Articles de revues : « Pyroclastite »

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Picard, Christian, et Michel Piboule. « Pétrologie des roches volcaniques du sillon de roches vertes archéennes de Matagami – Chibougamau à l'ouest de Chapais (Abitibi est, Québec).1. Le groupe basal de Roy ». Canadian Journal of Earth Sciences 23, n^o 4 (1 avril 1986) : 561–78. http://dx.doi.org/10.1139/e86-056.

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In the northeastern part of the Abitibi orogenic belt, the Archean Matagami–Chibougamou greenstone belt (2700 Ma) includes a basal volcanic sequence named the Roy Group, unconformably overlain by a volcano-sedimentary series called the Opemisca Group.The Roy Group, to the west of the town of Chapais, consists of a thick, stratified, and polycyclic volcanic series (thickness = 11 000 m) resembling the large, western Abitibi submarine stratovolcanoes constructed by three mafic to felsic magmatic cycles. The first cycle (Chrissie Formation) shows lateral spreading and is composed only of a meta-andesite and felsic pyroclastite sequence of calc-alkaline affinity. The other two cycles (Obatogamau and Waconichi formations; then Gilman, Blondeau, and Scorpio formations) are characterized by a sequence of repeated MORB type basaltic lava flows of tholeiitic affinity and by intermediate to acid lava and pyroclastic sequences calc-alkaline affinity.The stratigraphic and petrographic data suggest emplacement of mafic lavas on an abyssal plain (Obatogamau Formation) or at a later time on the flanks of a large submarine volcanic shield (Gilman and Blondeau formations). The lava and felsic pyroclastite flows were formed by very explosive eruptions from central spreading type volcanoes above a pre-existing continental crust. In particular, the Scorpio volcanic rocks were emplaced on volcanic islands later dismantled by erosion.The contents and distribution of trace elements and rare earths show that basaltic lavas resulted from an equilibrium partial melting (F = 15–35%) of spinel lherzolite type mantle sources depleted to weakly enriched in Th, Ta, Nb, and light rare-earth elements (LREE), and from fractional crystallization at low pressure of feldspar, clinopyroxene, and olivine. The lavas and the felsic pyroclastites of the Waconichi and Scorpio formations appear to result from partial melting of a mantle source of lherzolite type enriched in LREE and involving some garnet. At a late stage, the melts were probably contaminated by some continental crust materials and then differentiated by fractional crystallization of plagioclase, amphibole, biotite, and magnetite. The lavas in the Chrissie Formation and the middle member of the Gilman Formation seem to result from partial melting of a mantle source enriched in LREE with a composition between the two described above. They were subsequently modified by fractional crystallization of the plagioclase, clinopyroxene, olivine, and titanomagnetite.In general, the mafic to felsic magmatic cycles observed are characterized by a thick sequence of repeated tholeiitic basalt flows similar to those of modern mid-oceanic ridges and by a lava and felsic pyroclastite sequence of calc-alkaline affinity comparable to those occurring in orogenic belts. The transition from one lava sequence to another is marked by a significant chemical discontinuity, and the mantle sources exhibit an increasing enrichment in LREE during a given magmatic cycle. A model is proposed to satisfactorily explain all the stratigraphic, petrographic, and geochemical data implying a hot spot type mechanism, which could be responsible for the cyclic, rising diapirs inside the stratified Archean mantle and for initiating the repeated mantle source meltings, depleted and enriched in LREE, respectively. [Journal Translation]

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Kazakov, A. I., O. V. Veselov et D. N. Kozlov. « Statistical analysis of the distribution of phreatic eruption products in the caldera of the Golovnin volcano (Kunashir Island, Kuril Islands) ». Geosystems of Transition Zones 5, n^o 1 (2021) : 14–26. http://dx.doi.org/10.30730/gtrz.2021.5.1.014-026.

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The paper presents the results of statistical processing of data on the thickness and size of the tephra fragments of andesidacite composition erupted as a result of a phreatic explosion in the caldera of Golovnin volcano about 1000 years ago. A petrochemical description of the products of volcanic activity of the crustal Golovnin volcano and its evolution process is presented based on geological and geophysical data. The relationship between the thickness of the tephra, the size of its fragments, and the distance to the eruption center was studied using the polynomial regressions of varying degrees and exponential distribution. The adequacy of the constructed models to the initial data is illustrated by determination coefficients. Tephra distribution models were constructed on the basis of a three-dimensional trend analysis. For the first time, a logarithmic model was used to describe the size of tephra fragments. The accuracy of the model used was estimated. A method for estimating the potential dispersion range of tephra fragments of a certain size was obtained. The work demonstrates the potential of mathematical statistics for describing the distribution of products of volcanic eruptions of a certain type. The results of this study are suitable for creating an information database of pyroclastite distribution across the Kuril-Kamchatka volcanic region.

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Huguet, David, Jean-Claude Thouret, Pierre Nehlig, Jeannine Raffy et Pierre Rochette. « Les lahars du strato-volcan du Cantal (Massif central, France) ; stratigraphie, modes de mise en place et implications paleo-geomorphologiques ». Bulletin de la Société Géologique de France 172, n^o 5 (1 septembre 2001) : 573–85. http://dx.doi.org/10.2113/172.5.573.

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Abstract Introduction: The study of lahar (Lh) deposits (a) describes sedimentary facies associations in a volcano-sedimentary system, (b) establishes the identification of criteria to recognize epiclastic deposits in fossil volcanic successions [Thouret, 1999] and (c) reconstructs paleo-landforms (stratocones, paleovalleys, and volcaniclastic fans) in an old volcanic massif. Lh deposits form the "complexe conglomeratique superieur" ("upper conglomeratic complex") [Brousse et al., 1972, 1975, 1977, 1980, 1989] associated with pyroclastic deposits and streamflow deposits above the "breche inferieure" ("lower breccia"), reinterpreted as debris-avalanche (DAv) deposits. From 9.5 to 6.5 Ma, a trachyandesitic stratovolcano has been built up. Several sector collapses generated DAv and an explosive activity produced pyroclastic-flow deposits. Pyroclastic deposits and both Lh and DAv deposits built up volcaniclastic fans. The study aims (a) to determine Lh deposit generations associated with paleo-landforms and (2) to use Lh deposits as landmarks to recognize some geomorphologic stages in the history of Cantal volcano (45 degrees N-2.5 degrees E; 2500 km 2 , approximately 380 km 3 , 1 855 m). Lahar generations: Lh deposits (9 km 3 ) cover 280 km 2 (fig. 1). They show two facies, clast-supported and matrix-supported debris-flow deposits (fig. 2 and 3), located as far as 20 km from the geographic centre (Puy Griou). Firstly, field observations and geochronological data enable us to distinguish as much as five Lh deposit generations. Secondly, geometric and stratigraphic relations, between Lh deposits and both pyroclastic and DAv deposits, allow us to decipher the genetic relations between distinct volcaniclastic formations. The Cere valley shows three Lh generations. The "Faillitoux" generation is interbedded with the schistose basement and the lava and pyroclastic deposits of the Elanceze massif (1571 m) (fig. 4). An ankaramitic lava (9.53+ or -0,5 Ma, K/Ar) [Nehlig et al., 1999], fitting into Lh deposits of the Elanceze massif post-dates the apparition of the first lahar generation. The "Curebourse" generation was emplaced above DAv deposits (fig. 2A and 5). Both DAv and Lh deposits of the "Curebourse" generation filled the paleo-Cere valley about 7.1 Ma. The "Thiezac" generation (>6.7 Ma, K/Ar) [Nehlig et al., 1999] (fig. 2C) overlies a thick pyroclastic deposit (fig. 4) and is not related to the DAv and the "Curebourse" generation. The fourth generation (Impradine valley) is stratigraphically and genetically associated with pyroclastic deposits located in the upper Impradine valley (fig. 5). These pyroclastic deposits are older than 7.96 Ma (K/Ar age on a trachyandesitic lava overlying Lh deposits) and result from pyroclastic deposits removed as Lh deposits downvalley. The fifth identified lahar generation is located in the Petite-Rhue valley, to the north of the volcano, where a 5-m-thick pumiceous pyroclastite (7.6+ or -0.03 Ma; 40 Ar/ 39 Ar) [Platevoet, 2000] is interstratified with Lh deposits in Cheylade. Genetic relations with pyroclastic deposits: To determine the nature of the relationships between Lh deposits and DAv deposits, we observed geometric relationships between both formations. Some Lh deposits of "Curebourse" generation filled paleothalwegs (fig. 6) cut into DAv deposits suggesting a remission stage after emplacement of DAv deposits. We did not identify sedimentologic features such as dewatering structures indicating that lahars evolved from the top or the front of DAv deposits. Thus, no obvious genetic link was clearly determined between Lh and DAv deposits. In the Impradine valley, we observe the transformation of these pyroclastic deposits in Lh deposits. A proximal pyroclastic facies (upper Impradine) (fig. 5), intruded by numerous dykes and intercalated with trachyandesitic lava, shows the proximity of a stratocone located 1,5 km to the South-East. Field observations indicate a stratigraphic link between pyroclastic and Lh deposits. Debris flows have removed pyroclastic deposits over a 6 km distance. Lh deposits are ungraded or inversely graded and show matrix- or clast-supported facies. About 50% of dense subrounded to rounded clasts were incorporated during the flow. The remaining 50% are dense trachyandesitic juvenile clasts derived from primary pyroclastic-flow deposits. Geomorphological implications: Determinations of five Lh deposit generations and observations of geometrical relations with volcaniclastic deposits (DAv and pyroclastic deposits) enable us to reconstruct paleo-landforms and some stages of the geomorphic evolution of Cantal. In this way, the Impradine volcaniclastic unit is a fragment of a volcaniclastic fan facing north-east (fig. 7). In the Cere valley, the "Faillitoux" generation is the remnant of a proximal section of a volcaniclastic fan facing south-west. These lahars flowed from a trachyandesitic stratocone located close to the Elanceze massif about 9.5 Ma ago (fig. 7). These paleo-stratocones were eroded and are no longer visible in the present geomorphic landscape. Lh deposits allow us to determine geomorphic inheritances, contemporaneous with the activity of the stratovolcano from 9.5 to 6.5 Ma. About 7.1 Ma, the paleo-Cere valley was filled with DAv and Lh deposits of the "Curebourse" generation. The "Curebourse" generation formed a volcaniclastic fan on the top of DAv deposits. DAv and Lh deposits, that are less resistant than the trachyandesitic Elanceze massif and Plomb-du-Cantal range, have been eroded. Accordingly, the Cere valley is being exhumed. The present-day drainage pattern occupies the paleothalweg. However, in distal positions, paleo-landforms are not as well preserved. The current drainage pattern does not use any more paleothalwegs in contrast to what is seen in proximal position (fig. 8).

