Gorringe Bank Research Articles

Primary production enhancement in a shallow seamount (Gorringe — Northeast Atlantic)

Gorringe bank is a shallow seamount having its summit within the euphotic layer. The purpose of this study was to test the hypothesis that the interaction of ocean currents with shallow water seamounts, as the Gorringe, has a significant effect on local upwelling and primary production. Three hydrographic surveys were carried out: one in autumn (October 2011) and two in summer (June and July 2012). Physical (salinity, temperature), chemical (nutrients, dissolved oxygen, pH, total alkalinity and suspended particulate matter) and biological (chlorophyll, pelagic primary production and phytoplankton composition and abundance) variables were measured and/or determined in the area of Gorringe Bank, in particular over and around the Ormonde and Gettysburg peaks. Multivariate analyses (PCA and MDS) were applied to environmental and phytoplankton data. Statistical analysis of historical satellite and model data was also carried out in order to analyze local hydrographic conditions and to compare sea surface temperature and chlorophyll concentrations over the peaks and off the peaks in different seasons. Pelagic primary production, measured by Dissolved Oxygen methodology, reached values up to 24.10mgCm−3h−1 in the vicinity of the peaks. Phytoplankton abundance ranged from 2.2×103 to 14×103cellsL−1, being the community composed mainly of chain-forming Diatoms like Chaetoceros sp., Dactyliosolen spp., Hemiaulus hauckii and Pseudonitzschia spp., in summer months, in zones of high hydrodynamics of the peaks. By contrast, at locations away of the seamount summits and in autumn, Coccolithophores species reached the same or higher percentage in total abundance than Diatoms, being Discosphaera tubifer and Calcidiscus leptoporus cf. the most abundant species. The combined results indicate the presence of a seasonal effect of Gorringe summits on local upwelling and enhancement of primary production reflected in higher abundance of phytoplankton in the vicinity of the peaks, with emphasis on the Gettysburg, and higher surface chlorophyll concentrations. Therefore, obtained results support the hypothesis of production enhancement.

The Seismicity of Portugal and Its Adjacent Atlantic Region from 1300 to 2014: Maximum Observed Intensity (MOI) Map

In this study, we considered earthquakes with a maximum observed intensity (MOI) Io≥V that occurred throughout the Portuguese mainland and its adjacent Atlantic region to produce the map of maximum intensities of Portugal. This map is based on a wide variety of historical and recent sources, including 175 earthquakes, over the period of 1300–2014. This MOI map allows the regions of high, medium, and low levels of seismic hazard to be highlighted. The entirety of Portugal has been affected by major seismic events, some of which have caused serious damage. In addition, offshore earthquakes have had significant impacts on the coastal cities located in the central and southern regions of the country. Because the southern region of mainland Portugal is more active than the northern region, the largest concentrations of events with Io≥VI are in the southern region, especially on the mainland near the city of Evora, in the Lisbon region, in the Lower Tagus Valley region, and along the Algarve coast, especially in the southwest region in Cape of Sao Vicente and the Gorringe Bank.

The 1755 Lisbon Tsunami at Vila do Bispo Municipality, Portugal

The numerical model of the 1755 Lisbon Tsunami was conducted at Vila do Bispo municipality. The tsunami source area of this historical event is assumed to be on the Gorringe Bank. Numerical model results of historical data have been validated by a combined analysis of eyewitnesses’ accounts, field surveys, geological records and archeological findings (conducted by previous authors). The coastal area has remained a mostly natural landscape since the 18thcentury, with popular beaches that increase the population potentially exposed to a tsunami, especially one occurring in summer. For these reasons, we use local tsunami hazard assessment as a criterion varying between moderate and critical. Results also show that the 16 low ground areas we surveyed were inundated between 15 and 30 minutes after the earthquake. For this reason, persons should act quickly in future to evacuate areas immediately after an earthquake and to move to higher ground. Results also show that safe, swift evacuation may be difficult in 50% of these areas, endangering special populations such as tourists. Tsunami information boards should therefore be put on beaches and evacuation exercises and drills should be implemented and practiced regularly.

