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  • Springer Science + Business Media  (7,174)
  • Elsevier  (4,645)
  • 1980-1984  (9,315)
  • 1925-1929  (2,504)
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  • 1
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    Elsevier
    In:  International Review of Cytology, 67 . pp. 171-214.
    Publication Date: 2018-10-29
    Description: This chapter discusses coral skeletogenesis, focusing on the morphology of the skeletogenic tissues. It reviews the light and electron microscope studies carried out in this regard, illustrating the example of the morphology of the skeletogenic tissues of the coral Pocillopora damicornis. A structural organic matrix is present in the adult skeleton of Pocillopora damicornis. One component of this structural matrix is present transiently at the growth surface of the skeleton. It consists of individual sheaths enveloping each forming aragonite crystal. These crystal sheaths, plus some small extracellular vesicles that are presumed to represent a precursor for the sheaths, are together implicated in the hypotheses for coral calcification. The hypotheses fall into the following three broad categories: (1) algal removal of possible inhibitory substances; (2) a general stimulatory effect of algal metabolism; and (3) algal contribution to a skeletal organic matrix.
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  • 2
    Publication Date: 2016-04-08
    Description: Isopach asymmetry, and sediment component changes in DSDP cores from the SE Atlantic (Orange Basin) support the hypothesis of major drainage system changes in SW Africa during late Cretaceous—Cenozoic time. This involved alternations in the use of the 28°S (modern Orange River) and 31°S (modern Olifants River) exit points across the western escarpment by rivers carrying run-off from the Upper Orange/Vaal catchment areas, as well as radical re-organizations of internal drainage geometry. It is postulated that during late Cretaceous times the 28°S exit was used, with the Middle Orange River following a course in the interior well to the south (up to 150 km) of its modern channel. Sediment discharge rates from this river were relatively high (at least 10 × 106 m3 yr−1), and resulted in rapid advancement of the continental margin sediment prism west of the mouth by large-scale slumping. The Palaeogene Orange/Vaal river exit was via the 31°S escarpment crossing, and during the later part of this period, the Cape Canyon was cut across the continental shelf and slope. A significant reduction in sediment discharge (to 2.0 × 106 m3 yr−1) suggests that the Lower Tertiary climate for SW Africa was drier than that of late Cretaceous times. However, aridity did not commence until late Miocene times, when the Orange/Vaal discharge had switched back to the 28°S exit. Modern sediment discharge rates (6.5 × 106 m3 yr−1) are relatively high and reflect soil erosion caused by agricultural activity. The two major alterations in exit point of the Orange/Vaal (late Cretaceous—early Tertiary, and late Oligocene—early Miocene) are related to periods of low sea level, which promoted river capture adjacent to the western escarpment. An additional factor in the first course change may have been the disruption of the Middle Orange channel by late Cretaceous igneous intrusions. Less important internal reorganizations of the drainage system are postulated in late Miocene—Pleistocene times. Economic implications for offshore diamond distribution are briefly mentioned.
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  • 3
    Publication Date: 2016-04-08
    Description: Acoustic basement lies at an average of between 6.0 and 6.5 sec two-way time below sea level in the southern Rockall Trough and northern Porcupine Abyssal Plain. The overlying sedimentary succession reaches maximum thicknesses of at least 4.0 sec, and can be divided by 3 regionally-developed seismic reflecting horizons, which are used as a framework to establish an acoustic stratigraphy for the area by selecting three “type” seismic sections. These reflectors are named, in ascending order, Shackleton, Charcot and Challenger. The area is crossed by E—W basement high structures, the Clare Lineament (which may be an easterly extension of the Charlie Gibbs Fracture Zone), that separates the Porcupine Abyssal Plain from the eastern part of southern Rockall Trough. Under the latter, the post-Shackleton acoustic sequence is thickened, as if dammed to the north of the Clare Lineament, whilst a further thickening, above reflector Charcot, occurs along a NE—SW line somewhat farther north into the southern Rockall Trough. This can also be related to shallow-lying acoustic basement features. Pre-Shackleton sediments overlie a very irregular basement topography. The acoustic characters of the various sediment packages are described and it is speculated that major changes in the sedimentary environments took place across reflectors Shackleton and Challenger, the latter probably establishing the modern bottom current circulation patterns. No ages can be unequivocally assigned to the main reflectors, but previously published data suggest a late Eocene—Oligocene age for Challenger. Possible lavas or sills are identified in the succession between reflectors Shackleton and Charcot.
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  • 4
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    Elsevier
    In:  Marine Geology, 54 (3-4). pp. 237-247.
    Publication Date: 2016-09-05
    Description: DSDP cores from areas of low (Site 505) and high heat flow (Site 504 B) near the Costa Rica Rift, together with seismic profiles from the Panama Basin, have been studied to determine the relationship between: (1) carbonate content and physical and acoustic properties; and (2) carbonate content, carbonate diagenesis and acoustic stratigraphy. Except for ash and chert layers, bulk density correlates strongly and linearly with carbonate content. Velocity is uniform downcore and only small variations at a small scale are measured. Thus an abrupt change in carbonate content will cause abrupt changes in acoustic impedance and should cause reflectors that can be detected acoustically. A comparison of seismic profiler reflection records with physical properties, carbonate content and reflection coefficients indicates that the main reflectors can be identified with ash layers, diagenetic boundaries, and carbonate content variations. Diagenesis of carbonate sediments is present at Site 504 B in a 260 m-thick ooze—chalk—limestone/chert sequence. These diagenetic sequences occur in areas of higher heat flow (200 mW m−2). Seismic profiler records can be used to map the extent and depth of these diagenetic boundaries.
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  • 5
    Publication Date: 2016-07-08
    Description: The cause of the climatically controlled fluctuations in the carbonate content of deep-sea sediments remains the subject of uncertainty and debate. Three variables are involved: supply of biogenic carbonate, loss by dissolution, and dilution by non-carbonate phases. It is suggested that 230Th, which is produced in the ocean at a constant rate provides a reliable reference for measuring variations in rate of sedimentation on a regional scale. Results of a preliminary analysis based on published data indicate that, for depths at and above the lysocline, the carbonate fluctuations observed in cores from the North Atlantic Ocean are due primarily to variations in the terrigenous clay input, which was 2–5 times higher during glacials than during interglacials. Carbonate deposition appears to have been somewhat reduced during glacials, but probably not by more than a factor of 2. From published 230Th232Th profiles it appears that the South Atlantic Ocean also received increased inputs of terrigenous clay during glacial periods.
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  • 6
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    Elsevier
    In:  Continental Shelf Research, 1 (4). pp. 405-424.
    Publication Date: 2016-10-11
    Description: Faunal structure is described for the planktonic molluscs of the Middle Atlantic Bight based on two years of seasonal data from the continental shelf. Collection and taxa groups are constructed using numerical classification and reciprocal averaging ordination. Discriminant analysis is used to relate surface collection groups to physical variables, then taxa group distribution among these collection groups is analyzed by nodal fidelity analysis. The areal distribution of dominant species is presented by season, as is their surface temperature-salinity distribution. Four communities are recognized on the continental shelf. A subarctic community, including Limacina retroversa, Paedoclione doliiformis, and Clione limacina, is advected down the central shelf region from the northeast. A Gulf Stream community of weak vertical migrators, including Limacina trochiformis, Cavolinia longirostris, Creseis conica, Atlanta peroni, and A. gaudichaudi, is introduced onto the shelf in occasional intrusions across the shelf-edge front. A depth-limited warm-water community of strong vertical migrators, including Limacina inflata, L. bulimoides, L. lesueuri, and Cavolinia inflexa is generally confined offshore of the 100-m isobath since the extent of their daily vertical migration is greater than the bottom depths on the continental shelf. A coastal community, including the larvae of Loligo pealei and of Ensis directus is found in coastal water of local origin and is generally confined within a coastal boundary layer.
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  • 7
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    Elsevier
    In:  Animal Behaviour, 28 (4). pp. 1123-1126.
    Publication Date: 2017-02-01
    Description: Pairs of individually recognizable male Octopus vulgaris were observed in a large seawater tank containing two suitable homes (brick pots or plastic buckets). None of the animals established exclusive occupancy of one home and for much of the time both animals were associated together at the same site. Usually one of the two homes was preferred and its occupant was most likely to be the larger animal, or the earlier resident if they were of equal size. Large animals were observed to take food forcefully from smaller octopus. An arm alignment interaction is described which, it is suggested, may be a means by which two octopuses establish their relative sizes.