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Šimon, Ladislav, Viera Kollárová et Monika Kováčiková. « Neogene volcanics of the Burda mountain range nearby Štúrovo, Slovakia ». Mineralia Slovaca 55, n^o 2 (décembre 2023) : 117–32. http://dx.doi.org/10.56623/ms.2023.55.2.2.

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The Neogene volcanic products of the Burda mountain range nearby Štúrovo belong to Burda Formation. At the base of the Burda Formation a succession of epiclastic volcanic rocks and pyroclastic rocks of andesites has developed. In the central part of the formation, the volcanic products associated with the activity of submarine volcanism of the Badenian age developed. Submarine extrusive volcanic domes of andesites are typical. In the upper part of the Burda Formation, pyroclastic and epiclastic facies of andesites were formed. Deposits of pyroclastic flows and redeposited pyroclastics are characterized by the presence of relics of petrified tree trunks, indicating transport from emergent forest-covered slopes from the higher levels of the volcanic edifice of the Börzsöny Mountains in todayʼs Hungary. This part of the Burda volcanics represents a transitional volcanic zone with the Börzsöny stratovolcano.

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Tommasi, Paolo, Luca Verrucci et Tatiana Rotonda. « Mechanical properties of a weak pyroclastic rock and their relationship with microstructure ». Canadian Geotechnical Journal 52, n^o 2 (février 2015) : 211–23. http://dx.doi.org/10.1139/cgj-2014-0149.

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The geotechnical behaviour of very weak pyroclastic rocks controls both the failure mechanisms at the margins of rock mesas, where historic hill towns are often sited, as well as the stability of old underground cavities in urban areas of Central Italy. The study focuses on the mechanical behaviour of one of the pyroclastic materials forming the Orvieto mesa (pozzolana), not unlike other pozzolanas in Central and Southern Italy and other pyroclastites from volcanic districts worldwide. The mechanical properties under static conditions of this weakly cemented rock are reported. A petrographic and physical characterization of the material was preliminary conducted, followed by a wide range of mechanical tests: oedometer, uniaxial, and isotropic compression tests and indirect tensile tests. The stress–strain and strength behaviours of the pozzolana are highlighted and compared with those of the rock materials of the pyroclastic formation (tuff). The mechanical behaviour of the pozzolana is related to its physical and textural characters, with special reference to continuity of the groundmass and porosity. Finally, the role of the material behaviour at the field scale is discussed.

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Nikashin, Konstantin I., et Svetlana O. Zorina. « Volcanogenic material in upper jurassic-lower cretaceous deposits of the Eastern Russian plate and its sources ». Izvestiya of Saratov University. New Series. Series : Earth Sciences 21, n^o 1 (25 mars 2021) : 49–57. http://dx.doi.org/10.18500/1819-7663-2021-21-1-49-57.

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. Widespread “camouflaged” pyroclastics including smectite, illite-smectite and heulandite are detected in the upper jurassic– lower cretaceous deposits of the Ulyanovsk-Saratov basin. Moreover, volcanic glasses are found in several stratigraphic units. The quantity of pyroclastic material in the study section (17–72%) is probably related to volcanic input in the basin. Concentrations of the trace and rare earth elements point to a predominantly acid source of ash material, except the Promzino and Ulyanovsk black shale formations linked to the mixed andesite-basaltic and felsic sources. Island arcs of the Northern Tethys basin and the High-Altitude Arctic Igneous Province are regarded as probable sources of the pyroclastic influx in the epeiric basin of the Russian Platform in the Jurassic-Early Cretaceous.

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Goldberd Harmuda Duva Sinaga, Winarto Silaban et Ady Frenly Simanullang. « Analysis of Coulomb Stress of Sumatera Earthquake Against Pyroclastic Flow of Mount Sinabung as Data Prone Volcano Disaster ». World Journal of Advanced Research and Reviews 13, n^o 1 (30 janvier 2022) : 793–803. http://dx.doi.org/10.30574/wjarr.2022.13.1.0086.

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The islands of Sumatra and Sinabung are located southwest of the Sundaland Continent which is a convergence route between the Indian-Australian Plate that infiltrates to the west of the Eurasian/Sundaland Plate. The increase in activity of Mount Sinabung was preceded by large earthquakes to the west and south while the eruption of Mount Sinabung produced pyroclastics. The purpose of this study is to find out the analysis of coulomb stress from the Sumatra Island earthquake to the pyroclastic flow of Sinabung as data on volcanic disasters. This study used the coulomb stress method with coulomb 3.3. The earthquake data analyzed was Mw, depth, and focal mechanism. The results of the analysis in the form of the direction of the spread of stress and the value of increased coulomb stress in Sinabung in 2014-2016. Sinabung's positive stress coulomb value in 2014 was 0.113 bar with a positive coulomb stress spread angle of 90o against sinabung pyroclastic flow. Sinabung's positive stress coulomb value in 2015 was 0.235 bar with a positive coulomb stress spread angle of 90o against sinabung pyroclastic flow. Sinabung's positive stress coulomb value in 2016 was 0.118 bar with a positive coulomb stress spread angle of 90o against sinabung pyroclastic flow. Coulomb stress analysis affects the direction of prioclastic flow by as far as 180o although it is not the same as the results in the field. This is because the peak of Sinabung has landslides in the southeast-south, thus opening a pyroclastic flow road to the southeast-south.

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Petrik, Attila, Barbara Beke, László Fodor et Réka Lukács. « Cenozoic structural evolution of the southwestern Bükk Mts. and the southern part of the Darnó Deformation Belt (NE Hungary) ». Geologica Carpathica 67, n^o 1 (1 février 2016) : 83–104. http://dx.doi.org/10.1515/geoca-2016-0005.

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Abstract Extensive structural field observations and seismic interpretation allowed us to delineate 7 deformation phases in the study area for the Cenozoic period. Phase D1 indicates NW–SE compression and perpendicular extension in the Late Oligocene–early Eggenburgian and it was responsible for the development of a wedge-shaped Paleogene sequence in front of north-westward propagating blind reverse faults. D2 is represented by E–W compression and perpendicular extension in the middle Eggenburgian–early Ottnangian. The D1 and D2 phases resulted in the erosion of Paleogene suites on elevated highs. Phase D2 was followed by a counterclockwise rotation, described in earlier publications. When considering the age of sediments deformed by the syn-sedimentary D3 deformation and preliminary geochronological ages of deformed volcanites the time of the first CCW rotation can be shifted slightly younger (~17–16.5 Ma) than previously thought (18.5–17.5 Ma). Another consequence of our new timing is that the extrusional tectonics of the ALCAPA unit, the D2 local phase, could also terminate somewhat later by 1 Myr. D4 shows NE–SW extension in the late Karpatian–Early Badenian creating NW–SE trending normal faults which connected the major NNE–SSW trending sinistral faults. The D5 and D6 phases are late syn-rift deformations indicating E–W extension and NW–SE extension, respectively. D5 indicates syn-sedimentary deformation in the Middle Badenian–early Sarmatian and caused the synsedimentary thickening of mid-Miocene suites along NNE–SSW trending transtensional faults. D5 postdates the second CCW rotation which can be bracketed between ~16–15 Ma. This timing is somewhat older than previously considered and is based on new geochronological dates of pyroclastite rocks which were not deformed by this phase. D6 was responsible for further deepening of half-grabens during the Sarmatian. D7 is post-tilt NNW–SSE extension and induced the deposition of the 700 m thick Pannonian wedge between 11.6–8.92 Ma in the southern part of the study area.

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Byron, Benjamin D., Catherine M. Elder, Timothy D. Glotch, Paul O. Hayne, Lori M. Pigue et Joshua T. S. Cahill. « Evidence for Fine-grained Material at Lunar Red Spots : Insights from Thermal Infrared and Radar Data Sets ». Planetary Science Journal 4, n^o 9 (1 septembre 2023) : 182. http://dx.doi.org/10.3847/psj/acf134.

