Search

Your search keyword '"pyroclastic"' showing total 141 results
Start Over Descriptor "pyroclastic"
141 results on '"pyroclastic"'

101. THE EFFECTS OF VOLCANIC ASH FROM PUYEHUE-CAULLE RANGE ERUPTION ON THE SURVIVAL OF DICHROPLUS VITTIGERUM (ORTHOPTERA: ACRIDIDAE).

Author

FERNÁNDEZ-ARHEX, V., BUTELER, M., AMADIO, M. E., ENRIQUEZ, A., PIETRANTUONO, A. L., STADLER, T., BECKER, G., and BRUZZONE, O.

Subjects
*VOLCANIC ash, tuff, etc., *DICHROPLUS, *ORTHOPTERA, *GRASSHOPPERS, *DIATOMACEOUS earth
Abstract

The aim of this work was to evaluate the toxicity of volcanic ash from the volcanic complex Puyehue- Caulle Range on the grasshopper, Dichroplus vittigerum, and compare the results with the effect of diatomaceous earth, an organic pesticide. To test this, we carried out 2 experiments: (i) an acute toxicity test, which consisted of exposing adults of D. vittigerum differentially to volcanic ash and diatomaceous earth, and (ii) a study to determine the survival time of the adult stage by separately exposing the insects to diatomaceous earth and volcanic ash, and by simulating with fans the wind gusts that occur naturally in the area of influence of the volcano. The laboratory data showed that constant exposure to volcanic ash and diatomaceous earth induces mortality in adult grasshoppers. Interestingly, the toxicities of the 2 products were very similar. These results suggest that the onset of the volcanic eruption with the consequent suspension of the pyroclastic material in the air may have had a negative impact on D. vittigerum populations through the mortality of individual adults. In summary, volcanic ash has an insecticidal effect similar to that of diatomaceous earth. [ABSTRACT FROM AUTHOR]

Published
2013

102. Effects and Behavior of Pyroclastic and Lahar Deposits of the 2010 Merapi Eruption Based on High-resolution Optical Imagery

Author

Jean-François Oehler, Soo Chin Liew, Jean-Claude Thouret, Avijit Gupta, Akhmad Solikhin, and Dewi Sri Sayudi

Subjects
geography, geography.geographical_feature_category, Lahar, Drainage basin, High resolution, Pyroclastic rock, Earth and Planetary Sciences(all), General Medicine, Sinuosity, high-resolution imagery, lahars, Facies, 2010 Merapi eruption, Limited capacity, pyroclastic, Geomorphology, Channel (geography), Geology, radar
Abstract

The 26 October-23 November 2010, eruption is Merapi's largest event (VEI 4) over the past 140 years. We tracked and identified the 2010 Merapi's PDC deposits in the most impacted catchment (South) using high-resolution optical (from GeoEye and SPOT-5 satellites as well as low altitude photograph) imagery. We show that high-resolution imagery enables mapping with unprecedented detail the effects of the 2010 eruption in the summit area and across the most devastated catchment on Merapi. We investigated the relationships between the morphology of the river channel, and the apparent behavior of the PDCs and lahars, as deduced from over-banking processes. The 2010 pyroclastic deposits cover an area of ∼27 km2 in the Gendol-Opak catchment, i.e. 35% of the total deposit area. We analyze how unconfined PDCs with over-bank and veneer facies, as well as two types of surges have mantled widespread areas on both sides of the Gendol valley which contain the confined PDC deposits. Geometric and geomorphic characteristics that allow over bank and veneer deposits beyond the main valley are: limited cross-sectional areas under 1500 m2 and the decreasing longitudinal rate of channel confinement. Subsequent lahars six months after the eruption have devastated several villages along the Gendol River 20km from the summit on the ring plain. Small areas down-valley was affected by over-bank lahars once pyroclastic deposits were remobilized 3.8km farther than the PDC front. The over-bank and avulsed lahars can be attributed to the limited capacity (200-250 m2) of river channels and meandering river (sinuosity index of 1.25) across the lowest-angle (

Published
2015
Full Text
View/download PDF

103. A COMPARATIVE ANALYSIS OF LOCALIZED DARK-MANTLE DEPOSITS ON THE MOON

Author

Gustafson, Olaf

Subjects
Geology, Moon, Pyroclastic, Spectra, Volatile, Volcanic
Abstract

Volcanic deposits on the Moon offer an invaluable opportunity to study its interior and geologic evolution. Volcanic materials erupted onto the surface represent samples of the interior, whose properties provide information about magma source regions at depth, conditions encountered during ascent and eruption, the thermal history of the Moon, and its volatile budget. In addition, some lunar volcanic deposits contain valuable resources, such as iron, titanium, oxygen, and volatile elements, that could be utilized in-situ to support sustained exploration of the Moon and other solar system bodies. Several landmark orbital missions to the Moon were conducted in the early 2000s which provide new insights into the morphology and composition of relatively small (kilometer-scale) volcanic features that were previously undetected or poorly resolved. For this work I used high-resolution images, multi- and hyper-spectral mapping, and digital elevation models from the Lunar Reconnaissance Orbiter Cameras and Laser Altimeter, the Kaguya Terrain Camera and Multiband Imager, and the Chandrayaan-1 Moon Mineralogy Mapper to identify, study, and compare localized dark-mantle deposits across the Moon. These features are often presumed to be emplaced by pyroclastic volcanism. First, I surveyed the Moon to search for unidentified pyroclastic deposits and identified twelve probable previously unidentified deposits based on albedo, texture, morphology, and geologic setting. Next, I investigated potential dark mantling deposits on the Southeast Limb of the Moon, a region consisting of highlands terrain located SE of Mare Fecunditatus, south of Mare Smythii, and north of Mare Australe. I examined the physical and spectral properties of these deposits to constrain their composition and mode of emplacement, identify interdeposit variations, and draw conclusions about regional and subsurface geologic processes. Based primarily on morphology and topography, I concluded that many of the SE Limb deposits previously identified as pyroclastic in origin were likely effusively emplaced. I also identified three previously unmapped pyroclastic deposits. I found that the volcanic deposits in this area comprise three major spectral groups, similar to either Mare Fecunditatis, Mare Australe, or glassy pyroclastic deposits elsewhere on the Moon, and conclude that volcanism across the SE Limb was likely fed from at least two distinct magma source regions. Finally, I investigated known pyroclastic deposits on the NE Limb of the Moon, an area bounded by Mare Frigoris to the NW, Mare Serenitatis to the SW, Mare Crisium to the south, and Mare Humboldtianum to the NE. Spectral reflectance patterns indicated these deposits have broadly similar spectral properties, consistent with a mixture of juvenile glasses and orthopyroxene-rich highlands wall rock from the vents. But glass concentrations were found to vary significantly, suggesting diversity in eruption conditions. The Gauss pyroclastics were especially glass rich, and the Gauss S(a) deposit was determined to have a hybrid pyroclastic/effusive morphology and spectral properties intermediate between glassy pyroclastics and clinopyroxene-rich maria. There is a division between high-titanium pyroclastics in the western portion of the NE Limb and low-titanium pyroclastics in the eastern portion, suggesting at least two phases of volcanism across the NE Limb. Together, these findings provide important insights into lunar pyroclastic volcanism and support development of increasingly sophisticated models of lunar volcanic processes. My refinement of the catalog of lunar pyroclastic deposits and their physical and spectral properties illuminates the range of characteristics that these features can exhibit and geologic settings where they can occur. Documentation of detailed deposit characteristics indicates that simple models of Vulcanian-style emplacement are not sufficient to explain the diversity of observed features, implying a wider range of eruption styles (and inferred volatile contents) associated with these eruptions. Similarities and differences among deposits regionally and globally suggest that while many properties can be explained by local eruption dynamics, regional factors also have an influence.

Published
2020

104. Geologic mapping of Inari: A large Venusian corona dominated by subsurface processes

Author

Mahoney, Serenity

Subjects
corona, geologic mapping, Inari, pit chains, pyroclastic, Venus
Abstract

Venus and Earth are planets similar in size, mass, and presumed internal heat budget, and thus one might expect similar processes of heat transfer recorded at the surface. However, Venus lacks plate tectonics and therefore its heat transfer mechanisms are unknown. Due to the planets’ similarities, understanding heat transfer processes on Venus can give insight into Earth’s processes and those of other planets. NASA’s Magellan mission employed synthetic aperture radar (SAR) to penetrate Venus’ dense atmosphere to view and image 98% of the surface. Linear mesolands form broad zones, characterized by fracture zone terrain, that connect contemporary volcanic rises. Inari Corona is a unique tectonomagmatic structure within the fracture zone. Unlike many fracture zone coronae, Inari Corona sits relatively isolated and it lacks obvious evidence of volcanic activity at the surface; both of these characteristics contribute to preservation of its rich geologic history. I constructed broad and detailed geologic maps of Inari Corona in order to understand its geologic history and thus gain insight into geologic processes of heat transfer through the lithosphere at this location. Geologic mapping of structural elements revealed three key points: 1) Inari Corona is much larger than previously proposed (>1,000 km vs 300 km diameter); 2) Inari Corona is dominated by subsurface processes, as opposed to extensive surface flows; and 3) Inari Corona evolved dynamically through time and space. In addition, Inari Corona preserves two types of features/deposits that play a critical role in Inari evolution: 1) the extensive development of pit chains, and 2) possible extensive pyroclastic flow deposits. Radial and concentric pit chains, evidence of subsurface processes, dominate Inari Corona’s center. Pit chains occur on numerous planetary surfaces including Earth, Moon, and Mars; however, the pit chains on Venus differ from those on other bodies based on width, length, spacing, and penetrative development across extensive regions (up to 100,000 km2). Surface deposits that cover preexisting features are mainly focused on Inari Corona’s outermost flanks; however, patches of surface cover (veneer) appear randomly across Inari, only partially obscuring features. Patches of veneer may result from selective deposition and erosion from pyroclastic flow deposits. Veneer patches are huge (potentially covering 150,000 km2) compared to relatively minor deposits recently reported (covering up to 40,000 km2).

