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The Madeira Island lower slope has been build-up mostly by along slope-processes associated with mass movement deposits as seen in GEBCO bathymetry, multibeam bathymetry, Parasound echosounder profiles and multichannel seismic reflection profiles. A plastered contourite drift (Madeira Drift) developed on this lower slope, being composed of seismic units D1, D2 and D3. The most probable water mass responsible for its deposition is the Antarctica Bottom Water (AABW). The youngest sediments of seismic units D2 and D3 are affected by gravity-driven processes, probably slumps and debris flows, which moved downslope towards west. Parasound profiles show evidences of such mass movements on present-day seabottom (e.g. diffraction hyperbolae echoes) but also of past-events buried within the contourite sediments. These older debris flows are recognized by semitransparent/transparent acoustic facies and lenticular shape. Versión del editor

[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. published

3 3 pp DHA/NEC 2011 3 - 4 de Fevereiro

Bathymetry data collected with a multibeam echo sounder around Pico Island, Azores (Portugal), reveal a remarkable series of lava flows on the island's shelf with a variety of pristine structures that suggest how lava behaves on entering water. Many flows are dendritic in plan view, some with channels and tumuli. Dendritic geometries are interpreted to arise from flow fronts repeatedly arrested by enhanced cooling and magma pressure subsequently causing new breakouts. Cascades of elongated flow fingers also occur, with individual fingers of comparable diameters to the largest known megapillows. Some flows have wide transverse clefts, in cases separating flows into segments, which are interpreted as caused by their upper surfaces having solidified, while their still-fluid cores allowed the surfaces to extend. A number of flows moved onto the shelf as large bodies, stopped, and then sourced smaller lobes forming the dendritic patterns. This two-stage evolution and the tumuli (which lie on a low gradient immediately below a steep nearshore gradient) suggest that, after initial emplacement and development of a crust by cooling, some flows pressurized. Once movements ceased and viscous stresses dissipated, magma static pressure developed from the weight of flow interiors passing over cliffs and nearshore gradients. One group of flows traverses the island's submarine slope, so direct supply of lava to the slopes is possible, although volumetrically how important it is to the island's internal composition is difficult to tell from these data. On the basis of observed strong surf erosion of historical flows, these delicate structures probably could not have survived passage through a moving sea level unmodified by erosion so they are unlikely to be pre-Holocene subaerial flows. They are interpreted to have formed in the Holocene from flows penetrating sea level or possibly some from nearshore tube openings or vents. Such flows and abundant clastic deposits are ephemeral features that become remobilized by surf during times of lower sea level. The shelves of active volcanic islands are therefore active geologically and are far from being simple products of erosional truncation as was once envisaged. Mitchell, Neil C. Beier, Christoph Rosin, Paul L. Quartau, Rui Tempera, Fernando 153 AMER GEOPHYSICAL UNION WASHINGTON 281XH

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. 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