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Abstract Lunar red spots are small spectrally red features that have been proposed to be the result of non-mare volcanism. Studies have shown that a number of red spots are silicic, and are spectrally distinct from both highlands and mare compositions. In this work, we use data from LRO Diviner, Mini-RF, and Arecibo to investigate the material properties of 10 red spots. We create albedo maps using Diviner daytime solar reflectance data to use as an input to our improved thermophysical model, and calculate the rock abundance (RA) and H-parameter values that best fit Diviner nighttime thermal infrared radiance measurements. The H-parameter can be considered analogous to the thermal inertia of the regolith, with a high H-parameter corresponding to low thermal inertia. We find that the red spots generally have low RA, and do not have a uniform H-parameter but contain localized regions of high H-parameter. We additionally find that the red spots have a low circular polarization ratio (CPR) in many of the same locations that show a low RA and high H-parameter. Low RA, high H-parameter, and low CPR indicate a relative lack of rocks larger than ∼10 cm, which is consistent with previous findings of a mantling of fine-grained pyroclastic material for at least three red spots. Areas with high H-parameter but that do not show clear signs of pyroclastics in other data sets may be evidence of previously undiscovered pyroclastics, or could be due to the unique physical properties (e.g., porosity, rock strength/breakdown resistance) of the rocks that make up the red spots.

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Chékaraou, Mahamane M. S., et Moussa Konaté. « Permian Ages of “Younger Granites” from Mounio Province (Gouré area, Southeastern Niger) ». European Journal of Environment and Earth Sciences 2, n^o 6 (8 décembre 2021) : 27–35. http://dx.doi.org/10.24018/ejgeo.2021.2.6.220.

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African formations intruded by the “Younger Granites” ring complex. In the study area, the “Younger Granites” are represented by volcanic to acid plutonic rocks with hyperalkaline trends (pyroclastic rocks, rhyolites, microgranites, granites, syenites), forming in the North, a circular structure called Gouré ring complex. Preliminary geochronological datings of the Mounio granites have yielded Carboniferous ages. However, recent investigations carried out in this province have identified structures similar to Pan-African deformation structures, such as folds and several generations of schistosity/foliation. Analysis of the relationship between deformation and magmatism has removed any ambiguity regarding the relative age of the deformation. This study focuses on the radiometric dating of the “Younger Granites” of Gouré area, in order to update the geochronological data. Thus, three samples (pyroclastitic rock, rhyolite, microgranite) were dated by the K-Ar method on total rock using a mass spectrometertype MI 1201 IG. Radiometric dating results assign a Lower Permian age (293-287 Ma) to the “Younger Granites” Ring Complex of the Mounio Province in Niger, classically considered to be Carboniferous in age.

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Kostyleva, V. V., E. V. Shchepetova et A. E. Kotelnikov. « Upper Cretaceous rhyolitic ashes in the Utes Derevyannykh Gor area (Novaya Sibir Island, the New Siberian Islands) ». RUDN Journal of Engineering Researches 20, n^o 1 (15 décembre 2019) : 37–47. http://dx.doi.org/10.22363/2312-8143-2019-20-1-37-47.

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The article is concerned with the first finds of rhyolite ashes in Upper Cretaceous sediments of Novaya Sibir Island. In the course of the field work in the area of cape Utes Derevyannykh Gor in 2016, four layers of unlithified fine-grained ashes were found in the Turonian-Coniacian coal-bearing Derevyannye Gory Formation. The article presents the results of petrographic, X-ray diffractometric and microprobe analysis of pyroclastics from ash layers. A typification of volcanogenic-terrigenous deposits is proposed. Thin section of the samples were investigated on a polarizing microscope. X-ray phase analysis of the clay fraction was carried out using a DRON-3 diffractometer. X-ray microanalysis of vitroclasts were carried out on a scanning electron microscope “Jeol JSM-6480LV” with the microprobe analyzer “Oxford Instruments INCA-Energy 350”. It was established that Derevyannye Gory Formation is composed of rhyolitic tuffites, among which fine-grained crystal-vitroclastic and vitroclastic ashes of low and normal alkaline high-potassium rhyolites with thickness up to 2.5 m. Low pyroclastics sediments are not widespread. New data on the structure and composition of the Derevyannye Gory Formation confirm the hypothesis of previous researchers, that sedimentation in the Late Cretaceous in the area of Novaya Sibir Island was accompanied by explosive acidic volcanism. The main purpose of the article is to discuss the sources of pyroclastic material for the territory of the New Siberian Islands in the Turonian-Coniacian age. The conclusion is made about the territorial proximity of the paleovolcanic eruption center to the area of sedimentation. It is assumed that the paleovolcanic centers were located within the present territory of Kotelny, Zemlya Bunge, Faddeevsky islands and, probably, were inherited from the Early Albian stage.

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LAMERA, S., K. ST SEYMOUR, C. VAMVOUKAKIS, M. KOULl, E. PARASKEVAS et G. PE-PIPER. « The Polychnitos ignimbrite of Lesvos island ». Bulletin of the Geological Society of Greece 34, n^o 3 (1 janvier 2001) : 917. http://dx.doi.org/10.12681/bgsg.17118.

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Miocene volcanism on Lesvos was particularly explosive giving rise to two extensive pyroclastic formations, the Sigri pyroclastics to the west and the Polychnitos ignimbrite to the east of the island. The Polychnitos ignimbrite at 17.2±0.5 Ma (Borsi et al.1972) is part of the shoshonitic succession on Lesbos which ranges in composition from basalt to rhyolite and is both underlain and overlain by calcalkaline volcanic rocks (Pe-Piper and Piper 1993) resting on a late Paleozoic metamorphic basement which has acted as an impediment to the free flow of the ignimbrite. The Polychnitos ignimbrite consists of eight lithological units, six of which are presumed to be facies of the same ignimbrite sheet ("PK", "PU", "MGF I, II, III", "Z"). Ignimbrite deposition at elevated temperatures is advocated by its columnar jointing, eutaxitic texture, gas escape structures and glassy zones of intense welding. The typical mineral assemblage of all Polychnitos ignimbrite units consists of plagioclase, Kfeldspar and biotite. It displays phenocryst microtextures indicative of magma mixing. Magma mixing is corroborated of glasses of two discrete compositions. Lithic clast measurements indicate a northeasterly trending fissure vent passing from the northeastern corner of the Kalloni Gulf.

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ΜΑΡΑΝΤΟΣ, Ι., Γ. ΚΟΣΙΑΡΗΣ, Β. ΠΕΡΔΙΚΑΤΣΗΣ, Σ. ΚΑΡΑΝΤΑΣΗ, Β. ΚΑΛΟΕΙΔΑΣ et Χ. ΜΑΛΑΜΗ. « Evaluation of altered pyroclastics from Rhodope prefecture, Thrace, Greece as constituents of pozzolanic cements ». Bulletin of the Geological Society of Greece 34, n^o 3 (1 janvier 2001) : 1155. http://dx.doi.org/10.12681/bgsg.17176.

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In the Komotini Tertiary basin, tuffs of various types are alternated with tuffites, siltostones, sandstones and marls forming a thick volcanosedimentary sequence. The tuffs are characterised as ash-, fine ash- and in some cases as welded ash tuffs. Crystal-,lappili- and breccia tuffs also occur. The tuffs are built up of glass shards, pumice shards and crystal fragments which are cemented by glassy material. Crystal fragments are represented by quartz crystals. Plagioclase, albite, sanidine and biotite exist as well. Essentially, the vitric parts of the tuffs are altered to zeolites (heulandite 2 and/or mordenite, analcime, laumontite / scolecite), clay minerals (smectite, kaolinite +/or mixed layer I/S of regular type), Si02 minerals (quartz, cristobalite) and K-feldspar. For the purposes of this study, firstly, standard portland cement concrete specimens and concrete specimens with pyroclastic material from three different places, replacing portland cement by 20%, were prepared. The mineralogical composition of the samples under study and the area where they come from, is as follows: a. Iampolis: analcime + quartz + K-feldspar + albite + Illite/Smectite b. Darmeni : analcime + quartz + K-feldspar + albite + calcite c. Skaloma : smectite + cristobalite + heulandite-2 + mordenite + K-feldspar + quartz The compressive strength of the prepared specimens after periods of 7 and 28 days was measured and the pozzolanic activity of the samples was calculated according to ASTM Standard C618. Following the first test, the pozzolanic activity of a second sample from Iampolis area was more extensively studied. The compressive strength of concrete specimens made of 100% Portland cement of 145 type, and concrete specimens that were prepared by replacing Portland cement in proportions of 10, 20, 30 and 40% was determined. From the results of this study it is concluded that the analcimic tuffs could be a potential source for pozzolanic cement. More extensive study is needed for the estimation of the percentage of the altered pyroclastics that gives the optimum results concerning the cement pozzolanic activity. The optimization of the pozzolanic properties of the altered pyroclastics by calcination may be investigated as well.

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Ghazi, Mohammad, Emile A. Pessagno, Mohsen Kariminia, R. A. Duncan et A. A. Hassanipak. « Tectonostratigraphy of the Khoy Complex, northwestern Iran ». Stratigraphy 2, n^o 1 (2005) : 49–64. http://dx.doi.org/10.29041/strat.02.1.03.