Published
2020

105. Volcanic reconstruction of the Paleoproterozoic Stroud Breccia: Understanding the transition from a primitive to mature arc and its impact on VMS ore-formation, Snow Lake, Manitoba, Canada.

Author

DeWolfe, Y.M., Gibson, H.L., and Austin-Fafard, S.

Subjects
*BRECCIA, *FELSIC rocks, *MASS-wasting (Geology), *VOLCANIC ash, tuff, etc., *RHYOLITE, *PUMICE
Abstract

• The Paleoproterozoic Stroud Breccia is a result of subaqueous pyroclastic volcanism. • It represents continued early rifting of the primitive arc at Snow Lake. • It marks the transition to the overlying mature arc at Snow Lake. • It delineates synvolcanic faults and associated subsidence structures. • These structures controlled ore-formation in the Anderson sequence below. The Stroud Breccia is a ≤400 m thick package of dominantly felsic volcaniclastic rocks within the Paleoproterozoic Snow Lake arc assemblage. It stratigraphically overlies the ore-interval for the Anderson, Stall and Rod volcanogenic massive sulfide (VMS) deposits at Snow Lake, Manitoba, Canada and occupies the stratigraphic interval between the underlying primitive arc Anderson sequence and the overlying mature arc Chisel sequence. The Stroud Breccia is interpreted to be a product of subaqueous pyroclastic and effusive, dominantly rhyolitic, volcanism, and concomitant subsidence. It consists of felsic tuff to lapilli-tuff, crystal-rich felsic tuff, felsic lapillistone, felsic tuff breccia, mafic tuff to lapilli-tuff, heterolithic tuff breccia to breccia and rhyolite. The finer felsic volcaniclastic units are characterised by angular or broken quartz crystals, angular lithic rhyolite lapilli, and pumice. Fine ash, broken crystals and pumice suggest they were deposited by eruption-fed density currents associated with a phreatomagmatic eruption. The coarser felsic volcaniclastic units are characterized by blocks of strongly quartz-feldspar porphyritic rhyolite and pumice and are interpreted to have been deposited during the reworking of pyroclastic debris flow deposits on the seafloor during mass wasting events at fault scarps. Planar and cross laminations, graded beds and bomb sag structures suggest the mafic tuff to lapilli-tuff unit was deposited by a combination of subaqueous eruption-fed density currents and eruption driven ballistically emplaced ejecta, likely through subaqueous tephra jetting. Lithofacies analyses, and geochemistry has allowed comparison between the felsic volcanic rocks of the Stroud Breccia and those that host the Anderson, Stall and Rod VMS deposits. Detailed mapping has led to the identification of synvolcanic faults, defining basins and volcanic vents, that indicate that the process of incipient rifting of the Anderson sequence primitive arc continued during emplacement of the Stroud Breccia. These structures also define magma and fluid pathways critical in controlling the formation of the Anderson VMS deposits, meaning they represent deep-seated and long-lived structures that can be used as vectors to mineralization at depth. [ABSTRACT FROM AUTHOR]

Published
2020
Full Text
View/download PDF

106. Controls on the explosive emplacement of diamondiferous kimberlites: New insights from hypabyssal and pyroclastic units in the Diavik mine, Canada.

Author

Tovey, Madeline, Giuliani, Andrea, Phillips, David, and Moss, Stephen

Subjects
*CHROMITE, *KIMBERLITE, *HYDROTHERMAL alteration, *LAVA flows, *EXPLOSIVES, *GROUNDWATER analysis, *MINES & mineral resources, *MAGMAS
Abstract

Kimberlites are mantle-derived magmas that either crystallise as hypabyssal intrusions, erupt explosively after rapid ascent to the surface, or less commonly form lava lakes and flows, thereby creating texturally distinct kimberlite units. Efforts to fully understand the processes responsible for the explosive eruption of kimberlite magmas have been hindered by the widespread alteration and crustal contamination of most volcaniclastic kimberlites. To address this issue, we have undertaken a detailed petrographic and mineral chemical study of fresh (i.e. minimally altered) pyroclastic and hypabyssal kimberlites (HK) from the ca. 55-56 Ma A154 North and South kimberlite pipes in the Diavik Mine (Lac de Gras, Canada). These localities host exceptionally fresh kimberlites and are therefore ideally suited to this study. Kimberlite emplacement at A154 North and South initiated with the intrusion of hypabyssal kimberlite (external dykes), and was followed by the explosive formation of kimberlite pipes and volcaniclastic kimberlite infill. Subsequent kimberlite magmas intruded the volcaniclastic kimberlite units forming multiple cross-cutting, internal dykes. The studied volcaniclastic units feature abundant rounded magmaclasts and massive textures, suggestive of primary deposits. These units are classified as pyroclastic kimberlites (PK). Pyroclastic and hypabyssal kimberlite units at Diavik exhibit subtle mineral compositional differences. Samples from both internal HK units and PK units feature identical compositions for liquidus olivine rims (Mg# = 90.5 ± 0.1 and 90.7 ± 0.2, respectively), with a marginally lower Mg# of 90.2 ± 0.2 in olivine rims from the external HK dykes. Similarly, early-formed chromite compositions are the same for internal HK and PK units (Cr# = 79.1 ± 3.4 and 78.3 ± 5.7; Mg# = 60.0 ± 1.3 and 60.0 ± 2.2), but, differ in the external HK units (Cr# = 86.9 ± 2.7; Mg# = 52.8 ± 1.9). The internal HK and PK units also exhibit lower carbonate contents than the internal HK units. These compositional differences indicate that the external dykes were probably derived from slightly different primitive melt compositions to those parental to the internal HK and PK units. Spinel evolutionary trends from chromite to magnesian ulvӧspinel-magnetite (MUM) compositions are indistinguishable in internal HK and PK samples (Fe3+# = 47.2 ± 5.8 and 49.7 ± 9.3; Cr# = 25.7 ± 11.0 and 17.0 ± 14.0). These results demonstrate that the primitive melt compositions and early magmatic evolution processes are identical for the internal kimberlite units, regardless of whether the kimberlite melts erupted explosively or were emplaced as shallow intrusions. However, magmaclasts in the PK units contain higher abundances of phlogopite (<52 vol. %) and lower quantities of carbonate (<4 vol. %) than the groundmass of the hypabyssal kimberlite samples (<2 vol. % and 25–65 vol. %, respectively). This indicates that the explosively erupted magmas featured higher H 2 O/CO 2 ratios. In contrast, abundant carbonates, including dolomite, in the internal HK samples indicate that CO 2 , and therefore low H 2 O/CO 2 ratios, were retained during the emplacement of this magma, which likely prevented phlogopite crystallisation. Lower K and Rb whole-rock compositions for internal HK samples compared to PK samples, are attributed to the removal of these components in late-stage kimberlitic fluids, as indicated by hydrothermal alteration of the adjacent volcaniclastic kimberlite units. The above results clearly rule out variations in primitive melt composition and melt evolution trajectories as a primary control on the explosive behaviour of the kimberlite magmas at Diavik. Controls on kimberlite explosivity at Diavik are likely due to external factors, such as local stress regimes, the availability of groundwater (i.e. phreatomagmatism) and differing magma supply rates. • Melts parental to the Diavik kimberlites had at least two primitive compositions. • Hypabyssal and pyroclastic kimberlites have the same early melt evolutions. • Kimberlite emplacement style is independent of primary melt compositions. • The late evolution of kimberlite magmas is controlled by the emplacement mechanism. • Emplacement style is likely controlled by external factors, not melt composition. [ABSTRACT FROM AUTHOR]

Published
2020
Full Text
View/download PDF

107. Towards Identification of Zircon Populations in Permo-Carboniferous Rhyolites of Central Europe: Insight from Automated SEM-Mineral Liberation Analyses.