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  • 8
    Publication Date: 2018-07-25
    Description: Investigations of formation-fluid salinities in a transect from western Georgia to the edge of the Blake Plateau off the coast of Georgia show surprisingly similar hydrochemical features offshore and onshore. A fresh-brackish wedge of groundwater (〈25 g/kg total dissolved solids) lies beneath the shelf to a depth of ∼ 900 m. On land, brackish waters extend to a maximum depth of ∼ 1.2 km below sea level in Lowndes County, Georgia. In deeper horizons, hypersaline brines (〉 100 g/kg) occur in Lower Cretaceous (?) strata. These strata have a pronounced evaporitic (anhydritic) character in the offshore segment. Strong salinity gradients in interstitial waters signify buried evaporite deposits at drill sites beneath the Blake Plateau.
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  • 9
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    Elsevier
    In:  Amsterdam, Elsevier, vol. 81A and 81B, no. 22, pp. 65-70, (1405101733, 336 p.)
    Publication Date: 1984
    Keywords: Textbook of geophysics ; Earth model, also for more shallow analyses !
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  • 10
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    Elsevier
    In:  Amsterdam, I-VII + 329 pp., Elsevier, vol. 1, no. Publ. No. 12, pp. 127, (ISBN 3-540-44363-0)
    Publication Date: 1980
    Keywords: Geothermics ; application ; and ; prospection ; Earthquake hazard ; nuclear ; power ; plants ; Earthquake risk ; solar ; Energy (of earthquakes) ; pollution ; FROTH ; pp. ; 1-81, ; 279-288
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  • 11
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    Elsevier
    In:  Amsterdam, Elsevier, vol. Developments in Petroleum Science vol. 15A, no. Publ. No. 12, pp. 9, (ISBN: 0-12-636380-3)
    Publication Date: 1984
    Keywords: Borehole geophys. ; Textbook of geophysics ; GFZ ; RUB ; GMG ; 3.45.8 ; UniL ; IfGuG ; in ; Französisch
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  • 12
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    Elsevier
    In:  Amsterdam, 253 pp., Elsevier, vol. 10, no. 1, pp. 1-40, (ISBN: 3-540-23712-7)
    Publication Date: 1983
    Keywords: Textbook of geophysics ; Acoustics ; Seismics (controlled source seismology) ; Waves ; Wave propagation
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  • 13
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    Elsevier
    In:  Bull., Polar Proj. OP-O3A4, Signal Processing II: Theories and Applications, Bath, Elsevier, vol. 186, no. XVI:, pp. 689-692, (ISBN: 3-540-23712-7)
    Publication Date: 1983
    Keywords: Seismology ; Seismic arrays ; Spectrum ; Broad-band ; Data analysis / ~ processing ; f-k-Analysis ; Schuessler ; Schussler
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  • 14
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    Elsevier
    In:  Bull., Polar Proj. OP-O3A4, Signal Processing II: Theories and Applications, Leiden, Elsevier, vol. 11, no. XVI:, pp. 673-680, (ISBN: 3-540-23712-7)
    Publication Date: 1983
    Keywords: Seismology ; Seismics (controlled source seismology) ; Filter- ; Data analysis / ~ processing ; Schuessler ; Schussler
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  • 15
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    Elsevier
    In:  Bull., Polar Proj. OP-O3A4, Computer-aided Seismic Analysis and Discrimination, London, Elsevier, vol. 16, no. 4, pp. 97-109, (ISBN 0080419208)
    Publication Date: 1981
    Keywords: Group veloc. ; Velocity analysis
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  • 16
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    Elsevier
    In:  Bull., Open-File Rept., Signal Processing II: Theories and Applications, Orlando, Elsevier, vol. 37, no. 16, pp. 681-684, (ISBN 1-86239-165-3, vi + 330 pp.)
    Publication Date: 1983
    Keywords: Detectors ; Seismic arrays ; Seismology ; Schuessler ; Schussler
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  • 17
    Publication Date: 2016-05-30
    Description: A geochemical rock- and soil-sampling program was carried out in the vicinity of eight concealed “Cyprus type” deposits, occurring in marginal mafic to intermediate metapillow lavas of the Troodos Ophiolite Complex. The mineralization of massive and stockwork sulfide ore is characterized by the predominance of pyrite, intergrown with less chalcopyrite and minor amounts of sphalerite. Background values of Hg are in the range of 8–12 ppb for soils and 3–6 ppb for surface rocks. Anomaly/background ratios of 10:1 (soils) and 5:1 (rocks) have been found only, where Hg migrated along channels formed by faults cutting shallow-seated mineralization. Here, Hg sometimes shows significant correlations with Cu, Zn, Ba and exceptionally with Co. However in one case an Hg anomaly in soils and surface rocks was detected directly over a deposit. The use of Hg as indicator element for these types of deposits is therefore limited. Buried mineralization may be delineated more distinctly by Cu, Zn and Ba.
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  • 18
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    Elsevier
    In:  Journal of Colloid and Interface Science, 76 (2). pp. 541-556.
    Publication Date: 2016-11-30
    Description: A general method for simulating aerosol size distribution dynamics is developed. The method, based on dividing the particle size domain into sections and dealing only with one integral quantity in each section (e.g., number, surface area, or volume), has the advantages that the integral quantity is conserved within the computational domain and coagulations between all particle sizes are properly accounted for. To demonstrate the simplicity and accuracy of the method for a practical problem, the evolution of a power plant plume aerosol undergoing coagulation is simulated.
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  • 19
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    Elsevier
    In:  In: Progress in phycological research. Progress in phycological research, 2 . Elsevier, Amsterdam, pp. 333-386. ISBN 0-44480502-8
    Publication Date: 2018-10-12
    Type: Book chapter , NonPeerReviewed
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  • 20
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    Elsevier
    In:  Geochimica et Cosmochimica Acta, 45 (4). pp. 577-588.
    Publication Date: 2016-03-01
    Description: Generally, oxidative regeneration of phosphate from anoxic sediments is by microbially mediated sulfate reduction processes. Stoichiometric modelling of such reactions takes into consideration varying proportions of ‘decomposable’ organically bound P to account for the ratios among nutrients in depth-concentration profiles of near-surface sediments. New results of interstitial water composition from sediments underlying the water masses influenced by coastal upwelling of the eastern boundary current system off Peru indicate that dissolution of phosphatic fish debris represents a mechanism for remineralization of phosphate comparable to or larger in magnitude than that by oxidative regeneration of organically bound P. Dissolved interstitial phosphate from fish debris is revealed by an excess amount of phosphate over that predicted from a simple stoichiometric oxidative regeneration model and by anomalously high dissolved interstitial fluoride concentrations. Phosphate flux estimates based on diffusion from the sediment suggest that this mechanism may generate up to 10% of the nutrient pool in the waters of the Peru undercurrent. Partitioning of P among the two sources reveals further that fish debris phosphate is about four times more important than organically bound P in nutrient generation from sediments of the Peru continental margin. Not only does this mechanism of regeneration affect the nutrient cycling but may also control widespread phosphorite formation in this area.
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  • 21
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    Elsevier
    In:  Journal of Experimental Marine Biology and Ecology, 75 (2). pp. 171-190.
    Publication Date: 2016-04-25
    Description: The exchange of inorganic nutrients; ammonium, nitrate and reactive phosphate between burrows of the infaunal polychaete Nereis virens Sars and the overlying water was assessed using V-shaped sediment cores. Exchange was determined by monitoring ventilation current and nutrient concentration of in- and excurrent water. Ammonium supply appeared independent of overlying water concentrations, showing a constant release of 0.5 μmol·h−1 (for a 2-g individual + burrow system) at concentrations from 2 to 87 μM. Of this release ≈40% originated from worm excretion, and the rest from microbial mineralization. Nitrate and phosphate exchange appeared very sensitive to overlying water concentrations, having equilibrium (zero flux) at 10–15 and 3 μM, respectively. Below these concentrations nitrate showed a slight release (due to nitrification), whereas phosphate was released at a rate of 3.2 × 10−2 μmol·h−1 at 1 μM (mineralization and desorption). Above equilibrium they both were removed during water passage through worm burrows, reaching 0.4 μmol·h−1 for nitrate at 107 μM (nitrate reduction) and 3.7 × 10−2 μmol·h−1 for phosphate at 5.6 μM (adsorption processes). The burrow system apparently acted as a buffer for phosphate and, to some degree, nitrate in the overlying water. At the study site (Norsminde Fjord estuary) nereid burrows were estimated to increase the sediment-water interface 150%. About 17% of the water column was cycled through the sediment by Nereis each day. The worm + burrow system was estimated to release 95 μmol· m−2·h−1 ammonium to the overlying water, which was ≈76–90% of the total release of ammonium from the sediment (30–36% was worm excretion).