The hydrozoan fauna (Cnidaria: Hydrozoa) from the peaks of the Ormonde and Gettysburg seamounts (Gorringe Bank, NE Atlantic).

Twenty-seven species of hydroids were collected from the peaks (35-42 meters depth) of the Gorringe Bank (NE Atlantic) during the oceanographic campaign 'LusoExpedição Olympus 2008'. Twenty-one of these species are new for the Gorringe Bank that now has published records for a total of 37 hydroid species. Lafoeina tenuis, Sertularella ellisii and Clytia hemisphaerica were the most abundant hydroid species collected. Results revealed spatial differences in the composition of species assemblages along the summits of the Gorringe, as only 14 of the species sampled were found both in the Ormonde and Gettysburg seamounts. The large density of algae at the peaks of the seamounts sustain a considerable hydrozoan diversity (23 species), but visibly inhibits the establishment of hydroids to the rocky substrates (only 2 species found). All the known hydrozoan species from the peaks of the Gorringe were exclusively collected during summer, thus sampling in other seasons may reveal further hydrozoan diversity due to seasonal patterns of growth of algae and hydroids. Nevertheless, the reasonably high levels of hydrozoan biodiversity demonstrated only from a small portion the summits of the Gorringe, corroborate its seamounts as 'biodiversity hotspots'. In agreement with previous investigations with shallow-water molluscs and sponges, the shallow-water hydroid fauna of the Gorringe revealed greater biogeographical affinities with the Mediterranean and mainland Portugal. This is the first report of Eudendrium armatum outside of the Mediterranean.

Properties and pathways of Mediterranean water eddies in the Atlantic

Data from ship vertical casts (NODC data-set), ARGO profiling floats (Coriolis data-set) and RAFOS-type neutral density floats (WOCE data-set) are used to study characteristics of meddies in the Northeast Atlantic. In total 241 Mediterranean water eddies (meddies) and 236 parts of float trajectories within meddies are selected for detailed analysis. The results suggest that the meddy generation rate at the southern and southwestern Iberian Peninsula (Portimao Canyon, cap St. Vincent, Estremadura Promontory, Gorringe Bank) is 3 times that at the northwestern Iberian Peninsula (Porto-Aveiro Canyons, Cape Finisterre and Galicia Bank).Meddies generated south of Estremadura Promontory (the southern meddies), as compared to those generated north of it (the northern meddies), have smaller radii, smaller vertical extension, higher aspect ratio, higher Rossby number and higher stability (stronger potential vorticity anomaly). These latter properties result from the southern meddies higher relative vorticity and stronger buoyancy frequency anomaly.Away from the generation regions, meddy drift concentrates along four main paths: three quasi-zonal paths (Northern, Central, Southern) and a path following the African coast (Coastal). The quasi-zonal paths are aligned to the isolines of the ambient potential vorticity field. Several cross-path exchanges, identified in this work, are aligned to topographic rises. Northward translation of the northern meddies within the North Atlantic Current to the subpolar gyre is detected.Within the first 600km from the coast, meddy merger is proved to be a common event. This explains the observed difference in radii between the newly generated meddies and those away from the Iberian margin.The decay of the southern meddies proceeds mainly via the loss of their skirts and does not affect meddy cores until the latest stages. The decay of the northern meddies goes in parallel with the decay of their cores. In average meddy decay is achieved within 1–2years, although may take over 3years. Collisions with the Mid-Atlantic Ridge and seamounts sensibly decrease meddy lifetimes. Meddy decay also speeds up when meddies meet the Azores Current or the North Atlantic Current. A rapid drop in the number of meddies south of the Azores Current proves that it represents a dynamic barrier for weak meddies.

