraphic constraints and cross cutting relationships these palaeoshorelines are correlated with discrete high sea level stillstands during marine oxygen isotope stages mis 5e 5c 5a and 3 coastal elevation changes suggest the occurrence of a long term sustained uplift trend of the volcanic edifice since the last interglacial last 124 ka the uplift rates are not constant but display a progressive deceleration from maximum values of 1 5 1 58 m ka in the period between 124 and 100 ka down to the lowest values of 0 66 0 69 m ka which tend to be constant starting from 81 ka bp the long term deformation pattern of panarea suggests that a transitory volcano related component of uplift interplayed with the regional tectonic component affecting the sub volcanic basement which has undergone a persistent and widespread uplift since the mid pleistocene the volcano related component of uplift prevailing between 124 and 100 81 ka is interpreted as the result of visco elastic deformation mechanisms which characterize the progressive re equilibration of the shallow magmatic system following the incoming quiescence of the volcanic edifice the long term uplift values at panarea are higher than in the main portion of the western central aeolian arc where a mean uplift rate of 0 34 m ka was estimated since the last interglacial last 124 ka such a pattern of deformation on a regional scale may be a response to active deformation processes connected with the southeastward rollback of the subducting ionian slab which is still active only in correspondence with the eastern sector of the aeolian arc including panarea in the short term a localized submergence trend has been documented at the nearby islet of basiluzzo for the last 2 000 years likely connected to neo tectonic movements along main ne sw trending faults

emergence and evolution of santa maria island azores the conundrum of uplifted islands revisited the growth and decay of ocean island volcanoes are intrinsically linked to vertical movements while the causes for subsidence are better understood uplift mechanisms remain enigmatic santa maria island in the azores archipelago is an ocean island volcano resting on top of young lithosphere barely 480 km away from the mid atlantic ridge like most other azorean islands santa maria should be experiencing subsidence yet several features indicate an uplift trend instead in this paper we reconstruct the evolutionary history of santa maria with respect to the timing and magnitude of its vertical movements using detailed field work and 40ar 39ar geochronology our investigations revealed a complex evolutionary history spanning 6 m y with subsidence up to ca 3 5 ma followed by uplift extending to the present day the fact that an island located in young lithosphere experienced a pronounced uplift trend is remarkable and raises important questions concerning possible uplift mechanisms localized uplift in response to the tectonic regime affecting the southeastern tip of the azores plateau is unlikely since the area is under transtension our analysis shows that the only viable mechanism able to explain the uplift is crustal thickening by basal intrusions suggesting that intrusive processes play a significant role even on islands standing on young lithosphere such as in the azores

new insights on the evolution of the linosa volcano sicily channel from the study of its submarine portions abstract linosa island represents the emergent tip of a mostly submarine much wider volcanic edifice with at least 96 of its areal extent lying below sea level marine geological surveys carried out in 2016 and 2017 allowed to reconstruct the submarine portions of linosa and to characterize the main volcanic features providing new unexpected insights on the evolution of this little explored volcanic complex in particular the submarine setting of the nw offshore is represented by a 10 km long volcanic belt punctuated by a number of small eruptive cones appearing more recent with respect to the assumed mid late quaternary age of volcanism on the island this evidence suggests that the growth of the volcanic edifice has likely been more complex than that claimed on the base of subaerial volcanism only and supports a north westward migration of the activity over time the submarine southern flank of the volcanic edifice is also characterized by eccentric eruptive cones but mostly without evidences of recent activity the main processes responsible for the growth and evolution of linosa volcano and their possible relative chronology are discussed in the framework of what previously known on the base of the limited subaerial portions with implications on the potential hazard of the volcanic edifice considered as not active in recent times similarity with the pantelleria volcano located in the nw sicily channel are also evidenced especially for what regards the distribution and morphometric characteristics of eruptive cones occurring in the submarine portions of both islands