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  • 22
    Publication Date: 2016-04-12
    Description: Large Neogene slumps have affected over 260,000 km2 of the outer continental margin and adjacent Cape Basin off southwestern Africa. Individual structures cover areas up to 68,700 km2 and proximally are commonly composed of huge rotated sediment blocks up to 450 m thick and several kilometers across. Seismic shocks, possibly in conjunction with lower-slope undercutting by bottom-current erosion, are suggested as possible trigger mechanisms for these features which are all thought to be post-Pliocene (possibly Pleistocene) in age. Older slumps are also recognized along the margin and four cycles of sedimentation/slumping are identified: early Upper Cretaceous (I); late Upper Cretaceous (II); Palaeogene (III); and Neogene (IV). In the main part of the Orange Basin depocentre (west of Childs Bank) the Cretaceous slump styles are thought to represent Mississippi delta-type down-slope sediment cascades (with reverse faulting and mud diapirism) over 1 km thick which resulted from very rapid dumping of terrigenous material from the Orange River. Cainozoic slumps show a different tectonic style and locus and this is thought to reflect a change in sedimentation patterns which resulted from lower terrigenous input onto the margin, higher biogenic/authigenic sedimentation, and slowed crustal subsidence. A connection possibly exists between low sea level stands and the Cainozoic episodes of slumping.
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  • 23
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    Elsevier
    In:  Journal of Volcanology and Geothermal Research, 7 (1-2). pp. 107-137.
    Publication Date: 2016-09-12
    Description: Glass separates from 115 ash layers derived from the Kamchatkan (DSDP Site 192; 34 layers), the eastern Aleutian (DSDP Site 183; 56 layers) and the Alaska Peninsula (DSDP Site 178; 25 layers) volcanic arcs have been analyzed for up to 28 elements. In addition, the abundance and diversity of associated mafic phenocrysts have been evaluated. The resulting data set has made possible an evaluation of the late Miocene to Recent changes in composition of ashes derived from North Pacific volcanic arcs and of the factors controlling the evolution of highly siliceous magmas. We find no evidence for a general transition from arc tholeiite to calc-alkalic magma parentage of ashes derived from the volcanic arcs during the last 10 m.y., but instead find 0.1- to 0.5-m.y. intervals during which particular types of volcanism are prevalent. Most convincing is the transition from arc tholeiite to calc-alkalic for ashes derived from Kamchatka during the last 0.8 m.y., a change believed to be associated with a landward shift in the site of magma generation. Considered together, ashes derived from North Pacific volcanic arcs have been becoming more siliceous during the last 1.5 m.y. and may be associated with accelerated subduction during the same time interval. Hydrous phenocrysts (e.g., biotite) are typically associated with low-silica deep-sea ashes, but not with terrestrial volcanic rocks of comparable silica contents, suggesting the important role of water in the evolution of siliceous magma. REE patterns and relative abundances of mafic phenocrysts demonstrate the importance of fractional crystallization in controlling the evolution of highly siliceous arc magmas. REE increase with increasing silica, but become less concentrated in ashes with SiO2 〉 64%. Eu anomalies increase throughout the SiO2 range. Initial fractionation is dominated by clinopyroxene and plagioclase with amphibole strongly influencing fractionation above 64% SiO2.
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  • 24
    Publication Date: 2019-05-02
    Description: The squid Loligo opalescens (Cephalopoda, Mollusca) was reared in artificial sea water in a closed system consisting of two 1300-l circular tanks. When the squids reached mantle lengths of 20 to 30 mm, they were transferred to a 10 000-l closed system raceway. From hatching, mantle length increased exponentially at a mean rate of 1.69% per day throughout the experiment. The largest and longest-lived squid attained a maximal size of 77 mm mantle length in 8 months. Only live food organisms, which consisted of copepods, other crustaceans and fishes, were accepted by the squids. Mortality, attributed to starvation and fin damage, was greatest during the first 20 days and again between days 45 and 70.
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  • 25
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    Elsevier
    In:  Comparative Biochemistry and Physiology Part C: Comparative Pharmacology, 79 (1). pp. 131-142.
    Publication Date: 2017-12-11
    Description: 1. PCBs were administered to juvenile soles (Solea solea) with food. Homogenates of gut, liver, brain, dark skin, muscle and gills were analysed for their contents of individual PCB components. The relative contributions of individual components to total PCB were virtually indentical in the various organs sampled at the same day in a 275-day period. 2. During the experiment concentrations on a (pentane-extractable) lipid basis of most PCB components declined in all organs regardless of lipid metabolism. The results suggest that PCB patterns in organs are determined by equilibrium partitioning. So components remained mobilizable from organs whose lipid contents increased. This is in contrast with the idea that PCBs are taken up and stored in lipids under circumstances of increasing lipid content in organs. 3. The plateau-values of the steady-states of lipid based concentrations of PCB components decreased in all organs. This might have been due to changes in lipid contents or lipid composition in some organs.
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  • 26
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    Elsevier
    In:  Amsterdam, Elsevier
    Publication Date: 1980
    Keywords: Seismology ; Seismics (controlled source seismology) ; Wave propagation ; Waves ; Textbook of geophysics
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  • 27
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    Elsevier
    In:  Amsterdam, Elsevier, vol. 14 B, pp. 225, (ISBN 3-7643-7011-4)
    Publication Date: 1984
    Keywords: Applied geophysics ; seismic Migration ; Seismics (controlled source seismology) ; Acoustics
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  • 28
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    Elsevier
    In:  Tectonophysics, 94 (1-4). pp. 123-139.
    Publication Date: 2019-06-11
    Description: Many hotspot tracks appear to become the locus of later rifting, as though the heat of the hotspot weakens the lithosphere and tens of millions of years later the continents are split along these weakened lines. Examples are the west coast of Greenland-east coast of Labrador (Madeira hotspot), the south coast of Mexico-north coast of Honduras (Guyana hotspot), and the south coast of West Africa-north coast of Brazil (St. Helena hotspot). A modern day analog of a possible future rift is the Snake River Plain, where the North American continent is being “pre-weakened” by the Yellowstone hotspot track. This conclusion is based on reconstructions of the motions of the continents over hotspots for the past 200 million years. The relative motions of the plates are determined from magnetic anomaly isochrons in the oceans and the motion of one plate is chosen ad hoc to best fit the motions of the plates over the hotspots. However, once the motion of this one plate is chosen, the motions of all the other plates are prescribed by the relative motion constraints. In addition to the correlation between the predicted tracks and sites of later continental breakup, exposed continental shields correlate with the tracks. Their exposure may be the result of hotspot induced uplift which has led to erosion of their former platform sediment cover.