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Previous studies suggested that only one ophiolite, the “Khoy ophiolite", existed near Khoy, northwestern Iran. This thesis is no longer tenable. Combined investigations (biostratigraphic, chronostratigraphic, geochonometric, geochronologic, and geochemical) demonstrate that there are at least two and perhaps three ophiolite remnants in the Khoy area: (1) A Late Jurassic (early to middle Oxfordian: 156 Ma to 159 Ma 40Ar-39Ar on gabbro) remnant; (2) A Late Cretaceous (early Coniacian: Radiolaria) remnant (~N-MORB geochemistry); and, possibly, (3) A Late Cretaceous (latest Campanian) remnant (E-MORB geochemistry). Because it is impossible to use the term “Khoy ophiolite" in this report, we refer the ophiolitic rocks in the Khoy area to the “Khoy Complex” (sensu International Stratigraphic Guide). The sedimentary contact between Late Cretaceous (early Coniacian) red manganiferous ribbon chert lacking calc-alkaline volcanic contributions and overlying pyroclastics (tuff and tuff breccia) in the far northwestern part of the Khoy complex is of great tectonostratigraphic significance. This interface represents a sudden change from pelagic to pyroclastic sedimentation. Field evidence indicates that the contact is disconformable and is associated with a hiatus of unknown magnitude. Red ribbon chert (lacking calcalkaline contributions) in the same area overlies and is interbedded with N-MORB pillow basalt; early Coniacian Radiolaria were recovered from interpillow siliceous mudstone. We postulate that by the early Coniacian oceanic crust (covered with a veneer of Radiolarian ooze) had moved close enough to an island arc system to receive calc-alkaline pyroclastics. Tectonic melange in the Khoy Complex represents a subduction complex probably associated with the island arc noted above. Micrite (pelagic limestone) knockers in the tectonic melange belt contain Early Cretaceous (late Albian: Vraconian) planktonic foraminifera; Late Cretaceous (early Cenomanian) Radiolaria; Late Cretaceous (early Campanian to early Maastrichtian) planktonic foraminifera; Late Cretaceous (late Maastrichtian) planktonic foraminifera; and early Middle Eocene planktonic foraminifera. The age of the micrite knockers in the tectonic melange, suggests that subduction associated with island arc volcanism continued from the Early Cretaceous (latest Albian) to the Early Tertiary (early middle Eocene).

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Agustina, C., S. R. Utami et Z. Kusuma. « Can application of organic matter, cover crops and tree planting improve infiltration rate of soil covered by pyroclastic materials ? » IOP Conference Series : Earth and Environmental Science 1005, n^o 1 (1 mars 2022) : 012021. http://dx.doi.org/10.1088/1755-1315/1005/1/012021.

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Abstract Pyroclastic materials from volcanic eruption is easily compacted and may develop surface crust, which potentially decreases water infiltration. We conducted research in Ngantang, regularly affected by Mt. Kelud eruption, as an attempt to improve water infiltration using organic matter and cover crop. The organic matter (20 Mg.ha-1) used was sweet potato leaves (Bsp) and Tithonia diversifolia leaves (Btd). Cover crops (Arachis pintoi (Tap) and Tithonia diversifolia (Ttd)) and tree (Paraserianthes falcataria (P1)) were planted. Ring infiltrometer was used to measure infiltration rate on initial soil, on soils covered by pyroclastics after 3 months organic matter and cover crops application, and after one year tree planting. The result showed that infiltration rate of initial soil was significantly decreased with time, when covered by eruption materials. After 3 months application of organic matter and cover crops, infiltration rate was significantly higher than untreated soil covered by volcanic materials. Planting tree increased infiltration rate with the highest infiltration rate occurred in combination with organic matter Tithonia diversifolia leaves and Tithonia diversifolia cover crops. Infiltration rate increased with increasing total pores, but decreased with increasing of meso-pores, especially 12 months after application organic matter, together with planting cover crops and tree.

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Smith, T. E., P. E. Holm, N. M. Dennison et M. J. Harris. « Crustal assimilation in the Burnt Lake metavolcanics, Grenville Province, southeastern Ontario, and its tectonic significance ». Canadian Journal of Earth Sciences 34, n^o 9 (1 septembre 1997) : 1272–85. http://dx.doi.org/10.1139/e17-101.

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Three intimately interbedded suites of volcanic rocks are identified geochemically in the Burnt Lake area of the Belmont Domain in the Central Metasedimentary Belt, and their petrogenesis is evaluated. The Burnt Lake back-arc tholeiitic suite comprises basalts similar in trace element signature to tholeiitic basalts emplaced in back-arc basins formed in continental crust. The Burnt Lake continental tholeiitic suite comprises basalts and andésites similar in trace element composition to continental tholeiitic sequences. The Burnt Lake felsic pyroclastic suite comprises rhyolitic pyroclastics having major and trace element compositions that suggest that they were derived from crustal melts. Rare earth element models suggest that the Burnt Lake back-arc tholeiitic rocks were formed by fractional crystallization of mafic magmas derived by approximately 5% partial melting of an amphibole-bearing depleted mantle, enriched in light rare earth elements by a subduction component. The modelling also suggests that the Burnt Lake continental tholeiitic rocks were formed by contamination – fractional crystallization of mixtures of mafic magmas, derived by ~3% partial melting of the subduction-modified source, and rhyolitic crustal melts. These models are consistent with the suggestion that the Belmont Domain of the Central Metasedimentary Belt formed as a back-arc basin by attenuation of preexisting continental crust above a westerly dipping subduction zone.

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Shimomura, Makoto, Raditya Putra, Niken Angga Rukmini et Sulistiyani. « Numerical Simulation of Mt. Merapi Pyroclastic Flow in 2010 ». Journal of Disaster Research 14, n^o 1 (1 février 2019) : 105–15. http://dx.doi.org/10.20965/jdr.2019.p0105.

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A pyroclastic flow is one of the most dangerous hazardous phenomena. To escape a pyroclastic flow, the influenceable area must be evacuated before the flow occurs. Therefore, to predict the inundation area of a pyroclastic flow is important, and numerical simulation is a helpful tool in this prediction. This study simulated a pyroclastic flow by reproducing the pyroclastic flow of Mt. Merapi that occurred in 2010. However, necessary detailed information of the flow to conduct the simulation, such as total volume and the property of the pyroclastic flow material, flow rate, etc., were not available. Therefore, 20 simulations were conducted, varying the important conditions, such as the volume of pyroclastic material, inter-granular friction factor, and duration of the flow. The results showed that the volume of the pyroclastic material and inter-granular friction factor strongly control the flow characteristics. However, the friction factor does not result in a wide range of values; therefore, volume is the most influencing factor. The most suitable condition is a total volume of pyroclastic material of 30 × 106m3, a 5 min duration of flow, and a 0.6 friction factor.

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Mahood, Gail A. « Pyroclastic Rocks ». Eos, Transactions American Geophysical Union 66, n^o 9 (1985) : 92. http://dx.doi.org/10.1029/eo066i009p00092-03.

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Camus, G., et P. Boivin. « Pyroclastic rocks ». Tectonophysics 120, n^o 3-4 (décembre 1985) : 319–20. http://dx.doi.org/10.1016/0040-1951(85)90056-3.

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Wilson, L. « Pyroclastic rocks ». Physics of the Earth and Planetary Interiors 41, n^o 1 (décembre 1985) : 66–67. http://dx.doi.org/10.1016/0031-9201(85)90103-7.

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Druitt, Tim. « Pyroclastic rocks ». Earth-Science Reviews 23, n^o 3 (mai 1986) : 240–41. http://dx.doi.org/10.1016/0012-8252(86)90035-8.

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Heiken, Grant. « Pyroclastic rocks ». Geochimica et Cosmochimica Acta 49, n^o 4 (avril 1985) : 1083. http://dx.doi.org/10.1016/0016-7037(85)90321-7.

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McBirney, Alexander R. « Pyroclastic Rocks ». Journal of Volcanology and Geothermal Research 26, n^o 1-2 (octobre 1985) : 179–80. http://dx.doi.org/10.1016/0377-0273(85)90053-8.

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Barr, S. M. « Pyroclastic Rocks ». Sedimentary Geology 49, n^o 3-4 (octobre 1986) : 294. http://dx.doi.org/10.1016/0037-0738(86)90045-x.

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Wolf, K. H. « Pyroclastic rocks ». Lithos 18 (janvier 1985) : 61–64. http://dx.doi.org/10.1016/0024-4937(85)90006-4.

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Lopes, Rosana Peporine, et Mabel Norma Costas Ulbrich. « Geochemistry of the alkaline volcanicsubvolcanic rocks of the Fernando de Noronha Archipelago, southern Atlantic Ocean ». Brazilian Journal of Geology 45, n^o 2 (juin 2015) : 307–33. http://dx.doi.org/10.1590/23174889201500020009.