New and little known species of Celleporina Gray, 1848 (Bryozoa, Cheilostomata) from the Atlantic–Mediterranean region

Celleporina parvula, a species present in shallow waters along the NW African coast, is re-described from its original material. Celleporina fragilis, only known from the Canaries, and Celleporina derungsi, from south Portugal, are newly reported from the Gorringe Bank and NW Iberian Peninsula respectively. Two new species are described: Celleporina algarvensis n. sp., from south Portugal, and Celleporina mediterranea n. sp., from NW Mediterranean. The structure of the ooecium and its tabula, and the structure of the frontal wall in the genus Celleporina are discussed in the light of new observations.

Solenogastres (Mollusca) from expeditions off the South Iberian Peninsula, with the description of a new species

The class Solenogastres (sensu Salvini-Plawen, 1967) includes approximately 270 described species, 30% of which can be found off the Atlantic and Mediterranean coasts of Europe. From the Iberian Peninsula, 36 species are known, and six are cited from the Southern Peninsula from Gorringe Bank to Cabo de Gata. The results of a study of a collection of 81 specimens are presented here. Solenogastres were collected from seafloors off the South Iberian Peninsula during three expeditions: DEEPER [Desarrollo de Estudios de Ecosistemas de Profundidad bajo un Enfoque interdisciplinar] 0409, INDEMARES [Inventario y designación en la Red Natura 2000 en áreas marinas del Estado Español]/Chica 0610–0211 and INDEMARES/Alborán 0911. Analysis of the collected solenogaster specimens resulted in the discovery of a new species, which is described here as Alexandromenia avempacensis sp. nov, along with the identification of four already known species: Unciherpia hirsuta Garcia-Alvarez, Salvini-Plawen and Urgorri, 2001, which had not been reported from the South of the Peninsula before and Neomenia carinata Tullberg, 1875, Anamenia gorgonophila (Kowalevsky, 1880) and Dorymenia sarsii (Koren & Danielssen, 1877), whose presence in this area was already known. New anatomical and ecological data regarding these species are also provided. The anatomical reconstruction of the anterior and posterior body ends of Neomenia carinata is presented in addition to a more detailed and extensive description of its copulatory spicules. A broader and more complete description of the sclerites of this species is also provided. The study of the habitus, hard parts and histological sections of Dorymenia sarsii points towards a synonymy between D. sarsii and D. tortilis Scheltema & Schander, 2000. Ecological data related to the accompanying fauna and the type of substratum for each species described is also provided.http://zoobank.org/urn:lsid:zoobank.org:pub:EA987A53-FF5D-463F-A072-0EA99BCDA129

Lost fishing gear and litter at Gorringe Bank (NE Atlantic)

Studies concerning marine litter have received great attention over the last several years by the scientific community mainly due to their ecological and economic impacts in marine ecosystems, from coastal waters to the deep ocean seafloor. The distribution, type and abundance of marine litter in Ormonde and Gettysburg, the two seamounts of Gorringe Bank, were analyzed from photo and video imagery obtained during ROV-based surveys carried out at 60–3015m depths during the E/V Nautilus cruise NA017. Located approximately 125nm southwest of Portugal, Gorringe Bank lays at the crossroad between the Atlantic and the Mediterranean and is therefore characterized by an intense maritime traffic and fishing activities. The high frequency of lost or discarded fishing gear, such as cables, longlines and nets, observed on Gorringe Bank suggests an origin mostly from fishing activities, with a clear turnover in the type of litter (mostly metal, glass and to a much lesser extent, plastic) with increasing depth. Litter was more abundant at the summit of Gorringe Bank (ca. 4items·km−1), decreasing to less than 1item·km−1 at the flanks and to ca. 2items·km−1 at greater depths. Nevertheless, litter abundance appeared to be lower than in continental margin areas. The results presented herein are a contribution to support further actions for the conservation of vulnerable habitats on Gorringe Bank so that they can continue contributing to fishery productivity in the surrounding region.

