149 research outputs found
Large deep-seated slump structure off Ischia volcanic island, Eastern Tyrrhenian sea (Italy)
No full textIschia island is located over the Campania sector of Eastern
Tyrrhenian margin and represents the sub-aerial section of a
larger, E-W trending volcanic ridge including others submerged
or buried volcanic edifices. The island itself result from the
coalescence of a multitude of small to medium scale eruptions
leading to the emplacement of domes, lava flow and pyroclastic
deposits and ignimbrites (VEZZOLI et al., 1988) ranging from
alkali basalts to trachytes. The oldest basement dates back to 150
ky and crops out along the perimeter of the island especially to
the south. Latest eruption occurred in 1302 A.D. and together
with strong hydrothermal activity, ground uplift and seismic
shaking indicates the presence of a still active magmatic reservoir
at depth. Most recent (Holocene) magmatic activity with local
volcanic eruptions has clustered in the eastern island’s sector the
while central sector is dominated by the Mt. Epomeo, consisting
of an ignimbritic tuff (Green tuff Auct.) uplifted of 600-700 m in
the past 33ka.
In the past decade the island’s offshore has been the object of
extensive hydrographic and marine geophysical surveys that have
shown the structural complexity of the undersea sections and
have overall shown the importance of gravity failures in island’s
evolution. In particular a 1.5-3 km3 debris avalanche due to a
subaerial and/or submarine flank collapse was emplaced along
the steep and unbuttressed island’s flank during pre-historical or
even historical times (CHIOCCI & DE ALTERIIS, 2006; de Alteriis
et al., 2010) whereas three other similar deposits of comparable
volumes were found over the continental shelf to the west and to
the north (VIOLANTE et al, 2004; DE ALTERIIS & VIOLANTE,
2009).
Here we report a previously unrecognized deep-seated slump
structure and associated surficial mass wasting phenomena which
occur off Ischia south-western flank. Recently acquired
hydrological and geophysical data lead to identify the
morphological features and the internal organization of the failed
sediments which spread along the continental slope. The extent
of this deep-seated deformations and the deep structural levels
involved lead to investigate on the influence played by volcanic
processes on slope failure.
DATA AND METHODS
Our dataset was acquired during the geophysical cruise
PECOS 2010 carried out on R/V Urania (Consiglio Nazionale
delle Ricerche, CNR, Italy) between December 22th 2010 and
January 2nd 2011 in the frame of a project leaded by Istituto per
l’Ambiente Marino Costiero, (IAMC-CNR), Naples-Italy with
the collaboration of Dipartimento di Scienze della Terra e del
Mare (Palermo University), Palermo-Italy regarding coastal and
offshore slope instability in the Bay of Napoli.
The Ischia southern slope was explored through a multibeam
survey and a single-channel seismic survey. Acquisition was
carried out between 400 and 1200 m. The bathymetric data were
collected using a hull mounted Reson 8160 multibeam sonar.
Resolution resulted in a 20x20 m implemented with 50x50
gridded size provided by a previously collected data. The seismic
survey consisted of 6 dip-lines NNE-SSW run along the slope
and 5 cross lines parallel to the slope totalling 170 km. Average
spacing between diplines was slightly less than 1 km while
spacing between crosslines was variable from 1.2 to 2.5 km.
NNE-SSW and WNW-ESE directions. The acoustic source used
was a 1Kjoule high-energy power supply system with a multitips
(400) sparker array, fired at 2s time interval.
RESULTS
The collected data show that a wide submerged area of 350
km2, between 400 to 1200 m depths is undergoing slow-moving
deformation and associated secondary mass wasting phenomena.
Morphological features include trenches, counterscarps, bulging
and both extensional and contractional features while internal
deformations show typical landward dipping reflectors with
strong evidence of synsedimentary faulting and asymmetric
anticlines.
Deformation processes operate at various scales generating
folds with wavelength ranging from hundreds meters to
kilometers. Extensional and rotational rupture surfaces sole out at
various low-angle detachment planes located at depths from few
hundred meters to 1 kilometer in subsurface.
The internal organization of the failing mass shows different
pattern of deformation that allows the identification of three main units: 1) a basal unit consisting of a very broad, asymmetric
slump fold with a wavelength of about 5 km and amplitude of
some 100 m. The fold axis is not vertical and the three
dimensional interpretation indicates that the structure is not
cylindrical. The fold strictly correlates with a morphological
bulge seen on bathymetry at about 20 km south of Ischia Island.
