The morphology of insular shelves as a key for understanding the geological evolution of volcanic islands: Insights from Terceira Island (Azores)
01 May 2014-Geochemistry Geophysics Geosystems (John Wiley & Sons, Ltd)-Vol. 15, Iss: 5, pp 1801-1826
TL;DR: In this paper, the authors used bathymetry and high-resolution seismic reflection profiles 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.
Abstract: 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.
Citations
More filters
University of Cape Verde1, University of Vigo2, University of Lisbon3, Instituto Superior de Agronomia4, University of the Azores5, University of Las Palmas de Gran Canaria6, University of the Algarve7, University of La Laguna8, Universidade Federal de Santa Catarina9, Université libre de Bruxelles10, Staatliches Museum für Naturkunde Stuttgart11, University of Porto12, Williams College13
TL;DR: All marine groups studied suggest the exclusion of Cabo Verde from the remaining Macaronesian archipelagos and thus, CaboVerde should be given the status of a biogeographic subprovince within the West African Transition province.
Abstract: The Azores, Madeira, Selvagens, Canary Islands and Cabo Verde are commonly united under the term “Macaronesia”. This study investigates the coherency and validity of Macaronesia as a biogeographic unit using six marine groups with very different dispersal abilities: coastal fishes, echinoderms, gastropod molluscs, brachyuran decapod crustaceans, polychaete annelids, and macroalgae. We found no support for the current concept of Macaronesia as a coherent marine biogeographic unit. All marine groups studied suggest the exclusion of Cabo Verde from the remaining Macaronesian archipelagos and thus, Cabo Verde should be given the status of a biogeographic subprovince within the West African Transition province. We propose to redefine the Lusitanian biogeographical province, in which we include four ecoregions: the South European Atlantic Shelf, the Saharan Upwelling, the Azores, and a new ecoregion herein named Webbnesia, which comprises the archipelagos of Madeira, Selvagens and the Canary Islands.
119 citations
01 Apr 2012
TL;DR: In this paper, a multi-disciplinary study of the successive stages of development of Faial (Azores) during the last 1 Myr is presented, using high-resolution digital elevation model (DEM), and new K/Ar, tectonic, and magnetic data, in response to complex interactions between volcanic construction and mass wasting, including the development of a graben.
Abstract: The morpho-structural evolution of oceanic islands results from competition between volcano growth and partial destruction by mass-wasting processes. We present here a multi-disciplinary study of the successive stages of development of Faial (Azores) during the last 1 Myr. Using high-resolution digital elevation model (DEM), and new K/Ar, tectonic, and magnetic data, we reconstruct the rapidly evolving topography at successive stages, in response to complex interactions between volcanic construction and mass wasting, including the development of a graben. We show that: (1) sub-aerial evolution of the island first involved the rapid growth of a large elongated volcano at ca. 0.85 Ma, followed by its partial destruction over half a million years; (2) beginning about 360 ka a new small edifice grew on the NE of the island, and was subsequently cut by normal faults responsible for initiation of the graben; (3) after an apparent pause of ca. 250 kyr, the large Central Volcano (CV) developed on the western side of the island at ca 120 ka, accumulating a thick pile of lava flows in less than 20 kyr, which were partly channelized within the graben; (4) the period between 120 ka and 40 ka is marked by widespread deformation at the island scale, including westward propagation of faulting and associated erosion of the graben walls, which produced sedimentary deposits; subsequent growth of the CV at 40 ka was then constrained within the graben, with lava flowing onto the sediments up to the eastern shore; (5) the island evolution during the Holocene involves basaltic volcanic activity along the main southern faults and pyroclastic eruptions associated with the formation of a caldera volcano-tectonic depression. We conclude that the whole evolution of Faial Island has been characterized by successive short volcanic pulses probably controlled by brief episodes of regional deformation. Each pulse has been separated by considerable periods of volcanic inactivity during which the Faial graben gradually developed. We propose that the volume loss associated with sudden magma extraction from a shallow reservoir in different episodes triggered incremental downward graben movement, as observed historically, when immediate vertical collapse of up to 2 m was observed along the western segments of the graben at the end of the Capelinhos eruptive crises (1957-58).
71 citations
TL;DR: In this paper, multibeam bathymetry, high-resolution seismic reflection profiles, and sediment samples are used to characterize the morphology of the insular shelves adjacent to Pico Island.
Abstract: 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.
48 citations
TL;DR: In this article, the authors used bathymetric and seismic reflection data to analyze the main volcanic, tectonic and mass-wasting features of Terceira offshore.
Abstract: 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.
46 citations
Cites background or methods or result from "The morphology of insular shelves a..."
...1 and 2 and Quartau et al. 2014)....
[...]
...1 and Quartau et al. 2014)....
[...]
...Besides lava flows on the insular shelf, commonly representing the progradation of subaerial lava flows into the sea (Quartau et al. 2014), and some other less common volcanic morphologies present in deep-water, such as lava terraces in the lower flank of SR, the volcanic features can be divided into two main types: volcanic cones and linear eruptive centers (Figs....