A new carnivorous sponge,Chondrocladia robertballardisp. nov. (Porifera: Cladorhizidae) from two north-east Atlantic seamounts

Carnivorous sponges (Porifera: Cladorhizidae) are a particularly interesting group of species typically occurring in deep-sea habitats. In this study a new species, Chondrocladia(Chondrocladia)robertballardisp. nov., is described from specimens collected on two large north-east Atlantic seamounts – the Gorringe and Galicia Banks – located off the Iberian Peninsula. The holotype, collected on the Gorringe Bank by ROV, is a large, dichotomously branched and stalked sponge with translucent spheres in the middle of secondary axes and a rhizoid basal fixation system. Direct observations on the habit of the new species were made from the ROV. The paratypes, collected on the Galicia Bank by dredge and trawling, are fragments of different sizes. The skeleton is composed of a single class of styles and isochelae. All specimens were collected at similar depths (1400–1738 m) within the upper bathyal, and at the same longitude but separated by 670 km. A synthesis of the geographic as well as bathymetric distribution of this genus is presented. The species is compared with all known species of this genus worldwide.

In situ observation of chimaerid species in the Gorringe Bank: new distribution records for the north-east Atlantic Ocean

In the framework of the R.V. Nautilus exploration programme, remotely operated vehicle (ROV) surveys were conducted at bathyal depths in the Gorringe Bank. Video transects revealed the presence of the chimaerids Chimaera opalescens and Hydrolagus affinis in the region. An identification key for the north-east Atlantic species of the family Chimaeridae is proposed.

Constraints on the geodynamic evolution of the Africa–Iberia plate margin across the Gibraltar Strait from seismic tomography

Geophysical studies point to a complex tectonic and geodynamic evolution of the Alboran Basin and Gulf of Cadiz. Tomographic images show strong seismic waves velocity contrasts in the upper mantle. The high velocity anomaly beneath the Alboran Sea recovered by a number of studies is now a well established feature. Several geodynamic reconstructions have been proposed also on the base of these images. We present and elaborate on results coming from a recent tomography study which concentrates on both the Alboran and the adjacent Atlantic region. These new results, while they confirm the existence of the fast anomaly below the Alboran region, also show interesting features of the lithosphere-asthenosphere system below the Atlantic. A high velocity body is imaged roughly below the Horseshoe Abyssal plain down to sub-lithospheric depths. This feature suggests either a possible initiation or relic subduction. Pronounced low velocity anomalies pervade the upper mantle below the Atlantic region and separate the lithospheres of the two regions. We also notice a strong change of the upper mantle velocity structure going from south to north across the Gorringe Bank. This variation in structure could be related to the different evolution in the opening of the central and northern Atlantic oceans.

Seismic and gravity constraints on the nature of the basement in the Africa‐Eurasia plate boundary: New insights for the geodynamic evolution of the SW Iberian margin

AbstractWe present a new classification of geological domains at the Africa‐Eurasia plate boundary off SW Iberia, together with a regional geodynamic reconstruction spanning from the Mesozoic extension to the Neogene‐to‐present‐day convergence. It is based on seismic velocity and density models along a new transect running from the Horseshoe to the Seine abyssal plains, which is combined with previously available geophysical models from the region. The basement velocity structure at the Seine Abyssal Plain indicates the presence of a highly heterogeneous, thin oceanic crust with local high‐velocity anomalies possibly representing zones related to the presence of ultramafic rocks. The integration of this model with previous ones reveals the presence of three oceanic domains offshore SW Iberia: (1) the Seine Abyssal Plain domain, generated during the first stages of slow seafloor spreading in the NE Central Atlantic (Early Jurassic); (2) the Gulf of Cadiz domain, made of oceanic crust generated in the Alpine‐Tethys spreading system between Iberia and Africa, which was coeval with the formation of the Seine Abyssal Plain domain and lasted up to the North Atlantic continental breakup (Late Jurassic); and (3) the Gorringe Bank domain, made of exhumed mantle rocks, which formed during the first stages of North Atlantic opening. Our models suggest that the Seine Abyssal Plain and Gulf of Cadiz domains are separated by the Lineament South strike‐slip fault, whereas the Gulf of Cadiz and Gorringe Bank domains appear to be limited by a deep thrust fault located at the center of the Horseshoe Abyssal Plain.