Author

Przybyło, Arkadiusz, Pietranik, Anna, Schulz, Bernhard, and Breitkreuz, Christoph

Subjects
ZIRCON, SCANNING electron microscopes
Abstract

Zircon is a main mineral used for dating rhyolitic magmas as well as reconstructing their differentiation. It is common that different populations of zircon grains occur in a single rhyolitic sample. The presence of both autocrystic and antecrystic zircon grains is reflected in their strongly varied chemical compositions and slight spread of ages. However, postmagmatic processes may induce lead loss, which is also recorded as a spread of zircon ages. Therefore, new approaches to identify different zircon populations in rhyolitic rocks are needed. In this study, we suggest that detailed examination of zircon positions in the thin sections of rhyolitic rocks provides valuable information on zircon sources that can be used to identify autocrystic and antecrystic zircon populations. Automated Scanning Electron Microscope (SEM) analyses are of great applicability in determining this, as they return both qualitative and quantitative information and allow for quick comparisons between different rhyolite localities. Five localities of Permo-Carboniferous rhyolites related to post-Variscan extension in Central Europe (Organy, Bieberstein, Halle, Chemnitz, Krucze) were analyzed by automated SEM (MLA-SEM). The samples covered a range of Zr whole rock contents and displayed both crystalline and glassy groundmass. Surprisingly, each locality seemed to have its own special zircon fingerprint. Based on comparisons of whole rocks, modal composition and SEM images Chemnitz ignimbrite was interpreted as containing mostly (or fully) antecrystic zircon, whereas the Bieberstein dyke was shown to possibly contain both types, with the antecrystic zircon being associated with disturbed cumulates. On the other hand, Organy was probably dominated by autocrystic zircon, and Krucze contained dismembered, subhedral zircon in its matrix, whereas Halle zircon was located partly in late veins, filling cracks in laccolith. Both localities may, therefore, contain zircon populations that represent later stages than the crystallization of the main rhyolitic body. [ABSTRACT FROM AUTHOR]

Published
2020
Full Text
View/download PDF

108. Shallow marine basaltic volcanism of the Machadodorp Member (Silverton Formation, Pretoria Group), Transvaal Basin, South Africa — An example of Paleoproterozoic explosive intraplate volcanic activity in an epeiric embayment.

Author

Lenhardt, Nils, Bleeker, Wouter, Ngwa, Caroline Neh, and Aucamp, Tarryn

Subjects
*THOLEIITE, *BRECCIA, *VOLCANISM, *GEOCHEMICAL modeling, *INTRAPLATE volcanism, *TRACE elements, *TURBIDITES
Abstract

• First lithofacies analysis of the Paleoproterozoic Machadodorp Member (Silverton Formation, Transvaal Supergroup, South Africa). • Interpretation as ancient seamount volcanism in an intra-cratonic setting under incipient rifting conditions. • Variable ancient mantle enrichment is responsible for the trace elements variations observed in the Machadodorp rocks. The early Paleoproterozoic Machadodorp Member of the Silverton Formation (Pretoria Group, Transvaal Supergroup), South Africa, is an example of ancient submarine explosive volcanism in an intra-cratonic setting under incipient rifting conditions. The Silverton Formation consists of three different members, which include, in ascending order, the Boven Member, the Machadodorp Member and the Lydenburg Member. The formation is primarily characterized by the muddy sediments of the Boven and Lydenburg members, which formed in a relatively shallow submarine environment, predominantly as sub-storm wave-base pelagic deposits, within an epeiric embayment on the Kaapvaal Craton. The subaqueous Machadodorp Member volcanic activity is mostly distributed in the eastern part of the basin. So far, the volcanism of the Machadodorp Member has not been studied in detail. Therefore, a detailed facies analysis of its volcanism was initiated, allowing constraints on its volcanic evolution. The Machadodorp Member consists of a basal unit of basaltic sheet lava, followed by a fining-upward succession of volcaniclastic rocks, ranging from breccias, tuff-breccias and tuffs, rich in fluidal-shaped clasts, to laminated tuffs that are related to subaqueous mass flows, and a final sheet lava that characterized the end of volcanic activity in the section studied. The Machadodorp Member rocks are tholeiitic basalts in composition, with all samples plotting in the low-TiO 2 suite. Fractional crystallization of clinopyroxene, olivine and plagioclase was the predominant evolutionary process as illustrated by mineral chemistry and major element geochemical modeling. AFC (Assimilation and Fractional Crystallization) processes could not account for all the trace element variations, nor for the arc-like signatures observed on the primitive mantle normalized plots. Variable ancient mantle enrichment beneath this area is a more plausible cause for the trace elements variations observed in the Machadodorp rocks. Trace element modeling indicates that the parental composition of these rocks was a variably enriched spinel lherzolite source. Such enrichment must have occurred before 3 Ga during episodes of arc collision and subduction. [ABSTRACT FROM AUTHOR]

Published
2020
Full Text
View/download PDF

109. First evidence for the presence of Andisols in the dry-hot environment of the Arabian Shield.

Author

Sulieman, Magboul M, Sallam, Abdelazeem Sh., Al-farraj, Abdullah S., and Brevik, Eric C.

Subjects
*MINERALS, *ARID soils, *SOIL profiles, *ANDOSOLS, *VOLCANIC soils, *CLAY minerals, *KAOLINITE, *KAOLIN
Abstract

• The presence of Andisols was demonstrated in the hot dry harrats. • Allophane, imogolite, and ferrihydrite were documented in the studied soils. • Smectite, kaolin, and mica dominated the crystalline clay minerals. • Andic soil properties are attributed to the influence of paleoclimatic conditions. Saudi Arabia has many volcanoes and extensive basaltic lava fields known as harrats located along the western part of the Arabian Shield sub-parallel to the Red Sea. The soils developed on these volcanic materials have not yet been investigated. Forty representative soil profiles were selected from six harrats and their morphological and physicochemical properties as well as their mineralogical compositions were characterized using standard chemical, XRD, SEM, and TEM techniques. The main objective of this study was to determine if the soils developed from basaltic rocks in the harrats of the Arabian Shield are Andisols. The results revealed that all representative profiles had volcanic glass content that ranged from 15 to 40%, P-retention capacity >35%, and acid oxalate extractable A1 o + 1/2 Fe o that ranged from 0.44 to 2.20%. The crystalline clay minerals were dominated by smectite, kaolin (kaolinite/halloysite), and mica (illite), whereas, chlorite-hydroxy-interlayered vermiculite (Ch-HIV), palygorskite, Ca-zeolites, and pseudo-chlorite were present as minor components. Small amounts of allophane, imogolite, and ferrihydrite made up the poorly-crystalline clay minerals. All representative profiles satisfied the criteria for andic soil properties, and were classified as Torrands due to the presence of an aridic soil moisture regime in the area. Paleoclimatic conditions that existed in the Arabian Peninsula over the last few thousand years are consistent with the formation of andic and/or vitric soil properties. Because of this, Andisols developed from pyroclastic parent materials and are now present in dry-hot conditions. The presence of Andisols in the study area was demonstrated, and was mainly attributed to the influence of Pleistocene paleoclimatic conditions. [ABSTRACT FROM AUTHOR]

Published
2020
Full Text
View/download PDF

110. Monitoring and behavior of unsaturated volcanic pyroclastic in the Metropolitan Area of San Salvador, El Salvador

Author

José A. Chávez, José Landaverde, Reynaldo López Landaverde, and Václav Tejnecký

Subjects
0211 other engineering and technologies, Pyroclastic rock, 02 engineering and technology, Mass wasting, Suction, Silt, 010502 geochemistry & geophysics, 01 natural sciences, 021101 geological & geomatics engineering, 0105 earth and related environmental sciences, Hydrology, Unsaturated, geography, Multidisciplinary, geography.geographical_feature_category, Research, Pyroclastic, Landslide, Debris, Flowslide, Volcano, Erosion, Tierra Blanca Joven, Soil moisture sensor, Surface runoff
Abstract

Field monitoring and laboratory results are presented for an unsaturated volcanic pyroclastic. The pyroclastic belongs to the latest plinian eruption of the Ilopango Caldera in the Metropolitan Area of San Salvador, and is constantly affected by intense erosion, collapse, slab failure, sand/silt/debris flowslide and debris avalanche during the rainy season or earthquakes. Being the flowslides more common but with smaller volume. During the research, preliminary results of rain threshold were obtained of flowslides, this was recorded with the TMS3 (a moisture sensor device using time domain transmission) installed in some slopes. TMS3 has been used before in biology, ecology and soil sciences, and for the first time was used for engineering geology in this research. This device uses electromagnetic waves to obtain moisture content of the soil and a calibration curve is necessary. With the behavior observed during this project is possible to conclude that not only climatic factors as rain quantity, temperature and evaporation are important into landslide susceptibility but also information of suction–moisture content, seepage, topography, weathering, ground deformation, vibrations, cracks, vegetation/roots and the presence of crust covering the surface are necessary to research in each site. Results of the field monitoring indicates that the presence of biological soil crusts a complex mosaic of soil, green algae, lichens, mosses, micro-fungi, cyanobacteria and other bacteria covering the slopes surface can protect somehow the steep slopes reducing the runoff process and mass wasting processes. The results obtained during the assessment will help explaining the mass wasting problems occurring in some pyroclastic soils and its possible use in mitigation works and early warning system.

