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  • 1
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    Interaction of pyroclastic density currents with human settlements: Evidence from ancient Pompeii (2012)
    Geological Society of America
    Details
    Publication Date: 2021-06-15
    Description: Integrating field observations and rock-magnetic measurements, we report how a turbulent pyroclastic density current interacted with and moved through an urban area. The data are from the most energetic, turbulent pyroclastic density current of the A.D. 79 eruption of Vesuvius, Italy, which partially destroyed the Roman city of Pompeii. Our results show that the urban fabric was able to divide the lower portion of the current into several streams that followed the city walls and the intracity roads. Vortices, revealed by upstream particle orientations and decreases in deposit temperature, formed downflow of obstacles or inside cavities. Although these perturbations affected only the lower part of the current and were localized, they could represent, in certain cases, cooler zones within which chances of human survival are increased. Our integrated field data for pyroclastic density current temperature and flow direction, collected for the first time across an urban environment, enable verification of coupled thermodynamic numerical models and their hazard simulation abilities.
    Description: Published
    Description: 441-444
    Description: 3.6. Fisica del vulcanismo
    Description: 4.3. TTC - Scenari di pericolosità vulcanica
    Description: JCR Journal
    Description: restricted
    Keywords: Vesuvius ; pyroclastic density current ; thermal remanent magnetization ; deposits ; magnetic fabric ; 04. Solid Earth::04.08. Volcanology::04.08.08. Volcanic risk
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 2
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    Influences of urban fabric on pyroclastic density currents at Pompeii (Italy): 1. Flow direction and deposition (2007)
    American Geophysical Union
    Details
    Publication Date: 2021-06-15
    Description: To assess ways in which the products of explosive eruptions interact with human settlements, we performed volcanological and rock magnetic analyses on the deposits of the A.D. 79 eruption at the Pompeii excavations (Italy). During this eruption the Roman town of Pompeii was covered by 2.5 m of fallout pumice and then partially destroyed by pyroclastic density currents (PDCs). Anisotropy of magnetic susceptibility measurements performed on the fine matrix of the deposits allowed the quantification of the variations in flow direction and emplacement mechanisms of the parental PDCs that entered the town. These results, integrated with volcanological field investigations, revealed that the presence of buildings, still protruding through the fallout deposits, strongly affected the distribution and accumulation of the erupted products. All of the PDCs that entered the town, even the most dilute ones, were density stratified currents in which interaction with the urban fabric occurred in the lower part of the current. The degree of interaction varied mainly as a function of obstacle height and density stratification within the current. For examples, the lower part of the EU4pf current left deposits up to 3 m thick and was able to interact with 2- to 4-m-high obstacles. However, a decrease in thickness and grain size of the deposits across the town indicates that even though the upper portion of the current was able to decouple from the lower portion, enabling it to flow over the town, it was not able to fully restore the sediment supply to the lower portion in order to maintain the deposition observed upon entry into the town.
    Description: Published
    Description: B05213
    Description: 4.3. TTC - Scenari di pericolosità vulcanica
    Description: 3.6. Fisica del vulcanismo
    Description: JCR Journal
    Description: reserved
    Keywords: Pompeii ; facies ; magnetic fabric ; pyroclastic density currents ; 04. Solid Earth::04.08. Volcanology::04.08.08. Volcanic risk
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 3
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    Influences of urban fabric on pyroclastic density currents at Pompeii (Italy): 2. Temperature of the deposits and hazard implications (2007)
    American Geophysical Union
    Details
    Publication Date: 2021-06-15
    Description: During the A.D. 79 eruption of Vesuvius, Italy, the Roman town of Pompeii was covered by 2.5 m of pyroclastic fall pumice and then partially destroyed by pyroclastic density currents (PDCs). Thermal remanent magnetization measurements performed on the lithic and roof tile fragments embedded in the PDC deposits allow us to quantify the variations in the temperature (Tdep) of the deposits within and around Pompeii. These results reveal that the presence of buildings strongly influenced the deposition temperature of the erupted products. The first two currents, which entered Pompeii at a temperature around 300–360°C, show drastic decreases in the Tdep, with minima of 100–140°C, found in the deposits within the town. We interpret these decreases in temperature as being the result of localized interactions between the PDCs and the city structures, which were only able to affect the lower part of the currents. Down flow of Pompeii, the lowermost portion of the PDCs regained its original physical characteristics, emplacing hot deposits once more. The final, dilute PDCs entered a town that was already partially destroyed by the previous currents. These PDCs left thin ash deposits, which mantled the previous ones. The lack of interaction with the urban fabric is indicated by their uniform temperature everywhere. However, the relatively high temperature of the deposits, between 140 and 300°C, indicates that even these distal, thin ash layers, capped by their accretionary lapilli bed, were associated with PDCs that were still hot enough to cause problems for unsheltered people.