Morphotectonics of the Gorringe Bank summit, eastern Atlantic Ocean, based on high-resolution multibeam bathymetry

High-resolution swath bathymetry of the Gorringe Bank, located along the Europe–Africa obliquely convergent plate boundary offshore SW Portugal, allowed investigation of its shallow-depth morphotectonic structure as a contribution to understanding the interplay of sea-level changes and active deformation of the region. Dominant ENE–WSW to NNE–WSW, and subordinate NW–SE trending morphologic alignments were mapped on the Digital Terrain Model (DTM) built from multibeam data for both the Gettysburg and Ormonde summits of the bank. Based on appraisal of regional structural and seismological data, the dominant and subordinate sets are interpreted to reflect dip-slip to left-oblique reverse faults, and normal faults or dyke-like joints, respectively. Several terrace remnants were mapped on the DTM and were grouped into five orders at depths ranging from ∼40 to ∼120 m. Morphological features suggest that the terraces were formed in a coastal environment likely during Middle–Late Pleistocene sea-level changes. The terraces are probably polycyclic, implying minor vertical tectonic motion. However, the whole terrace set (except the deeper and younger one, which was mainly shaped during the LGM lowstand) is consistently up to ∼10 m lower at Ormonde in the east relative to Gettysburg in the west, suggesting displacement across a NNE–SSW striking fault mapped in the saddle between the two seamounts. The structure assemblage is argued to represent the shallow splay system of a crustal-scale fault ramp underlying the bank. The ENE–WSW reverse faults have a southward polarity and, together with the overall northwest tilt of the bank, point to displacement toward the Horseshoe Abyssal Plain to the south at least at upper crustal levels.

Seismic evidence of exhumed mantle rock basement at the Gorringe Bank and the adjacent Horseshoe and Tagus abyssal plains (SW Iberia)

The Gorringe Bank is a gigantic seamount that separates the Horseshoe and Tagus abyssal plains offshore SW Iberia, in a zone that hosts the convergent boundary between the Africa and Eurasia plates. Although the region has been the focus of numerous investigations since the early 1970s, the lack of appropriate geophysical data makes the nature of the basement, and thus the origin of the structures, still debated. In this work, we present combined P-wave seismic velocity and gravity models along a transect that crosses the Gorringe Bank from the Tagus to the Horseshoe abyssal plains. The P-wave velocity structure of the basement is similar in the Tagus and Horseshoe plains. It shows a 2.5–3.0km-thick top layer with a velocity gradient twice stronger than oceanic Layer 2 and an abrupt change to an underlying layer with a five-fold weaker gradient. Velocity and density is lower beneath the Gorringe Bank probably due to enhanced fracturing, that have led to rock disaggregation in the sediment-starved northern flank. In contrast to previous velocity models of this region, there is no evidence of a sharp crust–mantle boundary in any of the record sections. The modelling results indicate that the sediment overlays directly serpentinite rock, exhumed from the mantle with a degree of serpentinization decreasing from a maximum of 70–80% under the top of Gorringe Bank to less than 5% at a depth of ∼20km. We propose that the three domains were originally part of a single serpentine rock band, of nature and possibly origin similar to the Iberia Abyssal Plain ocean–continent transition, which was probably generated during the earliest phase of the North Atlantic opening that followed continental crust breakup (Early Cretaceous). During the Miocene, the NW–SE trending Eurasia–Africa convergence resulted in thrusting of the southeastern segment of the exhumed serpentinite band over the northwestern one, forming the Gorringe Bank. The local deformation associated to plate convergence and uplift could have promoted pervasive rock fracturing of the overriding plate, leading eventually to rock disaggregation in the northern flank of the GB, which could be now a potential source of rock avalanches and tsunamis.