Published
2016
Full Text
View/download PDF

111. Petrographic and Geochemical Characteristics of the Middle Triassic Volcaniclastic Deposits from Lika, (External Dinarides, Croatia)

Author

Ostrelič, Damjan, Smirčić, Duje, Drwiła, Małgorzata, Kotlarek, Paulina, and Kubalski, Jacek Piotr

Subjects
Middle Triassic, volcaniclastic deposits, autoclastic, pyroclastic, External Dinarides, Croatia
Abstract

Different types of volcaniclastic rocks are reported in several localities in the External Dinarides. Many authors dealt with magmatic rocks and associated volcaniclastics from the External Dinarides (Poljak & Tajder, 1941 ; Pamić, 1985 ; Lugović & Majer, 1981 ; Marci et al., 1991 ; Aljinović et al., 2010.). Hyaloclastic deposits associated with basalts have never been described so far. Therefore, this paper will present the Middle Triassic hyaloclastic deposits and associated basalts that crop out in vicinity of Donje Pazarište - DP. The deposits are surrounded with shales and brown volcanogenic sandstones, crystaloclastic feldspar rich tuffs, vitroclastic tuffs, and grey pelagic limestones with chert interlayers and chert nodules. Investigated basalts and hyaloclastic deposits are in contact, while their relation to surrounding lithologies is not clearly visible. Nevertheless, they are all assigned to Middle Triassic. Petrographic analysis revealed 3 lithotypes present in the recorded succession: 1) pillow basalts ; 2) faint bedded hyaloclastites with basalt clasts and 3) matrix dominated shard rich basalt hyaloclastite. Hyaloclastic rocks are formed by autoclastic processes by quenching at the edges of coherent basalt flows and cold water (McPhie et al., 1991). Occurrence of pillow basalts and laterally present pelagic limestones suggest that the deposition of basalts and hyaloclastites took place in the deep/pelagic marine environment. Mixing of olivine basalt, limestone and highly altered basalt clasts in the hyaloclastic lithotypes indicate the existence of the older magmatic effusions, and resedimentation processes.

Published
2016

112. Atmospheric injection of sulfur from the Medusae Fossae forming events.

Author

Ojha, Lujendra, Karunatillake, Suniti, and Iacovino, Kayla

Subjects
*GAMMA ray spectrometer, *JELLYFISHES, *VOLCANIC gases, *SULFUR, *VOLCANIC ash, tuff, etc., *GAMMA ray spectrometry
Abstract

A plethora of in-situ bulk chemical and mineralogical analyses, remote sensing data, and geochemical models suggest that the Martian crust is sulfur(S)-rich, exceeding the S content of terrestrial basalts by almost an order of magnitude. The main source of crustal S on Mars is the volcanic exhalation of SO 2 and H 2 S gases. Volcanic ash, expelled along with gases, may be a sink for up to 30% of the exhaled S gas species. We analyze the elemental composition of the Martian shallow sub-surface using the Mars Odyssey Gamma Ray Spectrometer to find areas that are simultaneously enriched in constituents of major volcanic gases such as S, Cl, and H 2 O. A large sedimentary deposit of likely pyroclastic origin called the Medusae Fossae Formation (MFF) is located within this region of possibly extensive alteration by volcanic gases. Based on reasonable terrestrial analog estimates that the MFF scavenged, at maximum, 30% of the exhaled S gas species, we find that a significant amount of S (>1017 kg) would have been delivered to the atmosphere over the time it took for the MFF to be deposited on Mars. The mass of the S emitted from the MFF-forming event(s) is up to 8 orders of magnitude higher than the mass of S emitted from the largest Quaternary volcanic eruption on Earth. Thus, volcanic degassing from the MFF forming events could have significantly affected surface geological processes, climate evolution, and habitability of Mars. • The Medusae Fossae Formation (MFF) is simultaneously enriched in S, Cl, and H2O. • The enrichment of S, Cl, and H2O at the MFF could be due to volcanic degassing. • The S/Cl molar ratio of the MFF corroborates enrichment by volcanic degassing. • The MFF forming events could have supplied a huge amount of atmospheric S. [ABSTRACT FROM AUTHOR]

Published
2019
Full Text
View/download PDF

119. A cone on Mercury: Analysis of a residual central peak encircled by an explosive volcanic vent

Author

Alice Lucchetti, Rebecca J. Thomas, Susan J. Conway, Gabriele Cremonese, Mahesh Anand, David A. Rothery, Matteo Massironi, Cristina Re, ITA, USA, GBR, The Open University [Milton Keynes] (OU), Centro di Ateneo di Studi e Attività Spaziali 'Giuseppe Colombo' (CISAS), Universita degli Studi di Padova, INAF - Osservatorio Astronomico di Padova (OAPD), Istituto Nazionale di Astrofisica (INAF), School of Physical Sciences [Milton Keynes], Faculty of Science, Technology, Engineering and Mathematics [Milton Keynes], The Open University [Milton Keynes] (OU)-The Open University [Milton Keynes] (OU), and The Natural History Museum [London] (NHM)

Subjects
010504 meteorology & atmospheric sciences, Explosive material, chemistry.chemical_element, Pyroclastic rock, Volcanism, 01 natural sciences, [SDU.STU.PL]Sciences of the Universe [physics]/Earth Sciences/Planetology, Impact crater, Hydrocode modelling, 0103 physical sciences, [SDU.STU.VO]Sciences of the Universe [physics]/Earth Sciences/Volcanology, Petrology, 010303 astronomy & astrophysics, Cratering, Explosive volcanism, Mercury, Pyroclastic, Space and Planetary Science, Astronomy and Astrophysics, 0105 earth and related environmental sciences, geography, geography.geographical_feature_category, Landform, Geophysics, Mercury (element), chemistry, Volcano, 13. Climate action, Crest, Geology
Abstract

International audience; We analyse a seemingly-unique landform on Mercury: a conical structure, encircled by a trough, and surrounded by a 23,000 km 2 relatively bright and red anomaly of a type interpreted elsewhere on the planet as a pyroclastic deposit. At first glance, this could be interpreted as a volcanically-constructed cone, but if so, it would be the only example of such a landform on Mercury. We make and test the alternative hypothesis that the cone is the intrinsic central peak of an impact crater, the rim crest of which is visible beyond the cone-encircling trough, and that the trough is a vent formed through explosive volcanism that also produced the surrounding bright, red spectral anomaly. We test this hypothesis by comparing the morphology of the cone and the associated landform assemblage with morphologically-fresh impact craters of the same diameter as the putative host crater, and additionally, by modelling the original morphology of such a crater using a hydrocode model. We show that the present topography can be explained by formation of a vent completely encircling the crater's central peak and also make the observation that explosive volcanic vents frequently occur circumferential to the central peaks of impact craters on Mercury. This indicates that, although this cone initially appears unique, it is in fact an unusually well-developed example of a common process by which impact-related faults localize magma ascent near the centre of impact craters on Mercury, and represents an extreme end-member of the resulting landforms.

Published
2015
Full Text
View/download PDF

121. Experimental study of dense pyroclastic density currents using sustained, gas-fluidized granular flows

Author

Timothy H. Druitt, Peter James Rowley, Olivier Roche, Raymond Alexander Fernand Cas, Laboratoire Magmas et Volcans (LMV), Institut national des sciences de l'Univers (INSU - CNRS)-Université Jean Monnet [Saint-Étienne] (UJM)-Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Observatoire de Physique du Globe de Clermont-Ferrand (OPGC), Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), School of Geosciences, Monash University [Clayton], Observatoire de Physique du Globe de Clermont-Ferrand (OPGC), and Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Jean Monnet - Saint-Étienne (UJM)-Centre National de la Recherche Scientifique (CNRS)

Subjects
Mass flux, Sustained supply, 010504 meteorology & atmospheric sciences, Flow (psychology), Pyroclastic flow, analogue modelling, 010502 geochemistry & geophysics, 01 natural sciences, Pore water pressure, Geochemistry and Petrology, Phase (matter), [SDU.STU.VO]Sciences of the Universe [physics]/Earth Sciences/Volcanology, Geotechnical engineering, Fluidization, pyroclastic, 0105 earth and related environmental sciences, Density current, Mechanics, fluidisation, Pore pressure, Flume, Flow conditions, Flow velocity, Earth Sciences, Experiments, Geology
Abstract

International audience; We present the results of laboratory experiments on the behaviour of sustained, dense granular flows in a horizontal flume, in which high-gas pore pressure was maintained throughout the flow duration by continuous injection of gas through the flume base. The flows were fed by a sustained (0.5–30 s) supply of fine (75 ± 15 μm) particles from a hopper; the falling particles impacted an impingement surface at concentrations of ~3 to 45 %, where they densified rapidly to generate horizontally moving, dense granular flows. When the gas supplied through the flume base was below the minimum fluidization velocity of the particles (i.e. aerated flow conditions), three flow phases were identified: (i) an initial dilute spray of particles travelling at 1–2 m s−1, followed by (ii) a dense granular flow travelling at 0.5–1 m s−1, then by (iii) sustained aggradation of the deposit by a prolonged succession of thin flow pulses. The maximum runout of the phase 2 flow was linearly dependent on the initial mass flux, and the frontal velocity had a square-root dependence on mass flux. The frontal propagation speed during phase 3 had a linear relationship with mass flux. The total mass of particles released had no significant control on either flow velocity or runout in any of the phases. High-frequency flow unsteadiness during phase 3 generated deposit architectures with progradational and retrogradational packages and multiple internal erosive contacts. When the gas supplied through the flume base was equal to the minimum fluidization velocity of the particles (i.e. fluidized flow conditions), the flows remained within phase 2 for their entire runout, no deposit formed and the particles ran off the end of the flume. Sustained granular flows differ significantly from instantaneous flows generated by lock-exchange mechanisms, in that the sustained flows generate (by prolonged progressive aggradation) deposits that are much thicker than the flowing layer of particles at any given moment. The experiments offer a first attempt to investigate the physics of the sustained pyroclastic flows that generate thick, voluminous ignimbrites.