2) A wedge shaped intermediate unit characterized by
discontinuous and folded reflectors, locally showing basal
detachment planes and compressional features. 3) A surficial
slump unit affecting the upper and middle slope characterized by
a basal decollément surface and normal growth faults that sole
out at depths ranging from 70 to 40 m in subsurface. It is still
unclear whether the landslide process can be favored by the
volcano-tectonic evolution and rapid vertical accretion of Ischia
volcano or is solely due to possibly volcanic spreading of the
Ischia Island.
REFERENCES
CHIOCCI, F. L. & DE ALTERIIS, G. (2006) - The Ischia debris
avalanche. First, clear submarine evidence in the
Mediterranean of a volcanic island pre-historic collapse.
Terra Nova, 18, 202–209.
DE ALTERIIS, G., INSINGA D. ET AL. (2010) - Age of submarine
debris avalanches and tephrostratigraphy offshore Ischia
Island, Tyrrhenian Sea, Italy. Marine Geology 278 (2010) 1–
18.
DE ALTERIIS, G. & VIOLANTE, C. (2009) - Catastrophic
landslides off Ischia volcanic island (Italy) during prehistory.
In: C. Violante, (ed.) Geohazard in Rocky Coastal Areas.
Geological Society, London, Special Publications, 322, 73–
104.
VEZZOLI, L. (1988) Island of Ischia. Quaderni de ‘La Ricerca
Scientifica’ Progetto finalizzato ‘Geodinamica’, CNR
Monografie finali, 10.
VIOLANTE, C., BUDILLON, F., ET AL. (2004) - Submerged
hummocky topographies and relations with landslides on the
northwestern flank of Ischia island, southern Italy. In:
‘Occurrence and mechanisms of flow-like landslides in
natural slopes and earthfills’, Sorrento, 14–16 May 2003.
AGI, 2, 309–315
La geologia marina del Golfo di Napoli e della Penisola Sorrentina
No full textDall'inizio del secolo vi è stato un notevole sviluppo di indagini e studi sulle aree marine della Campania, sia a grandi profondità sia lungo la fascia costiera, realizzati soprattutto nell'ambito di progetti scientifici finalizzati e di cartografia geologica (CNR, INGV, Dipartimento Protezione Civile, Progetto CARG).
Si rammenta che non esiste alcuna differenza concettuale tra geologia marina e terrestre e tantomeno tra geologia marina e geologia subacquea, ma possono variare le metodologie e le scale d’indagine.
Si illustrano pertanto metodologie e risultati di indagini marine profonde e rilevamenti subacquei conseguiti negli ultimi anni, sia alla scala di tutto il Golfo di Napoli sia lungo l'ambiente costiero, che stanno permettendo una nuova lettura ed interpretazione dell'intero sistema geologico terrestre e marino della Campania
The Ischia debris avalanche: first clear submarine evidence in the Mediterranean of a volcanic Island pre-historic collapse
No full textSector or flank collapse with related debris avalanches is increasingly recognized as a relatively common volcanic behaviour, in particular, for large, hot-spot related oceanic islands. Here, we report the case of a catastrophic collapse that occurred at Ischia volcanic island in prehistorical times and was driven by the volcano-tectonic uplift of Mt Epomeo, the major relief of the island. The collapse left a subaerial to submarine horseshoe scar on the southern flank of the island and generated a debris avalanche incorporating thousands of giant blocks dispersed as far as 50 km from the island. During the emplacement, part of the debris avalanche evolved into a debris flow covering an area of 250-300 km(2). This constitutes the first, clear evidence of a submarine debris avalanche in the Mediterranean Sea. The major collapse was followed, and probably also preceded, by recurrent, less catastrophic terrestrial and underwater failures. Two other undersea hummocky deposits are found north and west of the island and might tentatively be correlated to the major southern collapse. Such volcanic behaviour, previously unknown for Ischia Volcano, has likely triggered tsunami waves over the entire Bay of Naples raising the question of their impact on prehistorical/historical communities
La geologia marina e subacquea del Golfo di Napoli e della Penisola Sorrentina
No full textSi descrivono le metodologie applicate e i risultati di indagini marine profonde e di rilevamenti geologici subacquei conseguiti negli ultimi anni, sia alla scala dell'intero Golfo di Napoli sia lungo l'ambiente costiero e in particolare della Penisola Sorrentina, che stanno permettendo una nuova lettura ed interpretazione del complesso quadro geologico all'interfaccia terra-mare di questo settore della Campania. I rilevamenti nel golfo, realizzati nell'ambito di progetti scientifici nazionali ed internazionali e di cartografia geotematica, hanno evidenziato la presenza sul fondo marino di affioramenti rocciosi finora non noti, di numerosi ordini di terrazzi marini erosivi e deposizionali a profondità ricorrenti, di cavità subacquee, paleosolchi di battente e paleofalesie modellati in varie litologie e infine di elementi geoarcheologici sommersi d'epoca greco-romana. Nell'insieme, queste morfologie e testimonianze rappresentano importanti geoindicatori di paleostazionamenti quaternari del livello marino e di movimenti verticali differenziali del suolo per cause tettoniche, vulcano-tettoniche e a luoghi bradisismiche anche d'epoca storica e recente