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<p>The Fernando de Noronha Archipelago presents, on its main island, a centrally-located stratigraphic unit, the Remédios Formation (age around 8 - 12 Ma) constituted by basal pyroclastic rocks intruded by dikes, plugs and domes of varied igneous rocks, capped by flows and pyroclastics of mafic to ultramafic rocks of the Quixaba Formation (age around 1 - 3 Ma), which is limited from the underlying unit by an extensive irregular erosion surface. A predominant sodic Remédios series (basanites, tephrites, tephriphonolites, essexite, phonolites) can be separated from a moderately potassic Remédios sequence (alkali basalts, trachyandesites, trachytes), both alkaline series showing mostly continuous geochemical trends in variation diagrams for major as well as trace elements, indicating evolution by crystal fractionation (mainly, separation of mafic minerals, including apatites and titanites). There are textural and mineralogical evidences pointing to hybrid origin of some intermediate rocks (e.g., resorbed pyroxene phenocrysts in basaltic trachyandesites, and in some lamprophyres). The primitive Quixaba rocks are mostly melanephelinites and basanites, primitive undersaturated sodic types. Geology (erosion surface), stratigraphy (two distinct units separated by a large time interval), petrography (varied Remédios Formation, more uniform Quixaba unit) and geochemistry indicate that the islands represent the activity of a protracted volcanic episode, fueled by intermittent melting of an enriched mantle, not related to asthenospheric plume activity.</p>

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Takebe, Mirai, Masao Ban, Motohiro Sato et Yuki Nishi. « The Temporal Variation of Magma Plumbing System of the Kattadake Pyroclastics in the Zao Volcano, Northeastern Japan ». Minerals 11, n^o 4 (18 avril 2021) : 430. http://dx.doi.org/10.3390/min11040430.

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The geologic and petrologic study of the Kattadake pyroclastics (around 10 ka) from the Zao volcano (NE Japan) revealed the structure of the magma plumbing system and the mixing behavior of the shallow chamber. The Kattadake pyroclastic succession is divided into lower and upper parts by a remarkable discontinuity. All rocks belong to medium-K, calc-alkaline rock series and correspond to ol-cpx-opx basaltic-andesite to andesite with 20–28 vol% phenocrystic modal percentage. All rocks were formed by mixing between andesitic magma and near aphyric basalt. The petrologic features of andesites of lower and upper parts are similar, 59–61 wt% SiO2, having low-An plagioclase and low-Mg pyroxenes, with pre-eruptive conditions corresponding to 960–980 °C, 1.9–3.5 kb, and 1.9–3.4 wt% H2O. However, the basalts were ca. 49.4 wt% SiO2 with Fo~84 olivine in the lower part and 51.8 wt% SiO2 with Fo~81 olivine and high-An plagioclase the in upper one. The percentage of basaltic magma in the mixing process was lower, but the temperature of the basalt was higher in the lower part than the upper one. This means that the shallow magma chamber was reactivated more efficiently by the hotter basalts and that the mixed magma with a 70–80% of melt fraction was formed by a smaller percentage of the basaltic magma.

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Goodwin, A. M., H. G. Thode, C. L. Chou et S. N. Karkhansis. « Chemostratigraphy and origin of the late Archean siderite–pyrite-rich Helen Iron Formation, Michipicoten belt, Canada ». Canadian Journal of Earth Sciences 22, n^o 1 (1 janvier 1985) : 72–84. http://dx.doi.org/10.1139/e85-006.

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The 2.7 Ga old Helen Iron Formation (HIF) with its uniquely large siderite–Pyrite orebody conformably overlies chemically altered rhyolite–dacite pyroclastic rocks, including an ottrelite-bearing alteration pipe, the product of exhalative venting in freshly accumulated pyroclastics. HIF, in turn, is conformably overlain by pillowed mafic lava flows.HIF internal stratigraphy is conformable from lower massive siderite–sulfide through middle sulfidic, carbonaceous chert, to upper magnetitic chert. Major- and trace-element and carbon- and sulfur-isotope data demonstrate cyclic fluctuations in chemical precipitation from early chemically complex to later chemically "simple" components.HIF development is attributed to seawater-charged volcanic exhalations in a transitory subaqueous cauldron subsidence basin. Volcanic exhalations contained (1) the main chemical components of HIF; (2) nutrients that triggered intense bacterial activity, the principal low-Eh-inducing agent; and (3) acidic components (e.g., HCI, HF), the principal low-pH-inducing agent. HIF carbonates (predominantly siderite) and sulfides (mainly pyrite) are of marine carbonate and marine sulfate origin, respectively. Organic activity was a vital catalyst in carbonate–sulfide precipitation. HIF is notably deficient in base and noble metals, thereby indicating low circulation–exhalation temperatures, in sharp contrast to contemporary hot, metal-rich geothermal brines at modern spreading ridge axes. This transient subaqueous late Archean volcanic environment, then, was unique in scale but not in kind.

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Ahmad, Asmita, Muchtar Salam Solle et Christianto Lopulisa. « Soil Development from Volcanic Ash Based on Different Pyroclastic Composition ». JOURNAL OF TROPICAL SOILS 24, n^o 3 (19 février 2020) : 135. http://dx.doi.org/10.5400/jts.2019.v24i3.135-140.

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Potential volcano in several provinces in Indonesia played a significant role in the formation and quality of soil development. Soils that developed from the volcanic ashes often thought to contribute greatly to improve soil fertility, without regard to the nature and composition of the volcanic ash produced. Volcanic ash generated from the results in volcanic activity has a different composition, there are basaltic, andesitic and granitic, thereby affecting the process of formation and characteristics of the soil. The Objective of this study is to determine the soil development from different types of pyroclastic generated from Lokon volcano in North Sulawesi. The coordinates of research was in 1o 21' 18.0" N and 124o 49' 20.2"E. this research used ARL Quant X (EDXRF Analyzer) for X-Ray Fluorescence (XRF), Shimadzu XRD-7000 for X-Ray Diffractometer (XRD), geology map (scale 1:250,000), topographic map (scale 1:50,000), XRD software, GIS 10.3 software. Soil analysis for texture, pH, C-Organic, and cation exchange capacity (CEC). There are two types of pyroclastic as the source of soil development from volcanic ash, there are; 1) basaltic pyroclastic with 43.26% Si02 that are resulted from the first magmatic eruption and 2) andesitic pyroclastic with 5.09% Si02 that are resulted from the late magmatic eruption. Basaltic pyroclastic contains Fe 37.63%, Al 11.35%, Ca 13.17% and Mg 5.69%, while andesitic pyroclastic contains Fe 38.35%, Al 6.87%, and Ca 8.61%. Rainfall ranges from 2000-3500 mm/yr helped the soil formation and influenced the character of the soil, such as sandy loam of soil texture, 3.08% of soil C-organic content, 23.24 cmol+/kg of CEC and 148.93 cmol+/kg of clay CEC. Clay minerals content of the soil is vermiculite, kaolinite and, halloysite. Cation supply from basaltic pyroclastic influenced the formation of vermiculite mineral, whereas andesitic pyroclastic more influences the formation of the kaolinite mineral. Formation of soil texture with a predominance of the sand fraction is more influenced by the type of andesitic pyroclastic that more resistant to weathering processes.Keywords: Soil; volcanic ash; pyroclastic; vermiculite; kaolinite

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Nehyba, Slavomír, et Daniel Nývlt. « Deposits of pyroclastic mass flows at Bibby Hill (Pliocene, James Ross Island, Antarctica) ». Czech Polar Reports 4, n^o 2 (1 juin 2014) : 103–22. http://dx.doi.org/10.5817/cpr2014-2-11.

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Sedimentological study of the southern slopes of Bibby Hill (relic of a Pliocene tuff cone) allows recognition of twelve lithofacies and three facies associations. Deposits of pyroclastic currents (both low- and high density pyroclastic currents) dominate over the deposits of pyroclastic flows. Products of suabaerial resedimented pyroclastic deposits play minor role. Vertical distribution of facies associations within the studied succession is not uniform. These differences in the distribution of facies associations are interpreted as response to variations in the intensity and type (Surtseyan, Taalian) of phreato-magmatic eruptions, water availability and morphology of the cone.

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Scarpati, Claudio, Annamaria Perrotta, Alberta Martellone et Massimo Osanna. « Pompeian hiatuses : new stratigraphic data highlight pauses in the course of the ad 79 eruption at Pompeii ». Geological Magazine 157, n^o 4 (17 février 2020) : 695–700. http://dx.doi.org/10.1017/s0016756819001560.

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AbstractA new stratigraphic survey of the pyroclastic deposits blanketing Pompeii ruins shows departures from prior reconstruction of the events that occurred inside the town during the two main phases (pumice fallout and pyroclastic density currents) of the ad 79 Vesuvius eruption. We document the depth and distribution of subaerial erosion surfaces in the upper part of the pyroclastic sequence, formed during two short-lived breaks occurring in the course of the second phase of the eruption. These pauses could explain why 50% of the victims were found in the streets during the pyroclastic density currents phase.

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Druitt, T. H. « Pyroclastic density currents ». Geological Society, London, Special Publications 145, n^o 1 (1998) : 145–82. http://dx.doi.org/10.1144/gsl.sp.1996.145.01.08.

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Shimomura, Makoto, Wilfridus F. S. Banggur et Agoes Loeqman. « Numerical Simulation of Pyroclastic Flow at Mt. Semeru in 2002 ». Journal of Disaster Research 14, n^o 1 (1 février 2019) : 116–25. http://dx.doi.org/10.20965/jdr.2019.p0116.