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  • 29
  • 30
    Publication Date: 1980-06-01
    Description: From August to October, 1976, La Soufrière de Guadeloupe was observed, and recorded with an automated sequence camera and numerous handheld cameras. During the period of observation, the nature of volcanic activity ranged from mild steam emission to moderately energetic phreatic eruptions. Background fumarolic activity (steam emission) was characterized by the emission of generally tephra-free steam clouds 50 to 150 m above the summit. The clouds rose buoyantly above the vent and were blown downwind at prevailing wind velocities. Phreatic eruptions were well-documented on September 22, October 2, and October 4. In the latter two eruptions, small bursts of tephra-laden steam erupted at intervals of 30 to 45 min, and rose from 350 to 500 m above the summit. In the largest observed eruption, that of October 2, the steam and tephra cloud rose to a maximum height of 600 to 650 m in 20 min. A white vapor cloud and a medium gray, tephra-laden cloud were erupted simultaneously from the summit vent and both were surrounded by a vapor collar: the clouds were thoroughly mixed within 1 km downwind of the summit. The concurrent growth of clouds from separate vents (summit and flank) implies a common source. Simultaneous eruption of tephra-free and tephra-laden clouds from the same vent is puzzling and implies: (i) lateral changes in the degree of alteration of dome rocks along the elongate vent, hence erodability of the dome lavas, or (ii) differences in the gas velocities. These «mixed» clouds moved westward, downwind and downslope as a density current, along the watersheds of the R. Noire and R. des Pères with an approximate velocity of 10 to 25 m/sec. Upon reaching the sea the clouds continued to move forward, but at a decreased velocity, and spread laterally, having left behind the restrictions of valley walls. A thin gray veneer of moist tephra, ranging from several cm thick near the dome to less than 1 mm thick several km downwind, was deposited along a narrow corridor southwest of the summit. Tephra from the phreatic eruptions consisted mostly of hydrothermally altered lithic, mineral, and glass fragments derived from dome lavas; no fresh (juvenile) pyroclasts were present in the tephra. Absence of juvenile tephra at La Soufrière supports the view that activity was due to groundwater circulating in a vapor-dominated geothermal system, probably driven by a shallow heat source. At La Soufrière, most vapor-dominated systems are located in elevated areas of groundwater recharge where groundwater movement is downward and outward. The sporadic phreatic eruptions may be related to the rate of recharge of meteoric waters within the dome, the decrease in pore pressure during fortnightly tidal minimums or both. Whatever the triggering mechanism, vapor-dominated fluids eroded vent walls during phreatic eruptions and carried out fine-grained, hydrothermally altered, pre-existing dome material as tephra. ©1980 Intern. Association of Volcanology and Chemistry of the Earth’s Interior
    Print ISSN: 0258-8900
    Electronic ISSN: 1432-0819
    Topics: Geosciences
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  • 31
    Publication Date: 1980-03-01
    Description: O’a is the largest of the Quaternary caldera volcanoes that punctuate the axis of the Ethiopian rift valley. The known volcanic history of O’a is brief: eruptions of restricted ash-flow tuffs and «tufolavas» were followed by extensive pumice deposition with intervening paleosols, lacustrine sediments, and flows of occasional welded tuffs and rare basalts. Ensuing caldera collapse at c. 0.24 m.y. ago was accompanied by emplacement of two massive ignimbrite flow units comprising a single cooling unit: the first was much more severely welded than the second which shows lahar characteristics. Post-caldera volcanism at O’a has been sparse compared with most other Ethiopian rift centres. O’a volcano exemplifies the common rift association of a caldera set tightly between two offset segments of the Wonji fault belt. The Wonji fault belt marks the youngest tectonism of the rift floor, and in the vicinity of O’a has been active in a major way since caldera subsidence. This faulting is clearly younger than the massive rift margin faulting, which to the northeast of O’a occurred during a tectonic climax dated at c. 1.0 m.y. ago. Radiometric analysis suggests a rather regular level of initial40Ar in O’a basalt lavas sampled near to their original vents. If this level also applies to near-vent basalts dated from other parts of the Ethiopian rift, a regional rift paroxysm of crustal extension and related silicic and basaltic volcanism is evident at c. 0.30–0.20 m.y. ago. Episodic dilatation and associated volcano-tectonism separated by long periods of quiescence appears to be a general feature of continental rift valleys. ©1980 Intern. Association of Volcanology and Chemistry of the Earth’s Interior
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  • 32
    Publication Date: 1982-09-01
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  • 33
    Publication Date: 1982-09-01
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  • 34
    Publication Date: 1982-09-01
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  • 35
    Publication Date: 1982-12-01
    Description: Some domean volcanoes built by acidic to intermediate lavas are described. They were intruded, probably in Pliocene, into the neogenic volcano-sedimentary formations of the volcanic Tabriz — Bazman Zone (Central Iran). Some of them are intrusive domes which certainly did not reach the existing topographical surface when emplaced; others are extrusive domes which exhibit some interesting features viz. : hypogenous emplacement of the Suleghan dome, typical ring shape of the Dastjerd dome, etc. A provisional classification of domean volcanism in proposed in conclusion.RésuméOn décrit quelques appareils volcaniques dôméens, constitués de laves acides à intermédiaires, mis en place probablement au Pliocène dans les formations volcano-sédimentaires de la zone volcanique de Tabriz — Bazman (Iran Central). Les uns sont des dômes intrusifs n’ayant certainement pas atteint la surface topographique contemporaine de leur mise en place; les autres sont des dômes extrusifs dont certains présentent des particularités interessantes: mise en place hypogène du dôme de Suleghan, forme typique en anneau du dôme de Dastjerd, etc. En conclusion, les auteurs proposent un essai de classification des appareils volcaniques dôméens. ©1982 Intern. Association of Volcanology and Chemistry of the Earth’s Interior
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  • 36
    Publication Date: 1982-09-01
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  • 37
    Publication Date: 1984-12-01
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  • 38
    Publication Date: 1984-12-01
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  • 39
    Publication Date: 1984-12-01
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  • 40
    Publication Date: 1984-12-01
    Description: An aircraft survey was carried out for the study of the gaseous and particulate emissions over Mt Etna Volcano in September 1983. Samples were collected in the range from 10 to 300 km; a satisfying conservation of the elemental composition of the aerosol has been observed. Some activity fluctuation, 150 km from the emitter, was attributed to an ash fall episode. Sampling assumed that some crustal elements in the volcanic aerosol can be used to measure the plume dilution factor. New estimations of volcanic particulate fluxes are given. ©1984 Intern. Association of Volcanology and Chemistry of the Earth's Interior
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  • 41
    Publication Date: 1982-09-01
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  • 42
    Publication Date: 1982-09-01
    Description: This paper describes the main lines of investigation for the volcanic and geothermal research in Kamchatka. Methods of gas sampling in the field and gas extraction from rocks are also described. ©1982 Intern. Association of Volcanology and Chemistry of the Earth’s Interior
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  • 43
    Publication Date: 1982-09-01
    Description: The analyses of approximately 100 high temperature gas samples from erupting lavas of Surtsey, Erta Ale, Ardoukoba, Kilauea, Mount Etna and Nyiragongo exhibit erratic compositions resulting from analytical errors, condensation effects, reactions with sampling devices, and contamination by atmospheric gases, meteoric water and organic material. Computational techniques have been devised to restore reported analyses to compositions representative of the erupted gases. The restored analyses show little evidence of short-term variations. The principal species are H_2O, CO2, SO_2, H_2, CO, H_2S, S_2, and HCl. The O_2 fugacities range from nickel-nickel oxide to a half order of magnitude below quartz-magnetite-fayalite. There is no evidence for a unique magmatic gas composition; instead, the erupted gases show regular compositional trends characterized by decreasing CO2 with progressive outgassing. The gases from more alkaline lavas (Etna, Nyiragongo) are distinctly richer in CO2, while those from less alkaline (Surtsey) or tholeiitic lavas (Erta Ale, Ardoukoba) tend to be richer in H_2O. Kilauean gases range from CO2-rich to H_2O-rich. The total sulfur contents of the erupted gases show an excellent positive correlation with lava O_2 fugacity. All restored analyses are significantly lower in H_2O and enriched in sulfur and CO2 compared to the «excess volatiles». ©1982 Intern. Association of Volcanology and Chemistry of the Earth’s Interior
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  • 44
    Publication Date: 1982-09-01
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  • 45
    Publication Date: 1982-09-01
    Description: A field gas chromatograph, built in 1978, was used in the field to directly analyse volcanic gases before water vapor condensation. Tested in Vulcano (Italy), Kilauea (Hawaii) and Merapi (Indonesia), this field measurement technique provides the actual composition of the volcanic gas mixture. The technique avoids the depletion of sulfur gases and the dissolution of the acid gases in the condensed water during the cooling. Thus the mixture of H_2S and SO_2 in fumarolic and high temperature gases (up to 819°C) in equilibrium at the emission temperature was examined. ©1982 Intern. Association of Volcanology and Chemistry of the Earth’s Interior
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  • 46
    Publication Date: 1982-09-01
