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  • 1
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    Lava flow hazard at Nyiragongo volcano, D.R.C. 2. Hazard reduction in urban areas (2010)
    Springer-Verlag
    Details
    Publication Date: 2017-04-04
    Description: Mt. Nyiragongo is one of the most dangerous volcanoes in the world for the risk associated with the propagation of lava flows. In 2002 several vents opened along a huge system of fractures, pouring out lava which reached and destroyed a considerable part of Goma, a town of about 500,000 inhabitants on the shore of Lake Kivu. In a companion paper (Favalli et al. in Bull Volcanol, this issue, 2008) we employed numerical simulations of probable lava flow paths to evaluate the lava flow hazard on the flanks of the volcano, including the neighbouring towns of Goma (DRC) and Gisenyi (Rwanda). In this paper we use numerical simulations to investigate the possibility of significantly reducing the lava flow hazard in the city through the construction of protective barriers. These barriers are added to the DEM of the area as additional morphological elements, and their effect is evaluated by repeating numerical simulations with and without the presence of barriers. A parametric study on barrier location, size, shape and orientation led to the identification of barriers which maximize protection while minimizing their impact. This study shows that the highest hazard area corresponding to eastern Goma, which was largely destroyed by lava flows in 2002, cannot be effectively protected from future lava flows towards Lake Kivu and should be abandoned. On the contrary, the rest of the town can be sheltered from lava flows by means of two barriers that deviate or contain the lava within the East Goma sector. A proposal for the future development of the town is formulated, whereby “new” Goma is completely safe from the arrival of lava flows originating from vents outside its boundaries. The proposal minimizes the risk of further destruction in town due to future lava flows.
    Description: Published
    Description: 375-387
    Description: 2.1. TTC - Laboratorio per le reti informatiche, GRID e calcolo avanzato
    Description: 4.3. TTC - Scenari di pericolosità vulcanica
    Description: JCR Journal
    Description: reserved
    Keywords: Lava flow ; Nyiragongo ; Volcanic hazard ; Hazard mitigation ; Numerical simulations ; Lava barriers ; 04. Solid Earth::04.08. Volcanology::04.08.08. Volcanic risk ; 05. General::05.01. Computational geophysics::05.01.04. Statistical analysis ; 05. General::05.01. Computational geophysics::05.01.05. Algorithms and implementation
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 2
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    Lava flow hazard at Nyiragongo volcano, D.R.C. 1. Model calibration and hazard mapping (2010)
    Springer Berlin / Heidelberg
    Details
    Publication Date: 2017-04-04
    Description: The 2002 eruption of Nyiragongo volcano constitutes the most outstanding case ever of lava flow in a big town. It also represents one of the very rare cases of direct casualties from lava flows, which had high velocities of up to tens of kilometer per hour. As in the 1977 eruption, which is the only other eccentric eruption of the volcano in more than 100 years, lava flows were emitted from several vents along a N–S system of fractures extending for more than 10 km, from which they propagated mostly towards Lake Kivu and Goma, a town of about 500,000 inhabitants. We assessed the lava flow hazard on the entire volcano and in the towns of Goma (D.R.C.) and Gisenyi (Rwanda) through numerical simulations of probable lava flow paths. Lava flow paths are computed based on the steepest descent principle, modified by stochastically perturbing the topography to take into account the capability of lava flows to override topographic obstacles, fill topographic depressions, and spread over the topography. Code calibration and the definition of the expected lava flow length and vent opening probability distributions were done based on the 1977 and 2002 eruptions. The final lava flow hazard map shows that the eastern sector of Goma devastated in 2002 represents the area of highest hazard on the flanks of the volcano. The second highest hazard sector in Goma is the area of propagation of the western lava flow in 2002. The town of Gisenyi is subject to moderate to high hazard due to its proximity to the alignment of fractures active in 1977 and 2002. In a companion paper (Chirico et al., Bull Volcanol, in this issue, 2008) we use numerical simulations to investigate the possibility of reducing lava flow hazard through the construction of protective barriers, and formulate a proposal for the future development of the town of Goma.