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Mt. Semeru (3676 m asl.) is an active volcano in Indonesia. Mt. Semeru has a specific topography i.e., a large straight scar in its south-east flank. The geometry of the scar is approx. 2 km in length and 300–500 m width. The scar is connected to three major drainage channels: the Kobokan River, the Kembar River, and the Bang River. On December 29, 2002, a pyroclastic flow (PF) with an approximate volume of 3.25 × 106m3was generated and it traveled 9–11 km along the Bang River. This pyroclastic flow was the largest among the ones generated from 2002–2003 eruptions of Mt. Semeru. All prior recorded pyroclastic flows traveled 1–2.5 km along the Kembar channel. Thus, this pyroclastic flow suddenly changed its flow path, and it traveled more than three times longer than its antecedents. To investigate the cause of the sudden change, a simulated reproduction of this pyroclastic flow was carried out by employing the numerical simulation method proposed by Yamashita and Miyamoto (1993). Due to the uncertainty of the volume of each pyroclastic flow and the temporal change of deposition thickness, a total of 12 simulation cases were set up, with variations in the number of sequence events, the duration of inflow at the upper reach of the flow, and the inter-granular friction factor. The simulation results showed that to explain the sudden change in flow path, the Kembar channel, around 3 km from the vent, has to be buried by antecedent pyroclastic flows. Furthermore, the individual volumes of the prior flows must be less than 0.25–1× 106m3, with an inflow duration of less than 1 min. The friction factor must be set to be 0.5. By using the most acceptable case, the simulated pyroclastic flows were in good agreement with observed results. The results implied that careful investigation and continuous monitoring of the area at 1500–2000 m asl. on the south-east flank of Mt. Semeru are important to prepare for future pyroclastic flows.

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Spalletti, Luis, et Ferrán Colombo. « Architecture of intereruptive and syneruptive facies in an Andean Quaternary palaeovalley : the Huarenchenque Formation, western Argentina ». Andean Geology 46, n^o 3 (30 septembre 2019) : 471. http://dx.doi.org/10.5027/andgeov46n3-3170.

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The Huarenchenque Formation is a volcano sedimentary unit deposited to the east of the Plio-Quaternary Andean Magmatic Arc. In order to define depositional settings, two lithofacies associations (fluvial and pyroclastic) were defined. The fluvial facies association is composed of polymictic conglomerates with the predominance of basalt- dominated clasts, coarse- medium-grained conglomeratic sandstones and medium- to coarse-grained sandstones. These deposits occur as stacked or single bodies, display both sheet and channelized geometries, and contain a range of internal sedimentary structures, such as planar, low angle stratification and cross-bedding. This facies association is interpreted as the deposit of a multichannel fluvial system characterized by high bed load, steep gradient and non-cohesive bank materials. Facies and architecture of the fluvial deposits are the result of high bank full discharge related to rapid deglaciation of the Andean Last Glacial Maximum. The pyroclastic facies association is characterized by lapilli and ash tuffs deposited from air fall, pyroclastic density current, and density stratified surge mechanisms. In the Huarenchenque Formation the fluvial and the pyroclastic facies associations show a clear physical separation, suggesting that sedimentation occurred in two distinct (intereruptive and syneruptive) phases. During the long-lived intereruptive phases the sedimentary record corresponds mainly to the deposits of the gravelly braided fluvial system, whereas during syneruptive phases the fluvial valley was almost entirely occupied by primary pyroclastic deposits related to high-explosive episodes of the neighbor Andean strato-volcanoes. Although most of the cross-bedded sandstones and conglomerate sandstones are rich in basaltic fragments, some strata are composed almost entirely of pumiceous fragments, while in others there is a marked alternation between “basalt” and “pumiceous” foresets. These attributes reflect the preservation of intrabasinal pyroclastic fragments and allow suggest that: i. explosive volcanic events could be more frequent than reflected by the pyroclastic deposits themselves; ii. syneruptive pyroclastic materials could be eroded (even eliminated) by the fluvial system; iii. contributions of primary pyroclastic material persisted during intereruptive (fluvial-dominated) phases.

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Zhao, Ranlei, Xiao Xu, Wentao Ma, Cunlei Li, Qiushi Zhang et Qingyou Yue. « Reservoir Characteristics and Controlling Factors of Sedimentary Pyroclastic Rocks in Deep-Buried Basins : A Case Study of Yingtai Fault Depression, Southern Songliao Basin ». Energies 15, n^o 18 (9 septembre 2022) : 6594. http://dx.doi.org/10.3390/en15186594.

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In this article, based on core description, thin section, scanning electron microscope (SEM), well logging and reservoir physical properties, the reservoir controlling factors of sedimentary pyroclastic rocks in deep-buried basins are assessed via the relation between reservoirs and defining factors, including lithological characteristics, sedimentary microfacies and diagenesis. In addition, the contributing factors of anomalously high-porosity and high-permeability zone are analyzed. The lithological characteristics and diagenesis of the sedimentary pyroclastic rocks are closely related to reservoirs. The reservoir porosity–permeability of sedimentary pyroclastic rocks with large volcanic clastic particles is better than in those with small volcanic clastic particles. Sedimentary pyroclastic rocks with high content of unstable clastic particles, such as feldspar and rock debris, are easier to form the high-quality reservoirs than those with high content of quartz. The dissolution is the most important and direct reason to form the anomalously high-porosity and high-permeability zones of the sedimentary pyroclastic rocks in deep-buried basins. It is concluded that the size and composition of the clastic particles in the sedimentary pyroclastic rocks are the internal-controlling factors of the effective reservoirs, while the diagenetic fluid and the burial process are the external-controlling factors which form the effective reservoirs.

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Rukmini, Niken Angga, Sulistiyani et Makoto Shimomura. « Numerical Simulation of Historical Pyroclastic Flows of Merapi (1994, 2001, and 2006 Eruptions) ». Journal of Disaster Research 14, n^o 1 (1 février 2019) : 90–104. http://dx.doi.org/10.20965/jdr.2019.p0090.

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Merapi has become one of the most enticing volcanoes due to its activity over the past century. Although we have to agree that the 2010 VEI = 4 (Volcanic Explosivity Index, [1]) eruption is the greatest in its recorded history, Merapi is more famous for its shorter cycle of smaller scale, making it one of the most active volcanoes on Earth. Many mechanisms are involved in an eruption, and pyroclastic flow is the most dangerous occurrence in terms of volcanic hazard. A pyroclastic flow is defined as a high-speed avalanche consisted of high temperature mixture of rock fragments and gas, resulted from lava dome collapse and/or gravitational column collapse. Researchers have studied Merapi’s history and behavior, and numerical simulations are an important tool for future hazard mitigation. By utilizing numerical simulation on basal part of pyroclastic flow, we investigated the applicability of the simulation on pyroclastic flows from historical eruptions of Merapi (1994, 2001, and 2006). Herein, we present a total of 32 simulations and discuss the areas affected by pyroclastic flows and the factors that affect the simulation results.

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Grishin, S. Yu. « The main trends in the dynamics of vegetation on the territory affected by the catastrophic eruption of Bezymyanny Volcano on March 30, 1956 (Kamchatka) ». Известия Русского географического общества 151, n^o 5 (5 novembre 2019) : 32–47. http://dx.doi.org/10.31857/s0869-6071151532-47.

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The transformation of the vegetation cover in the impact zone of the 1956 eruption, in territories covered by various deposits, is considered. As a result of a gigantic eruption (VEI 5), vegetation was exposed to a series of different volcanic impacts. Five main categories of events are distinguished: the movement of material of a huge volume of volcano edifice over a large distance as a result of a giant clastic avalanch, the pyroclastic surge of a direct blast, the pyroclastic flows, the formation of a giant eruptive cloud and ashfalls, as well as the lahars. The volume of erupted (initially high-temperature) deposits was, according to various estimates, in the amount of 1.35-1.5 km3, the volume of cold deposits of a clastic avalanche was 0.5-0.8 km3. The volume of lahar was 0.5 km3. The area covered by the pyroclastic wave of the directed explosion was about 500 km2. Within this lesion zone, deposits of pyroclastic flows have occupied 30-40 km2, and clastic avalanche deposits from 35 to 60 km2. Below 900 m above sea level (a.s.l.) these deposits buried cover of subalpine dwarf alder (dominant species is Alnus fruticosa) and mountain meadow vegetation, as well as forest vegetation (dominant species is Betula ermanii) at its upper limit. Forest and partially dwarf alder vegetation was destroyed on a vast territory mainly under the influence of a pyroclastic wave (in the altitude range from 700-800 to 200 m a.s.l.), as well as lahars (in the range of 250-50 m a.s.l.). Primary successions occur in the alpine and partially subalpine zone on avalanche deposits and pyroclastic flows deposits, as well as in the upper part of the zone impacted by pyroclastic surge of the direct blast (40-45 km2). In part of the territories where thick deposits of the lahars were formed, primary successions also probably occurred. In the zone of primary successions, deposits of a clastic avalanche are settled by plants most slowly due to not-favourable edaphic factors. The process is somewhat more efficient on the deposits of pyroclastic flows (the same ratio was noted on the Shiveluch Volcano). The surface overlapped by deposits of the pyroclastic surge is populated relatively quickly. Secondary succession occurs in the zone of damage to the forest and dwarf trees by the influence of a pyroclastic wave, as well as in the zone of passage of the lahars. Restoring of vegetation to its previous state will take from 50 to ~500 years on different deposits and in different parts of an impact zone.