    Description: Sulphur isotopic compositions of pyrite, anhydrite and native sulphur in volcanic ashes discharged by the 1979 eruption of Ontake volcano, Nagano, Japan were determined. The isotopic data indicate that sulphate in anhydrite and a part of native sulphur were produced by the disproportionation reaction of sulphite formed by dissolution of SO_2 in volcanic gases into water which filled a mud reservoir probably located just below the crater zone. Some part of H_2S in volcanic gases was fixed as pyrite and some was oxidised to form native sulphur. Hydrothermal alteration of country rocks to form pyrite, anhydrite and clay minerals had proceeded in the mud reservoir before eruption at temperatures ranging from 110° to 185°C which were estimated by oxygen isotopic fractionation between anhydrite and water. ©1982 Intern. Association of Volcanology and Chemistry of the Earth’s Interior
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  • 47
    Publication Date: 1982-09-01
    Description: During the eruption of Mt Tolbachik volcano in 1975–1977 magmatic gases were collected by condensation and dissolution. The field system is described and discussed.ResumePendant l’éruption du volcan Tolbachik en 1975–1977 les auteurs ont utilisé un système de condensation par barbotage afin de récolter les condensats et les gaz magmatiques. La methode de prélèvement et décrite et discutée dans le détail. ©1982 Intern. Association of Volcanology and Chemistry of the Earth’s Interior
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  • 48
    Publication Date: 1982-09-01
    Description: Des sublimés ont été récoltés à l’Etna en 1976, le long d’un tube en silice. La mesure de la température du dépôt et l’analyse élémentaire par activation neutronique permettent de mieux comprendre des mécanismes magmatologiques, métallogéniques et volcanologiques.On Mount Etna, in June 1976, sublimates were collected on the wall of a silicatube. Temperatures of deposition were recorded along the tube and the atomic composition has been analysed by neutronic activation. It is possible with this technique to know the temperature of condensation or sublimation for the different elements. These results should help to better understand the magma/gas relationship. ©1982 Intern. Association of Volcanology and Chemistry of the Earth’s Interior
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  • 49
    Publication Date: 1982-09-01
    Description: The cooling of volcanic gases generates sublimates, condensates and gases. Condensates were sampled and analysed on different volcanoes: On Guadeloupe, phreatic eruptions occur when pH of condensates has maintained higher than 4 to 5 for 3 to 7 days. After the phreatic eruption, pH decreases to 1.5 to 2. At Pozzuoli and Vulcano it is possible to distinguish between gases washed by superficial waters (low mineral contents and high pH) and gases less affected by condensation and dissolution in the ground (high mineral contents and low pH).ResumeLes gaz volcaniques en se refroidissant donnent une phase solide: les sublimés, une phase liquide: les condensats et une phase gazeuse résiduelle. Les condensats ont été analysés sur place puis au laboratoire. Cette technique a été testée sur différents volcans: A la Soufriére de la Guadeloupe les éruptions phréatiques surviennent après des périodes de 3 à 7 jours où le pH des condensats est supérieur a 4 ou 5, ces éruptions sont toujours suivies d’une diminution du pH: 1,5 à 2 pendant plusieurs jours. A Pouzzoles et Vulcano les condensats des fumerolles lessivés par des acquifères superficielles ont des pH élevés et une faible mineralisation, les pH bas et les mineralisations élevées correspondant à des gaz peu affectés par les condensations dans le sol. ©1982 Intern. Association of Volcanology and Chemistry of the Earth’s Interior
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  • 50
    Publication Date: 1982-09-01
    Description: The flow rate of SO2, HCl and HF was calculated from a transfer coefficient obtained by measuring the concentration of a tracer gas (SF_6) emitted at the plume and analysed down wind with a field gas chromatograph. The results obtained are: SO2 = 2.3 pm 0.4 t/day \ HCl = 6.4 pm 0.4 t/day \ HF = 0.11 pm 0.3 t/day ©1982 Intern. Association of Volcanology and Chemistry of the Earth’s Interior
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  • 51
    Publication Date: 1982-09-01
    Description: A field system for analyzing gases was installed on line in a borehole into the geothermal field associated with Gorelyi volcano, which is close to Mutnovski volcano (Kamtchatka). The system consisted of a gas chromatograph and an electrode for sensing gases. Measurements were made for the duration of one week in July 1980. Variations in H_2 concentrations were less than 50%. No correlations were observed with regional seismic activity or with volcanic activity at Gorelyi volcano (10 km away). Measurements of H_2 during a longer period of time would allow a statistical treatment of the data.ResumeLe forage du gisement hydrothermal situé au pied du volcan Gorelyi au voisinage de Mutnovski (Kamtchatka) a été équipé d’un système de mesure « en ligne » de la composition des gaz. Les mesures ont été réalisées à l’aide d’un chromatographe en phase gazeuse et d’une électrode à membrane gazeuse. La mesure a durée une semaine en Juillet 1980. La variation de la concentration en H_2 n’éxcédait pas 50%. Aucune corrélation n’a pu étre faite ni avec l’activité sismique régionale enregistrée, ni avec celle du volcan voisin Gorelyi (situé à 10 km). La mesure de la concentration en H_2 pendant un temps plus long, permettrait seule un traitement statistique rigoureux. ©1982 Intern. Association of Volcanology and Chemistry of the Earth’s Interior
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  • 52
    Publication Date: 1982-06-01
    Description: Many examples of mixed magmas in banded lavas have been studied. Another type of mixed magmas or inhomogeneity of magma reservoir found in the 1962 lava flows of Miyake-zima Volcano erupted from fissures is reported. ©1982 Intern. Association of Volcanology and Chemistry of the Earth’s Interior
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  • 53
    Publication Date: 1982-06-01
    Description: This study discusses the focal mechanisms of 61 earthquakes and dynamic parameters of 97 earthquakes (m_i, ≥ 2.0 and focal depths 0–20 km) occurring in the region of the large Tolbachik fissure eruption in 1975–1978. Variations of these parameters during the different eruptive stages are examined. Three stages can be distinguished: 1) June 27–July 2, 1975 (from the beginning of the seismic preparation to the large earthquakes of July 2nd with M =5.0); 2) July 2nd-July 6th, 1975 (before the onset of eruption); 3) From July 6th, 1975 to the end of 1976 (during the eruption). During the second stage the 90° reorientation of the compression stress axes was observed; during the third stage the compression stress system returned to the initial strike. No variation in the orientation of the tension stress axes was noted during all these stages. Simultaneously with the reorientation of the compression stress axes in the volcanic earthquake foci during the second stage, the stress-drop values decreased strongly, whereas during the first stage these values were anomalously high. During the third stage the stress-drop values continued to decrease and approached the average regional values indicative of a calm period. All the estimates of parameters variations were made at 0.1 significance level. The above-mentioned temporal variations in the volcanic earthquake focal parameters are discussed in connection with the probable model of preparation and course of eruption. ©1982 Intern. Association of Volcanology and Chemistry of the Earth’s Interior
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  • 54
    Publication Date: 1982-06-01
    Description: Local eruptions of acid volcanic rocks occurred in the Central Aegean region around the Miocene-Pliocene boundary. Rhyolites outcrop on the Island of Antiparos, located in the central part of the Attic-Cycladic Massif. The age of these volcanic rocks ranges from 4.0 to 5.4 m.y., and chemical and Sr isotopic data suggest they were generated by partial melting of the continental crust. At the same time, along the border of the Attic-Cycladic Massif, i.e. on the island of Patmos and Caloyeri, local eruptions of Naalkaline basalts occurred. The whole of the eruptive activity is interpreted as an expression of the marked tensional tectonic phase which has affected the Central Aegean area since Middle Miocene. The contrasting nature of the erupted volcanic rocks (crustal and sub-crustal) is attributed to the different thermal state of the lithosphere beneath the two areas, as emphasized also by the presence of a wide granitic belt, of mainly Miocene age, which developed in the median sector of the Attic-Cycladic Massif. ©1982 Intern. Association of Volcanology and Chemistry of the Earth’s Interior
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  • 55
    Publication Date: 1982-06-01
    Description: The Vulture complex is made up of foiditic, tephritic, phonolitic-trachytic and phonolitic products. New rock analyses have been performed in order to ascertain whether the various rock types derive from a unique parental magma and, if so, to define its nature. The data presented support that the Vulture suite originated from a foiditic melt which had differentiated at low pressures. The main process determining the foidite → → tephrite → phonolitic trachyte evolution seems to be the crystal fractionation of mainly clinopyroxenes, and opaques, with the contribution of plagioclases and haüyne too in the tephrite → trachyte evolution. Additionary role must have been played by a mixing of melts at different evolution stages occurred in a shallow seated magma chamber. ©1982 Intern. Association of Volcanology and Chemistry of the Earth’s Interior
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  • 56
    Publication Date: 1982-06-01
    Description: On February 20th, 1979, 142 inhabitants of Dieng Plateau (Indonesia) were asphyxiated by poisonous gases during a mild phreatic eruption. From later fields gas collection and analysis, the casualties are considered to be due to CO2 rich volcanic gases. ©1982 Intern. Association of Volcanology and Chemistry of the Earth’s Interior
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  • 57
    Publication Date: 1984-12-01