Located on the northern coast of Santa Maria Island (Azores Archipelago, central North Atlantic), the Lagoinhas section preserves a carbonate buildup correlated with Marine Isotope Substage (MIS) 5e, the warmest interval of the Last Interglacial. The buildup is formed mainly by crustose coralline algae (CCA) identified as Spongites sp., and some subordinate crusts of Lithophyllum sp. and Neogoniolithon sp., as well as cf. Titanoderma sp. Extant CCA buildups are not recorded in the archipelago. Herein, we describe in detail the morphological and taphonomical features of the Lagoinhas CCA buildup and interpret the environment in which it grew. Additionally, this buildup is compared with another of similar age, exposed in the Prainha-Praia do Calhau section on the island's opposite southern coast. The hydrodynamic regime appears to play a crucial role in the development of Azorean CCA buildups during the MIS 5e. We thank Direccao Regional da Ciência e Tecnologia (Regional Government of the Azores), FCT (Fundação para a Ciência e a Tecnologia) of the Portuguese Government, and Camara Municipal de Vila do Porto for financial support. We also acknowledge the field assistance of Camara Municipal de Vila do Porto. We are grateful to the organizers and participants of the 16 editions of the International Workshop Palaeontology in Atlantic Islands who helped with fieldwork (2002 2020). A.C.R. was supported by a grant SFRH/BPD/117810/2016 from FCT (Fundação para Ciência e Tecnologia), Portugal. S.P.A. and R.S.R. acknowledge their research contracts (IF/00465/2015 and IF/01641/2015, respectively) funded by Fundação para a Ciência e a Tecnologia (FCT). C.S.M. is benefiting from a PhD grant M3.1.a/F/100/2015 from Fundo Regional para a Ciência e Tecnologia (FRCT). This work was supported by FEDER funds through the Operational Programme for Competitiveness Factors -COMPETE, by Portuguese National Funds through FCT under the projects UID/BIA/50027/2013, UID/BIA/00329/2013-2023, POCI-01-0145-FEDER-006821, PLATMAR (PTDC/GEO-GEO/0051/2014) and under DRCT-M1.1.a/005/Funcionamento-C-/2016 (CIBIO-A) project from FRCT, and by FEDER funds (in 85%) and by funds of the Regional Government of the Azores (15%) trough Programa Operacional Acores 2020, in the scope of the projects "AZORESBIOPORTAL -PORBIOTA": ACORES-01-0145FEDER-000072 and VRPROTO -Virtual Reality PROTOtype: the geological history of "Pedra-que-pica": ACORES-01-0145-FEDER000078. A.U. benefited from additional support by the Jagiellonian University. info:eu-repo/semantics/publishedVersion

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 < 1000 m) indicate a lower evolutionary maturity with respect to the larger ones; they are, in fact, formed along the sectors of the island where younger volcanic products are exposed, such as to the north and south of Monte dei Porri. The depths of the shelf edges, mostly at - 110 m (in the areas not affected by later mass-wasting), suggest that these coastal sectors were relatively stable or even slightly uplifted after erosion during Last Glacial Maximum. Moreover, several interacting factors (such as lithology of volcanic products, fetch and exposure to prevailing storms, degree of submarine erosion, relative sea level changes) have been taken into account to explain the morphological setting of the different shelf and coastal sectors of Salina. 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.

19 pages, 12 figures, 2 tables, supplementary material http://dx.doi.org/10.1007/s00445-015-0905-3, Terceira Island, in the Azores Archipelago, lies at the intersection of four submarine volcanic ridges. New high-resolution bathymetric and seismic reflection data have been used to analyze the main volcanic, tectonic and mass-wasting features of the island offshore. Volcanic features such as linear volcanic centers, and pointy and flat-topped cones are mainly concentrated on the narrow western and north-western ridges, characterized by an overall rugged morphology. Fault scarps dominate mainly the broad eastern and south-eastern ridges, which are characterized by an overall smooth and terrace-like morphology. On the eastern ridge, faults form a series of horsts and grabens related to the onshore Lajes Graben. The strikes of the fault scarps, linear volcanic centers and alignment of volcanic cones on the ridges reveal two main structural trends, WNW–ESE and NNW–SSE, consistent with the main tectonic structures observed on the Azores Plateau. In contrast, a large variability of strike was observed in inter-ridge areas, reflecting the relative importance of regional and local stresses in producing these structures. Mass-wasting features are subordinate and mostly represented by hundred meter-wide scars that indent the edge of the insular shelf surrounding the island, apart from two large, deeper scars identified on the southern steep flank of the western ridge. Finally, the remarkable morpho-structural differences between the western and eastern ridges are discussed in the framework of the evolution of the Terceira volcanic edifice and hypothesized to reflect successive stages of ridge evolution. © 2015, Springer-Verlag Berlin Heidelberg, Data acquisiton was conducted within the framework of the project >Features of Azores and Italian Volcanic Islands (FAIVI)>, supported by the European Commission 7th Framework Programme under EUROFLEETS grant agreement no. 228344

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.