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Gravitational, erosional, sedimentary and volcanic processes on the submarine environment of Selvagens Islands (Madeira Archipelago, Portugal)

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Gravitational, erosional, sedimentary and volcanic processes on the submarine environment of Selvagens Islands (Madeira Archipelago, Portugal). / Santos, Rúben; Quartau, Rui; Brum da Silveira, António; Ramalho, Ricardo; Rodrigues, Aurora.

In: Marine Geology, Vol. 415, 105945, 01.09.2019.

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Santos, Rúben ; Quartau, Rui ; Brum da Silveira, António ; Ramalho, Ricardo ; Rodrigues, Aurora. / Gravitational, erosional, sedimentary and volcanic processes on the submarine environment of Selvagens Islands (Madeira Archipelago, Portugal). In: Marine Geology. 2019 ; Vol. 415.

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@article{d775d5d81dd149718e4e286477c160b9,
title = "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.",
keywords = "Faults, ridges and volcanic cones, Landslides and channels, Madeira Archipelago, Sediment wave fields and scours, Selvagens Islands",
author = "R{\'u}ben Santos and Rui Quartau and {Brum da Silveira}, Ant{\'o}nio and Ricardo Ramalho and Aurora Rodrigues",
year = "2019",
month = "9",
day = "1",
doi = "10.1016/j.margeo.2019.05.004",
language = "English",
volume = "415",
journal = "Marine Geology",
issn = "0025-3227",
publisher = "Elsevier B.V.",

}

RIS - suitable for import to EndNote

TY - JOUR

T1 - Gravitational, erosional, sedimentary and volcanic processes on the submarine environment of Selvagens Islands (Madeira Archipelago, Portugal)

AU - Santos, Rúben

AU - Quartau, Rui

AU - Brum da Silveira, António

AU - Ramalho, Ricardo

AU - Rodrigues, Aurora

PY - 2019/9/1

Y1 - 2019/9/1

N2 - 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.

AB - 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.

KW - Faults, ridges and volcanic cones

KW - Landslides and channels

KW - Madeira Archipelago

KW - Sediment wave fields and scours

KW - Selvagens Islands

UR - http://www.scopus.com/inward/record.url?scp=85067828424&partnerID=8YFLogxK

U2 - 10.1016/j.margeo.2019.05.004

DO - 10.1016/j.margeo.2019.05.004

M3 - Article

AN - SCOPUS:85067828424

VL - 415

JO - Marine Geology

JF - Marine Geology

SN - 0025-3227

M1 - 105945

ER -