    Description: Published
    Description: 363-374
    Description: 2.1. TTC - Laboratorio per le reti informatiche, GRID e calcolo avanzato
    Description: 4.3. TTC - Scenari di pericolosità vulcanica
    Description: JCR Journal
    Description: reserved
    Keywords: Lava flow ; Nyiragongo ; Volcanic hazard ; Numerical simulations ; 04. Solid Earth::04.08. Volcanology::04.08.08. Volcanic risk ; 05. General::05.01. Computational geophysics::05.01.04. Statistical analysis ; 05. General::05.01. Computational geophysics::05.01.05. Algorithms and implementation
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 3
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    Stiffnites. Part II (2012)
    INGV
    Details
    Publication Date: 2017-04-04
    Description: The dynamics of a stiffnite are here inferred. A stiffnite is a sheet-shaped, gravity-driven submarine sediment flow, with a fabric made up of marine ooze. To infer stiffnite dynamics, order of magnitude estimations are used. Field deposits and experiments on materials taken from the literature are also used. Stiffnites can be tens or hundreds of kilometers wide, and a few centimeters/ meters thick. They move on the sea slopes over hundreds of kilometers, reaching submarine velocities as high as 100 m/s. Hard grain friction favors grain fragmentation and formation of triboelectrically electrified particles and triboplasma (i.e., ions + electrons). Marine lipids favor isolation of electrical charges. At first, two basic assumptions are introduced, and checked a posteriori: (a) in a flowing stiffnite, magnetic dipole moments develop, with the magnetization proportional to the shear rate. I have named those dipoles as Ambigua. (b) Ambigua are ‘vertically frozen’ along stiffnite streamlines. From (a) and (b), it follows that: (i) Ambigua create a magnetic field (at peak, 〉1 T). (ii) Lorentz forces sort stiffnite particles into two superimposed sheets. The lower sheet, L+, has a sandy granulometry and a net positive electrical charge density. The upper sheet, L–, has a silty muddy granulometry and a net negative electrical charge density; the grains of sheet L– become finer upwards. (iii) Faraday forces push ferromagnetic grains towards the base of a stiffnite, so that a peak of magnetic susceptibility characterizes a stiffnite deposit. (iv) Stiffnites harden considerably during their motion, due to magnetic confinement. Stiffnite deposits and inferred stiffnite characteristics are compatible with a stable flow behavior against bending, pinch, or other macro instabilities. In the present report, a consistent hypothesis about the nature of Ambigua is provided.
    Description: Published
    Description: 780-804
    Description: 3.3. Geodinamica e struttura dell'interno della Terra
    Description: JCR Journal
    Description: open
    Keywords: Submarine sediment flows ; Magnetic fabric and anisotropy ; Magnetic confinement ; Shear polymer media ; Triboelectric fragmentation ; Magnetic dipole Ambigua ; 04. Solid Earth::04.04. Geology::04.04.04. Marine geology ; 04. Solid Earth::04.04. Geology::04.04.08. Sediments: dating, processes, transport ; 04. Solid Earth::04.05. Geomagnetism::04.05.07. Rock magnetism
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 4
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    Stiffnites. Part I (2012)
    INGV
    Details
    Publication Date: 2017-04-04
    Description: I identify the early phases of a particular kind of gravity-driven submarine sediment flow, that I have named immature stiffnite. The mature flow dynamics is originally presented in an accompanying report, referred to here as Pareschi [2011]. An immature stiffnite is constituted by a liquefied flowing mixture of muddy to sandy particles (sea floor ooze) in contact or in close proximity to each other, with inter-granular pores saturated in water. Sliding hard grains, including microshells, fragment during its motion. To infer the dynamics of an immature stiffnite, I consider deposits from the literature. In the literature, however, those deposits have not been well defined and they have often been confused with turbidites. Turbidites are water currents with suspended fine sediments that progressively settle-out down an incline. Stiffnites are triggered by events that create overpressure in intergrain pore water of the sea floor over wide areas. A peak of magnetic susceptibility can occur at the base of an immature stiffnite deposit.
    Description: Published
    Description: 762-778
    Description: 3.3. Geodinamica e struttura dell'interno della Terra
    Description: JCR Journal
    Description: open
    Keywords: Submarine gravity-driven sediment flows ; Landslide and asteroid tsunamis ; Grain fragmentation-turbidites ; Subduction/thrust earthquakes ; 04. Solid Earth::04.04. Geology::04.04.04. Marine geology ; 04. Solid Earth::04.04. Geology::04.04.08. Sediments: dating, processes, transport ; 04. Solid Earth::04.05. Geomagnetism::04.05.07. Rock magnetism
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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