    Description: Published
    Description: B05214
    Description: 4.3. TTC - Scenari di pericolosità vulcanica
    Description: 3.6. Fisica del vulcanismo
    Description: JCR Journal
    Description: reserved
    Keywords: Pompeii ; temperature ; magnetic fabric ; pyroclastic density currents ; 04. Solid Earth::04.08. Volcanology::04.08.08. Volcanic risk
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 4
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    Influences of urban fabric on pyroclastic density currents at Pompeii (Italy), part II: temperature of the deposits and hazard implications (2007)
    Details
    Publication Date: 2017-04-04
    Description: During the AD 79 eruption of Vesuvius, Italy, the Roman town of Pompeii, was covered by 2.5 m fallout pumice and then partially destroyed by pyroclastic density currents (PDCs). Thermal remanent magnetization (TRM) measurements performed on the lithic and roof tile fragments embedded in the PDC deposits allow us to quantify the variations in the temperature (Tdep) of the deposits within and around Pompeii. These results reveal that the presence of buildings strongly influenced the deposition temperature of the erupted products. The first two currents which entered Pompeii at a temperature around 300-360 ºC, show drastic decreases in the Tdep, with minima of 100-140 ºC found in the deposits within the town. We interpret these decreases in temperature as being the result of localized interactions between the PDCs and the city structures, which were only able to affect the lower part of the currents. Down flow of Pompeii, the lowermost portion of the PDCs regained its original physical characteristics, emplacing hot deposits once more. The final, dilute PDCs entered a town that was already partially destroyed by the previous currents. These PDCs left thin ash deposits which mantled the previous ones. The lack of interaction with the urban fabric is indicated by their uniform temperature everywhere. However, the relatively high temperature of the deposits, between 140 and 300 ºC, indicates that even these distal, thin ash layers, capped by their accretionary lapilli bed, were associated with PDCs that were still hot enough to cause problems for unsheltered people.
    Description: Published
    Description: open
    Keywords: Pompeii ; temperature ; magnetic fabric ; pyroclastic density currents ; 04. Solid Earth::04.08. Volcanology::04.08.99. General or miscellaneous
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 5
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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)
    Type: article
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  • 6
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    TINITALY/01: a new Triangular Irregular Network of Italy (2008)
    Editrice Compositori
    Details
    Publication Date: 2019-11-04
    Description: A new Digital Elevation Model (DEM) of the natural landforms of Italy is presented. A methodology is discussed to build a DEM over wide areas where elevation data from non-homogeneous (in density and accuracy) input sources are available. The input elevation data include contour lines and spot heights derived from the Italian Regional topographic maps, satellite-based global positioning system points, ground based and radar altimetry data. Owing to the great heterogeneity of the input data density, the DEM format that better preserves the original accuracy is a Triangular Irregular Network (TIN). A Delaunay-based TIN structure is improved by using the DEST algorithm that enhances input data by evaluating inferred break-lines. Accordingly to this approach, biased distributions in slopes and elevations are absent. To prevent discontinuities at the boundary between regions characterized by data with different resolution a cubic Hermite blending weight S-shaped function is adopted. The TIN of Italy consists of 1.39×109 triangles. The average triangle area ranges from 12 to about 13000 m2 accordingly to different morphologies and different sources. About 50% of the model has a local average triangle area 〈500 m2. The vertical accuracy of the obtained DEM is evaluated by more than 200000 sparse control points. The overall Root Mean Square Error (RMSE) is less than 3.5 m. The obtained national-scale DEM constitutes an useful support to carry out accurate geomorphological and geological investigations over large areas. The problem of choosing the best step size in deriving a grid from a TIN is then discussed and a method to quantify the loss of vertical information is presented as a function of the grid step. Some examples of DEM application are outlined. Under request, an high resolution stereo image database of the whole Italian territory (derived from the presented DEM) is available to browse via internet.
    Description: Published
    Description: 407-425
    Description: 5.4. TTC - Sistema Informativo Territoriale
    Description: JCR Journal
    Description: open
    Keywords: Italy ; triangular irregular network ; DEM ; interpolation method ; 04. Solid Earth::04.04. Geology::04.04.08. Sediments: dating, processes, transport
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 7
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    Influences of urban fabric on pyroclastic density currents at Pompeii (Italy), part I: Flow direction and deposition (2007)
    Details
    Publication Date: 2020-02-24
    Description: To assess ways in which the products of explosive eruptions interact with human settlements we performed volcanological and rock-magnetic analyses on the deposits of the AD 79 eruption at the Pompeii excavations (Italy). During this eruption the Roman town of Pompeii was covered by 2.5 m of fallout pumice and then partially destroyed by pyroclastic density currents (PDCs). Anisotropy of magnetic susceptibility (AMS) measurements performed on the fine matrix of deposits allowed the quantification of the variations in flow direction and emplacement mechanisms of the parental PDCs that entered the town. These results, integrated with volcanological field investigations revealed that the presence of buildings, still prodruting throught the fallout deposits, strongly affected the distribution and accumulation of the erupted products. All PDCs that entered the town, even the most dilute ones, were density stratified currents in which interaction with the urban fabric occurred in the lower part of the current. The degree of interaction varied mainly as a function of obstacle height and density stratification within the current. For examples, the lower part of the EU4pf current left deposits up to 3 meters thick and was able to interact with 2-to-4-meter-high obstacles. However, a decrease in thickness and grain size of the deposits across the town indicates that, even though the upper portion of the current was able to decouple from the lower portion, enabling it to flow over the town, it was not able to fully restore the sediment supply to the lower portion in order to maintain the deposition observed upon entry into the town.
    Description: Submitted
    Description: open
    Keywords: Pompei ; facies ; magnetic fabric ; pyroclastic density currents ; 04. Solid Earth::04.08. Volcanology::04.08.99. General or miscellaneous
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: manuscript
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  • 8
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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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