Published
2014
Full Text
View/download PDF

122. The pyroclastic komatiite complex at Sattasvaara in northern Finland

Author

M. Saverikko

Subjects
komatiitic basalt, komatiite, pyroclastic, petrography, chemical analyses, greenstone belt, Archean evolution, central Lapland, Finland, Baltic Shield, Geology, QE1-996.5
Abstract

The Sattasvaara komatiite complex is part of an extensive zone of explosive komatiitic volcanism which may have been a significant stage in the Lapponian evolution regarded as Archean. This volcanism took place at the latest 2.43 Ga ago and appears to have been connected with cratonic rifting in the Baltic Shield. The complex was formed by fissure eruptions rather than central-vent eruptions, at the margin of a restricted depositional basin. Effusive, explosive and mixed eruption phases were separated by erosional periods and the komatiitic volcanism was succeeded by mafic effusions and explosive eruptions. The Sattasvaara complex is composed of interchanging amphibole rocks, or komatiitic basalts, and amphibole-chlorite rocks or (basaltic)komatiites, and encloses minor serpentinitic and peridotitic rocks as terminal komatiite flows and picrite plugs. However, main part of the komatiites has discharged earlier and is present as intercalations in graphitic slate zone beneath the Sattasvaara complex. The komatiitic rocks were originally co-magmatic according to their gradual rock suite. The komatiitic basalt (MgO 9‒18 wt.% anhydrous basis) shows signs of fractional crystallization of pyroxene and plagioclase, whereas the (basaltic) komatiite (MgO 18‒29 wt.% anhydrous basis) contains pyroxene and olivine phenocrysts and the komatiite (MgO>29 wt.% anhydrous basis) is olivine-pyroxene cumulate both in distinct flows and lower parts of the (basaltic)komatiite flows. The erupting lavas differed physically and discharged in unlike manner: eruptions of the fluid komatiitic basalt were Hawaiian-type and the ones of the viscous (basaltic)komatiite were Strombolian-type. The initial komatiite flows were most fluidal and flowed after the manner of flood eruptions. Pyroclasticity is associated with the (basaltic)komatiite that is dominantly fragmentary, consisting of lithic, vitric and crystal ejecta; subordinate lava flows are largely block lavas. The voluminous explosive eruptions appear to have been magmatic in origin. Also, a minor pyroclastic breccia is formed by the komatiitic basalt that is usually present in massive or pillowed lava flows; these exceptional volcanic explosions have possibly caused by hydromagmatic eruptions. The komatiitic rocks may have been source of the gold contained in chromian marbles and quartzite-conglomerates nearby the Sattasvaara complex and the komatiitic volcanism seems to have caused iron-manganoferrous emanations in its periphery.

Published
1985
Full Text
View/download PDF

124. The Effects of Volcanic Ash from Puyehue-Caulle Range Eruption on the Survival of Dichroplus vittigerum

Author

Fernandez Arhex, Valeria Cristina, Buteler, Micaela, Amadio, María Emilia, Enriquez, Andrea Soledad, Pietrantuono, Ana Laura, Stadler, Teodoro, Becker, G., and Bruzzone, Octavio Augusto

Subjects
CIENCIAS AGRÍCOLAS, Agronomía, reproducción y protección de plantas, volcanic ash, purl.org/becyt/ford/4.1 [https], insecticide, grasshopper, Agricultura, Silvicultura y Pesca, pyroclastic, diatomaceous earth, purl.org/becyt/ford/4 [https]
Abstract

The aim of this work was to evaluate the toxicity of volcanic ash from the volcanic complex Puyehue-Caulle Range on the grasshopper, Dichroplus vittigerum, and compare the results with the effect of diatomaceous earth, an organic pesticide. To test this, we carried out 2 experiments: (i) an acute toxicity test, which consisted of exposing adults of D. vittigerum differentially to volcanic ash and diatomaceous earth, and (ii) a study to determine the survival time of the adult stage by separately exposing the insects to diatomaceous earth and volcanic ash, and by simulating with fans the wind gusts that occur naturally in the area of influence of the volcano. The laboratory data showed that constant exposure to volcanic ash and diatomaceous earth induces mortality in adult grasshoppers. Interestingly, the toxicities of the 2 products were very similar. These results suggest that the onset of the volcanic eruption with the consequent suspension of the pyroclastic material in the air may have had a negative impact on D. vittigerum populations through the mortality of individual adults. In summary, volcanic ash has an insecticidal effect similar to that of diatomaceous earth. Fil: Fernandez Arhex, Valeria Cristina. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Patagonia Norte. Estación Experimental Agropecuaria San Carlos de Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Buteler, Micaela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Patagonia Norte. Instituto de Investigación en Biodiversidad y Medioambiente; Argentina Fil: Amadio, María Emilia. Universidad Nacional del Comahue. Centro Regional Universitario Bariloche; Argentina Fil: Enriquez, Andrea Soledad. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Patagonia Norte. Estación Experimental Agropecuaria San Carlos de Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Pietrantuono, Ana Laura. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Patagonia Norte. Estación Experimental Agropecuaria San Carlos de Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Stadler, Teodoro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mendoza. Instituto de Medicina y Biología Experimental de Cuyo; Argentina Fil: Becker, G.. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Patagonia Norte. Estación Experimental Agropecuaria San Carlos de Bariloche; Argentina Fil: Bruzzone, Octavio Augusto. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Patagonia Norte. Estación Experimental Agropecuaria San Carlos de Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Patagonia Norte; Argentina

Published
2013

125. A Semi-Empirical Method to Calculate the Permeability of Homogeneously Fluidized Pyroclastic Material

Author

Alain Burgisser, Institut des Sciences de la Terre d'Orléans - UMR7327 (ISTO), Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, and Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Bureau de Recherches Géologiques et Minières (BRGM) (BRGM)

Subjects
010504 meteorology & atmospheric sciences, [SDE.MCG]Environmental Sciences/Global Changes, Extrapolation, Pyroclastic rock, Mechanics, Elutriation, 010502 geochemistry & geophysics, 01 natural sciences, Permeability (earth sciences), Geophysics, Settling, Geochemistry and Petrology, polydisperse, [SDU.STU.VO]Sciences of the Universe [physics]/Earth Sciences/Volcanology, Geotechnical engineering, Fluidization, permeability, fluidization, Material properties, Porosity, pyroclastic, Geology, 0105 earth and related environmental sciences
Abstract

International audience; This work postulates that highly polydisperse materials have an effective size distribution that controls permeability. Existence of such effective distribution implies that not all clasts participate to the permeable network resisting to gas flow and that clasts smaller than the minimal effective size are elutriated. When this concept is coupled to a generalized Blake-Kozeny equation, the resulting semi-empirical law links permeability to material properties only (bed void fraction, clast sizes and densities). After calibration of an experimental constant, it is able to replicate within ± 0.6 log unit experimentally measured permeabilities of both loosely packed and expanded beds made of highly polydisperse (from 1 μm to 4 mm) pyroclastic deposits that were resampled so as to ensure homogeneous fluidization. The presence of an experimentally calibrated constant and the necessary absence of segregation during fluidization limit the extrapolation of the proposed law to any pyroclastic bed. Satisfactory fitting of the experimental values, however, confirms that the permeability of homogeneously fluidized beds is controlled by a balance between settling and elutriation. This balance suggests a first-order link between permeability and bed expansion, which has implications on the kinetics of dense pyroclastic flows.

Published
2012
Full Text
View/download PDF

126. Kepsut Volkaniklerinin Jeolojisi Ve Petrolojisi

Author

Yarar, Orhun Serhat, Altunkaynak, Şafak, Jeoloji Mühendisliği, Geological Engineering, and Jeoloji Mühendisliği Ana Bilim Dalı

Subjects
Petroloji, jeolojik evrim, Jeoloji Mühendisliği, Petrography, Geological evolution, Jeoloji, izotop jeokimyası, volcanology, Geological Engineering, piroklastik, geochemical features, Petrogenesis, jeolojik özellikler, pyroclastic, Petrology, geologic evolution, geologic features, Geology, Kepsut volkanikleri, jeokimyasal özellikler, Kepsut volcanics, Jeokimya, Geological features, Geochemistry, volkanoloji, isotope geochemistry, Geochemical features
Abstract

Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2012, Thesis (M.Sc.) -- İstanbul Technical University, Institute of Science and Technology, 2012, İnceleme alanı Balıkesir iline bağlı Kepsut ilçesi ve çevresini kapsamaktadır. Bu çalışma ile inceleme alanında yüzeyleyen ve Kepsut volkanitleri olarak adlandırılan volkanik kayaçların iç ayırtları yapılmış, birbiri ile ve çevre kayaçlarla ilişkileri saptanmış, petrografik ve jeokimyasal (ana-iz element ve Sr-Nd izotop) özellikleri incelenmiştir. Bu veriler birlikte değerlendirilerek KB Anadolu’nun bu kesiminde magmatizmanın nasıl bir evrim geçirdiği ortaya konulmaya çalışılmıştır. Kepsut ilçesi ve çevresinde yaklaşık 160 km2’lik bir yayılıma sahip olan çalışma alanın içinde başlıca 4 kaya topluluğu yer almaktadır. Bunlar yaşlıdan gence doğru; a) Temel kayaları b) Kepsut Volkanitleri ve c) Çökel Topluluk d) Alüvyon’dur. Temel kayaları amfibolit-yeşilşist fasiyesinde metamorfizmaya uğramış Sakarya kıtaına ait Kara kaya kompleksi birimlerinden Nilüfer birimi ile temsil edilir. Erken Miyosen yaşlı Kepsut volkanitleri ve Çökel Topluluk temel kayalarını uyumsuzlukla örtmektedir. Kepsut volkanitleri andezit-bazaltik andezit ve dasit-riyolit bileşimli lavlar ve bunlarla ilişkili piroklastik kayaçlardan oluşur. Kepsut volkanitlerini oluşturan Andezit –bazaltik andezit grubu lavların çıkış merkezi Eyüpbükü civarında saptanan bir strato-volkandır. Dasit-Riyolit domları ise bu strato-volkanın çevresinde KB-GD ve KD-GB yönünde dizilmiş (kırık erüpsiyonları) domlarla ilişkilidir. Kepsut volkanitleri pliniyen-sub pliniyen türü patlamalarla üretilmiştir. Farklı volkanik grupları temsil eden kaya örneklerinden elde edilen ana-iz element ve Sr-Nd izotop verileri Kepsut volkanitlerinin zenginleşmiş manto kaynağından türemiş, kıta kabuğundan kirlenmiş melez bir bileşime sahip olduğuna işaret etmektedir. Melez bileşimli bu magma asimilasyon ve buna eşlik eden fraksiyonel kristallenme (AFC) yolu ile evrimleşerek bazaltik andezitten riyolite değişen bileşimdeki lavları oluşturmuştur. İnceleme alanında yer alan gerek felsik (dasit-riyolit grubu) gerekse ortaç-mafik (andezit-bazaltik andezit grubu) lavlar ortak kökenlidir ve Batı Anadolu çarpışma sonrası (post collisional) magmatizmasının ürünlerini temsil etmektedir., This study presents a detailed geology map, volcanic stratigraphy and major-trace element geochemistry (combined with Sr-Nd-Pb isotope compositions) of Kepsut volcanites exposed in and around the Kepsut town of Balıkesir. In Kepsut (Balıkesir) and surroundings four main rock groups are distinguished. These are from bottom to the top as follows; a) Basement rocks b) Kepsut volcanites and c)Sedimentary association d)Alluvion Kepsut volcanites have two main rock groups; andezite-basaltic andezit lavas and associated pyroclastic rocks and dacite-rhyolite lavas and related pyroclastic rocks. Petrographically, they display hemicrystalline porphritic texture. Andesite-basaltic andesite group shows hyalopilitic, pilotaxitic, intersertal, glameroporiphiric, trachytic textures, Dacite-rhyolite lavad have generally hyalopilitic and vitrophyric texture and as a consequence of devitrification, spherulitic texture was mainly found. The relationships between these volcano-stratigraphic groups and their areal distributions in the study area indicate that the Kepsut volcanites were produced by plinian-sub-plinian eruptions of strato volcanoes and small vents aligned along NW-SE and NE-SW around this strato volcano. Kepsut volcanites, geochemically, are basaltic andesite, andesite, dacite and rhyolitic in composition that is consistent with petrographical investigations on same samples. The studied volcanic rock samples are subalkaline and generally calc-alkaline in character. . Both andesite-basaltic andesite and dacite-rhyolite groups belonging to Kepsut volcanites have similar major-trace element characteristics and Sr-Nd-Pb isotope compositions indicating that they are co-genetic and were originated from a common magma. The Sr-Nd isotopic signatures and trace element characteristics of volcanic association indicate that the Kepsut volcanites originated from a hybrid magma which was derived from enriched lithospheric mantle and was contaminated by the continental crustal components. The compositional variations observed in these granitoids are interpreted as a result of open system processes (AFC) rather than a reflection of closed system processes (FC). New major-trace element geochemical data and Sr-Nd isotope compositions obtained from this study and geology of the study area together with regional correlations are in good agreement with enriched-mantle derived and crustally contaminated magmas of post collisional tectonic setting., Yüksek Lisans, M.Sc.

Published
2012

128. Detailed Mapping of Pyroclastic Flow Deposits by SAR Data Processing for an Active Volcano in the Torrid Zone

Author

Asep Saepuloh and Koike, Katsuaki

Subjects
RADARSAT-1, Pyroclastic, Geostatistical Method, Mt. Merapi
Abstract

Field mapping activity for an active volcano mainly in the Torrid Zone is usually hampered by several problems such as steep terrain and bad atmosphere conditions. In this paper we present a simple solution for such problem by a combination Synthetic Aperture Radar (SAR) and geostatistical methods. By this combination, we could reduce the speckle effect from the SAR data and then estimate roughness distribution of the pyroclastic flow deposits. The main purpose of this study is to detect spatial distribution of new pyroclastic flow deposits termed as P-zone accurately using the β°data from two RADARSAT-1 SAR level-0 data. Single scene of Hyperion data and field observation were used for cross-validation of the SAR results. Mt. Merapi in central Java, Indonesia, was chosen as a study site and the eruptions in May-June 2006 were examined. The P-zones were found in the western and southern flanks. The area size and the longest flow distance were calculated as 2.3 km2 and 6.8 km, respectively. The grain size variation of the P-zone was mapped in detail from fine to coarse deposits regarding the C-band wavelength of 5.6 cm., {"references":["S. A. Carn, \"Application of Synthetic Aperture Radar (SAR) imagery to\nvolcano mapping in the humid tropics: A case study in East Java,\nIndonesia\", Bulletin of Volcanology, vol. 61, 1999, pp. 92-105.","D. Massonnet, P. Briole, and A. Arnaud, \"Deflation of Mt. Etna\nmonitored by spaceborne radar interferometry\", Nature, vol. 375, 1995,\npp567-570.","F. Sigmundsson, P. Durnand, and D. Massonnet, \"Opening of an eruptive\nfissure and seaward displacement at Piton de la Fournaise volcano\nmeasured by RADARSAT satellite radar interferometry\", GRL, vol. 26,\n1999, pp. 533-536.","H.A. Zebker, P. Rosen, S. Hensley, and P. Mouginis-Mark, \"Analysis of\nactive lava flows on Kilauea volcano, Hawaii, using SIR-C radar\ncorrelation measurement\", Geology, vol. 24, 1996, 495-498.","B. Voight, E. K. Constantine, S. Siswowidjoyo, R. and Torley, \"Historical\neruptions of Merapi volcano, Central Java, Indonesia, 1768-1998\", J.\nVol. and Geoth. Res., vol. 100, 2000, pp. 69-138.","N. Shepherd, \"Extraction of beta nought and sigma nought from\nRADARSAT CDPF products\", Report AS97-5001 Rev. 2, Canadian\nSpace Agency, Ottawa, Ont., Canada, 1998.","N. F. Glenn and J. R. Carr, \"Establishing a relationship between soil\nmoisture and RADARSAT-1 SAR data obtained over the Great Basin,\nNevada, U.S.A.\", Canadian Journal of Remote Sensing, Vol. 30, No. 2,\n2004, pp. 176-181.","R. F. Fudali and W. G. Melson, \"Ejecta velocities, magma chamber\npressure and kinetic energy associated with the 1968 eruption of Arenal\nvolcano\", Bulletin of Volcanology, vol. 35, 1971, pp. 383-401.","G. Lube, S. J. Cronin, T. Platz, A. Freundt, J. N. Procter, C. Henderson,\nand M. F. Sheridan, \"Flow and deposition of pyroclastic granular flows: a\ntype example from the 1975 Ngauruhoe eruption, New Zealand\", Journal\nof Volcanology and Geothermal Research, vol. 161, 2006, pp. 165-186."]}

Published
2009
Full Text
View/download PDF

129. Aufbau und pyroklastische Abfolge eines kleinen quartären (?) Maars im Pali Aike Vulkanfeld, Santa Cruz, Argentinien

Author

Miguel J. Haller and Károly Németh

Subjects
geography, geography.geographical_feature_category, Pyroclastic rock, Ecological succession, Archaeology, Maar, BASALT, PYROCLASTIC, Ciencias de la Tierra y relacionadas con el Medio Ambiente, Volcano, PHREATOMAGMATIC, General Earth and Planetary Sciences, Geología, TUFF RING, SCORIA, MAAR, Quaternary, Geology, CIENCIAS NATURALES Y EXACTAS
Abstract