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Banggur, Willi FS, Cahya Patria, Estu Kriswati, Mirzam Abdurrachman, Gede Suantika, Devy Kamil Syahbana, Richard Korompis et al. « Numerical Simulation of Pyroclastic Flow of Karangetang Volcano Based on 2015 Eruption Activity ». Journal of Geoscience, Engineering, Environment, and Technology 9, n^o 1 (1 avril 2024) : 1–13. http://dx.doi.org/10.25299/jgeet.2024.9.1.14217.

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On May 7-9, 2015 the eruptive activity of Mount Karangetang released pyroclastic flows towards the Batuawang River for 3.6 km and hit Kora kora village which is located south of the Main Crater. This pyroclastic flow originated from lava flows during the effusive eruption period. MODIS satellite image hotspot data shows the lava flow extrusion rate and total volume at the peak began to increase since April 2015 and continued to show an increase until December 2015, with the estimated volume and lava extrusion rate on April 22, 2015 reaching 4.16x106 m3 and 0.53 m3/s, respectively, and on December 9, 2015 the volume reached 1.67x107 m3 with a lava extrusion rate of 1.97 m3/s. The results of field checks show that this pyroclastic flow is dominated by block and ash, and by using numerical simulations show the deflection of pyroclastic flow in accordance with the flow field of the Batuawang river, and the splash of pyroclastic flow towards Kora kora village in addition to the location adjacent to the river flow and also controlled by the narrowing of the river channel due to the accumulation of material in the flow field. A total of 8 numerical simulation cases have been carried out, and in our opinion with an input volume of 500 x103 m3 and a flow material friction of 0.5 is a case that corresponds to a flow event that reaches a distance of 3.6 km from the Main Crater. Taking into account the current activity conditions we used the same parameters to estimate the area that could be affected by pyroclastic flows in the future. Numerical simulation show that the pyroclastic flow traveled 5 km in a south-southwest direction from the top of the main crater.

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Crosta, G. B., et P. Dal Negro. « Observations and modelling of soil slip-debris flow initiation processes in pyroclastic deposits : the Sarno 1998 event ». Natural Hazards and Earth System Sciences 3, n^o 1/2 (30 avril 2003) : 53–69. http://dx.doi.org/10.5194/nhess-3-53-2003.

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Abstract. Pyroclastic soils mantling a wide area of the Campanian Apennines are subjected to recurrent instability phenomena. This study analyses the 5 and 6 May 1998 event which affected the Pizzo d’Alvano (Campania, southern Italy). More than 400 slides affecting shallow pyroclastic deposits were triggered by intense and prolonged but not extreme rainfall. Landslides affected the pyroclastic deposits that cover the steep calcareous ridges and are soil slip-debris flows and rapid mudflows. About 30 main channels were deeply scoured by flows which reached the alluvial fans depositing up to 400 000 m3 of material in the piedmont areas. About 75% of the landslides are associated with morphological discontinuities such as limestone cliffs and roads. The sliding surface is located within the pyroclastic cover, generally at the base of a pumice layer. Geotechnical characterisation of pyroclastic deposits has been accomplished by laboratory and in situ tests. Numerical modelling of seepage processes and stability analyses have been run on four simplified models representing different settings observed at the source areas. Seepage modelling showed the formation of pore pressure pulses in pumice layers and the localised increase of pore pressure in correspondence of stratigraphic discontinuities as response to the rainfall event registered between 28 April and 5 May. Numerical modelling provided pore pressure values for stability analyses and pointed out critical conditions where stratigraphic or morphological discontinuities occur. This study excludes the need of a groundwater flow from the underlying bedrock toward the pyroclastic cover for instabilities to occur.

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Morgan, G. A., E. R. Jawin, B. A. Campbell, G. W. Patterson, A. M. Bramson, C. A. Nypaver, J. D. Stopar, L. M. Jozwiak, A. M. Stickle et S. S. Bhiravarasu. « Radar Perspective of the Aristarchus Pyroclastic Deposit and Implications for Future Missions ». Planetary Science Journal 4, n^o 11 (1 novembre 2023) : 209. http://dx.doi.org/10.3847/psj/ad023a.

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Abstract The Aristarchus plateau represents one of the most complex volcanic provinces on the lunar surface and is host to the largest pyroclastic deposit on the Moon. Lunar pyroclastic deposits offer a window into the Moon’s interior and represent a valuable resource to support a sustained human presence. We present a new analysis of the Aristarchus pyroclastic deposit using Mini-RF bistatic radar data at wavelengths of 4.2 and 12.6 cm. Building on previous Earth-based Arecibo Observatory radar studies at 12.6 and 70 cm, we place further constraints on the spatial extent of the pyroclastic deposit and investigate the clast size distribution and provenance of foreign material distributed within the formation. Concentrations of blocky material >0.5 cm in diameter and suspended within the upper decimeters of the pyroclastic deposit are associated with potential buried mare flows along the rim of Vallis Schröteri and discrete pockets of primary material ejected by the Aristarchus impact. Unraveling the deposit from nonpyroclastic materials and the surrounding landscape creates new constraints with which to reconstruct the volcanic history of the region. From a future mission perspective, the identification of primary Aristarchus material distributed across the plateau offers an opportunity to sample diverse volcanic lithologies within an area that could be sampled by a single Commercial Lunar Payload Services mission. In terms of lunar resource in situ utilization, such ejected material also represents a contaminant; thus, radar data provide an invaluable tool to identify pristine pyroclastic material for mission planners.

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Hayashi, Naoki, Yudzuru Inoue, Tatsuichiro Kawano et Jun Inoue. « Phytoliths as an indicator of change in vegetation related to the huge volcanic eruption at 7.3 ka in the southernmost part of Kyushu, southern Japan ». Holocene 31, n^o 5 (19 avril 2021) : 709–19. http://dx.doi.org/10.1177/0959683620988057.

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Volcanic eruptions can have a significant influence on adjacent ecosystems; however, little is known about the long-term vegetation change related to eruptions. In this study, we examined phytolith records in paleosols at multiple sites in the southern Kyushu District, Japan, to assess the influence of the Kikai caldera eruption 7300 years ago on vegetation. Our results show the vegetational difference before and after the eruption in the study region. Specifically, in the area where the pyroclastic flows distributed more thickly, the original evergreen forest was replaced by Andropogoneae grasslands after the eruption, which has been dominating the landscape in this area for at least 900 years. By contrast, in areas only mildly affected by pyroclastic flows, despite the temporary replacement of forest by grassland, the forest developed and flourished within several hundreds of years of the eruption. This is because a large amount of pyroclastic flow would have devastated all of the vegetation, whereas smaller amounts would have left some untouched forest sites within refugia. Our findings suggest that the vegetation varied significantly depending on the amount of pyroclastic flow reaching the area, even within the pyroclastic flow distributed region.

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Kurniati, Suwardi, Budi Mulyanto, Budi Nugroho, Welly Herman et Erlina Rahmayuni. « Mineralogical properties of pyroclastic materials from Mount Merapi, Indonesia ». BIO Web of Conferences 99 (2024) : 05007. http://dx.doi.org/10.1051/bioconf/20249905007.

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Mount Merapi, located in Indonesia, is known as one of the most active volcanoes globally, often resulting in volcanic eruptions that produce pyroclastic materials. These materials from Mount Merapi’s eruptions have the potential to influence soil fertility in areas affected by the volcanic activities. This study aims to analyze the mineralogical properties of pyroclastic materials from Mount Merapi. The methodology involves collecting pyroclastic material samples from the 2010 eruption of Mount Merapi, followed by analysis using various mineralogical techniques such as polarized microscopy, X-ray diffraction, petrographic analysis, and wet chemical analysis. The findings offer detailed insights into the mineral composition, types of clay minerals, overall elemental presence, and the rock types forming these minerals in the pyroclastic materials. Variations in mineral composition are observed in the pyroclastic materials from Mount Merapi. Predominant minerals, including the plagioclase, pyroxene, and hornblende groups, are distinctly identified. These minerals’ presence suggests their susceptibility to weathering, categorized as easily weatherable minerals. This tendency for weathering is shown by the presence of elements like Na, Ca, and Mg in these minerals, which are crucial macro-nutrients for plant growth.

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PETERSON, D. W. « Volcanic Deposits : Pyroclastic Rocks. » Science 227, n^o 4682 (4 janvier 1985) : 48–49. http://dx.doi.org/10.1126/science.227.4682.48-a.

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Battaglia, Maurizio. « On pyroclastic flow emplacement ». Journal of Geophysical Research : Solid Earth 98, B12 (10 décembre 1993) : 22269–72. http://dx.doi.org/10.1029/93jb02059.

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Freundt, A., et H. U. Schmincke. « Abrasion in pyroclastic flows ». Geologische Rundschau 81, n^o 2 (juin 1992) : 383–89. http://dx.doi.org/10.1007/bf01828605.

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Yusoff, Nik Yuszrin, Zulhazman Hamzah, Fatimah Kayat et Zulhisyam A.K. « Assessment on Diversity and Abundance of Araceae in Limestone and Pyroclastics Areas in Gua Musang, Kelantan, Malaysia ». Journal of Tropical Resources and Sustainable Science (JTRSS) 1, n^o 1 (15 août 2021) : 16–24. http://dx.doi.org/10.47253/jtrss.v1i1.665.