gravitational erosional sedimentary and volcanic processes on the submarine environment of selvagens islands madeira archipelago portugal abstract volcanic oceanic islands are the emerged portions of large volcanoes that rise abruptly from the ocean floor although the geological record of these islands provide some insights into the evolution of their entire volcanic edifices for a complete picture it is essential to study the islands submarine pedestals and surrounding settings in this study we document the submarine morphology of the selvagens islands madeira archipelago portugal and relate it with their subaerial evolution in order to gain a more complete insight on the evolutionary history of these islands to this purpose we employed bathymetric surfaces backscatter mosaics and subbottom profiler data integrated with geological observations of the subaerial part of the islands our study reveals the presence of a complex submarine morphology composed mainly of two deeply eroded central volcanoes the edifices of selvagem grande and selvagem pequena and a less eroded saddle like ridge related to a fissural volcanic system located between them other secondary landforms generated by volcanism erosion gravitational collapses and possible faulting activity are also present whilst the building of the two central volcanoes relates to the older volcanic stages of both islands the fissural system with a general ne sw trend is probably contemporaneous of the younger volcanic stages of selvagem grande the shelf of selvagem grande also features the eroded remains of numerous relatively young volcanic cones seemingly forming several nw se and ne sw lineaments the same direction observed onshore for the younger volcanic stage of this edifice the shelves break of both selvagens was affected by multiple landslide scars and channel headwalls the channels constitute a large drainage network that fans out in a radial pattern along the flanks of both central edifices in the deeper parts of this submarine drainage large sediment wave fields are observed in some locations with wavelengths of 300 1 900 m and 2 45 m in height these tend to form cyclic steps that change gradually downslope to antidunes and their origin is attributed to sediment density flows that suffer hydraulic jumps when their channel confinement ends and the slope gradient decreases from 7 to 2 5 several scour features are also found at 3 300 4 000 m water depth being 3 20 km in width 10 20 km in length rectangular or u shaped in cross section and 40 100 m deep they occur around the base of the submarine edifices where seafloor gradients change to 3 0 0 5 their origin is also related to hydraulic jumps of unconfined sediment density flows which are able to erode the seafloor and create these features these morphologies are a testimony to how volcanic erosional and depositional processes conjugate to shape the flanks of a very long lived volcanic island system one of the oldest in the north atlantic ocean

morphology of the faial island shelf azores the interplay between volcanic erosional depositional tectonic and mass wasting processes 1 the extents of volcanic island shelves result from surf erosion which enlarges them and volcanic progradation which reduces them however mass wasting tectonics and sediment deposition also contribute to their morphology in order to assess the relative significance of these various processes we have mapped in detail faial island s shelf in the azores archipelago based on interpretation of geophysical and geological data the nearshore substrates of the island down to 30 50 m depth are rocky and covered by volcaniclastic boulder deposits formed by surf action on now submerged lava flows below those depths sandy and gravel volcaniclastic beds dominate building clinoforms up to the shelf edge in some sectors of the coast prograding lava has narrowed the shelf but in contrast to nearby pico island we find fewer submarine emplaced lavas on the shelf in this island we interpret the distance between the coastline and the shelf edge as almost entirely a result of a straightforward competition between surf erosion and lava progradation in which erosion dominates therefore shelf width can be used as a proxy for coastline age as well as for wave energy exposure the stratigraphy of shelf deposits in boomer seismic data is examined in detail to assess the roles of different sediment sources accommodation space and wave exposure in creating these deposits we also show evidence of mass wasting at the shelf edge and discuss the possible origins of slope instability finally we discuss the contributing role of tectonics for the development of the shelf

reply to comment by marques et al on the insular shelves of the faial pico ridge azores archipelago a morphological record of its evolution

geomorphological evolution of montserrat west indies importance of flank collapse and erosional processes analysis of topography and new swath bathymetry as well as geophysical data provides information about aerial and submarine morphological features and mass transfer processes on montserrat the island has a characteristic shallow c 4000 years ago or the boxing day event during the current eruption 26 december 1997 montserrat9s older volcanic centres the centre hills and silver hills illustrate the third stage of evolution extinction and erosion magma production long term erosion and total sedimentation rates on montserrat have been estimated as 0 17 km 3 ka 1 0 0125 km 3 ka 1 and 0 11 km 3 ka 1 i e 1 1 cm ka 1 respectively