An approximately 200 m long, 3 m thick continuous outcrop of a near vent crater rim tephra sequence from a young phreatomagmatic volcano of the Pali Aike Volcanic Field (Santa Cruz Province, Argentina) is one of the few outcrops where the eruptive sequence of the phreatomagmatic volcanoes of this field can be studied. Regardless of the large number of morphological features such as lake filled depressions, suggestive of the existence of maar volcanoes in the Pali Aike Volcanic Field, exposed tephra ring sequences are rare. The newly identified tephra ring section documents an eruption history of a maar that erupted through a “soft rock” environment and formed a shallow maar basin, currently filled with saline lake water. The tephra ring is rich in pre-volcanic sedimentary material. A fine grained tephra succession with abundant glassy pyroclasts indicates effective magma/water interaction and the presence of high energy bedforms suggests subsequent transportation and deposition from high energy base surges. Irregularly interbedded accidental lithic fragment rich beds suggest temporal collapse of the volcanic conduit of the active vent. The common appearance of cauliflower and breadcrust bombs together in the coarse grained tephra beds suggest that during magma/water interaction certain part of the uprising melt could have reached the surface without significant contact with the ground water. Ein etwa 200 m langer und 3 m mächtiger Aufschluss in einem schlotnahen Kraterwall eines jungen Vulkans des Pali Aike Vulkanfeldes (Provinz Santa Cruz, Argentinien) ermöglicht – als einer der wenigen Aufschlüsse – die Untersuchung der eruptiven Sequenz der phreatomagmatischen Vulkane dieses Feldes. Ungeachtet der großen Zahl von morphologischen Merkmalen wie seegefüllte Senken, die auf Maarvulkanismus hindeuten, sind aufgeschlossene Tephraringsequenzen selten. Der neu gefundene Kraterrandanschnitt dokumentiert die Eruptionsgeschichte eines Maares, das durch ein unverfestigtes Nebengestein eruptierte. Diese Eruption formte ein flaches Maarbecken, das heute mit einem Salzsee gefüllt ist. Die Tephra ist reich an prävulkanischem sedimentärem Material. Eine feinkörnige Tephraabfolge mit vielen Glaspyroklasten spricht für einen effektiven Magma-Wasser-Kontakt, und das Vorhandensein von Hochenergie-Ablagerungsstrukturen legt einen abschließenden Transport und Ablagerung aus hochenergetischen „base surges“ nahe. Unregelmäßig eingeschaltete Schichten, die reich an Gesteinsfragmenten sind, zeigen den zeitweiligen Kollaps des Förderschlotes. Das häufige Vorkommen von Blumenkohl- und Brotkrustenbomben in den grobkörnigen Tephraschichten belegt, dass während der MagmaWasser-Interaktion bestimmte Teile der aufsteigenden Schmelze die Oberfläche ohne deutlichen Kontakt mit dem Grundwasser erreicht haben könnten. Fil: Haller, Miguel Jorge F.. Universidad Nacional de la Patagonia "San Juan Bosco"; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; Argentina Fil: Németh, Karoly. Eötvös University. Department of Regional Geology; Hungría. Massey University; Nueva Zelanda

Published
2006

130. The Kızılcaören Fluorıte-Barite-Ree Deposits Associated With Tertiary Alkaline Volcanics, Sivrihisar, Eskişehir

Author

Gültekin, Ali Haydar and Örgün, Yüksel

Subjects
Mineralization, Rare Earth Elements, Alkaline Volcanism, Pyroclastic, Cevherleşme, Piroklastik, Alkali Volkanizma, Hidrotermal, Hydrothermal, Nadir Toprak Elementleri
Abstract

% 0.2 ThO₂ içerikli 0.4 milyon ton, yaklaşık % 3.0 Ce+La+Y içerikli 4 milyon ton rezervlerin saptandığı Kızılcaören F-Ba-REE yatakları Kızılcaören’nin (Sivrihisar-Eskişehir) yaklaşık 25 km kuzeyinde yer alır. Ana cevher minerallerini fluorit, barit ve daha az olarak da bastnaesit oluşturur. Brockit ve monazit ise aksesuar mineralleri teşkil eder. Tersiyer alkali volkanizması ile yakın ilişki içinde olan cevherleşme, klastik ve piroklastik kayaçlar içinde çoğunlukla hidrotermal damarlar şeklinde gelişmiştir. Veriler, yatağın daha derinlerde bulunması muhtemel olan bir karbonatit kütlesinden hidrotermal solusyonlarca sökülmüş materyalin daha üst seviyelerde yataklanması şeklindeki remobilizasyon teorisini destekler görünmektedir., The F-Ba-REE deposits containing 0.2 % Th0₂ with 0.4 million tons reserve and containing approximately 3.0 % Ce+La+Y with 4 million tons reserve has been situated about 25 km south of Kızılcaören, Eskişehir. Major ore minerals consist of fluorite, barite, and a lesser amont of bastnasite. Brockite and monazite seem to be accessory minerals. The mineralization is in close association with Tertiary alkaline volcanism and mostly occurs in the form of hydrothermal veins in the elastics and pyroclastic rocks. All the evidence seem to support the remobilization theory related to a possible carbonatite mass which located in a deeper zone.

Published
2000

131. Behaviour of particle-laden flows into the ocean: Experimental simulation and geological implications

Author

McLeod, Paul, Carey, Steven, Stephen, J., Sparks, R., McLeod, Paul, Carey, Steven, Stephen, J., and Sparks, R.

Abstract

The behaviour of subaerial particle-laden gravity currents (e.g. pyroclastic flows, lahars, debris flows, sediment-bearing floods and jokulhlaups) flowing into the sea has been simulated with analogue experiments. Flows of either saline solution, simple suspensions of silicon carbide (SiC) in water or complex suspensions of SiC and plastic particles in methanol were released down a slope into a tank of water. The excess momentum between subaerial and subaqueous flow is dissipated by a surface wave. At relatively low density contrasts between the tank water and the saline or simple suspensions, the flow mixture enters the water and forms a turbulent cloud involving extensive entrainment of water. The cloud then collapses gravitationally to form an underwater gravity current, which progresses along the tank floor. At higher density contrasts, the subaerial flow develops directly into a subaqueous flow. The flow slows and thickens in response to the reduced density contrast, which is driving motion, and then continues in the typical gravity current manner. Complex suspensions become dense flows along the tank floor or buoyant flows along the water surface, if the mixtures are sufficiently denser or lighter than water respectively. Flows of initially intermediate density are strongly influenced by the internal stratification of the subaerial flow. Material from the particulate-depleted upper sections of the subaerial flow becomes a buoyant gravity current along the water surface, whereas material from the particulate-enriched lower sections forms a dense flow along the tank floor. Sedimentation from the dense flow results in a reduction in bulk density until the mixture attains buoyancy, lifts off and becomes a secondary buoyant flow along the water surface. Jokulhlaups, lahars and debris flows are typically much denser than seawater and, thus, will usually form dense flows along the seabed. After sufficient sedimentation, the freshwater particulate mixture can lift off

Published
1999

132. Precisiones terminológicas entre mecanismos de fragmentación y emplazamiento de rocas volcanoclásticas

Author

Martínez González, R. M., Lago San José, Marceliano, Vaquer Navarro, R., Arranz, Enrique, and Valenzuela Ríos, J. I.

Subjects
Emplacement mechanisms, Pyroclastic, Epiclastic, Volcaniclastic, Fragmentation mechanisms
Abstract

Recent volc anic erup tion s have p ro v id e d firs t-h a n d data fo r the study o f «pyroclastic» deposit mechanisms. This study adds to the term «pyroclastic» a depositional meaning. As a result of this expanded meaning, the term «pyroclastic» is not only used for a fragmentation mechanism, but also for a way of em pla cem ent. Taking in to ac c o u n t th e im p o rta n c e , o f volcaniclastic deposits fo r basin analysis, we propose, when using the term «pyroclastic», to clearly state the differences between fragmentation and emplacement mechanisms

Published
1996

133. Fragmentation and emplacement mechanisms of volcaniclastic rocks: a terminological review

Author

Martínez González, R. M., Lago San José, Marceliano, Vaquer Navarro, R., Arranz, Enrique, and Valenzuela Ríos, J. I.

Subjects
Emplacement mechanisms, Pyroclastic, Epiclastic, Volcaniclastic, Fragmentation mechanisms
Abstract

Recent volc anic erup tion s have p ro v id e d firs t-h a n d data fo r the study o f «pyroclastic» deposit mechanisms. This study adds to the term «pyroclastic» a depositional meaning. As a result of this expanded meaning, the term «pyroclastic» is not only used for a fragmentation mechanism, but also for a way of em pla cem ent. Taking in to ac c o u n t th e im p o rta n c e , o f volcaniclastic deposits fo r basin analysis, we propose, when using the term «pyroclastic», to clearly state the differences between fragmentation and emplacement mechanisms

Published
1996

134. Jurassic voicanicíastic rocks of Albentosa-1 (Iberian Chain, Teruel): fragmentation and emplacement mechanisms

Author

Martínez González, R. M., Valenzuela Ríos, J. I., Lago San José, Marceliano, Vaquer Navarro, R., and Arranz, Enrique

Subjects
Iberian Chain, Sierra de Javalambre, Autoclastic, Pyroclastic, Dry base surge
Abstract

In the Sierra de Javalambre a volcaniclastic outcrop (Albentosa-1) showing monomict volcanic breccia and polymict volcanic sandstone and breccia, with planar and festoon cross lamination, is analysed. Data suggest that this volcanism was extruded in a subaerial or shallow water marine environment

Published
1995

135. Las rocas volcanoclásticas jurásicas de Albentosa-1 (Cordillera ibérica, Teruel): Mecanismos de fragmentación y emplazamiento

Author

Martínez González, R. M., Valenzuela Ríos, J. I., Lago San José, Marceliano, Vaquer Navarro, R., and Arranz, Enrique

Subjects
Iberian Chain, Sierra de Javalambre, Autoclastic, Pyroclastic, Dry base surge
Abstract