[...]
...Here, the planar surface identified at −30/−40 m can be considered to be result of wave erosion of scarcely cohesive volcanic products (Quartau et al. 2014), similarly to what was observed at Dom João de Castro...
[...]
...Here, the planar surface identified at −30/−40 m can be considered to be result of wave erosion of scarcely cohesive volcanic products (Quartau et al. 2014), similarly to what was observed at Dom João de Castro bank in 1720 (Weston 1964; Pascoal et al. 2006) or, more recently, at Surtla and other…...
[...]
TL;DR: In this paper, a comprehensive review of the biota living in the mid North Atlantic during the late Neogene and the Quaternary is presented, focusing on the MIS 5e fossil record of the Azores archipelago.
43 citations
References
More filters
TL;DR: A coupled model of the Northern Hemisphere ice sheets and ocean temperatures, forced to match an oxygen isotope record for the past million years compiled from 57 globally distributed sediment cores, finds that during extreme glacial stages, air temperatures were 17.8 °C lower than present, with a 120 ± 10 m sea level equivalent of continental ice present.
Abstract: 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.
676 citations
"The morphology of insular shelves a..." refers background in this paper
...This depth is a landmark given that sea level has never been below it in the last 370 ka [Bintanja et al., 2005]....
[...]
...Since 370 ka until the present, sea level has fluctuated roughly between the present-day position and 2123 m below that level [the deepest lowstands, see Figure 5a adapted from Bintanja et al., 2005]....
[...]
379 citations
"The morphology of insular shelves a..." refers background in this paper
...…the understanding of how these islands evolve [Schmincke, 2004], but it was only in the last two decades that researchers have started systematic surveying with side-scan and multibeam sonars around their submarine slopes [e.g., Holcomb and Searle, 1991; Krastel et al., 2001; Moore et al., 1994]....
[...]
...Decades of subaerial geological mapping have contributed considerably to the understanding of how these islands evolve [Schmincke, 2004], but it was only in the last two decades that researchers have started systematic surveying with side-scan and multibeam sonars around their submarine slopes [e.g., Holcomb and Searle, 1991; Krastel et al., 2001; Moore et al., 1994]....
[...]
TL;DR: In this paper, rare earths (RE) in basalts erupted within the rift of the Mid-Atlantic Ridge show a progressive change from light-RE enriched to depleted patterns from the Azores Platform (40°N) down to 33°30′N.
289 citations
"The morphology of insular shelves a..." refers background in this paper
...…interaction between the triple junction of the Eurasian (Eu), Nubian (Nu), and North American (NA) plates [e.g., Laughton and Whitmarsh, 1974; Saemundsson, 1986], and a magmatic anomaly that some authors consider to be the Azores hotspot [Cannat et al., 1999; Gente et al., 2003; Schilling, 1975]....
[...]
TL;DR: This paper showed that steep flanks formerly attributed to tilting or marine erosion have been reinterpreted as landslide headwalls mantled by younger lava flows, and suggested that seacliffs previously attributed to marine erosion of many additional islands may instead be headwall of still other landslides.
Abstract: GLORIA sidescan sonar surveys have shown that large landslides are ubiquitous around the submarine flanks of Hawaiian volcanoes, and GLORIA has also revealed large landslides offshore from Tristan da Cunha and El Hierro. On both of the latter islands, steep flanks formerly attributed to tilting or marine erosion have been reinterpreted as landslide headwalls mantled by younger lava flows. Large landslides have also been inferred from several oceanic islands elsewhere by other workers using different evidence, and we suggest that seacliffs previously attributed to marine erosion of many additional islands may instead be headwalls of still other landslides. These landslides occur in a wide range of settings and probably represent only a small sample from a large population. They may explain the large volumes of archipelagic aprons and the stellate shapes of many oceanic volcanoes. Large landslides and associated tsunamis pose hazards to many islands.
234 citations
"The morphology of insular shelves a..." refers background in this paper
...…the understanding of how these islands evolve [Schmincke, 2004], but it was only in the last two decades that researchers have started systematic surveying with side-scan and multibeam sonars around their submarine slopes [e.g., Holcomb and Searle, 1991; Krastel et al., 2001; Moore et al., 1994]....
[...]
TL;DR: In this article, a mathematical model was used to investigate the development of wave-cut shore platforms with constant sea level, considering the effects of deep water wave height spectra, period and wavelength, breaker height and depth, breaker type, the width and bottom roughness of the surf zone, the gradient of the submarine slope, an erosional threshold related to the strength of the rocks, the number of hours each year in which the water level is at each intertidal elevation and the amount and persistence of the debris at the cliff foot.
214 citations
"The morphology of insular shelves a..." refers background in this paper
...As wave-cut surfaces become wider and more gently sloping, erosion rates tend to decrease through time because of wave attenuation [Trenhaile, 2000]....
[...]
...The maximum depth that these lowstands attained delimits the extent of the edifices at the erosional level because these rock surfaces develop in the zone of the most effective wave erosion, i.e., at, or close to the water surface [Trenhaile, 2000, 2001]....
[...]