    Description: A succession of heterogeneous pyroclastites with contrasted composition (hawaiite-trachyte) and homogeneous intermediate lava flows (benmoreite) is present at Puy de la Nugère (Chaîne des Puys, Massif Central, France). Mineralogical disequilibrium assemblages are present in both the explosive en effusive products. Textural, mineralogical and geochemical data on these formations are compatible with a magma mixing model. The origin of the trachyandesitic rocks in the alkaline suite of Chaîne des Puys would be controlled by fractional crystallization and magma mixing. ©1984 Intern. Association of Volcanology and Chemistry of the Earth's Interior
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  • 58
    Publication Date: 1984-12-01
    Description: A systematic petrographic and chemical study of chronologically ordered lava samples collected during the 1983 Etna eruption, has shown minor fluctuating variations in crystallinity and chemistry, apparently correlated with variations in the rate of effusion. Comparison with the compositional variations observed in the lavas emitted during the 1971–1983 period, has revealed a repeated evolutional tendency suggesting a small size shallow storage system periodically refilled, as in 1983, by more primitive magma. ©1984 Intern. Association of Volcanology and Chemistry of the Earth's Interior
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  • 59
    Publication Date: 1984-12-01
    Description: The Quaternary central volcano Longonot is situated on the floor of the Gregory Rift Valley, Kenya, at 0° 55′ S, 36° 25′ E. Although the majority of its products are lavas and pyroclastics of pantelleritic trachyte composition, small volumes of alkali basalt magma have been coerupted with pantelleritic trachyte magma to produce mixed lavas. These lavas were the first products following each of three caldera collapses and mark the start of three successive cycles of whole-rock chemical variation with time. For the first two mixed-lava eruptions identified, field, petrographic and mineralogical evidence suggests that the contrasting magmas comingled, and in places hybridized, during eruption. Whole-rock geochemistry requires the alkali basalt component to have been contaminated prior to coeruption with trachyte. Syenite is suggested as a possible contaminant of the basalt component in the last two mixed-lava eruptions. Field and whole-rock chemical evidence points to the trachyte magma chamber being underlain by a basalt magma root zone. Inputs of fresh basalt magma into the root zone may have initiated each pre-caldera pyroclastic event and subsequent caldera formation and may have also caused the trachyte magma to overturn and commence a fresh cycle of chemical evolution. Some of the hot, buoyant basalt magma was able to leak towards the surface up peripheral fractures where it was coerupted with the initial trachyte magma of each cycle. ©1984 Intern. Association of Volcanology and Chemistry of the Earth's Interior
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  • 60
    Publication Date: 1984-12-01
    Description: The Holocene volcanic activity which built up the present terminal cones of Pico de Orizaba and Popocatepetl in eastern Mexico, was characterized by repeated pyroclastic Saint-Vincent type eruptions. Radiocarbon data show that these paroxysmal events occurred at more or less regular intervals, and were followed by moderate activity producing ash and pumice falls and andesitic lava flows from the summit craters. Typical ash and scoria pyroclastic flows exhibit a heterogeneous composition given by the interaction of a dacitic component with a more basic andesitic one. Scoria bombs are characterized by banded to emulsified textures, mineralogical desequilibrium assemblages and linear chemical variations on element-element plots as exemplified by the Loma Grande flow at Pico. Periodic replenishments of the magmatic reservoir could be the major phenomenon that started mixing and consequently triggered the pyroclastic eruptions. ©1984 Intern. Association of Volcanology and Chemistry of the Earth's Interior
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  • 61
    Publication Date: 1984-12-01
    Description: The water steam convection existing below a fumarolic area creates hydraulic, thermal and electric anomalies, the electric anomaly being probably the most correlated to a change of the deep thermal activity. The anomaly range depends on the position of the site connected with the configuration of the magmatic activity, but also on the local hydrogeologic conditions. The spatial and temporal surveillance of the eruptions based on these convective data should take into consideration these conditions.ResumeLa convection de la vapeur d'eau formée en profondeur dans une zone fumerollienne crée en surface une anomalie hydrique, thermique et électrique, cette dernière pouvant être la plus sensible à une variation de l'activité thermique profonde. L'amplitude des anomalies dépend de la position du site par rapport à la configuration de l'activité magmatique, mais aussi des conditions hydrogéologiques locales. La surveillance spatiale et temporelle des éruptions à partir du phénomène convectif hydrique doit tenir compte de ces conditions. ©1984 Intern. Association of Volcanology and Chemistry of the Earth's Interior
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  • 62
    Publication Date: 1984-12-01
    Description: Une campagne de mesures de contraintes a eu lieu en 1983 au voisinage de l'Etna. Ces mesures, effectuées par une technique de surcarottage au fond de forages peu profonds (5 à 6 mètres), montrent un changement radical du régime des contraintes entre la région au Sud de l'Etna et le pied du versant Nord de l'edifice volcanique.An in-situ rock stress survey was carried out in the Etna region in 1983. Measurements made with the overcoring technique at the bottom of shallow (5–6 m deep) boroholes have shown a strong variation in stress field between the region on the South of Etna and the zone at the northern foot of the volcano. ©1984 Intern. Association of Volcanology and Chemistry of the Earth's Interior
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  • 63
    Publication Date: 1984-12-01
    Description: A long range transport model and its application to an Etna plume are described. The model is a classical segmented plume lagrangian trajectory model. Firstly, air mass trajectories are computed by using the actual winds observed at the E.C.M.W.F. (Reading U.K.). The model then determines 5-day trajectories starting every 3 hours and made of 3-hour segments. Vertical movements of air parcels are taken into account by using the vertical component of the synoptic wind. Secondly, diffusion, SO_2 to SO_4 transformation and dry deposition are calculated for each trajectory segment. Sensitivity tests are presented and the results of the simulation for an experimental field period (21–25 september 1983) are examined. ©1984 Intern. Association of Volcanology and Chemistry of the Earth's Interior
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  • 64
    Publication Date: 1984-12-01
    Description: During the entire life of Cantal volcano, the main lava types were emitted during rather separated stages of activity. Basalts are scarce in the trachyandesitic complexes, whereas latites are very uncommon in the basaltic units. In both cases, incomplete mechanical mixing would have been active in their genesis as it is suggested by field and microscopic observations. Sanissage composite dome is formed of poorly mixed acid and basic lavas, with still clearly observable reaction relationship between components. Combe de Saure plug shows a dispersion of tiny (smaller than 1 cm) trachyandesitic relics within a prevalent basaltic groundmass, the result of which being a nearly homogeneous melt, so called « leucobasalt », with D.I. similar to that of a hawaiitic rock. From these observations it is suggested that a large part of intermediate Cantal lavas (D.I similar to those from hawaiites-mugearites-benmoreites) may derive from homogeneized mixing, when new basaltic magma entered the chamber filled with differentiated melt. ©1984 Intern. Association of Volcanology and Chemistry of the Earth's Interior
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  • 65
    Publication Date: 1984-12-01
    Description: Depuis septembre 1980, des mesures de la concentration de Radon dans le sol ont été entreprises sur l'Etna en vue d'étudier le comportement de ce gaz radioactif naturel vis-à-vis de l'activité du volcan et de son utilisation en tant qu'un des paramètres possibles de la prévision des éruptions volcaniques. La technique de mesure employée est celle des détecteurs solides de traces nucléaires plastiques (LR-115 type II, Kodak Pathé). Le réseau implanté, principalement en collaboration avec les mesures de température du sol ( Archambault et al. ) et de polarisation spontanée ( M. Aubert ) comprend une vingtaine de stations sitées sur le versant Sud et Sud-Est du volcan. Les densités de traces de particules alpha observées varient de 50 à 2000 traces/cm2/semaine selon la localisation des stations, malgré un bruit de fond à peu près constant. Sur l'ensemble des résultats aucune règle de variation saisonnière de l'émanation n'apparaît; certaines zones présentent les plus fortes densitésen hiver (Torré del Filosofo, Vulcarollo), d'autres au printemps (Etna Sud, Citelli). Le problème majeur de cette technique est la nécessité, pour obtenir une analyse fine de la variation de l'émanation du radon-222, de changer tous les 15 jours ou tous les mois les échantillons. Nous espérons remédier à ce problème par l'emploi de sondes de mesures automatiques, dont la mise au point est en cours, et pouvant être reliées au système Argos déjà existant.Since September 1980, measurements of radon concentration in the ground have been carried out on Etna using Radon as a forerunner geophysical parameter of volcanic eruptions. The technique used is the Solid State Nuclear Tracks detectors' method (LR 115 Type II, Kodak). The stations network, in connection with soil temperature ( Archambault et al. , 1980) and spontaneous polarisation measurements ( M. Aubert , pers. commun.) is composed of 20 stations located on the southern and south-eastern flanks of the volcano. The observed alpha track densities vary between 50 and 2000 tracks/cm2/week according to the location for a background almost constant. Seasonal variations seem to affect measurements, but their influence seems to be governed by no rule. The main problem in the used technique is the necessity of changing the detectors every two weeks or every month in order to obtain a good analysis of the variations in Rn-222 concentration. In order to remedy such deficiency, an automatic electronic device which can be connected with the yet existing Argos system is being arranged. ©1984 Intern. Association of Volcanology and Chemistry of the Earth's Interior
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  • 66
    Publication Date: 1984-12-01