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

morpho bathymetric and seismo stratigraphic analysis of the insular shelf of salina aeolian archipelago to unveil its late quaternary geological evolution abstract the distribution and morphological characteristics of the shelves around salina island have been analyzed and integrated with observations from onshore geological field studies in order to improve knowledge about its evolution and to demonstrate how shelf width depth can be used as proxies for reconstructing the development of the volcanic edifice insular shelves form essentially through marine erosion of volcanic centres during stages of reduced or inactive volcanism and are representative of their original extension shelves having larger widths commonly 1000 m and deeper edges over 125 m depth experienced wave erosion during successive cycles of sea level fluctuations and subsidence after their formation thus being indicative of a relatively older age of the eroded volcanic centres accordingly we document offshore salina the occurrence of presently submerged and largely dismantled volcanic centres namely pizzo capo north and fossa delle felci south predating the oldest subaerial products exposed on the adjacent coastal sectors these offshore centres have subsided after their erosion and are no more documented on land furthermore the finding of the largest and deepest shelf around the subaerial remnants of pizzo di corvo volcanic edifice allows relating it to an earlier stage of evolution of salina shedding light on contradictory radiometric ages on land narrower shelves commonly on the whole our results show the importance of integrated field and marine studies to unravel the geological evolution of insular volcanoes and to obtain inferences on their vertical mobility

a fossil coral perspective on western tropical pacific climate 350 ka 1 the nature of tropical climate variability 350 ka is addressed using 18o and sr ca records from a modern and a fossil coral from vanuatu southwestern tropical pacific ocean modern el nino events at vanuatu produce positive coral 18o and sr ca anomalies similar anomalies observed in the fossil coral records suggest that el nino was operative 350 kyr ago seasonal variations in coral sr ca a sea surface temperature sst proxy have the same amplitude in both corals whereas seasonal 18o variations are smaller in the fossil coral than in the modern coral this is consistent with displacement of the south pacific convergence zone toward the southwest during the boreal summer 350 ka mathematical modeling results preclude warmer sst and higher sss at vanuatu during this time but permit the surface ocean to be 2 c cooler and 0 2 psu fresher than today assessing the potential of variations in late quaternary seawater sr ca remains the largest obstacle to accurately reconstructing tropical sst using pristine fossil corals

evolution of the north flank of tenerife by recurrent giant landslides geomorphologic analysis of submarine and subaerial surface features using a combined topographic bathymetric digital elevation model coupled with onshore geological and geophysical data constrain the age and geometry of giant landslides affecting the north flank of tenerife shaded relief and contour maps and topographic profiles of the submarine north flank permit the identification of two generations of post shield landslides older landslide materials accumulated near the shore 40 km and comprise 700 km3 of debris thickening towards a prominent axis suggests one major landslide deposit younger landslide materials accumulated 40 70 km offshore and comprise the products of three major landslides the la orotava landslide complex the icod landslide and the east dorsal landslide complex each with an onshore scar a proximal submarine trough and a distal deposit lobe estimated lobe volumes are 80 80 and 100 km3 respectively the old post shield landslide scar is an amphitheatre 20 25 km wide partly submarine now completely filled with younger materials age width relationships for tenerife s coastal platform plus onshore geological constraints suggest an age of ca 3 ma for the old collapse young landslides are all less than 560 ka old the la orotava and icod slides involved failures of slabs of subaerial flank to form the subaerial la orotava and icod valleys offshore they excavated troughs by sudden loading and basal erosion of older slide debris the onshore east dorsal slide also triggered secondary failure of older debris offshore the slab like geometry of young failures was controlled by weak layers deep drainage channels and flank truncation by marine erosion the partly submarine geometry of the older amphitheatre reflects the absence of these features relatively low h l ratios for the young slides are attributed to filling of the slope break at the base of the submarine edifice by old landslide materials low aspect ratios of the failed slabs and channelling within troughs post shield landslides on tenerife correlate with major falls in sea level reflecting increased rates of volcanism and coastal erosion and reduced support for the flank landslide head zones have strongly influenced the pattern of volcanism on tenerife providing sites for major volcanic centres

