1,721,107 research outputs found
olcanic Islands and Seamounts
No full textRecent advances in seafloor imagery systems have enabled the extensive mapping of submarine volcanic areas, depicting with unprecedented detail a large spectrum of landforms. They can be grouped in two main types: volcanic and erosive-depositional landforms, reflecting the interplay between constructive and destructive forces that control the growth and morphological evolution of volcanic edifices. Volcanic landforms mainly include primary volcanic constructs (cones, lava flows and delta, undifferentiated bedrock outcrops), but also volcano-tectonic features, such as caldera collapses. Erosive-depositional landforms typically cover most part of the volcanic flanks and include features related to wave erosion and sea-level fluctuations (insular shelves and guyots), gravity-driven instability processes (landslide scars), and density gravity flows (gullies, canyons, fan-shaped features, sediment waves). However, despite the large number of marine studies realized until now, we are still far from having a complete mapping of these areas as well as reliable models for the correct interpretation of several landforms, mainly because of the paucity of direct observations. A systematic monitoring of active processes is essential to understand the genesis and evolution of such phenomena; repeated multibeam surveys are playing a key role in this regard. Also the comparison and parameterization of these landforms in different settings can provide insights on the main factors controlling their genesis. But it is necessary to set shared and standardized protocols for the interpretation and analysis of morpho-bathymetric data, also in consideration of the exponential increase in data availability from these areas, whose study is becoming crucial for several disciplines
Unexpected fast rate of morphological evolution of geologically-active continental margins during Quaternary. Examples from selected areas in the Italian seas
No full textIn the last few decades, seafloor imagery systems have drastically changed our vision of a mostly regular
and depositional marine landscape, evidencing how erosive and mass-wasting processes are widespread
in the marine environments, with particular reference to geologically-active areas. Most of the previous
studies have focused on the characterization of these features, whereas a very few ones have tried to
estimate what is the extent and order of magnitude of erosion rates in these areas. In this paper, we show
several examples from some of the most geologically-active margins off Southern Italy aimed to a)
quantify the spatial extent of such processes, b) better understand the role of submarine erosion in the
morphogenesis of the coastal sector, and c) try to roughly estimate the order of magnitude of erosion
rates in these areas. The results are impressive, with mass-wasting features widespread from coast down
to 2600, affecting from the 52% up to 97% of the whole continental slope. Because of the narrow or
totally lacking shelves in these areas, mass-wasting processes often occur close to the coast and match
embayment of the coast, so indicating a key role in the morphogenesis of coastal sector, with significant
implication on the related geohazard. Finally, based on a morphological approach integrated by available
stratigraphic constraints we have roughly estimated average erosion rates in these areas, ranging from
(at least) some mm/year to a few cm/year, i.e., some hundreds of meters up to kilometers eroded in each
eustatic cycle. Despite the large uncertainties of these estimates as well as their spatial and temporal
variability in response to regional and local factors, the obtained values are very high and they should be
considered for future model of margin evolution, source-to-sink computation and marine/coastal geohazard
assessment
Submarine gullies on Italian upper slopes and their relationship with volcanic activity: a 20 years later revisitation of a Bill Normark pioneer work.