Notes on a mating event of the deep-sea crab Chaecon affinis in the Gorringe Bank (NE Atlantic)

The deep-water red crab Chaceon affinis is the largest species of the family Geryonidae. Unlike other species of the same genus, C. affinis is not yet subject to intense commercial exploitation but it has been appointed as a new target resource in European waters, in spite of the lack of information on its biology, life cycle and distribution, which is essential to provide advice for a sustainable exploitation. Here we report for the first time the presence of C. affinis in the Gorringe Bank and give the first account of the mating behavior of this species. All mating pairs were found at the interface of the Mediterranean Outflow Water with North Atlantic Deep Water, suggesting that environmental parameters associated with the interface of these water masses may be relevant for mating in this species. The majority of C. affinis was mating which is an indication of synchrony and reproductive seasonality. A biennial female reproductive cycle is hypothesized, involving molting and mating in the first year with subsequent oviposition during the autumn, and spawning during spring of the second year. We suggest that synchrony and seasonality in the reproduction of C. affinis is linked to the formation of phytoplankton blooms in surface waters, with females carrying embryos from autumn to spring, possibly timing the release of planktotrophic larvae to exploit a seasonal peak in surface productivity and its export.

A complex picture of associations between two host mussels and symbiotic bacteria in the Northeast Atlantic

Among chemosymbiotic metazoans found at deep-sea hydrothermal vents, cold seeps and organic falls, members of the mussel clade Bathymodiolinae (Bivalvia: Mytilidae) have evolved interactions with a higher diversity of bacterial lineages than other bivalve groups. Here, we characterized the bacteria associated with "Bathymodiolus" mauritanicus and Idas-like specimens from three sites in the Northeast Atlantic (two mud volcanoes in the Gulf of Cadiz and one seamount of the Gorringe Bank). Phylogenetic analysis of bacterial 16S rRNA-encoding gene sequences demonstrated that "B". mauritanicus has a dual symbiosis dominated by two phylotypes of methane-oxidising bacteria and a less abundant phylotype of a sulphur-oxidising bacterium. The latter was the dominant phylotype in a sympatric population of Idas-like mussels at the Darwin mud volcano. These results are the first report of a bacterial phylotype shared between two deep-sea mussels from divergent clades. This sulphur-oxidising bacterium was absent from Idas-like specimens from the other two sites (Gorringe Bank and Meknès mud volcano), in which bacterial clone libraries were dominated by other Gammaproteobacteria related to symbionts previously identified in Idas modiolaeformis from the Eastern Mediterranean. All Idas-like specimens studied herein are closely related and also related to I. modiolaeformis. However, they probably display different associations with bacteria, with the possible absence of both methane- and sulphur-oxidising symbionts at the Gorringe Bank. These results draw a very complex picture of associations between mussels and bacteria in the Northeast Atlantic, which could be highly variable depending on locale characteristics of the habitats.

The earthquakes of 29 July 2003, 12 February 2007, and 17 December 2009 in the region of Cape Saint Vincent (SW Iberia) and their relation with the 1755 Lisbon earthquake

The Cape Saint Vincent region is of major seismological interest for its tectonic complexity and for the occurrence of the great 1755 Lisbon earthquake. No structure capable of generating such a large earthquake has yet been convincingly identified, but all authors agree that there is a possibility of a similar earthquake occurring offshore of the Cape sometime in the future. To shed some light on the region's dynamics, we here examine the mechanism of the three largest earthquakes to have occurred in the last 40years west of the Cape – 29 July 2003 (Mw=5.3), 12 February 2007 (Mw=6.1), and 17 December 2009 (Mw=5.5). By inversion of the body waves and the kinematic slip distribution, we estimated the three earthquakes to have had similar characteristics (dimensions, maximum slip, stress drop, source time function, focal depth, and rupture velocity), although there were differences in the geometry of the rupture that reflect the great seismotectonic complexity of the zone. The focal mechanisms of the 2003 and 2007 earthquakes were similar, corresponding to thrusting motion, but the 2009 earthquake had a dip-slip motion in a vertical plane. As deduced from the slip distributions, the three shocks show NE–SW rupture planes, with the energy released propagating to the NE, compatible with the regional NW–SE horizontal compression produced by the convergence of the Eurasian and African plates. Applied to the generation of the 1755 Lisbon earthquake, this direction of faulting would correspond to a complex rupture along NE–SW trending thrust faults at the Gorringe Bank, the Horseshoe Scarp, and the Marquis de Pombal Fault, with the rupture propagating to the NE towards the Portuguese coast. Such a model could explain that unusually large and tsunami-generating earthquake.

