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  • 1
    In: Sedimentology, Wiley, Vol. 68, No. 4 ( 2021-06), p. 1400-1438
    Abstract: 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 〈 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.
    Type of Medium: Online Resource
    ISSN: 0037-0746 , 1365-3091
    URL: Issue
    RVK:
    Language: English
    Publisher: Wiley
    Publication Date: 2021
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  • 2
    In: Journal of Quaternary Science, Wiley, Vol. 23, No. 8 ( 2008-12), p. 777-785
    Type of Medium: Online Resource
    ISSN: 0267-8179 , 1099-1417
    URL: Issue
    Language: English
    Publisher: Wiley
    Publication Date: 2008
    detail.hit.zdb_id: 2031875-3
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  • 3
    In: Sedimentology, Wiley, Vol. 67, No. 7 ( 2020-12), p. 3595-3618
    Abstract: Sedimentary rocks are rarely preserved on reefless volcanic oceanic islands because their sediments are mostly exported from coastal areas towards the deep sea and such islands typically undergo subsidence. In contrast, the exceptional geological record of the uplifted Santa Maria Island (Azores) provides a unique opportunity to gain insight on such coastal systems. This study focuses on a locality at Ponta do Cedro (eastern Santa Maria Island), which features a series of marine fossiliferous sediments wedged between steep lava deltas. As demonstrated by local structure, these sediments correspond to clinoforms deposited on the steep submarine slope of an active volcanic island, implying transport from shallow waters to greater depths and subsequent colonization by benthic communities. Rapid volcanic progradation eventually sealed the deposits, allowing for their preservation and providing a rare snapshot of the ecology during those intervals, in addition to insights on sedimentary dynamics along submarine island slopes. This study reveals spatial relationships between wedges of sedimentary bodies encapsulated by lavas in the Ponta do Cedro section, and interprets depositional processes preserved in those strata based on sedimentological and palaeontological data. The dynamics of the environment are mostly related to relative sea‐level changes, intense volcanic activity and regional uplift during the Neogene.
    Type of Medium: Online Resource
    ISSN: 0037-0746 , 1365-3091
    URL: Issue
    RVK:
    Language: English
    Publisher: Wiley
    Publication Date: 2020
    detail.hit.zdb_id: 2020955-1
    detail.hit.zdb_id: 206889-8
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  • 4
    In: Sedimentology, Wiley, Vol. 69, No. 4 ( 2022-06), p. 1547-1572
    Abstract: Formulae for sediment thresholds of motion are commonly based on flume experiments on rounded quartz particles and it is unclear how well they predict thresholds in natural settings. Here, sediment threshold shear stresses were calculated from one such formula using surface grain‐size data from 112 sites around Santa Maria Island, Azores. To compare with those stresses, a Simulating Waves Nearshore model was run for three typical winter months to predict shelf stress maxima due to waves. As wind‐driven and other circulations also increase stresses, the model predictions are under‐estimates. Comparison of the two stress estimates suggests that the whole shelf of the island was mobile during extreme conditions. However, three forms of evidence contradict this. First, 129 rollovers of sandy clinoforms lying in 30 to 200 m water depths around the island were identified from boomer seismic data. It has been suggested that such rollovers mark depths at which hydrodynamic stresses fall beneath the sediment threshold of motion. Second, differences in grain‐size diversity between carbonate‐free and whole sediment indicate where carbonate particle fragmentation occurs. Third, seabed images reveal variations in ripple character and presence. The combined data suggest that deposition has occurred in the middle and outer shelf, overlapping where the model predicts sediment mobilization. However, by decreasing the model bottom shear stress or increasing the shear stress at threshold of motion by a factor of two to three, deposition is predicted to have occurred immediately deeper than the shallow active rollovers. Therefore, in practice, the ratio of wave‐imposed shear stress to stress at threshold of motion is two to three times smaller than predicted. This is speculated to be due to the presence of widespread hard substrates and other features shielding particles between them from wave stresses. Alternatively, the threshold of motion is higher than expected from the formulae for these sediments dominated by bioclastic particles.
    Type of Medium: Online Resource
    ISSN: 0037-0746 , 1365-3091
    URL: Issue
    RVK:
    Language: English
    Publisher: Wiley
    Publication Date: 2022
    detail.hit.zdb_id: 2020955-1
    detail.hit.zdb_id: 206889-8
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  • 5
    In: Biological Reviews, Wiley, Vol. 94, No. 3 ( 2019-06), p. 1116-1142
    Abstract: A synthetic model is presented to enlarge the evolutionary framework of the General Dynamic Model (GDM) and the Glacial Sensitive Model (GSM) of oceanic island biogeography from the terrestrial to the marine realm. The proposed ‘Sea‐Level Sensitive’ dynamic model (SLS) of marine island biogeography integrates historical and ecological biogeography with patterns of glacio‐eustasy, merging concepts from areas as diverse as taxonomy, biogeography, marine biology, volcanology, sedimentology, stratigraphy, palaeontology, geochronology and geomorphology. Fundamental to the SLS model is the dynamic variation of the littoral area of volcanic oceanic islands (defined as the area between the intertidal and the 50‐m isobath) in response to sea‐level oscillations driven by glacial–interglacial cycles. The following questions are considered by means of this revision: ( i ) what was the impact of (global) glacio‐eustatic sea‐level oscillations, particularly those of the Pleistocene glacial–interglacial episodes, on the littoral marine fauna and flora of volcanic oceanic islands? ( ii ) What are the main factors that explain the present littoral marine biodiversity on volcanic oceanic islands? ( iii ) How can differences in historical and ecological biogeography be reconciled, from a marine point of view? These questions are addressed by compiling the bathymetry of 11 Atlantic archipelagos/islands to obtain quantitative data regarding changes in the littoral area based on Pleistocene sea‐level oscillations, from 150 thousand years ago (ka) to the present. Within the framework of a model sensitive to changing sea levels, we discuss the principal factors affecting the geographical range of marine species; the relationships between modes of larval development, dispersal strategies and geographical range; the relationships between times of speciation, modes of larval development, ecological zonation and geographical range; the influence of sea‐surface temperatures and latitude on littoral marine species diversity; the effect of eustatic sea‐level changes and their impact on the littoral marine biota; island marine species–area relationships; and finally, the physical effects of island ontogeny and its associated submarine topography and marine substrate on littoral biota. Based on the SLS dynamic model, we offer a number of predictions for tropical, subtropical and temperate volcanic oceanic islands on how rates of immigration, colonization, in‐situ speciation, local disappearance, and extinction interact and affect the marine biodiversity around islands during glacials and interglacials, thus allowing future testing of the theory.