geological evolution of the volcanic island la gomera canary islands from analysis of its geomorphology abstract erosion and landslide processes played an important role in shaping the geomorphology of the canary islands but for the heavily eroded la gomera island those processes have been unclear we conducted an integrated study of its offshore extension onshore geology and links between them in order to determine the geomorphological evolution of the island relative to the rest of the archipelago the characteristics of the island s barrancos and its interfluves have led us to differentiate four types of morphological areas whose fluvial networks are in different stages of evolution those barrancos offshore are interrupted by la gomera s shelf and its erosion has been much greater than for the rest of the canary islands such erosion is both a function of time and varied swell action la gomera s insular slope is carved by a system of submarine canyons and channels that have morphology indicative of turbidity current erosion many of the barrancos onshore and the canyons offshore have steps or knickpoints some are the result of varied resistance to erosion and others are explained by other mechanisms a ridge whose crest is covered by cone like shape structures is interpreted as of volcanic origin with the particularity that it lacks onshore continuation the opposite of what has been observed elsewhere in the canary islands also in contrast with the other islands of the archipelago la gomera s margin does not seem to have resulted from destructive mass wasting and the only offshore sign of catastrophic events are the presence of two embayments along la gomera s northern shelf edge and a lobe structure on the insular apron at 3000 m depth these features may be the remains of the catastrophic failures that took place on the island 9 4 8 7 ma ago alternatively they could be due to recent catastrophic failures on the upper slope due to sediment steeping since the conclusion of the main volcanic activity 4 0 ma ago la gomera has been intensively eroded by gradual fluvial denudation and secondary failures la gomera s insular margin reveals much regarding its evolution but more comprehensive studies including seismic and coring are needed to understand its whole geological history

stratigraphy and significance of brown tuffs on the aeolian islands southern italy abstract brown tuffs bt are volcaniclastic ash deposits prominently represented in the stratigraphic profiles of all the aeolian islands and capo milazzo on the northern coast of sicily detailed stratigraphy and tephrochronology together with available radiometric ages suggest that they were emplaced over a long time interval spanning from the end of the last interglacial period ca 80 ka bp up to 4 5 ka bp age of the overlying punte nere pyroclastic products on vulcano the most complete bt succession is documented on lipari where 14 distinct and successive units are subdivided by the interbedding of widespread tephra layers local volcanic products paleosols and epiclastic deposits and the occurrence of local erosive surfaces inter island occurrence of ischia tephra a widely known tephra layer in the aeolian archipelago dated at 56 ka bp and monte guardia pyroclastics from lipari dated at 22 20 ka bp subdivides the bt succession in upper ubt intermediate ibt and lower bt units lbt which can be correlated at regional level the lbt was emplaced between 80 and 56 ka bp the ibt between 56 and 22 ka bp and the ubt between 20 and 4 5 ka bp on the basis of stratigraphy similarity in lithology and textural features morphology of glass fragments composition and consistency of thickness and grain size variations ubt units correlate with piano grotte dei rossi tuffs on vulcano island they were generated by pulsating hydromagmatic explosive activity giving rise to pyroclastic density currents spreading laterally from a source located inside the la fossa caldera on vulcano island composition is in agreement with this hypothesis since ubt compositional features match those of vulcano magmas erupted in that period the effect of co ignimbrite ash clouds or associated fallout processes from sustained eruptive columns is seen to explain the presence of ubt in areas further away from the suggested source e g salina and lipari islands and capo milazzo the origin of ubt exposed on panarea island is still a matter of debate due to contrasting compositional data due to large uniformity of lithological textural and componentry characters with respect to the ubt the lower portions of the bt succession lbt ibt are considered to be the result of recurrent large scale hydromagmatic eruptions of similar type moreover for the ibt units the correlation with monte molineddo 3 pyroclastics of vulcano island on the basis of lithological compositional and stratigraphic matching again suggests source s related to the vulcano plumbing system and located within the la fossa caldera