Deep-seated gravity instability of the southern apron of the Ischia volcanic island (Tyrrhenian Sea, Italy)
No full textIschia Island is an active volcano representing the emerged sector of an E-W trending volcanic ridge largely extending undersea. Its collapsing behaviour, mainly in the form of fast-moving, terrestrial and submarine debris avalanches, has been recognized during the Holocene, but much less is known about previous gravity-driven processes. Using high-resolution multibeam bathymetric data and seismic reflection profiles, we provide evidence that the Island's southwestern flank has been involved in a slow-moving, deep-seated slope deformation that has displaced large volumes of its apron since the Late Pleistocene and until very recent or contemporary times. A long tongue of deformed seafloor, spreading up to 45 km from the Island over an area of 330 km2, between 500 and 1300 m water depths, has been detected along its southwestern slope. Different types of mass movements, genetically associated with each other, characterize this landslide: 1) a basal slump anticline, corresponding to a bulge on the bathymetry detaching at about 400 m sub-bottom depth; 2) an intermediate-mass movement chiefly consisting of debris avalanches and debris/turbiditic flows; 3) an upper mass movement consisting of hundred-metre size slumps detaching at relatively shallow depths. Conservative estimates indicate that at least 50 km3 of volcano-clastic and hemipelagic deposits have been mobilized, most of which comprise the basal slump anticline. This submarine landslide can be explained as a gravity failure of the continental slope unrelated to volcanism or rather as a process related to the dynamics of the volcanic edifice, which would imply volcano-spreading
Tradeoff between accuracy and computational cost of Euler and Runge Kutta ODE solvers for the Izhikevich spiking neuron model
No full textThe Izhikevich spiking neuron model is one of the most used in neural engineering and computational neuroscience. Due to its trade-off between physiological plausibility and computational efficiency it is being used also in embedded systems with constrained computational resources. Thus, it is crucial to find a compromise between computational cost and error while numerically integrating the equations of the model. This work aims at quantifying the error produced by fixed step Ordinary Differential Equation (ODE) solvers. Our focus is to provide design hints that could be useful for embedded neural engineering applications. We evaluated three types of input and three ODE solvers: Euler, Runge Kutta 2, Runge Kutta 4. First, we generated a dataset of spike trains to draw conclusions on their general behavior while varying the discretization step. Then we showed that, within a single non-interrupting spike train, the spike delay is positive and accumulates linearly with the spike count. Finally, we introduced a robust method to assess the discretization limits. This method exploits the Victor Purpura distance and confirms that the limits depend on the spike train duration. Our results lead the way to a robust and systematic investigation of the trade-off between computational cost and discretization accuracy of fixed step ODE solvers for neuronal models
The use of high resolution elevation histograms for mapping submergedterraces: tests from the Eastern Tyrrhenian Sea and the Eastern Atlantic Ocean
No full textHistogram plots can be used as a cost- and time-efficient tool to detect horizontal or gently dipping
geomorphic surfaces within a background regional topography. One of the main classes of these
surfaces is typified by terraces formed during marine still-stands. This contribution uses elevation
histogram plots as morphometric indicators for detecting the possible existence of concealed terrace
orders in Digital Elevation Models (DEMs) derived by the processing of bathymetric data. The
approach is particularly useful when dealing with submerged terraces and platforms, because of the
obvious difficulties in mapping those surfaces. The advantage of using this indicator consists in the
rapid identification of DEM recurrent bathymetric values. This tool is most powerful when dealing
with shortly developed terraces and/or multiple terrace orders, whose detection could have been
missed by direct observation.