No full textMultibeam bathymetry and high-resolution seismic profiles depict in detail the characteristics of submarine gullies present in the upper continental slope offshore of the mouths of the Tiber and Volturno Rivers in the Tyrrhenian Sea and the Simeto River in the Ionian Sea. Upper slope gullies are interpreted as depositional features, growing because of faster aggradation on intergully areas with respect to their axes. The dispersal of river-flood sediment through plunging of hyperpycnal flows has been interpreted to be the limiting factor in sedimentation in gully axes. However, the generation of hyperpycnal flows requires a sediment concentration of several tens of kilograms per cubic meter in the river flows to overcome the higher density of seawater. This threshold is difficult to reach in medium-sized rivers (i.e., catchment basin of 500–5000 km2), such as the Tiber and Volturno. Two alternative scenarios of enhanced sediment availability for these rivers have been proposed. The first scenario is related to sea-level fall and lowstand stages, when the climate conditions may have been different and a huge amount of unconsolidated, fine-grained sediment deposited during the previous highstand stage may have been eroded from the river valleys, coastal plain valleys and shelf delta, as suggested in pioneering work of one of the authors (Chiocci) and Bill Normark. This scenario might explain the formation of some of the gullies offshore of the Tiber River mouth, which developed during the last glacial maximum; however, it is unable to explain the gullies within deposits related to transgressive and highstand system tracts, such as offshore of the Simeto and Volturno River mouths. An alternative scenario is thus proposed on the basis of the relationship observed between the studied rivers and the presence of large volcanic edifices in their catchment basins. Explosive volcanic activity could have drastically modified their catchment basins and caused a sudden and large supply of loose tephras, increasing the sediment load in watercourses and consequently favoring the development of gully-forming hyperpycnal flows. The timing of volcanic activity on the three study areas matches, in fact, the presence or absence of gullies in upper slope depositional sequences
Statistica morfometrica di dati ecometrici multifascio come strumento per l'interpretazione di lineamenti di pericolosità geologica dei fondali.
No full textSubmarine evidences of multiple large-scale lateral collapse on the eastern Stromboli flank: insights for the reassessment of collapse recurrence period and tsunami hazard
No full textFirst evidence of large scale lateral collapse on the eastern flank of Stromboli Volcano
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Offshore evidence of large–scale lateral collapse on the eastern flank of Stromboli, Italy, due to structurally–controlled, bi-lateral flank instability
No full textNew detailed swath bathymetry and long-range side scan sonar data on the submerged flanks of Stromboli, integrated with seismic data and seabed sampling, indicate that repeated lateral instability processes occurred on the eastern flank of the volcano, although no debris avalanche deposits were known before the high-resolution exploration of the seabed. This flank of the island is opposite to the northwestern side, more evidently affected by repeated flank collapses, and this setting is evidence for a structurally-controlled, bilateral flank instability of the volcanic edifice.
Evidence of at least two large-scale lateral collapses is represented by a superficial hummocky megablock field, partially outcropping on the middle-lower eastern submerged slope, and by a chaotic unit (estimated volume is 1-2 km(3)) actually embedded within the volcaniclastic sequence at the foot of the submerged flank. A main submarine scar open towards the SE is carved in the upper slope on the eastern flank of the island, being partially filled with gravity flow deposits owing to the present-day depositional setting of the volcano's submerged flank. A morphological continuity can be envisaged between this submerged scar and an inferred subaerial one, likely encompassing the Rina Grande depression and several minor nested landslide scars recognized on the eastern Stromboli flank. A spatial and temporal reconstruction of possible events is proposed. The chaotic debris avalanche unit, buried within the volcaniclastic apron at the slope base and partially reworked in its distall part within the Stromboli Canyon floor, is thought to be the result of a lateral collapse event (called Paleostromboli Lateral Collapse, PLC, as it likely occurred in the earlier stages of the subaerial development of the island) affecting a wide sector of the eastern Stromboli flank. The megablock field might instead result from a more superficial debris avalanche deposit, partially eroded by gravity flows currently acting on the seabed. It is tentatively related to the recent subaerial scar morphologies affecting the Vancori units (and for this reason named Vancori Lateral Collapse, VLC). Displaced materials have lower volume and mobility than the PLC. (C) 2009 Elsevier B.V. All rights reserved
The Italian MaGIC Project: A first-order geohazard assessment by means of regional seafloor mapping
No full textOver the past decades interest for marine geohazard assessment has rapidly grown up, driven by the increasing exploitation of natural resources, the emplacement of bottom-lying structures (cables and pipelines) and by the development of coastal areas, whose infrastructures increasingly protrude to the sea. At the same time, recent advances in seafloor mapping techniques have greatly improved our knowledge of geomorphic features that can be regarded as geohazard indicators, such as volcanic vents, slide scars, canyon headscarps, and fault-related seafloor unevenness. The national Project MaGIC (Marine Geohazards along the Italian Coast) is aimed at depicting potential geohazards based on the acquisition of highresolution bathymetry and on the production of maps of the geohazard -related geomorphic features for most of the Italian continental margins
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