    Description: L'éruption du 28-3-1983 a été précédée, dans la nuit entre le 27 et 28 Mars, par l'ouverture de fractures sur le flanc sud de l'Etna entre les côtes 2900 et 2300. Ces ruptures correspondent à des failles à rejet surtout vertical et à des fentes. La disposition générale dessine un graben d'orientation N-S à NE-SW, dont la largeur se réduit progressivement de 80 m à environ 25 m au point d'émission des laves, alors que le rejet vertical des failles augmente vers le sud (maximum 1 m 50). En quelques points on a pu noter une légère composante en décrochement. L'extension horizontale provoquée par l'ouverture de ce graben a été estimée à environ 3 m. Ces donnés sont confrontées à celles obtenues par d'autres méthodes et leur interprétation est discutée en rapport avec le mécanisme de l'éruption et les relations entre magmatisme et tectonique.The Etna eruption of March 28th, 1983 was preceded, during the night between March 27th and 28th, by the opening of fractures on the southern flank of Mt. Etna between 2300 and 2900 meters a.s.l. The fractures are essentially dip-slip faults and fentes . The resulting general pattern is that of a graben oriented from N-S to NE-SW that becomes progressively narrow passing from about 80 m to 25 m in width at the lava flow emission site, while the vertical fault throw increases towards the south reaching there the maximum value of 1.50 m. In a few places it was possible to detect a slight horizontal component of movement. The horizontal opening due to the graben formation has been estimated to be about 3 m in width. These data have then been compared with others obtained using different methods and their interpretation has been discussed in relation to the eruption mechanism and the relationships between magmatism and tectonics. ©1984 Intern. Association of Volcanology and Chemistry of the Earth's Interior
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  • 67
    Publication Date: 1984-12-01
    Description: L'Etna a connu, de 1977 à 1983, une période d'activité exceptionnelle, tant par la fréquence et l'extension des fracturations latérales de l'édifice que par la violence et la répétition des paroxysmes aux cratères centraux. L'éruption multifissurale de 1971 et l'éruption excentrique de 1974 sur le flanc Ouest apparaissent comme les prodromes de l'activité actuelle. Celle-ci a débuté en juillet 1977 par l'exacerbation de l'activité sommitale qui, de modérée persistante, est devenue paroxysmique et intermittente. Jusqu'en mars 1978, le Cratère NE a eu ainsi une vingtaine d'éruptions tout à fait inusitées, ne durant que quelques jours ou même quelques heures, avec puissantes fontaines de lave et coulées rapides atteignant jusqu'à 5 km de long. D'autres paroxysmes uniquement explosifs ont eu lieu en avril 1980 au Cratère Central, puis au Cratère SE. Un début d'activité persistante (mai-août 1980) dans cette dernière bouche a été interrompu par la reprise de violentes manifestations explosivo-effusives au Cratère NE en septembre 1980 et février 1981. Les éruptions latérales surtout ont été remarquables: en avril-juin 1978 (fracturation du versant SE, de 3000 à 2600 m d'altitude), août 1978 (SE, ENE, 3000–2300 m), novembre 1978 (SE, 3000–1650 m), août 1979 (SE, E, NE, 3000–1600 m), mars 1981 (NNW, 2600–1120 m), mars-août 1983 (S, 2700–2260 m). Les 4 premières de ces éruptions ont été précédées et accompagnées de violentes fontaines de lave au Cratère SE. Toutes ont été accompagnées ou suivies d'explosions phréatiques, principalement à la bouche Ouest du Cratère Central. La coulée du 4 août 1979 sur le flanc oriental est descendue en une demi-journée près du village de Fornazzo. Celle du 17 mars 1981 — la plus désastreuse — a, dans les 14 h qui ont suivi son apparition, coupé toutes les communications terrestres au pied Nord de l'Etna, sur un front par endroits large de 800 m: en moins de 5 jours, 18 × 106 m3 de lave ont été émis, recouvrant 6 km2 de terres en grande partie cultivables. Du 28 mars au 8 août 1983, les laves s'épanchant de façon tranquille, mais à un rythme soutenu, ont lentement enseveli plusieurs propriétés et implantations touristiques du versant Sud, entre 2300 et 1100 m d'altitude. Chacun de ces paroxysmes éruptifs se signale par des augmentations considérables de l'amplitude du tremor séismique, dont l'intensité n'est cependant pas directement liée à l'importance des phénomènes observés. Il est probable que la turbulence due à la montée du magma dans les conduits principaux influe notablement sur l'énergie du tremor: de fait, celui-ci est très réduit après la phase paroxysmique initiale (par exemple 1983), bien que l'effusion de lave persiste. Avant les éruptions, l'énergie du tremor atteint des niveaux relativement élévés pendant des intervalles de temps qui durent de 1 à 5 mois. Ce phénomène peut résulter d'un mécanisme de recharge du système de fractures et de dykes conduisant, à plus ou moins brève échéance, à l'événement éruptif. Plusieurs périodes de recharge peuvent se succéder avant une même éruption (3 avant celle de 1983). Dans les quelques jours qui précèdent certains paroxysmes (août 1979, sept. 1980, févr. et mars 1981), on constate une rapide diminution de l'amplitude du tremor, qui peut être associée à des variations du champ de contrainte déterminant, localement, la genèse de fractures nouvelles ou la fermeture/ouverture de fractures pré-existantes.A period of exceptional eruptive activity for both size and frequency of lateral eruptions, and violence of paroxysms at the summit craters characterized Etna from 1977 to 1983. The complex fissure eruption of 1971 and the eccentric eruption of 1974 on the W flank appear to be precursors of the present activity, which began in July 1977 with the change in style of summit eruptions from moderate persistent activity to intermittent paroxysms. The NE Crater produced a score of such unusual eruptions up to March 1978, lasting a few days or even a few hours with powerful lava fountaining and flows up to 7 km long with high effusion rates. Other solely explosive paroxysms occurred in April 1980 in the Chasm (Central Crater) and later at the SE Crater. A return to a period of gentle persistent activity (May–August 1980) at the latter vent was interrupted by the recommencement of violent explosive and effusive events at the NE Crater in September 1980 and February 1981. Particularly remarkable lateral (flank) eruptions occurred in April–June 1978 (fracturing of the SE slope from 3000 to 2600 m altitude), August 1978 (SE, ENE, 3000–2300 m), November 1978 (SE, 3000–1650 m), August 1979 (SE, E, NE, 3000–1600 m), March 1981 (NNW, 2600–1120 m) and March–August 1983 (S, 2700–2260 m). The first four of these eruptions were preceded and accompanied by violent lava fountaining at the SE Crater. All were accompanied and/or followed by phreatic explosions, principally from the Bocca Nuova (or W Central Crater). The flow emitted on 4th August 1979 from the eastern flank reached next to the village of Fornazzo in half a day. That of 17 March 1981 — the most destructive — cut all communications (roads and railways) round the northern foot of the mountain in the 14 hours following its appearance. It was in places 800 m wide, and in less than 5 days, 18 × 106 m3 of lava had been emitted, covering 6 km2 of largely agricultural land. From 28th March to 6th August 1983, the slow but sustained emission of lava gradually covered and destroyed several tourist installations between 2300 and 1100 m altitude. Each of these eruptive paroxysms was marked by a substantial increase in the trace amplitude of harmonic seismic tremor, the intensity of which being not directly proportional to the observed activity. It is likely that turbulence caused by the rising of magma in the main conduits had an important effect in the energy of the tremor: this is considerably reduced after the initial paroxysmal phase ( e.g. in 1983), yet the lava effusion may continue. Tremor energy attains relatively high levels from 1 to 5 months before eruptions. This may be caused by the recharging of the system of dykes and fissures, leading up to an eruptive event after a variable period. Several distinct periods of recharging may precede one eruption (there were three before the 1983 eruption). In the few days preceding the start of some of the eruptions (Aug. 1979, Sep. 1980, Feb. and Mar. 1981), a rapid diminution in the amplitude of tremor occurred. This may be associated with changes in the stress field caused by the opening of new fractures or the closing/opening of pre-existing ones. ©1984 Intern. Association of Volcanology and Chemistry of the Earth's Interior
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  • 68
    Publication Date: 1984-12-01
    Description: En juin et juillet 1983, pendant l'éruption, on a procédé à une campagne de mesures magnéto-telluriques sur l'Etna. Elle a consisté en l'exécution de six sondages lents et d'une cinquantaine de mesures audio-magnéto-telluriques (AMT). On discute l'interprétation tant géophysique que structurale des données recueillies en tenant compte des conditions particulières dans lesquelles l'opération s'est effectuée. La méthode AMT identifie très bien la fracture majeure liée à l'éruption qui se manifeste par un baisse très sensible de la résistivité apparente. Les sondages lents, pour leur part, mettent en évidence des formations conductrices qu'il est difficile d'accorder avec le schéma proposé par R. Schick et al . L'observation d'une évolution dans le temps de certaines mesures en AMT est discutée ainsi que les conséquences qu'on pourrait en tirer quant à la surveillance directe ou indirecte de la situation du magma en profondeur.Magneto-telluric measurements were carried out during the Etna eruption in June–July 1983. Six slow soundings and about 50 audiomagneto-telluric (AMT) measurements formed the survey programme. Geophysical and structural interpretations of data are given with taking into account the particular operational conditions. The major fracture associated with the eruption has been identified by the AMT method quite well in a very clear low of the apparent resistivity. On the other hand, slow soundings have shown conductive rock formations which it is difficult to fit the Schick et al. 's model. The time evolution of certain AMT measurements is discussed together with the possible implication for a direct or indirect surveillance of the magma situation in depth. ©1984 Intern. Association of Volcanology and Chemistry of the Earth's Interior
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  • 69
    Publication Date: 1984-12-01