late holocene vertical deformation along the coast of pantelleria island sicily channel italy abstract according to historical reports the north eastern coastal sector of the volcanic pantelleria island sicily channel italy was uplifted up to 1 0 m a s l in the year preceding the october 1891 offshore eruptive event to better understand the nature and timing of coastal uplift a detailed survey of morphological and biological indicators of raised palaeo shorelines has been carried out along the island coastline this survey identified raised palaeo shoreline levels at three elevation ranges 2 5 4 2 m a s l highest 1 5 2 7 m a s l intermediate and 0 4 1 0 m a s l lowest radiocarbon dating on samples of corals and vermetids placed tight temporal constraints on the uplifting of the raised shorelines in general they indicate that the north eastern sector of the island centred on the area of cala del gadir has undergone major uplifting tilting the island towards the southwest from 900 years ago applying accurate corrections for sea level variations the total amount of volcano tectonic uplift can be estimated uplift rates up to 5 mm a suggest that the vertical deformation was caused by inflation processes related to magmatic intrusion along feeding fissures

thermal regime of the southeast indian ridge between 88 e and 140 e remarks on the subsidence of the ridge flanks 1 the flanks of the southeast indian ridge are characterized by anomalously low subsidence rates for the 0 25 ma period less than 300 m ma 1 2 between 101 e and 120 e and less than 260 m ma 1 2 within the australian antarctic discordance aad between 120 e and 128 e the expected along axis variation in mantle temperature 50 c is too small to explain this observation even when the temperature dependence of the mantle physical properties is accounted for we successively analyze the effect on subsidence of different factors such as variations in crustal thickness the dynamic contribution of an old detached slab supposedly present within the mantle below the aad and depletion in m a parameter here defined as the ubiquitously distributed melt fraction within the asthenosphere these effects may all contribute to the observed anomalously low subsidence rate of the ridge flanks with the most significant contribution being probably related to the depletion in m however these effects have a deep seated origin that cannot explain the abruptness of the transition across the fracture zones that delineate the boundaries of the aad near 120 e and near 128 e respectively

offshore transport and sand body formation evidence from a steep high energy shoreface southeastern australia abstract elongate shore parallel sand bodies lie on the lower shoreface of the embayed and cliffed coast of central new south wales australia these sand bodies are 10 to 30 m thick extend almost continuously for 40 km parallel to the coast and display a pronounced convexity on the sea floor in profile sediment sampling and detailed seismic reflection and side scan sonar profiling provide evidence that the upper part of these large lobate sand bodies consists chiefly of sand transported downslope from the upper shoreface and surf zone the sand bodies consist entirely of marine sand probably derived locally from retreating embayed beaches and in part from sandstone cliffs channels and sediment lobes oriented normal to the shoreline and internal structure indicate growth by seaward progradation and surface morphology indicates coalescing of lobes and damming of bed load sediment against bed rock ridges in water depths of 70 to 80 m the precise mechanism or mechanisms of seaward transport on the shoreface is unresolved we surmise that during storm events disturbance by large waves and seaward transport by downwelling bottom currents result in sand movement onto and across the sand body surface at depths of 40 to 80 m concurrent modification of the sand bodies by shore parallel processes is suggested by textural trends bed forms and the overall alongshore continuity of the sand bodies