Two types of alkaline volcanics in the southwestern Iberian margin: The causes of their diversity

The diverse geodynamic conditions of the parental magma’s melting are responsible for the compositional diversity of the alkaline volcanics near the southwestern margin of Iberia. The petrological-geochemical data show that the volcanics of the Gorringe Bank originated within the continental plate. The parental melilitite melts depleted in silica and anomalously enriched with trace elements could have been generated only in deep settings with a low degree of metasomatically enriched mantle matter melting. The volcanic melilitite-nephelinite-phonolite series is widespread in alkaline provinces of the Eurasian, African, and other continental plates. The Ampere, Josephine, and other seamounts and islands of the region are largely composed of volcanic rocks belonging to the picrobasalt-hawaiite-mugearite association. Their parental magmas were generated within the oceanic plate at shallower depths under a higher degree of moderately enriched oceanic lithospheric mantle melting. Both series of volcanics were formed under the influence of mantle plumes.

Large, deepwater slope failures: Implications for landslide-generated tsunamis

Research Article| October 01, 2012 Large, deepwater slope failures: Implications for landslide-generated tsunamis Claudio Lo Iacono; Claudio Lo Iacono * 1Unidad de Tecnología Marina, CSIC, 08003 Barcelona, Spain2National Oceanography Centre, Southampton SO14 3ZH, UK *E-mails: loiacono@utm.csic.es; cllo@noc.ac.uk. Search for other works by this author on: GSW Google Scholar Eulàlia Gràcia; Eulàlia Gràcia 1Unidad de Tecnología Marina, CSIC, 08003 Barcelona, Spain Search for other works by this author on: GSW Google Scholar Filippo Zaniboni; Filippo Zaniboni 3Universitá di Bologna, Departimento di Fisica e Astronomia, 40127 Bologna, Italy Search for other works by this author on: GSW Google Scholar Gianluca Pagnoni; Gianluca Pagnoni 3Universitá di Bologna, Departimento di Fisica e Astronomia, 40127 Bologna, Italy Search for other works by this author on: GSW Google Scholar Stefano Tinti; Stefano Tinti 3Universitá di Bologna, Departimento di Fisica e Astronomia, 40127 Bologna, Italy Search for other works by this author on: GSW Google Scholar Rafael Bartolomé; Rafael Bartolomé 1Unidad de Tecnología Marina, CSIC, 08003 Barcelona, Spain Search for other works by this author on: GSW Google Scholar Douglas G. Masson; Douglas G. Masson 2National Oceanography Centre, Southampton SO14 3ZH, UK Search for other works by this author on: GSW Google Scholar Russell B. Wynn; Russell B. Wynn 2National Oceanography Centre, Southampton SO14 3ZH, UK Search for other works by this author on: GSW Google Scholar Nuno Lourenço; Nuno Lourenço 4Estrutura de Missão para a Extensão da Plataforma Continental, P-2770047 Paco De Arcos, Portugal Search for other works by this author on: GSW Google Scholar Manuel Pinto de Abreu; Manuel Pinto de Abreu 4Estrutura de Missão para a Extensão da Plataforma Continental, P-2770047 Paco De Arcos, Portugal Search for other works by this author on: GSW Google Scholar Juan José Dañobeitia; Juan José Dañobeitia 1Unidad de Tecnología Marina, CSIC, 08003 Barcelona, Spain Search for other works by this author on: GSW Google Scholar Nevio Zitellini Nevio Zitellini 5Istituto di Scienze Marine, CNR, 40129 Bologna, Italy Search for other works by this author on: GSW Google Scholar Author and Article Information Claudio Lo Iacono * 1Unidad de Tecnología Marina, CSIC, 08003 Barcelona, Spain2National Oceanography