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The study was conducted in Gua Musang, Kelantan, namely; Kuala Koh N 04° 52’ 02.2”/ E 102° 26’ 33.3” (represents pyroclastics area) and Tanah Puteh N 04° 46’ 11.9”/ E 101° 58’ 35.5” (represents limestone area). A square plot (100 x 100 m) was set-up in both locations for sampling of Araceae. The result shows diversity of Araceae in limestone (28 species ha-1 ) is higher as compared to pyroclastics area (21 species ha-1). The most abundant species in limestone are Anadendrum microstachyum, Homalomena griffithii, Rhaphidophora tenuis and Schismatoglottis brevicuspis. In pyroclastics area, the most abundant is S. calyptrata followed by, S. scortechinii, S. brevicuspis and A. microstachyum. The common species in both areas was hemiepiphytic R. mangayi. The least abundant species in limestone are Amorphophallus sp. and Homalomena Chamaecladon Supergroup. Meanwhile, Scindapsus perakensis, Homalomena Cyrtocladon Supergroup, H. pontederiifolia and Aglaonema simplex were counted as least abundant species in pyroclastics area. Geological features, topography (whether on-slope, on-ridge or edge of stream), and altitude are the most influencing factor on distribution and abundance of aroids species.

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Burgisser, Alain, et George W. Bergantz. « Reconciling pyroclastic flow and surge : the multiphase physics of pyroclastic density currents ». Earth and Planetary Science Letters 202, n^o 2 (septembre 2002) : 405–18. http://dx.doi.org/10.1016/s0012-821x(02)00789-6.

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De Vita, P., et V. Piscopo. « Influences of hydrological and hydrogeological conditions on debris flows in peri-vesuvian hillslopes ». Natural Hazards and Earth System Sciences 2, n^o 1/2 (30 juin 2002) : 27–35. http://dx.doi.org/10.5194/nhess-2-27-2002.

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Abstract. The paper illustrates some results of research carried out to assess factors triggering debris flows which involve the pyroclastic overburdens covering carbonate mountains around Vesuvius. The aims of the research were to reconstruct a relationship between rainfall and debris flow occurrence and to highlight empirical hydrological thresholds through rainfall pattern analysis. The research was also aimed at investigating hydrogeological features of a pyroclastic cover-carbonate bedrock system to analyse factors inducing temporary hydraulic flow, critical for pyroclastic soil stability. The results of research are the following: i) rainfall pattern highlights empirical hydrological thresholds that differentiate the Lattari and Salerno Mountains from the Sarno Mountains; ii) in some sample areas of the Sarno Mountains close to the trigger zones of the landslides of May 1998 strong variation in hydraulic conductivity has been found in the first few meters below the surface; iii) these permeability variations would seem to justify temporary perched water tables that might affect the stability of the pyroclastic mantle.

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Gase, Andrew C., John H. Bradford et Brittany D. Brand. « Estimation of porosity and water saturation in dual-porosity pyroclastic deposits from joint analysis of compression, shear, and electromagnetic velocities ». GEOPHYSICS 83, n^o 3 (1 mai 2018) : ID1—ID11. http://dx.doi.org/10.1190/geo2017-0234.1.

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In situ measurements of porosity and water saturation of pyroclastic deposits have the potential to improve interpretations of geology and hydrology in volcanic regions, and to provide more accurate estimates of dense rock equivalent for volcanic eruptions. However, rock-property models must consider the dual-porosity structure of pyroclastic deposits (i.e., vesicles within pumices and intergranular pores). Vesicularity, intergranular porosity, and water saturation all affect the density, elasticity, and dielectric properties of pyroclastic materials, which control seismic and electromagnetic velocities. The data from active seismic and ground-penetrating radar (GPR) techniques may improve porosity and water saturation estimation if the responses of seismic and electromagnetic velocities to porosity and water saturation variations are complementary in pyroclastic deposits. We developed a dual-porosity petrophysical model to calculate seismic and electromagnetic velocities of pyroclastic deposits with known intergranular porosity, vesicularity, and water saturation, and we tested our ability to estimate porosity and water saturation from field measurements of seismic and electromagnetic velocities in pyroclastic deposits at Mount St. Helens, Washington, USA. Our petrophysical model demonstrates that seismic velocities are more sensitive to intergranular porosity and less sensitive to vesicularity; electromagnetic velocity is primarily controlled by volumetric water content. In a multioffset GPR and active seismic case study, seismic first-arrival traveltime tomography and multichannel analysis of surface waves can resolve high-velocity anomalies caused by porosity reduction. Joint petrophysical inversion of electromagnetic and seismic velocities indicates that although intergranular porosity and water saturation are well-constrained (i.e., standard deviations of approximately 0.05), quantitative estimates of vesicularity remain less certain (i.e., standard deviation of approximately 0.21), due to weak sensitivity.

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Loeqman, Agoes, Nana Sulaksana, A. Helman Hamdani et Wening Sulistri. « Pemodelan Aliran Awanpanas (Aliran Piroklastik) Sebagai Data Pendukung Peta Kawasan Rawan Bencana Gunungapi (Studi Kasus Gunungapi Sinabung Sumatra Utara) Pyroclastic Flows Modeling As A Supporting Data For Volcanic Hazard Map (Case Study Sinabung Volcano-North Sumatra) ». Jurnal Lingkungan dan Bencana Geologi 8, n^o 1 (1 avril 2017) : 1. http://dx.doi.org/10.34126/jlbg.v8i1.162.

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ABSTRAKIndonesia mempunyai 127 gunungapi aktif dan berdasarkan sejarah erupsi 67 di antaranya merupakan gunungapi berbahaya. Erupsi gunungapi memiliki risiko merusak dan mematikan tidak hanya bagi masyarakat yang bermukimdi sekitarnya tapi juga menyebabkan bencana bagi masyarakat luas. Salah satu bahaya primer erupsi gunungapi adalah aliran awanpanas, produk erupsi gunungapi yang sampai saat ini paling banyak menyebabkan jatuhnya korban jiwa, untuk itu diperlukan suatu simulasi/pemodelan untuk mengetahui pola aliran awanpanas guna mendukung penentuan Kawasan Rawan Bencana (KRB) erupsi gunungapi.Simulasi/pemodelan aliran awanpanas ini dibuat berdasarkan data Model Elevasi Digital (DEM) dan memanfaatkan aplikasi Sistem Informasi Geografis (GIS), dengan output berupa representasi dinamis dari kecepatan aliran awanpanas, ketebalan deposit, dan daerah terdampak, dengan studi kasusGunungapi Sinabung Sumatra Utara. Setelah erupsi terakhir 1200 tahun lalu peningkatan aktivitas Gunungapi sinabung ditandai dengan terjadinya letusan freatik pada periode Agustus-September 2010. Setelah 3 tahun beristirahat, aktivitas erupsi kembali terjadi sejak September 2013 hingga saat ini. Aktivitas erupsi berupa pertumbuhan kubah lava dan luncuran awanpanas telah mengakibatkan jatuhnya korban jiwa serta memaksa penduduk mengungsi menjauhi daerah bahaya.Simulasi/pemodelan aliran awanpanas Gunungapi Sinabung karena runtuhnya kubah lava dibuat ke berbagai arah dengan skenario volume kubah lava ; 1, 2 dan 3 juta m3. Hasil overlay antara daerah landaaan awanpanas dengan skenario 3 juta m3 pada Peta KRB menunjukan jangkauan aliran awanpanas pada sektor tenggara, barat dan timurlaut telah sedikit melewati batas KRB III (kawasan sangat berpotensi terlanda awan panas, aliran lava, guguran lava dangas beracun).Kata kunci : awanpanas, Simulasi/model, titan2d, KRBABSTRACTIndonesia has 127 active volcanoes and based on historical eruption, 67 of them are dangerous. Volcano eruption having destructive risk and deadly, not only for the people who lived around, but also caused disaster for large society. One of the primary danger of volcano eruption is the pyroclastic flow, volcano eruption products that until recently was the most caused the loss of life, therefore necessary creating a simulation/modeling to know pyroclastic flow pattern to support of a determination the Volcanic hazard map. Pyroclastic flow Simulation/modeling is made based on the Digital Elevation Model (DEM) data and using Geographical Information System (GIS) application, with output of representation dynamic from the pyroclastic flow velocity, the thickness of deposit, and affected areas, with case Sinabung Volcano in North Sumatra.Since lates eruption about 1.200 years ago, Increased activity Sinabung volcano started by phreatic eruptions during August – September 2010. After three years of rest, eruption activity occurs again on September 2013 until today, with lava dome growth and pyroclastic flow acitvity have caused casualties and forcing residents were being evacuated away from the danger area.The pyroclastic flow simulation/modeling due the lava dome collapse is made into various directions with scenario of lava dome volume ; 1, 2 and 3 million m3. The results of overlay between areas affected by pyroclastic flow model with scenario 3 million m3 and volcanic hazard map showed the range of pyroclastic flow to the southeast, west and northeast sector reached the limit of zone III at volcanic hazard map (Very potentially affected by pyroclastic flow, lava flow, lava avalanche, and toxic volcanic gas ).Keywords : pyroclastic, simulation/modeling Titan2D, volcanic hazard map

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