    Description: An extensive set of samples representative of the evolution of Etna since the beginning of its activity in the Quaternary has been analyzed for trace element contents by neutron activation on whole rock samples. Major element data were taken from Tanguy (1980). Several petrogenetic processes have played a role in the observed chemical variations: binary trace element plots form linear arrays extrapolating to the origin for most second row and higher transition elements and the rare alkali metals thus indicating their hygromagmaphile (HYG) character; 3d transition elements show two types of behavior when plotted against an HYG element. Concentrations remain relatively constant for the less evolved rocks in the range from tholeiite through transitional basalts to alkali basalts. On the contrary, concentrations drop rapidly in the series evolving from alkali basalts to trachytes; in addition to the latter two general trends, geochemical regularities specific to Etnean lavas are born out. Rare alkali metals, as well as potassium, for instance, show a trend of abnormal enrichment in the most recent historical eruptions. The recurrence in time of rather primary magmas indicates that the petrogenetic evolution of the lavas cannot be explained by the differentiation of a single batch of mantle derived magma. However, the chemical composition of the mantle source has remained relatively homogeneous with a nature very near the chondritic one. Mineralogically, the source must differ from that for oceanic basalts to account for Th/Ta differences. Early tholeiitic primary magma evolving into later alkali basalts is adequately modeled by variations of the degree of partial melting of a closed system source. Highly evolved products have episodically been emitted as a result of extensive crystal fractionation, during which no basalts are erupted. These episodes are abruptly interrupted by the eruption of basalts presumably indicating recharge of the magma plumbing system by pristine mantle derived material. Selective contamination in alkali elements from the sedimentary basement is also indicated by the data. The presence of partially digested sedimentary xenoliths is an additional argument for this process. ©1984 Intern. Association of Volcanology and Chemistry of the Earth's Interior
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  • 70
    Publication Date: 1980-06-01
    Description: Tertiary volcanic rocks of Carriacou occupy two-thirds of the island. The volcanics include volcaniclastics, lava flows and dome lavas and range in composition from basalts to andesites. Carriacou basalts fall into two petrographic types (a) clinopyroxene-plagioclase-phyric basalts and (b) olivine microphyric basalts; the latter having higher MgO and lower Al_2O_3 than the clinopyroxene basalts. Both types are unusually rich in mafic minerals compared with Lesser Antilles basalts in general, although similar types have been reported from the nearby island of Grenada. The potash to silica ratios are relatively high and confirm the similarity between Carriacou and Grenada basalts and the differences between these basalts and basalts from other islands of the Lesser Antilles. The basaltic andesites and andesites from Carriacou correspond closely in mineralogical and chemical composition with typical andesites found elsewhere in the Lesser Antilles. The geochemistry of the volcanics shows that the olivine microphyric basalts display tholeiitic affinities whereas the clinopyroxeneplagioclase-phyric basalt, basaltic andesites and andesites are calcalkaline. The compositional gradation in both the geochemistry and mineralogy of these volcanics suggests that fractional crystallization played an important role in the derivation of the various magma. ©1980 Intern. Association of Volcanology and Chemistry of the Earth’s Interior
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  • 71
    Publication Date: 1980-03-01
    Description: In the frame of a geochemical surveillance survey of Vulcano, the phreatic waters, mainly from wells located at the Northern basis of the active volcanic centre, were studied over a time span of sixteen months. On the basis of fundamental chemical composition, contamination by a shallow aquifer of brackish water and hydrothermal alteration of rocks seem the main processes to which the observed chemical picture can be attributed. An R-mode factor analysis procedure allowed to distinguish a principal factor associated to sodium, magnesium, chloride, possibly representing the contribution of the brackish aquifer, and three minor but distinct factors. These are respectively associated to calcium and sulfate, hydrogencarbonate, boric acid, and are considered as reflecting the influence of gaseous compounds from volcanic emanations. The variation in time of this influence appears in correlation with the variation of the observed temperature at the hottest fumaroies of the crater. ©1980 Intern. Association of Volcanology and Chemistry of the Earth’s Interior
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  • 72
    Publication Date: 1980-06-01
    Description: Stratigraphic studies on the active and potentially active volcanoes of the Lesser Antilles have revealed two main types of andesitic pyroclastic deposit. One with dense clasts in a poorly vesicular ash represents nuée ardente eruptions of Pelean type and the other group of vesicular pumice and ash represent both Plinian airfall and ash-pumice flow eruptions. The pumiceous deposits can be divided into airfall lapilli, airfall ash, crystal-pumice surge, ashpumice flow and ash hurricane types. No pumice eruptions have been witnessed in the Lesser Antilles during the period of written history although the stratigraphy of archaeological sites shows they occurred in pre-Columbian times. Detailed stratigraphic studies of Mt. Pelée, Martinique, and the Quill, St. Eustatius, show that, throughout their history, pumice eruptions have alternated with nuée ardente eruptions with approximately equal frequency. The widespread occurrence of pumiceous deposits on many of the West Indian volcanoes and the frequent alternations in the stratigraphic sections suggest the high probability that they will be witnessed in the future. On Martinique, some on the late prehistoric pumiceous pyroclastic flow deposits (the ash hurricanes) have been traced 20 km from the central vent to the out-skirts of Fort de France, indicating that they are the major hazard in the Lesser Antilles. Measured stratigraphic sections show that the Pelean type nuée ardente deposits are separated from the pumiceous pyroclastic deposits by others of intermediate vesicularity and appearance. The presence of such deposits of intermediate vesicularity could provide a future warning of impending change in pyroclastic style. As no such deposits formed on Mt. Pelée this century the present «safer» episode of nuée ardente (Pelean type) activity is expected to continue. ©1980 Intern. Association of Volcanology and Chemistry of the Earth’s Interior
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  • 73
    Publication Date: 1980-03-01
    Description: The paper describes the course of the Large Tolbachik fissure eruption taking place in Kamchatka from July 6, 1975 to December 10, 1976. The eruption zone extended for 30 km. The formation of monogenic scoria cones nearly 300 m high, lava tubes and basalt sheets up to 80 m thick and more than 40 km2 in area and subsidence of the Plosky Tolbachik summit caldera to a depth of more than 400 m were observed during the eruption. The volume of eruption products amounted to more than 2 km3. It was the largest basalt eruption which has taken place in the Kurile-Kamchatka volcanic belt in historic time. ©1980 Intern. Association of Volcanology and Chemistry of the Earth’s Interior
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  • 74
    Publication Date: 1980-03-01
    Description: The paper discusses the results of geodetic investigations performed in the region of the large 1975–1976 Tolbachik fissure eruption in Kamchatka. Using data from repeated triangulation and trigonometric levelings, horizontal and vertical displacements have been detected in an area of 3,500 km2. Two zones have been recognized: the tension and uplift zone that is probably due to magma intrusion from depths to the surface along the line of new cones and the extensive compensative subsidence zone located at a distance of 20–50 km from the nearest newly-formed cones. Measurements made with small distance measuring device showed the dynamics of feeding basalt dykes intrusion and made it possible to determine their width (a little greater than 1 m) and magma and gas overpressure (50–250 bar). Data have been obtained on dimensions and growth of cones and on vertical ground deformation in the area of new cones during and after the eruption. ©1980 Intern. Association of Volcanology and Chemistry of the Earth’s Interior
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  • 75
    Publication Date: 1980-03-01
    Description: The temperature of the Crater Lake of the active volcano Ruapelm has been recorded by Temperature Telemetry Buoys, to determine if lake temperature is correlated with volcanic activity. These buoys had to be specially designed to cope with the unfavourable environment of Crater Lake. A buoy contains a thermistor to measure the lake temperature, and a radio transmitter to transmit a short signal every few minutes, the interval between signals being a function of temperature. The temperature records obtained from these buoys show that the temperature near the lake surface can vary considerably within a few hours. Some of these variations appear to be caused by disturbances in convective heat transfer occurring in the lake. The occurrence of these short term temperature variations means that there is no simple relation between Crater Lake temperatures and the volcanic activity of Ruapehu. Some rapid increases in temperature followed volcanic earthquakes, but one of the biggest increases in temperature occurred just before a group of earthquakes upder the lake. ©1980 Intern. Association of Volcanology and Chemistry of the Earth’s Interior
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  • 76
    Publication Date: 1980-03-01
    Description: The gas composition of recent thermal waters is in perfect conformity with their geologictectonic positions. The composition of gas-liquid inclusions in the basic-hyperbasic xenoliths of basaltoid lavas depends on the depth from which xenoliths are supplied. (The depth is determined by using the methods of geological thermobarometers). By comparing available data we came to the conchision that the gas compositions of thermal waters reflect the depth of generation of deep fluid which heats them and depends on the penetration depth of the fluid-conducting fissure zones. ©1980 Intern. Association of Volcanology and Chemistry of the Earth’s Interior
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  • 77