In the Sierra de Javalambre a volcaniclastic outcrop (Albentosa-1) showing monomict volcanic breccia and polymict volcanic sandstone and breccia, with planar and festoon cross lamination, is analysed. Data suggest that this volcanism was extruded in a subaerial or shallow water marine environment

Published
1995

136. Geology and Eruptive History of the Late Oligocene Nathrop Volcanics, Central Colorado Volcanic Field

Author

Emery, William Daniel

Subjects
Geology, Volcanology, Colorado, Central Colorado Volcanic Field, vitrophyre, welding, pyroclastic, pyroclastic fall, pyroclastic flow, Ruby Mountain, Sugarloaf Mountain, Nathrop
Abstract

The Nathrop Volcanics consist of rhyolite lava and pyroclastic deposits located on the eastern shoulder of the upper Arkansas Graben in south-central Colorado and are part of the extensive late Eocene-Oligocene Central Colorado Volcanic Field. Deposits of the Nathrop Volcanics at Ruby Mountain consist of a lower lithic-rich lapilli tuff (ca. 3 m thick) with multiple layers that are reversely graded with respect to pumice clasts and are overlain by an approximately 30 m thick lithic-poor tuff breccia containing pumice blocks up to 1 m in diameter. The upper portion of the tuff breccia transitions up into a 5 m thick, moderately to densely welded tuff (vitrophyre), which in turn is overlain by a 20 m thick flow-banded rhyolite. A similar stratigraphic sequence is found at Sugarloaf Mountain (

Published
2011

137. Mid-Miocene Magmatic System Development in the Northwestern United States

Author

Brueseke, Matthew Edward

Subjects
Geochemistry, Geology, Steens Mountain, Oregon Plateau, Miocene, flood basalts, 40Ar/39Ar, Yellowstone, Steens Basalt, Owyhee-Humboldt, Santa Rosa-Calico, silicic volcanism, andesite, dacite, basalt, rhyolite, Nevada, Oregon, McDermitt, continental volcanism, pyroclastic
Abstract

This dissertation investigates the spatial, temporal, geochemical, and petrologic development and evolution of mid-Miocene volcanic systems in the southeastern Oregon Plateau region of Oregon and Nevada. This integrated field and laboratory investigation conclusively demonstrates that flood basalt volcanism occurred on the Oregon Plateau over at least a 2 m.y. duration, and provides the first comprehensive view into the development of a mid-Miocene Oregon Plateau volcanic field and its relationship with regional flood basalt volcanism. The first portion of this study focuses on the geochemical and chronostratigraphic characteristics of flood basalt lava flows in the vicinity of Steens Mountain, Oregon. New 40Ar/39Ar ages and recalculated literature ages from the Steens Basalt type section illustrate that multiple magmatic centers were present locally, and that Oregon Plateau flood basalt activity was coeval with the main phase of Columbia River Basalt Group volcanism. The remainder of this study focuses on the Santa Rosa-Calico volcanic field (SC) of northern Nevada in order to better define and understand the link between mid-Miocene Oregon Plateau mafic and silicic volcanism. In the SC, mafic through silicic eruptive loci and shallow intrusive bodies are exposed along broadly north-south trending alignments, coincident with regional lithospheric structures. At least sixteen physically and compositionally distinct units are exposed in the SC representing approximately 2 m.y. of magma production. Local mafic volcanism was dominated by the eruption of Steens Basalt magmas. SC silicic magmas were produced by basaltic magma induced crustal melting of granitoid upper crust and erupted from diverse vent types and locations. At least four distinct intermediate (andesite-dacite) magmatic systems also are documented. Physical, chemical, and isotopic data indicate that open-system petrogenetic processes played a substantial role in the generation of these magmas and also influenced the chemical characteristics of SC mafic and silicic units. The complex array of physical and chemical characteristics and processes displayed and documented by SC units provide an exceptional example of how compositionally diverse volcanic fields develop. Moreover, these complexities establish an important link between regional mid-Miocene mafic magma production and the generation of silicic-dominated volcanic fields on the Oregon Plateau.

Published
2006

139. The Submarine Record of a Large-Scale Explosive Eruption in the Vanuatu Arc: ~1 Ma Efate Pumice Formation

Author

White, J.D.L., Smellie, J.L., Clague, D.A., Raos, AM, McPhie, J, White, J.D.L., Smellie, J.L., Clague, D.A., Raos, AM, and McPhie, J

Abstract

The Efate Pumice Formation (EPF) is the record of a major explosive eruption that occurred in the Vanuatu arc, southwestern Pacific, at about 1 Ma. The EPF is the oldest stratigraphic unit of the Efate Island Group and consists of a succession of non-welded, trachydacitic pumice breccia and shard-rich sand and silt beds with a minimum thickness of ~500 m and a minimum bulk volume of approximately 85 km3. The lower part (Efate Pumice Breccias) of the EPF comprises very thick beds composed almost exclusively of glassy, trachydacitic, pumice fragments with ragged terminations. In contrast, the upper part (Rentabau Tuffs) consists of up to 70 m of well-bedded and well-sorted shard-rich sand and silt. The clast population of this upper part comprises >95 % glassy or formerly glassy shards, but fossil foraminifera are a ubiquitous and important non-volcanic component. Some glass shards have blocky, equant shapes and arcuate fracture surfaces, features typically associated with the influence of external water during fragmentation, but most are cuspate and platy bubble-wall shards. Pyroclast morphologies indicate that the Efate Pumice Breccias were largely generated by magmatic-volatile-driven (dry), explosive fragmentation processes, and lithofacies characteristics indicate deposition in below-storm-wave-base environments, from eruption-sourced, water-supported density currents of waterlogged pumice. The Rentabau Tuffs are interpreted to represent a change to hydromagmatic activity in response to waning discharge that allowed ingress of water (presumably seawater) to the vent(s).

140. The Submarine Record of a Large-Scale Explosive Eruption in the Vanuatu Arc: ~1 Ma Efate Pumice Formation

Author

White, J.D.L., Smellie, J.L., Clague, D.A., Raos, AM, McPhie, J, White, J.D.L., Smellie, J.L., Clague, D.A., Raos, AM, and McPhie, J

Abstract

The Efate Pumice Formation (EPF) is the record of a major explosive eruption that occurred in the Vanuatu arc, southwestern Pacific, at about 1 Ma. The EPF is the oldest stratigraphic unit of the Efate Island Group and consists of a succession of non-welded, trachydacitic pumice breccia and shard-rich sand and silt beds with a minimum thickness of ~500 m and a minimum bulk volume of approximately 85 km3. The lower part (Efate Pumice Breccias) of the EPF comprises very thick beds composed almost exclusively of glassy, trachydacitic, pumice fragments with ragged terminations. In contrast, the upper part (Rentabau Tuffs) consists of up to 70 m of well-bedded and well-sorted shard-rich sand and silt. The clast population of this upper part comprises >95 % glassy or formerly glassy shards, but fossil foraminifera are a ubiquitous and important non-volcanic component. Some glass shards have blocky, equant shapes and arcuate fracture surfaces, features typically associated with the influence of external water during fragmentation, but most are cuspate and platy bubble-wall shards. Pyroclast morphologies indicate that the Efate Pumice Breccias were largely generated by magmatic-volatile-driven (dry), explosive fragmentation processes, and lithofacies characteristics indicate deposition in below-storm-wave-base environments, from eruption-sourced, water-supported density currents of waterlogged pumice. The Rentabau Tuffs are interpreted to represent a change to hydromagmatic activity in response to waning discharge that allowed ingress of water (presumably seawater) to the vent(s).

141. The Submarine Record of a Large-Scale Explosive Eruption in the Vanuatu Arc: ~1 Ma Efate Pumice Formation

Author

White, J.D.L., Smellie, J.L., Clague, D.A., Raos, AM, McPhie, J, White, J.D.L., Smellie, J.L., Clague, D.A., Raos, AM, and McPhie, J

Abstract

The Efate Pumice Formation (EPF) is the record of a major explosive eruption that occurred in the Vanuatu arc, southwestern Pacific, at about 1 Ma. The EPF is the oldest stratigraphic unit of the Efate Island Group and consists of a succession of non-welded, trachydacitic pumice breccia and shard-rich sand and silt beds with a minimum thickness of ~500 m and a minimum bulk volume of approximately 85 km3. The lower part (Efate Pumice Breccias) of the EPF comprises very thick beds composed almost exclusively of glassy, trachydacitic, pumice fragments with ragged terminations. In contrast, the upper part (Rentabau Tuffs) consists of up to 70 m of well-bedded and well-sorted shard-rich sand and silt. The clast population of this upper part comprises >95 % glassy or formerly glassy shards, but fossil foraminifera are a ubiquitous and important non-volcanic component. Some glass shards have blocky, equant shapes and arcuate fracture surfaces, features typically associated with the influence of external water during fragmentation, but most are cuspate and platy bubble-wall shards. Pyroclast morphologies indicate that the Efate Pumice Breccias were largely generated by magmatic-volatile-driven (dry), explosive fragmentation processes, and lithofacies characteristics indicate deposition in below-storm-wave-base environments, from eruption-sourced, water-supported density currents of waterlogged pumice. The Rentabau Tuffs are interpreted to represent a change to hydromagmatic activity in response to waning discharge that allowed ingress of water (presumably seawater) to the vent(s).

Catalog

Books, media, physical & digital resources
See catalog results