Centre, Southampton SO14 3ZH, UK Eulàlia Gràcia 1Unidad de Tecnología Marina, CSIC, 08003 Barcelona, Spain Filippo Zaniboni 3Universitá di Bologna, Departimento di Fisica e Astronomia, 40127 Bologna, Italy Gianluca Pagnoni 3Universitá di Bologna, Departimento di Fisica e Astronomia, 40127 Bologna, Italy Stefano Tinti 3Universitá di Bologna, Departimento di Fisica e Astronomia, 40127 Bologna, Italy Rafael Bartolomé 1Unidad de Tecnología Marina, CSIC, 08003 Barcelona, Spain Douglas G. Masson 2National Oceanography Centre, Southampton SO14 3ZH, UK Russell B. Wynn 2National Oceanography Centre, Southampton SO14 3ZH, UK Nuno Lourenço 4Estrutura de Missão para a Extensão da Plataforma Continental, P-2770047 Paco De Arcos, Portugal Manuel Pinto de Abreu 4Estrutura de Missão para a Extensão da Plataforma Continental, P-2770047 Paco De Arcos, Portugal Juan José Dañobeitia 1Unidad de Tecnología Marina, CSIC, 08003 Barcelona, Spain Nevio Zitellini 5Istituto di Scienze Marine, CNR, 40129 Bologna, Italy *E-mails: loiacono@utm.csic.es; cllo@noc.ac.uk. Publisher: Geological Society of America Received: 22 Mar 2012 Accepted: 23 Apr 2012 First Online: 09 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 © 2012 Geological Society of America Geology (2012) 40 (10): 931–934. https://doi.org/10.1130/G33446.1 Article history Received: 22 Mar 2012 Accepted: 23 Apr 2012 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Claudio Lo Iacono, Eulàlia Gràcia, Filippo Zaniboni, Gianluca Pagnoni, Stefano Tinti, Rafael Bartolomé, Douglas G. Masson, Russell B. Wynn, Nuno Lourenço, Manuel Pinto de Abreu, Juan José Dañobeitia, Nevio Zitellini; Large, deepwater slope failures: Implications for landslide-generated tsunamis. Geology 2012;; 40 (10): 931–934. doi: https://doi.org/10.1130/G33446.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Deepwater landslides are often underestimated as potential tsunami triggers. The North Gorringe avalanche (NGA) is a large (∼80 km3 and 35 km runout) newly discovered and deepwater (2900 m to 5100 m depth) mass failure located at the northern flank of Gorringe Bank on the southwest Iberian margin. Steep slopes and pervasive fracturing are suggested as the main preconditioning factors for the NGA, while an earthquake is the most likely trigger mechanism. Near-field tsunami simulations show that a mass failure similar to the NGA could generate a wave >15 m high that would hit the south Portuguese coasts in ∼30 min. This suggests that deepwater landslides require more attention in geo-hazard assessment models of southern Europe, as well as, at a global scale, in seismically active margins. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Melilitites in the alkaline volcanic succession of the Gorringe bank, Southwestern Portugal

Melilitites were found for the first time in the alkaline volcanics of the Gorringe bank. With allowance for previous studies, this indicates the existence of a common melilitite-nephelinite-phonolite alkaline series, which is widely spread as lava fields, dikes, and diatremes in the continental magmatic provinces of Europe, Africa, Asia, and America, often accompanying the formation of carbonatite complexes. This is considered as one of the evidence in support of the continental nature of the alkaline volcanism of the bank. The fact that the volcanics contain fragments of plutonic rocks, which are usually observed in the carbonatitebearing alkaline complexes (melteigites, ijolites, nepheline syenites), makes it possible to suggest the presence of alkaline intrusions of such type at a shallow depth.