Two case-studies characterized by the presence of a single terracing event are tested: the southern
slope of the Ischia Island and the top of the Palinuro Seamount, both located in the Eastern
Tyrrhenian Sea Margin. Elevation histograms are used for terrace order computation in a more
complex setting, the Gorringe Bank, located offshore SW Portugal in the Eastern Atlantic Ocean.The results show that a joint use of elevation histogram computation and geomorphologic analysis
can be particularly efficient in the study of planar surfaces
Large deep-seated gravitational slide off Ischia volcanic island, Eastern Tyrrhenian sea (Italy)
No full textIschia island develops at the edge of the shelf area and represents the sub-aerial section of a larger, E-W trending
volcanic ridge including others submerged or buried volcanic edifices. In the past decade the island’s offshore
has been the object of extensive hydrographic and marine geophysical surveys that have shown the structural
complexity of the undersea sections and have overall shown the importance of gravity failures in island’s evolution.
In this paper we report a previously unreported deep-seated slump structure and associated surficial mass wasting
phenomena which occur off Ischia south-western flank. Recently acquired hydrological and geophysical data lead
to identify the morphological features and the internal organization of the failed sediments which spread along
the continental slope. The extent of this deep-seated deformations and the deep structural levels involved lead to
investigate on the influence played by volcanic processes and regional tectonics on slope failure.
The Ischia southern slope was explored through a multibeam survey and a single-channel seismic survey.
Acquisition was carried out from aboard the R/V Urania at depths between 400 and 1200 m. The bathymetric data
were collected using a hull mounted Reson 8160 multibeam sonar. Resolution resulted in a 20x20 m implemented
with 50x50 gridded size provided by a previously collected data. Seismic survey consisted of 6 seismic lines run
along the slope spaced 1 km between them and 5 cross lines. The acoustic source used was a 1Kjoule high-energy
power supply system with a multi-tips (400) sparker array, fired at 2s time interval.
The collected data show that a wide submerged area of 350 km2, between 400 to 1200 m depths is undergoing
slow-moving deformation and associated secondary mass wasting phenomena. Morphological features include
trenches, counterscarps, bulging and both extensional and contractional features while internal deformations show
typical landward dipping reflectors with strong evidence of synsedimentary faulting and asymmetric anticlines.
Deformation processes operate at various scales generating folds with wavelength ranging from hundreds meters to kilometers. Extensional and rotational rupture surfaces sole out at various low-angle detachment planes located
at depths from few hundreds meters to 1 kilometer in subsurface
Morfologie e strutture di apparati vulcanici sommersi nel Canale d'Ischia (Mar Tirreno)
No full textL'esplorazione del Canale d'Ischia mediante indagini ecografiche e rilevamenti geomorfologici con immersioni subacquee ha permesso di ricostruire la fisiografia di quest'area campana, caratterizzata dai relitti degli edifici vulcanici sommersi della Catena, delle Formiche di Vivara e dei Ruommoli. La secca dei Ruommoli è il risultato di un'azione morfogenetica manifestatasi soprattutto in ambiente subaereo. La secca delle Formiche di Vivara è il relitto di un centro eruttivo indipendente e più antico rispetto al vulcano di Vivara. Alla base dei tufi ialoclastitici da cui è formata è stata rilevata la presenza di una breccia vulcanica costituita in massima parte da xenoliti lavici. A poche centinaia di metri a sudovest di questa secca è stata rilevata la presenza di corpi lavici isolati a forma di cupola. Sono stati osservati lembi di terrazzi d'abrasione marina tra -16 e -24 m di profondità e in particolare una superficie spianata con paleofalesia a -16/18 m che rappresenta il risultato di un episodio morfogenetico significativo e ricorrente. Tale livello si correla a quello di base delle cavità sottomarine della secca delle Formiche di Vivara, formatesi in ambiente costiero durante una stasi del livello marino precedente all'ultimo picco glaciale
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