    Type of Medium: Online Resource
    ISSN: 1464-7931 , 1469-185X
    URL: Issue
    Language: English
    Publisher: Wiley
    Publication Date: 2019
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  • 6
    In: Sedimentology, Wiley, Vol. 60, No. 7 ( 2013-12), p. 1769-1785
    Abstract: Oceanic islands – such as the Azores in the mid‐North Atlantic – are periodically exposed to large storms that often remobilize and transport marine sediments along coastlines, and into deeper environments. Such disruptive events create deposits – denominated tempestites – whose characteristics reflect the highly dynamic environment in which they were formed. Tempestites from oceanic islands, however, are seldom described in the literature and little is known about storm‐related sediment dynamics affecting oceanic island shelves. Therefore, the geological record of tempestite deposits at oceanic islands can provide invaluable information on the processes of sediment remobilization, transport and deposition taking place on insular shelves during and after major storms. In Santa Maria Island (Azores), a sequence of Neogene tempestite deposits was incorporated in the island edifice by the ongoing volcanic activity (thus preserved) and later exposed through uplift and erosion. Because it was overlain by a contemporary coastal lava delta, the water depth at the time of deposition could be inferred, constituting an excellent case‐study to gain insight on the still enigmatic processes of insular shelf deposition. Sedimentological, palaeontological, petrographic and palaeo‐water depth information allowed the reconstruction of the depositional environment of these sediments. The sequence typifies the characteristics of a tempestite (or successive tempestites) formed at ca 50 m depth, in a steep, energetic open insular shelf, and with evidence for massive sediment remobilization from the nearshore to the middle or outer shelf. The authors claim that cross‐shelf transport induced by storm events is the main process of sediment deposition acting on steep and narrow shelves subjected to high‐energetic environments, such as the insular shelves of open‐sea volcanic islands.
    Type of Medium: Online Resource
    ISSN: 0037-0746 , 1365-3091
    URL: Issue
    RVK:
    Language: English
    Publisher: Wiley
    Publication Date: 2013
    detail.hit.zdb_id: 2020955-1
    detail.hit.zdb_id: 206889-8
    SSG: 13
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  • 7
    Online Resource
    Online Resource
    Wiley ; 2019
    In:  Earth Surface Processes and Landforms Vol. 44, No. 15 ( 2019-12), p. 2982-3006
    In: Earth Surface Processes and Landforms, Wiley, Vol. 44, No. 15 ( 2019-12), p. 2982-3006
    Abstract: Erosion of volcanic islands ultimately creates shallow banks and guyots, but the ways in which erosion proceeds to create them over time and how the coastline retreat rate relates to wave conditions, rock mass strength and other factors are unclear. The Capelinhos volcano was formed in 1957/58 during a Surtseyan and partly effusive eruption that added an ~2.5 km 2 tephra and lava promontory to the western end of Faial Island (Azores, central North Atlantic). Subsequent coastal and submarine erosion has reduced the subaerial area of the promontory and created a submarine platform. This study uses historical information, photos and marine geophysical data collected around the promontory to characterize how the submarine platform developed following the eruption. Historical coastline positions are supplemented with coastlines interpreted from 2004 and 2014 Google Earth images in order to work out the progression of coastline retreat rate and retreat distance for lava‐ and tephra‐dominated cliffs. Data from swath mapping sonars are used to characterize the submarine geometry of the resulting platform (position of the platform edge, gradient and morphology of the platform surface). Photographs collected during SCUBA and ROV dives on the submarine platform reveal a rugged surface now covered with boulders. The results show that coastal retreat rates decreased rapidly with time after the eruption and approximately follow an inverse power‐law relationship with coastal retreat distance. We develop a finite‐difference model for wave attenuation over dipping surfaces to predict how increasing wave attenuation contributed to this trend. The model is verified by reproducing the wave height variation over dipping rock platforms in the UK (platform gradient 1.2° to 1.8°) and Ireland (1.8°). Applying the model to the dipping platform around Capelinhos, using a diversity of cliff resistance predicted from known lithologies, we are able to predict erosion rate trends for some sectors of the edifice. We also explore wider implications of these results, such as how erosion creates shallow banks and guyots in reef‐less mid‐oceanic archipelagos like the Azores. © 2019 John Wiley & Sons, Ltd. © 2019 John Wiley & Sons, Ltd.
    Type of Medium: Online Resource
    ISSN: 0197-9337 , 1096-9837
    URL: Issue
    Language: English
    Publisher: Wiley
    Publication Date: 2019
    detail.hit.zdb_id: 1479188-2
    SSG: 14
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